q:Mosfet Switch

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

Thanks Chris

Robert Baer wrote:

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.

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.

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

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.

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.

I stand corrected.