How to Build a High Efficiency Class-D Audio Amplifier using MOSFETs

This Class-D audio amplifier circuit converts an analog audio signal into a high-efficiency pulse-width modulation (PWM) switching signal to drive a speaker load. The system begins by taking an audio input from a 3.5 mm audio jack. An LM358 operational amplifier is used to condition and process the input signal. Meanwhile, an NE555 timer IC operates as an oscillator to generate a continuous triangular carrier wave. The processed audio signal and the triangular carrier wave are compared to produce a PWM signal, where the duty cycle varies in proportion to the audio amplitude. Because driving power MOSFET gates directly from low-power control ICs can be inefficient and slow, an IR2110 high-and-low-side gate driver IC is employed. The IR2110 translates the PWM signals to drive two IRF640 power MOSFETs configured in a switching totem-pole arrangement. These MOSFETs rapidly switch the main power rail on and off at a high frequency, delivering amplified power pulses to the output stage. A 26uH inductor combined with output filtering capacitors smooths the high-frequency switching pulses back into an analog audio waveform that can drive a speaker via the screw terminals. Power regulation across the control circuitry is maintained using LM7812 and LM7805 voltage regulators, supported by a network of decoupling capacitors (including 102 pF, 103 pF, 104 pF, 105 pF, 224 pF, 22uF, 470uF, 220uF, and 100uF capacitors) to stabilize supply rails, alongside UF4007 diodes for switching protection and 10K trim potentiometers for manual calibration.