US Patent 7102332 Control apparatus for automotive generator

An A/D conversion device includes a counter for counting a clock signal fed from a clock signal generator, a D/A converter for converting a digital output of the counter into an analog value, a comparator for comparing an analog output of the D/A converter and an analog field current detection value fed from a current detecting resistor and outputting a result of comparison, an AND circuit for calculating a logical product of an output signal of the comparator and the clock signal fed from the clock signal generator and outputting the logical product to the counter, and a memory for storing the output of the counter according to a transfer signal. The output of the counter is reset when a reset signal is input thereinto.