LED constant-current driving circuit with fault diagnosis and protection functions

Abstract

The utility model provides an LED constant current drive circuit with fault diagnosis and protection functions, an input end of a voltage conversion circuit is connected with a power supply end, and an output end of the voltage conversion circuit outputs a reference voltage; the power supply end of the reference constant-current source circuit is connected with the output end of the voltage conversion circuit, the constant-current input end of the reference constant-current source circuit is connected with the cathode of the LED, the constant-current output end of the reference constant-current source circuit is connected with the node D, and the anode of the LED is connected with the power supply end; one end of a resistor R2 is connected with the output end of the voltage conversion circuit, and the other end of the resistor R2 is connected with a node D; the first connecting end of the switching device Q4 is connected with the node D, and the second connecting end is grounded; the first detection end of the load diagnosis unit is connected with the positive electrode of the LED, the second detection end is connected with the negative electrode of the LED, and the output end is connected with the control end of the switching device Q4. Compared with the prior art, the load fault of the whole circuit is automatically diagnosed, triggered and closed by hardware, and does not depend on chip judgment.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially a kind of LED constant current drive circuit with diagnostic fault and protection function. BACKGROUND

[0002] Prior art scheme realizes the constant current control of LED by the constant current drive chip of step-down, and the pulse width of PWM (Pulse Width Modulation, i.e. pulse width modulation) signal is adjusted to stabilize the load current of LED, please refer to Figure 1 It is the function block diagram of a kind of constant current drive chip of step-down in prior art, and the topology of DCDC (DC-to-DC converter, i.e. direct current-direct current converter) is used to be reformed into constant current drive scheme, and inductance needs to be switched by switching, which can cause chip heating and EMC (Electromagnetic Compatibility, i.e. electromagnetic compatibility) problem.

[0003] Therefore, it is necessary to propose a new technical scheme to solve the above problems. UTILIT Y MODEL CONTENTS

[0004] One of the purposes of the utility model is to provide a kind of LED constant current drive circuit with diagnostic fault and protection function, and the whole circuit load fault is triggered to close by hardware automatic diagnosis, not dependent on chip judgment.In addition, the topology structure of DCDC is avoided in the whole circuit, the same LED constant current function is realized, and the EMC radiation to the outside is reduced.

[0005] According to one aspect of the utility model, the utility model provides a kind of LED constant current drive circuit with diagnostic fault and protection function, which includes LED, voltage conversion circuit, reference constant current source circuit and load diagnosis circuit, the input end of the voltage conversion circuit is connected with power supply terminal Vbat, and its output end outputs reference voltage Vbg, the reference voltage Vbg is generated based on the voltage of the power supply terminal Vbat by the voltage conversion circuit;The power supply end A of the reference constant current source circuit is connected with the output end of the voltage conversion circuit, the constant current input end B thereof is connected with the negative pole of the LED, and the constant current output end C thereof is connected with node D, and the positive pole of the LED is connected with the power supply terminal Vbat;Load diagnosis circuit includes resistance R2, switching device Q4 and load diagnosis unit, one end of the resistance R2 is connected with the output end of the voltage conversion circuit, and the other end thereof is connected with the node D;The first connecting end of the switching device Q4 is connected with the node D, and its second connecting end is grounded;The first detection end of the load diagnosis unit is connected with the positive pole of the LED, the second detection end thereof is connected with the negative pole of the LED, and the output end thereof is connected with the control end of the switching device Q4.

[0006] Compared with the prior art, the whole circuit load fault of the utility model adopts hardware automatic diagnosis trigger closing, which is not dependent on chip judgment. In addition, the whole circuit avoids using the topology structure of DCDC, realizes the same LED constant current function, and reduces the EMC radiation to the outside. BRIEF DESCRIPTION OF DRAWINGS

[0007] In order to more clearly illustrate the technical scheme of the embodiments of the utility model, the following will briefly introduce the drawings needed to be used in the embodiment description, obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can also be obtained according to these drawings without creating labor intensity. Wherein:

[0008] Figure 1 It is a functional block diagram of a buck constant current drive chip in the prior art;

[0009] Figure 2 It is a circuit schematic diagram of the LED constant current drive circuit with diagnostic fault and protection function in one embodiment of the utility model. DETAILED DESCRIPTION

[0010] In order to make the above purpose, features and advantages of the utility model more apparent and easy to understand, the following will make further detailed description to the utility model by combining with the drawings and specific embodiments.

[0011] The "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the utility model. The "in one embodiment" appearing in different places in the specification is not all referring to the same embodiment, and is not a separate or selective embodiment mutually exclusive with other embodiments. Unless specifically stated, the words of coupling, connection, connection, connection in this paper mean that the electrically connected words are directly or indirectly connected, such as A and B are connected, which includes that A and B are directly electrically connected, and A is connected with B through electric components or circuit.

[0012] In the description of the utility model, it is understood that the orientation or position relationship indicated by the terms "upper", "lower", "front", "rear", "positive", "back", "left", "right", "vertical", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the utility model and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation to the utility model.

[0013] Please refer to Figure 2As shown, it is the circuit schematic of the LED constant current driving circuit with diagnostic fault and protection function in one embodiment of the utility model. Figure 2 The LED constant current driving circuit with diagnostic fault and protection function shown comprises LED1, voltage conversion circuit 210, reference constant current source circuit 220 and load diagnostic circuit 230.

[0014] The input end of voltage conversion circuit 210 is connected with power supply end Vbat, and the output end thereof outputs reference voltage Vbg, which is generated by voltage conversion circuit 210 based on the voltage of power supply end Vbat.

[0015] The power supply end A of reference constant current source circuit 220 is connected with the output end of voltage conversion circuit 210, the constant current input end B thereof is connected with the negative pole of LED1, the constant current output end C thereof is connected with node D, and the positive pole of LED1 is connected with power supply end Vbat. Load diagnostic circuit 230 comprises resistance R2, switching device Q4 and load diagnostic unit 232. One end of resistance R2 is connected with the output end of voltage conversion circuit 210, and the other end thereof is connected with node D (or constant current output end C). The first connection end of switching device Q4 is connected with node D (or constant current output end C), and the second connection end thereof is grounded. The first detection end of load diagnostic unit 232 is connected with the positive pole of LED1, the second detection end thereof is connected with the negative pole of LED1, and the output end thereof is connected with the control end of switching device Q4.

[0016] Load diagnostic unit 232 controls switching device Q4 to be turned on or turned off by detecting whether LED1 works normally, so as to control whether reference constant current source circuit 220 works. When load diagnostic unit 232 detects that LED1 works normally, the output end of load diagnostic unit 232 outputs the first logic level of control signal, switching device Q4 is turned on, and reference constant current source circuit 220 works to generate constant current from constant current input end B to constant current output end C. When load diagnostic unit 232 detects that LED1 is open-circuited, the output end of load diagnostic unit 232 outputs the first logic level of control signal, switching device Q4 is turned on, and reference constant current source circuit 220 does not work. When load diagnostic unit 232 detects that LED1 is short-circuited, the output end of load diagnostic unit 232 outputs the second logic level of control signal, switching device Q4 is turned off, and reference constant current source circuit 220 does not work.

[0017] In Figure 2In the shown embodiment, the load diagnosis unit 232 comprises a diode D2, a switching device Q1, a switching device Q9, a resistor R1, a resistor R5, a resistor R7, a resistor R20, a resistor R21 and a resistor R22. Among them, the positive electrode of the diode D2 is connected with the positive electrode of the LED1, and the negative electrode is connected with the first connection end of the switching device Q9; one end of the resistor R20 is connected with the second connection end of the switching device Q9, and the other end is grounded; one end of the resistor R7 is connected with the second connection end of the switching device Q9, and the other end is connected with the output end of the load diagnosis unit 232; one end of the resistor R5 is connected with the output end of the load diagnosis unit 232, and the other end is grounded; the first connection end of the switching device Q1 is connected with the negative electrode of the LED1, the control end is connected with the first connection end through the resistor R1, and the second connection end is connected with the control end of the switching device Q9 through the resistor R21; one end of the resistor R22 is connected with the second connection end of the switching device Q1, and the other end is grounded. Among them, the diode D2 provides a PN junction voltage difference.

[0018] When the LED1 works normally, the switching device Q1 is off, the switching device Q9 is on, and the output end of the load diagnosis unit 232 outputs a high level (which can be called the first logic level of the control signal), so as to make the switching device Q4 conduct; when the LED1 is open circuit, the switching device Q1 is off, the switching device Q9 is on, and the output end of the load diagnosis unit 232 outputs a high level (which can be called the first logic level of the control signal), so as to make the switching device Q4 conduct; when the LED1 is short circuit, the switching device Q1 is on, the switching device Q9 is off, and the output end of the load diagnosis unit 232 outputs a low level (which can be called the second logic level of the control signal), so as to make the switching device Q4 off.

[0019] In Figure 2 In the shown specific embodiment, the switching device Q1 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q1 are the drain, the source and the gate of the NPN type triode respectively;

[0020] The switching device Q4 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q4 are the drain, the source and the gate of the NPN type triode respectively; the switching device Q9 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q9 are the source, the drain and the gate of the PNP type triode respectively; the forward conduction voltage drop of the LED1 is greater than the PN junction voltage drop of the diode D2.

[0021] The reference constant current source circuit 220 comprises resistors R17, R18, R19, NPN transistor Q7 and NPN transistor Q8. The first connection end of the NPN transistor Q8 is connected to the power supply end A of the reference constant current source circuit 220 via the resistor R17, the control end thereof is connected to the first connection end thereof, and the second connection end thereof is grounded via the resistor R18. The first connection end of the NPN transistor Q7 is connected to the constant current input end B of the reference constant current source circuit 220, the control end thereof is connected to the control end of the NPN transistor Q8, and the second connection end thereof is connected to the constant current output end C of the reference constant current source circuit 220 via the resistor R19. The NPN transistor Q7 and the NPN transistor Q8 constitute a current mirror, and the NPN transistor Q7 is used to mirror the current flowing through the NPN transistor Q8.

[0022] When the LED 1 is normally working, the switching device Q4 is turned on, the NPN transistor Q7 is turned on, and thus the reference constant current source circuit 220 works. When the LED 1 is open-circuited, the switching device Q4 is turned on, the NPN transistor Q7 is turned off, and thus the reference constant current source circuit 220 does not work. When the LED 1 is short-circuited, the switching device Q4 is turned off, the NPN transistor Q7 is turned off, and thus the reference constant current source circuit 220 does not work.

[0023] The voltage conversion circuit 210 comprises resistors R10, R11, R13, R14, R16, a voltage stabilizing tube D3, an NPN transistor Q5 and an NPN transistor Q6. The first connection end of the NPN transistor Q5 is connected to the power supply end Vbat, the second connection end thereof is connected to the output end of the voltage conversion circuit 210, and the control end thereof is connected to the first connection end of the NPN transistor Q6 via the resistor R10. The second connection end of the NPN transistor Q6 is connected to the negative electrode of the voltage stabilizing tube D3, and the positive electrode of the voltage stabilizing tube D3 is grounded. One end of the resistor R13 is connected to the output end of the voltage conversion circuit 210, and the other end thereof is connected to the control end of the NPN transistor Q6. One end of the resistor R14 is connected to the control end of the NPN transistor Q6, and the other end thereof is grounded. One end of the resistor R16 is connected to the first connection end of the NPN transistor Q5, and the other end thereof is connected to the control end of the NPN transistor Q5. One end of the resistor R11 is connected to the first connection end of the NPN transistor Q5, and the other end thereof is connected to the second connection end of the NPN transistor Q6. The voltage stabilizing tube D3 is used to provide a stable voltage. The voltage conversion circuit 210 is used to provide a reference voltage input for the reference constant current source circuit 220 and to provide an upper pull power supply for the load diagnosis circuit 230.

[0024] Figure 2The LED constant current driving circuit with diagnostic fault and protection function shown further comprises a power supply circuit 240, which comprises a power supply V2, a switch S2 and a capacitor C1. One end of the switch S2 is connected with the power supply V2, and the other end is connected with a power supply end Vbat. One end of the capacitor C1 is connected with the power supply end Vbat, and the other end is grounded. The capacitor C1 is used for filtering the power supply end Vbat. The power supply V2 can be a stable power supply 24V. The switch S2 is used for simulating power-on and power-off of the power supply. The LED1 can be an actual single white LED (or white load).

[0025] The working principle of the LED constant current driving circuit with diagnostic fault and protection function shown will be specifically introduced below. Figure 2 The working principle of the LED constant current driving circuit with diagnostic fault and protection function shown will be specifically introduced below.

[0026] Parameter definition

[0027] 1. The voltage at the node of the resistors R13 and R14 is Vr13_r14

[0028] 2. The voltage at the node of the resistors R7 and R20 is Vr7_r20

[0029] 3. The zener voltage of the zener diode D3 is Vd3_zener

[0030] 4. The PN junction voltage of the diode D2 is Vd2_pn

[0031] 5. The voltage of the LED1 is Vled

[0032] 6. The PN junction voltage of the transistor Q6 is Vq6_pn

[0033] 7. The base current of the transistor Q6 is iq6_b

[0034] 8. The collector current of the transistor Q6 is iq6_c

[0035] 9. The amplification factor of the transistor Q6 is β6

[0036] 10. The emitter voltage of the transistor Q5 is Vq5_e

[0037] 11. The PN junction voltage of the transistor Q5 is Vq5_pn

[0038] 12. The base voltage of the transistor Q5 is Vq5_b

[0039] 13. The base current of the transistor Q5 is iq5_b

[0040] 14. The PN junction voltage of the transistor Q1 is Vq1_pn

[0041] 15. The PN junction voltage of the transistor Q9 is Vq9_pn

[0042] 16. The base current of the transistor Q9 is iq9_b

[0043] 17. The amplification of the transistor Q9 is β9

[0044] 18. The collector current of the transistor Q9 is iq9_c

[0045] 19. The saturation voltage of the transistor Q9 is Vq9sat_ce

[0046] 20. The base current of the transistor Q4 is iq4_b

[0047] 21. The collector current of the transistor Q4 is iq4_c

[0048] 22. The PN junction voltage of the transistor Q4 is Vq4_pn

[0049] 23. The saturation voltage of the transistor Q4 is Vq4sat_ce

[0050] 24. The amplification of the transistor Q4 is β4

[0051] 25. The PN junction voltage of the transistor Q8 is Vq8_pn

[0052] 26. The collector current of the transistor Q8 is iq8_c

[0053] 27. The collector current of the transistor Q7 is iq7_c

[0054] When the switch S2 is closed, the stable voltage is given to simulate the upstream product, and the LED1 works normally. The principle analysis is as follows:

[0055] 1. The power supply (or stable power supply) V2 passes through the resistor R11 and the zener diode D3 to make the zener diode D3 obtain the starting working current, id3≈(V2-Vd3_zener) / R11;

[0056] 2. The voltage at the node of the resistor R13 and R14 is Vr13_r14≈Vd3_zener+Vq6_pn, then the emitter voltage of the transistor Q5 is Vq5_e, Vq5_e≈((R13+R14) / R14)*Vr13_r14;

[0057] 3. The base current of Q6 i6_b≈((Vq5_e-Vr13_r14) / R13)-Vr13_r14 / R14, iq6_c≈i6_b*β6, which is the maximum current flowing through the transistor Q6; the base voltage of Q5 Vq5_b≈Vq5_e-Vq5_pn, then the maximum base current of Q5 i5_b_max≈iq6_c-(V2-Vq5_b) / R16, by the above analysis, the resistance values of R13, R14, R10, R16 can control the base current of Q5, so as to control the driving ability of the collector current of Q5;

[0058] 4. Vq5_e is used as a voltage reference source for the reference constant current source circuit 220, and also as a pull-up source for the resistance R2. Vq5_e passes through the resistance R2 to the emitter of the transistor Q7, so that the pn junction of the transistor Q7 is reverse-biased and cut off (or turned off);

[0059] 5. The power supply V2 passes through the diode D2 to the pn junction of the transistor Q9, the resistance R21, and the resistance R22 to form a path 1, and another path is formed by the power supply V2 passing through the LED1, the resistance R1, the pn junction of the transistor Q1, and the resistance R22 to form a path 2. Since Vled>Vd2_pn, (V2-Vled-Vq1_pn)<(V2-Vd2_pn-Vq9_pn), which causes the transistor Q1 in the path 2 to be cut off (or turned off), i.e., only the path 1 works, the transistor Q9 is turned on, and the base current iq9_b≈(V2-Vd2_pn-Vq9_pn) / (R21+R22) flows through the transistor Q9. Assuming that the transistor Q9 is saturated and turned on, then iq9_c≈(V2-Vd2_pn-Vq9sat_ce-Vq4_pn) / R7+(V2-Vd2_pn-Vq9sat_ce) / R20. By analyzing iq9_b*β9>iq9_c, the assumption is true, the transistor Q9 is saturated and turned on, which makes the transistor Q4 conduct, iq4_b≈(V2-Vd2_pn-Vq9sat_ce-Vq4_pn) / R7-Vq4_pn / R5. Assuming that the transistor Q4 is saturated and turned on, then iq4_c≈(Vq5_e-Vq4sat_ce) / R2+(Vq5_e-Vq8_pn-Vq4sat_ce) / (R17+R19)*β7. By analyzing iq4_b*β4>iq4_c, the assumption is true, the transistor Q4 is saturated and turned on;

[0060] 6. Due to the saturation conduction of the triode Q4, the triode Q7 will also enter the conduction state from the analysis of the cut-off state of step 4 above, the LED1 works normally, the working current is limited by the triode Q8, iq7_c≈(R18 / R19)*iq8_c, iq8_c≈(Vq5_e-Vq8_pn) / (R17+R18), by analyzing the proportion of the adjusting resistors R18 and R19, the current proportion flowing through the LED1 can be controlled, by the values of the resistors R17 and R18, the current flowing through the triode Q8 can be controlled, and then the current of the LED1 is controlled;

[0061] ■The switch S2 is closed to simulate the upstream product to give a stable voltage, and the LED1 works abnormally. The principle analysis is as follows:

[0062] LED1 open circuit state

[0063] 1. The power supply V2 passes through the diode D2 to the pn junction of the triode Q9, the resistor R21, and the resistor R22. Since the LED1 is open, the triode Q1 is cut off (or turned off), that is, only the triode Q9 is turned on, and the base current flowing through the triode Q9 is iq9_b≈(V2-Vd2_pn-Vq9_pn) / (R21+R22). Assuming that the triode Q9 is saturated and turned on, then iq9_c≈(V2-Vd2_pn-Vq9sat_ce-Vq4_pn) / R7+(V2-Vd2_pn-Vq9sat_ce) / R20. By analyzing iq9_b*β9>iq9_c, the assumption is true, Q9 is saturated and turned on, so that the triode Q4 is turned on, iq4_b≈(V2-Vd2_pn-Vq9sat_ce-Vq4_pn) / R7-Vq4_pn / R5, and assuming Q4 is saturated and turned on, then iq4_c≈(Vq5_e-Vq4sat_ce) / R2+(Vq5_e-Vq8_pn-Vq4sat_ce) / (R17+R19)*β7. By analyzing iq4_b*β4>iq4_c, the assumption is true, and the triode Q4 is saturated and turned on;

[0064] 2. Then there will be current flowing through the resistor R2, the triode Q4, and into the ground. The triode Q7 has no loop due to the open circuit of the LED1, and the triode Q7 does not work (or is turned off). The triode Q8 will have a certain current iq8_c≈(Vq5_e-Vq8_pn) / (R17+R18), but will not cause other circuit abnormal work, and will not damage the product itself;

[0065] LED1 short circuit state

[0066] 1. The power supply V2 passes through the pn junction of the diode D2, the resistor R21, and the resistor R22 to form path 1. The other path is that the power supply V2 passes through the resistor R1, the pn junction of the transistor Q1, and the resistor R22 to form path 2. Since LED1 is short-circuited, then (V2 - Vq1_pn) > (V2 - Vd2_pn - Vq9_pn), which causes the transistor Q9 in path 1 to be cut off (or turned off). That is, only path 2 works and the transistor Q1 is turned on.

[0067] 2. From the analysis in 1, when the transistor Q9 is cut off, the voltage at the node of the resistors R7 and R20 is Vr7_r20 ≈ 0V. Then Vr7_r20 < Vq4_pn, which causes the transistor Q4 to enter the cut-off state. The collector voltage of the transistor Q4 is Vq5_e, which causes the transistor Q7 to enter the cut-off state because the pn junction is reverse-biased. The transistor Q7 does not work (or is turned off), and no continuous power consumption exists on the collector and emitter of the transistor Q7, thus avoiding heat problems.

[0068] Through the above comprehensive analysis, in the normal working state, LED1 can work within the set constant current range, and when the circuit is abnormal, no additional heat is generated in the power path continuously.

[0069] In summary, the LED constant current drive circuit with fault diagnosis and protection functions provided by the present utility model has the following beneficial effects:

[0070] 1. For the entire circuit load fault of the present utility model, hardware automatic diagnosis and trigger shutdown are adopted, without relying on chip judgment.

[0071] 2. The entire circuit of the present utility model avoids using the DCDC topology structure, realizes the same LED constant current function, and reduces the external EMC radiation.

[0072] It should be noted that any modification made by those skilled in the art to the specific implementation manner of the present utility model does not depart from the scope of the claims of the present utility model. Correspondingly, the scope of the claims of the present utility model is not limited solely to the foregoing specific implementation manner.

Claims

1. An LED constant current driving circuit with a diagnostic fault and protection function, characterized in that, It includes LED, voltage conversion circuit, reference constant current source circuit and load diagnosis circuit, The input end of the voltage conversion circuit is connected with the power supply end Vbat, and the output end outputs reference voltage Vbg which is generated by the voltage conversion circuit based on the voltage of the power supply end Vbat; The power supply end A of the reference constant current source circuit is connected with the output end of the voltage conversion circuit, the constant current input end B is connected with the negative electrode of the LED, and the constant current output end C is connected with node D, and the positive electrode of the LED is connected with the power supply end Vbat; The load diagnosis circuit includes resistance R2, switching device Q4 and load diagnosis unit, one end of the resistance R2 is connected with the output end of the voltage conversion circuit, and the other end is connected with the node D; the first connection end of the switching device Q4 is connected with the node D, and the second connection end is grounded; the first detection end of the load diagnosis unit is connected with the positive electrode of the LED, the second detection end is connected with the negative electrode of the LED, and the output end is connected with the control end of the switching device Q4.

2. The LED constant current driving circuit with diagnosis fault and protection function according to claim 1, wherein, when the load diagnosis unit detects that the LED works normally, the output end of the load diagnosis unit outputs the first logic level of the control signal, the switching device Q4 is turned on, and the reference constant current source circuit generates constant current from the constant current input end B to the constant current output end C; when the load diagnosis unit detects that the LED is open circuit, the output end of the load diagnosis unit outputs the first logic level of the control signal, the switching device Q4 is turned on, and the reference constant current source circuit does not work; when the load diagnosis unit detects that the LED is short circuit, the output end of the load diagnosis unit outputs the second logic level of the control signal, the switching device Q4 is turned off, and the reference constant current source circuit does not work.

3. The LED constant current driving circuit with diagnosis fault and protection function according to claim 2, wherein, the load diagnosis unit includes diode D2, switching device Q1, switching device Q9, resistance R1, resistance R5, resistance R7, resistance R20, resistance R21 and resistance R22, the positive electrode of the diode D2 is connected with the positive electrode of the LED, and the negative electrode is connected with the first connection end of the switching device Q9; one end of the resistance R20 is connected with the second connection end of the switching device Q9, and the other end is grounded; one end of the resistance R7 is connected with the second connection end of the switching device Q9, and the other end is connected with the output end of the load diagnosis unit; one end of the resistance R5 is connected with the output end of the load diagnosis unit, and the other end is grounded; the first connection end of the switching device Q1 is connected with the negative electrode of the LED, the control end is connected with the first connection end through the resistance R1, and the second connection end is connected with the control end of the switching device Q9 through the resistance R21; one end of the resistance R22 is connected with the second connection end of the switching device Q1, and the other end is grounded.

4. The LED constant current drive circuit with diagnostic fault and protection function according to claim 3, wherein when the LED works normally, the switch device Q1 is off, the switch device Q9 is on, and the switch device Q4 is on; when the LED is open circuit, the switch device Q1 is off, the switch device Q9 is on, and the switch device Q4 is on; when the LED is short circuit, the switch device Q1 is on, the switch device Q9 is off, and the switch device Q4 is off.

5. The LED constant current drive circuit with diagnostic fault and protection function according to claim 4, wherein the switch device Q1 is an NPN type triode, the first connection end, the second connection end and the control end of the switch device Q1 are the drain, the source and the gate of the NPN type triode respectively; the switch device Q4 is an NPN type triode, the first connection end, the second connection end and the control end of the switch device Q4 are the drain, the source and the gate of the NPN type triode respectively; the switch device Q9 is a PNP type triode, the first connection end, the second connection end and the control end of the switch device Q9 are the source, the drain and the gate of the PNP type triode respectively; and the forward on voltage drop of the LED is greater than the PN junction voltage drop of the diode D2.

6. The LED constant current drive circuit with diagnostic fault and protection function according to claim 1, wherein the reference constant current source circuit comprises a resistance R17, a resistance R18, a resistance R19, an NPN type triode Q7 and an NPN type triode Q8, the first connection end of the NPN type triode Q8 is connected to the power supply end A of the reference constant current source circuit through the resistance R17, the control end is connected to the first connection end, and the second connection end is grounded through the resistance R18; the first connection end of the NPN type triode Q7 is connected to the constant current input end B of the reference constant current source circuit, the control end is connected to the control end of the NPN type triode Q8, and the second connection end is connected to the constant current output end C of the reference constant current source circuit through the resistance R19.

7. The LED constant current drive circuit with diagnostic fault and protection function according to claim 6, wherein when the LED works normally, the switch device Q4 is on, and the NPN type triode Q7 is on; when the LED is open circuit, the switch device Q4 is on, and the NPN type triode Q7 is off; and when the LED is short circuit, the switch device Q4 is off, and the NPN type triode Q7 is off.

8. The LED constant current drive circuit with diagnostic fault and protection function according to any one of claims 1-7, wherein the voltage conversion circuit comprises a resistance R10, a resistance R11, a resistance R13, a resistance R14, a resistance R16, a voltage stabilizing tube D3, an NPN type triode Q5 and an NPN type triode Q6, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first connecting end of the NPN type triode Q5 is connected with the power supply end Vbat, the second connecting end is connected with the output end of the voltage conversion circuit, and the control end is connected with the first connecting end of the NPN type triode Q6 through the resistor R10; the second connecting end of the NPN type triode Q6 is connected with the negative electrode of the stabilizing tube D3, and the positive electrode of the stabilizing tube D3 is grounded; one end of the resistor R13 is connected with the output end of the voltage conversion circuit, and the other end is connected with the control end of the NPN type triode Q6; one end of the resistor R14 is connected with the control end of the NPN type triode Q6, and the other end is grounded; one end of the resistor R16 is connected with the first connecting end of the NPN type triode Q5, and the other end is connected with the control end of the NPN type triode Q5; one end of the resistor R11 is connected with the first connecting end of the NPN type triode Q5, and the other end is connected with the second connecting end of the NPN type triode Q6.

9. The LED constant current driving circuit with diagnostic fault and protection function according to claim 1, characterized in that, It also comprises a power supply circuit, The power supply circuit comprises a power supply V2, a switch S2 and a capacitor C1, one end of the switch S2 is connected with the power supply V2, and the other end is connected with the power supply end Vbat; one end of the capacitor C1 is connected with the power supply end Vbat, and the other end is grounded.

10. The LED constant current driving circuit with diagnostic fault and protection function according to claim 1, characterized in that, The LED is a single white light LED.

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