LED power supply

Abstract

The invention provides an LED power supply, which adopts constant-voltage and constant-current control, is configured to supply power to an LED device, and comprises an isolated DC-DC conversion circuit with a primary side and a secondary side, and a control module. The control module comprises a first control unit, a feedback circuit, a first switch, a second switch and an optical coupler. The first control unit is electrically connected to the primary side and is configured to control the operation of the isolated DC-DC conversion circuit. The optical coupler is used for electrically isolated signal transmission and comprises a transmitter and a receiver which are electrically connected to the secondary side and the first control unit respectively. When the output voltage is lower than the threshold voltage, the first switch is turned off, the second switch is turned on, so that the optical coupler is triggered to generate a trigger signal at the receiver, and the first control unit controls the isolated DC-DC conversion circuit to stop running based on the trigger signal.

Description

Technical Field

[0001] The present disclosure relates to a power supply, and more particularly to an LED (light-emitting diode) power supply. Background Art

[0002] The control of the output voltage and current of the LED power supply can be divided into constant voltage control (CV), constant current control (CC), constant voltage constant current control (CV / CC) and constant power control (CP). Figure 1 The voltage-current characteristic curves corresponding to each control mode are shown.

[0003] Conventional LED power supplies use constant voltage control, which outputs a fixed output voltage, and the output current increases with the load. When an overload occurs, the current rises and triggers the overcurrent protection. However, in the case of constant voltage control, in order to avoid false triggering of the overcurrent protection, the trigger current of the overcurrent protection must be greater than the full load current by a certain degree (for example, 30%), which will require the design of the LED power supply to retain more margin, but in the design of UL Class 2 output requiring 24V / 100W, the overcurrent protection design of 1.3 times the rated current cannot be accepted.

[0004] For this reason, most current LED power supplies adopt constant voltage and constant current control. When the output load is less than the rated load, the LED power supply operates in constant voltage control mode and outputs a fixed output voltage, and when the output load is greater than or equal to the rated load, the LED power supply operates in constant current control mode and outputs a fixed output current, thereby significantly reducing the margin reserved by the LED power supply for overload protection.

[0005] However, there have been several LED light bar fires in Japan recently, caused by rainwater seeping into the LED module and causing a local micro short circuit. Under constant voltage and constant current control, the output micro short circuit causes the output load to be greater than the rated load. After the LED power supply detects it, it will work in the constant current control mode. Although the LED power supply will reduce the output voltage due to the increase in the micro short circuit amplitude of the LED load, the LED power supply will continue to provide a fixed output current. Even if the LED lamp load generates an arc due to the micro short circuit and eventually causes the LED lamp load to smoke and catch fire, this LED power supply cannot activate the short circuit protection function.

[0006] Therefore, how to develop an LED power supply that can improve the above-mentioned prior art is an urgent need. Summary of the invention

[0007] The purpose of the present disclosure is to provide an LED power supply that adopts constant voltage and constant current control and can start protection and stop operation in real time when the output voltage is lower than a threshold voltage. Thus, the LED power supply of the present disclosure can stop operation in real time when the output voltage is abnormal (for example, but not limited to a load micro short circuit) to achieve protection of the LED power supply and the LED device it powers.

[0008] To achieve the above-mentioned purpose, the present disclosure provides an LED power supply, which adopts constant voltage and constant current control, is structured to power LED devices, and includes an input end, an output end, an isolated DC-DC conversion circuit and a control module. The isolated DC-DC conversion circuit has a primary side and a secondary side electrically connected to the input end and the output end, respectively, and is structured to receive an input voltage from the input end and provide an output voltage to the output end. The control module includes a first control unit, a feedback circuit, a first switch, a second switch and an optical coupler. The first control unit is electrically connected to the primary side and is structured to control the operation of the isolated DC-DC conversion circuit. The feedback circuit is electrically connected to the output voltage and includes a first resistor, a first diode and a second resistor connected in series. The first switch is electrically connected to the feedback circuit. The second switch is electrically connected to the first switch. The optical coupler is used for electrically isolated signal transmission, and includes a transmitter and a receiver electrically connected to the secondary side and the first control unit, respectively. When the output voltage is lower than the threshold voltage, the first switch is turned off and the second switch is turned on so that the optical coupler is triggered to generate a trigger signal at the receiver, and based on the trigger signal, the first control unit controls the isolated DC-DC conversion circuit to stop running. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The voltage-current characteristic curves of various output control methods for conventional LED power supplies are shown.

[0010] Figure 2 FIG. 4 is a schematic diagram of the circuit structure of the LED power supply according to the first embodiment of the present disclosure.

[0011] Figure 3 exemplify Figure 2 The relationship curve between the output voltage and output current of the LED power supply.

[0012] Figure 4 for Figure 2 Schematic diagram of the working timing of the LED power supply.

[0013] Figure 5 exemplify Figure 2 Experimental waveform of LED power supply.

[0014] Figure 6 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a second embodiment of the present disclosure.

[0015] Figure 7 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a third embodiment of the present disclosure.

[0016] Figure 8 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a fourth embodiment of the present disclosure.

[0017] Description of reference numerals:

[0018] 1: LED power supply

[0019] 11: Isolated DC-DC conversion circuit

[0020] 12: Control module

[0021] 13: Input terminal

[0022] 14: Output

[0023] Vin: input voltage

[0024] Vo: output voltage

[0025] Io: output current

[0026] 121: First control unit

[0027] 122: Second control unit

[0028] 123: The first optical coupler

[0029] Q1: First switch

[0030] FB: Feedback terminal

[0031] 124: Transmitter

[0032] 125: Receiver

[0033] Vcc1, Vcc2: supply voltage

[0034] I1: Threshold current

[0035] V1: Rated voltage

[0036] V2: threshold voltage

[0037] CV: Constant voltage control terminal

[0038] CC: Constant current control terminal

[0039] D1, D2: diodes

[0040] R1: Resistor

[0041] Q2: Second switch

[0042] R2: Resistor

[0043] C1: Capacitor

[0044] A: Node

[0045] B: Node

[0046] R3, R4: resistors

[0047] C2, C3: capacitors

[0048] D3, D4: diodes

[0049] Va: voltage on node A

[0050] Vb: voltage on node B

[0051] Vtha: Threshold

[0052] Vthb: Threshold

[0053] 126: Transmitter

[0054] 127a, 127b, 127c: Receiver

[0055] 1a, 1b, 1c: LED power supply

[0056] 12a, 12b, 12c: Control module

[0057] R5: Resistor

[0058] C4: Capacitor

[0059] PT: Protection trigger terminal

[0060] C5: Capacitor

[0061] Q3: The third switch

[0062] Q4: The fourth switch

[0063] 15: Trigger circuit

[0064] Q5: The fifth switch

[0065] Q6: The sixth switch DETAILED DESCRIPTION

[0066] Some typical embodiments that embody the features and advantages of the present disclosure will be described in detail in the following description. It should be understood that the present disclosure can have various changes in different implementations without departing from the scope of the present disclosure, and the descriptions and illustrations therein are essentially for illustrative purposes rather than for limiting the present disclosure.

[0067] Figure 2FIG. 1 is a schematic diagram of the circuit structure of the LED power supply of the first embodiment of the present disclosure. Figure 2 As shown, the LED power supply 1 of the present disclosure adopts constant voltage constant current control (CV / CC), and is structured to power an LED device (not shown), and includes an isolated DC-DC conversion circuit 11, a control module 12, an input terminal 13, and an output terminal 14. The isolated DC-DC conversion circuit 11 has a primary side and a secondary side electrically connected to the input terminal 13 and the output terminal 14, respectively, wherein the primary side is used to receive an input voltage Vin from the input terminal 13, and after conversion by the isolated DC-DC conversion circuit 11, the secondary side provides the output voltage Vo and output current Io of the LED power supply 1 to the output terminal 14. In some embodiments, the input voltage Vin received by the input terminal 13 is provided to the primary side of the isolated DC-DC conversion circuit 11 via a power factor correction circuit (not shown). The control module 12 includes a first control unit 121, a second control unit 122, a feedback circuit, a first switch Q1, a second switch Q2, and an optical coupler (including but not limited to the first optical coupler 123).

[0068] The first control unit 121 is electrically connected to the primary side of the isolated DC-DC converter circuit 11 and is configured to control the operation of the isolated DC-DC converter circuit 11, and the first control unit 121 has a feedback terminal FB. The feedback circuit is electrically connected to the output voltage Vo and includes a resistor R1, a diode D1 (Zener diode) and a resistor R2 connected in series. The first switch Q1 is electrically connected to the feedback circuit and the second switch Q2. The first optical coupler 123 is used for electrically isolated signal transmission and includes a transmitter 124 and a receiver 125, wherein the transmitter 124 and the receiver 125 are electrically connected to the secondary side of the isolated DC-DC converter circuit 11 and the first control unit 121, respectively. The second control unit 122 is electrically connected to the secondary side of the isolated DC-DC converter circuit 11 and the transmitter 124, and is configured to detect the output voltage Vo and the output current Io and generate a control signal. The control signal generated by the second control unit 122 is transmitted to the feedback terminal FB of the first control unit 121 via the optical coupler 123, so that the first control unit 121 controls the operation of the isolated DC-DC converter circuit 11 according to the control signal.

[0069] Figure 3 exemplify Figure 2 The relationship curve between the output voltage and output current of the LED power supply. Figure 2 and Figure 3As shown, when the output load of the LED power supply 1 is less than the rated load, the isolated DC-DC conversion circuit 11 operates in a constant voltage control mode, at which time the first switch Q1 is turned on, the second switch Q2 is turned off, the output current Io is less than the threshold current I1, and the isolated DC-DC conversion circuit 11 outputs a fixed output voltage Vo (equal to the rated voltage V1). When the output load is greater than or equal to the rated load, the isolated DC-DC conversion circuit 11 operates in a constant current control mode. In the constant current control mode, if the output voltage Vo is greater than the threshold voltage V2, the second switch Q2 remains turned off, and the isolated DC-DC conversion circuit 11 outputs a fixed output current Io (equal to the threshold current I1); and if the output voltage Vo is lower than the threshold voltage V2, the second switch Q2 is turned on so that the optical coupler is triggered and a trigger signal is generated in the receiver, and based on the trigger signal, the first control unit 121 controls the isolated DC-DC conversion circuit 11 to stop operating. The threshold voltage V2 can be, for example but not limited to, equal to 80% of the rated voltage V1, and the specific size of the threshold voltage V2 can be set according to actual needs.

[0070] Specifically, in Figure 2 In the first embodiment shown, if the output voltage Vo is lower than the threshold voltage V2, the second switch Q2 is turned on to connect the supply voltage Vcc1 of the second control unit 122 to the ground, and the optical coupler 123 is triggered to generate a trigger signal at the receiver 125. The trigger signal increases the voltage level of the feedback terminal FB of the first control unit 121, so that the first control unit 121 activates the protection function and controls the isolated DC-DC converter circuit 11 to stop running.

[0071] Thus, the LED power supply 1 of the present disclosure can stop running in real time when the output voltage Vo is abnormal (for example but not limited to a load micro short circuit), so as to protect the LED power supply 1 and the LED device it powers.

[0072] Please refer to Figure 2 .At Figure 2In the first embodiment shown, the control module 12 further includes a constant voltage control terminal CV, a constant current control terminal CC, and diodes D2 and D3. The first end of the transmitter 124 is electrically connected to the secondary side of the isolated DC-DC converter circuit 11, the second control unit 122, and the output terminal 14, the second end of the transmitter 124 is electrically connected to the anodes of the diodes D2 and D3, and the cathodes of the diodes D2 and D3 are electrically connected to the constant voltage control terminal CV and the constant current control terminal CC, respectively. The constant voltage control terminal CV is configured to receive a control signal generated by the second control unit 122 when the output load is less than the rated load, wherein the control signal is transmitted to the first control unit 121 via the constant voltage control terminal CV and the first optical coupler 123, so that the first control unit 121 controls the isolated DC-DC converter circuit 11 to operate in a constant voltage control mode according to the control signal. The constant current control terminal CC is configured to receive a control signal generated by the second control unit 122 when the output load is greater than or equal to the rated load and the output voltage Vo is greater than the threshold voltage V2, wherein the control signal is transmitted to the first control unit 121 via the constant current control terminal CC and the first optical coupler 123, so that the first control unit 121 controls the isolated DC-DC conversion circuit 11 to operate in a constant current control mode according to the control signal.

[0073] In addition, the feedback circuit also includes a resistor R3, a capacitor C1, a diode D4 (Zener diode) and a capacitor C2. The two ends of the resistor R1 are electrically connected to the output voltage Vo and the node A, the cathode and the anode of the diode D1 are electrically connected to the node A and the first end of the resistor R2, and the two ends of the resistor R3 are electrically connected to the output voltage Vo and the node B. The first end, the second end and the third end of the first switch Q1 are electrically connected to the node B, the anode of the diode D1 and the second end of the resistor R2. The two ends of the capacitor C1 are electrically connected to the node B and the third end of the first switch Q1, and the cathode and the anode of the diode D4 are electrically connected to the node B and the first end of the second capacitor C2. The second switch Q2 is electrically connected to the anode of the diode D4 and the capacitor C2. In addition, the control module 12 also includes a resistor R4 and a capacitor C3 connected in series between the output voltage Vo and the ground terminal, wherein the resistor R4 and the capacitor C3 are electrically connected to the output voltage Vo and the ground terminal, respectively, and the connection point between the resistor R4 and the capacitor C3 is also electrically connected to the second control unit 122. The first switch Q1 may be, for example, but not limited to, an NPN transistor, wherein the first terminal, the second terminal, and the third terminal of the first switch Q1 are respectively a collector, a base, and an emitter. The second switch Q2 may be, for example, but not limited to, a field effect transistor, wherein the first terminal, the second terminal, and the third terminal of the second switch Q2 are respectively a drain, a gate, and a source.

[0074] It should be noted that in Figure 2In the first embodiment shown, the first end, the second end and the third end of the second switch Q2 are electrically connected to the second control unit 122, the anode of the diode D4 and the ground end, respectively. In the first embodiment, in addition to transmitting the control signal for controlling the isolated DC-DC converter circuit 11 to operate in the constant voltage or constant current control mode, the first optical coupler 123 is also used to generate a trigger signal when the output voltage Vo is lower than the threshold voltage V2 to enable the first control unit 121 to start the protection function to control the isolated DC-DC converter circuit 11 to stop operating. The specific operating principle is described as follows.

[0075] See also Figure 2 and Figure 4 ,in Figure 4 for Figure 2 The working sequence diagram of the LED power supply. Figure 4 In FIG. 1 , FB represents the voltage level at the feedback terminal FB, Va is the voltage at the node A, and Vb is the voltage at the node B. Since the voltage Va at the node A is proportional to the output voltage Vo of the LED power supply 1, the voltage Va can reflect the change in the magnitude of the output voltage Vo. Figure 2 and Figure 4 As shown, when the LED power supply 1 is initially started, the output voltage Vo gradually increases, and correspondingly, the supply voltage Vcc1 gradually increases, and because the output voltage Vo does not reach the preset threshold of the constant voltage control, the voltage level on the feedback terminal FB is maintained at a high potential. In the process of establishing a high potential, the first switch Q1 and the second switch Q2 are both in the off state at first, and the voltage Va on the node A gradually increases. When the voltage Va is less than the threshold value Vtha, the RC circuit formed by the resistor R3 and the capacitor C1 is charged, so that the voltage Vb on the node B gradually increases. The time for the voltage Va to gradually increase from zero to the threshold value Vtha is the RC delay time. When the voltage Va rises to the threshold value Vtha, the first switch Q1 switches to the on state, so that the RC circuit discharges and the voltage Vb drops to zero. When the output voltage Vo is greater than the threshold voltage V2, the voltage Va is correspondingly greater than the threshold value Vtha. It should be noted that the first control unit 121 has a protection delay time when the feedback terminal FB initially establishes a high potential to avoid false triggering of the protection function due to the high potential of the feedback terminal FB. When the output voltage Vo reaches the preset constant voltage control threshold, the second control unit 122 starts feedback control, the voltage level on the feedback terminal FB returns to a low potential, the first switch Q1 remains in the on state, and the second switch Q2 remains in the off state.

[0076] Then, assuming that the output voltage Vo gradually decreases due to an abnormal state, the voltage Va will also decrease accordingly. When the voltage Va drops below the threshold value Vtha, the first switch Q1 switches to the off state, and the RC circuit is charged to increase the voltage Vb. When the voltage Vb rises to the threshold value Vthb, the second switch Q2 switches to the on state, causing the power supply voltage Vcc1 to be grounded, the second control unit 122 stops generating the control signal, and the voltage level of the feedback terminal FB is increased to a high potential. After the voltage level of the feedback terminal FB is at a high potential for a period of time exceeding a preset time, the first control unit 121 activates the protection function to control the isolated DC-DC conversion circuit 11 to stop running.

[0077] Figure 5 exemplify Figure 2 The experimental waveform of the LED power supply. Figure 5 As shown, when a micro short circuit occurs in the output LED lamp load or the LED lamp load is overpowered, the LED power supply 1 will operate in constant current control. If the LED micro short circuit or overpower situation becomes more serious, the output voltage Vo will drop accordingly. When the output voltage Vo drops to the set threshold, the protection function can be activated in real time to stop the operation of the LED power supply 1 to quickly reduce the output current Io, thereby avoiding damage to the LED power supply 1 and the LED device it powers.

[0078] As can be seen from the foregoing, the focus of the present disclosure is that when the output voltage Vo is too low (i.e., lower than the threshold voltage V2), through the operation of the feedback circuit and the first switch Q1, the second switch Q2 can be turned on to trigger the corresponding optical coupler to generate a trigger signal in its receiver, thereby causing the first control unit 121 to control the isolated DC-DC converter circuit 11 to stop operating based on the trigger signal to achieve protection. It should be noted that the specific method of setting and triggering the optical coupler and the first control unit 121 controlling the isolated DC-DC converter circuit 11 to stop operating based on the trigger signal is actually not limited to the example of the first embodiment. Several possible implementations will be illustrated below.

[0079] Figure 6 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a second embodiment of the present disclosure. Figure 6 Zhongyu Figure 2 Similar structures or elements are denoted by the same reference numerals and will not be described in detail herein. Figure 2 The difference between the power supply 1 and Figure 6 In the LED power supply 1a, the optical coupler of the control module 12a further includes a second optical coupler. Figure 6As shown, the two ends of the transmitter 126 of the second optical coupler are electrically connected to the output voltage Vo and the first end of the second switch Q2, respectively, the second end and the third end of the second switch Q2 are electrically connected to the anode of the diode D4 and the second end of the capacitor C2, respectively, and the two ends of the receiver 127a of the second optical coupler are electrically connected to the power supply voltage Vcc2 of the first control unit 121 and the protection trigger terminal PT. When the output voltage Vo is lower than the threshold voltage V2, based on the feedback circuit (the operating principle is the same as the first embodiment), the first switch Q1 is turned off, the second switch Q2 is turned on to trigger the second optical coupler, and the receiver 127a of the second optical coupler generates a trigger signal to increase the voltage level of the protection trigger terminal PT, thereby enabling the first control unit 121 to start the protection function to control the isolated DC-DC conversion circuit 11 to stop running. In some embodiments, the control module 12a further includes a resistor R5 and a capacitor C4, wherein the resistor R5 is electrically connected between the receiver 127a of the second optical coupler and the power supply voltage Vcc2 of the first control unit 121, and the two ends of the capacitor C4 are electrically connected to the protection trigger terminal PT and the ground terminal. It can be seen that in the second embodiment, the first optocoupler 123 is used to transmit a control signal for controlling the isolated DC-DC converter circuit 11 to operate in a constant voltage or constant current control mode, and the second optocoupler is used to generate a trigger signal when the output voltage Vo is lower than the threshold voltage V2, so that the first control unit 121 starts the protection function due to the increase in the voltage level of the protection trigger terminal PT, thereby controlling the isolated DC-DC converter circuit 11 to stop operating.

[0080] Figure 7 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a third embodiment of the present disclosure. Figure 7 Zhongyu Figure 6 Similar structures or elements are denoted by the same reference numerals and will not be described in detail herein. Figure 6 The difference between the power supply 1a and Figure 7 In the LED power supply 1b, the arrangement position of the receiver of the second optical coupler of the control module 12b is different. Figure 6As shown, in the third embodiment, the two ends of the receiver 127b of the second optical coupler are electrically connected to the protection trigger terminal PT and the ground terminal of the first control unit 121, respectively. Therefore, when the output voltage Vo is lower than the threshold voltage V2, based on the feedback circuit (the operation principle is the same as the first embodiment), the first switch Q1 is turned off, the second switch Q2 is turned on to trigger the second optical coupler, and the receiver 127b of the second optical coupler generates a trigger signal to reduce the voltage level of the protection trigger terminal PT, thereby enabling the first control unit 121 to start the protection function to control the isolated DC-DC conversion circuit 11 to stop running. In some embodiments, the control module 12b further includes a capacitor C5, wherein the capacitor C5 is connected in parallel to the receiver 127b of the second optical coupler. It can be seen that in the third embodiment, the first optocoupler 123 is used to transmit a control signal for controlling the isolated DC-DC converter circuit 11 to operate in a constant voltage or constant current control mode, and the second optocoupler is used to generate a trigger signal when the output voltage Vo is lower than the threshold voltage V2, so that the first control unit 121 activates the protection function due to the reduction of the voltage level of the protection trigger terminal PT, thereby controlling the isolated DC-DC converter circuit 11 to stop operating.

[0081] Figure 8 FIG. 4 is a schematic diagram of a circuit structure of an LED power supply according to a fourth embodiment of the present disclosure. Figure 8 Zhongyu Figure 7 Similar structures or elements are denoted by the same reference numerals and will not be described in detail herein. Figure 7 The difference between the power supply 1b is that in Figure 8 In the LED power supply 1c, the receiver of the second optical coupler of the control module 12c is arranged at a different position, and the control module 12c includes a third switch Q3, a fourth switch Q4 and a trigger circuit 15. Figure 8As shown, in the fourth embodiment, the third switch Q3 and the fourth switch Q4 are configured to rectify the input voltage Vin to provide the power supply voltage Vcc2 of the first control unit 121, the first end of the receiver 127c of the second optical coupler is electrically connected to the power supply voltage Vcc2 of the first control unit 121, and the trigger circuit 15 is electrically connected to the second end of the receiver 127c of the second optical coupler and the sixth switch Q6. When the output voltage Vo is lower than the threshold voltage V2, based on the feedback circuit (the operation principle is the same as that of the first embodiment), the first switch Q1 is turned off, the second switch Q2 is turned on and the second optical coupler is triggered, the receiver 127c of the second optical coupler generates a trigger signal, and the trigger circuit 15 is activated when receiving the trigger signal to turn off the third switch Q3, and then turn off the fourth switch Q4. At this time, the power supply voltage Vcc2 of the first control unit 121 is grounded, so that the first control unit 121 controls the isolated DC-DC conversion circuit 11 to stop running. It can be seen that in the fourth embodiment, the first optocoupler 123 is used to transmit a control signal for controlling the isolated DC-DC converter circuit 11 to operate in a constant voltage or constant current control mode, and the second optocoupler is used to generate a trigger signal when the output voltage Vo is lower than the threshold voltage V2, so that the first control unit 121 stops generating the control signal due to the grounding of the power supply voltage Vcc2, thereby stopping the operation of the isolated DC-DC converter circuit 11 for protection.

[0082] In addition, the trigger circuit 15 may be, for example but not limited to Figure 8 The third switch Q3 and the fifth switch Q5 may be NPN transistors, and the fourth switch Q4 and the sixth switch Q6 may be PNP transistors, but the present invention is not limited thereto.

[0083] In summary, the present disclosure provides an LED power supply that adopts constant voltage and constant current control, and can start protection and stop operation in real time when the output voltage is lower than the threshold voltage. Thus, the LED power supply of the present disclosure can stop operation in real time when the output voltage is abnormal, so as to protect the LED power supply and the LED device it powers.

[0084] It should be noted that the above are only preferred embodiments for illustrating the present disclosure, and the present disclosure is not limited to the embodiments described. The scope of the present disclosure is determined by the claims. Moreover, the present disclosure may be modified in various ways by those skilled in the art, but all of them are within the scope of the claims.

Claims

1. An LED power supply adopting constant voltage and constant current control and configured to power an LED device, and comprising: an input terminal and an output terminal; an isolated DC-DC converter circuit having a primary side and a secondary side electrically connected to the input terminal and the output terminal respectively, and configured to receive an input voltage from the input terminal and provide an output voltage to the output terminal; and A control module, comprising: a first control unit, electrically connected to the primary side and configured to control the operation of the isolated DC-DC conversion circuit; a feedback circuit electrically connected to the output voltage and comprising a first resistor, a first diode and a second resistor connected in series, a first switch electrically connected to the feedback circuit; a second switch electrically connected to the first switch; and an optical coupler for electrically isolating signal transmission and comprising a transmitter and a receiver electrically connected to the secondary side and the first control unit, respectively; When the output voltage is lower than a threshold voltage, the first switch is turned off and the second switch is turned on so that the optical coupler is triggered to generate a trigger signal in the receiver, and based on the trigger signal, the first control unit controls the isolated DC-DC conversion circuit to stop running.

2. The LED power supply as claimed in claim 1, wherein when the output load of the LED power supply is less than a rated load, the isolated DC-DC conversion circuit operates in a constant voltage control mode, the first switch is in an on state, the second switch is in an off state, the output current of the isolated DC-DC conversion circuit is less than a threshold current, and the output voltage is fixedly equal to a rated voltage.

3. The LED power supply as described in claim 2, wherein when the output load is greater than or equal to the rated load, the isolated DC-DC conversion circuit operates in a constant current control mode; in the constant current control mode, if the output voltage is greater than the threshold voltage, the first switch is in an on state, the second switch is in an off state, and the output current is equal to the threshold current; if the output voltage is lower than the threshold voltage, the first switch is in an off state, the second switch is in an on state, and the first control unit controls the isolated DC-DC conversion circuit to stop operating. 4 . The LED power supply as claimed in claim 3 , wherein the threshold voltage is equal to 80% of the rated voltage.

5. The LED power supply as claimed in claim 3, wherein the optical coupler comprises a first optical coupler, and the control module further comprises: A second control unit is electrically connected to the secondary side and the transmitter of the first optocoupler, and is configured to detect the output voltage and the output current and generate a control signal, wherein the control signal is transmitted to a feedback end of the first control unit via the first optocoupler, and the first control unit controls the operation of the isolated DC-DC conversion circuit according to the control signal.

6. The LED power supply as claimed in claim 5, wherein the control module further comprises: a constant voltage control terminal, electrically connected to the transmitter of the first optical coupler, configured to receive the control signal generated by the second control unit when the output load is less than the rated load, the control signal being transmitted to the first control unit via the constant voltage control terminal and the first optical coupler, and the first control unit controlling the isolated DC-DC converter circuit to operate in the constant voltage control mode according to the control signal; and A constant current control end is electrically connected to the transmitter of the first optical coupler and is configured to receive the control signal generated by the second control unit when the output load is greater than or equal to the rated load and the output voltage is greater than the threshold voltage. The control signal is transmitted to the first control unit via the constant current control end and the first optical coupler. The first control unit controls the isolated DC-DC converter circuit to operate in the constant current control mode according to the control signal.

7. The LED power supply as described in claim 6, wherein the control module further includes a second diode and a third diode, the second diode is electrically connected between the emitter of the first optical coupler and the constant voltage control end, and the anode and cathode of the second diode are electrically connected to the emitter and the constant voltage control end of the first optical coupler, respectively, the third diode is electrically connected between the emitter of the first optical coupler and the constant current control end, and the anode and cathode of the third diode are electrically connected to the emitter and the constant current control end of the first optical coupler, respectively.

8. The LED power supply as claimed in claim 5, wherein the feedback circuit further comprises a third resistor, a first capacitor, a fourth diode and a second capacitor, two ends of the first resistor are electrically connected to the output voltage and a first node respectively, a cathode and an anode of the first diode are electrically connected to the first node and the first end of the second resistor respectively, two ends of the third resistor are electrically connected to the output voltage and a second node respectively, a first end, a second end and a third end of the first switch are electrically connected to the second node, the anode of the first diode and the second end of the second resistor respectively, two ends of the first capacitor are electrically connected to the second node and the third end of the first switch respectively, a cathode and an anode of the fourth diode are electrically connected to the second node and the first end of the second capacitor respectively, and the second switch is electrically connected to the anode of the fourth diode and the second capacitor; the control module further comprises a fourth resistor and a third capacitor connected in series between the output voltage and the ground terminal, the fourth resistor and the third capacitor are electrically connected to the output voltage and the ground terminal respectively, and a connection point between the fourth resistor and the third capacitor is also electrically connected to the second control unit.

9. The LED power supply as claimed in claim 8, wherein a first voltage on the first node is proportional to the output voltage, when the output voltage is greater than the threshold voltage, the first voltage is correspondingly greater than a first threshold, the first switch is in an on state, a second voltage on the second node is zero, and the second switch is in an off state; and when the output voltage is less than the threshold voltage, the first voltage is correspondingly less than the first threshold, the first switch is in an off state, and the second voltage rises to switch the second switch to an on state.

10. The LED power supply as claimed in claim 9, wherein the first end, the second end and the third end of the second switch are electrically connected to the second control unit, the anode of the fourth diode and the ground end respectively, when the output voltage is lower than the threshold voltage, the second switch is turned on to connect the power supply voltage of the second control unit to the ground, the receiver of the first optical coupler generates the trigger signal to increase the voltage level of the feedback end, thereby enabling the first control unit to activate a protection function to control the isolated DC-DC conversion circuit to stop operating.

11. The LED power supply as claimed in claim 9, wherein the optical coupler further comprises a second optical coupler, the two ends of the transmitter of the second optical coupler are respectively electrically connected to the output voltage and the first end of the second switch, the second end and the third end of the second switch are respectively electrically connected to the anode of the fourth diode and the second end of the second capacitor, and the two ends of the receiver of the second optical coupler are respectively electrically connected to the supply voltage and the protection trigger end of the first control unit; when the output voltage is lower than the threshold voltage, the second switch is turned on to trigger the second optical coupler, and the receiver of the second optical coupler generates the trigger signal to increase the voltage level of the protection trigger end, thereby causing the first control unit to activate the protection function to control the isolated DC-DC conversion circuit to stop running.

12. The LED power supply as claimed in claim 9, wherein the optical coupler further comprises a second optical coupler, the two ends of the transmitter of the second optical coupler are respectively electrically connected to the output voltage and the first end of the second switch, the second end and the third end of the second switch are respectively electrically connected to the anode of the fourth diode and the second end of the second capacitor, and the two ends of the receiver of the second optical coupler are respectively electrically connected to the protection triggering end of the first control unit and the grounding end; when the output voltage is lower than the threshold voltage, the second switch is turned on to trigger the second optical coupler, and the receiver of the second optical coupler generates the trigger signal to reduce the voltage level of the protection triggering end, thereby causing the first control unit to activate the protection function to control the isolated DC-DC conversion circuit to stop running.

13. The LED power supply as claimed in claim 9, wherein the optical coupler further comprises a second optical coupler, the two ends of the transmitter of the second optical coupler are respectively electrically connected to the output voltage and the first end of the second switch, the second end and the third end of the second switch are respectively electrically connected to the anode of the fourth diode and the second end of the second capacitor, and the first end of the receiver of the second optical coupler is electrically connected to the supply voltage of the first control unit; the control module further comprises a third switch, a fourth switch and a trigger circuit, the third switch and the fourth switch are configured to rectify the input voltage to provide the supply voltage of the first control unit, the trigger circuit is electrically connected to the second end of the receiver of the second optical coupler and a sixth switch; when the output voltage is lower than the threshold voltage, the second switch is turned on to trigger the second optical coupler, the receiver of the second optical coupler generates the trigger signal, and the trigger circuit turns off the third switch when receiving the trigger signal, thereby turning off the fourth switch, and at this time, the supply voltage of the first control unit is grounded, so that the first control unit controls the isolated DC-DC conversion circuit to stop running.

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