# open collector question

Discussion in 'Electronic Basics' started by [email protected], Oct 20, 2006.

1. ### Guest

I have an open collector toggle signal, instead of get on/off at 24
volts and grnd, I would like to get -12v to +12v, I am not an
electronics guy but with a little knowledge in the field, could anyone
tell me how to do this? Great thanks in advance for any posts..

2. ### Guest

That's a good question. It's been a long time since I designed a
transistor circuit and I wasn't all that good at the time.

Maybe a Class B, push-pull circuit would work. Look at just the
transistor part of these circuits, for example:

http://www.ele.tut.fi/teaching/7401003/Lk04-05/Measurementinstructions04-05.pdf

If you described the problem more precisely, you might get some experts

3. ### Jonathan KirwanGuest

So, you have a 24V supply, an open collector output tied to the +24V
via a resistor and you want this to become -12V to +12V relative to
ground? What's the toggle signal hooked to? How fast does it
operate? What will it be hooked to? Do you have access to any other
supply rails?

In other words, can you describe the situation more completely?

Jon

4. ### Bob MastaGuest

I'm assuming your open collector transistor has the emitter at
ground, in the middle of your +/-12 supplies. If so, then one
easy solution is to connect the base of a PNP device to the
open collector through a current limit resistor... try 10k for
starters. Connect the emitter of the PNP to +12, and the
load on the open collector can go to -12 (or gnd... anything
lower than +12). If for some reason you really need an NPN
open collector on -12 pulling from +12. just continue this
trick and feed the PNP collector through a resistor to the
base of the NPN.

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

5. ### ChrisGuest

Hi, Gary. The first thing you're going to have to do is get +12V and
-12V supplies. You can get the +12V from the +24V with an LM7812, a
positive 12V regulator, like this (view in fixed font or M\$ Notepad):

| ____
| +24V | | +12V
| o----o----|7812|----o-----o
| | |____| +|
| --- | ---
| --- | ---
| .1uF| | 10uF|
| | | |
| o----o------o-------o-----o
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Now for the negative voltage, you can use a 555 as a voltage inverter
like this:

|
| +12V +12V +12V
| | + +
| .-. | |
| | |24K .---o----o---. C = 100uF 25V
| | | | 8 4 | D = 1N4002
| '-' | | C
| | | |
| o-----o7 | +|| D -11.3V
| | | 3o---||--o----|<--o----o
| .-. | | || | |
| | |56K | 555 | V C ---
| | | .--o6 | D - ---
| '-' | | | | +|
| | | | | | |
| o--o--o2 | === ===
| | | | GND GND
| --- | 1 5 |
| --- '---o----o---'
| | 3.3nF |
| === ===
| GND GND
|(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

As long as you don't need more than 20mA or so from your negative
supply, this will work pretty well. Feel free to post again if an
unregulated 11.3V doesn't do it.

You're almost there. Now, if you can live with 0V in = +12V out and
24V in = -12V out, a simple transistor will do the job, like this:

|
| +12V +12V
| | |
| .-. |
| 10K| | |
| | | |
| 1N4002 '-' |
| Vin ___ | |<
| o-|<--|___|-o-| 2N3906
| 10K |\
| +24V/0V |
| o
| |
| .-.
| 2.2K 1/2W| |
| | |
| '-'
| |
| -11.3V
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Now that you've got one possible answer, how about posting again and
describing why this one won't work? If this is too complicated for
your skill level, there are simpler (and more expensive) solutions, I