CN219477585U - Under-voltage protection circuit - Google Patents

Abstract

The utility model discloses an under-voltage protection circuit which is characterized by comprising a voltage detection circuit with a first voltage output end and a second voltage output end, wherein an external power supply is connected to the voltage detection circuit, the first voltage output end of the voltage detection circuit is connected with a return difference circuit, the second voltage output end of the voltage detection circuit is connected with the return difference circuit and a control switch circuit, and the control switch circuit is also connected with an EN pin of a DC-DC chip. The undervoltage protection points are regulated according to actual load conditions, and can be accurately regulated through a plurality of resistors, so that the overload burning out of the load is prevented; the return difference circuit can effectively prevent the triode Q2 from being in a critical state of on and off, and prevent the triode Q1 from being continuously on and off to influence the normal control chip operation of the EN pin of the DC-DC chip.

Description

Under-voltage protection circuit

Technical Field

The utility model relates to an under-voltage protection circuit, and belongs to the field of design of automobile illumination protection circuits.

Background

Since the birth of LEDs (light emitting diodes), LEDs have been attracting attention because of their small size, low energy consumption, sturdiness and durability, long life, safety, low voltage, wide application range, rich colors, high light quality, and other excellent properties.

Today, high-end vehicle types are basically composed of LEDs. In order to meet the increasingly complex lamplight show requirement of high-end vehicle types, a DC-DC (direct current to direct current) chip is often used for supplying power to a matrix IC (integrated circuit) through voltage conversion on the design of a vehicle lamp, then an MCU (micro control unit) controls each channel of the matrix IC through CAN/LIN signals, each channel controls 1 or 2 LEDs, and the complex lamplight show effect is realized by controlling the sequential lighting of the LEDs of different channels. However, DC-DC chips typically use a constant power scheme when used, and when their input voltage is less than a design value, the current will also exceed the design threshold. Excessive current tends to damage components in the circuit, resulting in product damage. In order to avoid this, it is necessary to perform shutdown protection at the time of low-voltage input of the product.

Disclosure of Invention

The utility model aims to solve the technical problems that: in a DC-DC circuit using a constant power scheme, at low voltage inputs, the current may exceed a design threshold, damaging components in the circuit, resulting in product damage.

In order to solve the technical problem, the technical scheme of the utility model provides an undervoltage protection circuit, which is characterized by comprising a voltage detection circuit with a first voltage output end and a second voltage output end, wherein an external power supply is connected to the voltage detection circuit, the first voltage output end of the voltage detection circuit is connected with a return difference circuit, the second voltage output end of the voltage detection circuit is connected with the return difference circuit and a control switch circuit, and the control switch circuit is also connected with an EN pin of a DC-DC chip.

Preferably, the voltage detection circuit includes a resistor R1, a resistor R3, a resistor R6, a zener diode ZD1, and a transistor Q2; the collector of the triode Q2 is connected with an external power supply through a resistor R1, and the second voltage output end is led out from between the collector of the triode Q2 and the resistor R1; the emitter of the triode Q2 is grounded; a resistor R6 is connected between the emitter and the base of the triode Q2 in a bridging way; the base electrode of the triode Q2 is connected with the anode of the voltage stabilizing diode ZD1, the cathode of the voltage stabilizing diode ZD1 is connected with the first voltage output end and one end of a resistor R3, and the other end of the resistor R3 is connected with an external power supply.

Preferably, the return difference circuit comprises a resistor R5, a resistor R7, a resistor R8, a resistor R9, a capacitor C1 and a triode Q3; after the capacitor C1 is connected in parallel with the resistor R7, one end of the capacitor C is grounded, and the other end of the capacitor C is connected with the first voltage output end; the collector of the triode Q3 is connected with the first voltage output end through a resistor R5; the base electrode of the triode Q3 is connected with the second voltage output end through a resistor R8; the emitter of the triode Q3 is grounded, and a resistor R9 is connected between the emitter and the base of the triode Q3 in a bridging way.

Preferably, the control switch circuit comprises a resistor R2, a resistor R4 and a triode Q1; the base electrode of the triode Q1 is connected with the second voltage output end through a resistor R2; the collector electrode of the triode Q1 is connected with the EN pin of the DC-DC chip; the emitter of the triode Q1 is grounded, and a resistor R4 is connected between the emitter and the base of the triode Q1 in a bridging way.

Compared with the existing circuit, the undervoltage protection circuit provided by the utility model has the following advantages:

1. the undervoltage protection points are regulated according to actual load conditions, and can be accurately regulated through a plurality of resistors, so that the overload burning out of the load is prevented;

2. the return difference circuit can effectively prevent the triode Q2 from being in a critical state of on and off, and prevent the triode Q1 from being continuously on and off to influence the normal control chip operation of the EN pin of the DC-DC chip.

The undervoltage protection circuit disclosed by the utility model has the advantages of simple circuit structure, mature application and comprehensive functional consideration, can well protect loads, prevents undervoltage and overcurrent damage, and is safe and reliable.

Drawings

Fig. 1 is a circuit diagram of an undervoltage protection circuit disclosed in this embodiment.

Detailed Description

The utility model will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present utility model and are not intended to limit the scope of the present utility model. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present utility model, and such equivalents are intended to fall within the scope of the utility model as defined in the appended claims.

Referring to fig. 1, an undervoltage protection circuit disclosed in this embodiment is composed of a voltage detection circuit, a return difference circuit and a control switch circuit 3.

The voltage detection circuit is composed of resistors R1, R3 and R6, a voltage stabilizing diode ZD1 and a triode Q2. The current enters from VCC and flows through the resistors R3 and R7 to form a loop, and the voltage at Va is. When the voltage at Va is greater than the breakdown voltage of zener diode ZD1 by 5.1V, zener diode ZD1 breaks down and the voltage reaches the base of transistor Q2. Let the base voltage of the transistor Q2 be V _Q2b Then V _Q2b =va-5.1V. When V is _Q2b When the voltage is less than 0.7V, the triode Q2 is cut off, V _R1 Is a high voltage; when V is _Q2b When the voltage is greater than 0.7V, the transistor Q2 is conducted, the collector is communicated with the emitter to be grounded, V _R1 The relative voltage is 0V.

The return difference circuit is composed of resistors R5, R7, R8 and R9, a capacitor C1 and a triode Q3. V (V) _R1 When the voltage is high voltage, V _Q3b Also at high voltage. When VCC is increased gradually, V is satisfied _Q3b <0.7v、V _Q3b >When 0.7V, the triode Q3 is conducted to enable the resistors R5 and R7 to form a parallel circuit, the overall resistance value is reduced after parallel connection, and the voltage at the Va position is reduced to enable V _Q2b The voltage drops. When VCC continues to increase, let V _Q2b When=0.7v, transistor Q2 is turned on, V _R1 =0V、V _Q3b =0v, transistor Q3 is off, resistor R5 turns off the loop, voltage at Va increases, V _Q2b In this case much greater than 0.7V. Preventing V from appearing _Q2b The critical state when=0.7v makes triode Q2 constantly switch on and off, also makes triode Q1 constantly switch on and off, influences the control of the EN foot of DC-DC chip, makes DC-DC chip also be in operation and turn off constantly switch-over state, influences car light normal operating. When VCC is initially at normal voltage and gradually decreases, V is satisfied _Q2b >At 0.7V, transistor Q2 is on and transistor Q3 is off. When VCC falls to satisfy V _Q2b When=0.7v, transistor Q2 is in the critical state of on and off. Transistor Q3 is on as long as transistor Q2 is off. After the triode Q3 is conducted, the resistor R5 is connected into a loop to form a parallel connection state with the resistor R7, the overall resistance value is reduced after the parallel connection, and the voltage at the Va position is reduced, so that V _Q2b The voltage is far less than 0.7V, ending the critical state of transistor Q2.

The control switch circuit is composed of resistors R2 and R4 and a triode Q1. When transistor Q2 is in the off state, current is drawn from VCC through resistors R2, R4 to ground. When V is _Q1b >The triode Q1 is conducted at 0.7V, the EN pin of the DC-DC chip is pulled to the ground, and the DC-DC chip is in an off state. When transistor Q2 is in on state, V _R1 =0v, at this time V _Q1b =0v, transistor Q1 turns off, and the EN pin state of the DC-DC chip provides high voltage from the DC-DC chip side, causing the chip to be in an operational state.

The working process of the circuit is as follows:

normal voltage condition:

the voltage enters the circuit from VCC through resistor R3 to Va. Due to the intrinsic characteristics of zener diode ZD1 (operating in the reverse breakdown region), when the voltage at Va is greater than 5.1V, zener diode ZD1 breaks down and the voltage reaches the base of transistor Q2. When the base voltage of the transistor Q2 is larger than 0.7V, the transistor Q2 is conducted, and the collector is connected with the emitter to be grounded. At this time, the collector relative voltage of the transistor Q2 is 0V. Since the collector relative voltage of the transistor Q2 is 0V, the base of the transistor Q3 is also 0V, and is in an off state. The EN pin of the DC-DC chip is not grounded, and the state provides high voltage from the aspect of the DC-DC chip, so that the chip is in an operating state.

Under-voltage condition:

when the voltage is lower than the normal value, i.e. the current enters from VCC and passes through the resistor R3 to Va, the voltage is smaller than the sum of the breakdown voltage of the zener diode ZD1 and the conduction voltage of the base electrode of the transistor Q2, i.e. At this time, the transistor Q2 is in an off state, and a current flows from VCC through the resistor R1, and flows through the resistor R2, the resistor R4, the resistor R8, and the resistor R9, respectively, to the ground. Let the potential at the lower end of the resistor R1 in FIG. 1 be V _R1 Then->. Let the base potential of the transistor Q3 be V _Q3b Then->. When V is _Q3b >At 0.7V, the transistor Q3 is turned on and the resistor R5 is connected to ground. At this time, the resistor R5 and the resistor R7 form a parallel circuit to change the potential at Va from the original oneReduced to->. Let Va be Va' after the reduction. A decrease in potential at Va' preventing the potential at Va from being at va=v _ZD1 +V _Q2b The critical state of (2) is that the triode Q2 is continuously switched on and off, and the triode Q1 is also that the triode Q1 is continuously switched on and off, so that the control of the EN pin is influenced, the chip is also in the state of continuous switching between running and off, and the normal running of the car lamp is influenced. Let the base potential of the transistor Q1 be V _Q1b Then. The EN pin of the DC-DC chip is usually the control switch pin, i.e. when V _EN When the voltage is larger than the set value, the DC-DC chip operates, V _EN And when the value is smaller than the set value, the DC-DC chip is closed. The set value of the EN pin of the general DC-DC chip is 3V-5V. When V is _Q1b >At 0.7V, the transistor Q1 is turned on and the EN pin potential is pulled to ground, i.e., V _EN =0, at this time, the DC-DC chip is turned off, realizing the under-voltage protection function.

Claims (4)

1. The undervoltage protection circuit is characterized by comprising a voltage detection circuit with a first voltage output end and a second voltage output end, wherein an external power supply is connected to the voltage detection circuit, the first voltage output end of the voltage detection circuit is connected with a return difference circuit, the second voltage output end of the voltage detection circuit is connected with the return difference circuit and a control switch circuit, and the control switch circuit is further connected with an EN pin of a DC-DC chip.

2. The undervoltage protection circuit of claim 1, wherein the voltage detection circuit comprises a resistor R1, a resistor R3, a resistor R6, a zener diode ZD1, and a transistor Q2; the collector of the triode Q2 is connected with an external power supply through a resistor R1, and the second voltage output end is led out from between the collector of the triode Q2 and the resistor R1; the emitter of the triode Q2 is grounded; a resistor R6 is connected between the emitter and the base of the triode Q2 in a bridging way; the base electrode of the triode Q2 is connected with the anode of the voltage stabilizing diode ZD1, the cathode of the voltage stabilizing diode ZD1 is connected with the first voltage output end and one end of a resistor R3, and the other end of the resistor R3 is connected with an external power supply.

3. The undervoltage protection circuit of claim 1, wherein the return difference circuit comprises a resistor R5, a resistor R7, a resistor R8, a resistor R9, a capacitor C1, and a transistor Q3; after the capacitor C1 is connected in parallel with the resistor R7, one end of the capacitor C is grounded, and the other end of the capacitor C is connected with the first voltage output end; the collector of the triode Q3 is connected with the first voltage output end through a resistor R5; the base electrode of the triode Q3 is connected with the second voltage output end through a resistor R8; the emitter of the triode Q3 is grounded, and a resistor R9 is connected between the emitter and the base of the triode Q3 in a bridging way.

4. The undervoltage protection circuit of claim 1, wherein the control switch circuit comprises a resistor R2, a resistor R4, and a transistor Q1; the base electrode of the triode Q1 is connected with the second voltage output end through a resistor R2; the collector electrode of the triode Q1 is connected with the EN pin of the DC-DC chip; the emitter of the triode Q1 is grounded, and a resistor R4 is connected between the emitter and the base of the triode Q1 in a bridging way.