O/T Driving a Mosfet

JohnKennedy · Joined: 12 May 2004 Posts: 38

Hi

I have a new application where I need to drive a P channel Power Mosfet. Can this be done succesfully direct from a PIC or is it best to have a driver circuit?

I won't be switching on anf off rapidly it will just be a straight forward on and then an off some time later (likely to 10's of minutes or hours rather than seconds).

Thought I would ask if any one has any experience of this, any advice welcome.

TIA

JFK

dyeatman · Joined: 06 Sep 2003 Posts: 1924 Location: Norman, OK

Depending on the MOSFET drive requirements you can drive it directly from the PIC however, even if you could, I would recommend a driver in between to protect the PIC (or put the PIC in a socket so it can easily be replaced!). Depending on your current requirements you may be able to use something like the ULN2803 or ULN2804. I use these a lot to drive relays and solenoids.

MikeW · Joined: 15 Sep 2003 Posts: 184 Location: Warrington UK

there shouldnt be a problem, but it depends on how the circuit is of course.

If the PIC is running off 5 volts, and so is the mosfet, then a simple resistor from +5 to gate, 100K, 'cos the PIC will power up as an input.

put a 1K-10K in series with the gate if you are not switching in the Khz.

make sure the vgs is suitable for switching at 5 volts

I have used mosfets driven straight from PIC loads of time, without any problems.

fundamentally, there is not a problem

Hope this helps.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

The first question is what voltages are you working with? Presumably the FET is in the positive supply to the load. Is the positive supply the same as the VCC of the PIC? If the voltage is higher you will need a driver, probably a small N-FET or NPN bipolar. What is the threashold voltage of the P-FET gate?
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