关键词: 开关电源, 脉冲宽度调制, 频率抖动, 电磁干扰, 振荡器, 频谱分析

Abstract: In order to reduce the electromagnetic interference（EMI）of switching power, the main content of this paper is the frequency jitter technology using in monolithic switching power supply, and briefly introduces the frequency jitter technology and its theory. The paper designs a relaxation oscillator which has the function of frequency jitter. Then we focused on the structure design and theory. of oscillator based on the theory of relaxation oscillator which has the function of frequency jitter. The result shows that the frequency jitter technology could effectively decrease the magnitude of all kinds of harmonic waves and we could achieve of goal of eliminating electromagnetic interference. What's more, we mainly discuss the frequency jitter model from jitter range and jitter period, and the result of spectrum analysis indicates that the harmonic waves of the jitter model which the jitter range is±7％ and the jitter period is 128T can decrease 6 dB at least and the peak value of higher harmonic decrease more obviously. It meets 6 dB engineering margin requirement, so that can eliminate the electromagnetic interference more effectively.

Key words: switching power supply, PWM, frequency jitter, EMI, oscillator, spectrum analysis