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[on:]

Hello, I've been looking at the circuit below (from Arduino Robotics) and had a question

Am I correct in thinking that when the signal mosfets are open then the P-channel mosfets will be closed?

Also to control mosfets with an arduino should I be using PWM?

[Reply #1 on:]

When S1 is switch on it pulls the P1's gate negative and turns it on.  R1 and R2 are much too large, something like 470 ohms is going to ensure fast switch-off of P1 and P2 (important to avoid shoot-through).  The gates of N1, N2, S1, S2 need 180 ohm resistors to limit the drive current from the Arduino pins.  These 4 n-channel MOSFETs must be logic level.  P1 and P2 can be 10V gate drive or logic level.

Go and complain to Arduino robotics about this poor circuit!

[Reply #2 on:]

Thanks, I think I understand. I need to do a bit more research into Mosfets.

According to the book the 10k resistors are to protect against back emf.

[Reply #3 on:]

According to the book the 10k resistors are to protect against back emf.
   

You sure you are reading that book correctly? I can't see how a resistor protects against a negative voltage.

[Reply #4 on:]

You sure you are reading that book correctly? I can't see how a resistor protects against a negative voltage.

You are right that was something else.