Sean H. Breheny wrote:

> With a switcher,however,we could forget PWM and just supply a
> continuous variable voltage to the motor.  The current would stay the
> same and the RPM would linearly follow the voltage.  The efficiency
> would not change much over the whole RPM range.

  Your analysis regarding motor performance is correct.  Implementation
of switchmode control as you describe essentially consists of using PWM
whilst providing a series inductor and commutation diode.  The
commutation diode(s) may already be part of an H-bridge or if the FETs
may be operated "backwards", they may function as such.
--
  Cheers,
        Paul B.