I found an aplication (ST Design Tip - DT0001), that suggests a way of controlling motor speed, using a PWM signal on the DIR input. Works fine for speed. Note: we are not using a micro as shown in the DT90001. We are using our design. And using PWM to drive DIR, for speed control. Our PWM frequency is between 1K-5K.
We were expecting to get the correct speed control, while maintaining the same torque we have for FWD/REV directions. But we get a drastic loss of torque.
Let me say too, that in the forward direction, we can meet our torque requirements. In the reverse direction we can meet our torque requirements. But with PWM signal connected, to the DIR, we can't meet our torque requirements.
I'm thinking this is because we are reversing the current through the motor and what we wind up with is correct speed, but this reversing of current, gives us an average current, and therefore an average torque, which is quite less than what we need. Does this explain the loss of torque?
If this is true, is there anything that can be done, to regain the torque lost due to using the DIR with PWM signal?
If not true, what could be causing the loss of torque, using PWM signal on DIR pin?
Thanks,
Mike
