PFC control circuit and PFC circuit with same used

Abstract

The invention discloses a PFC control circuit which is applied to a PFC circuit with a filter capacitor. On the basis of an existing PFC control circuit, a sampling circuit and a differential processing circuit are added on the PFC circuit. The sampling circuit generates a first sampling signal positively related to a current signal of the filter capacitor, the differential processing circuit conducts differential processing on the first sampling signal to obtain a compensating signal, and the compensating signal is input into a comparison circuit of the PFC control circuit. Compared with the prior art, according to the PFC control circuit, input currents are lower in the period that the compensating signal is not zero, and the input currents are higher in the period that the compensating signal is zero, therefore, peak points of the input currents are made to move backwards, the phase difference between input voltage and the input currents is reduced, namely the current signal can follow changes of a voltage signal in a more matched mode, and the power factor of the PFC circuit is increased. The invention further discloses the PFC circuit comprising the PFC control circuit.

Description

technical field [0001] The present application relates to the technical field of power electronics, in particular to a PFC control circuit and a PFC circuit using the same. Background technique [0002] A power factor correction circuit (Power Factor Correction, PFC), including a direct current DC / DC conversion circuit and a PFC control circuit, is applied to rectification and conversion equipment from alternating current to direct current (AC / DC) (such as switching power supply, electronic rectifier, etc.). Wherein, the input end of the DC / DC conversion circuit is connected to the power grid through a rectification bridge, and the output end provides a corresponding DC voltage for the load; the PFC control circuit controls the on-off time of the main switch S1 in the DC / DC conversion circuit. Improve the power factor (Power Factor, PF) of the voltage conversion process. In the prior art, the control mode of the PFC control circuit mainly includes switch current control and...

AI Technical Summary

Problems solved by technology

[0003] In order to reduce high-frequency pollution to the power grid, filter capacitors are usually connected in parallel at the input and / or output of the rectifier bridge; figure 1 and figure 2 The waveform diagrams of the input voltage Vin and input current Iin of the PFC circuit are shown before and after the filter capacitor is increased; comparison figure 1 and figure 2 It can be seen that due to the characteristic that the capacitor current leads its voltage by 90°, after adding the filter capacitor, the input current Iin of the AC side of the PFC circuit is also ahead of the input voltage Vin, and the waveform of Iin is distorted, resulting in a decrease in the power factor of the PFC circuit and power loss Increase

Images