Class-D Amplifier You Can Hear

Power electronics

A comparator turns the audio and a triangle carrier into a two-level PWM wave, a half-bridge switches it, and a Butterworth $LC$ filter with $f_c=1/(2\pi\sqrt{LC})$ recovers the audio. The filter gain at the audio and carrier frequencies is computed live, and Listen plays the actual signal, so the carrier whine is audible when the filter fails to remove it.

live circuit · mode=full audible carrier whine

Drag a value tag to change that part. Click a wire to clip a probe on.

causal signal trace paused

Compare audio with the carrier The comparator outputs high while the audio exceeds the triangle carrier, so the duty cycle follows the audio.

t_{\mathrm{stage}}=\htmlData{math-slot=value}{\mathtt{0.00}}\,\mathrm{s}

step 1 / 4 Compare audio with the carrier

Notebook · 11 parts · 12 wires · natural-sampling PWM + 2nd-order LC filter

recommended lab 17 of 18

Place an LC cutoff between the audio band and the PWM carrier.

Builds on: Closed-Loop Buck Converter

predict · then test

You double the filter capacitance $C$ . What happens to the carrier residual at the speaker?

Commit before the explanation appears. This is a prediction, not a quiz score.

governing model

|H(f)| = \dfrac{1}{\sqrt{(1 - r^2)^2 + 2r^2}},\; r = \dfrac{f}{f_c} \;\cdot\; f_c = \dfrac{1}{2\pi\sqrt{LC}}

structural inventory

audio + triangle carrier
PWM comparator
half-bridge switch
$LC$ filter + speaker

boundaries

audio $100\ \mathrm{Hz}$ – $2\ \mathrm{kHz}$
carrier $4$ – $20\ \mathrm{kHz}$ (slowed into earshot)
$f_c: 0.5$ – $50\ \mathrm{kHz}$

diagnosis challenge Fault identity withheld: infer it from the changed outputs first.

Notebook · 11 parts · 12 wires · natural-sampling PWM + 2nd-order LC filter

You double the filter capacitance CCC. What happens to the carrier residual at the speaker?

You double the filter capacitance $C$ . What happens to the carrier residual at the speaker?