Soft start method of LLC resonant converter

Abstract

The invention discloses a soft start method of an LLC resonant converter. The LLC resonant converter comprises a bridge-type switching circuit, a resonance circuit, a transformer, a rectifying circuit and a filtering circuit which are all connected in sequence, wherein the resonance circuit is composed of a resonant inductor and a resonant capacitor connected in series. According to the method, the initialized duty ratio of a driving signal is D0, and the initialized driving frequency is f0, wherein the value of the D0 ranges from 0 to 15 percent, the value of the f0 ranges from 1.5fr to 2.5fr, and the fr is the resonant frequency. The duty ratio of the driving signal and the driving frequency respectively increase and decrease linearly along with time or respectively increase and decrease exponentially along with time, so that while the duty ratio of the driving signal increases to 50 percent, the driving frequency decreases to the resonance frequency fr, and soft start of the LLC resonant converter is achieved. Through the method, impact current occurring in the start process of the resonant circuit can be restrained, the start time is short, a driving circuit is easy to obtain, and cost is low.

Description

technical field [0001] The invention belongs to the technical field of DC / DC converters, and more specifically relates to a soft start method for an LLC resonant converter. Background technique [0002] High efficiency, high power density, and high reliability have always been the development direction of switching power supply products. The LLC resonant converter can realize zero-voltage conduction of the input bridge switch tube and zero-current turn-off of the output rectifier diode, and can work at high frequency state, so it has the advantages of high efficiency, small size, and good electromagnetic compatibility, and has received extensive attention in recent years. [0003] Normally, the LLC resonant converter works at the resonant frequency point to obtain the best efficiency, but when starting, if it is started directly at the resonant point, since the resonant impedance is 0, and the output side filter capacitor is usually used to fully suppress the ripple However...

AI Technical Summary

Problems solved by technology

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a soft start method of the LLC resonant converter, which effectively solves the problem of high requirements on the drive circuit and long start-up time of the LLC resonant converter in the prior art. , can suppress the inrush current that occurs when the resonant circuit starts, the start-up time is short, the drive circuit is easy to implement, and the cost is low

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