To miniaturize an electronic apparatus, by a method wherein a pulse- width modulation circuit is constituted of a logic circuit to which a clock signal and a comparator output are inputted and which outputs a logical product result as a pulse-width modulation signal.
A control voltage 101 (Vf) and a reference voltage 102 (Vr) are inputted to an error amplifier 110 so as to be amplified. A clock signal 103 (CLK) is inputted to a sawtooth-wave generation circuit 120, and sawtooth waves 125 are generated. Then, the output 115 of the error amplifier 110 is inputted to the noninverting input terminal of a comparator 130, the output 125 of the sawtooth-wave generation circuit 120 is inputted to the inverting input terminal of the comparator 130, and a logic signal 135 is outputted to a NAND circuit 140. The NAND circuit 140 can obtain the output 145 of a pulse signal which is pulse-width modulated by the clock signal 103, by the logic output 135 of the comparator 130 and by an output inhibit signal 104.
INABA MASAMITSU
SUKEGAWA KEIICHI
HITACHI HARAMACHI SEMI CONDUCT