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Switching help

  1. Aug 29, 2006 #1
    Hi,
    I'm designing a circuit in pspice and having some trouble with the switching. In my circuit in pspice I'm using an ideal voltage controlled switch model "S" and using a vpulse to control it. My current through the switch needs to be bidirectional, and maxing around 80mA with an average around 30-40mA. The switching time should be fast compared to a microsecond.

    I'm not sure whether to use a BJT, a FET, an IGBT, a combination, or perhaps something else altogether.

    I want something that I can model in pspice, and then be able to build on a breadboard.

    Let me know if anything comes to mind.

    Thanks,
    Justin
     
  2. jcsd
  3. Aug 29, 2006 #2

    berkeman

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    Staff: Mentor

    Does PSPICE have a relay macro? Microcap 8 does. Is there anything about relays in the PSPICE Help menu?
     
  4. Aug 29, 2006 #3
    To be honest, finding part models in pspice is more than a hassle. Are you saying that I should use a relay? I forgot to mention, the switch that I use has to have low power dissipation at the currents I'm working with. Ideally the power dissipation should be below 10mW, not sure if this is feasible.
    Thanks,
    Justin
     
  5. Aug 29, 2006 #4

    berkeman

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    Staff: Mentor

    Well, if you want fast switching times on the order of a microsecond, then I guess a relay would be a non-physical model to use in your simulation. You should use something more like what you will use in the real circuit. Look for an Analog Switch (which is made out of several complimentary CMOS transistors generally).
     
  6. Aug 30, 2006 #5
    Thanks for the help, analog switches look promising.
    Justin
     
  7. Aug 30, 2006 #6
    Hmm, slight problem, I've been looking at analog switches, and they seem to fit the bill pretty well except the ones I've looked at have maximum voltage swings across the in and out terminals of around 5V. I need something that can handle voltage swings around 40V. I'll keep looking, but let me know if there's another device that will satisfy this requirement.
    Thanks,
    Justin
     
  8. Aug 30, 2006 #7

    berkeman

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    Staff: Mentor

    One option would be to look at how an analog switch is typically constructed (with the complementary CMOS pass devices), and make your own with high-voltage CMOS transistors. I think that's basically how solid state relays are made, and they accommodate higher voltages.
     
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