LED constant-current driving circuit with open-short circuit protection function

Abstract

The utility model provides an LED constant-current driving circuit with an open-short circuit protection function, and the circuit is characterized in that a first connection end of a power supply switch Q1 is connected with a power supply, and a second connection end of the power supply switch Q1 is connected with an input end of a constant-current control circuit; the output end of the constant current control circuit is connected with the input end of the LED lamp string, the output end of the LED lamp string is grounded, and when the power supply switch Q1 is switched on and the LED lamp string works normally, the output end of the constant current control circuit outputs constant current; when the power supply switch Q1 is switched on and the LED lamp string is in an open circuit state, the output end of the constant current control circuit has no current output; the detection end of the open-short circuit detection circuit is connected with the input end of the LED lamp string, and the output end of the open-short circuit detection circuit is connected with the control end of the power supply switch Q1. Compared with the prior art, the LED driving circuit is simple in circuit design, can drive an LED in a constant-current manner, and can perform open-circuit and short-circuit protection on the LED; the circuit adopts a pure hardware design scheme, the number of used components is very small, and the design cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially relates to a LED constant current drive circuit with open short circuit protection function. BACKGROUND

[0002] LED has many advantages, is widely used in each industry, and with the technical development of LED, the life and reliability of LED are higher and higher, and the drive protection circuit of LED is more and more important.But the circuit design of LED constant current drive circuit with open short circuit protection function on the existing market is complex, and the application cost is higher, which is not conducive to the requirement of low cost and small design space.Specifically, the product application circuit design is complex, generally needs integrated chip to do constant current drive and software to judge open short circuit fault, and the development cycle is longer, and the development amount is larger;Many electronic components are needed, and the space occupation of PCB is more, so the small space application product requirement cannot be met.

[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems. CONTENT OF UTILITY MODEL

[0004] One of the purposes of the utility model is to provide a LED constant current drive circuit with open short circuit protection function, which is simple in circuit design, can drive LED in constant current, and can also protect LED from open short circuit;The circuit is a pure hardware design scheme, and the number of components used is very small, which greatly reduces the design cost.

[0005] According to one aspect of the utility model, the utility model provides a LED constant current drive circuit with open short circuit protection function, it includes LED lamp string, constant current control circuit, power supply switch Q1 and open short circuit detection circuit, power supply switch Q1's first connecting terminal links with power supply Vbat, its second connecting terminal links with constant current control circuit's input end C, constant current control circuit's output end D links with LED lamp string's input end, LED lamp string's output end ground connection, when power supply switch Q1 is turned on and LED lamp string is in normal work, constant current control circuit's output end D exports constant current, when power supply switch Q1 is turned on and LED lamp string is in open circuit state, constant current control circuit's output end D has no current output, open short circuit detection circuit's detection end A links with LED lamp string's input end, its output end B links with power supply switch Q1's control end, open short circuit detection circuit exports corresponding control signal through detecting whether LED lamp string's input end is low level, control signal exports through output end B to control power supply switch Q1 is turned on or is turned off, when power supply switch Q1 is turned on and LED lamp string is in open circuit state, open short circuit detection circuit exports high level through its detection end A to make constant current control circuit's output end D have no current output.

[0006] Further, when detecting that the input end of the LED lamp string is low, the control signal output by the output end B of the open short circuit detection circuit is a first logic level to control the power supply switch Q1 to be turned off; when the input end of the LED lamp string is not detected to be low, the control signal output by the output end B of the short circuit detection circuit is a second logic level to control the power supply switch Q1 to be turned on; when the power supply switch Q1 is turned on and the LED lamp string is in an open circuit state, the open short circuit detection circuit outputs a high level through its detection end A to make the constant current control circuit generate a first current from its input end C to the ground end, and the first current is smaller than the constant current output by the output end D of the constant current control circuit.

[0007] Further, the open short circuit detection circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, and a switching device Q2, one end of the resistor R1 is connected with the first connecting terminal of the power supply switch Q1, and the other end thereof is connected with the output end B of the open short circuit detection circuit; the first connecting terminal of the switching device Q2 is connected with the output end B of the open short circuit detection circuit through the resistor R2, the second connecting terminal thereof is grounded, and the control end thereof is connected with the detection end A of the open short circuit detection circuit through the resistor R3; one end of the resistor R4 is connected with the power supply Vbat, and the other end thereof is connected with the detection end A of the open short circuit detection circuit.

[0008] Further, when the input end of the LED lamp string is detected as low level, the switching device Q2 is turned off, so that the output end B of the open-circuit detection circuit controls the power supply switch Q1 to be turned off; when the input end of the LED lamp string is not detected as low level, the switching device Q2 is turned on, so that the output end B of the open-circuit detection circuit controls the power supply switch Q1 to be turned on; when the power supply switch Q1 is turned on and the LED lamp string is in an open-circuit state, the open-circuit detection circuit outputs a high-level voltage value through the detection end A, which is equal to the voltage value of the power supply Vbat.

[0009] Further, the constant current control circuit comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switching device Q3; the positive electrode of the diode D1 is connected with the input end C of the constant current control circuit, and the negative electrode thereof is connected with the positive electrode of the diode D2; the negative electrode of the diode D2 is grounded through the resistor R5; the first connection end of the switching device Q3 is connected with the input end C of the constant current control circuit through the resistor R6, the control end thereof is connected with the negative electrode of the diode D2, and the second connection end thereof is connected with the output end D of the constant current control circuit.

[0010] Further, when the LED lamp string is in a normal working state, the open-circuit detection circuit controls the power supply switch Q1 to be turned on through the output end B, so that the switching device Q3 is turned on and the diodes D1 and D2 are forward biased, thereby the constant current control circuit generates the constant current flowing through the resistor R6, the switching device Q3 and the LED lamp string in sequence; when the LED lamp string is in an open-circuit state, the open-circuit detection circuit controls the power supply switch Q1 to be turned on through the output end B, and the open-circuit detection circuit outputs a high level through the detection end A, so that the switching device Q3 is turned off and the diodes D1 and D2 are reverse biased, thereby the output end D of the constant current control circuit has no current output, and the constant current control circuit generates a first current flowing through the resistor R6, the first connection end and the control end of the switching device Q3, and the resistor R5 to the ground end in sequence.

[0011] Further, the power supply switch Q1 is a PNP type triode, the first connection end, the second connection end and the control end of the power supply switch Q1 are the emitter, the collector and the base of the PNP type triode respectively; the switching device Q2 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q2 are the collector, the emitter and the base of the NPN type triode respectively; the switching device Q3 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP type triode respectively.

[0012] Furthermore, the resistance values ​​of resistors R1 and R2 are selected to satisfy the following conditions: when the switching device Q2 is turned on, the voltage across resistor R1 is greater than the on-state voltage threshold of the power supply switch Q1, so that the power supply switch Q1 is in the on state; the resistance value of resistor R5 is greater than the resistance value of resistor R6.

[0013] Compared with the prior art, the circuit design of this utility model is simple. It can drive the LED with constant current and also protect the LED from open and short circuits. The circuit is a pure hardware design scheme with very few components, which greatly reduces the design cost. [Attached Image Description]

[0014] To more clearly illustrate the technical solutions of 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. Among them:

[0015] Figure 1 This invention provides an LED constant current drive circuit with open / short circuit protection in one embodiment.

Detailed Implementation Methods

[0016] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms coupling, connection, linking, and interconnection used herein to indicate electrical connection mean direct or indirect connection. For example, A being connected to B includes both a direct electrical connection between A and B and a connection between A and B via electrical components or circuits.

[0018] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "back", "positive", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0019] Referring to Figure 1 As shown in the figure, it is a circuit schematic diagram of the LED constant current driving circuit with open short circuit protection function in an embodiment of the utility model. Figure 1 The LED constant current driving circuit with open short circuit protection function shown in the figure comprises an LED lamp string LED1, a constant current control circuit 110, a power supply switch Q1 and an open short circuit detection circuit 120.

[0020] The first connection end of the power supply switch Q1 is connected with the power supply Vbat, and the second connection end thereof is connected with the input end C of the constant current control circuit 110; the output end D of the constant current control circuit 110 is connected with the input end (or the positive electrode) of the LED lamp string LED1, and the output end (or the negative electrode) of the LED lamp string LED1 is grounded; when the power supply switch Q1 is turned on and the LED lamp string LED1 is in normal working state, the output end D of the constant current control circuit 110 outputs constant current (i.e. the constant current control circuit 110 works normally); when the power supply switch Q1 is turned on and the LED lamp string LED1 is in open circuit state, the output end D of the constant current control circuit 110 outputs no current (i.e. the constant current control circuit 110 cannot work normally). The detection end A of the open short circuit detection circuit 120 is connected with the input end of the LED lamp string LED1, and the output end B thereof is connected with the control end of the power supply switch Q1; the open short circuit detection circuit 120 generates corresponding control signal by detecting whether the input end (or the positive electrode) of the LED lamp string LED1 is low level, and the control signal is output through the output end B to control the power supply switch Q1 to be turned on or turned off; when the power supply switch Q1 is turned on and the LED lamp string LED1 is in open circuit state, the open short circuit detection circuit 120 outputs high level through the detection end A to make the output end D of the constant current control circuit 110 output no current.

[0021] When the input end (or the positive electrode) of the LED lamp string LED1 is detected to be low level, the control signal output by the output end B of the open short circuit detection circuit 120 is the first logic level to control the power supply switch Q1 to be turned off; when the input end (or the positive electrode) of the LED lamp string LED1 is not detected to be low level, the control signal output by the output end B of the short circuit detection circuit 120 is the second logic level to control the power supply switch Q1 to be turned on; when the power supply switch Q1 is turned on and the LED lamp string LED1 is in open circuit state, the open short circuit detection circuit 120 outputs high level through the detection end A to make the constant current control circuit 110 generate the first current from the input end C to the ground end, and the first current is smaller than the constant current output by the output end D of the constant current control circuit 110.

[0022] The open short circuit detection circuit 120 comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4 and a switching device Q2, wherein one end of the resistor R1 is connected with the first connection end of the power supply switch Q1, and the other end thereof is connected with the output end B of the open short circuit detection circuit 120; the first connection end of the switching device Q2 is connected with the output end B of the open short circuit detection circuit 120 through the resistor R2, and the second connection end thereof is grounded, and the control end thereof is connected with the detection end A of the open short circuit detection circuit 120 through the resistor R3; one end of the resistor R4 is connected with the power supply Vbat, and the other end thereof is connected with the detection end A of the open short circuit detection circuit 120.

[0023] When the input end (or the anode) of the LED lamp string LED1 is detected as low (indicating that the LED lamp string LED1 is in the short circuit state), the switching device Q2 is turned off, so that the output end B of the open short circuit detection circuit 120 controls the power supply switch Q1 to be turned off; when the input end of the input end (or the anode) of the LED lamp string LED1 is not detected as low (indicating that the LED lamp string LED1 is in the non-short circuit state), the switching device Q2 is turned on, so that the output end B of the open short circuit detection circuit 120 controls the power supply switch Q1 to be turned on; when the power supply switch Q1 is turned on and the LED lamp string LED1 is in the open circuit state, the voltage value of the high level output by the detection end A of the open short circuit detection circuit 120 is equal to the voltage value of the power supply Vbat.

[0024] The constant current control circuit 110 comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switching device Q3, wherein the anode of the diode D1 is connected with the input end C of the constant current control circuit 110, and the cathode thereof is connected with the anode of the diode D2; the cathode of the diode D2 is grounded through the resistor R5; the first connection end of the switching device Q3 is connected with the input end C of the constant current control circuit 110 through the resistor R6, the control end thereof is connected with the cathode of the diode D2, and the second connection end thereof is connected with the output end D of the constant current control circuit 110.

[0025] When the LED lamp string LED1 is in the normal working state, the open short circuit detection circuit 120 controls the power supply switch Q1 to be turned on through the output end B thereof, so as to make the switching device Q3 be turned on and make the diode D1 and the diode D2 be forward biased, thereby the constant current control circuit 110 generates the constant current flowing through the resistor R6, the switching device Q3 and the LED lamp string LED1 in sequence;

[0026] When the LED string LED1 is in open circuit state, the open-short circuit detection circuit 120 controls the power supply switch Q1 to be turned on through its output end B, and the open-short circuit detection circuit 120 outputs high level through its detection end A, so as to make the switching device Q3 be turned off and make the diode D1 and the diode D2 be reversely biased, thereby the output end D of the constant current control circuit 110 has no current output, and the constant current control circuit 110 generates the first current which sequentially flows through the resistor R6, the first connection end and the control end of the switching device Q3, and the resistor R5 to the ground end.

[0027] In Figure 1 In the specific embodiment shown in the figure, the power supply switch Q1 is a PNP type triode, the first connection end, the second connection end and the control end of the power supply switch Q1 are the emitter, the collector and the base of the PNP type triode respectively; the switching device Q2 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q2 are the collector, the emitter and the base of the NPN type triode respectively; the switching device Q3 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP type triode respectively.

[0028] In Figure 1 In the specific embodiment shown in the figure, the resistance values of the resistor R1 and the resistor R2 are selected to satisfy: when the switching device Q2 is turned on, the voltage value of the voltage division on the resistor R1 is greater than the turn-on voltage threshold of the power supply switch Q1, so as to make the power supply switch Q1 be in the turn-on state; the resistance value of the resistor R5 is greater than the resistance value of the resistor R6.

[0029] The working principle of the LED constant current driving circuit with open-short circuit protection function shown in the figure will be specifically introduced as follows. Figure 1

[0030] 1、When the system is in normal working state, after the power supply is powered on, the power supply Vbat is divided by the resistor R3, the resistor R4 and the loop of the LED string LED1, the switching device Q2 is an NPN type triode, which can satisfy the turn-on condition of the switching device Q2, so the switching device Q2 is saturated and turned on, the collector of the switching device Q2 is pulled down to 0V, and after the power supply Vbat is divided by the resistor R1 and the resistor R2, the saturation turn-on condition of the PNP type triode Q1 is satisfied, so the power supply switch Q1 is turned on.

[0031] ​2. The constant current control circuit 110 consists of diodes D1 and D2, resistor R6, switching device Q3, and resistor R5. Because diodes D1 and D2 are connected in series, the voltage drop Vf of each diode is approximately 0.7V. Diodes D1 and D2 are connected in parallel with the BE terminals (i.e., the base and emitter of the transistor) of switching device Q3 and resistor R6. Therefore, the voltage Vbe across the BE terminals of switching device Q3 and the voltage across resistor R6 are clamped to: 2 * 0.7V = 1.4V. Since the PN junction of the transistor has a fixed voltage, Vbe = 0.7V. Thus, the voltage across resistor R6 is fixed at: VR6 = 1.4V - 0.7V = 0.7V. The current flowing through LED1 in the LED string is: 0.7V / R6. Because the resistance of resistor R6 is a fixed value, the current flowing through LED1 in the LED string is also a constant value regardless of changes in the external voltage. Thus, when an external power supply is connected, after the voltage is divided by diodes D1 and D2 and resistor R5 (at this time, diodes D1 and D2 are forward biased), PNP transistor Q3 will conduct, and the current of LED string LED1 will be a constant value. That is to say, when LED string LED1 is working normally, the open / short circuit detection circuit 120 controls the power supply switch Q1 to conduct through its output terminal B, so that switching device Q3 conducts and diodes D1 and D2 are forward biased, thereby the constant current control circuit 110 generates a constant current that flows sequentially through resistor R6, switching device Q3, and LED string LED1.

[0032] 3. When LED1 in the LED string is short-circuited, the input terminal (positive terminal) of LED1 will be pulled down to 0V. Because resistor R3 is connected to the base of switching device Q2 and the input terminal (positive terminal) of LED1, the base voltage of switching device Q2 is also 0V. Since switching device Q2 is an NPN transistor, it will be cut off (or turned off). The collector voltage of switching device Q2 will be raised to the same value as the power supply Vbat. Because power supply switch Q1 is a PNP transistor, and power supply Vbat is connected to the base of power supply switch Q1 and the collector of switching device Q2 through resistors R1 and R2, power supply switch Q1 will be turned off. Power supply Vbat cannot supply power to the downstream constant current control circuit 110 and LED1, thus protecting the downstream circuit from damage due to the short circuit of LED1.

[0033] 4、When the LED string LED1 is open circuit, because the collector of the PNP type triode Q3 is connected to the power supply Vbat through the resistor R4, at this time the collector voltage of the switching device Q3 is equal to the power supply Vbat voltage, after the PN junction voltage between the BE of the switching device Q3, the base voltage value of the triode Q3 is: Vbat-0.7V, because the diode D1 and D2 tube voltage drop Vf is about 0.7V, so the voltage value after the power supply Vbat through two diodes will be less than Vbat-0.7V, so the constant current control circuit 110 cannot work normally because of the reverse bias of the diode D1 and D2, and the current value through the resistor R6 is: (Vbat-0.7V) / (R6+R5), and the value of the resistor R5 is generally very large, so after calculation, it can be known that when the LED string LED1 is open circuit, the current value through the resistor R6 can be ignored, so the circuit will not be damaged because of the open circuit of the LED string LED1.

[0034] In summary, the LED constant current driving circuit with open short circuit protection function has the following beneficial effects:

[0035] 1、The circuit provided by the utility model has the advantages of simple circuit design, constant current driving of LED, and open short circuit protection of LED.

[0036] 2、The circuit is a pure hardware design scheme, the number of components used is small, and the design cost is greatly reduced.

[0037] 3、The utility model can reduce the current of the whole system to a very low value after the LED is open circuit, so as to avoid damage to other circuits due to excessive power consumption of the circuit.

[0038] 4、The utility model can directly cut off the power supply after the LED is short circuit, so as to protect the circuit from being damaged by the whole circuit due to the short circuit of the LED.

[0039] It should be pointed out that any modification made by the skilled person to the specific embodiment of the utility model does not deviate from the scope of the claims of the utility model. Accordingly, the scope of the claims of the utility model is not limited to the foregoing specific embodiments.

Claims

1. An LED constant current driving circuit with open short circuit protection function, characterized in that, It includes LED light string, constant current control circuit, power supply switch Q1 and open short circuit detection circuit, The first connection end of the power supply switch Q1 is connected with the power supply Vbat, and the second connection end is connected with the input end C of the constant current control circuit; The output end D of the constant current control circuit is connected with the input end of the LED light string, and the output end of the LED light string is grounded. When the power supply switch Q1 is turned on and the LED light string is in normal working state, the output end D of the constant current control circuit outputs constant current; when the power supply switch Q1 is turned on and the LED light string is in open circuit state, the output end D of the constant current control circuit outputs no current. The detection end A of the open short circuit detection circuit is connected with the input end of the LED light string, and the output end B is connected with the control end of the power supply switch Q1. The open short circuit detection circuit generates corresponding control signal by detecting whether the input end of the LED light string is low level, and the control signal is output through the output end B to control the power supply switch Q1 to be turned on or turned off. When the power supply switch Q1 is turned on and the LED light string is in open circuit state, the open short circuit detection circuit outputs high level through the detection end A to make the output end D of the constant current control circuit output no current.

2. The LED constant current driving circuit with open short circuit protection function according to claim 1, wherein When it is detected that the input end of the LED light string is low level, the control signal output by the output end B of the open short circuit detection circuit is first logic level to control the power supply switch Q1 to be turned off; When it is not detected that the input end of the LED light string is low level, the control signal output by the output end B of the short circuit detection circuit is second logic level to control the power supply switch Q1 to be turned on; When the power supply switch Q1 is turned on and the LED light string is in open circuit state, the open short circuit detection circuit outputs high level through the detection end A to make the constant current control circuit generate first current from the input end C to the ground end, and the first current is smaller than the constant current output by the output end D of the constant current control circuit.

3. The LED constant current driving circuit with open short circuit protection function according to claim 2, wherein The open short circuit detection circuit includes resistance R1, resistance R2, resistance R3, resistance R4 and switch Q2, One end of the resistance R1 is connected with the first connection end of the power supply switch Q1, and the other end is connected with the output end B of the open short circuit detection circuit. The first connection end of the switch Q2 is connected with the output end B of the open short circuit detection circuit through the resistance R2, the second connection end is grounded, and the control end is connected with the detection end A of the open short circuit detection circuit through the resistance R3. One end of the resistance R4 is connected with the power supply Vbat, and the other end is connected with the detection end A of the open short circuit detection circuit.

4. The LED constant current driving circuit with open short circuit protection function according to claim 3, wherein When the input end of the LED lamp string is detected as low, the switch device Q2 is turned off, so that the output end B of the open-short circuit detection circuit controls the power supply switch Q1 to be turned off; When the input end of the LED lamp string is not detected as low, the switch device Q2 is turned on, so that the output end B of the open-short circuit detection circuit controls the power supply switch Q1 to be turned on; When the power supply switch Q1 is turned on and the LED lamp string is in an open circuit state, the voltage value of the high level output by the detection end A of the open-short circuit detection circuit is equal to the voltage value of the power supply Vbat.

5. The LED constant current driving circuit with open-short circuit protection function according to claim 4, characterized in that, the constant current control circuit comprises a diode D1, a diode D2, a resistor R5, a resistor R6 and a switch device Q3, the anode of the diode D1 is connected with the input end C of the constant current control circuit, and the cathode thereof is connected with the anode of the diode D2; the cathode of the diode D2 is grounded through the resistor R5; the first connection end of the switch device Q3 is connected with the input end C of the constant current control circuit through the resistor R6, the control end thereof is connected with the cathode of the diode D2, and the second connection end thereof is connected with the output end D of the constant current control circuit.

6. The LED constant current driving circuit with open-short circuit protection function according to claim 5, characterized in that, when the LED lamp string is in a normal working state, the open-short circuit detection circuit controls the power supply switch Q1 to be turned on through the output end B thereof, so that the switch device Q3 is turned on and the diodes D1 and D2 are forward biased, thereby the constant current control circuit generates the constant current flowing through the resistor R6, the switch device Q3 and the LED lamp string in sequence; when the LED lamp string is in an open circuit state, the open-short circuit detection circuit controls the power supply switch Q1 to be turned on through the output end B thereof, and the open-short circuit detection circuit outputs a high level through the detection end A thereof, so that the switch device Q3 is turned off and the diodes D1 and D2 are reverse biased, thereby the output end D of the constant current control circuit has no current output, and the constant current control circuit generates a first current flowing through the resistor R6, the first connection end and the control end of the switch device Q3, and the resistor R5 to the ground end in sequence.

7. The LED constant current driving circuit with open-short circuit protection function according to claim 5, characterized in that, the power supply switch Q1 is a PNP type triode, and the first connection end, the second connection end and the control end of the power supply switch Q1 are the emitter, the collector and the base of the PNP type triode respectively; the switch device Q2 is an NPN type triode, and the first connection end, the second connection end and the control end of the switch device Q2 are the collector, the emitter and the base of the NPN type triode respectively; the switch device Q3 is a PNP type triode, and the first connection end, the second connection end and the control end of the switch device Q3 are the emitter, the collector and the base of the PNP type triode respectively.

8. The LED constant current driving circuit with open short circuit protection function according to claim 5, characterized in that, the resistance values of the resistors R1 and R2 are selected to satisfy that when the switch device Q2 is turned on, the voltage value of the voltage division on the resistor R1 is greater than the turn-on voltage threshold of the power supply switch Q1, so that the power supply switch Q1 is in the turn-on state; the resistance value of the resistor R5 is greater than the resistance value of the resistor R6.

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