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Positive and negative pulse amplification circuit

Discussion in 'Electronic Design' started by captoro, Apr 23, 2013.

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  1. captoro

    captoro Guest

    I have a circuit composed of Lm393 with 12v power supply.
    I can output two synchronous pulses: +12v and -12v
    I would like to put a coil between so I get a 24v difference.
    Taking the positive side and hooking it up to the coil and a mosfet after the coil.
    Can I use the -12v as my drain on the mosfet ?
    I dont want to blow anything up so thats why I am asking what would be best way to do this. I also heard that i needed to one mosfet for positive and one mosfet for negative side ....
    any ideas?

  2. Jamie

    Jamie Guest

    Trying to picture that in my head, Is that a cascode config
    you're after?

  3. captoro

    captoro Guest

    how do you post an image here ??

  4. captoro

    captoro Guest

    I'll explain a bit better:

    I have two LM393 with a 12v power supply.
    One of the LM393 is outputting pulses at +12v and the other LM393 at -12V.
    I would like to pulse a motor with that 24v difference.
    Obviously I cannot drive the motor with the LM393.
    So I thought of pulsing n-channel mosfet to drive the motor.
    If I had only the positive side to take of I would connect the drain to the motor and source to ground. What is confusing me is that I have a virtual -12v ground. How do I drive a motor with the 24v difference (+12v to -12v) ?

  5. whit3rd

    whit3rd Guest

    If you want 24V, why not use a 24V power supply on the LM393?

    The outputs are good for 6 mA (guaranteed) current, and
    are 'off' half the time, so you'll get less than a tenth watt for
    your motor (at 12V) . Will that be a problem?

    An oscillator and coil, with tap, can make any voltage you'd like
    (the Ford model A got kilovolts from a 6V battery this way).
  6. Jamie

    Jamie Guest

    If you have a virtual ground to give you a -12 volts, then that means
    you have a 24v source to start with?

    Turning on the fet is simple, use an R to your virtual ground to the
    gate, connect the source to the -12 supply leg. when the comparator
    is in the off set, meaning the open collector is not on, the gate
    common R will switch the FET on. This is because the source is sitting
    at a -12, which looks like +12V at the gate if the source was on the
    common, Of course you need the open collector to also be connected to
    the gate along with the virtual ground R.

    THe motor can be connected to the Drain of the Mfet while the other
    pole is connected to the +12V. This will give you the 24 volts to the
    motor while splitting the rail via a v-ground for the rest of your circuit.

    Basically you only need one comparator sitting on a split rail, when
    the output is off, the gate R to common will turn on the MFET.

    of course this does not give you a bridge so if you are thinking about
    reversing the motor, then you need some more semi-conductors.

  7. Phil Allison

    Phil Allison Guest

    "John Fields"
    ** This is our old friend "lerameur".

    Making sense is not part of his modus operandi.

    My take on his latest insanity is that he wants to drive a 24V DC motor
    using a 12V DC supply by feeding the motor with pulses of alternating

    Motor will act like mule.

    .... Phil
  8. Jasen Betts

    Jasen Betts Guest

    You'll need more than just that to get 24V from a 12V supply.
  9. captoro

    captoro Guest

    My bad,

    i was looking at a schematic and I thought the voltage was starting at 0v to 12-v drop. But after making the circuit i realize that the voltage was at 12v and dropping to 0v .....
    honest man mistake ;)
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