From: WarmSpgs@aol.com
Message-ID: <89.1292de2e.2985b417@aol.com>
Date: Sun, 27 Jan 2002 14:50:47 EST
Subject: Re: LF: Envelope shaping and class D
To: rsgb_lf_group@blacksheep.org
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In a message dated 1/27/02 2:39:19 PM Eastern Standard Time, 
sm6lkm.jbeab@swipnet.se writes:

<< Another way to control the output power is to vary the phase
 of the driving signal to one of the sides of a full bridge amp'.
 Some kind of variable delay / phase shifter would do the trick.
 
 If the two "totem poles" (a word used in the ancient world of TTL
 logic - meaning two transistors in series between +V and GND)
 in the bridge are driven in phase, there will be no voltage difference
 between the "midpoints" - zero output power. If they are driven in
 antiphase, 180 deg's, like in the Decca (Jeep!?) full output will result.
 The output power can be set to any convenient value by simply
 adjusting the phase shift between 0 and 180 deg's.
 
 No efficiency penalty and no need for a PWM modulator! >>

Interesting idea, Johan, but I believe you'll find that if you drive the 
amplifiers with a sinewave, there is an efficiency penalty; whereas, if you 
drive them with a square wave, you actually have made a PWM modulator.

73,
John