12 to 9 volts dc
Brian S Walden
the problem is that it requires 9 volts and 1/2 amp.
I'm not a e.e., but from the course in college (a few years, now)
I remember something like this (12 to 9 volts) is just a resistor,
a zener diode, and an NPN transistor.
I figure someone should have done this already with real parts.
So if you'd like to share a schematic with me, I'd be very
grateful.
Thanks in advance,
Brian S Walden
--
Brian S Walden
AT&T Bell Labs, Whippany, NJ
att!attbl!brian.s.walden
Duke McMullan n5gax
(Brian S Walden) writes:
>I want to take my old Sony Dicsman D-5 in the car with me,
>the problem is that it requires 9 volts and 1/2 amp.
OK: First, let's think 13.6 volts, not 12. That's the actual (as opposed to
nominal) voltage when you're running the engine.
Second, you _can_ use a resistor/zener_diode/buffer_transistor circuit such as
the one you mention, but there are easier ways.
We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you
can come up with a 4.5 volt zener, then just put the zener in series with the
load:
+ 12V o----------------|<-----------o + 9.1V
4.5V
zener
diode
Negative is ground, of course. Note that the zener diode is installed "back-
ward" to the way normal diodes are placed. It's used in "reverse conduction"
mode. A problem is that that diode is dropping 4.5 volts at half an amp...
that comes to 2.25 watts. As a safety fudge, you'd want a diode that could
handle twice that...say, 5 watts. 5 watt zeners aren't cheap. Also, note
that that drop assumes a significant current being drawn. As the current gets
very small (<1mA, typically), the voltage will start to rise. This _usually_
isn't a problem, but for a CYA it can't hurt to put a small load...say, an LED
with a current-limiting resistor (2.2 kilohms or so)...across the 9V side.
This will stabilize the current, and give you a pilot lamp to boot.
Stick a 3/4 amp or so fuse in the circuit, too. Slo-blo is recommended.
Again, note the polarity of that diode.
Also, be warned: If that zener should develop an internal short, the full
13.6 volts will be dumped into your load. If you install it backward, you
will get just under 13 volts into your load. If you're lucky, the fuse will go
before your DiskMan. _If_ you're lucky....
There's also a junk-box solution: 1 amp silicon rectifiers are widely avail-
able, cheap, and many of us have a bunch lying around. The forward drop on a
silicon diode is nominally 0.7V; actually 0.626 is a _very_ good average fig-
gure. Lesee...0.626 into 4.6 is...7.3bleep, so if we use seven rectifiers in
series, we lose about 4.4 volts leaving us with just under 9.2 volts. The
circuit looks like this:
+12V o------->|-->|-->|-->|-->|-->|-->|-------------o +9V
seven silicon rectifiers, 1A at 50V or so.
This time, note that the diodes all point downstream the way they're "sup-
posed" to. If you need more current, it's easy to find 6A or even 10A
rectifiers. Consider the rectifiers as all one component, then install the
fuse and pilot light as before. Each diode dissapates about 0.626 times
the current. Stay under 1 amp, and you should be safe. The PIV of the
rectifiers isn't a worry, and 50V is about the lowest (and cheapest) type
you'll find.
You have some more safety here, too. Failure of more than one of the diodes
(shorting-type failure, that is) is pretty unlikely in any situation that
doesn't involve a blown fuse.
Another advantage is that all the components pass the strongest test of
availability that I know. Radio Schlock carries 'em....
Best o' luck,
d
PS -- A final caveat: It's unlikely to happen, but make sure you have _sili-
con_ (not germanium) diodes, and make sure they're not Schottky or "hot car-
rier" silicon diodes. All those diodes have a forward drop of about 0.3V, and
if you're using a rectifier chain, you're like to do unpleasant things to your
load. Germanium rectifiers are rare, and Schottky rectifiers are both rare
and expensive. If you're worried about it, you can measure the forward drop
very easily: Just put the diode in series with a small load (say, a flash-
light lamp) powered with a battery, and measure the drop with a voltmeter. It
should be between 0.6 and 0.7 volts.
d
--
"Got to slap these Goddamn Third World nations around, Flynn," he said,
"until they learn some manners." -- Gregory MacDonald, from _Flynn_
Duke McMullan n5gax nss13429r phon505-255-4642 ee53...@triton.cirt.unm.edu
Michael A. Covington
>In article <1991Feb10.2...@cbnewsl.att.com> wa...@cbnewsl.att.com
>(Brian S Walden) writes:
>>I want to take my old Sony Dicsman D-5 in the car with me,
>>the problem is that it requires 9 volts and 1/2 amp.
>
>OK: First, let's think 13.6 volts, not 12. That's the actual (as opposed to
>nominal) voltage when you're running the engine.
>
>Second, you _can_ use a resistor/zener_diode/buffer_transistor circuit such as
>the one you mention, but there are easier ways.
>
>We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you
>can come up with a 4.5 volt zener, then just put the zener in series with the
>load:
>
>+ 12V o----------------|<-----------o + 9.1V
> 4.5V
> zener
> diode
>
The voltage in the car is not a constant 13.6V;
it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.)
You don't want a constant voltage DROP, you want a constant
voltage OUTPUT. A 7809 regulator chip will do the trick.
Duke McMullan n5gax
>>We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you
>>can come up with a 4.5 volt zener, then just put the zener in series with the
>>load:
>>
>>+ 12V o----------------|<-----------o + 9.1V
>> 4.5V
>> zener
>> diode
>>
> NO! You'll fry a Discman.
> The voltage in the car is not a constant 13.6V;
> it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.)
>
> You don't want a constant voltage DROP, you want a constant
> voltage OUTPUT. A 7809 regulator chip will do the trick.
Well, on your car, perhaps. ;^)
Seriously, Mike, I'm going by experience here...so your mileage may vary.
I've used the chain-of-seven diodes for quite a few years, and never any
damage to any electronics. Some years back, I used a 7806 in TO-3, nicely
mounted on a heat sink, to power a little tape player. It worked just fine --
for about seven months. Then something went wrong with the '06. Fortunately,
I was wearing the headset at the time. The volume increased significantly,
and the motor speeded up. I didn't know what the problem was, but I had the
instinct to yank the plug out of the cassette player. It survived without
damage; I didn't. I burned my hand when I thoughtlessly picked up the regu-
lator.
I've observed battery voltages below 12V on occasion -- when the motor wasn't
running, and when the battery was getting a bit low. I've never -- NEVER --
observed anything that would push a meter up to 17V on any vehicle I've worked
with. Measured with a 'scope, things might be different, but it's likely the
power supply filter caps would swallow such transients without difficulty.
In any event, I've never had any equipment failures of this sort, nor of the
voltage reducer, either.
One could easily add a voltage clamp if this is worrisome, however. Across
the output, put a string of diodes (or a zener) with a conduction voltage of
say, 10 to 10.5 volts (16 or 17 rectifiers, if you're doing it that way).
If the output voltage rises enough to turn that diode/diode-string on, it
will clamp the output voltage at that point, and will blow the fuse if the
voltage tries to rise much higher.
Messy? Sure, but unless you have a pretty shaky voltage regulator, it should
give you sufficient reduction to operate your equipment, and sufficient saf-
ety with the shunt circuit to protect it. Twenty-four rectifiers take up a
bit of room, but what's your equipment worth?
A safety shunt of this sort is also a good idea with IC regulators. I've seen
those fail often enough (not just the tale told above) to make me pretty wary
of relying only on God and Mammon to see that they don't wind up with their
pass transistor shorted. The same thing applies to discrete circuitry.
Note that I have not installed a shunt on the reducers I use: risky, perhaps.
But, again, I've not had any problems with those circuits...ever.
d
PS -- Now, watch me smoke a nine-volt appliance later this week....
d
PPS -- Recently, someone's .sig said: "If there's one thing software types are
sure of, it's that smoke is a hardware problem."
Jeff DePolo
In article <1991Feb11....@athena.cs.uga.edu> mcov...@athena.cs.uga.edu (Michael A. Covington) writes:>
>>We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you
>>can come up with a 4.5 volt zener, then just put the zener in series with the
>>load:
> The voltage in the car is not a constant 13.6V;
> it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.)
>
> You don't want a constant voltage DROP, you want a constant
> voltage OUTPUT. A 7809 regulator chip will do the trick.
Amen to that. At idle speed, my car shows right around 14 volts, slightly
higher on cold days. At 1000+ RPM's, it's right around 14.5 volts. With
the engine off, it's in the 12.5 volt range. I have seen voltages
above 15 in some cars, especially when cold as some of the modern
systems boost up the altnerator voltage to quickly charge the battery
(the premise here is that when a battery is at less than full charge,
it should be brought back up ASAP in case the trip is going to be too
short to fully charge it at a normal voltage, according to a mechanic).
The 7809 should handle your 1/2 amp, but may need a heat sink. A better
way to go is to use a 78H09 (H for high-current) and mount it to
some sort of a metal object, preferably using a heatsink. The cost of
a 78H09 is about $2.00. You can try a 7809 (probably available at
*gasp* Radio Shack) first, but if it gets too hot, it will (or should
I say, it is supposed to) shut itself off. It's definately going to be
warm, so don't touch it if you've been using it for a while.
I wouldn't use a zener unless I had a crowber with it as well (requires
another zener, an SCR, and a few resistors).
--- Jeff
--
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199
dep...@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia)
University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
Jon Panek
15-16V while the engine's running. A constant voltage drop setup, like the
in-line zener, or the chain of Si diodes is not a very robust solution.
The simple solution is the 7809. Make sure the power rating on the '09
is enough to handle the expected dissipation: P = EI, where E is the
voltage *difference* between the engine (use 15-18V) and the output of
the device (9V) -- this gives E of ~9V. I is the current
needed by the discman. This gives you power in watts. Note that devices
higher than about 0.5W require proper heat-sinking to achieve their max
ratings...
I sure wouldn't want to risk *my* discman on a junkbox solution...
Good luck!
Jonathan Panek
Hewlett-Packard, Andover Division
pa...@hp-and.an.hp.com
(508) 687-1501
Erick Parsons
>the problem is that it requires 9 volts and 1/2 amp.
>
>I'm not a e.e., but from the course in college (a few years, now)
>I remember something like this (12 to 9 volts) is just a resistor,
>a zener diode, and an NPN transistor.
Good Memory Brian
>I figure someone should have done this already with real parts.
>So if you'd like to share a schematic with me, I'd be very
>grateful.
Here goes:
----------
The circuit that you're thinking of is this (Very) basic regulator,
An Emitter follower or Current amplifier... This one uses a PNP, other
variations can be used.
13.6 _______E C______ +9 VDC Regulated voltage, amplified Current
\ / (Relative to the Base that is)
_\/__/_ This is a PNP POWER X-sistor.
|
|B
__|___
/\ Zener Diode 9.7 Volts 1/4 Watt
/__\ 1/2 Watt to be safe
|
|
/
\ ___Current limiting Resistor (To save the Zener
/ From overcurrent and all it's nasty side fx)
\ 285 Ohms, 1/4 watt again 1/2 watt to be safe.
|
__________|_________ Ground for + 9VDC
|
___|___
_____
___ Chassis Ground
Theory of Operation:
--------------------
The Car voltage (said to be 11-17 VDC) passes through the Emitter base
Junction to the Zener Diode where it Dumps any voltage OVER the value
of the 9.7V Zener (~2-8 VDC in this case) through the current limiting
resistor to ground.
The voltage 'at the base' will be reflected to the Collector, it always
is. The Current 'through the base emitter junction' will be amplified. So
with these two rules of transistor operation out of the way we can see that:
The 9.7 V Zener will always apply 9.7 volts to the base of the transistor.
which will magically appear at the collector (minus .7 for the PN junction)
Current flows from the battery through the emitter/base through the zener
and through the resistor to ground. It is this amount of current through
this circuit that will determine how much current will be available at the
collector.
A 1/2 amp eh? Take a typical Beta of a Power transistor at about 35, In Your
case you would need, leseee... 1/2 amp divided by 35 is....
yup .014 amps, 14 milliamps
thru the emitter/base
So ~4VDC / .014 would make the resistance needed to limit the current
in the base emitter circuit about... 285 Ohms (or so).
(Remember the 9 volts doesn't flow through the zener & resistor just the)
(excess voltage, or .. 13.6 (average) -9 = ~4 VDC)
The Zener Diode and the resistor would have to have a wattage of
*at least* .014 * (17-9) or .112 Watts, not even a 1/4 watt.
Just to be safe make them 1/2 watt as the price differance is not that
much.
The transistor will have to be large enough to handle 500 Milliamps,
preferably more.You will more than likely have to re-compute the
value of the resistor for the Beta of the transistor that you buy.
Don't forget the heat sinks !
All-in-All:
-----------
This is a pretty basic circuit but works well as a regulator. After all
this though, I would have to agree with about everyone else in saying ...
Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into
a cigarette lighter plug. I heat sinked it through the metal contact clips
which contact the lighter receptacle *AND* drilled 8 holes in the thing
for some air flow. The thing gets warm but not half as warm as it did when
it wasn't heat sinked !! Worked from Sacramento to Las Vegas without a
hitch, about an 8 or 9 hour drive.
Another advantage of using a prefab regulator is that they have thermal
shutdowns incorporated into them which will save all should the current
draw cause too much heat. Circuit diagrams are usually include on the
back of the package should you decide to get one from Radio Slack.
-------------------------------------------------------------------------
Disclaimer, Datclaimer, Every which way claimer: This is not meant as
a 'complete' circuit to use for powering electronic equipment but is merely
a start (if I didn't screw something up here, in which case forget that
you read this and take all liability upon thyself for any consequential
damage that may arise from the use or construction of this circuit.)
There I said it...
-------------------------------------------------------------------------
What a Crock !!
-------------------------------------------------//-------------------------
(ames att sun)!pacbell! ----> sactoh0!pacengr!americ!erk Multitasking,
ucbvax!ucdavis!csusac! --/ // Never leave
uunet!msac! -/ Erick Parsons \Sacramento Ca Home Without it
--------------------------------------------\X/-----------------------------
Please Don't Wait...
Adam S. Denton
In article <erk....@americ.UUCP> e...@americ.UUCP (Erick Parsons) writes:
>>In article <1991Feb10.2...@cbnewsl.att.com> wa...@cbnewsl.att.com (Brian S Walden) writes:
>>I want to take my old Sony Dicsman D-5 in the car with me,
>>the problem is that it requires 9 volts and 1/2 amp.
>>
>>I'm not a e.e., but from the course in college (a few years, now)
>>I remember something like this (12 to 9 volts) is just a resistor,
>>a zener diode, and an NPN transistor.
>
>Good Memory Brian
>
>>I figure someone should have done this already with real parts.
>>So if you'd like to share a schematic with me, I'd be very
>>grateful.
>
>Here goes:
>----------
The posted circuit will do nicely to fry the Discman. The series PNP
will saturate, essentially shorting the collector to the emitter,
giving about 13.6 V (13.8-.2) to the Discman:
> \ / (Relative to the Base that is)
> _\/__/_ This is a PNP POWER X-sistor.
> |
> |B
> __|___
> /\ Zener Diode 9.7 Volts 1/4 Watt
> /__\ 1/2 Watt to be safe
> |
> |
> /
> \ ___Current limiting Resistor (To save the Zener
> / From overcurrent and all it's nasty side fx)
> \ 285 Ohms, 1/4 watt again 1/2 watt to be safe.
> |
> __________|_________ Ground for + 9VDC
> |
> ___|___
> _____
> ___ Chassis Ground
>
>
>Theory of Operation:
The B-E junction of the PNP establishes 13.8-.7=13.1V on the base,
NOT 9.7V as intended!! Use the following, which is very common:
IN (13.8V) -+---- c e ----- OUT=9.0V
| \___/
R | b
|------+
|
-----
/_\ Zener
|
GND
The transistor is NPN, 2N2222/3904/4401/etc. variety.
R is typically 100-1000 ohms. The diode is 9.1V Zener (for 8.4V out)
or 10.0V Zener (for 9.3V out). Example: Zener = 9.1V,
output current = 0.5A, Beta=50 (2n2222), -> base current = 0.5/50 = 10mA.
Want minimum zener current to be 20%, or 2mA, for reliable operation
at minimum input voltage of 12V, so total current thru R is 1.2*10=12mA.
At 12V in, base is at 9.1, so R must be smaller than (12V-9.1V)/12mA=
241 ohms. Use 220 or 180 for reliability. At 1/2 amp and 16V input,
the transistor will dissipate (16V-8.4V)*0.5A = 3.8 watts.
Oops! Can't use 2n2222 etc. -- try a heat-sunk 2n3055 (overkill!).
This has beta of 30, so you'll need to re-calculate the value of
R (I get 145 ohms; use 120). R's wattage: P=V^2/R = (16-9.1)^2/120
=0.396 W; use 1/2 or 1 watt. R's current: (16-9.1)/120 = 57.5mA.
Zener wattage is thus P=VI=(9.1)(.0575) = 0.523 -- use a 1 watt unit.
Now you're all set!
Enhancement: Bypass the Zener to ground with a large electrolytic
(100uF) to improve ripple rejection. If you do this, DO NOT SHORT
the output, as the cap will discharge through the b-e junction,
causing meltage of the transistor.
Another solution is to use a 7809 if you can find one, or a
7805 with a 3V Zener (or 3-4 series-connected diodes) in series
with the ground lead. If you go the latter route you will need
capacitors at the input, output, and ground terminals of the 7805
to GROUND in order to ensure stability.
Adam Denton
a...@mtqua.att.com
Jim E. Dunne
> Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into
Can you provide part numbers and makers? When I was investigating
a power supply for my 9V electric guitar effects, I could only find
12, 8, and 5 Volt regulators in the TI book. I know there are
"adjustable" ones, but I operate on the KISS principle when it comes
to circuits! I'm trying to get 9V from a really dirty 12V wall-type
transformer, and ended up with a 12V regulator chip, and thus the very
problem that is the subject of this thread. Why do they only seem to
make those screwy values when all my DC items are 3, 6, and 9 volts???
Thanks for the circuit, anyway.
--
Jim Dunne Motorola Inc. uunet!motcid!dunne
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Things are more like they are now than they ever were before. - Eisenhower
Joe Keane
>this though, I would have to agree with about everyone else in saying ...
>Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into
>a cigarette lighter plug. I heat sinked it through the metal contact clips
>which contact the lighter receptacle *AND* drilled 8 holes in the thing
>for some air flow. The thing gets warm but not half as warm as it did when
>it wasn't heat sinked !! Worked from Sacramento to Las Vegas without a
>hitch, about an 8 or 9 hour drive.
I have to second the comment about using a regulator chip. Anything you hack
together from discrete components probably won't compare. Those little guys
have lots of transistors, so duplicating their functionality would be costly
and take up a lot of space. Their performance is generally very good, with
wide input tolerance and very low output impedence.
But the more important issue is what happens under abnormal conditions. Most
regulator chips have current foldback and thermal shutdown so they won't burn
out or fry your device when things get bad. This is what distinguishes a good
circuit from a hack.
Rob Fugina
>From article <erk....@americ.UUCP>, by e...@americ.UUCP (Erick Parsons):
>> Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into
> Can you provide part numbers and makers? When I was investigating
Try 7809 for a +9v regulator.
> "adjustable" ones, but I operate on the KISS principle when it comes
What's the "KISS" principle?
> problem that is the subject of this thread. Why do they only seem to
> make those screwy values when all my DC items are 3, 6, and 9 volts???
> Thanks for the circuit, anyway.
Why 3, 6, and 9? Because that's what corresponds to 2, 4, and 6 1.5 volt
batteries... BUT, the values I've seen for voltage regulator chips are
5, 9, 12, 15, 18, and 24...
Rob ro...@cs.umr.edu
Tom Bruhns
> Can you provide part numbers and makers? When I was investigating
> a power supply for my 9V electric guitar effects, I could only find
> 12, 8, and 5 Volt regulators in the TI book. I know there are
> "adjustable" ones, but I operate on the KISS principle when it comes
> to circuits! I'm trying to get 9V from a really dirty 12V wall-type
>--
>
> Jim Dunne Motorola Inc. uunet!motcid!dunne
(hee-hee-hee -- you're with Motorola and can't find semiconductors?? ;-)
Try, for example, Panasonic AN7805, -06, -07, -08, -09, -10, -12, -15,
-18, -20, and -24, all from Digi-Key, on Pg. 46 of their Jan-Feb 91
catalog. Similar series for negative voltages, all at 1 amp max,
and down to 4 volts in a 100 mA series. But personally, I prefer the
adjustable ones because it keeps my personal parts stock lower, at
very little additional hassle. And for efficiency, try the new
switching regulator series from National or a similar one from Linear
Technology. Another favorite of mine is a LM2941CT: it's adjustable,
and designed so if you _reverse_ the input polarity, it gracefully
stops destructive electrons from visiting your circuit. Also handles
high input voltages fairly well. Also has low drop-out voltage (low
input-output differential required for operation).
Paul Elliott x225
> ----------
> The circuit that you're thinking of is this (Very) basic regulator,
> An Emitter follower or Current amplifier... This one uses a PNP, other
> variations can be used.
STOP! Don't build this! It won't work!
I fully expect to be one of dozens replying in horror to this circuit,
so I will stop here. In the remote chance that no one else covers the details,
I will probably follow up.
Ok, I will stop *here* ;-)
--
Paul M. Elliott Optilink Corporation (707) 795-9444
{uunet, pyramid, pixar, tekbspa}!optilink!elliott
"If I had known it was harmless I would have killed it myself." - P.K. Dick
Bob Myers
>An Emitter follower or Current amplifier... This one uses a PNP, other
>variations can be used.
>
>
Before anyone builds the circuit shown in the referenced article, please note
that it is incorrect - it WILL NOT work if built as shown.
There are two problems (or one, depending on how you look at it); the
transistor is backwards (C for E) and the resistor is in the wrong place.
A corrected version is as follows:
+ 13V in -------------\ /------------------> +9V out
| C \ / E
\ ---------
/ | B NPN power transistor
\ R |
/ |
| |
----------
|
----/
/ /\
/ \ 9.7V (or 9.6V) Zener diode
----
|
|
GND -----------------------------------------> GND
Here's how it works:
The regulation of the output voltage depends on the fact that the B-E drop
of a silicon transistor is a *fairly* constant 0.6-0.7V, depending on the
current through this junction. Thus, if the base is held to a constant
voltage (which it is here by the Zener), the emitter will be this voltage
minus the B-E drop. So, with a 9.6-9.7V Zener, we should get about 9V
out at the emitter. The "lost" voltage (the difference between the input and
output voltages) is not "dumped by the Zener, but appears across the transistor
C-E. This is one drawback of this type of regulator - the voltage across the
transistor (which will increase as the input voltage increases), multiplied
by the output current, represents power which is doing nothing more than
heating up the transistor. In other words, a linear regulator (which this is)
isn't particularly efficient. (And note that you MUST have some minimum drop
across the transistor - at a bare minimum, about 1.4V, and more reasonably
2V - to make sure that the transistor is biased properly.)
The resistor R supplies both the Zener current and the base current of the
transistor. The Zener current needs to be enough such that the Zener diode
is sufficiently past the "knee" in its characteristic curve such that the
voltage across the diode is reasonably stable; the base current required is
determined by the maximum required output current and the minimum expected
beta of the transistor. A Zener current of a few tens of mA at most is
usually sufficient; if we say we want 20 mA through the Zener, and expect
1A load current with a transistor beta of 20 (meaning 50 mA base current),
then the resistor must supply 70 mA with a drop of (13.6 - 9.7), or 3.9V.
This calls for a resistor of 3.9V/70 mA = 55.7 ohms *maximum*; we'd probably
wind up with a 51 ohm part here (nearest standard value). (Note that these
numbers are examples only - use you own Zener requirements and transisor beta,
etc., to get the right resistor for your application.) Also, please note that
using a value slightly under the calculated maximum simply means that more
current will be available to the Zener/base junction - and what isn't taken
by the base will go through the Zener. Check to make sure that you won't have
*too much* Zener current under any possible load/transistor combination - if
you're in trouble here, go to a heftier Zener. The power rating of the
resistor should be selected based on its expected power dissipation under the
worst-case conditions (use at least the next larger standard rating).
It's also a good idea to add some additional filtering to a regulator like
this, in the form of capacitance at the input and output and across the Zener.
If a capacitor across the output is used, a diode connected backwards across
the transistor may be a good idea as well - to prevent any possible damage
from trying to "run the regulator backwards" when the input power is
shut down (or any other situation arises where the "output" voltage is higher
than the "input."
Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not
Ft. Collins, Colorado | those of my employer or any other
my...@fc.hp.com | sentient life-form on this planet.
Adam S. Denton
My analog stand-bys (soldering iron, bare wire, perfboard, long-nose
pliers) just won't cut it. So it's time I equipped myself for wire-wrapping.
I am starting from scratch, and am looking to find out:
- which tools out there are good, and which aren't (I have heard to
avoid the Just-Wrap, for example)
- sources for those good wire-wrap tools
- good sources for wire-wrap wire
- Do people prefer bulk or pre-stripped wire?
- Do people prefer the power wrappers or wrapping by hand?
- How many different colors of wire do I need to "stock"?
- Are there any opinions on what the best (or reasonably good) of
the hand tools (strip, cut, wrap, unwrap) and the best power
tools (ditto) are, and where to get them?
- how about those accessories like pins, WW IC sockets, etc.?
I don't mind the cost of quality; I intend to be wire-wrapping for many
years to come, so I'd rather get *good* tools rather than *cheap* tools,
if there is a distinction.
Thanks in advance, and any opinions are appreciated! E-mail and posting
are both fine. I will summarize if there's interest.
P.S. Thanks to all those who responded regarding crystal vendors!!
Adam Denton
a...@mtqua.att.com
Paul Elliott x225
> DON'T use the posted circuit -- you will cause Discman Frying.
I knew someone would follow up on this -- good treatment!
> Another solution is to use a 7809 if you can find one, or a
> 7805 with a 3V Zener (or 3-4 series-connected diodes) in series
> with the ground lead. If you go the latter route you will need
> capacitors at the input, output, and ground terminals of the 7805
> to GROUND in order to ensure stability.
I understand that it is *not* good practice to boost the output of
the 78XX-series regulators by putting diodes (Zener or otherwise)
in the ground lead. Something to do with the short-circuit protection
(I haven't analysed it myself).
I prefer the LM317-series of regulators. These let you set the
output Voltage with two resistors and are more stable than the 78XX
regulators. If you *must* use the 78XX regulators in boosted-
output Voltage applications, here's what I do:
You can use a series resistor from the ground pin to circuit-ground,
or better a resistor from output to the ground pin, and another from
the ground pin to ground:
7805
------------
in o----|in out|-----+-----o out
| gnd | |
-----+------ R1
| |
+-----------+
Iq -> |
R2
|
-----
---
-
The regulator quiescent current (Iq) flows from the gnd pin, through R2
to ground, and is typically 4.75 mA in the 7805.
The Voltage across R1 will be 5V (for a 5V regulator), and the current
through it will be 5V/R1.
Set the value of R1 so the current through it is about 5 * Iq, to provide
for some swamping of Iq variations. This gives a R1 value of:
R = E / I, R = 5V / 23.75mA, R1 = 210 Ohms
(approx, use 220 for I(R1) = 22.7mA
Choose R2 so that the current through it (Iq + I(R1)) gives the Voltage
drop required to boost the regulator output to the desired value:
Vout = 9V (in this example)
Vreg = 5V (for the 7805)
Vboost = 4V
I(R2) = Iq + I(R1), I(R2) = 4.75mA + 22.7mA, I(R2) = 27.5mA (approx)
R2 = Vboost / I(R2), R2 = 4V / 27.5mA, R2 = 145 Ohm (approx)
If you use a 120 Ohm resistor for R2, you get:
Vout = Vreg + (R1 * I(R2)), Vout = 5V + 3.3V, Vout = 8.3V
Power dissipation in R1 is about 0.114W, in R2 is about 0.133W
All in all, the LM317 is a better bet, though.
Geoff Steckel - Sun BOS Hardware CONTRACTOR
a FAQ file.
The LM317 is a good chip for this sort of linear stepdown application.
BUT:
the automotive alternator/battery/voltage regulator combination can produce
violent transients, AND
most power semiconductor devices fail shorted under these conditions
Do you really want to send the 140 V load dump or the 1500 V spike through
your homebuilt regulator into your $200+ portable stereo? I didn't think so.
(:-) The monolithic voltage regulator can only do so much.
You want at least a series fuse, a zener/MOV overvoltage protector, and some
RFI/EMI protection - the little microprocessor in a Discman gets confused easily.
Reverse voltage protection is nice, too. Only about $2 for parts, too.
Could someone who has them accessable (= not under 1000Kg junk in attic) post
references to application notes, etc., describing the automotive electrical
environment? I will as soon as I find mine, but that might not be soon...
geoff steckel (gw...@wjh12.harvard.EDU)
(...!husc6!wjh12!omnivore!gws)
Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line.
This posting is entirely the author's responsibility.
Jeff DePolo
>The LM317 is a good chip for this sort of linear stepdown application.
>BUT:
> the automotive alternator/battery/voltage regulator combination can produce
> violent transients, AND
> most power semiconductor devices fail shorted under these conditions
>
>Do you really want to send the 140 V load dump or the 1500 V spike through
>your homebuilt regulator into your $200+ portable stereo? I didn't think so.
>(:-) The monolithic voltage regulator can only do so much.
>
>You want at least a series fuse, a zener/MOV overvoltage protector, and some
>RFI/EMI protection - the little microprocessor in a Discman gets confused easily.
>Reverse voltage protection is nice, too. Only about $2 for parts, too.
I think this is getting a bit silly. First of all, the adapter that
Sony sells doesn't have that much stuff in it - probably a simple
regulator, maybe a filter cap for minor de-spiking, reverse polarity
protection (diode), and a fuse. That's it. There is no RFI/EMI protection,
no MOV, _maybe_ a zener for OV. How much do you think they're going to give
you in a $20 adapter (maybe $5 worth of parts)?
The easiest way I can think of is also the simplest (KISS). Take a
78H09 regulator, mount it to something (a very small project box),
put a back-biased diode across the 12v input, and a fuse in-line with
the output. Total cost: $4.00 + cost of cigarette lighter plug.
EMI/RFI - forget it. An MOV is your only hope of protecting the unit
from high-voltage spikes, but again, I've never seen the need. Look
at all of the car electronics that don't use them - is everyone else
wrong? I don't think so. It's overkill, IMHO.
Adam S. Denton
>I understand that it is *not* good practice to boost the output of
>the 78XX-series regulators by putting diodes (Zener or otherwise)
>in the ground lead. Something to do with the short-circuit protection
>(I haven't analysed it myself).
Sounds reasonable; I have never done this myself. The data books all
use resistors anyway. Serves me right for brainstorming...!!
>I prefer the LM317-series of regulators. These let you set the
So do I! Why I forgot to mention it, I don't know. The only concern
is that the 317 (like the 78's) requires a minimum differential voltage (the
value eludes me at the moment) which isn't too small (maybe 2-3V). On
the other hand, the transistor ckt can technically operate with a very
small differential (~0.4V) but that can throw the various part values
way out of whack. The LM2931 series are good for low dropouts but
can't hack the current (i.e. 100mA is their limit). Those new
National mini-switchers look pretty nice...gotta try 'em soon.
[good explanation on using resistors with 78XX deleted]
>All in all, the LM317 is a better bet, though.
Yup. Although I have a vaccuum-tube circuit that's better :-) :-)
> Paul M. Elliott Optilink Corporation (707) 795-9444
Adam Denton
a...@mtqua.att.com
Jim E. Dunne
> (hee-hee-hee -- you're with Motorola and can't find semiconductors?? ;-)
OK, I'm a software hack in Cellular. Hardware devices crash when
they see me comin'! Actually, right upstairs from me, where I knew
they had scads of data books, I found out they had a cache of sample
parts too. I raided the cabinet, only to find 5, 8, and 12 V
regulators! Oh well, I grabbed an LM317 adjustable. To the mailers
who said the adjustable needed only two resistors, well the data book
shows otherwise. Nothing I can't handle, but it'd be so nice to
have it all on-chip... guess I'll hunt for a 7809 next. Thanks to
all who helped.
Long live the KISS principle...
-- Keep It Simple Stupid (Softwarejock)!
--
Jim Dunne Motorola Inc. uunet!motcid!dunne
Rob Warnock
(Adam S. Denton) writes:
+---------------
| ...So it's time I equipped myself for wire-wrapping...
| I don't mind the cost of quality; I intend to be wire-wrapping for many
| years to come, so I'd rather get *good* tools rather than *cheap* tools,
| if there is a distinction.
Yes, there is a distinction. There is a great difference in quality between
*any* of the "cheap" tools and just about any of the expensive ones, but not
so much difference among the expensive ones. I happen to be happy with both
Gardner-Denver (the orignal Wire-Wrap trademark holder) and OK Machine Tools.
Absolutely the best thing to have for volume (or many years) work is a
line-powered (i.e., no batteries) wrap gun, with a cut+strip+wrap bit/sleeve.
Note: I am *not* talking about "Slit-N-Wrap", but the professional power wrap
bit which has a slot in the side of the sleeve. When you push the end of an
unstripped wire into the bit, the end comes out of the slot in the sleeve.
When you pull the trigger [having placed the bit over the pin first!], the
rotation of the bit pinches the wire against the edge of the slot in the
sleeve and cuts the end off, thereby measuring precisely the length of wire
that will be wrapped. Then, the (designed) friction between the wire and
the hole (that you've poked the wire into) "snaps" the insulation, and pulls
it off the end of the wire as it's wrapped. [Note: You want to get the bit
and sleeve combination for a "modified wrap", that wraps the first 2 turns
*with* insulatioin, for strength.]
Now prepare yourself for a bit of sticker shock: These things are *not* cheap!
Prices do vary, so shop around, but here are some typical values:
- Wrap gun (base unit, no bits) $ 80.00
- Bit/sleeve combo, #30 wire,
modified wrap, *not* self-stripping $ 35.00
- Bit/sleeve combo, #30 wire,
modified wrap, self-cutting/stripping
(as described above) $200.00
That's right, you can pay $180 to $250 for the bit/sleeve combo alone!
And you'll have to replace them after a couple of years of medium use,
or a year of 8-hours-a-day-bench-tech use. But I happen to think it's
well worth it. With a self-stripping bit, the work goes 2-5 *times* as
fast (depending what you would have been using for cutting/stripping
without it). Everyone I know who's serious about wire-wrap uses them.
-Rob
-----
Rob Warnock, MS-1L/515 rp...@sgi.com rp...@pei.com
Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc.
2011 N. Shoreline Blvd.
Mountain View, CA 94039-7311
Bakul Shah
>I am starting from scratch, and am looking to find out:
> - which tools out there are good, and which aren't (I have heard to
> avoid the Just-Wrap, for example)
> - sources for those good wire-wrap tools
> - good sources for wire-wrap wire
> - Do people prefer bulk or pre-stripped wire?
> - Do people prefer the power wrappers or wrapping by hand?
> - How many different colors of wire do I need to "stock"?
> - Are there any opinions on what the best (or reasonably good) of
> the hand tools (strip, cut, wrap, unwrap) and the best power
> tools (ditto) are, and where to get them?
> - how about those accessories like pins, WW IC sockets, etc.?
>
>I don't mind the cost of quality; I intend to be wire-wrapping for many
>years to come, so I'd rather get *good* tools rather than *cheap* tools,
>if there is a distinction.
Having just gone through this process here is my 40 Paisa's worth
(at the official rate).
Currently I have a friend's OK Industries WW tool and bought, on a
trial basis, an R3 series Wire-Wrap brand tool (made by Cooper
Tools. I believe these used to be sold under the Gardner-Denver
name). These are somewhat comparable in price, both are power
tools, and I am using 30 gauge cut-strip-wrap bit+sleeve with
each. I am buidling two different ckt boards, and since I wanted
to compare the two tools, I used the R3 for one ckt and the OKI on
the other. I think I will end up buying th R3 tool for a number
of reasons. It is lighter, has a much better ergonomic design and
is very comfortable to use, easier to thread a wire, looks nicer,
has rechargeable batteries and can supposedly do 1100 wraps per
charge (the OKI runs off of 110V), can be used for wrapping as
well as unwrapping, seems to be more reliable etc. The wire broke
frequently on the OKI but not on the R3. Now admitedly, this is a
very incomplete comparison, some things may be peculiar to the
units I used (i.e. not a class property) so you should make your
own comparison if you can.
I found that many more stores carry the OKI tools and if you do
find Wire-Wrap brand tools, they are usually more expensive.
Fry's Electronics, here in Sillyvalley, sold me the R3 tool for
about $180 (even though the price sticker on it was for $199.95!).
They didn't have the CSW bit/sleeve or the CSW wire, which I got
from Com-Kyl -- call up Cooper tools for a dealer name in your
area. The few, commonly known, stores that I tried were way more
expensive, so do call around. Try to get tools on a trial basis
so that if you don't like them after some use you can return them.
Pre-stripped wire is much more expensive so I don't use it.
Stripping by hand takes some time and stripping real short wire is
a pain. I prefer CSW bits for faster work but they are much more
expensive than the normal ones (about three times). One other
thing to consider is whether to by a tool with backforce or none
(an internal spring that let the bit push back upto a point
without your having to gently move the tool back). Some people
prefer backforce device, I don't even though I am just a beginner.
If you buy a normal bit (not CSW), get the `modified wrap' bit --
it wraps a some insulated wire as well for better withstanding of
vibrations.
As for number of colors to stock, I'd like some ideas for more
experienced people. I use a small number of colors, one for each
logical group of signals (such as data bus, control signals, VCC,
ground and so on).
The R3 can be used for unwrapping as well, by switching the
battery connection but I just use a hand tool for that. That
will change if ever I make massive mistakes!
30 guage wire works for most everything but I'd like to know what
people use for VCC and ground. Do they wire-wrap with a thicker
guage or solder? Also what about decoupling caps? I am using
inline caps (like so: ------O-----) and solder one between vcc and
gnd directly on a socket *before* inserting it in the board. But
there must be a better way. (You can get sockets with caps
already attached but I didn't find them in all sizes and they
were expensive).
As for sockets I don't know which ones are the best or what are
the best / cheapest sources for them but would like to find out!
Packs for two/three sockets are expensive so buy the largest size
packets you are likely to use. I'd also like to know of
inexpensive sources for the socket ID tags, perf board and such.
Let me also say I'd rather directly go to printed circuit boards
if at all possible; that is what I usually do. If you are
reasonably careful in designing, using CAD tools, have access to
simulators (atleast for checking out PAL logic), can afford one or
two rounds of PCB making + circuit layout and want more than a
couple of copies, PCBs are the way to go. Whenever possible I put
control signals I may want to change in PALs and leave some free
space and IO pins in each PAL so that most changes do not require
any major ripping up.
So... does anyone know of PCB houses that will make a small number
of two/four/six layer PCBs inexpensively? Does anyone know of
people who will do circuit layout for a reasonable price?
Hope this was useful. I also hope people with much more
experience than I will give us the benefit of their experience.
I'd like to see even more discussions of practical aspects of
circuit design, fabrication, routing, rules of thumb, sources of
components & tools, services available, new techniques and
technologies and new, interesting components etc. etc. It would
also be nice if that sort of information can be organized,
compiled and posted occasionally. If I weren't so busy *and*
disorganized I'd volunteer :-(
Sorry about going on and on.
-- Bakul Shah
b...@BitBlocks.COM
..!{ames,apple,decwrl,pyramid,sun,uunet}!amdcad!light!bvs
PS: Here are some useful numbers.
Cooper Tools: 919 362 7510, FAX: 800 423 6175
Tool:
R3 27600AD8 -- standard, 110V (for the battery charger)
R3 27610AD7 -- backforce, 110V
R3 27650AD3 -- standard, 220V
R3 27600AD2 -- backforce, 220V
30 guage CSW Bit: 990764
30 guage CSW sleeve: 990765
42
I can't find the OKI catalog right now.
Geoff Steckel - Sun BOS Hardware CONTRACTOR
>In article <1991Feb28....@cbnewsj.att.com> a...@cbnewsj.att.com
>(Adam S. Denton) writes:
>| ...So it's time I equipped myself for wire-wrapping...
>
>*any* of the "cheap" tools and just about any of the expensive ones, but not
>so much difference among the expensive ones. I happen to be happy with both
>Gardner-Denver (the orignal Wire-Wrap trademark holder) and OK Machine Tools.
I prefer Gardner-Denver. The OK units need Tender Loving Care or they
spit at you (more exactly, twist your wire into globs and scream loudly
from mismated gears).
>Absolutely the best thing to have for volume (or many years) work is a
>line-powered (i.e., no batteries) wrap gun, with a cut+strip+wrap bit/sleeve.
The self-cutting and self-stripping bits are wonderful - BUT!!!!
All the cut/strip/wrap bits I've used have ABSOLUTELY REQUIRED the use
of special wire. If you use the standard Kynar insulation wire wrap wire
you will destroy your $200 bit!!
The special wire is made with insulation which
1) slips off the wire easily
2) cuts cleanly
If the insulation fails to do either of these the cutting edges in the
bit are bent, and they are impossible to fix.
The right wire costs about the same as regular wire wrap wire.
Use the kind recommended by the bit manufacturer.
I would never use a slit-n-wrap for anything other than a paperweight.
Battery or hand powered wire wrap guns are useful for doing a repair
or other small number of wires.
Ed Hall
>From article <517...@hplsla.HP.COM>, by to...@hplsla.HP.COM (Tom Bruhns):
>
>> (hee-hee-hee -- you're with Motorola and can't find semiconductors?? ;-)
>
> OK, I'm a software hack in Cellular. Hardware devices crash when
> they see me comin'! Actually, right upstairs from me, where I knew
> they had scads of data books, I found out they had a cache of sample
> parts too. I raided the cabinet, only to find 5, 8, and 12 V
> regulators! Oh well, I grabbed an LM317 adjustable. To the mailers
> who said the adjustable needed only two resistors, well the data book
> shows otherwise.
You are correct--the databook shows two bypass capacitors, both optional.
One is at the regulator input, and is needed when the power supply filter
capacitor is an appreciable distance from the regulator (e.g. in a wall
wart, as is quite common these days). The other is at the regulator
output, and improves transient response (i.e. better regulation when
the load varies at a high frequency, such as with digital logic).
If you look at the databook for the 78XX, you'll see the same optional
capacitors. All that the LM317 adds is two resistors, and a great
deal of convenience. I find that using a single part for a variety
of voltages (including odd values) is a LOT simpler than having to use
a different part for a different voltage.
> Long live the KISS principle...
> -- Keep It Simple Stupid (Softwarejock)!
As a software jock myself, I agree. That's why I prefer to have a
single procedure that I can call with a variety of parameters rather
than a different procedure for each parameter.
-Ed Hall
edh...@rand.org