Hi Andrew
Didn’t say it did. But I did effectively say this.
I do agree with this
Especially if the motor in question is driven by the now popular “H” bridge.
I have noticed that with most H bridge circuits (I can’t say all as I just non’t know) that switch diagonally opposite Mosfets to apply the voltage you almost always NEVER get a flywheel diode (or in this case 2 diodes in series) Directly across the motor. One always gets to the motor via the motor supply. This has the effect of clamping the reverse voltage to the supply value and effectively applies a reverse voltage across the motor. This can be easily observed using an oscilloscope (with the mains ground disconnected so no accidental shorts) directly across the motor. Starting from standstill apply the PWM. you will see the positive ppm voltage but also a negative voltage the same amplitude and width as the wanted pulse. Net result, zero volts and no movement. This could continue until something like 20% duty cycle or maybe more. When the width of the PWM exceeds the negative pulse the motor starts to move. At this point the width of the negative pulse rapidly decreases and the motor will race up to about 20% speed. It can then be backed off a bit but never to a slow crawl.
This is digressing a bit and is not really the subject under discussion. I have oscilloscope pictures demonstrating this and can post them along with a description if enough interest. I have found that where this slow start is required using a relay to change direction produces better and predictable results. There are lots of scenarios where a slow start from standstill is required.
Cheers Bob
