> Perhaps you are right, but the book from which I learned the most about
> class C and D amps (Radio Frequency Electronics by Jon Hagen, not a
> really great book, although I don't know it to be flat out wrong
> anywhere) describes class C amps as saturated switches and class D amps
> as totem-pole saturated switches (two transistors, like a digital
inverter).

I always thought that class C meant using pulses to excite a tank circuit to
resonance, and class D is some form of pulse modulation with the output
signal derived from the pulses average.  Class D usually implies filtering
to get rid of the high frequency pulses, but is intended to produce some
arbitrary waveform, not to resonate a tank circuit.

The college dorm AM transmitter I mentioned in an earlier post had a class C
push-pull output.  The switching elements alternately pulled down on
opposite ends of a center tapped primary.  The modulation signal acted like
the power supply at the center tap.  Both halves of the primary and the
secondary were carefully adjusted for resonance at the desired frequency.
Each switch was only on a small fraction of the cycle.  About 10% if I
remember right, for a total of 20% "on".  The tank circuit was free wheeling
the remaining 80% of the time.  A push-pull driver like this has the
advantage of generating far less power in the even harmonics.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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