Hi Everybody. Attached is a schematic of a 555 controlled PWM that drives a child's 12V ride on car. This isn't exactly the answer to this thread but maybe can give some ideas. The circuit limits the speed of a 100 RPM motor on the axle to about 25 RPM to keep the car slow. The 1uF cap on pin 5 gives a slight ramp-up delay for smooth starting. Making this cap smaller will eliminate the delay. It's important to use the FR602 fast recovery rectifier across the motor. A standard 6A rectifier will get hot but can be used on the B+ feed from the battery. I used a logic level FET to drive the motor but I'm sure a standard FET would work the same. The heatsink on the FET doesn't have to be big either - it's rated at about 40 amps with a very low on resistance. Hope this helps.
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