Motor Driver Assistance

[cl10Greg]

Hello everyone,

I am designing a simple LSD motor drive and I am having unexpected results. I attached a drawing of the schematic. When I turn on the arduino, the LED turns on and I am not able to modify it with my pot. I am basically taking a reading of pot on an analog pin and modifying the pwm out of pin 5 on an arduino duevmilo (sp?).

So some more details. I am trying to use a PMOS with a PWM to raise the logic level to a 12V PWM signal so I have a low on resistance for the NMOS. The PMOS is pulled up with a 10K resistor on the gate. The PMOS has a 10K resistor to ground that is tied to the gate of the NMOS. This ties the NMOS to ground with a pull down resistor. Do when the PMOS is turned on the 12V signal is PWM'd to the NMOS because it is the path of least resistance. This should result in a PWM control of the motor but like I said, the signal is not working. I am running out the door currently so I haven't had a chance to scope the signal but I will check the signal and voltages by tomorrow and look back at this. Thanks for any help you can give me!

 

[strantor]

I think with that 10K pullup resistor on the gate of your PMOS it's going to be constantly on. Also if it ever did turn off, with that 10K pulldown resistor on the gate of you NMOS, it might not turn off, as the gate capacitance has to bleed off through it. not too sure about that though.

 

[ronv]

While the input to the board may be 12 volts the micro runs on 5 volts. So it can't turn off the PFET.
Why not drive a logic level NFET directly?