Full-bridge LLC resonant converter and synchronous rectification driving method thereof

Abstract

The invention relates to a full-bridge LLC resonant converter and a synchronous rectification driving method thereof. The resonant converter comprises an input end (Vin), an inversion network circuit (11), a resonant network circuit (13), a transformer (T), a rectification filter network circuit (15), an output load (R0) and an output end (Vout) and also comprises a synchronous driving device (17), wherein the synchronous driving device (17) is used for obtaining a resonant period (t<r>) through calculation according to a resonant current (i<Lr>) extracted from the resonant network circuit (13), comparing switching frequency (f<s>) with resonant frequency (f<r>) to obtain a comparison result, determining driving signals (u<g1>&u<g4> and u<g2>&u<g3>) of a primary-side switching tube and driving signals (u<gSR1> and u<gSR1>) of a secondary-side synchronous rectification tube according to the comparison result, and separately sending the driving signals to the inversion network circuit (11) and the rectification filter network circuit (15) so as to control the working of the inversion network circuit (11) and the rectification filter network circuit (15). According to the embodiment of the invention, the synchronous rectification on / off time is determined by comparing the switching frequency with the resonant frequency, the working of the full-bridge LLC resonant converter is flexibly controlled, and the full-bridge LLC resonant converter has the advantages of the simplicity, practicability, high implementability, low cost and the like.

Description

technical field [0001] The invention relates to the technical field of digital circuits, in particular to a full-bridge LLC resonant converter and a synchronous rectification driving method. Background technique [0002] In recent years, the full-bridge LLC resonant converter can realize the turn-on of the primary switch tube ZVS and the turn-off of the secondary rectifier diode ZCS in a wide load range, there is no reverse recovery problem, and the leakage inductance of the transformer can be used to replace the resonant inductance, etc. Advantages have gradually attracted widespread attention from the industry. [0003] However, when outputting low voltage and high current, the rectification loss accounts for a considerable proportion of the total loss due to the increase in the forward conduction voltage drop of the secondary diode of the full-bridge LLC resonant converter, which is not conducive to the improvement of efficiency. Therefore, in order to improve this situa...

AI Technical Summary

Problems solved by technology

However, due to the bandwidth, delay and CPU processing time of the detection device, the turn-on timing of the synchronous rectifier will lag, resulting in a lag in the turn-off time.

Turn-on hysteresis affects efficiency, turn-off hysteresis causes circulating current, reverse flow of energy

[0012] For this reason, scholars have made a lot of efforts and attempts in synchronous rectification driving of full-bridge LLC resonant converters. Neglecting the current transformer CT itself will bring a large loss, which will inevitably increase the difficulty of PCB routing on the secondary side and limit the increase in power density

At the same time, the turn-on sequence of the synchronous rectifier will also be delayed by the bandwidth, delay and CPU processing time of the detection device, so that the turn-off time will also lag

[0013] The literature "A Universal Adaptive Driving Scheme for Synchronous Rectification in LLC Resonant Converters" uses FPGA to implement adaptive control of synchronous rectification tubes in full-bridge LLC resonant converters. This method has a high utilization rate, but it requires the anti-interference design of the circuit board Very high and very expensive

[0014] In summary, the current methods of driving synchronous rectifiers have limitations in terms of cost, computational complexity, power density, and measurement accuracy.

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