Posted on May 9, 2012

In this circuit, a 2-MHz clock is divided by eight in Ul, providing a stable 250-kHz carrier. Ql and Q2 buffer the clock and provide a low-impedance drive for op amp U4, which is a high-gain amplifier and integrator. U4 accepts audio inputs and converts the 250-kHz square wave into a triangular wave. The summed audio and triangular-wave signal is applied to the input of comparator U7, where it is compared with a de reference to produce a pulse-width modulated signal at the output of U7.

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The output devices switch between the +50 V and -50 V rails in a complementary fashion, driving the output filter that is a sixth-order Butterworth low-pass type, which demodulates the audio and attenuates the carrier and higli frequency components. Feedback is provided R1; amplifier gain is R1R,. Specifications: 200 W continuous power into a 4-flload; 20 to 20kHz frequency response +0.5, -1.0 dB at 200 W; THD, !MD (";; 0.5% at 200 W; 1.5-V rms input for rated output; 69 dB SIN ratio, A weighting; 6.6-V ms slew rate.

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