i set up a basic lm324 15kz uni-directional pwm motor controller. this goes to a tc4422 mosfet driver and then to 2 irfp4668 mosfets that are in parallel. there is one 10 Ohm gate resistor that both fets share .. selected at random since i have no idea why one would use a powerful driver and then reduce its power.(NOT the question at hand) and a gate diode bypassing the gate resistor to allow fast turn off.
i'm using a second voltage source for the motor/mosfets so i can use more voltage. when both the lm324 and secondary motor/fet loop get the same voltage(+-12v) it works great.
when i give the mosfet/motor loop like 45v and the lm324 12v, as i turn the pwm pot it seems to jump from 0 to 10% instantly (not so at lower voltage) but most importantly, the motor surges between the pwm corresponding to the current pot setting and 100% pwm at a very specific pot setting around
50%. this is not the case when i use 24v for the motor loop and 12v for the pwm generating part.
i dont know why, but im guessing i need a bigger gate resistor. i will try that because i think it solved the problem for me in the past with a tiny motor, but i dont know if its the right solution. heck, i may just need a
100nf cap somewhere(there are none on the power side of it besides the cap required by the driver.. v+ to gnd to help with instantaneous power to gate)
thanks alot!
end goal is 150vdc, 55mph bicycle. everything but the controller is finished.