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q:Mosfet Switch

Discussion in 'Electronic Design' started by Chris, Jul 29, 2005.

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  1. Chris

    Chris Guest

  2. Robert Baer

    Robert Baer Guest

    The circuit is useable with a 12V supply, but could destroy the gate
    of the FET if the supply was 15V or more.
    Perhaps a change so the gate drive cannot be moer than 10V would help.
    Make sure that you use a good heatsink on the FET.
    Be advised that the power ratings of FETS cannot be achieved unless
    one cools the die to -55C and uses a drive under a microsecond per
    minute or longer.
    And in some cases, not even then.
     
  3. Chris

    Chris Guest

    how would i limit the voltage? the amperage load i need is < 1amp

    Thanks
    Chris
     
  4. Mochuelo

    Mochuelo Guest

    I assume the "GND" to the left of the 4N36 is different to the "GND"
    to the right of it, because otherwise you don't need an optocoupler.

    On a side note, I recommend you to draw schematics always placing the
    higher voltages at the top.
     
  5. Robert Baer

    Robert Baer Guest

    The most negative voltage is at the bottom, which is acceptable.
     
  6. Robert Baer

    Robert Baer Guest

    Use a zener and a dropping resistor.
    Since you indicate a paltry 1 amp or less,a 5V drive would be
    acceptable for most FETs - if you do not care about high speed.
     
  7. Mochuelo

    Mochuelo Guest

    ?

    At the bottom there is "+12V", and at the top there is "GND", so not
    good.

    Besides, it is not a typo. It can't be -12 V, because the channel
    inside the PMOS would never turn on, the parasitic diode across it
    would always conduct, and the BJT inside the optocoupler would be
    wrongly connected.
     
  8. Robert Baer

    Robert Baer Guest

    I stand corrected.
     
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