Blue LED at 3.3V
rich
find have a Vf equal to or greater than 3.3V.
I am curious how others are dealing with this.
Thanks
Rich
Tim Wescott
That pretty much demands a voltage boost of some sort. Depending on how
many lights you have, how much power you're willing to waste, how much
design time you want to spend and how expensive you want the final
product to be, your choices sort of boil down to a switcher with
inductors and diodes and all that, or a current pump.
Most of us would solve this problem by looking for a suitable IC.
_Some_ of us would do it with two transistors, an inductor, and a cap,
then brag about only needing one $.001 resistor instead of three.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Jim Thompson
wrote:
>On 05/25/2010 10:18 AM, rich wrote:
>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>> find have a Vf equal to or greater than 3.3V.
>>
>> I am curious how others are dealing with this.
>
>That pretty much demands a voltage boost of some sort. Depending on how
>many lights you have, how much power you're willing to waste, how much
>design time you want to spend and how expensive you want the final
>product to be, your choices sort of boil down to a switcher with
>inductors and diodes and all that, or a current pump.
>
>Most of us would solve this problem by looking for a suitable IC.
>_Some_ of us would do it with two transistors, an inductor, and a cap,
>then brag about only needing one $.001 resistor instead of three.
And some of us would brag about doing it right ;-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
The only thing bipartisan in this country is hypocrisy
John Larkin
I have some nice Osram blues that are OK at 1 mA and 2.65 volts,
bright at 10 mA, 3.1 volts. So you could just get by with a resistor
or current limiter from 3.3. You could use one of my famous beta
limiter circuits.
I sometimes make my "3.3" volt supplies actually 3.5 or 3.6. Most
other parts don't mind.
Or use a booster.
John
Spehro Pefhany
<rsoenn...@gmail.com> wrote:
Probably in a lot of applications where people choose a blue LED there
is a higher voltage (eg. 5V) supply present as well.
Here is one way to do with about 2-3 cents worth of parts (3 tiny SMT
jellybean parts, no inductors) if you have a microcontroller doing the
driving:
+3.3V
|
|
|
.--|--.
| | |
Cs | V |
Rs | - |
|| ___ | | | eg. BAV99
-||--|___|--|- + |
|| | | |
Port pin | V |
| - |
'--|--'
|
|
V LED (Blue or White only)
-
|
|
===
GND
AC on the port pin => ON, either level of DC => OFF
Or you could search on, say, LTC's website and find a $5 chip which
will be designed for the purpose (blue LEDs are electrically the same
as white LEDs in most cases, so all those white LED drivers will
typically work equally well with blue LEDs).
John Larkin
wrote:
>On 05/25/2010 10:18 AM, rich wrote:
>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>> find have a Vf equal to or greater than 3.3V.
>>
>> I am curious how others are dealing with this.
>
>That pretty much demands a voltage boost of some sort. Depending on how
>many lights you have, how much power you're willing to waste, how much
>design time you want to spend and how expensive you want the final
>product to be, your choices sort of boil down to a switcher with
>inductors and diodes and all that, or a current pump.
>
>Most of us would solve this problem by looking for a suitable IC.
>_Some_ of us would do it with two transistors, an inductor, and a cap,
>then brag about only needing one $.001 resistor instead of three.
One resistor:
ftp://jjlarkin.lmi.net/LED_boost.JPG
John
Jan Panteltje
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in
<b93ov5hd2c0t71ma2...@4ax.com>:
Yup, my blue one drops 2.66 V
Extremely bright at 3.5 mA.
ftp://panteltje.com/pub/low_current_LEDs_img_1964.jpg
in that picture it is at 10% PWM with 180 Ohm in series fro ma 3.3V PIC output.
Tim Wescott
Connected to jjlarkin.lmi.net.
421 Service not available, remote server has closed connection
ftp>
Tim Wescott
How is it at cold, though?
Tim Wescott
AFAIK a white LED is just a blue LED chip with some fluorescent material
in the package that makes enough "whatever else" to make it look white.
They look exceedingly blue to me -- I don't know if that's because they
are, or because I'm color deficient in green and don't see them the same
as other people do.
Spehro Pefhany
wrote:
>AFAIK a white LED is just a blue LED chip with some fluorescent material
>in the package that makes enough "whatever else" to make it look white.
Usually a blue chip with yellow phosphor. There maybe some that are
made differently.
>They look exceedingly blue to me -- I don't know if that's because they
>are, or because I'm color deficient in green and don't see them the same
>as other people do.
They make them with different color temperatures these days,
especially those designed for illumination.
rich
FTP link does not work...
Jan Panteltje
<rsoenn...@gmail.com> wrote in
<730ce605-fd72-4d2c...@23g2000pre.googlegroups.com>:
>> One resistor:
>>
>> ftp://jjlarkin.lmi.net/LED_boost.JPG
>>
>> John
>
>FTP link does not work...
Works OK here.
Dave Platt
> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
> find have a Vf equal to or greater than 3.3V.
>
> I am curious how others are dealing with this.
Google "Joule Thief". This is the way it's usually done in small LED
flashlights - the sorts powered by one or two AA or button cells.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Tim Wescott
> On 05/25/2010 11:00 AM, John Larkin wrote:
>> On Tue, 25 May 2010 10:18:11 -0700 (PDT), rich
>> <rsoenn...@gmail.com> wrote:
>>
>>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>>> find have a Vf equal to or greater than 3.3V.
>>>
>>> I am curious how others are dealing with this.
>>>
>>> Thanks
>>>
>>> Rich
>>
>> I have some nice Osram blues that are OK at 1 mA and 2.65 volts,
>> bright at 10 mA, 3.1 volts. So you could just get by with a resistor
>> or current limiter from 3.3. You could use one of my famous beta
>> limiter circuits.
>>
>> I sometimes make my "3.3" volt supplies actually 3.5 or 3.6. Most
>> other parts don't mind.
>
> How is it at cold, though?
>
voltage at 25C, with a 20% increase at -20C and a 40% increase at -40C.
"Fading blue"?
John Larkin
wrote:
>On 05/25/2010 11:10 AM, John Larkin wrote:
>> On Tue, 25 May 2010 10:22:59 -0700, Tim Wescott<t...@seemywebsite.now>
>> wrote:
>>
>>> On 05/25/2010 10:18 AM, rich wrote:
>>>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>>>> find have a Vf equal to or greater than 3.3V.
>>>>
>>>> I am curious how others are dealing with this.
>>>
>>> That pretty much demands a voltage boost of some sort. Depending on how
>>> many lights you have, how much power you're willing to waste, how much
>>> design time you want to spend and how expensive you want the final
>>> product to be, your choices sort of boil down to a switcher with
>>> inductors and diodes and all that, or a current pump.
>>>
>>> Most of us would solve this problem by looking for a suitable IC.
>>> _Some_ of us would do it with two transistors, an inductor, and a cap,
>>> then brag about only needing one $.001 resistor instead of three.
>>
>> One resistor:
>>
>> ftp://jjlarkin.lmi.net/LED_boost.JPG
>>
>> John
>>
>tim@servo:~$ ftp jjlarkin.lmi.net
>Connected to jjlarkin.lmi.net.
>421 Service not available, remote server has closed connection
>ftp>
I can just doubleclick on the link in Agent, and Firefox opens the
image.
It's like Spehro's idea, but with a schmitt-trigger oscillator.
John
David Eather
David Eather
John Larkin
wrote:
>On 05/25/2010 11:27 AM, Tim Wescott wrote:
Since LEDs get more efficient when they're cold, there is a thevenin
drive impedance that results in nearly constant brightness over
temperature.
John
Don Klipstein
rich wrote:
1: Check out the latest and greatest offerings by Cree and Nichia. I
somewhat remember that many of these have forward voltage drop typically
3.2V at 20 mA.
And consider their forward voltage drop at 4-5 mA, or even less.
Further, consider that these typically have ratio of photometric output
to current peaking at 1.6 to 4 mA, and at 4 mA this ratio is usually about
1.3 times that at 20 mA. (If characterized at 20-30 mA and with maximum
continuous current anywhere around 30 mA.)
One more thing - good latest-and-greatest Cree and Nichia ones have
about twice the efficiency of most of the others. (Although their good
ones may be mostly through-hole ones.)
(Don't forget about 4-lead 7.5-7.62 mm square ones having .2 inch lead
spacing, characterized at 30 mA and having maximum current at least 35 mA.
The good ones of those do wonders at 4-5 mA and have decently wide viewing
angle, and Cree ones are available from Digi-Key.)
==============
If you have a higher budget for cost and for space, how about the
surface-mount DigiKey-available Cree XPEBLU-L1-R250-00Y01?
That one has typical voltage drop of 3.2V at 350 mA and maybe minimum
luminous output of 30.6 lumens at 30.6 mA.
At 50 mA, the typical voltage drop is down to about 2.85 volts according
to the 2nd of the 3 graphs in the datasheet page marking itself as "8" in
http://www.cree.com/products/pdf/XLampXP-E.pdf
At 50 mA, luminous output at 50 mA looks to me around 18, maybe 19% of
that achieved at 50 mA, meaning likely 5.5 to 6 lumens. This is according
to the second of 3 graphs in the page marked as "10" in the above
datasheet.
That page appears to me to indicate ratio of light output to current not
decreasing or at least not by much as current decreases down to maybe 25
or 20 mA. That curve makes me think probably 2.2-2.5 lumens at 20 mA.
The light distribution pattern in the 2nd of the 2 graphs in the above
datasheet, on its page marked as 11, makes me think that the light
distribution pattern is close to lambertian. With 60 degrees off-axis
being shown a bit bit higher than lambertian, I would guesstimate that
ratio of on-axis-candela to lumens is about 3, maybe as low as 2.9
(guesstimating).
So, so-far, this LED appears to me to have on-axis intensity of in or
near the ballpark of 733 to 862 millicandela at 20 mA. And with
2xtheta-half (nominal viewing angle) around 125-130 degrees. And likely
having typical voltage drop of 2.8 volts, maybe 2.76 at current so low.
One more thing to keep in mind - InGaN blue and green LEDs often have
peak wavelength and accordingly color varying slightly with voltage.
The peak wavelength usually varies slightly but noticeably inversely with
current.
The above Cree blue LED has dominant wavelength (a color specification
largely meaning hue) of 465 nm min, 485 nm max. This makes me think 475
nm typ. My experience with cree makes me suspect 476-477. That is a
"turquoise blue", close to the color of cyan printer ink, but a bit
deeper, pushing showing of a tinge of greenishness.
At around 6% of characterization current, I expect the dominant
wavelength to be probably at least 480 nm, maybe even 485-plus nm. This
usually looks like a noticeably somewhat greenish shade of blue.
At least that is much more bluish than "blue-green" and "traffic-signal-
green" LEDs, with typical dominant wavelength usually 497-507 nm, often
around 505 nm. If you are familiar with the color of the 486.1 nm
"H-Beta" line of hydrogen, keep that one in mind.
The 485-486 nm ballpark of wavelengths tends to appear to be a very
slightly greenish turquoise blue *when viewed brightly* (such as looking
into a 700-plus mcd LED),
and gets closer to an only slightly bluish side of blue-green *when
viewed dimly* (such as being in a room illuminated by this with at most a
few lumens).
Another thing - at 20 mA, I would not worry about heatsinking the LED's
thermal connection.
If your SMT soldering can accomodate the thermal pad, then I would
advise a trace 1.2 mm or .04-.05 inch wide under it, extending out to the
sides, overlayed with some sort of "buterfly wings" if you are capable of
achieving such layout, merely to make things a little better, as in
probably capable of handling 60 maybe 100 mA. Don't forget to deploy a
rectangular pad under the LED's thermal pad in your PCB layout so that you
don't get solder mask in the way. And I do like solder mask on copper
layout intended for heatsinking - solder mask has much higher emissivity
of thermal radiation than bare metal has.
And to the 3.2 mm wide (longer dimension) solder pads for the electrical
connections - I would run traces of width 3 mm or .12 inch, at least in
the 12.7 mm / 1/2 inch within these pads. Doing this heatsinks the LED
slightly, whether or not you can do tricks with thermal design of PCB
layout to the LED's thermal pad. This gets more important if you can't
solder to the central thermal pad. Wide traces to the LED's electrical
connections should make the LED safe to run at 30-40 mA as I guesstimate,
so that has high chance of achieving (or improving) this LED's safety of
being run at 20 mA.
Maybe you get enough light from this "high power" LED at 10 mA (with
typical voltage drop likely in the 2.72-2.8 volt range) - at which point I
see no need for thermal considerations, despite this LED differing from
low power ones by having maybe moderately higher thermal resistance
between the "junction" and the electrical leads (especially the
cathode one in the case of many LED chip chemistries including all
that I have heard of for blue).
--
- Don Klipstein (d...@misty.com)
Don Klipstein
>On 25 May 2010 10:22:59 -0700, Tim Wescott <t...@seemywebsite.now> wrote:
>
>>On 05/25/2010 10:18 AM, rich wrote:
>>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>>> find have a Vf equal to or greater than 3.3V.
>>
>>many lights you have, how much power you're willing to waste, how much
>>design time you want to spend and how expensive you want the final
>>product to be, your choices sort of boil down to a switcher with
>>inductors and diodes and all that, or a current pump.
>>
>>Most of us would solve this problem by looking for a suitable IC.
>>_Some_ of us would do it with two transistors, an inductor, and a cap,
>>then brag about only needing one $.001 resistor instead of three.
>
>One resistor:
>
>ftp://jjlarkin.lmi.net/LED_boost.JPG
Dear John Larkin,
I like that one! It's notably simple, as in being a DC-to-DC
converter having only 4 components (excluding the often-advised
capacitor across the power supply leads of the IC - .1 uF 25V cheapie
ceramic capacitor is an often-advised occaisionally-necessary item
that gets the component count up to 5, 6 if you also count the LED.
Component count may get to 6 excluding the LED, 7 including it, if
this boost converter gets good enough to overpower the LED or deliver
more output power than desired, so as to necessitate adding a resistor in
series with the LED.
I would like to add that efficiency is likely to improve if the non-LED
diode (a reaistor is offered as a workable alternative) is a Schottky one.
I would look into Schottky diodes with breakdown voltage 30V at most,
maybe 20V, and rated to handle 1 amp or less, maybe much less. Come to
think of it, much less to get improvement towards shorter switching times.
It does appear to me that the shown capacitor and resistor are "left to
the student". I would like to make that capacitor .01 uF merely from
knowing that one is a common cheap part. I could gain desire to make it
smaller in consideration of likely oscillation frequency considering a
desired value for the shown resistor...
I would want to make that resistor 100K max to "make this cleaner", and
I have a liking to get oscillation frequency into the 50 to
mildly-above-100 KHz ballpark, in order to make the oscillation frequency
ultrasonic to humans and most pets (even though dB acoustic pressure is
impressively low to negligible likely less than 30 1 meter away).
Also I would want the oscillation frequency to be not-too-close to the
common ones for TV/VCR/DVD common consumer devices. But if the LED emits
at a shorter wavelength, as in/near blue, that is less-likely a problem.
If that problem comes up anyway, I would primarily put a longpass filter
in front of the consumer device sensor - as in Wratten preferably 92,
secondarily 29, tertiarily 25 or equivalents including Schott glass
longpass optical filters (regardless ofwho supplies longpass optical
filters based on Schott glass products), having part numbers starting with
RG and including afterwards 630 to 670.
Don Klipstein
How are these data as function of temperature faring when current is
25 or 20 or 15 % of "characterizing current", when efficiency is improved
by current into the range of 15-25% of "characterizing current", in
addition to lower temperature that favors increase of ratio of light
output to LED current, more-so when the LEDs in question are underpowered?
Jan Panteltje
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in
<vd2pv55vqabddc91b...@4ax.com>:
I wanted to say:
Just use resistor to heat up the LED.
Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one,
and mount it next to the lED in parallel with the supply...
Now somebody could invent a LED with all that build in, photo sensor too,
to keep light output at a progammable (I2C perhaps) level.
Little switcher inside? Current limiter... This is the age of integration,
logic level I2C input.
Uwe Hercksen
Tim Wescott schrieb:
> AFAIK a white LED is just a blue LED chip with some fluorescent material
> in the package that makes enough "whatever else" to make it look white.
>
> They look exceedingly blue to me -- I don't know if that's because they
> are, or because I'm color deficient in green and don't see them the same
> as other people do.
Hello,
they mix the blue light with yellow light from the fluorescent material,
but it is a very narrow blue band and a very broad yellow band. If you
look at a spectrum diagram of the resulting light it looks very
different to white light from the sun or from a ligth bulb with a
glowing tungsten wire.
Bye
David Eather
Hi,
Could you post his circuit on www.filedropper.com or www.filefactory.com
or something similar - I just can connect.
Rich Webb
Some may indeed by bi-chromic but the ones that I've examined recently
with a handheld spectroscope have a remarkably even spectrum from about
420 to 680 nm. It's not a quantitative instrument but there were no
obvious emission or absorption lines. Surprised me, in a good way.
--
Rich Webb Norfolk, VA
David Eather
Nah, A one wire interface with parasitic power.
Spehro Pefhany
<pNaonSt...@yahoo.com> wrote:
>I wanted to say:
>Just use resistor to heat up the LED.
>Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one,
>and mount it next to the lED in parallel with the supply...
>
>Now somebody could invent a LED with all that build in, photo sensor too,
>to keep light output at a progammable (I2C perhaps) level.
>Little switcher inside? Current limiter... This is the age of integration,
>logic level I2C input.
Maybe a TEC and controller to control the wavelength?
Do you really want LEDs with 80 page manuals (and 5 pages of errata)?
;-)
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
John Larkin
Klipstein) wrote:
>In article <ti4ov551ahdt2po32...@4ax.com>, John Larkin wrote:
>>On 25 May 2010 10:22:59 -0700, Tim Wescott <t...@seemywebsite.now> wrote:
>>
>>>On 05/25/2010 10:18 AM, rich wrote:
>>>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>>>> find have a Vf equal to or greater than 3.3V.
>>>
>>>That pretty much demands a voltage boost of some sort. Depending on how
>>>many lights you have, how much power you're willing to waste, how much
>>>design time you want to spend and how expensive you want the final
>>>product to be, your choices sort of boil down to a switcher with
>>>inductors and diodes and all that, or a current pump.
>>>
>>>Most of us would solve this problem by looking for a suitable IC.
>>>_Some_ of us would do it with two transistors, an inductor, and a cap,
>>>then brag about only needing one $.001 resistor instead of three.
>>
>>One resistor:
>>
>>ftp://jjlarkin.lmi.net/LED_boost.JPG
>
> Dear John Larkin,
>
> I like that one! It's notably simple, as in being a DC-to-DC
>converter having only 4 components (excluding the often-advised
>capacitor across the power supply leads of the IC - .1 uF 25V cheapie
>ceramic capacitor is an often-advised occaisionally-necessary item
>that gets the component count up to 5, 6 if you also count the LED.
I usually do multilayer boards with power and ground planes. A few
bypass caps will do for the whole board, so I don't put one per chip
like in olden days.
>
> Component count may get to 6 excluding the LED, 7 including it, if
>this boost converter gets good enough to overpower the LED or deliver
>more output power than desired, so as to necessitate adding a resistor in
>series with the LED.
The average LED current is set by the R and C values, so you don't
need another resistor.
>
> I would like to add that efficiency is likely to improve if the non-LED
>diode (a reaistor is offered as a workable alternative) is a Schottky one.
>I would look into Schottky diodes with breakdown voltage 30V at most,
>maybe 20V, and rated to handle 1 amp or less, maybe much less. Come to
>think of it, much less to get improvement towards shorter switching times.
The danger is that the drop of the diode+LED had better be less than
the max supply voltage. So silicon might be better in some cases.
>
> It does appear to me that the shown capacitor and resistor are "left to
>the student". I would like to make that capacitor .01 uF merely from
>knowing that one is a common cheap part. I could gain desire to make it
>smaller in consideration of likely oscillation frequency considering a
>desired value for the shown resistor...
>
> I would want to make that resistor 100K max to "make this cleaner", and
>I have a liking to get oscillation frequency into the 50 to
>mildly-above-100 KHz ballpark, in order to make the oscillation frequency
>ultrasonic to humans and most pets (even though dB acoustic pressure is
>impressively low to negligible likely less than 30 1 meter away).
R and C have to be selected to get the desired LED current. There's a
second invisible capacitor, Cin of the gate, that's involved too.
Hmmm, neither C may matter. It might all cancel out. Somebody should
do the math.
John
George Herold
>
> - Show quoted text -
+3.3V----+-----------+
| |
|\| V This is diode or R
| \ -
+--+| >--+-CC---+
| | / | |
| |/| | V light comes out here
+------RR--+ -
|
GND
The IC is a schmitt trigger. (And connected to ground also...
connection not shown)
George H.
Jan Panteltje
<spef...@interlogDOTyou.knowwhat> wrote in
<pl3qv51sgc9qpu3gi...@4ax.com>:
>On Wed, 26 May 2010 10:10:52 GMT, the renowned Jan Panteltje
><pNaonSt...@yahoo.com> wrote:
>
>
>>I wanted to say:
>>Just use resistor to heat up the LED.
>>Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one,
>>and mount it next to the lED in parallel with the supply...
>>
>>Now somebody could invent a LED with all that build in, photo sensor too,
>>to keep light output at a progammable (I2C perhaps) level.
>>Little switcher inside? Current limiter... This is the age of integration,
>>logic level I2C input.
>
>Maybe a TEC and controller to control the wavelength?
>
>Do you really want LEDs with 80 page manuals (and 5 pages of errata)?
>;-)
Oh well, one gets used to things :-)
John Larkin
<spef...@interlogDOTyou.knowwhat> wrote:
>On Wed, 26 May 2010 10:10:52 GMT, the renowned Jan Panteltje
><pNaonSt...@yahoo.com> wrote:
>
>
>>I wanted to say:
>>Just use resistor to heat up the LED.
>>Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one,
>>and mount it next to the lED in parallel with the supply...
>>
>>Now somebody could invent a LED with all that build in, photo sensor too,
>>to keep light output at a progammable (I2C perhaps) level.
>>Little switcher inside? Current limiter... This is the age of integration,
>>logic level I2C input.
>
>Maybe a TEC and controller to control the wavelength?
>
>Do you really want LEDs with 80 page manuals (and 5 pages of errata)?
>;-)
>
>
>Best regards,
>Spehro Pefhany
We don't yet use any parts with thousand-page datasheets, but we do
have a couple over 800. And the longer the manual, the worse it seems
to be.
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
.
.
.
>Hmmm, neither C may matter. It might all cancel out. Somebody should
>do the math.
Who better than the designer?
Besides, that circuit won't work as drawn.
Jim Thompson
Klipstein) wrote:
Copy of a scheme by Bob Hirschfeld, at National, 40 years ago...
called "The Miser"... ran on a 1.5V cell.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
The only thing bipartisan in this country is hypocrisy
Jim Thompson
Wonder why? Wonder how Larkin will excuse that away ?:-)
whit3rd
> I need to drive a blue led from 3.3V. Most of the SMD blue leds I
> find have a Vf equal to or greater than 3.3V.
Wherever you got your 3.3V from, there's probably OTHER power
available. Use that.
Regulated 3.3V power is unsuitable for this task. If that's blocking
you, re-engineer it so it doesn't.
John Larkin
<jfi...@austininstruments.com> wrote:
>On Wed, 26 May 2010 07:24:46 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>.
>.
>.
>
>>Hmmm, neither C may matter. It might all cancel out. Somebody should
>>do the math.
>
>Who better than the designer?
I have a day job. An idea isn't a design.
>
>Besides, that circuit won't work as drawn.
Why not? The schmitt needs to be an inverter to oscillate of course,
but that should be obvious to anyone who posts to s.e.d. The point is
that a clock, a cap, and a diode will boost 3.3 volts nicely, to drive
a 3 volt LED. One could even eliminate the resistor!
Better than any ideas you or JT posted. C'mon, do us a 555 thing. Or
something with 85 transistors.
John
Jim Thompson
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Wed, 26 May 2010 11:19:43 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>>On Wed, 26 May 2010 07:24:46 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>.
>>.
>>.
>>
>>>Hmmm, neither C may matter. It might all cancel out. Somebody should
>>>do the math.
>>
>>Who better than the designer?
>
>I have a day job. An idea isn't a design.
>
>>
>>Besides, that circuit won't work as drawn.
>
>Why not? The schmitt needs to be an inverter to oscillate of course,
>but that should be obvious to anyone who posts to s.e.d. The point is
>that a clock, a cap, and a diode will boost 3.3 volts nicely, to drive
>a 3 volt LED. One could even eliminate the resistor!
>
>Better than any ideas you or JT posted. C'mon, do us a 555 thing. Or
>something with 85 transistors.
>
>John
>
Excuses! Excuses! Excuses!
Inverter or buffer, it can't work as drawn. Your day job certainly
isn't circuit design :-)
David Eather
Jim Thompson
wrote:
Theory of "operation" is left as an exercise for the student :-)
John Larkin
The schmitt has to be an inverter to oscillate, of course. I left out
the bubble.
RR could be a short, then it would oscillate faster!
John
Jim Thompson
Excuses! Excuses! Excuses! Where does a capacitor belong? (Giving
you the benefit of even having a clue :-)
Grant
John Larkin
Sure. CMOS ICs have input capacitance. I guess JT doesn't know much
about CMOS ICs.
I obviously left out the cap, on purpose, to hit the "one resistor"
target. It *will* oscillate without a discrete cap. What else could it
possibly do?
John
Jim Thompson
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
At a ridiculous speed, IF at all.... giving him the doubt that he
"left off the bubble"... what a dork fish :-)
Larkin huffs a lot. While he huffs and puffs and blows-hard, I design
custom CMOS every day, but I leave the bull shit out of mine.
Has Larkin EVER posted a working circuit... one that didn't need
additional bull shit as an added ingredient ?:-)
Don Klipstein
>On Wed, 26 May 2010 12:26:16 +0200, Uwe Hercksen
><herc...@mew.uni-erlangen.de> wrote:
>>
>>Tim Wescott schrieb:
>>
>>> AFAIK a white LED is just a blue LED chip with some fluorescent material
>>> in the package that makes enough "whatever else" to make it look white.
>>>
>>> They look exceedingly blue to me -- I don't know if that's because they
>>> are, or because I'm color deficient in green and don't see them the same
>>> as other people do.
>>
>>but it is a very narrow blue band and a very broad yellow band. If you
>>look at a spectrum diagram of the resulting light it looks very
>>different to white light from the sun or from a ligth bulb with a
>>glowing tungsten wire.
>
>Some may indeed by bi-chromic but the ones that I've examined recently
>with a handheld spectroscope have a remarkably even spectrum from about
>420 to 680 nm. It's not a quantitative instrument but there were no
>obvious emission or absorption lines. Surprised me, in a good way.
I find the spectrum to be smooth, but not even.
I see the spectrum running low in truly and fairly violet wavelengths.
(Shorter than 430 nm, though that actually means little as far as
practical illumination is concerned since in that part of the spectrum,
human vision has low sensitivity.)
Another irregularity that I see is the "blue peak" - usually visible to
me as a "brightish hump" in the spectrum, even if I merely use a CD as a
diffraction grating to view the spectrum. The reduction in diversity of
blue/bluish wavelengths has some negative impact on color rendering
properties, probably minor.
The next irregularity that I see is a dip/weakness in the blue-green to
bluish side of mid-green. I find that to have a minor negative effect on
color rendering. Another thing I find that to have is to make the light's
"scotopic/photopic ratio" or "s/p ratio" less than that of daylight or
blackbody radiation of the same color. That affects illumination ability
in dimmer environments where scotopic vision or mesopic vision (both
scotopic and photopic are significantly functioning) is the vision mode
that is being used.
After that, comes the irregularity of surplus of yellow and
yellow-orange and shortage of mid-green (even if shortage is only on
bluish side of mid-green) and shortage of mid-red. (The "red shortage"
is even worse in the deep red, but that matters less due to low
sensitivity of human vision to deep red.)
This irregularity causes dulling of the color of green things, and
dulling and darkening of the color of red things.
As the years have gone by, it appears to me that the color rendering
index of white LEDs (excluding enhanced or high CRI models) has drifted
downwards, from 75-plus of older ones around and before 2000 to around
65 for the highest efficency recent ones as of 2009. One reason is that
advancement of the phosphors used for these included narrowing the
yellowish emission band of the phosphor to produce less bluish-green and
blue-side-mid-green and less deep red and deeper mid-red, and more yellow
and greenish-yellow.
Another is that the "blue peak" wavelength has been shifted shorter in
highest-efficiency white LEDs, from around 467 nm in the late 1990's to
closer to 450 nm now. Shifting the "blue peak" towards 450 or upper 440's
of nm makes that spectral feature hit the "blue peak" of human vision
better, and that means less blue light has to escape the LED in question
to make white light, and more of the blue light can be converted to
yellowish light that human vision is more sensitive to in photometric
terms. However, this shift does deepen the "blue-green valley" and also
decreases s/p ratio.
For examples of white LEDs:
Older style spectrum: Nichia NSPW500S, NSPW500CS. Especially NSPW500S,
some of which may still be available from some nationally-selling-to-
hobbyists electronic surplus outfits. That LED is often noted as a 5600
MCD white LED. These have nominal color temperature of 6500 K, but appear
to me more like 6000 K. I determined a Nichia NSPWF50DS to have s/p
ratio of 2.3, which is only slightly short of the 2.36 of a 6000K
blackbody or the 2.45 of 6500K.
An extreme newer style spectrum: Nichia NSPWR70CSS-K1, which Nichia
claims to achieve 150 lumens out per watt in at 20 mA. I have personally
tested these to achieve 140-145 lumens/watt at 20 mA by a method prone to
erring on the conservative side. The nominal color temperature is 5000 K.
I have determined s/p ratio to be 1.7, while a 5000K blackbody achieves
2.15. I have also determined *some* red object color/brightness
rendering properties and a few other color rendering properties that I
can determine numerically to be like those of a common fluorescent lamp
whose CRI is 62, so I "guesstimate" that this LED's CRI (specifically the
Ra8 CRI) is 62-65.
I can name two other nominally 5000K LEDs stated by their manufacturer
to have CRI of 65, at least IIRC: Citizen / Cecol CL-L233-C13N and
CL-654-C1N. One was on and the other was hardly behind the bleeding
cutting edge of overall luminous efficacy for LEDs of their power class
when they became available, with convenient higher voltage drops
(muti-chip), considering competition that was actually available then,
even at ~3.2-3.5V voltage drop. The lower efficiency of those two even
has its 8 chips isolated from each other (16 contact package) and IIRC
rated to be paralleled with each other, allowing choice of 3 options for
voltage drop.
Phil Hobbs
Might need a cap at the input, but otherwise OK, I think. If you make
the resistor big enough, the input capacitance of the inverter should
make it work fine. Nice low parts count.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Jim Thompson
I think you'd need to tailor the rate to accommodate the source/sink
capability of the inverter (not shown, bubble to be imagined :-)
Phil Hobbs
Urinating contests aren't my cup of tea. ;)
Spehro Pefhany
<pcdhSpamM...@electrooptical.net> wrote:
>
>Might need a cap at the input, but otherwise OK, I think. If you make
>the resistor big enough, the input capacitance of the inverter should
>make it work fine. Nice low parts count.
>
>Cheers
>
>Phil Hobbs
A typical blue LED won't actually be off with a Si diode in series and
3.3V, even without considering temperature and tolerance on the 3.3V.
Can be fixed with two Si diodes in series the way I drew it (but even
that might be a bit marginal) or use a red LED for the diode.
Jim Thompson
<pcdhSpamM...@electrooptical.net> wrote:
But John "I left out the bubble" Larkin makes it so-o-o-o easy ;-)
I think he's the one going senile. He claims it's me, but I feel (and
think) like an 18 year old :-)
Phil Hobbs
Feeling that way is the first symptom. ;)
Jim Thompson
<pcdhSpamM...@electrooptical.net> wrote:
Nah! I thinks like an 18 year-old, then I falls asleep ;-)
Don Klipstein
>On Wed, 26 May 2010 21:55:56 -0400, Phil Hobbs
><pcdhSpamM...@electrooptical.net> wrote:
<I snip to this point to edit for space>
>>Urinating contests aren't my cup of tea. ;)
<I snip a bit more to edit for space, with hope of maintaining attribution>
>But John "I left out the bubble" Larkin makes it so-o-o-o easy ;-)
>
>I think he's the one going senile. He claims it's me, but I feel (and
>think) like an 18 year old :-)
How about when I feel like an 18-year-old? When I do, there are
usually none willing around!
(Besides, I have exchanged vows with someone that I love, and I have
fulfilled them for over 20 years without exception of so much as a
second, and my main barrier to being married to him is marriage law
where I live... unlike a fair portion of New England, along with all of
Canada, Belgium, Spain, South Africa and Holland [IIRC].)
Bitrex
Using the specs from the 74HC14, in this circuit it oscillates at about
140Khz with a 1 meg resistor:
Version 4
SHEET 1 880 680
WIRE 128 192 112 192
WIRE 224 192 192 192
WIRE 112 256 112 192
WIRE 224 256 224 192
WIRE 224 256 192 256
FLAG 144 96 0
FLAG 144 16 Vcc
FLAG 288 336 0
FLAG 288 112 Vcc
FLAG 112 320 0
SYMBOL Digital\\schmtinv 128 128 R0
SYMATTR InstName A1
SYMATTR SpiceLine Td = 5n
SYMATTR Value2 Vhigh=3.3 Vt=0.85 Vh=0.56
SYMBOL voltage 144 0 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3.3
SYMBOL res 208 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 1MEG
SYMBOL cap 288 176 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 27 62 VTop 0
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL res 272 176 R0
SYMATTR InstName R3
SYMATTR Value 220
SYMBOL LED 272 272 R0
SYMATTR InstName D1
SYMATTR Value NSCW100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 272 96 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL cap 96 256 R0
SYMATTR InstName C2
SYMATTR Value 3.5p
TEXT -6 54 Left 0 !.tran 0.1
John Larkin
Yup, it's perfectly reasonable. 5 pF, 1M, tau is 5 usec. Right in the
ballpark.
What else could it possibly do than oscillate?
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Wed, 26 May 2010 11:19:43 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>>On Wed, 26 May 2010 07:24:46 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>.
>>.
>>.
>>
>>>Hmmm, neither C may matter. It might all cancel out. Somebody should
>>>do the math.
>>
>>Who better than the designer?
>
>I have a day job.
---
If you don't have the time to devote to proving that what you profess
here is true, then why are you here?
---
>An idea isn't a design.
---
OK, but you put the idea to paper and fleshed it out by arranging all
of the components just so, which turned it into a design.
Not a very good one, but a design nonetheless.
---
>>Besides, that circuit won't work as drawn.
>
>Why not? The schmitt needs to be an inverter to oscillate of course,
>but that should be obvious to anyone who posts to s.e.d.
---
So, instead of striving for accuracy, you're sloppy and expect others
to find and correct your slovenly mistakes?
---
>The point is that a clock, a cap, and a diode will boost 3.3 volts nicely,
>to drive a 3 volt LED. One could even eliminate the resistor!
---
More rope, Mr. Larkin?
Which resistor would that be?
The one from the output of the Schmitt to the input, or the one you
tout could replace the diode connected to Vcc?
---
>Better than any ideas you or JT posted.
---
Sometimes, crap is worse than nothing at all.
---
>C'mon, do us a 555 thing. Or
>something with 85 transistors.
---
Trying to take the heat off of yourself with a little gratuitous
nonsense, huh?
Geez, John, you get more like Sloman every day!
Anyways, I have a better idea; let's take a look at your circuit VS
Bitrex's:
Version 4
SHEET 1 880 680
WIRE -128 16 -528 16
WIRE 336 16 -128 16
WIRE 336 32 336 16
WIRE -128 64 -128 16
WIRE 128 128 80 128
WIRE 224 128 192 128
WIRE 240 128 224 128
WIRE 336 128 336 112
WIRE 336 128 304 128
WIRE 336 160 336 128
WIRE -528 176 -528 16
WIRE -336 176 -384 176
WIRE -240 176 -272 176
WIRE -224 176 -240 176
WIRE -128 176 -128 128
WIRE -128 176 -160 176
WIRE 80 192 80 128
WIRE 112 192 80 192
WIRE 224 192 224 128
WIRE 224 192 192 192
WIRE -128 224 -128 176
WIRE -384 256 -384 176
WIRE -352 256 -384 256
WIRE -240 256 -240 176
WIRE -240 256 -272 256
WIRE 80 256 80 192
WIRE 336 272 336 240
WIRE -384 288 -384 256
WIRE -528 368 -528 256
WIRE -384 368 -384 352
WIRE -384 368 -528 368
WIRE -128 368 -128 288
WIRE -128 368 -384 368
WIRE 80 368 80 320
WIRE 80 368 -128 368
WIRE 336 368 336 336
WIRE 336 368 80 368
WIRE -528 416 -528 368
FLAG -528 416 0
SYMBOL Digital\\schmtinv 128 64 R0
SYMATTR InstName A1
SYMATTR SpiceLine Td = 5n
SYMATTR Value2 Vhigh=3.3 Vt=0.85 Vh=0.56
SYMBOL res 208 176 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 1MEG
SYMBOL cap 304 112 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 40 29 VTop 0
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL res 320 144 R0
SYMATTR InstName R3
SYMATTR Value 220
SYMBOL LED 320 272 R0
SYMATTR InstName D1
SYMATTR Value NSCW100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 320 16 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL cap 64 256 R0
SYMATTR InstName C2
SYMATTR Value 3.5p
SYMBOL cap -160 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 10n
SYMBOL voltage -528 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 3.3
SYMBOL res -256 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 1e6
SYMBOL cap -400 288 R0
SYMATTR InstName C4
SYMATTR Value 3.5p
SYMBOL LED -144 224 R0
SYMATTR InstName D2
SYMATTR Value NSCW100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL Digital\\schmtinv -336 112 R0
SYMATTR InstName A2
SYMATTR SpiceLine Td = 5n
SYMATTR Value2 Vhigh=3.3 Vt=0.85 Vh=0.56
SYMBOL diode -144 64 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
TEXT -520 392 Left 0 !.tran 10e-5
---
I went ahead and used his values in your circuit since his works
pretty well, but it seems like you left out the 220 ohm resistor.
I guess that was because you _wanted_ those huge spikes in the output
of A2, huh?
Or were you "on purpose" sloppily depending on the totem pole
transistors to come out of saturation and do the resistor's job, but
you just haven't gotten around to saying anything about it?
Spehro Pefhany
<bit...@de.lete.earthlink.net> wrote:
>
>Using the specs from the 74HC14, in this circuit it oscillates at about
>140Khz with a 1 meg resistor:
Well, you'd expect something of the order of 2*R*C where C is
something like five puffs, so 100kHz-ish, rough order of magnitude.
John Devereux
> On Wed, 26 May 2010 15:59:34 -0700, John Larkin
> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Thu, 27 May 2010 08:51:22 +1000, Grant <o...@grrr.id.au> wrote:
>>
>>>On Wed, 26 May 2010 15:29:21 -0700, Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> wrote:
>>>
>>>>On Wed, 26 May 2010 15:10:15 -0700, John Larkin
>>>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>>>
>>>>>On Wed, 26 May 2010 07:31:33 -0700 (PDT), George Herold
>>>>><ghe...@teachspin.com> wrote:
>>>>>
[...]
I didn't notice - it was pretty obvious to me what the idea was. It's a
sketch of an idea, not a schematic entered into a cad system. I thought
it was very nice, impressively minimalistic. I like the idea of using
the input capacitance as a component. And as others have pointed out it
in fact it runs at perfectly reasonable frequencies (lower than I would
have guessed without calculating it).
[...]
--
John Devereux
John Larkin
<jfi...@austininstruments.com> wrote:
>On Wed, 26 May 2010 11:48:28 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Wed, 26 May 2010 11:19:43 -0500, John Fields
>><jfi...@austininstruments.com> wrote:
>>
>>>On Wed, 26 May 2010 07:24:46 -0700, John Larkin
>>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>>
>>>.
>>>.
>>>.
>>>
>>>>Hmmm, neither C may matter. It might all cancel out. Somebody should
>>>>do the math.
>>>
>>>Who better than the designer?
>>
>>I have a day job.
>
>---
>If you don't have the time to devote to proving that what you profess
>here is true, then why are you here?
Just to fool around with ideas and learn things.
>---
>
>>An idea isn't a design.
>
>---
>OK, but you put the idea to paper and fleshed it out by arranging all
>of the components just so, which turned it into a design.
No, that was a scribble, just an idea. I did no math and it had no
values.
>
>Not a very good one, but a design nonetheless.
It could be useful, both for powering LEDs and for generating bias
voltages, like a little negative voltage for a gaasfet. Or both at the
same time. A schmitt oscillator deesn't need a capacitor just because
you're used to seeing one.
Why do ideas offend you so?
>---
>
>>>Besides, that circuit won't work as drawn.
>>
>>Why not? The schmitt needs to be an inverter to oscillate of course,
>>but that should be obvious to anyone who posts to s.e.d.
>
>---
>So, instead of striving for accuracy, you're sloppy and expect others
>to find and correct your slovenly mistakes?
I don't expect anything, except whining from you and JT.
>---
>
>>The point is that a clock, a cap, and a diode will boost 3.3 volts nicely,
>>to drive a 3 volt LED. One could even eliminate the resistor!
>
>---
>More rope, Mr. Larkin?
>
>Which resistor would that be?
The obvious one.
>
>The one from the output of the Schmitt to the input, or the one you
>tout could replace the diode connected to Vcc?
Tout? Did you used to be a newspaper reporter in junior high school or
something?
>---
>
>>Better than any ideas you or JT posted.
>
>---
>Sometimes, crap is worse than nothing at all.
>---
>
>>C'mon, do us a 555 thing. Or
>>something with 85 transistors.
>
>---
>Trying to take the heat off of yourself with a little gratuitous
>nonsense, huh?
>
>Geez, John, you get more like Sloman every day!
Sloman doesn't do electronics. I had 5 or arguably 6 seriously good
ideas yesterday, things that *will* be rigorously implemented and
sold. And of course a bunch of silly ideas. If you aren't willing to
create silly ideas, and make mistakes doing it, you're not going to
ever come up with the seriously good ones. The rigor can come later.
The guys who immediately criticize ideas, instead of riffing on them,
are always the guys who have few of their own.
So rail on!
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
Nice try, but ideas don't offend me at all; they make me a living.
What does offend me is patronizing little shits like you.
---
>>>>Besides, that circuit won't work as drawn.
>>>
>>>Why not? The schmitt needs to be an inverter to oscillate of course,
>>>but that should be obvious to anyone who posts to s.e.d.
>>
>>---
>>So, instead of striving for accuracy, you're sloppy and expect others
>>to find and correct your slovenly mistakes?
>
>I don't expect anything, except whining from you and JT.
---
It's not whining John, it's criticism.
Of course, since you hold yourself in such high regard that critcism
of you falls on deaf ears, you must try to disguise what it really is
by demeaning it, so you call it "whining".
---
>>>The point is that a clock, a cap, and a diode will boost 3.3 volts nicely,
>>>to drive a 3 volt LED. One could even eliminate the resistor!
>>
>>---
>>More rope, Mr. Larkin?
>>
>>Which resistor would that be?
>
>The obvious one.
---
OK, then, why would it be bad idea to eliminate that resistor?
---
>>
>>The one from the output of the Schmitt to the input, or the one you
>>tout could replace the diode connected to Vcc?
>
>Tout? Did you used to be a newspaper reporter in junior high school or
>something?
---
What a strange response...
What are you trying to say?
---
>>>Better than any ideas you or JT posted.
>>
>>---
>>Sometimes, crap is worse than nothing at all.
>>---
>>
>>>C'mon, do us a 555 thing. Or
>>>something with 85 transistors.
>>
>>---
>>Trying to take the heat off of yourself with a little gratuitous
>>nonsense, huh?
>>
>>Geez, John, you get more like Sloman every day!
>
>Sloman doesn't do electronics.
---
I wasn't talking about electronics.
---
>I had 5 or arguably 6 seriously good
>ideas yesterday, things that *will* be rigorously implemented and
>sold. And of course a bunch of silly ideas. If you aren't willing to
>create silly ideas, and make mistakes doing it, you're not going to
>ever come up with the seriously good ones. The rigor can come later.
---
Hey, that's a pretty neat trick; patting yourself on the back while
spouting platitudes!
How typically Larkinese...
---
>The guys who immediately criticize ideas, instead of riffing on them,
>are always the guys who have few of their own.
---
Geez, John, I did your circuit up in LTspice and played it alonside
Bitrex's well-thought-out version, and yours was flat.
I then attached the circuit list to my last post, but I've seen no
response to it from you and it was, in fact, snipped.
Again typical Larkinese... "If it's not complimentary, make it go
away".
---
>So rail on!
---
That's the plan!
JF
Jim Thompson
<jfi...@austininstruments.com> wrote:
>On Thu, 27 May 2010 08:22:46 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Thu, 27 May 2010 06:02:29 -0500, John Fields
>><jfi...@austininstruments.com> wrote:
>>
>>
>>Just to fool around with ideas and learn things.
>>
>>
>>
>>No, that was a scribble, just an idea. I did no math and it had no
>>values.
>>
>>
>>It could be useful, both for powering LEDs and for generating bias
>>voltages, like a little negative voltage for a gaasfet. Or both at the
>>same time. A schmitt oscillator deesn't need a capacitor just because
>>you're used to seeing one.
>>
>>Why do ideas offend you so?
>---
>Nice try, but ideas don't offend me at all; they make me a living.
>
>What does offend me is patronizing little shits like you.
>---
>
>
>>
>>I don't expect anything, except whining from you and JT.
>
>---
>It's not whining John, it's criticism.
>
>Of course, since you hold yourself in such high regard that critcism
>of you falls on deaf ears, you must try to disguise what it really is
>by demeaning it, so you call it "whining".
>---
>
>>
>>The obvious one.
>
>---
>OK, then, why would it be bad idea to eliminate that resistor?
>---
>
>>
>>Tout? Did you used to be a newspaper reporter in junior high school or
>>something?
>
>---
>What a strange response...
>
>What are you trying to say?
>---
>
>>
>>Sloman doesn't do electronics.
>
>---
>I wasn't talking about electronics.
>---
>
>>I had 5 or arguably 6 seriously good
>>ideas yesterday, things that *will* be rigorously implemented and
>>sold. And of course a bunch of silly ideas. If you aren't willing to
>>create silly ideas, and make mistakes doing it, you're not going to
>>ever come up with the seriously good ones. The rigor can come later.
>
>---
>Hey, that's a pretty neat trick; patting yourself on the back while
>spouting platitudes!
>
>How typically Larkinese...
>---
>
[multi-snipped]
An Obama wannabe ?:-)
John Larkin
Oh, your sim is crap. Look at the currents through D2 and D3!
You added R3 to the second circuit to make up for the absurd schmitt
model you're using.
If you try hard enough, you can break any circuit and reject any idea.
Keep it up.
John
John Larkin
<spef...@interlogDOTyou.knowwhat> wrote:
>On Wed, 26 May 2010 21:36:02 -0400, the renowned Phil Hobbs
><pcdhSpamM...@electrooptical.net> wrote:
>
>>
>>Might need a cap at the input, but otherwise OK, I think. If you make
>>the resistor big enough, the input capacitance of the inverter should
>>make it work fine. Nice low parts count.
>>
>>Cheers
>>
>>Phil Hobbs
>
>A typical blue LED won't actually be off with a Si diode in series and
>3.3V, even without considering temperature and tolerance on the 3.3V.
>
>Can be fixed with two Si diodes in series the way I drew it (but even
>that might be a bit marginal) or use a red LED for the diode.
>
This is nice:
+3.3
|
|
led
|
|
c
+3.3-------R-------b BCX70K
e
|
|
|
gnd
R is 330K maybe. Current will be around 5 mA down to Vcc-Vled of maybe
0.2 volts. The BCXs are beta-binned, plenty tight enough for an LED.
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Thu, 27 May 2010 12:22:29 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>
>>Geez, John, I did your circuit up in LTspice and played it alonside
>>Bitrex's well-thought-out version, and yours was flat.
>>
>>I then attached the circuit list to my last post, but I've seen no
>>response to it from you and it was, in fact, snipped.
>
>Oh, your sim is crap. Look at the currents through D2 and D3!
---
It's not my sim that's crap, it's your circuit that's allowing that to
happen.
---
>You added R3 to the second circuit to make up for the absurd schmitt
>model you're using.
---
Sorry, Charlie, I had nothing to do with it; Im just the messenger.
That's Bitrex's improvement of your circuit and the Schmitt is just a
big old fast dumb inverting switch with a little hysteresis on the
front end which can source and sink all the current your pig of a
circuit demands.
---
>If you try hard enough, you can break any circuit and reject any idea.
---
When they're broken from the get-go you don't have to try hard at all,
the damned things just fall apart in your hands.
---
>Keep it up.
---
I'll try.
John Larkin
<jfi...@austininstruments.com> wrote:
>On Thu, 27 May 2010 11:07:57 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Thu, 27 May 2010 12:22:29 -0500, John Fields
>><jfi...@austininstruments.com> wrote:
>>
>>
>>>Geez, John, I did your circuit up in LTspice and played it alonside
>>>Bitrex's well-thought-out version, and yours was flat.
>>>
>>>I then attached the circuit list to my last post, but I've seen no
>>>response to it from you and it was, in fact, snipped.
>>
>>Oh, your sim is crap. Look at the currents through D2 and D3!
>
>---
>It's not my sim that's crap, it's your circuit that's allowing that to
>happen.
Hang a 0.1 ohm resistor from the schmitt output to ground. Measure the
current. Report back.
That's no HC14!
John
Jim Thompson
Jim Thompson
Surf on "LM3909 replacement with low power consumption"
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Thu, 27 May 2010 14:57:38 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>>On Thu, 27 May 2010 11:07:57 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Thu, 27 May 2010 12:22:29 -0500, John Fields
>>><jfi...@austininstruments.com> wrote:
>>>
>>>
>>>>Geez, John, I did your circuit up in LTspice and played it alonside
>>>>Bitrex's well-thought-out version, and yours was flat.
>>>>
>>>>I then attached the circuit list to my last post, but I've seen no
>>>>response to it from you and it was, in fact, snipped.
>>>
>>>Oh, your sim is crap. Look at the currents through D2 and D3!
>>
>>---
>>It's not my sim that's crap, it's your circuit that's allowing that to
>>happen.
>
>Hang a 0.1 ohm resistor from the schmitt output to ground. Measure the
>current. Report back.
>
>That's no HC14!
---
And there's no need for it to be, since what we're interested in
finding out about your circuit is, initially, how it behaves using a
perfect driver. (well, a driver with with a 1 ohm source resistance,
which is what LTspice's gates default to.)
With that in mind it's clear that even with a perfect driver, your
circuit, which pushes 150mA spikes which decay to essentially 0mA in
4ns every 10 microseconds or so through the LED, won't work.
More's the pity for a poor little HC14 running at 3.3V, which can only
source or sink currents on the order of 10mA or so before the Rds(on)
of the output transistors starts dropping enough voltage to starve the
LED.
The conclusion then is, I'm pretty sure, that since you specified a
Schmitt trigger inverter for your driver which needs to be made out of
unobtanium, your idea/design/sketch/scribble/whatever, as drawn, is
dead in the water.
Oh, and about getting rid of the timing resistor to speed things up?
If you fix the circuit, you might want to talk to the FCC before you
start selling anything...
Just an idea...
JF
John Larkin
<jfi...@austininstruments.com> wrote:
And it has picosecond rise and fall times. Which is why there are
insane currents *in both directions* in the diode and the LED.
>
>With that in mind it's clear that even with a perfect driver, your
>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>4ns every 10 microseconds or so through the LED, won't work.
It actually does work with a perfect driver, as your sim shows. It
works better with a real-world CMOS part and properly chosen values.
You don't believe in charge pumps?
You also boogered the schmitt thresholds to totally unrealistic
values, for some reason. Probably to make the second circuit work.
>
>More's the pity for a poor little HC14 running at 3.3V, which can only
>source or sink currents on the order of 10mA or so before the Rds(on)
>of the output transistors starts dropping enough voltage to starve the
>LED.
You were just complaining that the circuit pushes too much current
into the LED, now you are complaining that it pushes too little.
The output impedance of an HC14 is a nice match to the LED. The
average LED current depends on the switching frequency and the value
of the cap. I = CVF and all that. That can be *designed* as needed. Or
broken, if you prefer.
But ancient HC, and especially modern Tiny cmos parts, can drive a lot
more than 10 mA at 3.3 volts.
>
>The conclusion then is, I'm pretty sure, that since you specified a
>Schmitt trigger inverter for your driver which needs to be made out of
>unobtanium, your idea/design/sketch/scribble/whatever, as drawn, is
>dead in the water.
You picked a perfectly stupid Spice model for the schmitt so that you
could make it not work to your satisfaction. Do you specialize in
making things not work?
>
>Oh, and about getting rid of the timing resistor to speed things up?
>
>If you fix the circuit, you might want to talk to the FCC before you
>start selling anything...
I said it would scream. But there are lots of digital circuits around,
on BIG boards, that run at hundreds of MHz. We do that all the time.
Four dacs, clocked at 128 MHz:
ftp://jjlarkin.lmi.net/DSC01786.JPG
Scary stuff. Being a 555 guy, you probably don't deal with MHz very
often.
My circuit is similar to Spehro's. Attack him for a while.
At least you got the schmitt to oscillate, as JT said it wouldn't.
Attack him, too. Canes and walkers at 20 paces maybe.
John
Jim Thompson
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
As shown.
>Attack him, too. Canes and walkers at 20 paces maybe.
>
>John
"Engineered" all the way ?:-) This Yo-Yo has a history of ba-a-a-ad
circuit posts.
John Fields
---
That's nice???
It seems kinda fugly to me...
It's just a plain old common emitter, sorted for beta and forced into
taking center stage, while Hfe(t) and Vce(sat) are really running the
show.
On one hand it might stop the LED from glowing when Vbe = 0V but, on
the other, what is it you don't understand about:
"I need to drive a blue led from 3.3V. Most of the SMD blue leds I
find have a Vf equal to or greater than 3.3V.
I am curious how others are dealing with this.
Thanks
Rich"
Clearly, by interposing Vce(sat) between the supply and the LED you've
reduced the current available to the LED and dimmed its output in a
clumsy way.
Can you dig yourself out of this pit into which you've fallen with
other than invective?
John Larkin
You got it!
>On one hand it might stop the LED from glowing when Vbe = 0V but, on
>the other, what is it you don't understand about:
>
>"I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>find have a Vf equal to or greater than 3.3V.
>
>I am curious how others are dealing with this.
>
>Thanks
>
>Rich"
>
>Clearly, by interposing Vce(sat) between the supply and the LED you've
>reduced the current available to the LED and dimmed its output in a
>clumsy way.
Read my reply to him. I noted that most blue LEDs actually need less
than 3.3 volts, and that if his really do need more, use a charge
pump. If his LED does work on 3.1 or less, my little transistor thing
delivers a decently constant current. If they need much less, a
resistor will do. I think I said that somewhere too.
If I said that iron is a metal, you'd crank up Spice and prove it
wrong.
>
>Can you dig yourself out of this pit into which you've fallen with
>other than invective?
Since you have proven by simulation that charge pumps don't work, I'm
in big trouble. So is Maxim.
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
IWith that in mind it's clear that even with a perfect driver, your
>>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>>4ns every 10 microseconds or so through the LED, won't work.
>
>It actually does work with a perfect driver, as your sim shows.
---
Nope. Unfortunately, you don't have a perfect driver, so your scheme
is bogus, from the start.
---
>It
>works better with a real-world CMOS part and properly chosen values.
>You don't believe in charge pumps?
---
---
>
>My circuit is similar to Spehro's. Attack him for a while.
---
Why would I want to do that?
Spehro's a good guy who doesn't play the "I'm better than you are"
games, so why are you trying to recruit him into the fold of my
detractors?
---
>At least you got the schmitt to oscillate, as JT said it wouldn't.
>Attack him, too. Canes and walkers at 20 paces maybe.
>
>John
---
JT and I have had words about what it takes to turn a comparator into
a VCO, which is something that seems to be beyond your ken.
So you think it's all about attack, huh?
You're truly a philosophical idiot.
John Larkin
<jfi...@austininstruments.com> wrote:
You're a very bad circuit designer.
John
Jim Thompson
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Thu, 27 May 2010 21:22:51 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
[snip]
>>
>>You're truly a philosophical idiot.
>
>You're a very bad circuit designer.
>
>John
Speaking of yourself ?:-)
You're throwing some _really_ bad shit on the table, and it's going to
bounce back in your face.
Jim Thompson
<To-Email-Use-Th...@On-My-Web-Site.com> wrote:
>On Thu, 27 May 2010 20:23:53 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Thu, 27 May 2010 21:22:51 -0500, John Fields
>><jfi...@austininstruments.com> wrote:
>>
>[snip]
>>>
>>>You're truly a philosophical idiot.
>>
>>You're a very bad circuit designer.
>>
>>John
>
>Speaking of yourself ?:-)
>
>You're throwing some _really_ bad shit on the table, and it's going to
>bounce back in your face.
>
And you keep counting on the general amateur level of lurkers here to
let you get by with it.
I urge everyone to LTspice anything that Larkin throws out here,
particularly taking note of unrealistic clock speeds and resulting
current levels.
Bitrex
Looking over the circuit again I don't think that LTSpice inverter
models realistic output impedance. I hung a capacitor off the input to
model the gate capacitance, but I forgot to put one on the output to
substitute for the output impedance. It still seems to work fine with a
100 ohm resistor on the output. I put the 220 ohm resistor there
because I wanted to see what output voltage it was creating for
different component values, without it there the voltage just drops to
the forward voltage of the LED.
Has anyone thought to breadboard the circuit up? Surely that would
settle the dispute. I don't think I have any modern inverters lying
around, but I do have blue LEDs and some 74LS14s somewhere!
John Larkin
<bit...@de.lete.earthlink.net> wrote:
>John Larkin wrote:
>> On Thu, 27 May 2010 12:22:29 -0500, John Fields
>> <jfi...@austininstruments.com> wrote:
>>
>>
>>> Geez, John, I did your circuit up in LTspice and played it alonside
>>> Bitrex's well-thought-out version, and yours was flat.
>>>
>>> I then attached the circuit list to my last post, but I've seen no
>>> response to it from you and it was, in fact, snipped.
>>
>> Oh, your sim is crap. Look at the currents through D2 and D3!
>>
>> You added R3 to the second circuit to make up for the absurd schmitt
>> model you're using.
>>
>> If you try hard enough, you can break any circuit and reject any idea.
>> Keep it up.
>>
>> John
>>
>>
>
>
>Looking over the circuit again I don't think that LTSpice inverter
>models realistic output impedance.
It has zero rise and fall time and 1 ohm impedance. It will source or
sink 3 amps. And the schmitt thresholds are silly. That's why it's
pounding so much current into all the junctions in both directions.
I wish I could buy a gate like that!
I hung a capacitor off the input to
>model the gate capacitance, but I forgot to put one on the output to
>substitute for the output impedance. It still seems to work fine with a
>100 ohm resistor on the output. I put the 220 ohm resistor there
>because I wanted to see what output voltage it was creating for
>different component values, without it there the voltage just drops to
>the forward voltage of the LED.
>
>Has anyone thought to breadboard the circuit up? Surely that would
>settle the dispute. I don't think I have any modern inverters lying
>around, but I do have blue LEDs and some 74LS14s somewhere!
And LS will need a low value resistor to oscillate, ballpark 1K,
because of its DC input current. So to get a sensibly low oscillation
frequency you'd need a real capacitor, not just Cin of the gate. A
CMOS schmitt will oscillate with a 1M resistor, or probably with a 1G
resistor.
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
---
Good point; here it is with real-world rise and fall times right out
of Philips' Data Handbook IC06:
SYMBOL res 208 176 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 1MEG
SYMBOL cap 304 112 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 40 29 VTop 0
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL res 320 144 R0
SYMATTR InstName R3
SYMATTR Value 220
SYMBOL LED 320 272 R0
SYMATTR InstName D1
SYMATTR Value NSCW100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 320 16 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL cap 64 256 R0
SYMATTR InstName C2
SYMATTR Value 5p
SYMBOL cap -160 160 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 10n
SYMBOL voltage -528 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 3.3
SYMBOL res -256 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 1e6
SYMBOL cap -400 288 R0
SYMATTR InstName C4
SYMATTR Value 5p
SYMBOL LED -144 224 R0
SYMATTR InstName D2
SYMATTR Value NSCW100
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL Digital\\schmtinv -336 112 R0
SYMATTR InstName A2
SYMATTR SpiceLine trise 100e-9 tfall 100e-9
SYMATTR Value2 Vhigh=3.3 Vt=1.65 Vh=0.5
SYMBOL diode -144 64 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL Digital\\schmtinv 128 64 R0
SYMATTR InstName A1
SYMATTR SpiceLine trise 100e-9 tfall 100e-9
SYMATTR Value2 Vhigh=3.3 Vt=1.65 Vh=0.5
TEXT -520 392 Left 0 !.tran 0 10e-5 1e-6
Happy now?
The currents are _still_ insane.
---
>>With that in mind it's clear that even with a perfect driver, your
>>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>>4ns every 10 microseconds or so through the LED, won't work.
>
>It actually does work with a perfect driver, as your sim shows.
---
If the criterion determining "works" is whether the LED will emit
light which can be detected by the human eye in a casual manner, then
I submit that 4ns wide pulses occurring at a rep rate of 100kHz won't
quite fill the bill.
---
>It works better with a real-world CMOS part and properly chosen values.
---
Neither of which you addressed earlier, with your cockamamie circuit,
while now you're pontificating as if you did.
---
>You don't believe in charge pumps?
---
Idiot.
What's that supposed to do, put me on the defensive?
---
>You also boogered the schmitt thresholds to totally unrealistic
>values, for some reason. Probably to make the second circuit work.
---
I just copied Bitrex's part without looking at the values, but changed
them, above, to half of Vcc +/- 0.5V, which is more realistic, and it
still oscillates.
The fact of the matter is, dolt, you can make the switching points
whatever you like and the thing will still oscillate.
---
>>More's the pity for a poor little HC14 running at 3.3V, which can only
>>source or sink currents on the order of 10mA or so before the Rds(on)
>>of the output transistors starts dropping enough voltage to starve the
>>LED.
>
>You were just complaining that the circuit pushes too much current
>into the LED, now you are complaining that it pushes too little.
---
Hmm...
You really _are_ rather thicker than I thought, since one example was
with a perfect driver and the other with real-world parts.
However, in either case, your circuit won't work.
---
>The output impedance of an HC14 is a nice match to the LED.
---
That depends on how much current the LED needs, since the higher it
goes, the lower the available output voltage from the gate.
---
>The average LED current depends on the switching frequency
>and the value of the cap. I = CVF and all that.
>That can be *designed* as needed. Or broken, if you prefer.
---
More platitudes...
---
>But ancient HC, and especially modern Tiny cmos parts, can drive a lot
>more than 10 mA at 3.3 volts.
---
Blah, blah, blah.
---
>>The conclusion then is, I'm pretty sure, that since you specified a
>>Schmitt trigger inverter for your driver which needs to be made out of
>>unobtanium, your idea/design/sketch/scribble/whatever, as drawn, is
>>dead in the water.
>
>You picked a perfectly stupid Spice model for the schmitt so that you
>could make it not work to your satisfaction.
---
Nope, I just used what was there.
---
>Do you specialize in making things not work?
---
Nope, I specialize in pointing out things that don't work.
Like, for instance, latching relays with infinite gain.
---
>>Oh, and about getting rid of the timing resistor to speed things up?
>>
>>If you fix the circuit, you might want to talk to the FCC before you
>>start selling anything...
>
>I said it would scream. But there are lots of digital circuits around,
>on BIG boards, that run at hundreds of MHz. We do that all the time.
---
Snipped ad.
---
>Scary stuff. Being a 555 guy, you probably don't deal with MHz very
>often.
---
Scary for you maybe, but you have no idea what I'm up to.
---
>My circuit is similar to Spehro's. Attack him for a while.
---
Why should I?
He's not an asshole.
---
>At least you got the schmitt to oscillate, as JT said it wouldn't.
---
He was right, too, since your initial "offering" was missing a bubble.
---
>Attack him, too.
---
BTDTGTTS
---
Canes and walkers at 20 paces maybe.
---
And you're getting younger???
John Larkin
<jfi...@austininstruments.com> wrote:
You still have a silly Schmitt model. It will put out 3 amps, not
realistic for a cmos logic part. That's why the peak currents are
high.
But as long as the gate can make full swing, the average LED current
depends on the frequency and the cap value. And every version you
posted, including this one, does push a reasonable abount of average
forward current into the LED.
I should hope it works. It's a simple charge pump. Your latest example
puts about 5.5 mA average forward current into the LED. You have
proved that my charge pump works, even with the unrealistic schmitt
model.
>---
>
>
>>>With that in mind it's clear that even with a perfect driver, your
>>>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>>>4ns every 10 microseconds or so through the LED, won't work.
>>
>>It actually does work with a perfect driver, as your sim shows.
>
>---
>If the criterion determining "works" is whether the LED will emit
>light which can be detected by the human eye in a casual manner, then
>I submit that 4ns wide pulses occurring at a rep rate of 100kHz won't
>quite fill the bill.
Average current makes light. Eyeballs respond to average light. Are
you suggesting that X microwatts of light are visible if DC, but
invisible if the same average amount of photons arrive in bunches?
Those big roadside billboards use multiplexed LEDs, each LED operating
at a low duty cycle. These are invisible to you?
>---
>
>>It works better with a real-world CMOS part and properly chosen values.
>
>---
>Neither of which you addressed earlier, with your cockamamie circuit,
>while now you're pontificating as if you did.
>---
>
>>You don't believe in charge pumps?
>
>---
>Idiot.
>
>What's that supposed to do, put me on the defensive?
If you claim charge pumps can't work, you've done that to yourself.
If you can't come up with values to make this charge pump work nicely,
you've compounded the damage. You so badly want it not to work that
you've stopped thinking like an engineer. That's a really bad sign,
letting your emotions suspend your ability to design. If you wanted it
to work, you'd let it work.
>---
>
>>You also boogered the schmitt thresholds to totally unrealistic
>>values, for some reason. Probably to make the second circuit work.
>
>---
>I just copied Bitrex's part without looking at the values, but changed
>them, above, to half of Vcc +/- 0.5V, which is more realistic, and it
>still oscillates.
>
>The fact of the matter is, dolt, you can make the switching points
>whatever you like and the thing will still oscillate.
Bitrex's circuit likes an asymmetric duty cycle, which is maybe why he
has the thresholds where they are. The asymmetry struck me
immediately, because an HC gate oscillator would be nearly symmetric.
>---
>
>>>More's the pity for a poor little HC14 running at 3.3V, which can only
>>>source or sink currents on the order of 10mA or so before the Rds(on)
>>>of the output transistors starts dropping enough voltage to starve the
>>>LED.
>>
>>You were just complaining that the circuit pushes too much current
>>into the LED, now you are complaining that it pushes too little.
>
>---
>Hmm...
>
>You really _are_ rather thicker than I thought, since one example was
>with a perfect driver and the other with real-world parts.
>
>However, in either case, your circuit won't work.
In all the cases you've simulated, it does work. So many people do
things like this that it's hardly "my" circuit. It was done with tubes
before I was born.
John
Bitrex
> Bitrex's circuit likes an asymmetric duty cycle, which is maybe why he
> has the thresholds where they are. The asymmetry struck me
> immediately, because an HC gate oscillator would be nearly symmetric.
>
I'm still new to LTSpice, I was a little confused about how the model
sets the thresholds and hysteresis. In datasheets the hysteresis is
defined as the difference between the high transition point and the low
transition point, in the model Vh seems to be the difference between the
high and low transition points and the midpoint, which is defined by the
Vt parameter. I think I've rectified most of my errors now...:)
John Larkin
If the Spice definitions aren't clear, you can just look at the gate
input triangle to see where it actually switches.
Most cmos schmitts will have their switch limits straddling Vcc/2,
maybe a bit less. A simple RC (or R with no obvious C!) should make a
pretty symmetric square wave.
I wonder how big R can be. 1 Gohm easily. Maybe 1 Tohm if everything
is clean. An open cmos gate input will hang high or low, whichever way
you leave it, for seconds at least. I had one floating cmos level last
week that took about 15 seconds after powerup to change state. That
might roughly correspond to a pA of leakage.
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Fri, 28 May 2010 09:54:50 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>>
>I should hope it works. It's a simple charge pump. Your latest example
>puts about 5.5 mA average forward current into the LED. You have
>proved that my charge pump works, even with the unrealistic schmitt
>model.
---
Well, I must admit that I dropped the ball on this one, but I think
you have too, in that you haven't considered how much current an HC14
(which is what I think the OP said he wanted to use) can source or
sink using a 3.3V supply.
I'd supply the numbers _I_ found, but since you seem to think it's
everyone's job but yours to flesh out the skeletons you dangle in
front of them, I'll leave that up to you, if you choose to pursue it.
---
>>>>With that in mind it's clear that even with a perfect driver, your
>>>>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>>>>4ns every 10 microseconds or so through the LED, won't work.
>>>
>>>It actually does work with a perfect driver, as your sim shows.
>>
>>---
>>If the criterion determining "works" is whether the LED will emit
>>light which can be detected by the human eye in a casual manner, then
>>I submit that 4ns wide pulses occurring at a rep rate of 100kHz won't
>>quite fill the bill.
>
>Average current makes light. Eyeballs respond to average light. Are
>you suggesting that X microwatts of light are visible if DC, but
>invisible if the same average amount of photons arrive in bunches?
---
Not at all.
What I'm suggesting is that if the duty cycle is low enough, even if
the LED is 100% efficient in turning current into light, it'll be
invisible.
---
>Those big roadside billboards use multiplexed LEDs, each LED operating
>at a low duty cycle. These are invisible to you?
---
Straw man.
---
>>>It works better with a real-world CMOS part and properly chosen values.
>>
>>---
>>Neither of which you addressed earlier, with your cockamamie circuit,
>>while now you're pontificating as if you did.
>>---
>>
>>>You don't believe in charge pumps?
>>
>>---
>>Idiot.
>>
>>What's that supposed to do, put me on the defensive?
>
>
>If you claim charge pumps can't work, you've done that to yourself.
---
But, since I've never claimed that charge pumps, per se, can't work,
your statement is nonsensical.
---
>If you can't come up with values to make this charge pump work nicely,
>you've compounded the damage.
---
Surely, since you've taken ownership of the circuit away from Speff,
it's incumbent on you, not me, to do the grunt work required to get a
satisfactory solution for the OP if he can't work it out for himself.
---
>You so badly want it not to work that
>you've stopped thinking like an engineer.
---
Au contraire!
I noticed, initially, that in your circuit you had drawn in a Schmitt
buffer instead of an inverter and commented that your circuit couldn't
work as drawn which was, and still is, true.
That's engineering thinking, I think, and I was just pointing out
something anyone in your organization should comment on, and which
you'd welcome, during a design review
You, of course, since we seem to be at odds with each other and you
want to be the king of sci.electronics.design, took umbrage at my
comment and, instead of a simple "Thanks, good catch," (which you
posted re. your earlier data sheet error on which I commented),
decided to play the "everyone knew what I meant" game instead of
owning up to having fucked up.
No big deal back then...
---
>That's a really bad sign,
>letting your emotions suspend your ability to design.
---
Why would you think that emotions suspend one's ability to design?
have you never heard Mozart?
---
>If you wanted it to work, you'd let it work.
---
It's not me that's holding it back, if _you_ want to prove it works,
flesh it out.
Let's see what you've got.
---
>In all the cases you've simulated, it does work. So many people do
>things like this that it's hardly "my" circuit. It was done with tubes
>before I was born.
---
Then it should be simple for you to come up with something which
really works instead of trying to slough the work off on someone
-anyone- else.
JF
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Fri, 28 May 2010 19:56:36 -0400, Bitrex
><bit...@de.lete.earthlink.net> wrote:
>
>>
>>> Bitrex's circuit likes an asymmetric duty cycle, which is maybe why he
>>> has the thresholds where they are. The asymmetry struck me
>>> immediately, because an HC gate oscillator would be nearly symmetric.
>>>
>>
>>I'm still new to LTSpice, I was a little confused about how the model
>>sets the thresholds and hysteresis. In datasheets the hysteresis is
>>defined as the difference between the high transition point and the low
>>transition point, in the model Vh seems to be the difference between the
>>high and low transition points and the midpoint, which is defined by the
>>Vt parameter. I think I've rectified most of my errors now...:)
>
>If the Spice definitions aren't clear, you can just look at the gate
>input triangle to see where it actually switches.
>
>Most cmos schmitts will have their switch limits straddling Vcc/2,
---
None that I've seen...
---
>maybe a bit less.
---
How much is "a bit less"?
Take a look at Philips' HC14.
it looks more like ECL than CMOS.
---
>Take a look at A simple RC (or R with no obvious C!) should make a
>pretty symmetric square wave.
---
Now there's the John Larkin I love...
Vague, himself, while demanding quantitative data from his critics...
---
>I wonder how big R can be. 1 Gohm easily. Maybe 1 Tohm if everything
>is clean. An open cmos gate input will hang high or low, whichever way
>you leave it, for seconds at least. I had one floating cmos level last
>week that took about 15 seconds after powerup to change state. That
>might roughly correspond to a pA of leakage.
---
See what I mean?
John Larkin
<jfi...@austininstruments.com> wrote:
>On Fri, 28 May 2010 09:13:40 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Fri, 28 May 2010 09:54:50 -0500, John Fields
>><jfi...@austininstruments.com> wrote:
>>>
>>I should hope it works. It's a simple charge pump. Your latest example
>>puts about 5.5 mA average forward current into the LED. You have
>>proved that my charge pump works, even with the unrealistic schmitt
>>model.
>
>---
>Well, I must admit that I dropped the ball on this one, but I think
>you have too, in that you haven't considered how much current an HC14
>(which is what I think the OP said he wanted to use) can source or
>sink using a 3.3V supply.
Wrong again! I don't know why you keep doing this.
My sketch didn't specify HC logic. All I did was post a scribble that
had a schmitt oscillator in it, followed by a cap+diode charge pump.
That was the idea I offered. You offered zero ideas.
I fact, an HC14 would easily charge-pump 5 mA average current into a
blue LED. But the HC series is ancient, and most more modern cmos
logic has even more drive capability at 3.3 volts.
>
>I'd supply the numbers _I_ found, but since you seem to think it's
>everyone's job but yours to flesh out the skeletons you dangle in
>front of them, I'll leave that up to you, if you choose to pursue it.
I offered an idea. For free. I didn't volunteer to do a detailed
design.
>
>What I'm suggesting is that if the duty cycle is low enough, even if
>the LED is 100% efficient in turning current into light, it'll be
>invisible.
Sure, less current makes less light, and you can break any circuit if
you use sufficiently stupid values. But all of your sims pushed
reasonable currents into the LED, so your "doesn't work" and "can't
work" and "cockamamie circuit" comments were doubly bizarre. Your own
sims are working examples of my circuit; you just didn't realize it.
>It's not me that's holding it back, if _you_ want to prove it works,
>flesh it out.
Why bother? I *know* that it works, and you have already proved that
it works.
And you proved that the schmitt+resistor thing *does* oscillate, as
another geezer swore it wouldn't.
John
John Larkin
<jfi...@austininstruments.com> wrote:
>On Fri, 28 May 2010 22:06:53 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Fri, 28 May 2010 19:56:36 -0400, Bitrex
>><bit...@de.lete.earthlink.net> wrote:
>>
>>>
>>>> Bitrex's circuit likes an asymmetric duty cycle, which is maybe why he
>>>> has the thresholds where they are. The asymmetry struck me
>>>> immediately, because an HC gate oscillator would be nearly symmetric.
>>>>
>>>
>>>I'm still new to LTSpice, I was a little confused about how the model
>>>sets the thresholds and hysteresis. In datasheets the hysteresis is
>>>defined as the difference between the high transition point and the low
>>>transition point, in the model Vh seems to be the difference between the
>>>high and low transition points and the midpoint, which is defined by the
>>>Vt parameter. I think I've rectified most of my errors now...:)
>>
>>If the Spice definitions aren't clear, you can just look at the gate
>>input triangle to see where it actually switches.
>>
>>Most cmos schmitts will have their switch limits straddling Vcc/2,
>
>---
>None that I've seen...
Name a few whose input switch limits don't straddle Vcc/2. Then I'll
name a few that do.
>---
>
>>maybe a bit less.
>
>---
>How much is "a bit less"?
Couple tenths of a volt maybe, at 3.3 supply. Most cmos inputs
transition a little below Vcc/2. It's not guaranteed, and there are
lots of cmos parts around, but that's the pattern. Hadn't you ever
noticed?
>
>Take a look at Philips' HC14.
>
>it looks more like ECL than CMOS.
Insane. ECL input transitions are at about 1.35 volts below Vcc,
independent of Vcc-Vee. And their outputs swing about two junction
drops.
The NXP HC14, with 4.5 volts Vcc, has datasheet typical switch levels
of 2.38 and 1.40. The mean of those two is 1.89. Vcc/2 is 2.25. So the
stuff I said is right.
>---
>
>>Take a look at A simple RC (or R with no obvious C!) should make a
>>pretty symmetric square wave.
>
>---
>Now there's the John Larkin I love...
>
>Vague, himself, while demanding quantitative data from his critics...
What don't you understand about "pretty symmetric"? Hint: the pulses
you simulated weren't very symmetric.
>---
>
>>I wonder how big R can be. 1 Gohm easily. Maybe 1 Tohm if everything
>>is clean. An open cmos gate input will hang high or low, whichever way
>>you leave it, for seconds at least. I had one floating cmos level last
>>week that took about 15 seconds after powerup to change state. That
>>might roughly correspond to a pA of leakage.
>
>---
>See what I mean?
A ballpark estimate of gate leakage current is useful. More than a
ballpark is useless for design purposes. Knowing that the leakage is
in the low pA range would allow one to use a 10M or 100M or 1G
oscillator resistor with perfect safety. You can't do that with a
classic 555.
So, how big a timing resistor is it safe to use with a CMOS 555?
John
Don Klipstein
in part:
>On Fri, 28 May 2010 09:13:40 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>>>>With that in mind it's clear that even with a perfect driver, your
>>>>>circuit, which pushes 150mA spikes which decay to essentially 0mA in
>>>>>4ns every 10 microseconds or so through the LED, won't work.
>>>>
>>>>It actually does work with a perfect driver, as your sim shows.
>>>
>>>---
>>>If the criterion determining "works" is whether the LED will emit
>>>light which can be detected by the human eye in a casual manner, then
>>>I submit that 4ns wide pulses occurring at a rep rate of 100kHz won't
>>>quite fill the bill.
>>
>>Average current makes light. Eyeballs respond to average light. Are
>>you suggesting that X microwatts of light are visible if DC, but
>>invisible if the same average amount of photons arrive in bunches?
>
>---
>Not at all.
>
>What I'm suggesting is that if the duty cycle is low enough, even if
>the LED is 100% efficient in turning current into light, it'll be
>invisible.
150 mA decaying to near zero over a 4 nanosecond pulse repeated every 10
microseconds: (Did I get that right?)
Suppose the average current during the pulse is 50 mA. Doing that for 4
every 10,000 nanoseconds would make the average current 20 microamps.
Since a usual blue LED is likely to be more efficient at 50 mA than at
20 uA, I would expect it to be brighter with this than with 20 uA steady
DC. (Ratio of photometric output to current usually peaks around 1.5-4
mA with these LEDs.) So, I would expect brightness typical of 30-40
microamps steady DC. That sounds to me on the dim side for an indicator
LED, but I do expect this to be visible.
If this blue LED is switched to 3.3V through a MOSFET, such as in a CMOS
IC, then the full 3.3V is available. A fair number of blue LEDs nowadays
on average need no more than 3.3V to push 20 mA through them, and that
would make them so bright at 20 mA that some of these come with warnings
to not stare into them. So, it sounds easy to me to get half a milliamp
or a milliamp through them from 3.3V without a boosting circuit. And at
this much current, many blue LEDs get plenty bright.
--
- Don Klipstein (d...@misty.com)
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Sun, 30 May 2010 18:49:16 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>>On Fri, 28 May 2010 09:13:40 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Fri, 28 May 2010 09:54:50 -0500, John Fields
>>><jfi...@austininstruments.com> wrote:
>>>>
>>>I should hope it works. It's a simple charge pump. Your latest example
>>>puts about 5.5 mA average forward current into the LED. You have
>>>proved that my charge pump works, even with the unrealistic schmitt
>>>model.
>>
>>---
>>Well, I must admit that I dropped the ball on this one, but I think
>>you have too, in that you haven't considered how much current an HC14
>>(which is what I think the OP said he wanted to use) can source or
>>sink using a 3.3V supply.
>
>Wrong again! I don't know why you keep doing this.
---
Doing what?
Didn't he say he needed to use a 3.3V supply?
Didn't he say was thinking about using an HC14?
---
>My sketch didn't specify HC logic. All I did was post a scribble that
>had a schmitt oscillator in it,
---
Ok, have it your way, but, no matter what you _think_ you posted, that
scribble didn't include anything that would oscillate.
---
>followed by a cap+diode charge pump.
>That was the idea I offered. You offered zero ideas.
---
Right.
I offered critique.
---
>I fact, an HC14 would easily charge-pump 5 mA average current into a
>blue LED. But the HC series is ancient, and most more modern cmos
>logic has even more drive capability at 3.3 volts.
>
>>
>>I'd supply the numbers _I_ found, but since you seem to think it's
>>everyone's job but yours to flesh out the skeletons you dangle in
>>front of them, I'll leave that up to you, if you choose to pursue it.
>
>I offered an idea. For free. I didn't volunteer to do a detailed
>design.
---
Bret Cahill rides again.
---
>>What I'm suggesting is that if the duty cycle is low enough, even if
>>the LED is 100% efficient in turning current into light, it'll be
>>invisible.
>
>Sure, less current makes less light, and you can break any circuit if
>you use sufficiently stupid values. But all of your sims pushed
>reasonable currents into the LED, so your "doesn't work" and "can't
>work" and "cockamamie circuit" comments were doubly bizarre. Your own
>sims are working examples of my circuit; you just didn't realize it.
>
>
>>It's not me that's holding it back, if _you_ want to prove it works,
>>flesh it out.
>
>Why bother? I *know* that it works, and you have already proved that
>it works.
>
>And you proved that the schmitt+resistor thing *does* oscillate, as
>another geezer swore it wouldn't.
---
Again, my original critique had to do with the lack of accuracy of
your scribble, which is what both of us geezers agreed upon.
End of story, as far as I'm concerned; rave on if you like...
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Sun, 30 May 2010 19:14:34 -0500, John Fields
><jfi...@austininstruments.com> wrote:
>
>>On Fri, 28 May 2010 22:06:53 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Fri, 28 May 2010 19:56:36 -0400, Bitrex
>>><bit...@de.lete.earthlink.net> wrote:
>>>
>>>>
>>>>> Bitrex's circuit likes an asymmetric duty cycle, which is maybe why he
>>>>> has the thresholds where they are. The asymmetry struck me
>>>>> immediately, because an HC gate oscillator would be nearly symmetric.
>>>>>
>>>>
>>>>I'm still new to LTSpice, I was a little confused about how the model
>>>>sets the thresholds and hysteresis. In datasheets the hysteresis is
>>>>defined as the difference between the high transition point and the low
>>>>transition point, in the model Vh seems to be the difference between the
>>>>high and low transition points and the midpoint, which is defined by the
>>>>Vt parameter. I think I've rectified most of my errors now...:)
>>>
>>>If the Spice definitions aren't clear, you can just look at the gate
>>>input triangle to see where it actually switches.
>>>
>>>Most cmos schmitts will have their switch limits straddling Vcc/2,
>>
>>---
>>None that I've seen...
>
>Name a few whose input switch limits don't straddle Vcc/2. Then I'll
>name a few that do.
---
Well, I'm talking "straddle" in the strict sense, which would mean
that the typical switch points would be equally displaced about Vcc/2.
But, OK.
For the Philips case we have:
Vt-typ Vt+max
1.4V 2.38V
| |
0V--------------+--------+--+---------------------4.5V
|
2.25V
Vcc/2
Straddle?
That's almost sidesaddle!
Even more intersting, the minimum and maximum thresholds for HC:
Vcc/2
2.25V
Vt+min | Vt+max
1.7V | 3.15
| | |
0V---------+--------+--+--+--------+--------------4.5V
| |
0.9V 2.0V
Vt-min Vt-max
Which says that for a device with a Vt+min of 1.7V, Vt-min will,
presumably, lie between 1.7V and 0.9V.
Your turn now; let's see even _one_ that straddles Vcc/2
symmetrically.
---
>>---
>>How much is "a bit less"?
>
>Couple tenths of a volt maybe, at 3.3 supply. Most cmos inputs
>transition a little below Vcc/2. It's not guaranteed, and there are
>lots of cmos parts around, but that's the pattern. Hadn't you ever
>noticed?
---
Huh???
If both transition points are below Vcc/2 how can they straddle it?
---
>>Take a look at Philips' HC14.
>>
>>it looks more like ECL than CMOS.
>
>Insane. ECL input transitions are at about 1.35 volts below Vcc,
>independent of Vcc-Vee. And their outputs swing about two junction
>drops.
---
Oops...
I was looking on the HCT page.
---
>>>Take a look at A simple RC (or R with no obvious C!) should make a
>>>pretty symmetric square wave.
>>
>>---
>>Now there's the John Larkin I love...
>>
>>Vague, himself, while demanding quantitative data from his critics...
>
>What don't you understand about "pretty symmetric"? Hint: the pulses
>you simulated weren't very symmetric.
>
---
Geez, John, you'll probably have to send that Katana in for sharpening
what with all the straw men you keep chopping down!
---
>>>I wonder how big R can be. 1 Gohm easily. Maybe 1 Tohm if everything
>>>is clean. An open cmos gate input will hang high or low, whichever way
>>>you leave it, for seconds at least. I had one floating cmos level last
>>>week that took about 15 seconds after powerup to change state. That
>>>might roughly correspond to a pA of leakage.
>>
>>---
>>See what I mean?
>
>A ballpark estimate of gate leakage current is useful. More than a
>ballpark is useless for design purposes.
---
For a sloppy designer or a sloppy design, that would probably be true.
---
>Knowing that the leakage is
>in the low pA range would allow one to use a 10M or 100M or 1G
>oscillator resistor with perfect safety. You can't do that with a
>classic 555.
---
Apples and oranges, since in normal use the leakage of the cap is so
high that it swamps the 10pA typical trigger and threshold leakage
currents.
---
>So, how big a timing resistor is it safe to use with a CMOS 555?
---
If the cap had absolutely no leakage and you used this circuit:
VCC
|
+-----------|------+
| +-------+8 |
[Rt] | +----+----+ |
| | 4|_ Vcc | |
| +-O|R OUT|-+-->OUT
| | |3
+----6-|TH |
| |__ |
+-----O|TR |
| 2| GND |
[Ct] +----+----+
| U1 7555 |1
+-----------+
|
GND
Then it would depend on how much the currents into and out of TH and
TR- (10pA at Vcc = 5V) affected the accuracy of the timing.
You figure it out...
JF
John Fields
---
Yes.
---
> Suppose the average current during the pulse is 50 mA. Doing that for 4
>every 10,000 nanoseconds would make the average current 20 microamps.
>
> Since a usual blue LED is likely to be more efficient at 50 mA than at
>20 uA, I would expect it to be brighter with this than with 20 uA steady
>DC. (Ratio of photometric output to current usually peaks around 1.5-4
>mA with these LEDs.) So, I would expect brightness typical of 30-40
>microamps steady DC. That sounds to me on the dim side for an indicator
>LED, but I do expect this to be visible.
---
OK.
---
> If this blue LED is switched to 3.3V through a MOSFET, such as in a CMOS
>IC, then the full 3.3V is available.
---
No, there will be some drop across the MOSFET.
---
>A fair number of blue LEDs nowadays
>on average need no more than 3.3V to push 20 mA through them, and that
>would make them so bright at 20 mA that some of these come with warnings
>to not stare into them. So, it sounds easy to me to get half a milliamp
>or a milliamp through them from 3.3V without a boosting circuit. And at
>this much current, many blue LEDs get plenty bright.
---
I don't have any data for Vcc = 3.3V, but for HC at 2V with a 1mA load
I see a drop of about 400mV in the gate's output, so you're probably
right.
John Larkin
Klipstein) wrote:
> If this blue LED is switched to 3.3V through a MOSFET, such as in a CMOS
>IC, then the full 3.3V is available. A fair number of blue LEDs nowadays
>on average need no more than 3.3V to push 20 mA through them, and that
>would make them so bright at 20 mA that some of these come with warnings
>to not stare into them. So, it sounds easy to me to get half a milliamp
>or a milliamp through them from 3.3V without a boosting circuit. And at
>this much current, many blue LEDs get plenty bright.
We use blue LEDs on our VME modules to indicate bus access. I started
with Cree SiC parts, driven by two paralleled 74F38 sections, 5 volts,
27 ohms. That was just barely OK.
As the parts kept getting better, my customers started complaining
about the blinding blue LEDs. So we keep ratcheting up the resistor.
We currently use a 2N7002 or BCX70 and 1K to +5.
This can't go on forever, since the LEDs have to eventually stop at
100% efficiency.
John
John Larkin
In the first sim you posted, the really fast one, the LED had an
average forward current of close to 5 mA. Measure it.
The later sims had nearly the same average LED currents. Do you know
why?
John
John Fields
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
---
Hmmm...
Since you weren't up front enough to explain why, or if, that's true,
and maybe take some lumps if you were found to be wrong, it sounds to
me like you're trying to set a trap so that, no matter what my
response might be, you'd impugn it with garbage which would then have
to be shown to be garbage and refuted.
Generally a huge PITA since the rate of new garbage in from a
detractor seems to increase as the old garbage in is disposed of.
As usual, it's much easier for a scoundrel to make up charges than it
is for his target to refute them, so unless you reveal what you're
holding in abeyance, I'm outta here...
Don Klipstein
In that case, the blue LED will really shine. Even if the current flows
through the LED during high current pulses that the LED handles half as
efficiently as it handles 5 mA steady DC, the LED will still be plenty
bright. Consider how bright most of these LEDs appear with 2-2.5 mA of
steady DC. That is usually 12.5-16% of the brightness that they achieve
with 20 mA of steady DC. Many of these are characterized at 20 mA and are
rated 30 mA maximum average and a fair subset of those come with warnings
that staring at them could cauase eye damage.
They are usually "good-and-bright" at 1 mA and they usually
achieve typical "indicator LED brightness" at ~~ .5 mA.
John Larkin
<jfi...@austininstruments.com> wrote:
OK, you don't know why all of your sims pumped about 5 mA into the
LED.
Of course it's because a charge pump outputs an average current
I = C*V*F
where V is how much the voltage across the cap changes every cycle.
Assuming a typical diode and blue LED, when the schmitt is low,
there's about 2.7 volts across the cap. When it's high, there's about
0.3 in the other direction. So delta-V is around 3. At 150 KHz and 10
nF, that works out to 4.5 mA, close enough.
It's that simple. As long as the schmitt can get close to the rails by
the end of each transition, the internal impedance of the schmitt, and
its rise/fall times, don't matter.
What's weird is that you used sims to prove that "my" circuit wouldn't
work, and all of your sims showed that it *does* work, but you
wouldn't believe it.
John
John Larkin
Klipstein) wrote:
The nice Infineon right-angle surface-mount blues look good as panel
indicators, backlighting a window in a sticker, at 2.5 mA. Our next
gadget will use light pipes to go from a top-firing surfmount LED to
just below a sliding cover.
Under ideal conditions, a good Agilent green LED up against my
eyeball, dark adapted, I could just detect light at about 700 pA.
John
JosephKK
<pNaonSt...@yahoo.com> wrote:
>On a sunny day (Tue, 25 May 2010 11:00:42 -0700) it happened John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote in
><b93ov5hd2c0t71ma2...@4ax.com>:
>
>>On Tue, 25 May 2010 10:18:11 -0700 (PDT), rich
>><rsoenn...@gmail.com> wrote:
>>
>>>I need to drive a blue led from 3.3V. Most of the SMD blue leds I
>>>find have a Vf equal to or greater than 3.3V.
>>>
>>>I am curious how others are dealing with this.
>>>
>>>Thanks
>>>
>>>Rich
>>
>>I have some nice Osram blues that are OK at 1 mA and 2.65 volts,
>>bright at 10 mA, 3.1 volts. So you could just get by with a resistor
>>or current limiter from 3.3. You could use one of my famous beta
>>limiter circuits.
>>
>>I sometimes make my "3.3" volt supplies actually 3.5 or 3.6. Most
>>other parts don't mind.
>>
>>Or use a booster.
>>
>>John
>
>Yup, my blue one drops 2.66 V
>Extremely bright at 3.5 mA.
> ftp://panteltje.com/pub/low_current_LEDs_img_1964.jpg
>in that picture it is at 10% PWM with 180 Ohm in series fro ma 3.3V PIC output.
>
Yikes. What are the greens running, 0.5 mA?
Don Klipstein
I sem to figure the greens may be dropping 2.6 volts. So, I figure
about 4 mA, 10% of the time to get an average current of .4 mA. Since
these LEDs are probably a little more efficient at 4 mA than at .4 mA,
I would expect brightness about typical for .5 mA. And I have some Cree
and Nichia green LEDs that are plenty bright at .5 mA.
John Larkin
My Osram greens, beautiful parts, are "dim" at 0.5 mA, 2.62 volts, and
"bright" at 5 mA, 2.9 volts.
John