Quasi-resonant control method, quasi-resonant system and quasi-resonant device for switching power supplies

Abstract

The invention provides a quasi-resonant device for switching power supplies. The quasi-resonant device comprises a sampling module used for sampling a transformer secondary degaussing time Tds according to a feedback signal Vsen of voltage output of a switching power supply after a switching tube of a quasi-resonant module in the switching power supply is closed, a valley bottom sampling module used for sampling a resonant valley bottom signal of the quasi-resonant module according to the Vsen, a fixed-proportion time generation module connected with the sampling module and used for generating time T at a preset proportion through Tds processing, and a logic processing module respectively connected with the valley bottom sampling module and fixed-proportion time generation module and used for acquiring the first valley bottom signal after the time T and using the first valley bottom signal as a switching signal to open the switching tube. According to the device, the efficiency can be increased, electromagnetic interference can be improved, the cost can be reduced, and switching loss and noise can be avoided. The invention further provides a quasi-resonant system for switching power supplies and a quasi-resonant control method for switching power supplies.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a quasi-resonance device, a quasi-resonance system and a quasi-resonance control method for a switching power supply. Background technique [0002] Today, with the popularity of portable electronic devices, switching power supplies have become the main power supply solutions for these electronic devices. At present, in low-power AC / DC switching power supplies, the primary control is often used to replace the high-cost secondary control (including TL431 and optocoupler). For example, a typical primary control switching power adapter circuit such as figure 1 As shown, among them, the alternating current is converted into high-voltage direct current through the π-type filter circuit composed of capacitors C2, C3 and inductor L1 after full-wave rectification (i.e., diodes D1, D2, D4, and D5 form a rectifier bridge) for the control chip IC1 Provide the start-up volt...

AI Technical Summary

Problems solved by technology

[0010] To sum up, the disadvantages of the existing technology are: the traditional PWM control method cannot realize ZVS or LVS, so the switching loss will be relatively large, and the EMI effect is not good. Although the QR mode control can realize ZVS or LVS, when When the output load is reduced or the input voltage is increased, the conduction time Ton of the MOS transistor will be reduced and the switching frequency will increase, which will lead to serious switching losses and intermittent switching and noise problems

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