PWM frequency vs dc motor speed

In this thread, raschemmel mentions that the speed of a PWM'd DC motor doubles or halves according to the PWM pin frequency.

In my 3 years on the forum, that's the first time I've ever seen that assertion, so I'm keen to hear what others have to say.

I suppose increased frequency would increase inductive reactance in the windings and reduced current/torque but not a linear relationship.

The motor speed will be proportional to the PWM frequency if and only if the pulse width remains constant so that the on/off ratio is proportional to the speed. That assumes, of course, that the pulse width remains less than the priod at the highest frequency.

The inductance won't affect the speed, it effectively acts a low pass filter and smooths out the current a bit.

Russell.

Wouldn’t That be PLM?

klubfingers:
Wouldn't That be PLM?

Err... Project Lifecycle Management ??

Russell.