q:mosfet circuit

http://chrispol.ath.cx:8080/switch.jpg

would this be the proper circuit to optically source current to a heavy
load?

Thanks

 

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.

 

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

 

Thanks guys does this look better?
http://chrispol.ath.cx:8080/switch.jpg

 

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