阅读说明：本技术 一种开关电源欠压保护电路 (Switching power supply under-voltage protection circuit ) 是由 刘安 徐光显 解光庆 陈波 汪张超 于 2020-04-29 设计创作，主要内容包括：本发明公开了电源欠压保护领域的一种开关电源欠压保护电路,包括比较电路、窗口设置开关电路以及保护开关电路,比较电路输入端连接基准信号与通过分压电阻获取的欠压采样信号,其输出端输出对比信号,窗口设置开关电路用于接收对比信号以控制其自身通断,保护开关电路连接电源控制器,用于接收对比信号以控制PWM控制器通断；分压电阻至少设有三个,并串联连接在输入电源与输入地之间,比较电路输入端连接在其中一组靠近输入电源且相邻的分压电阻的公共端,窗口设置开关电路输出端连接在另一组靠近输入地且相邻的分压电阻的公共端。本发明通过分压电阻阻值改变不同状态时输入电压在的欠压保护窗口电压,结构简单,易于计算,实用性高。(The invention discloses a switching power supply under-voltage protection circuit in the field of power supply under-voltage protection, which comprises a comparison circuit, a window setting switch circuit and a protection switch circuit, wherein the input end of the comparison circuit is connected with a reference signal and an under-voltage sampling signal acquired through a voltage-dividing resistor, the output end of the comparison circuit outputs a comparison signal, the window setting switch circuit is used for receiving the comparison signal to control the on-off of the window setting switch circuit, and the protection switch circuit is connected with a power supply controller and is used for receiving the comparison signal to control the on-off of a PWM (; the window setting switch circuit comprises at least three divider resistors, a comparison circuit and a window setting switch circuit, wherein the divider resistors are connected in series between an input power supply and an input ground, the input end of the comparison circuit is connected to the common end of one group of adjacent divider resistors close to the input power supply, and the output end of the window setting switch circuit is connected to the common end of the other group of adjacent divider resistors close to the input ground. The invention changes the voltage of the undervoltage protection window of the input voltage in different states through the resistance value of the divider resistor, and has simple structure, easy calculation and high practicability.)

1. A switching power supply under-voltage protection circuit comprises a comparison circuit, a window setting switch circuit and a protection switch circuit, wherein the input end of the comparison circuit is connected with a reference signal and an under-voltage sampling signal acquired through a divider resistor, the output end of the comparison circuit outputs a comparison signal, the window setting switch circuit is used for receiving the comparison signal to control the on-off of the window setting switch circuit, and the protection switch circuit is connected with a power controller and used for receiving the comparison signal to control the on-off of a PWM (pulse width modulation) controller; the window setting switch circuit is characterized in that at least three divider resistors are arranged and connected in series between an input power supply and an input ground, the input end of the comparison circuit is connected to the common end of one group of adjacent divider resistors close to the input power supply, and the output end of the window setting switch circuit is connected to the common end of the other group of adjacent divider resistors close to the input ground.

2. The undervoltage protection circuit of claim 1, wherein the comparator circuit comprises voltage dividing resistors R1, R2, R3, a voltage comparator N2, resistors R4 and R5, the non-inverting input terminal of the voltage comparator N2 is connected to the PWM controller reference terminal through a resistor R4, and the non-inverting input terminal of the voltage comparator N2 is connected to the input ground through a resistor R5; the voltage dividing resistors R1, R2 and R3 are sequentially connected in series between an input power supply and an input ground, and the inverting input end of the voltage comparator N2 is connected with the common end of the voltage dividing resistors R1 and R2.

3. The undervoltage protection circuit of claim 2, wherein the protection switch circuit comprises a switch V2, the output terminal of the switch V2 is connected to the COMP terminal of the PWM controller, and the driving terminal of the switch V2 is connected to the output terminal of the voltage comparator N2 through a resistor R6.

4. The undervoltage protection circuit of claim 2 or 3, wherein the window-setting switch circuit comprises a switch tube V3, an output end of the switch tube V3 is connected to a common end of voltage-dividing resistors R2 and R3, and a driving end of the switch tube V3 is connected to an output end of the voltage comparator N2 through a resistor R7.

Technical Field

The invention relates to the field of power supply under-voltage protection, in particular to a switching power supply under-voltage protection circuit.

Background

The switching power supply is widely applied to the fields of industry and national defense, and is widely applied to military and civil electronic systems such as aerospace, aviation, ships, weapons, railways, communication, medical electronics, industrial automation equipment and the like. When the switching power supply is started, the input voltage of the switching power supply is often rapidly increased from low voltage to rated voltage, and when the switching power supply works below the lowest working voltage, the switching power supply is easy to damage, so that undervoltage protection is an essential guarantee. The undervoltage protection circuit can greatly reduce the damage of the switching power supply in the starting stage and ensure the normal operation and personal safety of machine equipment. Because the input lead has voltage drop when the switch power supply is fully loaded, and the input lead has no voltage drop when the switch power supply is unloaded or has no output, the switch power supply can be continuously started and closed under the condition that the input voltage rises too slowly or vibrates at an undervoltage protection point, and the switch power supply is damaged. Therefore, the undervoltage protection circuit must be provided with an undervoltage protection window, when the input voltage rises, the undervoltage protection point voltage is high, and when the input voltage drops, the undervoltage protection point voltage is low, so that the switching power supply is not influenced by the input lead.

The undervoltage protection circuit has various forms, and most of the undervoltage protection circuits adopt a loop circuit at present, and an undervoltage protection window is set by using positive feedback of a voltage comparator, for example, chinese patent CN106972461A is a wide-range undervoltage protection circuit for a power supply with a hysteresis window, and the design of the hysteresis window and a flip-flop circuit of the patent is to change the potential of a non-inverting input end of the comparator by using the positive feedback of the comparator, so as to set the window. However, since the parameters of the window have a relationship with R1, R2, R3, R4, R5, and the output voltage of the comparator, and also have a relationship with the output voltage of the comparator and the power supply voltage, frequent debugging is required, and the window setting is troublesome.

In addition, a chinese patent CN201319558Y discloses a voltage dividing resistor circuit, a hysteresis control circuit and a logic control circuit, wherein the voltage dividing resistor circuit is composed of three resistors, the hysteresis control circuit is composed of a resistor and a transistor, and the logic control circuit is also composed of a resistor and a transistor, and the under-voltage locking circuit ensures that the switching power supply does not start by mistake when the input voltage rises and falls too slowly or does not adjust or even oscillate through the hysteresis control circuit. The principle of this patent, imagine better, but the logic control circuit in this patent uses the triode as the switch, and the triode is the current control device, and in addition, the dispersion of triode magnification is great, along with the slow under-voltage point that surpasses of input voltage, the triode passes through the amplification area earlier, then can get into the on-off state, and this will lead to hysteresis control circuit triode also to have the amplification interval to lead to the hysteresis window inaccurate. Therefore, the actual undervoltage point of each power supply will vary and not be suitable for accurate window setting control.

The application improves the defects in the prior art, and provides a switching power supply undervoltage protection circuit.

Disclosure of Invention

The invention aims to provide a switching power supply under-voltage protection circuit which adopts a simple circuit structure, is easy to set an under-voltage protection window and solves the problems in the prior art.

In order to achieve the purpose, the invention provides the following technical scheme:

a switching power supply under-voltage protection circuit comprises a comparison circuit, a window setting switch circuit and a protection switch circuit, wherein the input end of the comparison circuit is connected with a reference signal and an under-voltage sampling signal acquired through a divider resistor, the output end of the comparison circuit outputs a comparison signal, the window setting switch circuit is used for receiving the comparison signal to control the on-off of the window setting switch circuit, and the protection switch circuit is connected with a power controller and used for receiving the comparison signal to control the on-off of a PWM (pulse width modulation) controller; the window setting switch circuit comprises at least three divider resistors, a comparison circuit and a window setting switch circuit, wherein the divider resistors are connected in series between an input power supply and an input ground, the input end of the comparison circuit is connected to the common end of one group of adjacent divider resistors close to the input power supply, and the output end of the window setting switch circuit is connected to the common end of the other group of adjacent divider resistors close to the input ground.

As an improved scheme of the invention, the comparison circuit comprises voltage dividing resistors R1, R2, R3, a voltage comparator N2, resistors R4 and R5, wherein one path of a non-inverting input end of the voltage comparator N2 is connected with a PWM controller reference end through the resistor R4, and the other path of the non-inverting input end is connected with an input ground through the resistor R5; the voltage dividing resistors R1, R2 and R3 are sequentially connected in series between an input power supply and an input ground, and the inverting input end of the voltage comparator N2 is connected with the common end of the voltage dividing resistors R1 and R2.

As an improved scheme of the present invention, the protection switch circuit includes a switch tube V2, an output end of the switch tube V2 is connected to a COMP end of the PWM controller, and a driving end thereof is connected to an output end of a voltage comparator N2 through a resistor R6.

As an improved scheme of the present invention, the window setting switch circuit includes a switch tube V3, an output end of the switch tube V3 is connected to a common end of voltage dividing resistors R2 and R3, and a driving end thereof is connected to an output end of a voltage comparator N2 through a resistor R7.

Has the advantages that: in the invention, a comparison circuit firstly compares a reference signal voltage and an undervoltage protection signal voltage, outputs a comparison level to control the on-off of a window setting switch circuit and a protection switch circuit, when the comparison level is a low level, the window setting switch circuit and the protection switch circuit are cut off, a switch power supply normally works, when the comparison level is a high level, the protection switch circuit and the window setting switch circuit are switched on, the switch power supply has no output, partial divider resistance is short-circuited, and the undervoltage protection signal voltage is changed. The invention provides the under-voltage protection window voltage when the input voltage is in different states, the voltage value is obtained through the resistance value change of the divider resistor, the structure is simple, the calculation is easy, and the practicability is high.

Drawings

Fig. 1 is a schematic circuit diagram of the present invention.

Reference numbers in the figures: 1-a comparison circuit; 2-setting a switch circuit on the window; 3-protection of the switching circuit.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.