低占空比电流模式BUCK变换器反馈补偿

分析电流模式的变换器在高输入电压和低输出电压(即低占空比)和轻载条件下的工作特点,论述电流模式的变换器由于电流检测时间延时和前沿消隐时间所决定的系统最小导通时间问题。在一定频率下,最小导通时间决定允许的最大临界输入电压。轻载时,实际输入电压接近于最大临界输入电压时,系统由电流模式进入电压模式,反馈环节的相位裕量不足,产生振荡;实际输入电压高于最大临界输入电压时,系统强迫进入跳脉冲模式的工作方式,从而产生振荡和大的输出纹波。针对轻载时进入电压模式的特点,提出输出使用电解电容的解决方案,并给出相应的测量波形和结果,同时解释了使用电解电容增加相位裕量的原因。

Feedback compensation design for current mode buck converter at low duty cycle

The work characteristics of the current mode converter under the conditions of high input voltage and low output voltage,that is,low duty cycle and light output load are introduced.The minimum On time of PWM converter decided by the duration of leading edge blanking time and current detection time delay is discussed.At a certain frequency,the minimum On time decides the maximum critical input voltage.At light output load,when practical input voltage is close to the maximum critical input voltage,the system goes into the voltage mode from the current mode and oscillates due to insufficient phase margin at feedback link.When practical input voltage exceeds the maximum critical input voltage,the system is forced into skipping pulsed mode,thus the oscillation and big output ripple appear.According to the characteristics of entering voltage mode at light output load,the solution with using output electrolytic capacitance is proposed,the corresponding results and waveforms are given,and the reasons why the phase margin increases by using output electrolytic capacitance is also explained.