How to invert voltage polarity?

Discussion in 'General Electronics Chat' started by Allenph, Jun 20, 2015.

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  1. Allenph

    Thread Starter Member

    May 27, 2015
    I have a feeling that an Op-amp can get this out of the way pretty easily but I'm not sure exactly how.

    I have this...

    The oscillator works with some bugs (I'll be asking about that shortly in another question.) Eventually I would like M1 to be the switch for a buck converter. There's a problem with that.

    My oscillator output signal is positive. No problem. Just use an NPN channel MOSFET, right? I don't think so.

    NPN channel transistors, as far as I understand, can only be used after a voltage drop to ground. I.E. you use them to control whether a certain circuit has a path to ground or not. If I stick a resistor above M1 everything works fine. However, if I stick a buck converter above it, it doesn't workout fine because the buck converter is not a current shunt. (All of the voltage doesn't drop over the buck converter.)

    So, I could use a PNP channel MOSFET, the only problem with that is that my output signal is positive. Adding my positive output signal to a PNP channel MOSFET would just increase the depletion region...or increase already infinite resistance.

    Regardless of whether or not I really need to invert the signal (although I'm very interested in the solution to my problem) I think it would be a good thing to know how to invert a voltage.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Allen, rather starting a new thread with every question, how about just keeping it all in one thread...
  3. Wendy


    Mar 24, 2008
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