An overvoltage and undervoltage protection circuit

Abstract

The present invention discloses an overvoltage and undervoltage protection circuit, comprising an overvoltage detection part, an undervoltage detection part and a protection circuit part. The overvoltage detection part comprises a comparator U1A, a resistor R1 and a resistor R2. The inverting input terminal of the comparator U1A is connected to the midpoint of the resistor R1 and the resistor R2. The non-inverting input terminal of the comparator U1A is connected to a reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1A is connected to the output terminal of the comparator U1A through the resistor R5 and the diode D1. The undervoltage detection part includes a comparator U1B, a resistor R3 and a resistor R4. The inverting input terminal of the comparator U1B is connected to the midpoint of the resistor R3 and the resistor R4 and the output terminal of the comparator U1A. The non-inverting input terminal of the comparator U1B is connected to the reference voltage V ref =2.5V. The present invention connects two comparators in the chip LM2903 in series, thereby reducing the number of components used and the problem of occupying more I / O ports at the control receiving end. At the same time, only the same reference voltage needs to be provided, simplifying the over-voltage and under-voltage protection circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an overvoltage and undervoltage protection circuit. Background Art

[0002] Switching power supplies have the advantages of small size, low cost, stable output voltage and wide input voltage range. Therefore, they are widely used in various electronic products. Overvoltage and undervoltage protection are the most basic protection functions of switching power supplies. They prevent the input voltage from being too high or too low and causing damage to key components such as the power supply's chips and MOS tubes.

[0003] Existing overvoltage and undervoltage protection circuits have problems such as a relatively simple protection method, the use of many components, the occupation of many feedback signal interfaces, and the need to provide different reference voltages to the comparator. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes an over-voltage and under-voltage protection circuit.

[0005] The present invention proposes an overvoltage and undervoltage protection circuit, which includes an overvoltage detection part, an undervoltage detection part and a protection circuit part. The overvoltage detection part includes a comparator U1A, a resistor R1 and a resistor R2. The inverting input terminal of the comparator U1A is connected to the midpoint of the resistor R1 and the resistor R2. The non-inverting input terminal of the comparator U1A is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1A is connected to the output terminal of the comparator U1A through the resistor R5 and the diode D1. The undervoltage detection part includes a comparator U1B, a resistor R3 and a resistor R4. The inverting input terminal of the comparator U1B is connected to the midpoint of the resistor R3 and the resistor R4 and the output terminal of the comparator U1A. The non-inverting input terminal of the comparator U1B is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1B is connected to the output terminal of the comparator U1B through the resistor R6 and the diode D2. The protection circuit part includes a transistor T1, the base of the transistor T1 is connected to the output terminal of the comparator U1B through the resistor R7, and the emitter of the transistor T1 is connected to the V provided by the auxiliary power supply through the inductor L1. cc The collector of transistor T1 is connected to the power supply pin V of the control chip through resistor R8. cc connected.

[0006] Preferably, a capacitor C1 is connected between both ends of the resistor R2.

[0007] Preferably, a capacitor C2 is connected between both ends of the resistor R4.

[0008] Preferably, the comparator U1A is connected to a capacitor C3, and the comparator U1B is connected to a capacitor C4.

[0009] Preferably, capacitors C5 and C6 are connected to both ends of the inductor L1 , and capacitors C6 and C7 are connected to the emitter and collector of the transistor T1 .

[0010] In the present invention, the overvoltage and undervoltage protection circuit adopts the method of connecting two comparators in the chip LM2903 in series to combine the overvoltage detection part and the undervoltage detection part, thereby avoiding the need to provide different reference voltages and occupying more I / O ports at the receiving end of the control system, and simplifying the overvoltage and undervoltage protection circuit.

[0011] The present invention connects two comparators in the chip LM2903 in series, thereby reducing the number of components used and the problem of occupying more I / O ports at the control receiving end. At the same time, only the same reference voltage needs to be provided, simplifying the over-voltage and under-voltage protection circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a circuit diagram of an over-voltage and under-voltage protection circuit proposed by the present invention. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0014] Reference Figure 1 An overvoltage and undervoltage protection circuit includes an overvoltage detection part, an undervoltage detection part, and a protection circuit part. The overvoltage detection part includes a comparator U1A, a resistor R1, and a resistor R2. The inverting input terminal of the comparator U1A is connected to the midpoint of the resistor R1 and the resistor R2. The non-inverting input terminal of the comparator U1A is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1A is connected to the output terminal of the comparator U1A through the resistor R5 and the diode D1. The undervoltage detection part includes a comparator U1B, a resistor R3 and a resistor R4. The inverting input terminal of the comparator U1B is connected to the midpoint of the resistor R3 and the resistor R4 and the output terminal of the comparator U1A. The non-inverting input terminal of the comparator U1B is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1B is connected to the output terminal of the comparator U1B through the resistor R6 and the diode D2. The protection circuit part includes a transistor T1, the base of the transistor T1 is connected to the output terminal of the comparator U1B through the resistor R7, and the emitter of the transistor T1 is connected to the V provided by the auxiliary power supply through the inductor L1. cc The collector of transistor T1 is connected to the power supply pin V of the control chip through resistor R8. cc connected.

[0015] In the present invention, a capacitor C1 is connected between both ends of the resistor R2.

[0016] In the present invention, a capacitor C2 is connected between both ends of the resistor R4.

[0017] In the present invention, the comparator U1A is connected to a capacitor C3, and the comparator U1B is connected to a capacitor C4.

[0018] In the present invention, capacitors C5 and C6 are connected to both ends of the inductor L1 , and capacitors C6 and C7 are connected to the emitter and collector of the transistor T1 .

[0019] The present invention assumes that the operating voltage range of the switching power supply is Vmin≤V DC ≤Vmax,V ref Generally, 2.5V is used; R2 / (R1+R2)=V ref / V max , that is, R1=R2*(V max -V ref ) / V ref ; R4 / (R3+R4)=V ref / V min , that is, R3=R4*(V min -V ref ) / V ref ;R8=0;V cc This is the supply voltage for the LM2903 chip and the control chip. According to the specification, V cc =36V.

[0020] In the overvoltage detection circuit, the sampling voltage of the main power circuit is divided by resistors R1 and R2 and used as the inverting input of the comparator U1A. The reference voltage V ref =2.5V as the non-inverting input of comparator U1A; in the undervoltage detection circuit part, the output of the upper level overvoltage protection circuit comparator U1A and the sampling voltage of the main power circuit are divided by resistors R3 and R4, and then serve as the inverting input of comparator U1B. The reference voltage V ref =2.5V is used as the non-inverting input of the comparator U1B. The output of the comparator U1B is connected to the base of the transistor in the protection circuit, and the circuit is protected by controlling the on and off of the transistor.

[0021] When V DC >V max When the input voltage V in1 -=V DC *R2 / (R1+R2)>V max *R2 / (R1+R2), greater than the voltage V at the non-inverting input in1+=V ref =2.5V, so the comparator U1A outputs a low impedance state; the input voltage V in 2-=V DC *R4 / (R3+R4)>V min *R4 / (R3+R4), so U1B outputs high impedance. At this time, the over-voltage and under-voltage detection circuit outputs VG high impedance, and the transistor T1 in the front-end protection circuit that powers the chip is cut off, and V cc =0V, the chip stops working due to power failure, thus completing the protection of the circuit;

[0022] When V min ≤V DC ≤V max When the input voltage V in 1-=V DC *R2 / (R1+R2)<V max *R2 / (R1+R2), less than the voltage V at the non-inverting input in 1+=V ref =2.5V, U1A outputs high impedance state; the input voltage V in 2-=V DC *R4 / (R3+R4)>V min *R4 / (R3+R4), greater than the voltage V at the non-inverting input in 2+=V ref =2.5V, so U1B outputs low impedance. At this time, the over-voltage and under-voltage detection circuit outputs VG low impedance, and the transistor T1 in the front-end protection circuit that powers the chip is turned on, V cc =36V, the switching power supply maintains normal working state;

[0023] When V DC <V min When the input voltage V in 1-=V DC *R2 / (R1+R2) <V max *R2 / (R1+R2), less than the voltage V at the non-inverting input in 1+=V ref =2.5V, U1A outputs high impedance state; the input voltage V in -=V DC *R4 / (R3+R4) is greater than V min *R4 / (R3+R4), greater than the voltage V at the non-inverting input in 2+=V ref=2.5V, so U1B outputs high impedance. At this time, the over-voltage and under-voltage detection circuit outputs VG high impedance, and the transistor T1 in the front-end protection circuit that powers the chip is cut off, and V CC =0V, the chip stops working due to power failure, thus completing the protection of the circuit.

[0024] In the overvoltage detection circuit of the present invention, the sampling voltage of the main power circuit is divided by resistors R1 and R2 and used as the inverting input terminal of the comparator U1A. The reference voltage V ref =2.5V as the non-inverting input of comparator U1A; in the undervoltage detection circuit part, the output of the upper level overvoltage protection circuit comparator U1A and the sampling voltage of the main power circuit are divided by resistors R3 and R4 and serve as the inverting input of comparator U1B. The reference voltage V ref =2.5V is used as the non-inverting input of the comparator U1B. The output of the comparator U1B is connected to the base of the third terminal in the protection circuit. By controlling the on and off of the transistor, the circuit is protected.

[0025] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. An overvoltage and undervoltage protection circuit, characterized in that: It includes an overvoltage detection part, an undervoltage detection part and a protection circuit part. The overvoltage detection part includes a comparator U1A, a resistor R1 and a resistor R2. The inverting input terminal of the comparator U1A is connected to the midpoint of the resistor R1 and the resistor R2. The non-inverting input terminal of the comparator U1A is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1A is connected to the output terminal of the comparator U1A through the resistor R5 and the diode D1. The undervoltage detection part includes a comparator U1B, a resistor R3 and a resistor R4. The inverting input terminal of the comparator U1B is connected to the midpoint of the resistor R3 and the resistor R4 and the output terminal of the comparator U1A. The non-inverting input terminal of the comparator U1B is connected to the reference voltage V ref =2.5V, and the non-inverting input terminal of the comparator U1B is connected to the output terminal of the comparator U1B through the resistor R6 and the diode D2. The protection circuit part includes a transistor T1, the base of the transistor T1 is connected to the output terminal of the comparator U1B through the resistor R7, and the emitter of the transistor T1 is connected to the V provided by the auxiliary power supply through the inductor L1. cc The collector of transistor T1 is connected to the power supply pin V of the control chip through resistor R8. cc connected.

2. The over-voltage and under-voltage protection circuit according to claim 1, characterized in that: A capacitor C1 is connected between both ends of the resistor R2.

3. The over-voltage and under-voltage protection circuit according to claim 1, characterized in that: A capacitor C2 is connected between both ends of the resistor R4.

4. The over-voltage and under-voltage protection circuit according to claim 1, characterized in that: The comparator U1A is connected to a capacitor C3 , and the comparator U1B is connected to a capacitor C4 .

5. The over-voltage and under-voltage protection circuit according to claim 1, characterized in that: The two ends of the inductor L1 are connected to capacitors C5 and C6 respectively, and the emitter and collector of the transistor T1 are connected to capacitors C6 and C7 respectively.

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