> Ahh! So the PWM frequency should be high enough so that the current
> through the motor windings is nearly constant (DC + ripple).  You
> don't want to stop the current at all, just give it a place to go
> without loosing too much energy in diode losses.  That makes much more
> sense to me than my previous ramblings.

Yes (jumping in to the tail end of the discussion). It's difficult to
think through all the theory required here, and very easy to come to
a wrong conclusion.

So just to reinforce what you said...during the "off" phase you want
the armature current to carry on flowing as if nothing has happened.
The flyback diode provides a path for this current to flow in a loop.
Ideally the diode would have no voltage drop and the armature
would have zero resistance. As you know, when current is flowing
in a cuircuit and there is zero resistance there is no power
dissipated. Kind of like the current in the coil of a superconducting
magnet, for a short period of time.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz

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