Research And Realization Of Critical Conduction Mode Power Factor Correction Switching Converters

The input current of the critical conduction mode (CRM) power factor correction (PFC) Boost converter is deduced. The conclusion is obtained that the unit input power factor can be guaranteed if the conduction time in a half AC cycle is made constant. Steady-state analysis of the CRM PFC Boost converter is detailed. The relationship between the switch frequency and the input voltage and the input power are worked out, respectively. The stresses on each device and the output voltage ripple are analyzed. The design methods of CRM PFC Boost converters are summarized. Experiment and simulation results are in positive with the theoretical ones. The CRM PFC based flyback converter is also investigated. The input current is deduced. The relationship between the input power factor and the ratio of the reflected voltage and the maximum value of input peak voltage is obtained. The theoretical results are verified by simulation and experiments.A prototype of 120W/400V CRM PFC Boost converter is implanted with an input voltage range of AC175~265V. A high power factor of 0.997 is achieved.A prototype of 30W/15V CRM PFC flyback converter is implanted with an input voltage range of AC90~270V, the power factor of which reaches 0.956.