METHOD FOR GENERATING RECTANGULAR WAVE SIGNAL HAVING MAXIMUM DUTY RATIO, DUTY RATIO SETTING CIRCUIT, AND DC-DC CONVERTER

摘要

PROBLEM TO BE SOLVED: To provide a duty ratio setting circuit which can set the maximum duty ratio without occasionally fluctuating the ratio. ;SOLUTION: An error amplifier circuit 12 inputs a detected voltage VF and a reference voltage Vref and outputs the difference between the voltages VF and Vref to a comparator 15 as an error output voltage Vfb. The comparator 15 outputs a first output signal CT1 to an AND circuit 18 by comparing a triangular wave signal Vct from a triangular wave oscillating circuit 14 with the error output voltage Vfb. A pulse generator 16 generates a pulse signal PS having a prefixed pulse width for deciding the maximum duty ratio synchronously to the triangular wave signal Vct and outputs the signal PS to the AND circuit 18 through an inverter circuit 17. The AND circuit 18 inputs the first output signal CT1 and pulse signal PS and, when the duty ratio of the signal CT1 exceeds the maximum duty ratio, generates an output signal CT having the maximum duty ratio based on the pulse width of the pulse signal PS and outputs the signal CT.;COPYRIGHT: (C)2000,JPO