Switching control circuit and switching power supply device

摘要

A voltage detecting circuit of the present invention is formed of a differential amplifier and an H-detection filter circuit, and the differential amplifier amplifies a potential difference between an input voltage and a primary-side voltage to obtain a differential amplified voltage. The H-detection filter circuit extracts low frequency components of the differential amplified voltage to output a detection voltage. A DC/DC control IC outputs, to a control electrode of a transistor, a PWM signal obtained by shaping a pulse width based on the detection voltage, to thereby control an on/off operation of the transistor.

主权项

1. A switching control circuit for a predetermined switching power supply device,
said predetermined switching power supply device including:
a transformer having a primary winding part and a secondary winding part; anda switching element that converts a direct current input voltage into an alternating current voltage by an on/off operation to supply the alternating current voltage to said primary winding part, said switching control circuit comprising:
a differential amplifier that differentially amplifies voltages at both ends of said primary winding part to obtain an amplified voltage;a filter circuit that extracts low frequency components of said amplified voltage to obtain a detection voltage;an operation control part that performs a control process of controlling the on/off operation of said switching element based on said detection voltage; anda reference signal generating circuit that generates a reference signal changed over time from a first voltage to a second voltage higher than said first voltage, wherein said operation control part includes a comparison circuit that compares a comparison reference signal and said detection voltage to obtain a pulse width modulation (PWM) signal and applies the PWM signal to a control electrode of said switching element to perform said control process, the comparison reference signal including said reference signal and a phase shift reference signal having a shifted phase of said reference signal.