CN201393057Y - Overvoltage and undervoltage protection circuit - Google Patents

Abstract

An overvoltage and undervoltage protection circuit includes a switching power supply integrated circuit, a first voltage dividing circuit, a second voltage dividing circuit and a triode. The first voltage dividing circuit includes a first resistor and a second resistor. The second voltage dividing circuit includes a third resistor and a fourth resistor. The base of the transistor is connected to the common node of the first resistor and the second resistor, its collector is connected to the common node of the third resistor and the fourth resistor, and its emitter is grounded. The switching power supply integrated circuit includes an input pin, an enable pin and an output pin, the input pin is connected to an external input DC power supply, the enable pin is connected to the common node of the third resistor and the fourth resistor, and the output pin is used for The voltage of the input DC power supply applied to the output. The overvoltage and undervoltage protection circuit of the utility model uses the enable pin of the switching power supply integrated circuit to externally connect the first voltage divider circuit, the second voltage divider circuit and the triode to realize the overvoltage and undervoltage protection, and the cost is low, and the structure Simple.

Description

Overvoltage and undervoltage protection circuit

technical field

The utility model relates to a protection circuit, in particular to an overvoltage and undervoltage protection circuit.

Background technique

At present, various electronic products widely use switching power supply integrated circuits to achieve the purpose of undervoltage protection. The switching power supply integrated circuit usually has an enable pin, which is used to control the working state of the switching power supply integrated circuit. When the input voltage is higher than a certain fixed value, the switching power supply integrated circuit can work normally; otherwise, then stop working. Utilizing this feature, the undervoltage protection can be effectively realized, that is, when the voltage input to the product drops to a certain limit value, the product will stop working, which improves the reliability of the product.

However, only realizing the undervoltage protection of the circuit cannot better protect the circuit and improve product performance. In order to better protect the circuit and further improve product performance, the current circuit generally uses a combination of a switching power supply integrated circuit and a dedicated overvoltage protection integrated circuit to realize the overvoltage and undervoltage protection of the circuit. However, the cost of this method is relatively high. tall and complex.

Utility model content

In view of this, it is necessary to provide an overvoltage and undervoltage protection circuit, which can realize the overvoltage and undervoltage protection of the circuit, has low cost and simple structure.

An overvoltage and undervoltage protection circuit is used to realize the overvoltage and undervoltage protection of the circuit, including a switching power supply integrated circuit, a first voltage dividing circuit, a second voltage dividing circuit and a triode. Wherein, the first voltage dividing circuit includes a first resistor and a second resistor, one end of the first resistor is connected to an external input DC power supply; the second resistor is connected between the other end of the first resistor and the ground. The second voltage dividing circuit includes a third resistor and a fourth resistor, one end of the third resistor is connected to an external input DC power supply; the fourth resistor is connected between the other end of the third resistor and the ground. The base of the triode is connected to the common node of the first resistor and the second resistor, its collector is connected to the common node of the third resistor and the fourth resistor, and its emitter is grounded; wherein, when the input power supply voltage is too large, the first The voltage divider circuit causes the triode to conduct, and the enabling pin of the switching power supply integrated circuit is grounded through the triode, causing the voltage applied to the enabling pin of the switching power supply integrated circuit to be lower than the working voltage and make it stop working; when the input power supply voltage is too high Hours, the first voltage divider circuit causes the triode to be cut off, and the second voltage divider circuit causes the voltage applied to the enable pin of the switching power supply integrated circuit to be lower than its operating voltage to stop it from working.

An overvoltage and undervoltage protection circuit is connected between a voltage source and an integrated circuit, and is used to realize overvoltage and undervoltage protection for the integrated circuit. The integrated circuit includes a power supply terminal and an enabling pin. The overvoltage and The undervoltage protection circuit includes a first voltage divider circuit, a triode and a second voltage divider circuit. Wherein, the first voltage dividing circuit is connected between the voltage source and the ground, and is used to output the first voltage dividing signal; the base of the triode receives the first voltage dividing signal, and its collector is connected to the enabling pin of the integrated circuit. The emitter is grounded; the second voltage divider circuit is connected between the voltage source and the ground, and is used to output the second voltage divider signal to the enable pin of the integrated circuit. When the voltage of the power supply is too large, the first voltage division signal output by the first voltage division circuit turns on the triode, so that the voltage of the enable pin of the integrated circuit drops to the emitter voltage of the triode, and the emitter voltage is lower than that of the integrated circuit. The operating voltage of the circuit makes it stop working; when the power supply voltage is too small, the first divided voltage signal makes the triode cut off, and the second divided voltage signal output by the second divided voltage circuit is the voltage applied to the enable pin of the integrated circuit , the second divided voltage signal is lower than the operating voltage of the integrated circuit so that it stops working.

The overvoltage and undervoltage protection circuit of the utility model adopts the enable pin of the switching power supply integrated circuit to connect the first voltage divider circuit, the second voltage divider circuit and the triode externally, which can realize the overvoltage and undervoltage protection of the circuit, and the cost is low , and the structure is simple.

Description of drawings

FIG. 1 is a circuit diagram of an overvoltage and undervoltage circuit according to an embodiment of the present invention.

Detailed ways

FIG. 1 is a circuit diagram of an undervoltage and overvoltage protection circuit according to an embodiment of the present invention. In this embodiment, the undervoltage and overvoltage protection circuit includes a first voltage divider circuit 10 , a second voltage divider circuit 20 and a transistor Q1 for protecting the switching power supply integrated circuit U1 and the load circuit.

The first voltage divider circuit 10 includes a first resistor R1 and a second resistor R2, one end of the first resistor R1 is connected to an external input DC power supply, and the second resistor R2 is connected between the other end of the first resistor R1 and the ground. The second voltage dividing circuit 20 includes a third resistor R3 and a fourth resistor R4, one end of the third resistor R3 is connected to an external input DC power supply, and the fourth resistor R4 is connected between the other end of the third resistor R3 and the ground. The base of the transistor Q1 is connected to the common node of the first resistor R1 and the second resistor R2, its collector is connected to the common node of the third resistor R3 and the fourth resistor R4, and its emitter is grounded. Wherein, the switching power supply integrated circuit U1 includes an input pin (power supply terminal), an output pin and an enable pin. The input pin (power supply end) of the switching power supply integrated circuit U1 is connected to an external input DC power supply, and its output pin is used to output the voltage of the external input DC power supply, and its enable pin EN is connected to the third resistor R3 and the first resistor R3. Common node of four resistors R4.

As a further improvement of an embodiment of the present invention, the overvoltage and undervoltage protection circuit further includes a fifth resistor R5, one end of which is connected to the common node of the first resistor R1 and the second resistor R2, and the other end is connected to the base of the transistor Q1 Pole, used to limit the base current of transistor Q1.

In this embodiment, the input voltage of the overvoltage and undervoltage protection circuit is VIN, and the output voltage is VOUT. When the input voltage VIN of the enable pin EN of the switching power supply integrated circuit U1 is of a suitable size and can normally drive the switching power supply integrated circuit U1, the switching power supply integrated circuit U1 starts to work and outputs the voltage VOUT through the output pin. Wherein, the input voltage VEN of the enable pin of the switching power supply integrated circuit U1 is greater than 1V.

In this embodiment, the over-voltage and under-voltage protection circuit obtains a voltage V1 after being divided by the first voltage dividing circuit 10, V1=(VIN×R2)/(R1+R2). The voltage V2 is obtained after being divided by the second voltage dividing circuit 20, V2=(R4*VIN)/(R4+R3). When the input voltage VIN of the overvoltage and undervoltage protection circuit is too large, the voltage V1 is greater than the turn-on voltage of the transistor Q1, the transistor Q1 is turned on, and works in the amplification area, and the enable pin EN of the switching power supply integrated circuit U1 is grounded through the transistor Q1 , the voltage input to the enable pin EN of the switching power supply integrated circuit U1 will drop below 1V, and the switching power supply integrated circuit U1 will stop working, thereby realizing the function of overvoltage protection for the switching power supply integrated circuit U1 and the load circuit.

When the input voltage VIN of the overvoltage and undervoltage protection circuit is too small, the voltage VEN of the enable pin of the switching power supply integrated circuit U1 is equal to V2. When V2 drops below 1V, the switching power supply integrated circuit U1 stops working, thereby realizing the function of undervoltage protection for the switching power supply integrated circuit U1 and the load circuit.

The overvoltage and undervoltage protection circuit of the utility model adopts a small number of discrete components (such as resistors, triodes, etc.), and through the working characteristics of the enable pin of the integrated circuit, there is no need to use a dedicated overvoltage and undervoltage protection integrated circuit , the integrated circuit itself and the load circuit can be protected, the structure is simple, and the cost is low.

Claims (3)

1. overvoltage and under-voltage protecting circuit are used to realize the overvoltage and the under-voltage protection of circuit, it is characterized in that described overvoltage and under-voltage protecting circuit comprise:

First bleeder circuit comprises:

First resistance, the one end links to each other with the input DC power that adds;

Second resistance is connected between the other end and ground of described first resistance;

Second bleeder circuit comprises:

The 3rd resistance, the one end links to each other with the input DC power that adds;

The 4th resistance is connected between the other end and ground of described the 3rd resistance; And

Triode, its base stage are connected in the common node of described first resistance and described second resistance, and its collector electrode is connected in the common node of described the 3rd resistance and described the 4th resistance, its grounded emitter; And

The Switching Power Supply integrated circuit, comprise input pin, enable pin and output pin, described input pin is connected in the described input DC power that adds, described enable pin is connected in the common node of described the 3rd resistance and described the 4th resistance, and described output pin is used to export the voltage of the described input DC power that adds;

Wherein, when the voltage of the described input DC power that adds is excessive, described first bleeder circuit causes described triode conducting, the enable pin of described Switching Power Supply integrated circuit is by described triode ground connection, and the voltage that causes being added in the enable pin of described Switching Power Supply integrated circuit is lower than its operating voltage and it is quit work;

When the voltage of the described input DC power that adds is too small, described first bleeder circuit causes described triode to end, and the voltage that described second bleeder circuit causes being added in the enable pin of described Switching Power Supply integrated circuit is lower than its operating voltage and it is quit work.

2. overvoltage as claimed in claim 1 and under-voltage protecting circuit; it is characterized in that, also comprise the 5th resistance, an end is connected in the common node of described first resistance and described second resistance; the other end is connected in the base stage of described triode, is used to limit the base current of described triode.

3. overvoltage and under-voltage protecting circuit; be connected between voltage source and the integrated circuit, be used to realize overvoltage and under-voltage protection to described integrated circuit, described integrated circuit comprises power end and enable pin; it is characterized in that described overvoltage and under-voltage protecting circuit comprise:

First bleeder circuit is connected between described voltage source and the ground, is used to export first voltage division signal;

Triode, its base stage receive described first voltage division signal, and its collector electrode is connected to the enable pin of described integrated circuit, its grounded emitter;

Second bleeder circuit is connected between described voltage source and the ground, is used to export the enable pin of second voltage division signal to described integrated circuit;

Wherein, when the voltage of described voltage source is excessive, first voltage division signal of described first bleeder circuit output makes described triode conducting, thereby the voltage that makes the enable pin of described integrated circuit is reduced to the emitter voltage of described triode, and described emitter voltage is lower than the operating voltage of described integrated circuit and it is quit work; When described supply voltage is too small, described first voltage division signal is ended described triode, second voltage division signal of described second bleeder circuit output is the voltage of the enable pin that is added in described integrated circuit, thereby described second voltage division signal quits work because of the operating voltage that is lower than described integrated circuit makes it.

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