Abstract: A voltage regulator (11) provides a pulse width modulated voltage regulator output (40) to a drive circuit (37) to provide field coil excitation for a voltage generator (15-17) providing a charging signal for a battery (14). The voltage regulator output determines on/off states of an FET power switching device (28) coupled in series with a field coil (17) across a maximum power source voltage potential V.sub.BAT corresponding to battery voltage. The drive circuit includes a charge pump (26, 35, 36) with a low capacitance capacitor (26) coupled and decoupled across a source of voltage potential at a rate determined by a high frequency signal (41), provided by the regulator, having a frequency substantially in excess of the frequency of the voltage regulator output. The drive circuit includes a pair of switches (21, 35) which alternately couple one terminal of the capacitor to either battery voltage or ground potential in accordance with the voltage regulator output.

Abstract: A fixed frequency, variable duty cycle voltage regulator having a precision reference voltage source is provided. The reference voltage source has a variable temperature coefficient. The output of the precision reference voltage source is combined by a digitally switched attenuator to provide a staircase waveform to a comparator. This variable staircase waveform is compared against the output of an alternator. The comparator sets the output of a flip-flop to an off state when the staircase waveform goes below the output from the alternator. This removes the drive from a current switch which switches off the current flow through the field coil of the alternator.

Abstract: A fixed frequency, variable duty cycle voltage regulator having a precision reference voltage source is provided. The reference voltage source is a bandgap reference circuit including a plurality of series-connected diodes and having a variable temperature coefficient. The output of the precision reference voltage source is combined by a digitally switched attenuator to provide a staircase waveform to a comparator. This variable staircase waveform is compared against the output of an alternator. The comparator sets the output of a flip-flop to an off state when the staircase waveform goes below the output from the alternator. This removes the drive from a current switch which switches off the current flow through the field coil of the alternator. Current limiting protection is provided to the regulator output.