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Designing a switching circuit

  1. Sep 15, 2006 #1
    Hello All,

    Can someone give me some suggestions for a chip that can drive some high frequency mosfets to create an AC square wave? I am designing a circuit that pulses the voltage from a capacitor into some coils I am working with but I need the square wave to be AC and not DC. I want to use mosfets to do this but I'm not sure how to switch it so that it will be AC.

    Also, I am working with a rather wide frequency range for my experiments so whatever I come up with needs to be very adjustable (1KHz-7MHz). Even if I could come up with a couple of separate controllers that will cover the wide range, that would be fine too. I *think* that a 555 timer would work for the lower frequencies but what abut the higher ones?

    Jason O
  2. jcsd
  3. Sep 15, 2006 #2


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    Staff: Mentor

    You could just to a quick and dirty inverter RC oscillator. Use something like an HC14 Schmidt trigger inverter, and put a resistor from its output to its input, and put a cap on its input to ground. Or you can use 3 inverters in a row (still just the one RC) to make it work a little cleaner. You adjust the RC time constant to get the frequency.
  4. Sep 15, 2006 #3


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    Staff Emeritus
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    I don't really know what an "AC" or "DC" square wave even means to you.

    - Warren
  5. Sep 15, 2006 #4
    When I say AC square wave, I mean that the voltage changes from -V to +V rather than the DC square wave where the voltage changes from 0 to +V or 0 to -V.


    Thank you very much for the information. I've never heard of a HC14 Schmidt trigger inverter. Could you give me some more info on it or maybe a good source link? Also, it would be very helpful if you could make a basic circuit diagram of what you are describing.

    Thank you,
    Jason O
  6. Sep 15, 2006 #5
    are u making a stun gun?

    It's tough making a clean high frequency signal due to capacitance in the wiring and leads.

    if a signal goes from -5v to 5v, isn't it the same as 0 to 10v?
  7. Sep 16, 2006 #6
    Hi David,

    No I'm not working on any kind of weapons stuff. I'm experimenting with different obscure electrical effects such as the Barkhausen Effect, and electrostatic induction. Some of my tests involve the use of medium to high voltage spikes at specific frequencies. I will be experimenting with both the AC and DC square waves but so far, the AC ones seem to have the most pronounced effects.

    Jason O
  8. Sep 17, 2006 #7


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    Staff: Mentor

    You are not using standard terminology there. Both of the waveforms you are talking about are AC, since they are changing with time. One has a zero DC offset, and the other has a non-zero DC offset. DC means unchanging with time. You should try to use the standard terminology to avoid confusing others. (I'm not saying this to get on your case, I'm just trying to help you in your learning process.)

    Like figure 8 in this Fairchild app note:

    http://www.fairchildsemi.com/an/AN/AN-140.pdf#search="RC oscillator inverter schmidt"
  9. Sep 21, 2006 #8
    Hi berkeman,

    Thanks for the correction about the DC offsets. As for the control circuit. I *think* I found a setup that will work. I'll post the circuit diagram for it once I finish testing it out. Thanks for all your help.

    - Jason O
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