I am using this circuit to control a motor.
Initially I was using 12V PWM generated from a 555 astable circuit. I am now trying to make the circuit controllable via an 8051 Microcontroller
The problem seems to arise when I apply a digital PWM. The motor does opperate, but at a low torque/speed. The digital PWM is of course only 5V. Upon playing around with my circuit, I noticed that if I disconnect the 12V that's powering my H-Bridge, the motor will still run just fine. Thus, I've discovered that the H-Bridge is being completely powered by my PWM voltage.
Is there a way I can amp up the voltage of my PWM? I've tried Op Amps, but that limits the current being delivered and doesn't allow my motor to start. Or is there a way to make my H-Bridge use the voltage I power it with and only control speed/direction based on my PWM signals?