电流模式变换器输出LC滤波器对反馈环影响

The Output LC Filter Effect on Feedback Loop in Current Mode Converter

介绍了电流模式的变换器在实际应用中输出端加LC滤波器的原因,推导了输出无LC滤波和输出加LC滤波的负载传输特性,论述了输出加LC滤波对系统环路传输特性的影响。同时,基于实际的电流模式Buck变换器,测试了两种状态下的增益裕量和相位裕量,系统地探讨了输出端LC滤波器引入双极点的过程。输出端LC滤波器会引起环路的相位裕量不足,导致系统产生次谐波的振荡。给出通过减小系统带宽,使LC的双极点远离穿越频率,从而增加系统稳定性的方案。进一步探讨了由于温度降低,误差放大器的增益增加促使系统带宽的增加是系统更容易产生振荡的原因。

The reason of adding output LC filter in current mode converter is introduced.The transfer feature of output load without and with output LC filter is deduced.The effect on the system feedback loop with output LC filter is discussed.The phase and gain margin at two different operation states are tested based on the practical current mode Buck converter.The double poles are introduced into the feedback loop due to the output LC filter,which causes not enough phase margin in the system and sub harmonic oscillation shown in the relevant waveforms.The solution of decreasing the bandwidth of the system to make the double poles of LC filter far from the cross frequency,which increase the stability of the system is given.The reason of most likely oscillation at low temperature is that the increase in the gain of the amplifier at low temperature will expand the bandwidth of the system.