Undervoltage protection circuit and switching power supply thereof

Abstract

The embodiment of the invention provides an under-voltage protection circuit and a switching power supply thereof, and the under-voltage protection circuit comprises a voltage stabilizing circuit which is connected in series between an input voltage and a power supply voltage end of a driving chip, and when the input voltage rises to a stabilized voltage value of the voltage stabilizing circuit, the voltage stabilizing circuit is connected with the power supply voltage end of the driving chip; the voltage stabilizing circuit conducts a circuit between the input voltage and a power supply voltage end of the driving chip, so that the input voltage provides an initial starting voltage for the driving chip; the control circuit is arranged between an auxiliary winding and a power supply voltage end of the driving chip, and when the input voltage rises to a voltage threshold value of the control circuit, the control circuit conducts a circuit between the auxiliary winding and the power supply voltage end of the driving chip, so that the auxiliary winding and the power supply voltage end of the driving chip are switched on. Therefore, the auxiliary winding provides stable working voltage for the driving chip. According to the invention, the reliability and stability of circuit operation can be guaranteed rapidly, accurately and conveniently.

Description

technical field [0001] The present application relates to the field of control circuits, in particular to an undervoltage protection circuit and a switching power supply thereof. Background technique [0002] In the AC-DC / DC-DC power supply, the flyback circuit is usually the auxiliary power supply circuit in the power system and starts to work first, and its startup and shutdown are usually controlled by its own circuit module; the stable and controllable work of the flyback circuit The status has an important influence on the reliable operation of the whole power system. [0003] In the prior art, the flyback driver IC power supply pin of the flyback circuit has only one power supply VDD pin, and this kind of driver IC does not have a dedicated high-voltage HV pin, and its initial start-up still needs to obtain energy from the input voltage for the IC to work, so , the VCC pin will pass through a resistor R with a suitable resistance H Connected to the input voltage netw...

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Problems solved by technology

[0003] In the prior art, the flyback driver IC power supply pin of the flyback circuit has only one power supply VDD pin, and this kind of driver IC does not have a dedicated high-voltage HV pin, and its initial start-up still needs to obtain energy from the input voltage for the IC to work, so , the VCC pin will pass through a resistor R with a suitable resistance H Connected to the input voltage network, but the loss of this power supply structure is extremely large, which is not suitable for the requirements of high-efficiency power converters. As an improvement, on the basis of this structure, VDD will also be connected to the auxiliary winding through diode isolation; initial startup Still by R H The branch where it is located provides energy, and when the flyback circuit works stably, the auxiliary winding provides a relatively stable VCC voltage

[0004] The program though can be controlled by R H The resistance value or add a Zener tube with R H series to control the input undervoltage recovery voltage, but after the product works stably, as long as the input voltage exists, the product can provide VCC power supply through the auxiliary winding. It may be working, and the working state is unstable at the critical shutdown point of the input voltage, and the loss increases

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