Active clamp circuit in switching power supply

Abstract

The invention provides an active clamping circuit in a switching power supply. The active clamping circuit comprises an input rectifier bridge, an input filter capacitor, a switch tube, a free wheeling diode, a current sampling resistor, an upper voltage sampling resistor, a lower voltage sampling resistor, an active clamping module, a chip, an isolation transformer, an output rectifier diode and an output filter capacitor. The active clamping circuit has the following advantages: on the basis of the active clamping circuit structure, the system efficiency is improved substantially; the withstanding voltage of the MOS transistor is reduced; the peak voltage generated by the energy of a parasitic inductor is absorbed by the active clamping and thus the stable output of the circuit is realized; and because the auxiliary winding is removed, the chip area is reduced, so that the cost is lowered.

Description

technical field [0001] The invention relates to an active clamping circuit, in particular to an active clamping circuit in a switching power supply. Background technique [0002] figure 1 It is a passive clamping circuit in a traditional switching power supply. [0003] Such as figure 1 As shown, the passive clamping circuit mainly includes a rectifier bridge 201, an auxiliary winding 204, a resistor R1, a resistor R2, a resistor R3, a resistor R5, a diode 205, an output rectifier diode 212, an input filter capacitor 202, a capacitor 206, a capacitor 213, a switch The transistor 203 , the isolation transformer 211 , the chip 210 and the passive clamping module 209 , the passive clamping module 209 further includes a resistor R4 , a capacitor 208 and a diode 207 . [0004] This control method has a relatively simple circuit structure and low cost, so it is widely used in switching power supplies, but its disadvantages are also very obvious. The energy of the parasitic indu...

AI Technical Summary

Problems solved by technology

[0004] This control method has a relatively simple circuit structure and low cost, so it is widely used in switching power supplies, but its disadvantages are also very obvious. The energy of the parasitic inductance is prone to generate peak voltages, making the output unstable; and the passive clamp circuit itself consumes The energy is large, resulting in low power efficiency; and it needs to add an auxiliary winding in addition to the main winding and output winding, occupying the chip area, which not only reduces the system efficiency but also increases the cost

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