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Power switching circuit design

Discussion in 'General Electronics Discussion' started by andrew.grimm3, Dec 13, 2011.

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  1. andrew.grimm3


    Dec 7, 2011
    Hi. I need some help desigining a power switching circuit. I'm using a LM393 comparator and a IRFZ34N Mosfet transistor. I need to drive a 4.0A load that needs 50vDC. It needs to turn on the device when the input voltage signal hits 2.5vDC or higher and off when the input voltage signal is 2.4vDC and lower.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Hi Andrew,
    first you need to design a comparator to your needs, see for example here:
    Note that the LM393 has an open collector output which means, it cannot directly turn on the MOSFET (which needs a positive gate voltage to turn on).
    Depending on how fast you have to switch the MOSFET, you can use a pull-up resistor at the output of the comparator and connect the output/pull-up to the gate of the MOSFET. This will turn on the MOSFET a bit slowly, but turn it off very fast.
    If you nedd to turn on and off both fast, then you should add an active totem pole output stage after the Comparator. Or use an OpAmp instead, wiring it as a comparator. Thus you will have enough current to quickly charge and discharge the MOSFETs Gate, switching it faster.
    For the gate drive 5V should be sufficient for 4 A Ids.

  3. andrew.grimm3


    Dec 7, 2011
    Thanks Harold. That helps.
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