Flyback switching power supply

Abstract

The invention provides a flyback switching power supply, which comprises a voltage input unit, a starting unit, a switching power supply control chip, a flyback transformer, an auxiliary power supply winding, a clamping circuit, a transformer primary control circuit, a main voltage output circuit and a standby voltage output circuit, wherein two ends of the voltage input unit are connected to an external power supply and provide power for the starting unit; and the output end of the starting unit is connected to a power end of the switching power supply control chip. The flyback switching power supply further comprises a protection unit, wherein a first end of the protection unit is connected to the output end of the starting unit and one end of the auxiliary power supply winding, a second end of the protection unit is connected to the output end of the switching power supply control chip and the reference ground, and voltage at the output end of the starting unit is reduced below starting voltage of the switching power supply control chip when the external power supply is switched off. According to the invention, a problem of secondary start-up of the flyback switching power supply is effectively solved, and the stability of the system is improved.

Description

technical field [0001] The invention relates to the field of circuits, and more specifically relates to a flyback switching power supply for preventing secondary start. Background technique [0002] The flyback switching power supply is widely used in the power supply of electronic products due to its advantages of low cost and small size. In the high-voltage and wide-range input flyback switching power supply system, a single-tube flyback switching power supply is usually selected, and the starting circuit adopts a series resistance method. [0003] Such as figure 1 Shown is a schematic diagram of a typical flyback switching power supply in the prior art. The flyback switching power supply 100 includes: a voltage input unit 120, a switching power supply control chip 121, an auxiliary power supply winding 122, a flyback transformer 123, a transformer primary A control circuit 124 , a clamping circuit 125 , a main voltage output circuit 126 , and a standby voltage output ci...

AI Technical Summary

Problems solved by technology

[0005] However, when the voltage input unit 120 is powered off, since the capacitor C0 in the voltage input unit 120 will still charge the switching power supply control chip 121 through the resistor R1, when the power supply voltage of the switching power supply control chip 121 is charged to a certain voltage, the switch The power control chip 121 will restart again, thus causing a second startup problem and affecting the stability of the system

If the post-stage load of the switching power supply is connected to a DSP, etc., the program of the DSP, etc. will be tampered with, making the circuit unable to work normally.

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