Isolated FET

[DynamoBen]

I'm using a MOSFET for single direction motor speed control via PWM from a PIC. I'm thinking about isolating the power supply that is used for motor control (via the FET) from the supply used for the control electronics (PIC). What I'm unclear about is if the FETs common needs to be tied to the control electronics common. I know with a standard transistor you have to tie commons to one another; however I wasn't sure if that was the case with a MOSFET.

So tie commons, no isolation?
Don't tie commons, isolation (expect for PWM from PIC)?

[Pic_User]

I'm using a MOSFET for single direction motor speed control via PWM from a PIC. I'm thinking about isolating the power supply that is used for motor control (via the FET) from the supply used for the control electronics (PIC). What I'm unclear about is if the FETs common needs to be tied to the control electronics common. I know with a standard transistor you have to tie commons to one another; however I wasn't sure if that was the case with a MOSFET.

So tie commons, no isolation?
Don't tie commons, isolation (expect for PWM from PIC)?

Hi Ben,

The FET and it’s driver pretty much have to have a common connection. The idea is to make the gate a few volts higher than the source. So some connection has to be made to both, to complete the circuit.

Maybe you could make use of an optocoupler or optoisolater.

-Adam-

[DynamoBen]

Bummy, I guess an opto is the only option for isolation then. Thanks!