In message
,
" writes
Instead of just a simple
fan motor, it's a fan that's variable speed, driven by a PWM
signal.
If by PWM you mean pulse width modulation, then it would allow for
variable speed, but a DC motor is an inductive load and is not sensibly
controlled by such a system unless there is something in the circuit to
allow the peak voltage generated by the motor at pulse cut of to be
shunted to earth.
--
Clive