Class D amplifier for audio reproduction - is linked to preamplifier by optical coupler and has rectified mains power supply

摘要

The object of the circuit modification is to simplify the construction of the power amplifier. To achieve this the preamplifier (1), producing a pulse modulated output corresponding to the input signal (E), is coupled to the power amplifier driver (3) through an opto-coupler (2). Using light transmission the input signal to the driver amplifier is galvanically isolated from the preamplifier. This isolation permits the use of a simple power supply comprising a rectifier (4) and smoothing capacitor (C2) directly connected to the ac mains without a transformer. The rectifier can produce an effective voltage of 100V on the loudspeaker circuit from a 220V mains supply. With the employment of complementary FETs (T1,T2) the arrangement enables high power output. It is helpful if VMOS FETs are employed.