car PDM amplifier

elektor july/august 1983 1 car PDM amplifier T This power amplifier, designed for use in a car, delivers 10 W into 4 S2 and because it uses the principles of PDM (pulse duration modulation) its efficiency is nearly 100%. Basically it is an expanded version of the regenerative PDM amplifier described in Elektor July/August 1982. The block diagram is shown in figure 1. An op-amp drives a schmitt trigger, the output of which is integrated and fed back to the inverting input of the op-amp. The system regulates itself so that the voltage is the same at both inputs of the op-amp. That can only happen if the pulse width (or pulse duration) is variable, otherwise the circuit tries to change the oscil- lating frequency as a method of regulation. The heart of the PDM system (figure 2) is made up of 1C2, N 1 ... N6, Ti and T3. To build this up into a power amplifier an out-of-phase con- trol signal is formed by N7 ... N12. This is not the ideal situation as these are not part of the feedback...