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How to generate 22V pulses from TTL and a 22V supply

Discussion in 'General Electronics Discussion' started by Andymitchell, Apr 30, 2012.

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  1. Andymitchell

    Andymitchell

    3
    0
    Apr 30, 2012
    Hi Forum users,
    I am having trouble updating a circuit. The current circuit uses a TC4427 Mosfet driver with TTL input and 18V supply voltage to generate 0.5 to 2 usec 18V pulses.
    Now I need to generate slightly higher voltage pulses,22V this time. Unfortunately this is outside the range of the TC4427 (I've confirmed this by burning a few out)
    So does any body know how to increase the voltage of my pulses. The duty cycle ON:OFF is about 1:100 to 1:1000.
    My limitation is that I have a TTL source to trigger the pulse, but I can supply the 22V, no problem. It seems a simple problem to solve but its got me stumped:eek:
    Thanks for any ideas...
    P.S. I am slightly naiive electronically speaking even though I have developed several hundred digital circuits.
    Andy
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    You need a level shifter. Depending on the current you need out, this can be as simple as an NPN with the emitter to ground, the collector to a resistor to 22V and the base to a resistor to the TTL signal. If you need to source significant current, you will need to follow this with a PNP high side switch.

    Bob
     
  3. GonzoEngineer

    GonzoEngineer

    321
    2
    Dec 2, 2011
    How much current do you need to source and sink?
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    And how fast does it need to switch?

    Bob
     
  5. Andymitchell

    Andymitchell

    3
    0
    Apr 30, 2012
    Reply on 22v pulses

    I don't need to draw much current, maybe 50ma peak but much less than that on time average. I will build a test circuit with an npn and hope it is that simple. As far as speed goes I would be aiming for rise and fall times of no more than 100nsec.
    Thanks for your help.
    Andy
     
  6. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    50ma is a lot of current. You can't use the simplest (single transistor) version for that. For example, if you used a 100R resistor, that would drop 5V at 50ma. So you would need a level shifter followed by a push-pull pair. To make this out of discrete transistors it would be difficult to get the 100ns rise and fall times. I think you should look for a MOSFET driver chip that can handle the 22V.

    Bob
     
  7. Andymitchell

    Andymitchell

    3
    0
    Apr 30, 2012
    22v pulses

    The suppose this is where my problem began. The tc4227 that I have been using is a MOSFET device. But this can only be used up to 18 volts, I'm having trouble finding something that will work at 22v. I have tried to use capacitors and diodes to add pulses as in a Dickson multiplier but have only managed to get a distorted and not very useful pulse out. I expect that this was not the right thing to try. I will have another search on mosfets .
    Thanks
    Andy
     
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