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q:mosfet circuit

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

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  1. Chris

    Chris Guest

  2. I don't see the point of having the optocoupler in there, when you
    could connect the switch to the gate and do the same thing.

    I don't recognize the number on the fet.

    Oh, and you have the +12V and ground connections for the load reversed
    and you need some current limiting resistance in series with the LED.
    Something like 200 ohms should work.

    You will probably not get the full performance out of the fet with
    just 5 volts gate to source. Now, if you connect the collector of the
    optocoupler to +12, you will fully turn the mosfet on.
     
  3. Ban

    Ban Guest

    Sorry to say Chris, but you got almost everything wrong.
    1. you should limit the current through the LED with a series resistor. What
    you did will destroy the diode immediately.
    2. the phototransistor is connected wrongly. the emitter(pin4) goes to gnd,
    the collector(pin5) to the gate.
    3. The IRF9234 has 140m ohms channel resistance, with 10A this will make 14W
    dissipation, wow. Take a IRF4905 instead.
    Change the optocoupler to 4N36, which has 100% current transfer ratio
    instead of 30%. With 10mA input current, the 4N36 will sink 10 mA, so to be
    on the safe side, choose a R= 12V/3mA. A 3k9 will do
     
  4. Chris

    Chris Guest

  5. rayjking

    rayjking Guest

    Chris,
    This circuit will work however a rf stabilizing resistor should be added in
    series with the gate ( 300 ohms typically ) Every fet conducting currents
    over a few amps should have such a resistor.

    Ray
     
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