A method of circuit implementations on reducing EMI in the control chip of the switching power supply

According to suppressing noise source,this paper proposes a method of circuit implementations on reducing EMI in the control chip of the switching power supply based on the spread-spectrum theory.This method adopts triangular modulating signal to modulate the oscillator frequency.Because of the switching frequency of the switching power supply with PWM(Pulse-width modulation)controlling decided by the oscillator frequency,modulating the oscillator frequency is the same as modulating the switching frequency.So using this technology,the peak energy focusing on the switching frequency and its higher harmonic is expanded,and the EMI noise is reduced.According to analysis on spectrum of the oscillator's output pulse wave,it verifies the oscillator structure this paper proposed can realize reducing EMI noise source.