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介绍了一种能有效抑制开关电源芯片应用中,功率开关管电磁辐射干扰的频率抖动技术原理及其电路实现。采用调频技术,让调制信号去控制开关电源的工作频率,使其原有的频率发生偏移。这样,原先集中在狭窄频谱上的电磁辐射能量得以分布在较宽频谱范围,实现了对EM I的有效抑制。基于3μm的高压BCD工艺模型,在Cadence设计环境下,采用差分电路控制开关电源中振荡电容的充放电;用镜像电流选通电路调控电容充放电电流的大小,完成了带频率抖动振荡器的电路设计,给出了实验仿真的结果和电路拓扑结构。并使用MATLAB工具对功率开关管驱动信号中有/无频率抖动功能的输出波形进行了频谱特性的对比分析,得到了采用频率抖动技术大致可以减小EM I辐射幅值近一倍的结论。
A principle of frequency dithering that can effectively restrain the interference of the electromagnetic radiation of the power switch in the application of switching power supply chips and the circuit implementation are introduced. The use of FM technology, so that the modulation signal to control the switching power supply operating frequency, offset to its original frequency. In this way, the electromagnetic radiation energy originally concentrated on the narrow spectrum can be distributed over a wider spectrum and effective suppression of EM I is achieved. Based on the 3μm high-voltage BCD process model, the differential circuit is used to control the charging and discharging of the oscillating capacitor in the switching power supply under the Cadence design environment. The mirror current gating circuit is used to control the charging and discharging current of the capacitor, which completes the circuit with frequency jitter oscillator The design gives the experimental simulation results and circuit topology. And MATLAB tools were used to analyze the spectral characteristics of the output waveform with or without frequency dithering in the driving signal of the power switch. The conclusion that frequency dithering technique can reduce the amplitude of EM I radiation almost can be obtained.