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open collector question

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

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  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
    http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

    If you described the problem more precisely, you might get some experts
    to answer.
     
  3. 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 Masta

    Bob Masta Guest

    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
    dqatechATdaqartaDOTcom

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

    Chris Guest

    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
    suppose. Any additional information about your application would also
    be helpful -- we might see a roadblock you don't.

    Cheers
    Chris
     
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