Open circuit detection circuit, LED driving power supply and lamp

Abstract

The utility model discloses an open circuit detection circuit, which is applied to a constant-voltage LED driving power supply with a chopping dimming function, and comprises a first voltage detection unit connected with the output end of an AC / DC constant-voltage circuit in the constant-voltage LED driving power supply; the second voltage detection unit is connected with the output end of the chopping dimming circuit in the constant-voltage LED driving power supply; and an open circuit detection output unit connected with the first voltage detection unit and the second voltage detection unit and used for detecting the magnitude of the output voltage of the AC / DC constant voltage circuit and the chopping dimming circuit so as to output a final detection level according to the magnitude of the output voltage of the AC / DC constant voltage circuit when the duty ratio of the PWM signal received by the chopping dimming circuit is 100%, and when the duty ratio of the PWM signal is 0.1%-99.9%, a final detection level is output according to the magnitude of the output voltage of the chopping dimming circuit, so that the load state is obtained. The utility model also discloses an LED driving power supply and a lamp.

Description

Technical Field

[0001] The utility model relates to the technical field of LED lighting, and more specifically to an open circuit detection circuit, an LED driving power supply and a lamp. Background Art

[0002] With the development and popularization of smart home appliance control systems, people's demand for smart home appliance control systems is increasing. At present, the market has higher and higher requirements for smart dimming LED drivers, especially for smart constant voltage dimming LED drivers. In order to ensure the stable operation of LED lighting systems, it is usually necessary to detect and report the open circuit fault signal of the load (LED light strip, etc.).

[0003] However, for constant voltage LED driver power supply, the driver output is a constant voltage in both open circuit and normal light load states, with only slight changes in output current. The two states are difficult to distinguish. Currently, people use a sampling resistor in series in the output main circuit to detect the voltage change across the resistor to distinguish whether the load is open circuit or loaded. However, the sampling signal when light load is on is too weak, and it is easy to misjudge the light load as an open circuit. Moreover, the weak signal needs to be amplified, and there is a risk of mis-amplifying the interference signal, resulting in mis-detection. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide an open circuit detection circuit, an LED driving power supply and a lamp, so as to more accurately detect and distinguish whether the load is an open circuit or a normal light load, thereby reducing the probability of misjudgment.

[0005] In order to solve the above technical problems, according to one aspect of the utility model, an open circuit detection circuit is provided, which is applied to a constant voltage LED driving power supply with a chopper dimming function, and the open circuit detection circuit includes:

[0006] A first voltage detection unit, connected to the output end of the AC / DC constant voltage circuit in the constant voltage LED driving power supply, for obtaining the output voltage of the AC / DC constant voltage circuit;

[0007] A second voltage detection unit is connected to the output end of the chopper dimming circuit in the constant voltage LED driving power supply and the negative electrode of the LED light string, and is used to obtain the output voltage of the chopper dimming circuit;

[0008] An open circuit detection output unit is connected to the output ends of the first voltage detection unit and the second voltage detection unit, and is used to respectively detect the magnitudes of the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit when the duty cycles of the PWM signal received by the chopper dimming circuit are different, so as to output a final detection level according to the magnitude of the output voltage of the AC / DC constant voltage circuit when the duty cycle of the PWM signal received by the chopper dimming circuit is 100%, and to output a final detection level according to the magnitude of the output voltage of the chopper dimming circuit when the duty cycle of the PWM signal is 0.1%-99.9%, thereby detecting and knowing the load state of the constant voltage LED driving power supply.

[0009] To solve the above technical problems, according to another aspect of the utility model, an LED driving power supply is also provided, comprising an AC / DC constant voltage circuit, a chopper dimming circuit, a controller and the above open circuit detection circuit, wherein:

[0010] The AC / DC constant voltage circuit is connected between the power input terminal and the LED light source, and the LED light source includes at least one LED light string;

[0011] The chopper dimming circuit is connected to the AC / DC constant voltage circuit and is used to adjust the current input from the AC / DC constant voltage circuit to the LED light source according to the input PWM signal;

[0012] The controller is connected to the chopping dimming circuit and is used to output a PWM signal to the chopping dimming circuit according to an external instruction;

[0013] The open circuit detection circuit is connected to the output ends of the AC / DC constant voltage circuit and the chopper dimming circuit respectively to detect the output voltage of the AC / DC constant voltage circuit and the output voltage of the chopper dimming circuit respectively, thereby detecting the load state of the constant voltage LED driving power supply.

[0014] In order to solve the above technical problems, the utility model also provides a lamp, which includes the above LED driving power supply.

[0015] Compared with the prior art, the utility model is provided with a first voltage detection unit connected to the output end of the AC / DC constant voltage circuit in the constant voltage LED driving power supply and a second voltage detection unit connected between the output end of the chopper dimming circuit in the constant voltage LED driving power supply and the negative pole of the LED light string, and is also provided with an open circuit detection output unit, and the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit can be respectively detected and obtained through the first voltage detection unit and the second voltage detection unit, and then the magnitudes of the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit can be respectively detected through the open circuit detection output unit, and different levels can be output according to the magnitudes of the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit when the duty cycles of the PWM signals received by the chopper dimming circuit are different, thereby obtaining The invention discloses that the load state of the constant voltage LED driving power supply in different dimming working states is open circuit or normal with light load, that is, through the cooperation of the first voltage detection unit, the second voltage detection unit and the open circuit detection output unit, when the duty cycle of the PWM signal received by the chopping dimming circuit is 100%, the final detection level is output according to the output voltage of the AC / DC constant voltage circuit, and when the duty cycle of the PWM signal is 0.1%-99.9%, the final detection level is output according to the output voltage of the chopping dimming circuit, that is, the first voltage detection unit, the second voltage detection unit and the open circuit detection output unit complement each other when the duty cycle of the PWM signal is different, so as to achieve the purpose of accurately detecting and distinguishing whether the load is open circuit or normal with light load when the constant voltage LED driving power supply is in different dimming working states, and reduce the probability of misjudgment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a circuit block diagram of the LED driving power supply provided by the first embodiment of the utility model.

[0017] Figure 2 It is a circuit structure diagram of an AC / DC constant voltage circuit, a chopper dimming circuit and an LED light source in an LED driving power supply provided in the first embodiment of the utility model.

[0018] Figure 3 It is a circuit structure schematic diagram of an open circuit detection circuit in an LED driving power supply provided by the first embodiment of the utility model.

[0019] Figure 4 It is a circuit structure schematic diagram of an open circuit detection circuit in an LED driving power supply provided in the second embodiment of the utility model.

[0020] Figure 5 It is a circuit structure schematic diagram of an open circuit detection circuit in an LED driving power supply provided in the third embodiment of the utility model.

[0021] Figure 6 It is a circuit structure schematic diagram of an open circuit detection circuit in an LED driving power supply provided in the fourth embodiment of the utility model.

[0022] Figure 7 It is a circuit structure diagram of an open circuit detection circuit in an LED driving power supply provided in the fifth embodiment of the utility model.

[0023] Figure 8 It is a circuit structure diagram of an open circuit detection circuit in an LED driving power supply provided by a sixth embodiment of the utility model.

[0024] Fig. 9 It is a circuit structure diagram of an open circuit detection circuit in an LED driving power supply provided by the seventh embodiment of the utility model.

[0025] Fig.10 It is a circuit structure schematic diagram of an open circuit detection circuit in an LED driving power supply provided in the eighth embodiment of the present utility model. DETAILED DESCRIPTION

[0026] In order to enable ordinary technicians in the field to more clearly understand the purpose, technical solutions and advantages of the utility model, the utility model is further explained below in conjunction with the accompanying drawings and embodiments.

[0027] Reference Figure 1 , Figure 1 The schematic diagram of the circuit block diagram of the LED driving power supply 100 provided for the first embodiment of the utility model. In the embodiment shown in the accompanying drawings, the LED driving power supply 100 includes an AC / DC constant voltage circuit 11, a chopper dimming circuit 12, a controller 15 and an open circuit detection circuit 13, wherein the AC / DC constant voltage circuit 11 is connected between the power input terminal S and the LED light source 200, and is used to convert the mains electricity into a constant low-voltage DC voltage. It can be understood that the AC / DC constant voltage circuit 11 includes a transformer, and the LED light source 200 includes at least one LED light string. The chopper dimming circuit 12 is connected to the AC / DC constant voltage circuit 11, and is used to adjust the current input from the AC / DC constant voltage circuit 11 to the LED light source 200 according to the input PWM signal; in the prior art, a MOS tube Q3 is usually used in series in the loop of the AC / DC constant voltage circuit 11 and the LED light string, and the chopper dimming output function is realized by fast switching of the MOS tube Q3. Specifically, as Figure 2As shown, it includes a seventh diode D7, a filter capacitor EC1 and a MOS tube Q3, the seventh diode D7 is connected between the output end of the AC / DC constant voltage circuit 11 and the positive electrode LED+ of the LED light string, the gate of the MOS tube Q3 is connected to the controller 15, the drain is connected to the negative electrode LED- of the LED light string, its source and one end of the filter capacitor EC1 are grounded SGND, and the other end of the filter capacitor EC1 is connected to the seventh diode D7 and the positive electrode LED+ of the LED light string. In each PWM signal cycle of the chopping dimming circuit 12 of this embodiment, when the gate of the MOS tube Q3 receives a high level, the MOS tube Q3 is turned on, and the LED light string is lit; when the gate of the MOS tube Q3 receives a low level, the MOS tube Q3 is turned off, and the LED light string is extinguished, then the PWM signals of various duty cycles can be adjusted to achieve different durations of LED light emission in each cycle, thereby realizing the LED dimming output function. The controller 15 is connected to the chopping dimming circuit 12, and is used to output a PWM signal to the chopping dimming circuit 12 according to an external instruction. The open circuit detection circuit 13 includes a first voltage detection unit 131, a second voltage detection unit 132 and an open circuit detection output unit 133, wherein the first voltage detection unit 131 is connected to the output end of the AC / DC constant voltage circuit 11 in the constant voltage LED driving power supply 100, and is used to obtain the output voltage of the AC / DC constant voltage circuit 11; the second voltage detection unit 132 is connected to the output end of the chopping dimming circuit 12 in the constant voltage LED driving power supply 100 and the negative pole LED- of the LED lamp string, and is used to obtain the output voltage of the chopping dimming circuit 12; the open circuit detection output unit 133 is connected to the first voltage detection unit 131 The output end of the second voltage detection unit 132 is used to detect the magnitude of the output voltage of the AC / DC constant voltage circuit 11 and the chopper dimming circuit 12 respectively when the duty cycle of the PWM signal received by the chopper dimming circuit 12 is different, so as to output the final detection level according to the magnitude of the output voltage of the AC / DC constant voltage circuit 11 when the duty cycle of the PWM signal received by the chopper dimming circuit 12 is 100%, and output the final detection level according to the magnitude of the output voltage of the chopper dimming circuit 12 when the duty cycle of the PWM signal is 0.1%-99.9%, so as to detect and know the load state of the constant voltage LED driving power supply 100. It can be understood that the controller 15 can be implemented by a single chip microcomputer or a microcontroller, and the AC / DC constant voltage circuit 11 is an AC / DC constant voltage circuit commonly used by those skilled in the art, which will not be described in detail here.

[0028] Specifically, Figure 3As shown, in this embodiment, the first voltage detection unit 131 includes a rectifier and filter circuit, a voltage divider resistor circuit 1312 and a filter circuit, the rectifier and filter circuit includes a fifth diode D5 and a second electrolytic capacitor EC2, the voltage divider resistor circuit 1312 includes a sixth resistor R6 and an eighth resistor R8, the filter circuit includes a ninth resistor R9 and a third capacitor C3, wherein the positive electrode of the fifth diode D5 is connected to the output end of the AC / DC constant voltage circuit 11, and in this embodiment, it is connected to an independent winding T1D of the transformer in the AC / DC constant voltage circuit 11, and its negative electrode is connected to the positive electrode of the second electrolytic capacitor EC2 and the sixth resistor R6, the other end of the sixth resistor R6 is connected to the ninth resistor R9 and one end of the eighth resistor R8, the other end of the ninth resistor R9 is connected to one end of the third capacitor C3, and serves as the output end of the first voltage detection unit 131, and the other ends of the eighth resistor R8 and the third capacitor C3 and the negative electrode of the second electrolytic capacitor EC2 are all grounded SGND. Based on the above design, the voltage coupled from the winding T1D is rectified and filtered by the fifth diode D5 and the second electrolytic capacitor EC2 to obtain a DC voltage, which can be converted into a low voltage after passing through the voltage divider resistor circuit 1312 .

[0029] Further, in some embodiments, the first voltage detection unit 131 also includes a seventh current limiting resistor R7 and a first voltage regulator ZD1, the seventh current limiting resistor R7 is connected between the output end of the AC / DC constant voltage circuit 11 and the fifth diode D5, the cathode of the first voltage regulator ZD1 is connected to one end connected to the eighth resistor R8 and the sixth resistor R6, and the anode thereof is grounded SGND. Based on the above design, the first voltage regulator ZD1 can play the role of voltage clamping to prevent higher voltage from damaging the subsequent circuit. In this embodiment, when the first voltage detection unit 131 is working, the voltage pulse coupled from the winding T1D to the transformer is sequentially limited by the seventh current limiting resistor R7, rectified by the fifth diode D5, and filtered by the second electrolytic capacitor EC2, and the final output voltage V1 is a DC voltage, which can be divided by the voltage divider resistor circuit 1312 to obtain the required low voltage, and then low-pass filtered by the filter circuit to obtain the ideal stable DC voltage V1-1.

[0030] Continue to refer to Figure 3In some embodiments, the second voltage detection unit 132 includes a blocking capacitor C1, a clamping diode D3, a second filter capacitor C2, a second current limiting resistor R2, a second rectifier diode D2, a third current limiting resistor R3 and a pull-down resistor R4, one end of the blocking capacitor C1 is connected to the output end of the chopper dimming circuit 12 and the negative electrode LED- of the LED lamp string through the second current limiting resistor R2, the other end of the blocking capacitor C1 is connected to the positive electrode of the second rectifier diode D2 and the negative electrode of the clamping diode D3, the negative electrode of the second rectifier diode D2 is connected to the third current limiting resistor R3, the other end of the third current limiting resistor R3 is connected to the pull-down resistor R4 and one end of the second filter capacitor C2, and serves as the output end of the second voltage detection unit 132, the positive electrode of the clamping diode D3, the pull-down resistor R4 and the other end of the second filter capacitor C2 are all grounded SGND. Based on the above design, when the chopper dimming circuit 12 receives a PWM signal, after passing through the MOS tube Q3, LED- is a pulse voltage of the corresponding duty cycle (the low level is 0V, and the high level is the voltage of LED+). This pulse voltage is limited by the second current limiting resistor R2, and the DC blocking capacitor C1 blocks the DC and passes the AC to output a floating pulse voltage signal. The output pulse voltage signal passes through the clamping diode D3, and the low level of the pulse voltage signal is pulled to the ground SGND minus the voltage drop of the clamping diode D3, which is approximately 0V, that is, the low level of this pulse voltage signal is 0V and does not float. The stabilized pulse voltage signal is rectified by the second rectifier diode D2, limited by the third current limiting resistor R3, and filtered by the second filter capacitor C2 to obtain a stable voltage V2.

[0031] In this embodiment, the open circuit detection output unit 133 includes a first voltage comparison unit 1331, a second voltage comparison unit 1332 and a logic operation unit 1333, wherein the first voltage comparison unit 1331 is connected to the output end of the first voltage detection unit 131, and is used to compare whether the output voltage of the AC / DC constant voltage circuit 11 is greater than the reference voltage, and outputs a low level when the output voltage is greater than the reference voltage, and outputs a high impedance state when the output voltage is less than the reference voltage; the second voltage comparison unit 1332 is connected to the output end of the second voltage detection unit 132, and is used to detect the output voltage of the chopper dimming circuit 12, and outputs a high impedance state according to the output voltage of the chopper dimming circuit 12. The magnitude of the output voltage is a high impedance state when the duty cycle of the PWM signal received by the chopper dimming circuit 12 is 100%, a high impedance state when the duty cycle of the PWM signal is 0.1%-99.9% and the LED light string is open, and a low level is output when the duty cycle of the PWM signal is 0.1%-99.9% and the LED light string is working normally; the logic operation unit 1333 is connected to the first voltage comparison unit 1331 and the second voltage comparison unit 1332, and is used to perform logic and processing on the signals output by the first voltage comparison unit 1331 and the second voltage comparison unit 1332 to detect the load state of the constant voltage LED driving power supply 100. Based on the above design, the open circuit detection output unit 133 of the utility model outputs different levels according to the output voltages of the AC / DC constant voltage circuit 11 and the chopper dimming circuit 12 when the duty cycle of the PWM signal received by the chopper dimming circuit 12 is different, thereby knowing whether the load state of the constant voltage LED driving power supply 100 in different dimming working states is open circuit or normal with light load.

[0032] Specifically, in this embodiment, the first voltage comparison unit 1331 includes a switch tube Q1 and a pull-up resistor R12, the control end of the switch tube Q1 is connected to the output end of the first voltage detection unit 131, the output end of the switch tube Q1 is grounded SGND, and its input end is connected to the external power supply VCC through the pull-up resistor R12, and serves as the output end of the first voltage comparison unit 1331; preferably, the switch tube Q1 is a triode, the collector of the triode serves as the input end of the switch tube Q1, connected to the pull-up resistor R12, the emitter of the triode serves as the output end of the switch tube Q1, grounded SGND, and the base of the triode serves as the control end of the switch tube Q1, connected to one end where the ninth resistor R9 and the third capacitor C3 are connected. Based on the above design, when the duty cycle of the PWM signal is 100% and the LED load is open, the AC / DC constant voltage circuit 11 works in a relatively deep hiccup working state, the transformer's working pulse accounts for a very small proportion, resulting in very few pulses coupled out of the winding T1D, and the coupled voltage pulses are output after passing through the first voltage detection unit 131. The stable DC voltage V1-1 is output, because V1-1 is very low when unloaded and cannot reach the base conduction voltage of the switch tube Q1, the switch tube Q1 is cut off, and at this time the first voltage comparison unit 1331 outputs a high impedance state; and when the LED light string is lightly loaded or normally loaded, the AC / DC constant voltage circuit 11 works in a normal working state, the transformer's working pulse accounts for a very high proportion, resulting in a large number of pulses coupled out of the winding T1D, and the coupled voltage pulses are output after the first voltage detection unit 131. The stable DC voltage V1-1 is output, because when loaded, V1-1 is high, exceeding the base conduction voltage of the switch tube Q1, Q1 is turned on, and the collector of Q1 is pulled down, and at this time the first voltage comparison unit 1331 outputs a low level.

[0033] The second voltage comparison unit 1332 includes a switch tube Q2 and a pull-up resistor R1, the control end of the switch tube Q2 is connected to the output end of the second voltage detection unit 132, the output end of the switch tube Q2 is grounded SGND, and its input end is connected to the external power supply VCC through the pull-up resistor R1 and serves as the output end of the second voltage comparison unit 1332. Preferably, in this embodiment, the switch tube Q2 is also a triode, the collector of the triode serves as the input end of the switch tube Q2 and is connected to the pull-up resistor R1, the emitter of the triode serves as the output end of the switch tube Q2 and is grounded SGND, and the base of the triode serves as the control end of the switch tube Q2 and is connected to the third current limiting resistor R3 and one end of the second filter capacitor C2. Based on the above design, when the gate of the MOS tube Q3 receives a PWM signal with a duty cycle of 100%, the MOS tube Q3 is always turned on. At this time, no matter the load (LED light string) is open circuit or normally loaded, the switch tube Q2 in the second voltage comparison unit 1332 is turned off and outputs a high impedance state; and when the gate of the MOS tube Q3 receives a PWM signal with a duty cycle of 0.1%-99.9%, and the LED light string is lightly loaded or normally loaded, the LED- is a pulse voltage waveform with a duty cycle of 0.1%-99.9% (low voltage). The low level is 0V, and the high level is the voltage of LED+). This pulse voltage obtains a stable voltage V2 after passing through the second voltage detection unit 132. At this time, the voltage V2 is clamped to 0.7V by the Vbe of the switch tube Q2, and the switch tube Q2 is turned on and outputs a low level; when the duty cycle of the PWM signal is 0.1%-99.9% and the LED lamp string is open, LED- is a voltage waveform of 0V. This voltage outputs a voltage V2 of 0V after passing through the second voltage detection unit 132, and the switch tube Q2 is turned off and outputs a high impedance state.

[0034] In some embodiments, the logic operation unit 1333 includes an AND gate, which can be composed of two diodes, a first diode D1 and a fourth diode D4. The output ends of the first voltage comparison unit 1331 and the second voltage comparison unit 1332 are respectively connected to the cathodes of the fourth diode D4 and the first diode D1, and the anodes of the first diode D1 and the fourth diode D4 are connected and serve as the output end of the logic operation unit 1333.

[0035] In some embodiments, the open circuit detection circuit 13 can also be connected to the external smart device 300 through a pull-up resistor, that is, the positive electrodes of the first diode D1 and the fourth diode D4 can be connected to the external smart device 300 through a pull-up resistor, wherein the external smart device 300 can be a remote control, etc., and the pull-up resistor can be built in the external smart device 300. Figure 3The I / O interface in is an interface of an external intelligent device 300 with a built-in pull-up resistor. When the output of the logic operation unit 1333 is in an open circuit high impedance state, the I / O interface is at a high level. When the output is at a low level, the I / O interface is at a low level. Understandably, the open circuit detection circuit 13 can also be connected to the controller 15 through a pull-up resistor, and the pull-up resistor can be integrated into the interface of the controller 15, so that the load state of the LED driving power supply 100 at this time is sent to a mobile phone or other device for display through the controller 15 to prompt the user.

[0036] Combination Figure 1 and Figure 3 In the present invention, when the gate of the MOS tube Q3 receives a PWM signal with a duty cycle of 100%, the MOS tube Q3 is always turned on. At this time, no matter the load (LED light string) is open or normally loaded, the switch tube Q2 in the second voltage comparison unit 1332 is turned off and outputs a high impedance state. When the LED light string is open, because the AC / DC constant voltage circuit 11 will work in a relatively deep hiccup working state, the proportion of the working pulse of the transformer is very small, resulting in very few pulses coupled out of the winding T1D. The coupled voltage pulses are sequentially limited by the seventh current limiting resistor R7 in the first voltage detection unit 131, rectified by the fifth diode D5, and filtered by the second electrolytic capacitor EC2. The final output voltage V1 is a DC voltage. After the voltage is divided by the sixth resistor R6 and the eighth resistor R8 in the voltage dividing resistor circuit 1312, the required low voltage can be obtained. After low-pass filtering by the ninth resistor R9 and the third capacitor C3 in the filtering circuit, a stable DC voltage V1-1 can be obtained. Because V1-1 is very low when no-load, it cannot reach The base of the switch tube Q1 is turned on, and the switch tube Q1 is turned off. At this time, the first voltage comparison unit 1331 outputs a high impedance state, and the two output levels of the output ends of the first voltage comparison unit 1331 and the second voltage comparison unit 1332 are output through the AND gate of the logic operation unit 1333. The final detection level is a high impedance state. At this time, the I / O interface of the external intelligent device 300 with a built-in pull-up resistor is a high level; when the LED light string is lightly loaded or normally loaded, the AC / DC constant voltage circuit 11 works in a normal working state, and the proportion of the working pulse of the transformer is very high, resulting in a large number of pulses coupled out of the winding T1D. The coupled voltage pulses output a stable DC voltage V1-1 after the first voltage detection unit 131. Because V1-1 is high when loaded, it exceeds the base conduction voltage of the switch tube Q1, Q1 is turned on, and the collector of Q1 is pulled down. At this time, the first voltage comparison unit 1331 outputs a low level, and the output end of the logic operation unit 1333 outputs a low level, that is, the I / O interface is a low level at this time.

[0037] When the gate of the MOS tube Q3 receives a PWM signal with a duty cycle of 0.1%-99.9%, and the LED light string is lightly loaded or normally loaded, LED- is a pulse voltage waveform with a duty cycle of 0.1%-99.9% (the low level is 0V, and the high level is the voltage of LED+). This pulse voltage waveform is limited by the second current limiting resistor R2 in the second voltage detection unit 132, and the DC blocking capacitor C1 blocks the DC and passes the AC to output a floating pulse voltage signal. The output pulse voltage signal passes through the clamping diode D3, and the low level is pulled to the ground SGND minus the voltage drop of the clamping diode D3, which is approximately 0V, that is, the low level of this pulse signal is 0V, and it does not float. The stabilized pulse voltage signal is rectified by the second rectifier diode D2, limited by the third current limiting resistor R3, and filtered by the second filter capacitor C2 to obtain a stable voltage V2. At this time, the voltage V2 is clamped by the Vbe of the switch tube Q2 in the second voltage comparison unit 1332. When the voltage drops to 0.7V, the switch tube Q2 is turned on and outputs a low level. The first diode D1 pulls down the I / O interface, and the first voltage comparison unit 1331 outputs a low level when the AC / DC constant voltage circuit 11 works normally. The detection signal finally output by the open circuit detection circuit 13 is a low level, that is, the I / O interface is a low level at this time. When the duty cycle of the PWM signal is 0.1%-99.9% and the LED lamp string is open, LED- is a 0V voltage waveform. This voltage waveform is limited by R2 and blocked by C1 to pass AC, and is rectified by D2, limited by R3 and filtered by C2 in turn to output a 0V voltage V2. The switch tube Q2 in the second voltage comparison unit 1332 is turned off and outputs a high impedance state. The high impedance state output by the first voltage comparison unit 1331 and the high impedance state output by the second voltage comparison unit 1332 are output as a high impedance state after the detection signal is output through the AND gate. At this time, the I / O interface of the external intelligent device 300 with a built-in pull-up resistor is a high level.

[0038] As can be seen from the above, when the final detection signal is in a high impedance state, it can be determined that the load is open, and when the detection signal is at a low level, it can be determined that the load is lightly loaded or normally loaded. In the present utility model, since the 0.1% dimming depth is relatively high, if the LED load is a very small string of lights, which is equivalent to an extremely low load level, the detection result of the circuit part composed of the first voltage detection unit 131 and the first voltage comparison unit 1331 has a certain error. At this time, the final detection signal mainly depends on the detection result of the circuit part composed of the second voltage detection unit 132 and the second voltage comparison unit 1332. Similarly, when the dimming duty cycle is as high as 100%, the circuit part composed of the second voltage detection unit 132 and the second voltage comparison unit 1332 will uniformly judge the loaded and open circuit as the open circuit state, resulting in a misjudgment. At this time, the final detection signal mainly depends on the detection result of the circuit part composed of the first voltage detection unit 131 and the first voltage comparison unit 1331. The first voltage detection unit 131 and the first voltage comparison unit 1331 and the second voltage detection unit 132 and the second voltage comparison unit 1332 complement each other when the duty cycle of the PWM signal is different.

[0039] Reference Figure 4 , Figure 4 A schematic diagram of the circuit structure of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the second embodiment of the utility model. The difference between this embodiment and the above-mentioned first embodiment is that the switch tubes in the first voltage comparison unit 1331 and the second voltage comparison unit 1332 are different, and the rest of the structures are the same or similar. In this embodiment, the switch tube Q1 in the first voltage comparison unit 1331 is a MOS tube, the drain of the MOS tube is used as the input end of the switch tube Q1, connected to the pull-up resistor R12, its source is used as the output end of the switch tube Q1, grounded SGND, and the gate of the MOS tube is used as the control end of the switch tube Q1, connected to the end connected to the ninth resistor R9 and the third capacitor C3; and the switch tube Q2 in the second voltage comparison unit 1332 is also a MOS tube, the drain of the MOS tube is used as the input end of the switch tube Q2, connected to the pull-up resistor R1, its source is used as the output end of the switch tube Q2, grounded SGND, and the gate of the MOS tube is used as the control end of the switch tube Q2, connected to the end connected to the third current limiting resistor R3 and the second filter capacitor C2. This embodiment can also realize accurate detection of whether the load state of the constant voltage LED driving power supply 100 in different dimming working states is an open circuit or a normal light load.

[0040] Reference Figure 5 , Figure 5A schematic diagram of the circuit structure of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the third embodiment of the utility model. The difference between this embodiment and the above-mentioned first embodiment is that the specific structures of the first voltage comparison unit 1331, the second voltage comparison unit 1332 and the logic operation unit 1333 are different, and the remaining structures are the same or similar. In this embodiment, the first voltage comparison unit 1331 includes a first three-terminal voltage regulator IC1, a pull-up resistor R12, a third diode D3 and a tenth resistor R10, the control electrode of the first three-terminal voltage regulator IC1 is connected to the output end of the first voltage detection unit 131, the anode of the first three-terminal voltage regulator IC1 is grounded SGND, and its cathode is connected to the external power supply VCC through the pull-up resistor R12, and serves as the output end of the first voltage comparison unit 1331, the positive electrode of the third diode D3 is connected to the cathode of the first three-terminal voltage regulator IC1 through the tenth resistor R10, and the negative electrode of the third diode D3 is connected to the cathode of the first three-terminal voltage regulator IC1 Control electrode; the second voltage comparison unit 1332 includes a second three-terminal voltage regulator IC2, a pull-up resistor R1, a sixth diode D6 and an eleventh resistor R11, the control electrode of the second three-terminal voltage regulator IC2 is connected to the output end of the second voltage detection unit 132, the anode of the second three-terminal voltage regulator IC2 is grounded SGND, and its cathode is connected to the external power supply VCC through the pull-up resistor R1 and serves as the output end of the second voltage comparison unit 1332, the positive electrode of the sixth diode D6 is connected to the cathode of the second three-terminal voltage regulator IC2 through the eleventh resistor R11, and the negative electrode of the sixth diode D6 is connected to the control electrode of the second three-terminal voltage regulator IC2. Preferably, in this embodiment, the first three-terminal voltage regulator IC1 and the second three-terminal voltage regulator IC2 are both selected as three-terminal voltage regulators of model TL431. The logic operation unit 1333 includes an AND gate logic IC U3, the cathodes of the first three-terminal voltage regulator IC1 and the second three-terminal voltage regulator IC2 are respectively connected to the two input pins of the AND gate logic IC U3, and the output pin of the AND gate logic IC U3 serves as the output end of the logic operation unit 1333. Based on the above design, the third diode D3 and the tenth resistor R10 as well as the sixth diode D6 and the eleventh resistor R11 respectively form hysteresis circuits to prevent the first three-terminal voltage regulator IC1 and the second three-terminal voltage regulator IC2 from repeatedly operating at critical times.

[0041] In this embodiment, when the output voltage V1-1 of the first voltage detection unit 131 exceeds the reference voltage of 2.5V, the cathode of the first three-terminal regulator IC1 is pulled to the ground at a lower point, so that the I / O interface is also pulled down, and when the output voltage V2 of the second voltage detection unit 132 exceeds the reference voltage of 2.5V, the cathode of the second three-terminal regulator IC2 is pulled to the ground at a lower point, so that the I / O interface is also pulled down, otherwise the I / O interface is in a high-impedance state, and the external intelligent device 300 can know whether the load in the LED driver power supply 100 is open circuit or normally lightly loaded according to the level state of the final detection signal obtained by the detection.

[0042] Reference Figure 6 , Figure 6 A schematic diagram of the circuit structure of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the fourth embodiment of the utility model. The difference between this embodiment and the above-mentioned first embodiment is that the specific structures of the first voltage comparison unit 1331 and the second voltage comparison unit 1332 are different, and the remaining structures are the same or similar. In this embodiment, the first voltage comparison unit 1331 includes a first operational amplifier U2A, a thirteenth resistor R13, a fourteenth resistor R14 and a fifteenth resistor R15, the inverting input terminal of the first operational amplifier U2A is connected to the output terminal of the first voltage detection unit 131 through the fifteenth resistor R15, and the non-inverting input terminal thereof is connected to the reference voltage Vref1 through the fourteenth resistor R14, the output terminal of the first operational amplifier U2A is connected to the non-inverting input terminal through the thirteenth resistor R13, and the output terminal serves as the first voltage comparison unit 1331. The output end of the second voltage comparison unit 1332 includes a second operational amplifier U2B, a fifth resistor R5, a sixteenth resistor R16 and a seventeenth resistor R17. The inverting input end of the second operational amplifier U2B is connected to the output end of the second voltage detection unit 132 through the seventeenth resistor R17, and the non-inverting input end thereof is connected to the reference voltage Vref2 through the sixteenth resistor R16. The output end of the second operational amplifier U2B is connected to the non-inverting input end through the fifth resistor R5, and the output end serves as the output end of the second voltage comparison unit 1332. Based on the above design, the thirteenth resistor R13 and the first operational amplifier U2A and the fifth resistor R5 and the second operational amplifier U2B respectively realize the hysteresis comparator function. When the voltage input to the inverting input end is less than the reference voltage, the output states of the output ends of the first operational amplifier U2A and the second operational amplifier U2B are reversed.

[0043] In this embodiment, the first operational amplifier U2A and the second operational amplifier U2B can adopt push-pull output type operational amplifiers, wherein the fourteenth resistor R14 and the fifteenth resistor R15 as well as the sixteenth resistor R16 and the seventeenth resistor R17 are all input balancing resistors. When the output voltage V1-1 of the first voltage detection unit 131 exceeds the reference voltage Vref1, the first operational amplifier U2A outputs a low level. When the output voltage V2 of the second voltage detection unit 132 exceeds the reference voltage Vref2, the second operational amplifier U2B outputs a low level, otherwise it is a high level. The two level signals output by the first operational amplifier U2A and the second operational amplifier U2B are input to the logic operation unit 1333 to obtain the final detection signal, and are transmitted to the external intelligent device 300 through the I / O interface. Since the I / O interface at this time has a push-pull output function, the port of the external intelligent device 300 connected to the I / O interface may not require a pull-up resistor. It is understandable that in certain other embodiments, the first operational amplifier U2A and the second operational amplifier U2B may also adopt an open-drain output comparator, and the fourteenth resistor R14 and the fifteenth resistor R15 as input balancing resistors and the sixteenth resistor R16 and the seventeenth resistor R17 may not be set. Then, when the output voltage V2 of the second voltage detection unit 132 exceeds the reference voltage Vref2, the second operational amplifier U2B outputs a low level, otherwise it is in a high impedance state. The port of the external smart device 300 connected to the I / O interface of this embodiment requires a pull-up resistor.

[0044] Reference Figure 7 , Figure 7 The schematic diagram of the circuit structure of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the fifth embodiment of the utility model. The difference between this embodiment and the first embodiment mentioned above is that the specific structure of the open circuit detection output unit 133 is different, and the other structures are the same or similar. In this embodiment, the open circuit detection output unit 133 includes a logic control IC U4, and the two input pins of the logic control IC U4 are respectively connected to the output ends of the first voltage detection unit 131 and the second voltage detection unit 132, which are used to detect the magnitude of the output voltage of the AC / DC constant voltage circuit 11 and the chopper dimming circuit 12, and perform a logical AND operation on the detection results, so as to detect and obtain the load state of the constant voltage LED driving power supply 100. It can be seen that the functions of the first voltage comparison unit 1331 and the second voltage comparison unit 1332 in the above-mentioned embodiment are realized by the logic control IC U4 in this embodiment, and the circuit is more concise and flexible. Preferably, the logic control IC U4 can select a logic control IC of the SN74 series or the SL17 series.

[0045] In this embodiment, the output voltage V1-1 of the first voltage detection unit 131 is input into the logic control IC U4, and compared with the internal editable reference voltage to obtain data 1. When V1-1 exceeds the reference voltage, the data 1 is 0, and when it is less than the reference voltage, the data 1 is 1; the output voltage V2 of the second voltage detection unit 132 is input into the logic control IC U4, and compared with the internal editable reference voltage to obtain data 2. When V2 exceeds the reference voltage, the data 2 is 0, and when it is less than the reference voltage, the data 2 is 1; data 1 and data 2 are further logically ANDed inside IC3 to obtain data 3. If data 3 is 1, the logic control IC U4 outputs a high level, and if data 3 is 0, the logic control IC U4 outputs a low level, and is transmitted to the external intelligent device 300 through the I / O interface, and the port of the external intelligent device 300 connected to the I / O interface may not require a pull-up resistor.

[0046] Reference Figure 8 , Figure 8 The circuit structure diagram of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the sixth embodiment of the utility model. The difference between this embodiment and the first embodiment mentioned above is that the switch tube in the second voltage comparison unit 1332 is different, and the rest of the structures are the same or similar. In this embodiment, the switch tube Q2 in the second voltage comparison unit 1332 is a MOS tube, the drain of the MOS tube is used as the input end of the switch tube Q2, connected to the pull-up resistor R1, its source is used as the output end of the switch tube Q2, grounded SGND, and the gate of the MOS tube is used as the control end of the switch tube Q2, connected to the third current limiting resistor R3 and one end of the second filter capacitor C2. When the output voltage V2 of the second voltage detection unit 132 exceeds the gate conduction voltage of the MOS tube, the MOS tube is turned on, and the I / O interface is pulled down, otherwise the I / O interface is in a high impedance state. It can be seen that this embodiment can also realize the accurate detection of whether the load state of the constant voltage LED driving power supply 100 is open circuit or normal with light load under different dimming working states.

[0047] Reference Fig. 9 , Fig. 9The circuit structure diagram of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the seventh embodiment of the utility model. The difference between this embodiment and the first embodiment mentioned above is that the specific structure of the second voltage comparison unit 1332 is different, and the remaining structures are the same or similar. In this embodiment, the second voltage comparison unit 1332 includes a second operational amplifier U2B and a fifth resistor R5, the inverting input terminal of the second operational amplifier U2B is connected to the output terminal of the second voltage detection unit 132, and the non-inverting input terminal thereof is connected to the reference voltage Vref2, the output terminal of the second operational amplifier U2B is connected to the non-inverting input terminal through the fifth resistor R5, and the output terminal serves as the output terminal of the second voltage comparison unit 1332. In this embodiment, the second operational amplifier U2B adopts an open-drain comparator. When the output voltage V2 of the second voltage detection unit 132 exceeds the reference voltage Vref2, the second operational amplifier U2B outputs a low level, otherwise it is a high level. The two-level signals output by the switch tube Q1 and the second operational amplifier U2B are input to the logic operation unit 1333 to obtain the final detection signal, and are transmitted to the external intelligent device 300 provided with a pull-up resistor through the I / O interface.

[0048] Reference Fig.10 , Fig.10 The circuit structure diagram of the open circuit detection circuit 13 in the LED driving power supply 100 provided in the eighth embodiment of the utility model. The difference between this embodiment and the first embodiment mentioned above is that the specific structure of the second voltage comparison unit 1332 is different, and the other structures are the same or similar. In this embodiment, the second voltage comparison unit 1332 includes a second three-terminal voltage regulator IC2, a pull-up resistor R1, a sixth diode D6 and an eleventh resistor R11, the control electrode of the second three-terminal voltage regulator IC2 is connected to the output end of the second voltage detection unit 132, the anode of the second three-terminal voltage regulator IC2 is grounded SGND, and its cathode is connected to the external power supply VCC through the pull-up resistor R1 and serves as the output end of the second voltage comparison unit 1332, the positive electrode of the sixth diode D6 is connected to the cathode of the second three-terminal voltage regulator IC2 through the eleventh resistor R11, and the negative electrode of the sixth diode D6 is connected to the control electrode of the second three-terminal voltage regulator IC2. Preferably, in this embodiment, the second three-terminal voltage regulator IC2 uses a three-terminal voltage regulator of model TL431.

[0049] In this embodiment, when the duty cycle of the PWM signal is 0.1%-99.9%, the pulse voltage waveform of LED- (the low level is 0V, and the high level is the voltage of LED+) obtains a stable voltage V2 after passing through the second voltage detection unit 132. When the LED light string is lightly loaded or normally loaded, V2 exceeds the 2.5V reference voltage, and the cathode of the second three-terminal regulator IC2 is pulled down to a lower point. At this time, the first voltage comparison unit 1331 also outputs a low level, and the I / O interface is pulled down; when the LED light string is open, LED- is a voltage waveform of 0V, and after passing through the second voltage detection unit 132, V2 exceeds the 2.5V reference voltage. After the voltage detection unit 132 is turned on, a voltage V2 of 0V is obtained, which is less than the reference voltage of 2.5V, and a high impedance state is output. The first voltage comparison unit 1331 also outputs a high impedance state when it is unloaded, and the I / O interface is in a high impedance state. When the duty cycle of the PWM signal is 100%, the MOS tube Q3 is always turned on. At this time, no matter the load (LED light string) is open circuit or normally loaded, the second three-terminal regulator IC2 is not turned on, and the second voltage comparison unit 1332 outputs a high impedance state. At this time, the final detection signal of the open circuit detection circuit 13 depends on the first voltage detection unit 131 and the first voltage comparison unit 1331.

[0050] It is understandable that the first voltage comparison unit 1331 and the second voltage comparison unit 1332 in the first embodiment, the second embodiment, the third embodiment and the fourth embodiment can be randomly combined to form a new technical solution, or can be randomly combined with the logic operation unit 1333 in the third embodiment to form a new technical solution. For example, the second voltage comparison unit 1332 in the second embodiment can be used together with the first voltage comparison unit 1331 in the third embodiment or the fourth embodiment in the same open circuit detection circuit 13, and respectively connected to the first voltage detection unit 131 and the second voltage detection unit 132 to form a new technical solution, and the logic operation unit 1333 connected to the output ends of the first voltage comparison unit 1331 and the second voltage comparison unit 1332 can adopt the logic operation unit 1333 described in the first embodiment, or can also adopt the logic operation unit 1333 described in the third embodiment.

[0051] The utility model also provides a lamp, which includes the LED driving power supply 100 described in the above embodiment. Under different dimming working states, the first voltage detection unit 131 and the first voltage comparison unit 1331, the second voltage detection unit 132 and the second voltage comparison unit 1332 and the logic operation unit 1333 cooperate to realize the detection and accurate distinction of the load state, that is, when the dimming depth is high (the duty cycle is 0.1%) and the LED light string is an extremely small string of lights, or when the dimming duty cycle reaches 100%, an accurate detection signal can be obtained, and when the detection signal is in a high-impedance state, it can be determined that the load is open, and when the detection signal is at a low level, it can be determined that the load is lightly loaded or normally loaded, which can reduce the probability of misjudgment.

[0052] The above description is only a preferred embodiment of the utility model, and does not limit the utility model in any form. Those skilled in the art can make various equivalent changes and improvements based on the above embodiments, and all equivalent changes or modifications made within the scope of the claims should fall within the protection scope of the utility model.

Claims

1. An open circuit detection circuit, applied to a constant voltage LED driver with chopper dimming function, characterized in that: The open circuit detection circuit comprises: A first voltage detection unit, connected to the output end of the AC / DC constant voltage circuit in the constant voltage LED driving power supply, for obtaining the output voltage of the AC / DC constant voltage circuit; A second voltage detection unit is connected to the output end of the chopper dimming circuit in the constant voltage LED driving power supply and the negative electrode of the LED light string, and is used to obtain the output voltage of the chopper dimming circuit; An open circuit detection output unit is connected to the output ends of the first voltage detection unit and the second voltage detection unit, and is used to respectively detect the magnitudes of the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit when the duty cycles of the PWM signal received by the chopper dimming circuit are different, so as to output a final detection level according to the magnitude of the output voltage of the AC / DC constant voltage circuit when the duty cycle of the PWM signal received by the chopper dimming circuit is 100%, and to output a final detection level according to the magnitude of the output voltage of the chopper dimming circuit when the duty cycle of the PWM signal is 0.1%-99.9%, thereby detecting and knowing the load state of the constant voltage LED driving power supply.

2. The open circuit detection circuit according to claim 1, characterized in that: The open circuit detection output unit comprises: A first voltage comparison unit, connected to the output end of the first voltage detection unit, for comparing whether the output voltage of the AC / DC constant voltage circuit is greater than a reference voltage, and outputting a low level when the output voltage is greater than the reference voltage, and outputting a high impedance state when the output voltage is less than the reference voltage; a second voltage comparison unit, connected to the output end of the second voltage detection unit, for detecting the magnitude of the output voltage of the chopper dimming circuit, and outputting a high impedance state when the duty cycle of the PWM signal received by the chopper dimming circuit is 100% according to the magnitude of the output voltage of the chopper dimming circuit, outputting a high impedance state when the duty cycle of the PWM signal is 0.1%-99.9% and the LED light string is open, and outputting a low level when the duty cycle of the PWM signal is 0.1%-99.9% and the LED light string is working normally; A logic operation unit is connected to the first voltage comparison unit and the second voltage comparison unit, and is used to perform logic and processing on the signals output by the first voltage comparison unit and the second voltage comparison unit to detect the load state of the constant voltage LED driving power supply.

3. The open circuit detection circuit as claimed in claim 2, characterized in that: The first voltage comparison unit includes a first operational amplifier and a thirteenth resistor, the inverting input terminal of the first operational amplifier is connected to the output terminal of the first voltage detection unit, and the non-inverting input terminal thereof is connected to the reference voltage, the output terminal of the first operational amplifier is connected to the non-inverting input terminal through the thirteenth resistor, and the output terminal serves as the output terminal of the first voltage comparison unit.

4. The open circuit detection circuit according to claim 3, characterized in that: The first voltage comparison unit also includes a fourteenth resistor and a fifteenth resistor, the fourteenth resistor is connected between the non-inverting input terminal of the first operational amplifier and the reference voltage, and the fifteenth resistor is connected between the inverting input terminal of the first operational amplifier and the output terminal of the first voltage detection unit.

5. The open circuit detection circuit as claimed in claim 2, characterized in that: The first voltage comparison unit includes a switch tube and a pull-up resistor. The control end of the switch tube is connected to the output end of the first voltage detection unit. The output end of the switch tube is grounded, and its input end is connected to an external power supply through the pull-up resistor and serves as the output end of the first voltage comparison unit.

6. The open circuit detection circuit according to claim 2, characterized in that: The first voltage comparison unit includes a first three-terminal regulator and a pull-up resistor, the control electrode of the first three-terminal regulator is connected to the output end of the first voltage detection unit, the anode of the first three-terminal regulator is grounded, and the cathode is connected to an external power supply through the pull-up resistor and serves as the output end of the first voltage comparison unit.

7. The open circuit detection circuit according to claim 6, characterized in that: The first voltage comparison unit further includes a third diode and a tenth resistor, wherein the anode of the third diode is connected to the cathode of the first three-terminal regulator through the tenth resistor, and the cathode of the third diode is connected to the control electrode of the first three-terminal regulator.

8. The open circuit detection circuit as claimed in claim 2, characterized in that: The second voltage comparison unit includes a second operational amplifier and a fifth resistor, the inverting input terminal of the second operational amplifier is connected to the output terminal of the second voltage detection unit, and the non-inverting input terminal thereof is connected to the reference voltage, the output terminal of the second operational amplifier is connected to the non-inverting input terminal through the fifth resistor, and the output terminal serves as the output terminal of the second voltage comparison unit.

9. The open circuit detection circuit according to claim 8, characterized in that: The second voltage comparison unit also includes a sixteenth resistor and a seventeenth resistor, the sixteenth resistor is connected between the non-inverting input terminal of the second operational amplifier and the reference voltage, and the seventeenth resistor is connected between the inverting input terminal of the second operational amplifier and the output terminal of the second voltage detection unit.

10. The open circuit detection circuit according to claim 2, characterized in that: The second voltage comparison unit includes a switch tube and a pull-up resistor. The control end of the switch tube is connected to the output end of the second voltage detection unit. The output end of the switch tube is grounded, and its input end is connected to an external power supply through the pull-up resistor and serves as the output end of the second voltage comparison unit.

11. The open circuit detection circuit according to claim 5 or 10, characterized in that: The switch tube is a MOS tube, the drain of the MOS tube serves as the input end of the switch tube, the source of the MOS tube serves as the output end of the switch tube, and the gate of the MOS tube serves as the control end of the switch tube; or, the switch tube is a triode, the collector, emitter and base of the triode serve as the input end, output end and control end of the switch tube respectively.

12. The open circuit detection circuit according to claim 2, characterized in that: The second voltage comparison unit includes a second three-terminal regulator, a pull-up resistor, a sixth diode and an eleventh resistor. The control electrode of the second three-terminal regulator is connected to the output terminal of the second voltage detection unit. The anode of the second three-terminal regulator is grounded, and its cathode is connected to an external power supply through the pull-up resistor and serves as the output terminal of the second voltage comparison unit. The anode of the sixth diode is connected to the cathode of the second three-terminal regulator through the eleventh resistor, and the cathode of the sixth diode is connected to the control electrode of the second three-terminal regulator.

13. The open circuit detection circuit according to claim 2, characterized in that: The logic operation unit includes an AND gate, which is composed of two diodes, and the output ends of the first voltage comparison unit and the second voltage comparison unit are respectively connected to the cathode of a diode, and the anodes of the two diodes are connected and serve as the output end of the logic operation unit; or, the logic operation unit includes an AND gate logic IC, and the output ends of the first voltage comparison unit and the second voltage comparison unit are respectively connected to the two input pins of the AND gate logic IC, and the output pin of the AND gate logic IC serves as the output end of the logic operation unit.

14. The open circuit detection circuit according to claim 1, characterized in that: The open circuit detection output unit includes a logic control IC, and two input pins of the logic control IC are respectively connected to the output ends of the first voltage detection unit and the second voltage detection unit, and are used to detect the output voltages of the AC / DC constant voltage circuit and the chopper dimming circuit, and perform a logic AND operation on the detection results, so as to detect and obtain the load state of the constant voltage LED driving power supply.

15. The open circuit detection circuit according to claim 1, characterized in that: The first voltage detection unit includes a rectifier and filter circuit, a voltage-dividing resistor circuit and a filter circuit, the rectifier and filter circuit includes a fifth diode and a second electrolytic capacitor, the voltage-dividing resistor circuit includes a sixth resistor and an eighth resistor, and the filter circuit includes a ninth resistor and a third capacitor, wherein the positive electrode of the fifth diode is connected to the output end of the AC / DC constant voltage circuit, and the negative electrode thereof is connected to the positive electrode of the second electrolytic capacitor and the sixth resistor, the other end of the sixth resistor is connected to the ninth resistor and one end of the eighth resistor, the other end of the ninth resistor is connected to one end of the third capacitor and serves as the output end of the first voltage detection unit, and the other ends of the eighth resistor and the third capacitor and the negative electrode of the second electrolytic capacitor are all grounded.

16. The open circuit detection circuit according to claim 15, characterized in that: The first voltage detection unit also includes a seventh current limiting resistor and a first voltage regulator tube, the seventh current limiting resistor is connected between the output end of the AC / DC constant voltage circuit and the fifth diode, the cathode of the first voltage regulator tube is connected to one end where the eighth resistor and the sixth resistor are connected, and the anode thereof is grounded.

17. The open circuit detection circuit according to claim 1, characterized in that: The second voltage detection unit includes a DC blocking capacitor, a clamping diode and a second filter capacitor. One end of the DC blocking capacitor is connected to the output end of the chopper dimming circuit and the negative electrode of the LED light string. One end of the second filter capacitor is connected to the other end of the DC blocking capacitor and the negative electrode of the clamping diode and serves as the output end of the second voltage detection unit. The positive electrode of the clamping diode and the other end of the second filter capacitor are grounded.

18. The open circuit detection circuit according to claim 17, characterized in that: The second voltage detection unit also includes a second current limiting resistor, a second rectifier diode, a third current limiting resistor and a pull-down resistor, wherein the second current limiting resistor is connected between the DC blocking capacitor and the output end of the chopper dimming circuit, the second rectifier diode and the third current limiting resistor are connected in sequence between the cathode of the clamping diode and the second filter capacitor, one end of the pull-down resistor is connected to the third current limiting resistor and the second filter capacitor, and the other end is grounded.

19. An LED driving power supply, characterized in that: The invention comprises an AC / DC constant voltage circuit, a chopper dimming circuit, a controller and an open circuit detection circuit as described in any one of claims 1 to 18, wherein: The AC / DC constant voltage circuit is connected between the power input terminal and the LED light source, and the LED light source includes at least one LED light string; The chopper dimming circuit is connected to the AC / DC constant voltage circuit and is used to adjust the current input from the AC / DC constant voltage circuit to the LED light source according to the input PWM signal; The controller is connected to the chopping dimming circuit and is used to output a PWM signal to the chopping dimming circuit according to an external instruction; The open circuit detection circuit is connected to the output ends of the AC / DC constant voltage circuit and the chopper dimming circuit respectively to detect the output voltage of the AC / DC constant voltage circuit and the output voltage of the chopper dimming circuit respectively, thereby detecting the load state of the constant voltage LED driving power supply.

20. A lamp, characterized in that: Including the LED driving power supply as described in claim 19.

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