Need Help with Design
BobP122
Could use some help with configuring a:
1 Battery connected to
2. a Switch (2 contacts) connected to
3. a Transistor(& load)
The open switch switch turns on the transistor.
The closed switch turns off the transistor.
B+ > | | > Transistor (Switch open - Trans. OFF)
B+ > H > TrTransistor (Switch closed - Trans. ON)
Any Ideas?
Thanks
BobP
me
2113f4...@v29g2000hsf.googlegroups.com:
You could use resistor divider on the base to bias transistor on then
connect switch between base and ground (for NPN transistor). Closing the
contacts would then ground the base and turn the transistor off...
John Fields
---
Yeah, make up your mind.
In the one case you want the open switch to turn the transistor on and
the closed switch to turn it off, and in the other you want just the
opposite.
Which is it?
Fred Bloggs
You might recall from his post in the Basics NG that he wants to convert
a heating thermostat to a cooling thermostat. So when the tstat closes
on low setpoint, he wants to turn his cooling fan off, and when the
tstat opens at the high setpoint, he wants to turn his fan on...
Don Lancaster
Use an EXOR gate.
--
Many thanks,
Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: d...@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com
Eeyore
Don Lancaster wrote:
> Fred Bloggs wrote:
> >
> > You might recall from his post in the Basics NG that he wants to convert
> > a heating thermostat to a cooling thermostat. So when the tstat closes
> > on low setpoint, he wants to turn his cooling fan off, and when the
> > tstat opens at the high setpoint, he wants to turn his fan on...
>
> Use an EXOR gate.
Use a PIC !
Tah-dah !
Graham
max...@punkass.com
wrote:
I like pics, but in this case it's overkill and too big compared to a
tiny logic chip in a 5-pin SC70 package.
http://www.fairchildsemi.com/ds/NC%2FNC7SZ86.pdf
gearhead
As I recall from your other post, you hooked up a pnp darlington and
it worked. But it drains at least a milliamp from your battery while
the thermostat contacts remain closed shunting current away from the
darlington base, and you asked for a solution that uses less current.
Of course, you can't escape having some current going through the
contacts, but you can reduce it by an order of magnitude. View in
fixed font.
batt
|
,-------+-------,
| | |
100k | |
| / c load
+-----| |
| \ e |
| | _|
| +----||_
t-stat | |
| 100k |
| | |
'-------+-------'
|
gnd
For the npn transistor, you can choose from any number of small signal
transistors. Likewise, there are probably quite a few n-channel
mosfets that would serve to drive the load.
Brian
<max...@punkass.com> wrote in message
news:f3683c98-160c-48ab...@p69g2000hsa.googlegroups.com...
But they have the pics in sot23-6 now. Cheap too. I just used one in a
design, great for things with minimal I/O, like a toaster.
Fred Bloggs
I prefer discrete bipolar for this, more rugged and higher parts count.
Below is the circuit of the 4's, a standard Darlington with a fast-on
slow-off characteristic to overcome tstat contact bounce on close. Q3
and Q4 form an SCR latch activated on tstat opening with Q4 providing
base drive to the Darlington. The 4.7M in the base of Q3 provides more
than enough current to trigger the latch and draws a mere 3uA during
tstat closed state.
View in a fixed-width font such as Courier.
.
.
. Q1
. TIP42
. BATT--+-------------+------- e c ---+---->TO LOAD
. (+) | | b |
. | | R1 | |
. | +--[470]---+ |
. | | | |
. | | e c -'
. | | b
. | | R2 | Q2
. | '--[4.7k]----+ 2N4403
. | |
. | R3|
. | [4.7k]
. | | R4
. | D1 +--[4.7k]--.
. | TSTAT R5 1N4148| |
. +--||-+---+-----[47k]-|>|--+--|>|-----+
. | | | | 1N4148 |
. | [4.7M]| | D2 +|C1
. | R7| b R6 c ===
. '-------e c---[47k]----b 2N4403 |4.7u
. | 2N4401 e Q4 |
. | Q3 | |
. BATT-------+--------------------+----------+----
. (-) |
. ---
. ///
.
.
Fred Bloggs
Correction:
View in a fixed-width font such as Courier.
.
.
. Q1 pnp
. TIP42
. BATT--+-------------+------- e c ---+---->TO LOAD
. (+) | | b |
. | | R1 | |
. | +--[470]---+ |
. | | | |
. | | e c -'
. | | b
. | | R2 | Q2
. | '--[4.7k]----+ 2N4403
. | | pnp
. | R3|
. | [4.7k]
. | | R4
. | D1 +--[4.7k]--.
. | TSTAT R5 1N4148| |
. +--||-+---+-----[47k]-|>|--+--|>|-----+
. | | | | 1N4148 |
. | [4.7M]| | D2 +|C1
. | R7| b R6 c ===
. '-------e c---[47k]----b 2N4401 |4.7u
. | 2N4403 e Q4 npn |
. | Q3 pnp | |
BobP122
> On Sun, 20 Jan 2008 15:04:31 -0800 (PST), BobP122
>
> >Hi,
> >Could use somehelpwith configuring a:
> >1 Battery connected to
> >2. a Switch (2 contacts) connected to
> >3. a Transistor(& load)
> >The open switch switch turns on the transistor.
> >The closed switch turns off the transistor.
>
> >B+ > | | > Transistor (Switch open - Trans. OFF)
> >B+ > H > TrTransistor (Switch closed - Trans. ON)
> >Any Ideas?
>
> ---
> Yeah, make up your mind.
>
> In the one case you want the open switch to turn the transistor on and
> the closed switch to turn it off, and in the other you want just the
> opposite.
>
> Which is it?
Mea Culpa!
>B+ > | | > Transistor (Switch open - Trans. ON) (Open = ON)
>B+ > H > Transistor (Switch closed - Trans. OFF) (Closed = Off)
Corrected Version
Obviously if I can't even "state" the problem right - the solution
becomes more difficult.
I find it difficult to follow diagrams in 'text mode'. I thought mine
would be clearer - and it would have if only I had it right.
Thanks
gearhead
>
> - Show quoted text -
Bob, do you have your reader set to show posts in courier or a similar
font, with mono-spaced letters like a typewriter? The diagrams are
quite legible.
If they look like gobbledygook, it's because you have times roman or
some such "proportional" font.
Fred Bloggs
If push comes to shove, he can select, copy, and paste the text diagram
into Word or something similar, re-select the whole thing and then go
into a Format->Font->Courier. Or alternatively, he can open it in Google
Groups, and click on the More Options->Original menu item, displaying
the diagram in the original Courier format...actually looks like it
preserves the original font when it's copied from Google and pasted to
Notepad. These are fairly low tech methods.
Fred Bloggs
> 1 Battery connected to
> 2. a Switch (2 contacts) connected to
> 3. a Transistor(& load)
> The open switch switch turns on the transistor.
> The closed switch turns off the transistor.
>
> B+ > | | > Transistor (Switch open - Trans. OFF)
> B+ > H > TrTransistor (Switch closed - Trans. ON)
I don't really care for the really slow turn-off, so Q5 is added to snap
it off when C2-R7 detects Q1-Q2 dropping out. This one will be immune to
any reasonable tstat contact bounce, handles well over 50ms.
View in a fixed-width font such as Courier.
.
.
. Q1 pnp
. TIP42
. BATT-----+----------+-------- e c ----------+---------TO LOAD
. (+) | | b |
. | | R1 | |
. | +-[470]-+---+- e c -----+
. | | | b |
. | | | | Q2 |
. | | | R2 | 2N4403 |
. | | '-[4.7k]-+ pnp |
. | | | |0.47u
. | | | |C2
. | | Q5 pnp | ===
. |+ | TIP42 | |
. === +------- e c -------------------.
. | | b | | |
. | | | | R7 | |
. | .-------+--|<|-----+-------[4.7k]-' |
. | | | 1N4148 | |
. | | o D3 R3| |
. | | TSTAT [4.7k] |
. | | o | R4 |
. | | | +--[4.7k]--------+
. | | | R5 | |
. | | .---+-----[47k]-|>|--+--|>|-----+-----+
. | | | | 1N4148| 1N4148 | |
. | | [4.7M]| D1 | D2 +|C1A +|C1B
. | | R7| b R6 c === ===
. | '-----e c --[47k]--- b 2N4401 |4.7u |4.7u
. | | 2N4403 e Q4 npn | |
. | | Q3 pnp | | |
. BATT-----+------+--------------------+----------+-----+----
John Fields
---
Use a non-proportional font like Courier to read and write ASCII
schematics and the process becomes much easier.
ISTM that if you use a SPDT (or a SPSTNC) relay to run the fan the
solution to your problem becomes trivial:
BAT+>--+--------+
| TSTAT |
| / |C
| O O
| O NO | NC
| O--> |<--O
[COIL]- - -| |
| [FAN]
| |
BAT->--+------------+
That is, with the thermostat open the relay will be de-energized and
the fan will be running because the normally closed and common
contacts will be closed, but when the thermostat is closed the relay
will be energized, breaking the contact between the NC and C contacts,
turning the fan off.
JF
John Fields
wrote:
---
Hmm... I must have missed it.
ISTM this would be the easiest way: (View in Courier)
.BAT+>--+--------+
. | TSTAT |
. | / |C
. | O O
. | O NO | NC
. | O--> |<--O
. [COIL]- - -| |
. | [FAN]
. | |
.BAT->--+------------+
JF
BobP122
Hi,
I'll have open some pretty dust covered books - for the transistor
part of the ciruit at leat.
Am I following?
t-stat OPEN: Transistor OFF & Mosfet ON (Load Grounded ON)
t-stat CLOSED: Transistor ON & Mosfet OFF (Load Floating OFF )
Really nice simple solution with negligible power consumption in "Load
OFF" state.
Thanks
BobP
gearhead
>
> - Show quoted text -
you're very close --
with the thermostat open circuit, both the transistor and the mosfet
are ON, and so is the load.
with the thermostat contacts closed, the transistor and mosfet are
both OFF, and so is the load.
With the thermostat open circuit, the upper 100k resistor feeds
current into the base of the npn transistor, turning it on. In turn,
this provides a connection between the battery voltage and the mosfet
gate, which then turns on.
When the thermostat contacts close, they shunt current away from the
transistor base causing the transistor to turn off. That takes the
voltage away from the mosfet gate. The lower 100k resistor then
bleeds the charge off the mosfet gate, allowing it to turn off.
I forgot how much current you said the fan draws, but you might need a
mosfet in a TO-220 case. Look for Rds in the datasheet to figure out
how much power it will dissipate according to current squared times
Rds. The TO-220 can deal with a watt or two and not need a heatsink.
Radio Shack sells the IRF510, which has about half an ohm resistance.
You can get mosfets with much lower resistance than that, though.
Something I left out of the circuit is a freewheeling diode across the
fan. Connect the cathode (stripe) to the battery positive and the
anode to the other end of the fan, where it connects to the mosfet
drain. You take this precaution because when the mosfet turns off,
the inductance of the fan creates a pulse. With a diode across the
fan, the pulse travels harmlessly through the diode instead of hitting
the mosfet. If you have some 1N400x diodes on hand, you could use one
of them.
Mike
BobP122
>
> - Show quoted text -
Hi Mike (aka gearhead),
Boy, those books are dustier than I thought.
Thanks again
gearhead
> On Jan 26, 1:00 am, gearhead <nos...@billburg.com> wrote:
> > > > On Jan 20, 3:04 pm, BobP122 <JohnNico...@sympatico.ca> wrote:
>
> > > > > Hi,
> Boy, those books are dustier than I thought.
>
> - Show quoted text -
P.S. You might be able to use more than 100k. Try megohm resistors
and see how it works.
BobP122
>
> - Show quoted text -
Hi again Mike,
If you could indulge me one more 'elucidation'?
I'm dusting off some old books - analyzing your circuit.
Fets were an academic subject only for me - never to be used
(exception cmos chips).
They still intimidate me.
Wouldn't the FET part of your circuit when ON have B+ right at its
gate?
B+ to gate B+ thru resistor to gate
| \ e | | \ e |
| | _| t-stat | |
| +----||_ | 100k |
t-stat | | | | _|
| 100k | | +----||_
| | | | |
'--------+-------' '-------+---------'
| |
gnd gnd
Shouldn't it (perhaps) be: B+to gate thru Resistor?
Thanks again
BobP
gearhead
>
> - Show quoted text -
For a bipolar transistor, you would need a resistor in the gate to
limit current.
In contrast, mosfets are voltage-controlled devices. No dc current
flows into the gate, so you don't need a current-limiting resistor.
Just make sure the voltage appied to the gate doesn't exceed the Vgs
(gate-source voltage) listed on the datasheet, typically 20 volts.
The mosfet model includes a capacitor from gate to source, a very
*tiny* capacitor. You can find the actual capacitance on datasheets.
It measures in nanofarads or picofarads.
A mosfet contains a body diode from drain to source. For a n-mos, the
cathode corresponds to the drain and the anode corresponds to the
source. When you apply a voltage at the gate, it opens the channel
through the body of the mosfet and allows it to conduct like a
resistor. If you remove the voltage from the gate and drain the
charge from the capacitor, the channel shuts off and the mosfet
becomes a diode again, blocking current.
You only have a significant amount of current flowing in the gate when
switching the mosfet at high frequency and the gate capacitance
conducts ac. In an application like that you would probably put a
small resistor on the order of 10 ohms goes in the gate to prevent
ringing. I don't think ringing or oscillation will be a problem in
your application, but if you want to bung a 10 ohm resistor in there
it won't do any harm.
JeffM
> B+ to gate B+ thru resistor to gate
>
> | \ e | | \ e |
> | | _| t-stat | |
> | +----||_ | 100k |
> t-stat | | | | _|
> | 100k | | +----||_
> | | | | |
> '--------+-------' '-------+---------'
> | |
> gnd gnd
You are STILL trying to use a proportional font to make ASCII art.
http://groups.google.com/group/sci.electronics.design/msg/39df4eb59a9a78f9?q=zz-zz+*.*.non-proportional.font.like.Courier&fwc=1
To create this stuff, you have to LEAVE Google.
Use Notepad (monospaced font) then cut & paste back into Google.
To *read* ASCII prints from Google, there are 4 ways:
1) Copy & paste back into Notepad.
2) Click **More options** then **Show original**
3) At the top of the page click **Options** then **Fixed text**.
4) Append &fwc=1 to the URL and hit Enter.
(Preface that with a ? if one does not already exist.)
Before leaving the page,
you will probably want to click **Proportional text**.
.
.
...and B+ (plate supply) hasn't been in common use since ~1965
when tubes (and plates) pretty much disappeared.
Bipolars use Vcc (collector supply) and FETs use Vdd (drain supply).
BobP122
> BobP122 wrote:
> > B+ to gate B+ thru resistor to gate
>
> > | \ e | | \ e |
> > | | _| t-stat | |
> > | +----||_ | 100k |
> > t-stat | | | | _|
> > | 100k | | +----||_
> > | | | | |
> > '--------+-------' '-------+---------'
> > | |
> > gnd gnd
>
>
> To create this stuff, you have to LEAVE Google.
> Use Notepad (monospaced font) then cut & paste back into Google.
>
> To *read* ASCII prints from Google, there are 4 ways:
> 1) Copy & paste back into Notepad.
>
> 2) Click **More options** then **Show original**
>
> 3) At the top of the page click **Options** then **Fixed text**.
>
> 4) Append &fwc=1 to the URL and hit Enter.
> (Preface that with a ? if one does not already exist.)
>
> Before leaving the page,
> you will probably want to click **Proportional text**.
> .
> .
> ...and B+ (plate supply) hasn't been in common use since ~1965
> when tubes (and plates) pretty much disappeared.
> Bipolars use Vcc (collector supply) and FETs use Vdd (drain supply).
Hi Mike,
I'll have to stop saying "thanks" - well maybe just once more.
I must be trying your patience.
I'm bound to get something right sooner or later - just by accident -
law of probabilities.
BobP
gearhead
>
> - Show quoted text -
Bob, sometimes the guys here act a little stern with the newcomers.
Basically, like Jeff said, you can't type a post in Google using a
fixed font, but you can bring up notepad in windows, type your message
there, then paste the text into a Google groups post.
Hope you saw my other post with the explanation about mosfets.