Digital power amplifier for use with fluctuating DC supplies - has capacitor holding transistor energised even when supply drops to zero

摘要

The digital power amplifier has a transistor collector/emitter path coupled in series with the inductive load across a bridge rectifier output. The transistor base is connected to a chain of three resistors, a diode and a switch. The switch connects the diode end of the chain to one direct current supply pole. A second switch, synchronised with the first one, connects part of the chain over a capacitor to the other direct current supply pole. The capacitor (11) acts as an intermediate energy store for the transistor control signals such that the transistor (1) remains on even when the fluctuating direct current supply reaches zero.