Current-limiting method and current-limiting circuit of LLC resonant converter

Abstract

The invention discloses a current-limiting method and a current-limiting circuit of an LLC resonant converter. According to the current-limiting method, the controlled quantity of switching frequency output in a PI adjusting step is detected so as to judge whether a frequency modulation step is added for current-limiting operation. The provided current-limiting circuit comprises a comparing trigger circuit and a current injection circuit. The current-limiting circuit can correspondingly adjust the switching frequency of the LLC resonant converter under the working condition of abruptly adding resistance-capacitance load, thus limiting the current shock of a resonant circuit, protecting the power element of the resonant circuit and solving the false triggering problem of overcurrent protection. According to the current-limiting method and the current-limiting circuit for frequency modulation, the structure is simple, the cost is low, the response speed of frequency modulation is high under the condition of abruptly adding resistance-capacitance load, and the current of the resonant circuit can be limited in an expected current set value.

Description

technical field [0001] The invention belongs to the technical field of DC / DC converters, and more specifically relates to a current limiting circuit of 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 turn-on of the input bridge switch tube and zero-current turn-off of the output rectifier diode, and can work in a high-frequency state Therefore, it has the advantages of high efficiency, small size, and good electromagnetic compatibility, and has received extensive attention in recent years. [0003] Usually, the LLC resonant converter has the problem of resonant current impact during the start-up process. The commonly used LLC main circuit control method uses a variable frequency start-up method to limit the start-up resonant current, that is, it drops from a specific high switchin...

AI Technical Summary

Problems solved by technology

[0004] Aiming at the above defects or improvement needs of the prior art, the present invention provides a frequency modulation and current limiting method and circuit of an LLC resonant converter, which effectively solves the problem of the frequency modulation speed of the LLC resonant converter in the prior art when a resistive-capacitive load is suddenly added. Slow, the resonant current impact is too large

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