Digital pulse width modulator for power supply control

Abstract

A control for a pulse width modulated power supply. The control (14) uses a digital pulse width modulator (48, 48') to produce set and reset signals that determine the duration of control pulses supplied to the pulse width modulated power supply (12). In one embodiment, a plurality of analog-to-digital converters (50, 51, 53) convert analog signals indicative of different parameters monitored on the pulse width modulated power supply to digital values. Differences between the digital values and corresponding predefined desired reference values are determined, combined, and the result is input to a digital comparator (72) of the digital pulse width modulator. The digital comparator produces a reset signal when the combined differences equal a count of clock pulses accumulated on a counter (76). A second digital comparator compares the count to a predefined count and produces a set signal when the two digital values are equal. The set and reset signals are applied to a flip-flop (88) to produce the control pulses, and the set signal resets the counter to initiate the next count cycle. In a silicon CMOS embodiment having a limited switching frequency capability, the required resolution is achieved by using a vernier (94) to incrementally delay the reset signal based upon the least significant bits of the difference signal.