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try limiting Vgs to 10V, using a voltage divider. with the 10k resistor you already have, a 4.7 k resistor going from the gate to the switch should suffice. the 4.7k resistor and the gate capacitance will also serve to debounce the switch (to debounce it better add a 1 nF or 10nF cap across the 10k resistor). there are noise spikes every time you operate the switch, which the FET amplifies, and the burst of noise could be reflected by the load back into the FET. what is your load? is it a motor or other highly inductive device? if so, you might get an inductive spike that could kill the FET. yes there is a body diode in the FET, but that doesn't automatically protect the gate from being sent outside the +/-20Volt Vgs limit. when you check the D-S "junction" of a MOSFET, the gate should always be connected to the source during the test. also you said the device was heatsinked, which in the photo, it's not...
ke5frf, you appear to be trying to help, but I wonder if you know any more about FETs than I do.
ME TOO, and if I'm a genius, you are also, we both know something about FETs, maybe we're equal, It wasn't a put down!!!! and you have been respectful and supportive, Thank you, I didn't mean to offend.
Kinarfi
You may be right, but that is my goal, to drive a motor at 12 to 50 amps, do you have any suggestion? I know the FETs can handle the load as long as I don't turn them both on at the same time.I think that the biggest problem is that you are driving inductive loads.
Do you think the saturated NPN is sufficient? It's probably more so than the 5K resistor of the PMOS, correct?With an LM339 driving an NMOS, the pullup resistor turns it on. The saturating NPN output stage turns it off.
The saturating NPN will turn off the NMOS relatively quickly, compared to the turn on speed provided by a 5k resistor. The opposite is true for a PMOS - relatively fast turn on, slower turn off. Neither case is probably fast enough to drive the big MOSFETs you need for driving your motor, as Audioguru pointed out.Do you think the saturated NPN is sufficient? It's probably more so than the 5K resistor of the PMOS, correct?
The saturating NPN will turn off the NMOS relatively quickly, compared to the turn on speed provided by a 5k resistor. The opposite is true for a PMOS - relatively fast turn on, slower turn off. Neither case is probably fast enough to drive the big MOSFETs you need for driving your motor, as Audioguru pointed out.
Not specifically. Others here might have experience with specific parts. You can learn a lot by searching "mosfet drivers".Thanks,
Do you have any suggestions of how to speed things up?
Kinarfi