A Control System of Synchronous Rectifier in llc Converter

Abstract

A control system for a synchronous rectifier tube of an LLC converter, comprising a voltage sampling circuit, a high-pass filter circuit, a PI compensation and effective value detection circuit, and a control system with a microcontroller MCU as the core. Utilizing the principle that the unavoidable parasitic inductance and parasitic capacitance in the circuit cause the circuit waveform to oscillate, when the LLC converter operates at high frequency, the drain-source voltage of the synchronous rectifier V DS(SR) Through the sampling circuit, the change signal of the drain-source voltage during the off period is sent to the high-pass filter circuit and the PI compensation and effective value detection circuit to obtain the effective value amplification signal of the drain-source voltage oscillation signal caused by parasitic parameters, and through the microcontroller The MCU-based control circuit compares the relationship between the current value and the last collected value, thereby changing the conduction time of the synchronous rectifier in the next cycle, and finally enabling the synchronous rectifier to be turned off at the best turn-off point to achieve synchronous rectification Optimum efficiency work of the tube.

Description

technical field [0001] The invention relates to a control method of a synchronous rectifier tube of an LLC converter (resonant converter), in particular to a control system of a synchronous rectifier tube of an LLC resonant converter. Background technique [0002] With the continuous development of power technology, the LLC resonant converter has gradually become a recognized power topology. It has the inherent ZVS turn-on of the primary power tube and the ZCS turn-off advantage of the synchronous rectifier, which enables it to achieve higher efficiency than other traditional topologies. However, when the LLC resonant converter works at low voltage and high current output, due to the large on-resistance of the rectifier diode, its loss is greatly increased, thereby reducing the working efficiency. The proposal of synchronous rectification technology, by using the conduction of the power tube instead of the diode, because the conduction resistance of the power tube is smalle...

AI Technical Summary

Problems solved by technology

[0003] (1) The method of collecting the synchronous rectification current is the most accurate control method, which can accurately judge the opening and closing of the synchronous rectification tube, but the loss of the sampling resistor used for collecting the current is too large, and it is gradually not used;

[0004] (2) By collecting the drain-source voltage, the turn-off point of the synchronous rectifier will always switch back and forth between the forward conduction and reverse conduction states of the body diode, and the conduction of the body diode will bring additional conduction loss;

[0005] (3) The digital synchronous rectification technology of the microcontroller MCU can realize the adaptive conduction of the synchronous rectifier tube, but at high frequencies, due to the influence of parasitic parameters in the system, the difficulty of acquisition will increase, resulting in false opening and the occurrence of false shutdown

These parasitic parameters will cause the turn-on and turn-off of the synchronous rectifier to generate high-frequency oscillation signals, which will cause deviations in the detection of the sampling circuit or the microcontroller, thereby causing wrong control signals to be generated for the drive of the synchronous rectifier, affecting The working state of the converter reduces the working efficiency of the converter

Images