[sdiy] Low voltage synthesis?

Richie Burnett rburnett at richieburnett.co.uk
Sat Jan 15 14:59:49 CET 2022


Out of interest, how do you deal with distortion resulting from the load current free-wheeling through the body diodes during the switching dead-time without resorting to the use of global feedback?

This mechanism, and the variations in the frequency response of the output LC filter with different loudspeaker impedances were the two hardest problems to sort out in an "all digital Class-D amplifier" from my limited experience.

BTW, "Class-D" means different things to different people... There are RF power amplifiers used in big broadcast transmitters that use "Class-D" power amplifiers to efficiently generate many kilowatts of carrier power in the low Megahertz range. These switch directly at the RF carrier frequency followed by a filter to yield a nice clean sinusoidal output. They don't use PWM techniques to synthesise analogue waveforms like a Class-D audio amplifier or a motor drive inverter does. (There's also Class E, Class DE etc, used for radio applications like broadcast, induction heating, plasma generation, etc.)

-Richie,

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