P-Channel MOSFET woes - anyone know how to drive one of these things with Arduino? Answered
Hi all, I’m a hobbyist trying to build a digital controller / power monitor for a green power generator project built from an auto alternator. Hoping to use an arduino microprocessor & some simple transistor circuits to power an alternator’s field coil which at 13v can draw up to 10amps of power. From what I’ve read I think I need high side PWM switching because the alternator shares a common ground with its other electrical connections preventing me from using my usual novice NPN based bag-of-tricks. From my reading I assume some sort of PNP or P-Channel MOSFET is in order (components I sadly have no prior experience with). Alternativly I've read about using fancy high side controller ICs to drive regular NPNs but don't want to go that route.
So far everything seems to work except I clearly can’t figure this P-channel MOSFET out (IRF6540)! No matter what I try I always get a high voltage at the drain pin (full-on condition) regardless of what I do to the gate pin. I uploaded a portion of my schematic as a test circuit I think should work from my limited understanding and online tutorials: http://www.curtismasonjohnson.com/sandbox/ProblemCircuit.JPG
- The NPN driver in the drawing (2N3904) by itself works when tested with a voltmeter and toggling the input
- If I replace the p-channel mosfet with a PNP transistor it work as expected. Shouldn’t this mosfet work pretty much the same? My puny TIP127 PNP can't handle the current if I were to hook up the load.
- I’ve tried several IRF6540 components
- I’ve tried connecting the MOSFET’s ground pin via a current limiting resistor directly to ground. Also via the resistor to 13v. No voltage change on the drain pin in either case.
Clearly I’m missing something embarrassing and fundamental. I mentioned I’m a hobbiest, right - my day job is managing global marketing programs for fortune 500s and don't know anyone that knows anything about electronics! After years of electronics & robotics projects I’ve yet to be stumped to the point of needing help til now - amazing how much you can self-teach via google and such. This one has me beat – hope someone can help as I have no idea what to do next! Truely appreciated...