Active clamping forward switching power supply circuit

Abstract

Disclosed is an active clamping forward switching power supply circuit. On the basis of an LCL forward converter, the N<P1> dotted terminal of a transformer B is connected with a power supply, and the N<P2> dotted terminal is grounded; the N<P1> and N<P2> are in double-wire parallel winding; one end of a capacitor C1 is connected with the non-dotted terminal of the N<P1> while the other end is connected with the non-dotted terminal of the N<P2>; the dotted terminal of the N<P2> and a clamping network 400 which is connected with a C3 in series are connected with the power supply through a field effect transistor Q2, so that the conditions are realized as follows: when a Q1 is in a saturation switch-on state, N<P1> and N<P2> both can be excited, and a secondary side NS outputs energy; when the Q1 is switched off, an L1 outputs energy based on follow current, a D2 is synchronously switched off, the energy generated by exciting is clamped through the N<P2> via 400, the primary side is in an inductive state, the Q2 is switched on, the C3 and the primary side inductor are in resonance, and zero-voltage switching on of the Q1 is realized; in a light load state, the Q2 is switched on after several periods, and during the period, the end voltage of the C3 is increased in a step manner; when the Q2 is re-switched-on, the C3 and the primary side inductor are in resonance, and the zero-voltage switching on of the Q1 is realized, so that power consumption in driving the Q2 in the light load state is lowered; and consequently, the duty ratio can be greater than 0.5, demagnetized energy recycling can be realized, and the efficiency is improved in the light load state.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a single-end forward switching power supply using active clamping. Background technique [0002] At present, the switching power supply is widely used, and the industry is often called a converter. The basic forward converter in the forward switching power supply is an ideal isolated version of the Buck converter. Common topologies include single-ended forward converter, symmetrical drive Half-bridge converter, full-bridge converter, push-pull converter, symmetrical push-pull forward converter, etc. It should be mentioned that a symmetrical push-pull forward converter, such as Picture 1-1 As shown, this figure is quoted from Figure 5-14 on page 91 of "Switching Power Converter Topology and Design" written by Dr. Zhang Xingzhu, ISBN978-7-5083-9015-4, which is referred to as : Reference 1. [0003] Symmetrical push-pull forward converters are known in the patent literatur...

AI Technical Summary

Problems solved by technology

[0014] Figure 1-3 The technical solution also introduces some new problems, such as the duty cycle cannot be greater than 0.5, resulting in low power density, which cannot be achieved Figure 1-3 The zero voltage switch (Zero Voltage Switch, abbreviated as ZVS) of the switch tube Q1

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