I agree with AudioGuru on the very slow rise/fall times of the LM324 op amp. It's fine for the triangle wave portion of the circuit (at up to perhaps 5kHz), but it simply doesn't have the bandwidth to approach a true square wave output.

A fast comparator would be a good choice for replacing U2A.

As I said early on in the thread, op amps should not be used as comparators; they were not designed for such duty.

If you want a much more simple (and much better) design using a 555 timer IC, we could work something up.

An LM324 "runs out of gas" at about 7kHz. 555 timers can run at 500kHz+, or over 70x faster than an LM324. 555 timers have built-in comparators. They have up to 200mA source/sink output capability (when Vcc=16v), or about 150mA with Vcc at 12v. The best the LM324 can do is around 30mA.

 

Why not just use a dedicated PWM controller, like the ancient TPIC 2101 ($2.48 at DigiKey)? There are probably many similar controllers out there. You get controllable soft start and other goodies with it. The soft start would be an advantage for any sort of high-powered motor, particularly if you are riding something powered with it. If you want the intellectual challenge, then program a PIC to do the same thing.

Sorry, I just don't see the value in making a square peg (LM324) fit a round hole.

John

 

While a dedicated PWM controller would be a really good idea, availability might be a problem. 555 timers are available at any Radio Shack. This could be mighty handy if the trike breaks down and a quick replacement is necessary. 555 timers have been around for a long time, and they show no signs of going away.

Anyway, have a look at the attached. The 20 Ohm resistor should be attached right to the gate, as the 20k resistor. The 20k resistor is there in case of a failure of the drive electronics; in event of failure the gate will be pulled to 0v. R2 limits the current, and keeps the gate from oscillating. You'll need Q2/Q3 pairs, R2's and R3's for each MOSFET. You can substitute PN2907/PN2222 for the 2N2907/2N2222 pairs.