An Input Undervoltage Protection Circuit Based on TL431

Abstract

This utility model belongs to the field of power supply technology and discloses an input undervoltage protection circuit based on TL431, including port L and port N. Port N is connected to the positive terminal of diode D1 and pin 3 of rectifier bridge BRG1. Port L is connected to the positive terminal of diode D2 and pin 2 of rectifier bridge BRG1. Pin 1 of rectifier bridge BRG1 is connected to one end of capacitor C1 and the input terminal of resistor C1. The other end of capacitor C1 is connected to GND. Pin 4 of rectifier bridge BRG1 is connected to port GND. The beneficial effects of this utility model are: wide-range input undervoltage protection can be achieved by using TL431, and input undervoltage hysteresis function is provided after undervoltage protection.

Description

Technical Field

[0001] This utility model relates to the field of power supply technology, and in particular to an input undervoltage protection circuit based on TL431. Background Technology

[0002] As power supply equipment for electronic products, switching power supplies, in addition to meeting the basic performance requirements of the products, must also have their own protection measures, such as undervoltage, overcurrent, and overtemperature protection. When the input voltage of a switching power supply is too low, the power conversion efficiency decreases, leading to increased heat generation, reduced reliability, and even damage to the power supply. Therefore, it is necessary to introduce input voltage undervoltage protection into switching power supplies to ensure timely protection when the input voltage is too low.

[0003] Therefore, it is necessary to provide an input undervoltage protection circuit based on TL431 that has low cost, small PCB layout space, and good anti-interference capability. Utility Model Content

[0004] This utility model discloses an input undervoltage protection circuit based on TL431, which can effectively solve the technical problems involved in the background art.

[0005] To achieve the above objectives, the technical solution of this utility model is as follows:

[0006] An input undervoltage protection circuit based on TL431 includes port L and port N. Port N is connected to the positive terminal of diode D1 and pin 3 of rectifier bridge BRG1. Port L is connected to the positive terminal of diode D2 and pin 2 of rectifier bridge BRG1. Pin 1 of rectifier bridge BRG1 is connected to one end of capacitor C1 and the input terminal of resistor C1. The other end of capacitor C1 is connected to GND. Pin 4 of rectifier bridge BRG1 is connected to port GND.

[0007] The negative terminal of diode D1 is connected to the negative terminal of diode D2, one end of capacitor C18, and the input terminal of resistor one. The output terminal of resistor one is connected to one end of resistor R20, one end of resistor R51, one end of capacitor C2, and the reference terminal of TL431U5. The other end of capacitor C18 is connected to the other end of resistor R20, the other end of capacitor C2, the anode of TL431U5, one end of capacitor C21, and port GND. The cathode of TL431U5 is connected to the output terminal of resistor two, the other end of capacitor C21, and the cathode of Zener diode Z1.

[0008] The anode of the Zener diode Z1 is connected to one end of resistor R43, one end of capacitor C20, and pin 1 of the switching transistor Q9. The other end of resistor R43 is connected to the other end of capacitor C20, pin 3 of the switching transistor Q9, and port GND. Pin 2 of the switching transistor Q9 is connected to the negative terminals of diode D7 and diode D3. The positive terminal of diode D3 is connected to the other end of resistor R51. The positive terminal of diode D7 is connected to port FB.

[0009] As a preferred improvement of this utility model: the first resistor includes resistor R57, resistor R52, resistor R54 and resistor R53, one end of resistor R57 is the input terminal of the first resistor, the other end of resistor R57 is connected to one end of resistor R52, the other end of resistor R52 is connected to one end of resistor R54, the other end of resistor R54 is connected to one end of resistor R53, and the other end of resistor R53 is the output terminal of the first resistor.

[0010] As a preferred improvement of this utility model: the second resistor includes resistors R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, and R33. One end of resistor R30, one end of resistor R41, and one end of resistor R42 are connected and serve as the input terminal of the second resistor. The other end of resistor R30 is connected to the other end of resistor R41, the other end of resistor R42, one end of resistor R26, and resistor R33. One end of resistor R7 and one end of resistor R38 are connected. The other end of resistor R26 is connected to the other end of resistor R37, the other end of resistor R38, one end of resistor R25, one end of resistor R34 and one end of resistor R36. The other end of resistor R25 is connected to the other end of resistor R34, the other end of resistor R36, one end of resistor R22, one end of resistor R32 and one end of resistor R33. The other ends of resistor R22, R32 and R33 are connected and serve as the output terminal of resistor component two.

[0011] As a preferred improvement of this utility model: the port L and the port N are connected to the sampling points of the circuit to be protected, and the port FB is connected to the control chip of the circuit to be protected.

[0012] As a preferred improvement of this utility model, the circuit to be protected is AC.

[0013] As a preferred improvement of this utility model, the control chip is model OB2273 or OB2276.

[0014] As a preferred improvement of this utility model, the rectifier bridge BRG1 is model GBU608.

[0015] As a preferred improvement of this utility model, the port GND is grounded.

[0016] As a preferred improvement of this utility model: the switching transistor Q9 is a MOS transistor, wherein pin 1 is the gate, pin 2 is the drain, and pin 3 is the source.

[0017] The beneficial effects of this utility model are as follows:

[0018] By using the TL431, a wide range of input undervoltage protection is achieved, and the undervoltage protection has an input undervoltage hysteresis function, which has good anti-interference ability. The TL431 reference voltage is stable, the undervoltage protection point difference is small, the circuit uses few components, most of which are surface mount materials, resulting in low cost and small PCB layout space. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0020] Figure 1 This is a schematic diagram of an input undervoltage protection circuit based on TL431 according to this utility model;

[0021] Figure 2 This is a schematic diagram of the second resistive component of this utility model. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0024] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0025] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0027] Please see Figure 1As shown, this utility model provides an input undervoltage protection circuit based on TL431, including port L and port N. Port N is connected to the positive terminal of diode D1 and pin 3 of rectifier bridge BRG1. Port L is connected to the positive terminal of diode D2 and pin 2 of rectifier bridge BRG1. Pin 1 of rectifier bridge BRG1 is connected to one end of capacitor C1 and the input terminal of resistor 2. The other end of capacitor C1 is connected to GND. Pin 4 of rectifier bridge BRG1 is connected to port GND. The negative terminal of diode D1 is connected to the negative terminal of diode D2, one end of capacitor C18, and the input terminal of resistor 1. The output terminal of resistor 1 is connected to one end of resistor R20, one end of resistor R51, one end of capacitor C2, and the reference stage of TL431U5. The other end of C18 is connected to the other end of resistor R20, the other end of capacitor C2, the anode of TL431U5, one end of capacitor C21, and port GND. The cathode of TL431U5 is connected to the output terminal of resistor II, the other end of capacitor C21, and the cathode of Zener diode Z1. The anode of Zener diode Z1 is connected to one end of resistor R43, one end of capacitor C20, and pin 1 of switching transistor Q9. The other end of resistor R43 is connected to the other end of capacitor C20, pin 3 of switching transistor Q9, and port GND. Pin 2 of switching transistor Q9 is connected to the negative terminals of diodes D7 and D3. The positive terminal of diode D3 is connected to the other end of resistor R51. The positive terminal of diode D7 is connected to port FB. Ports L and N are connected to the sampling points of the circuit to be protected. Port FB is connected to the control chip of the circuit to be protected. The circuit to be protected is AC, and the control chip is of model OB2273, OB2276, etc. The rectifier bridge BRG1 is model GBU608, the port GND is grounded, and the switching transistor Q9 is a MOSFET, wherein pin 1 is the gate, pin 2 is the drain, and pin 3 is the source.

[0028] In one embodiment, the first resistor includes resistors R57, R52, R54, and R53. One end of resistor R57 is the input terminal of the first resistor, the other end of resistor R57 is connected to one end of resistor R52, the other end of resistor R52 is connected to one end of resistor R54, the other end of resistor R54 is connected to one end of resistor R53, and the other end of resistor R53 is the output terminal of the first resistor. The second resistor includes resistors R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, and R33 (e.g., R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, and R33). Figure 2One end of resistor R30, one end of resistor R41, and one end of resistor R42 are connected and serve as the input terminal of resistor element two. The other end of resistor R30 is connected to the other ends of resistor R41, R42, R26, R37, and R38. The other end of resistor R26 is connected to the other ends of resistor R37, R38, R25, R34, and R36. The other end of resistor R25 is connected to the other ends of resistor R34, R36, R22, R32, and R33. The other ends of resistors R22, R32, and R33 are connected and serve as the output terminal of resistor element two. It should be further noted that any other components used to achieve the above effects should fall within the inventive concept of this utility model and should be protected within the scope of this utility model.

[0029] Working principle:

[0030] The main function of this circuit is to implement input undervoltage protection based on the TL431, and it also has an undervoltage hysteresis function. U5 is a TL431, and its pin 1 reference voltage is 2.5V. The input AC voltage is rectified by diodes D1 and D2. R57, R52, R54, R53, and R20 form a resistor voltage divider circuit, and C18 is a high-voltage filter electrolytic capacitor. The input AC voltage passes through the rectifier bridge BRG1 and the electrolytic capacitor C1, and the rectified voltage is a DC voltage. The voltage across the electrolytic capacitor C1 is extracted, and after being divided by 12 resistors R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, and R33, it is connected to pin 3 of U5.

[0031] Under normal operating conditions, the voltage across VR20 reaches 2.5V, meaning the voltage at pin 1 of U5 reaches 2.5V. Pins 2 and 3 of U5 are conducting. At this time, the voltage on C1 forms a circuit to ground through R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, R33 and pins 2 and 3 of U5. Therefore, the Vgs voltage of Q9 is low, and pins D and S of Q9 are not conducting. The protection pin FB of the chip is not pulled low, and the chip works normally.

[0032] When V R20 When the voltage across the terminals is less than 2.5V, that is, when the voltage at pin 1 of U5 is below 2.5V, and pins 2 and 3 of U5 are cut off and not conducting, the voltage across C1, after passing through R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, and R33, forms a voltage divider with R43. R43The voltage across the two ends is the Vgs voltage of Q9, which, after series voltage division, becomes V. R43 When Vgs reaches the turn-on voltage of Q9, the D and S pins of Q9 are turned on, and the FB pin is pulled low to the negative output terminal, triggering the low-level protection of the IC's FB pin. At this time, it is the input undervoltage protection.

[0033] The undervoltage protection hysteresis function is implemented through R51, D3, and D7. D3 and D7 are reverse-current diodes to prevent voltage fluctuations at the FB pin or V. R20 The voltages of the two components interfere with each other; during undervoltage protection, because Q9 is grounded, R51 and R20 connected in parallel are equivalent to R57, R52, R54, R53, R20, and R51 forming a series voltage divider circuit, V R20 The voltage at pin 1 of U5 is lower than the voltage at protection time. The input voltage needs to be increased to raise the voltage at pin 1 of U5 to 2.5V before the undervoltage protection is released. Without this undervoltage hysteresis circuit, there is no hysteresis after the input is undervoltage, and the protection will be released quickly. The hysteresis value can be adjusted by adjusting the resistance value of R51.

[0034] Due to the operating voltage V of U5 KA The maximum value is 36V. If the V of AZ431AN is... KA When the voltage exceeds 36V, the 2.5V reference voltage of U5 will be unstable, and the reference voltage is prone to oscillation, leading to excessive deviation or even damage. Because this circuit is used for 90Vac~290Vac applications, when the input voltage is 290Vac, the voltage across C1 after rectification is 410V. If C1 is directly connected to pin 3 of U5, 410V far exceeds the required voltage. KA At a maximum voltage of 36V, U5 will break down and be directly damaged. Therefore, a voltage divider resistor is added to reduce the voltage at pin 3 of U5. R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, and R33 should be 1206 package resistors because the power rating of a 1206 package resistor cannot exceed 0.25W. Therefore, these resistors need to have large resistance values ​​to prevent them from burning out due to exceeding their power rating under high voltage. Because the resistance values ​​of R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32, and R33 are very large, the current flowing through pins 3 and 2 of U5 is very small when pins 3 and 2 are conducting. Therefore, a TL431 resistor with low current draw should be selected. The reasons for choosing 1206 stainless steel for R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, R32 and R33 are twofold: firstly, it can reduce costs, and secondly, it can reduce the space required for PCB layout.

[0035] The circuit parameters are as follows: In the voltage divider circuit for pin 1 of U5, resistor R57 has a resistance of 330KΩ, R52, R54, and R53 have resistances of 360KΩ, and R51 has a resistance of 120KΩ. These five resistors form the undervoltage protection point and recovery point for input undervoltage protection. The hysteresis resistor R51 determines the hysteresis value. Capacitor C18 has a capacitance of 10uF and is an electrolytic capacitor that filters and provides a stable voltage; its withstand voltage is 450V. C22 has a capacitance of 10nF and its function is to filter high-frequency interference, preventing malfunction of the U5 reference voltage. It also has a good interference removal effect for lightning strike and electrostatic discharge tests. Resistors R30, R25, R26, R22, R32, R34, R37, and R41 have resistances of 100KΩ, and R43 has a resistance of 10KΩ. These resistors determine the voltage drop of U5 after pins 3 and 2 are turned on. KA The withstand voltage should be less than 36V. When pins 2 and 3 of U5 are cut off, the Vgs voltage of Q9 reaches the Q9 conduction level, pulling down the voltage at pin FB to trigger protection. C20 is 10nF to prevent Q9 from being mis-conducted due to high-frequency signal interference, and it has good anti-interference capability against lightning strikes. Z1 is a 3.3V Zener diode to prevent the Vgs voltage of Q9 from being too high and breaking down the MOSFET Q9. D7 and D8 can be diodes with a withstand voltage of 1000V.

[0036] Circuit advantages: Wide-range undervoltage protection can be achieved using the TL431, and it has an undervoltage hysteresis function after undervoltage protection, providing excellent anti-interference capability. The TL431 reference voltage is stable, and the undervoltage protection point varies little. This circuit uses few components, most of which are surface-mount parts, resulting in low cost and small PCB layout space.

[0037] Although the embodiments of this utility model have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for this utility model. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, this utility model is not limited to the specific details and the illustrations shown and described herein.

Claims

1. An input undervoltage protection circuit based on TL431, characterized in that: It includes port L and port N. Port N is connected to the positive terminal of diode D1 and pin 3 of rectifier bridge BRG1. Port L is connected to the positive terminal of diode D2 and pin 2 of rectifier bridge BRG1. Pin 1 of rectifier bridge BRG1 is connected to one end of capacitor C1 and the input terminal of resistor 2. The other end of capacitor C1 is connected to GND. Pin 4 of rectifier bridge BRG1 is connected to port GND. The negative terminal of diode D1 is connected to the negative terminal of diode D2, one end of capacitor C18, and the input terminal of resistor one. The output terminal of resistor one is connected to one end of resistor R20, one end of resistor R51, one end of capacitor C2, and the reference terminal of TL431U5. The other end of capacitor C18 is connected to the other end of resistor R20, the other end of capacitor C2, the anode of TL431U5, one end of capacitor C21, and port GND. The cathode of TL431U5 is connected to the output terminal of resistor two, the other end of capacitor C21, and the cathode of Zener diode Z1. The anode of the Zener diode Z1 is connected to one end of resistor R43, one end of capacitor C20, and pin 1 of the switching transistor Q9. The other end of resistor R43 is connected to the other end of capacitor C20, pin 3 of the switching transistor Q9, and port GND. Pin 2 of the switching transistor Q9 is connected to the negative terminals of diode D7 and diode D3. The positive terminal of diode D3 is connected to the other end of resistor R51. The positive terminal of diode D7 is connected to port FB.

2. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: The first resistor includes resistors R57, R52, R54, and R53. One end of resistor R57 is the input terminal of the first resistor. The other end of resistor R57 is connected to one end of resistor R52. The other end of resistor R52 is connected to one end of resistor R54. The other end of resistor R54 is connected to one end of resistor R53. The other end of resistor R53 is the output terminal of the first resistor.

3. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: The second resistor element includes resistors R30, R41, R42, R26, R37, R38, R25, R34, R36, R22, and R33. One end of resistor R30, one end of resistor R41, and one end of resistor R42 are connected and serve as the input terminal of the second resistor element. The other end of resistor R30 is connected to the other end of resistor R41, the other end of resistor R42, one end of resistor R26, one end of resistor R37, and resistor R33. One end of R38 and the other end of resistor R26 are connected to the other ends of resistor R37, resistor R38, resistor R25, resistor R34 and resistor R36. The other end of resistor R25 is connected to the other ends of resistor R34, resistor R36, resistor R22, resistor R32 and resistor R33. The other ends of resistor R22, resistor R32 and resistor R33 are connected and serve as the output terminal of resistor element two.

4. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: Port L and port N are connected to the sampling points of the circuit to be protected, and port FB is connected to the control chip of the circuit to be protected.

5. The input undervoltage protection circuit based on TL431 according to claim 4, characterized in that: The circuit to be protected is powered by alternating current.

6. The input undervoltage protection circuit based on TL431 according to claim 4, characterized in that: The control chip model is OB2273 or OB2276.

7. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: The rectifier bridge BRG1 is model GBU608.

8. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: The port is grounded (GND).

9. The input undervoltage protection circuit based on TL431 according to claim 1, characterized in that: The switching transistor Q9 is a MOSFET, where pin 1 is the gate, pin 2 is the drain, and pin 3 is the source.

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