Control method of buck PFC (power factor correction)

Abstract

The invention discloses a control method of buck PFC (power factor correction). A source of an N-MOS (N-channel metal oxide semiconductor) tube in a flyback circuit is connected to a positive output of an output end. A series loop of a first inductance and a second capacitor is used as a demagnetization loop. When the N-MOS tube in the flyback circuit is on to excite a transformer, exciting current can power a load directly. When the N-MOS tube in the flyback circuit is off, the load is powered by the flyback output circuit, and a second primary side winding provides auxiliary power. During flyback, a voltage detecting control circuit 102 indirectly detects output voltage of a PFC circuit by detecting induced voltage of the second primary side winding, PWM (pulse-width modulation) duty ratio of pulse direct current at the next cycle is changed, and stable voltage output of the PFC circuit is achieved. By the control method, circuit topology is simplified, and circuits are easy to implement and practical.

Description

technical field [0001] The invention relates to an AC-DC circuit, in particular to an AC-DC converter for step-down power factor correction. Background technique [0002] Both industrial and civil use often need to change the AC voltage of various grids into DC, or even isolated DC. With the further requirements of the national standard for the power factor of electrical appliances, at present, switching power supplies with power consumption above 75W have a power factor. Requirements, that is, the working current waveform of the circuit is basically the same as the voltage waveform. [0003] At present, a power factor correction circuit has been adopted to solve this problem. The power factor correction circuit is referred to as a PFC circuit for short, which is an abbreviation of Power Factor Correction. [0004] Note: The 75W data comes from the Chinese national standard GB17625.1-1998, named "Limits of Harmonic Current from Low-Voltage Electrical and Electronic Equipmen...

AI Technical Summary

Problems solved by technology

For those skilled in the art, the maximum duty cycle is below 0.13, and the conversion efficiency of the circuit cannot be done well at the same cost. The computer uses the real component model, and the real component model uses the ones that can be found in the market. The best device, the simulated circuit efficiency is less than 86%

The background technology of "A Step-Down PFC Circuit" filed on July 31, 2012 with the application number 201210271808.4 analyzed the shortcomings of the BUCK topology PFC circuit in detail, and also proposed a new step-down PFC circuit, which solves the problem of too small duty cycle

The composition of the circuit is more complicated, and the circuit related to the feedback will also be more complicated

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