"Franc Zabkar"
** Why on earth does the PWM circuit run at 300Hz ??
This is far too low a frequency for good efficiency.
There will be large current pulses in the motor at almost any setting while
the brushes and motor windings will suffer from additional heating with no
benefit. Simply raise the frequency to say 3kHz and put a heatsink on that
Schottky diode and it will be far better job all round.
Using a higher frequency makes the current flowing in the motor become
nearer to steady DC at all duty cycles of the PWM. The Schottky diode will
then pass more average current (and less peak) during the "off " times in
the PWM so will dissipate more heat.
A correctly operating PWM drive provides the same kind of speed control over
a permanent magnet motor as variable DC voltage control does - but with
the high efficiency essential for battery powered vehicles and the like.
I note the circuit provides no " braking " function and this could be an
issue for some vehicles. Braking means placing a short on the motor to bring
it to a rapid stop.
..... Phil