Low-voltage power-off load impedance abnormity detection circuit for LED dimming

Abstract

The low-voltage power-off load impedance abnormity detection circuit comprises an LED constant-voltage dimming power supply, the output positive electrode of the LED constant-voltage dimming power supply is electrically connected with an LED light source through a relay, and the output positive electrode of the LED constant-voltage dimming power supply serves as output voltage and is electrically connected with the positive input end of a first operational amplifier comparator at the same time; the negative input end of the first operational amplifier comparator is connected with a low-voltage reference voltage, the output negative electrode of the LED constant-voltage dimming power supply is electrically connected with the negative electrode of a direct-current power supply, and the positive electrode of the direct-current power supply and the output end of the first operational amplifier comparator are electrically connected with a relay through an NMOS1. And the first operational amplifier comparator is used for comparing the output voltage with the low-voltage reference voltage and then outputting high and low levels to drive the NMOS1 to be switched on or switched off so as to control the on-off of the relay. According to the utility model, through power-off protection and load abnormity detection between the dimming power supply and the LED light source, power supply output and power supply of the LED light source are cut off when the dimming brightness is 0, so that the fire risk is reduced.

Description

Technical Field

[0001] The utility model relates to an LED dimming circuit, in particular to a low-voltage power-off load impedance abnormality detection circuit used for LED dimming. Background Art

[0002] In livestock and poultry farming lighting systems, traditional LED dimming products usually achieve dimming by controlling the output current or output voltage of the power supply. When the brightness of the lamp is 0, although the LED light source has been extinguished, the lamp is generally still in standby mode, and there is still a certain voltage at both ends of the LED light source. The light source used for farming is generally a 48V LED lamp tube, which works in the breeding house for a long time. Due to the humid environment in the breeding house and the high ammonia concentration, it is easy to cause corrosion of the internal circuit of the LED lamp tube and reduce the impedance. When the line impedance is reduced, the current in the circuit will increase, which may eventually cause the lamp tube to catch fire, causing huge losses to production. For this reason, it is necessary to disconnect the power supply of the LED light source when the brightness of the lamp is 0. Utility Model Content

[0003] In order to solve the above technical problems, the purpose of the utility model is to provide a low-voltage power-off load impedance abnormality detection circuit for LED dimming, which can disconnect the power output and the LED light source power supply when the brightness of the constant voltage LED dimming lamp is 0, so as to reduce the fire risk of the LED light source.

[0004] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0005] A low-voltage power-off load impedance anomaly detection circuit for LED dimming, characterized in that it includes an LED constant-voltage dimming power supply, an LED light source, a first operational amplifier comparator and a DC power supply, wherein the LED constant-voltage dimming power supply is used to power and dim the LED light source, the output positive pole of the LED constant-voltage dimming power supply is electrically connected to the LED light source through a relay, the output positive pole of the LED constant-voltage dimming power supply is also electrically connected to the positive input terminal of the first operational amplifier comparator as an output voltage, the negative input terminal of the first operational amplifier comparator is connected to a low-voltage reference voltage, the output negative pole of the LED constant-voltage dimming power supply is electrically connected to the negative pole of the DC power supply, the positive pole of the DC power supply and the output terminal of the first operational amplifier comparator are electrically connected to the relay through NMOS1, and the first operational amplifier comparator is used to compare the output voltage with the low-voltage reference voltage and then output a high or low level to drive the NMOS1 to turn on or off to control the on and off of the relay.

[0006] Furthermore, it also includes a second operational amplifier comparator and an impedance reference voltage, the output end of the impedance reference voltage is connected to the positive input end of the second operational amplifier comparator, the LED light source is electrically connected to the second operational amplifier comparator, the terminal voltage of the LED light source is input to the negative input end of the second operational amplifier comparator, and the output end of the second operational amplifier comparator is electrically connected to the positive input end of the first operational amplifier comparator through NMOS2; the second operational amplifier comparator is used to compare the impedance reference voltage with the terminal voltage of the negative input end and then output a high or low level to drive the NMOS2 to be cut off or turned on.

[0007] Furthermore, it also includes a first indicator light for indicating the working status of the relay and a second indicator light for indicating abnormal load impedance, the first indicator light is connected in series between the output end of the first operational amplifier comparator and the negative electrode of the DC power supply, and the second indicator light is connected in series between the output end of the second operational amplifier comparator and the negative electrode of the DC power supply.

[0008] Furthermore, a current limiting resistor and a diode are connected in series between the DC power supply and the LED light source in sequence.

[0009] Furthermore, both NMOS1 and NMOS2 are triodes or field effect transistors.

[0010] Furthermore, a fuse is connected between the cathode of the LED light source and the cathode of the DC power supply.

[0011] The utility model adopts the above technical solution, which has the following advantages and effects:

[0012] (1) The utility model provides a low-voltage power-off load impedance abnormality detection circuit for LED dimming, which is used for power-off protection and load abnormality detection between an LED constant-voltage dimming power supply and an LED light source. The output voltage of the LED constant-voltage dimming power supply is compared with a low-voltage reference voltage through a first operational amplifier comparator. When the dimming brightness is 0, the output voltage is lower than the low-voltage reference voltage, so that the first operational amplifier comparator outputs a low level to control the power output of the LED constant-voltage dimming power supply and disconnect the LED light source, thereby reducing the risk of fire.

[0013] (2) The utility model can also detect the equivalent impedance of the LED light source load to check whether there is a potential fault in the LED light source when the power output of the LED constant voltage dimming power supply and the power supply of the LED light source are disconnected. If it is detected that the equivalent impedance of the LED light source is reduced, the circuit will maintain the state where the power output and the power supply of the LED light source are disconnected, and the impedance abnormality alarm indicator light will be turned on to prompt the maintenance personnel to check and maintain the LED light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a circuit principle block diagram of the utility model.

[0015] Figure 2 for Figure 1 Circuit diagram of the first op amp comparator, relay, NMOS1 and low voltage reference voltage.

[0016] Figure 3 for Figure 1 Circuit diagram of the second operational amplifier comparator, NMOS2 and impedance reference voltage.

[0017] Figure 4 for Figure 1 Load impedance voltage measurement circuit diagram.

[0018] Figure 5 for Figure 1 Relay control indication circuit diagram.

[0019] In the figure: 1-LED constant voltage dimming power supply, 2-LED light source, 4-low voltage reference voltage, 5-DC power supply, 6-impedance reference voltage. DETAILED DESCRIPTION

[0020] The following will be combined with the accompanying drawings to describe the embodiments of the present invention in detail, so as to more clearly understand the purpose, characteristics and advantages of the present invention. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.

[0021] like Figure 1 The utility model provides a low-voltage power-off load impedance abnormality detection circuit for LED dimming, comprising an LED constant-voltage dimming power supply 1, an LED light source 2, a relay K1 and a first operational amplifier comparator U1, wherein the output positive electrode of the LED constant-voltage dimming power supply 1 is electrically connected to the LED light source 2 through the relay K1, and the output positive electrode of the LED constant-voltage dimming power supply 1 is also connected to the positive input terminal of the first operational amplifier comparator U1 as the output voltage, and the negative input terminal of the first operational amplifier comparator U1 is connected to the low-voltage reference voltage 3, the output negative electrode of the LED constant-voltage dimming power supply 1 is electrically connected to the negative electrode of the DC power supply 4, and the positive electrode of the DC power supply 4 and the output terminal of the first operational amplifier comparator U1 are electrically connected to the relay K1 through the NMOS1, and the first operational amplifier comparator U1 is used to compare the output voltage with the low-voltage reference voltage 3 and then output a high level to drive the NMOS1 to turn on so that the relay K1 is turned on and the LED light source 2 is powered on; or output a low level to disconnect the relay K1 and the LED light source 2 is powered off.

[0022] Specifically, the LED constant voltage dimming power supply is a 0-10V or PWM dimming power supply, and the DC power supply 4 is a 12V DC power supply. NMOS1 and NMOS2 are both triodes or field effect tubes. The LED constant voltage dimming power supply 1 is used to power the LED light source 2 and realize the dimming of the LED light source 2, and the relay K1 is used to control the on and off between the LED constant voltage dimming power supply 1 and the LED light source 3. When the dimming brightness of the LED light source 2 is 0, the relay is disconnected; when the dimming brightness is not 0, the relay is closed.

[0023] The positive output electrode of the LED constant voltage dimming power supply 1 is connected to the normally open terminal 1 of the relay K1. The positive output electrode is also connected to the positive input terminal of the first operational amplifier comparator U1 as the output voltage sampling point. The output terminal of the low voltage reference voltage 3 is connected to the negative input terminal of the first operational amplifier comparator U1. The negative output electrode of the LED constant voltage dimming power supply 1 is connected to the negative electrode of the DC power supply 4. The positive electrode of the DC power supply 4 is connected to the VCC terminal of the first operational amplifier comparator, the VCC terminal of the low voltage reference voltage 3, and the coil port 2 of the relay K1. The output terminal of the first operational amplifier comparator U1 is connected to the gate G of NMOS1, the drain D of NMOS1 is connected to the coil port 1 of the relay K1, the source of NMOS1 is connected to the negative output electrode of the LED constant voltage dimming power supply 1, and the normally open port 2 of the relay K1 is connected to the positive electrode of the LED light source 2.

[0024] When the detection circuit is working, the first op amp comparator U1 compares the voltage at its positive input terminal (output voltage of the LED constant voltage dimming power supply) with the voltage at its negative input terminal (low voltage reference voltage). When the voltage at the positive input terminal is higher than the voltage at the negative input terminal, the first op amp comparator U1 outputs a high level, driving NMOS1 to conduct so that the coil of relay K1 is powered on, the normally open port 1 and the normally open port 2 are turned on, and then the LED light source 2 is powered on and works normally. When the LED constant voltage dimming power supply 1 is dimmed to the minimum value 0, its output voltage is lower than the low voltage reference voltage 3, the first op amp comparator U1 outputs a low level, so that the coil of relay K1 is powered off, the normally open port 1 and the normally open port 2 of relay K1 are disconnected, so that there is no voltage on the LED light source 2, and finally the function of powering off the LED light source 2 when the dimming value is zero when the LED constant voltage dimming power supply 1 is dimmed is realized.

[0025] Furthermore, it also includes a second operational amplifier comparator U2 and an impedance reference voltage 5, the output end of the impedance reference voltage 5 is connected to the positive input end of the second operational amplifier comparator U2, the LED light source 2 is connected to the second operational amplifier comparator U2, the terminal voltage of the LED light source 2 is input to the negative input end of the second operational amplifier comparator, and the output end of the second operational amplifier comparator U2 is electrically connected to the positive input end of the first operational amplifier comparator U1 through NMOS2; the second operational amplifier comparator U2 is used to compare the impedance reference voltage 5 with the terminal voltage of the negative input end, and then output a low level to drive NMOS2 to cut off, or output a high level to drive NMOS2 to turn on to lower the positive input terminal voltage of the first operational amplifier comparator U1.

[0026] Specifically, the positive pole of the DC power supply 4 is also connected to the VCC terminal of the second operational amplifier comparator U2 and the VCC terminal of the impedance reference voltage 5, the output terminal of the impedance reference voltage 5 is connected to the positive input terminal of the second operational amplifier comparator U2, the source S of NMOS2 is connected to the output negative pole of the LED constant voltage dimming power supply 1, the normally open port 2 of the relay K1 is also connected to the negative input terminal of the second operational amplifier comparator U2, the output terminal of the impedance reference voltage 5 is connected to the positive input terminal of the second operational amplifier comparator U2, the output terminal of the second operational amplifier comparator 8 is connected to the gate of NMOS2, and the output positive pole of the LED constant voltage dimming power supply 1 is also connected to the drain D of NMOS2.

[0027] When the detection circuit is working, when the positive output electrode of the LED constant voltage dimming power supply 1 and the positive electrode of the LED light source 2 are disconnected, the DC power supply 4 supplies power to the LED light source 2, and the second operational amplifier comparator U2 compares the impedance reference voltage 5 with the voltage at the negative input terminal. If the voltage at the negative input terminal is higher than the impedance reference voltage 5, the second operational amplifier comparator U2 outputs a low level to the gate G of NMOS2, and the drain D and source S of NMOS2 are not conducting, which does not affect the normal operation of the circuit. When the line impedance of the internal circuit of the LED light source 2 is reduced due to humidity and corrosion in the air, the voltage at the negative input terminal of the second operational amplifier comparator U2 will be reduced to below the impedance reference voltage 5, and the second operational amplifier comparator U2 outputs a high level to the gate G of NMOS2. At this time, NMOS2 is turned on, pulling down the voltage at the positive input terminal of the first operational amplifier comparator U1, so that the first operational amplifier comparator U1 outputs a low level to the gate G of NMOS1, thereby disconnecting the drain D and source S of NMOS1, and then the coil of the relay K1 is always powered off, thereby ensuring that when the impedance of the LED light source 2 is reduced, the output of the LED constant voltage dimming power supply 1 and the LED light source 2 are disconnected, reducing the fire hazard caused by internal circuit failure of the LED light source 2.

[0028] Furthermore, a current limiting resistor 9 and a diode D6 are connected in series between the DC power supply 4 and the LED light source 2 , one end of the current limiting resistor 9 is electrically connected to the positive electrode of the DC power supply 4 , and the other end of the current limiting resistor 9 is connected to the diode D6 . The current limiting resistor 9 is used to reduce the current of the LED light source 2 .

[0029] Specifically, the negative input terminal of the second operational amplifier comparator U2 is connected to the “-” terminal of the current limiting resistor 9, and the “+” terminal of the current limiting resistor 9 is connected to the VCC terminal of the second operational amplifier comparator U2 and the positive electrode of the DC power supply 4, and is powered by the DC power supply 4. A diode D6 is connected in series between the common terminal formed by the negative input terminal of the second operational amplifier comparator U2 and the “-” terminal of the current limiting resistor 9 and the positive electrode of the LED light source 2, and the cathode of the diode D6 is connected to the positive electrode of the LED light source 2.

[0030] Since the resistance of the current limiting resistor 9 is relatively large, the current flowing through the LED light source 2 when the DC power supply 4 supplies power is very small, so there is no risk of fire when testing the impedance of the LED light source 2. The current limiting resistor 9, on the one hand, limits the current in the circuit when measuring the load impedance, and on the other hand, it is connected in series with the load so that the load impedance can be measured according to Ohm's law. When the DC power supply 4 supplies power to the current limiting resistor 9, the diode D6, and the LED light source 2, the second op amp comparator U2 compares the impedance reference voltage 5 with the voltage at the negative input terminal (diode D6+negative input terminal voltage).

[0031] Furthermore, a fuse F1 is connected between the negative electrode of the LED light source 2 and the negative electrode of the DC power supply 4. The output negative electrode of the LED constant voltage dimming power supply 1 and the negative electrode of the DC power supply 4 are connected to form a common terminal, and the fuse F1 is connected between the common terminal and the negative electrode of the LED light source 2. The fuse F1 provides protection for the entire circuit.

[0032] like Figure 2As shown. In the detection circuit, NMOS1 uses transistor Q1. The voltage of the positive electrode of the output of the LED constant voltage dimming power supply 1 is +48V, and 0V is the negative electrode of the output of the LED constant voltage dimming power supply 1. The +48V voltage positive electrode is connected to the first end of the resistor R2, and the second end of the resistor R2 is respectively connected to the first end of the resistor R3, the negative electrode of the voltage zener diode ZD1, and the third pin of the first operational amplifier comparator U1. The second end of the resistor R3 is respectively connected to the positive electrode of the voltage zener diode ZD1, and the first end of the resistor R1 is connected to the negative electrode (0V-PAD) of the output of the LED constant voltage dimming power supply 1. The first end of the resistor R4 is connected to the positive electrode (VCC terminal) of the DC power supply 4, the second end of the resistor R4 is respectively connected to the negative electrode of the voltage-stabilizing diode ZD2 and the second pin of the first operational amplifier comparator U1, the fourth pin of the first operational amplifier comparator U1 is connected to the negative electrode (AGND terminal) of the DC power supply 4, and the eighth pin of the first operational amplifier comparator U1 is respectively connected to the first end of the capacitor C1, the first end of the capacitor C2, the negative electrode of the diode D2, and the first pin of the power supply coil of the relay K1. The second ends of the capacitors C1 and C2 are connected to the AGND terminal, the second end of the voltage-stabilizing diode D2 is respectively connected to the second pin of the power supply coil of the relay K1 and the collector of the transistor Q1, the first pin of the first operational amplifier comparator U1 is connected to the first end of the resistor R5, the second end of the resistor R5 is connected to the first end of the resistor R6 and the base of the transistor Q1; the second end of the resistor R6 is connected to the emitter of the transistor Q1 and the AGND terminal. The +48V output positive electrode of the LED constant voltage dimming power supply 1 is connected to the third pin of the relay K1.

[0033] The +48V output voltage of the LED constant voltage dimming power supply 1 is input to the positive input terminal (pin 3) of the first operational amplifier comparator U1 after being divided by resistors R2 and R3. Resistor R4 and voltage zener diode ZD2 are connected in series to obtain a 5.1V low voltage reference voltage 3 which is input to the reverse input terminal of the first operational amplifier comparator U1. The first operational amplifier comparator U1 compares the voltage signal of its pin 3 with the low voltage reference voltage 3 of the pin 2. If the voltage of the pin 3 is higher than the reference voltage of the pin 2, the first operational amplifier comparator U1 outputs a high level voltage. At this time, transistor Q1 is turned on, relay K1 is closed, and its pins 3 and 4 are turned on; if the voltage of the pin 3 is lower than the reference voltage of the pin 2, the first operational amplifier comparator U1 outputs a low level voltage. At this time, transistor Q1 is turned off, relay K1 is disconnected, and its pins 3 and 4 are disconnected.

[0034] like Figure 3As shown. In the detection circuit, NMOS2 is a field effect tube Q4, and the current limiting resistor 9 is an adjustable resistor RP1. An impedance reference voltage is formed by the resistor R19, the voltage zener diode ZD4, the adjustable resistor RP1, and the resistor R20, and the abnormal impedance value can be preset by the adjustable resistor RP1. The first end of the resistor R19, the 8th pin of the second operational amplifier comparator U2, and the VCC end of the DC power supply 4 are connected, and the second end of the resistor R19 is connected to the second end of the resistor R18, the 1st pin and the 3rd pin of the adjustable resistor RP1, and the negative electrode of the voltage zener diode ZD4. The second end of the adjustable resistor RP1 is connected to the first end of the resistor R20, the second end of the resistor R20 is connected to the positive electrode and the AGND end of the voltage regulator diode ZD4, the first end of the resistor R18 is connected to the third end of the second operational amplifier comparator U2, the first end of the resistor R17 is connected to the second end of the second operational amplifier comparator U2, the first end of the second operational amplifier comparator U2 is connected to the second end of the resistor R16, the first end of the resistor R16 is connected to the base of the field effect transistor Q4, the drain of the field effect transistor Q4 is connected to the AGND end (the negative electrode of the DC power supply), the drain of the field effect transistor Q4 is connected to the first end of the resistor R15, the second end of the resistor R15 and Figure 1 The cathode of the Zener diode is connected.

[0035] When the relay K1 is closed, the second op amp comparator U2 compares the impedance reference voltage 5 (pin 3) with the voltage at pin 2 of the second op amp comparator U2. When the impedance reference voltage 5 is higher than the voltage at pin 2, pin 1 of the second op amp comparator U2 outputs a high-level voltage, driving the field effect transistor Q4 to turn on, thereby lowering the voltage of LOWV-TEST (node ​​voltage), causing pin 1 of the first op amp comparator U1 to output a low-level voltage, thereby disconnecting the relay K1.

[0036] like Figure 4 shown. Figure 4 The working voltage VCC end is the voltage when the impedance is measured by the volt-ampere method. In the detection circuit, the positive electrode (VCC end) of the DC power supply 4 is connected to the first end of the voltage-stabilizing diode D1, the second end of the voltage-stabilizing diode D2 is connected to the first end of the resistor R9, the first end of the resistor R10, and the source of the field effect transistor Q2, the drain of the field effect transistor Q2 is connected to the first end of the resistor R14, the second end of the resistor R14 is connected to the diode D6 ( Figure 1 The anode of the diode D6) and the resistor R17 ( Figure 2 The cathode of the diode D6 is connected to the 4th pin (+48V-VO) of the relay K1. The output cathode of the LED constant voltage dimming power supply 1 and the fuse F1 ( Figure 1The first end of the fuse F1 is connected to the output pad PAD-OUT-, the second end of the resistor R9 is connected to the positive electrode of the voltage stabilizing diode ZD3 and the 5th pin of the first operational amplifier comparator U1, the first end C1 of the resistor R7 is connected to the resistor R15 ( Figure 3 The second end of the first operational amplifier comparator U1 is connected to the first end of the first resistor R12, the second end of the resistor R12 is connected to the first end of the resistor R13 and the base of the transistor Q3, the resistor R13 and the emitter of the transistor Q3 are connected to the negative electrode (AGND terminal) of the DC power supply, the second end of the resistor R10 is connected to the gate of the field effect transistor Q2 and the first end of the resistor R11, and the second end of the resistor R11 is connected to the emitter of the transistor Q3.

[0037] Furthermore, the detection circuit also includes a first indicator light for indicating the working status of the relay and a second indicator light for indicating abnormal load impedance. The first indicator light is connected in series between the output end of the first operational amplifier comparator and the negative pole of the DC power supply, and the second indicator light is connected in series between the output end of the second operational amplifier comparator and the negative pole of the DC power supply.

[0038] Specifically, if Figure 5 As shown. The first end of the resistor R21 is connected to the first pin of the first operational amplifier comparator U1, the second end of the resistor R21 is connected to the positive electrode of the first indicator LED1, the first end of the resistor R22 is connected to the first pin of the second operational amplifier comparator U2, and the second end of the resistor R22 is connected to the positive electrode of the second indicator LED2. The negative electrodes of the first indicator LED1 and the second indicator LED2 are connected to the AGND end of the DC power supply. The first indicator LED1 is used to indicate the working status of the relay K1, and the second indicator LED2 is used to indicate the abnormal load impedance of the LED light source. During operation, when the first indicator LED1 is on, the relay K1 is closed, and when the second indicator LED2 is on, the load impedance is abnormal, and the relay K1 cannot be closed (is in the open state).

[0039] When the utility model is working, when the brightness of the LED light source 2 is adjusted to 0 (off), the output of the LED constant voltage dimming power supply 1 and the power supply of the LED light source 2 can be disconnected, thereby avoiding the fire hazard caused by abnormal load in the standby state of the dimming system. When the dimming brightness is not 0, the relay K1 is closed. When the output of the LED constant voltage dimming power supply 1 and the power supply of the LED light source 2 are disconnected, the equivalent impedance of the LED light source load is detected in real time. If the impedance is detected to be lower than the preset value, the output of the LED constant voltage dimming power supply 1 and the power supply of the LED light source 2 are kept disconnected, thereby reducing the risk of fire caused by partial abnormality of the LED light source during operation.

Claims

1. A low voltage power-off load impedance abnormality detection circuit for LED dimming, characterized in that: It includes an LED constant-voltage dimming power supply, an LED light source, a first operational amplifier comparator and a direct current power supply, wherein the LED constant-voltage dimming power supply is used to power and dim the LED light source, the output positive pole of the LED constant-voltage dimming power supply is electrically connected to the LED light source through a relay, the output positive pole of the LED constant-voltage dimming power supply is also electrically connected to the positive input terminal of the first operational amplifier comparator as an output voltage, the negative input terminal of the first operational amplifier comparator is connected to a low-voltage reference voltage, the output negative pole of the LED constant-voltage dimming power supply is electrically connected to the negative pole of the direct current power supply, the positive pole of the direct current power supply and the output terminal of the first operational amplifier comparator are electrically connected to the relay through NMOS1, and the first operational amplifier comparator is used to compare the output voltage with the low-voltage reference voltage and then output a high or low level to drive the NMOS1 to turn on or off to control the on / off of the relay.

2. A low-voltage power-off load impedance abnormality detection circuit for LED dimming according to claim 1, characterized in that: It also includes a second operational amplifier comparator and an impedance reference voltage, wherein the output end of the impedance reference voltage is connected to the positive input end of the second operational amplifier comparator, the LED light source is electrically connected to the second operational amplifier comparator, and the terminal voltage of the LED light source is input to the negative input end of the second operational amplifier comparator, and the output end of the second operational amplifier comparator is electrically connected to the positive input end of the first operational amplifier comparator through NMOS2; the second operational amplifier comparator is used to compare the impedance reference voltage with the terminal voltage of the negative input end, and then output a high or low level to drive the NMOS2 to be cut off or turned on.

3. A low-voltage power-off load impedance abnormality detection circuit for LED dimming according to claim 2, characterized in that: It also includes a first indicator light for indicating the working status of the relay and a second indicator light for indicating abnormal load impedance. The first indicator light is connected in series between the output end of the first operational amplifier comparator and the negative electrode of the DC power supply, and the second indicator light is connected in series between the output end of the second operational amplifier comparator and the negative electrode of the DC power supply.

4. A low-voltage power-off load impedance abnormality detection circuit for LED dimming according to claim 3, characterized in that: A current limiting resistor and a diode are connected in series between the DC power supply and the LED light source.

5. A low-voltage power-off load impedance abnormality detection circuit for LED dimming according to claim 4, characterized in that: The NMOS1 and NMOS2 are both triodes or field effect transistors.

6. A low-voltage power-off load impedance abnormality detection circuit for LED dimming according to claim 4, characterized in that: A fuse is connected between the cathode of the LED light source and the cathode of the DC power supply.

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