LED power supply

Abstract

To provide an LED power supply that immediately stops operation when an output voltage is abnormal, thereby protecting an LED device.SOLUTION: An LED power supply adopts constant voltage constant current control and includes an isolated DC-DC conversion circuit having primary and secondary sides and a control module. The control module includes a first control unit, a feedback circuit, a first switch, a second switch, and an optocoupler, and the first control unit is electrically connected to the primary side and configured to control the operation of the isolated DC-DC conversion circuit. The optocoupler is used for transmitting an electrically isolated signal and is electrically connected to the secondary side and the transmitter and receiver of the first control unit. When the output voltage is smaller than a threshold voltage, the first switch is turned off and the second switch is turned on, the optocoupler is triggered, and the receiver generates a trigger signal, and according to the trigger signal, the first control unit controls the isolated DC-DC conversion circuit to stop operating.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to power supplies, and more particularly to power supplies for LEDs (light-emitting diodes). [Background technology]

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

[0003] Conventional LED power supplies use constant voltage control, which outputs a fixed output voltage and the output current rises as the load increases. When the load increases, the current increases and the overcurrent protection is activated. In the case of constant voltage control, the trigger current of the overcurrent protection must be somewhat higher (e.g. 30%) than the full load current to avoid the overcurrent protection from being activated accidentally. This requires a margin in the design of the LED power supply, but the design of UL Class 2 output requirements 24V / 100W does not allow for an overcurrent protection design of 1.3 times the rated current.

[0004] For this reason, existing LED power supplies use 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. When the output load is equal to or greater than the rated load, the LED power supply operates in constant current control mode and outputs a fixed output current. This allows the LED power supply to significantly reduce the margin it needs to secure for overcurrent protection.

[0005] However, in recent years, LED lamp fires have been occurring frequently in Japan, and most of these are caused by rainwater seeping into the LED module and causing an internal short circuit. In constant voltage constant current control, if the output load becomes larger than the rated load due to an output short circuit, the LED power supply detects this and operates in constant current control mode. However, even if the output of the LED power supply drops due to an increase in the short circuit level of the LED load, the LED power supply continues to supply a fixed output current. There is a problem in that even if the LED lamp generates an arc due to a short circuit and the LED lamp eventually smokes or catches fire, the LED power supply cannot activate the short circuit protection function.

[0006] Therefore, there is currently an urgent need to develop an LED power supply that can improve the above-mentioned shortcomings of the prior art. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide an LED power supply, which adopts constant voltage constant current control and immediately activates a protection function to stop operation when the output voltage is below a threshold voltage. As a result, the LED power supply of the present invention immediately stops operation when the output voltage is abnormal (for example, but not limited to, a micro-short circuit of a load), and can protect the LED power supply and the LED device it supplies power to. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides an LED power supply. The LED power supply adopts constant voltage constant current control, is configured to supply power to an LED device, and includes an input end, an output end, an isolated DC-DC conversion circuit, and a control module. The isolated DC-DC conversion circuit is electrically connected to the primary side and the secondary side of the input end and the output end, and is configured to input an input voltage from the input end and output 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 configured 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 transmitting an electrically isolated signal, and includes a transmitter and a receiver electrically connected to the secondary side and the first control unit, respectively. When the output voltage is less than the threshold voltage, the first switch is turned off, the second switch is turned on, the optical coupler is triggered, and a trigger signal is generated in the receiver. Based on the trigger signal, the first control unit controls the operation of the isolated DC-DC conversion circuit to stop. [Brief description of the drawings]

[0009] [Figure 1] Illustrates the voltage-current characteristic curves of various output control methods for an LED power supply. [Diagram 2] FIG. 2 is an electric circuit diagram of the LED power supply according to the first embodiment of the present invention. [Diagram 3] Figure 2 shows the relationship between the output voltage and the output current of the LED power supply. [Figure 4] This shows the operation sequence of the LED power supply in Figure 2. [Diagram 5] Figure 2 shows the experimental waveforms of the LED power supply. [Figure 6] FIG. 6 is an electric circuit diagram of an LED power supply according to a second embodiment of the present invention. [Figure 7] FIG. 11 is an electric circuit diagram of an LED power supply according to a third embodiment of the present invention. [Figure 8] FIG. 11 is an electric circuit diagram of an LED power supply according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Some exemplary embodiments embodying the features and advantages of the present invention will be described in detail in the following description. Various modifications can be made in different aspects without departing from the scope of the present invention, and the detailed description and drawings of the invention are for the purpose of explaining the present invention, and are not intended to limit the scope of the present invention.

[0011] FIG. 2 is a schematic diagram of an LED power supply in a first embodiment of the present invention. As shown in FIG. 2, the LED power supply 1 of the present invention adopts constant voltage constant current control (CV / CC) and is configured to supply power to 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 includes a primary side and a secondary side electrically connected to the input terminal 13 and the output terminal 14, respectively, and the primary side is used to receive an input voltage Vin from the input terminal 13, and after being converted by the isolated DC-DC conversion circuit 11, supplies an output voltage Vo and an output current Io of the LED power supply 1 to the output terminal 14 via the secondary side. In another embodiment, the input voltage Vin received by the input terminal 13 is supplied to the primary side of the isolated DC-DC conversion circuit 11 via a power factor correction circuit (not shown). The control module 12 comprises 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 a first optical coupler 123).

[0012] The first control unit 121 is electrically connected to the primary side of the isolated DC-DC conversion circuit 11 and configured to control the operation of the isolated DC-DC conversion circuit 11. The first control unit 121 includes 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 transmitting an electrically isolated signal and includes a transmitter 124 and a receiver 125. The transmitter 124 and the receiver 125 are electrically connected to the secondary side of the isolated DC-DC conversion 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 conversion circuit 11 and the transmitter 124 and configured to detect the output voltage Vo and the output current Io to generate a control signal. The control signal generated by the second control unit 122 is transmitted to the feedback end FB of the first control unit 121 via the optical coupler 123, thereby causing the first control unit 121 to control the operation of the isolated DC-DC conversion circuit 11 in accordance with the control signal.

[0013] FIG. 3 shows the relationship between the output voltage and the output current of the LED power supply in FIG. 2. As shown in FIG. 2 and FIG. 3, 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 this time, the first switch Q1 is on, the second switch Q2 is off, the output current Io is smaller 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 equal to or greater than the rated load, the isolated DC-DC conversion circuit 11 operates in a constant current control mode. In the constant current control mode, when the output voltage Vo is greater than the threshold voltage V2, the second switch Q2 remains off, and the isolated DC-DC conversion circuit 11 outputs a fixed output current Io (equal to the threshold current I1). When the output voltage Vo is lower than the threshold voltage V2, the second switch Q2 is turned on, triggering the optical coupler to generate a trigger signal in the receiver, and based on the trigger signal, the first control unit 121 controls to stop the operation of the isolated DC-DC conversion circuit 11. The threshold voltage V2 can be, for example, 80% of the rated voltage V1, but is not limited thereto, and the specific magnitude of the threshold voltage V2 can be set according to actual needs.

[0014] specifically Specifically, in the first embodiment shown in Fig. 2, when the output voltage Vo is lower than the threshold voltage V2, the second switch Q2 turns on, grounding the supply voltage Vcc1 of the second control unit 122, triggering the optical coupler 123 to generate a trigger signal in the receiver 125. The trigger signal increases (raises) the voltage level (potential) of the feedback end FB of the first control unit 121, causing the first control unit 121 to activate a protection function and stop the isolated DC-DC conversion circuit 11. In this way,

[0015] In this way, the LED power supply 1 of the present invention immediately stops operation when an abnormality occurs in the output voltage Vo (for example, but not limited to, when a short circuit occurs due to a small load), thereby protecting the LED power supply 1 and the LED device that supplies power to it.

[0016] Please refer to Fig. 2. In the first embodiment shown in Fig. 2, the control module 12 further includes a constant voltage control terminal CV, a constant current control terminal CC, a diode D2, and a diode D3. A first terminal of the transmitter 124 is electrically connected to the secondary side of the isolated DC-DC conversion circuit 11, the second control unit 122, and the output terminal 14, and a second terminal 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 when the output load of the second control unit 122 is less than the rated load, and the control signal is transmitted to the first control unit 121 through the constant voltage control terminal CV and the first optical coupler 123, and the first control unit 121 controls the isolated DC-DC conversion circuit 11 to operate in a constant voltage control mode based on the control signal. The constant current control terminal CC is configured to receive a control signal generated when the output load of the second control unit 122 is equal to or less than the rated load and the output voltage Vo is greater than the threshold voltage V2, and the control signal is transmitted to the first control unit 121 via the constant current control terminal CC and the first optical coupler 123, and the first control unit 121 controls the isolated DC-DC conversion circuit 11 to operate in a constant current control mode based on the control signal.

[0017] The feedback circuit further includes a resistor R3, a capacitor C1, a diode D4 (Zener diode), and a capacitor C2. Both ends of the resistor R1 are electrically connected to the output voltage Vo and a node A, respectively, the cathode and anode of the diode D1 are electrically connected to the node A and a first end of the resistor R2, respectively, and both ends of the resistor R3 are electrically connected to the output voltage Vo and a node B, respectively. 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, respectively. Both ends of the capacitor C1 are electrically connected to the node B and a third end of the first switch Q1, respectively, and the cathode and anode of the diode D4 are electrically connected to the node B and a first end of the second capacitor C2, respectively. The second switch Q2 is electrically connected to the anode of the diode D4 and the capacitor C2. The control module 12 includes a resistor R4 and a capacitor C3 connected in series between the output voltage Vo and a ground terminal, 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 electrically connected to the second control unit 122. The first switch Q1 is, for example, but not limited to, an NPN transistor. The first end, the second end and the third end of the first switch Q1 are a collector, a base and an emitter, respectively. The second switch Q2 is, for example, but not limited to, a field effect transistor. The first end, the second end and the third end of the second switch Q2 are a drain, a gate and a source, respectively.

[0018] In the first embodiment shown in Fig. 2, the first terminal, the second terminal, and the third terminal of the second switch Q2 are electrically connected to the second control unit 122, the anode of the diode D4, and the ground terminal, respectively. In the first embodiment, the first optical coupler 123 not only transmits a control signal for operating the isolated DC-DC conversion circuit 11 in a constant voltage or constant current control mode, but also generates a trigger signal when the output voltage Vo is less than the threshold voltage V2, so that the first control unit 121 can activate a protection function to stop the operation of the isolated DC-DC conversion circuit 11. The specific operating principle is as follows.

[0019] Please refer to FIG. 2 and FIG. 4. FIG. 4 is a schematic diagram of the operation sequence of the LED power supply shown in FIG. 2. In FIG. 4, FB is the voltage level of the feedback terminal FB, Va is the voltage of node A, and Vb is the voltage of node B. Since the voltage Va of node A is proportional to the output voltage Vo of the LED power supply 1, the voltage Va can reflect the magnitude change of the output voltage Vo. As shown in FIG. 2 and FIG. 4, at the beginning of the start-up of the LED power supply 1, the output voltage Vo gradually rises, and the supply voltage Vcc1 also starts to rise steadily. Since the output voltage Vo does not reach the preset threshold of the constant voltage control, the voltage level of the feedback terminal FB is maintained at a high potential. In the process of establishing a high potential, at first, the first switch Q1 and the second switch Q2 are both in the off state, and the voltage Va of the node A gradually rises. When the voltage Va is less than the threshold Vtha, the RC circuit formed by the resistor R3 and the capacitor C1 is charged, and the voltage Vb of the node B also gradually rises. The time for the voltage Va to gradually rise from zero to the threshold Vtha is the RC delay time. When the voltage Va rises to the threshold Vtha, the first switch Q1 switches to the on state, 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 becomes greater than the threshold Vtha accordingly. Note that the first control unit 121 has a protection delay time when the feedback end FB first establishes a high potential to avoid malfunction of the protection function due to the high potential of the feedback end FB. When the output voltage Vo reaches the preset constant voltage control threshold, the second control unit 122 starts the feedback control, the voltage level of the feedback end FB returns to a low level, the first switch Q1 maintains the on state, and the second switch Q2 remains off.

[0020] When the output voltage Vo gradually decreases due to an abnormality, the voltage Va also decreases accordingly. When the voltage Va falls below the threshold Vtha, the first switch Q1 switches to the OFF state, the RC circuit is charged, and the voltage Vb increases. When the voltage Vb increases to the threshold Vthb, the second switch Q2 switches to the ON state, the supply voltage Vcc1 is grounded, the second control unit 122 stops generating the control signal, and the voltage level of the feedback terminal FB increases to a high potential. When the voltage level of the feedback terminal FB becomes abnormally high for a predetermined time, the first control unit 121 activates a protection function and controls the isolated DC-DC conversion circuit 11 to stop.

[0021] Figure 5 shows the experimental waveforms of the LED power supply in Figure 2. As shown in Figure 5, when the output LED load is micro-short circuited or the LED load is overpowered, the LED power supply 1 operates in constant current control mode. When the LED micro-short circuit or overpower situation becomes serious, the output voltage Vo decreases accordingly, and when the output voltage Vo falls below the set threshold, the protection function can be activated immediately to stop the supply of the LED power supply 1. This can rapidly reduce the output current Io and avoid damage to the LED power supply 1 and the LED device it supplies power.

[0022] As mentioned above, the key point of the present invention is that when the output voltage Vo is too low (i.e., lower than the threshold voltage V2), the feedback circuit and the operation of the first switch Q1 turn on the second switch Q2 to trigger the corresponding optical coupler to generate a trigger signal at the receiver, and the first control unit 121 is controlled to stop the operation of the isolated DC-DC conversion circuit 11 based on the trigger signal, thereby realizing protection. Note that the specific embodiment of the optical coupler installation, trigger method, and the first control unit 121 controlling to stop the operation of the isolated DC-DC conversion circuit 11 based on the trigger signal are not limited to the embodiment shown in the first embodiment. Several possible embodiments are exemplified below.

[0023] FIG. 6 is an electrical circuit diagram of an LED power supply according to a second embodiment of the present invention. The structures or components in FIG. 6 similar to those in FIG. 2 are indicated by the same reference numerals, and will not be described again. The difference from the power supply (power supply) 1 in FIG. 2 is that in the LED power supply 1a in FIG. 6, the optocoupler of the control module 12a further includes a second optocoupler. As shown in FIG. 6, both ends of the transmitter 126 of the second optocoupler 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 both ends of the receiver 127a of the second optocoupler are electrically connected to the supply voltage Vcc2 and the protection trigger end PT of the first control unit 121, respectively. When the output voltage Vo is less than the threshold voltage V2, based on the feedback circuit (the operation principle is the same as in the first embodiment), the first switch Q1 is turned off and the second switch Q2 is turned on to trigger the second optocoupler. The receiver 127a of the second optical coupler generates a trigger signal, increases the voltage level of the protection trigger terminal PT, activates the protection function of the first control unit 121, and controls the isolated DC-DC conversion circuit 11 to stop the operation. In another embodiment, the control module 12a further includes a resistor R5 and a capacitor C4. The resistor R5 is electrically connected between the receiver 127a of the second optical coupler and the supply voltage Vcc2 of the first control unit 121, and both ends of the capacitor C4 are electrically connected to the protection trigger terminal PT and the ground terminal, respectively. Thereby, in the second embodiment, the first optical coupler 123 transmits a control signal for the isolated DC-DC conversion circuit 11 to operate in a constant voltage or constant current control mode, and the second optical coupler generates a trigger signal when the output voltage Vo is less than the threshold voltage V2, and controls the first control unit 121 to activate the protection function and stop the operation of the isolated DC-DC conversion circuit 11 due to the increase in the voltage level of the protection trigger terminal PT.

[0024] FIG. 7 is an electrical circuit diagram of an LED power supply according to a third embodiment of the present invention. The structures or components in FIG. 7 similar to those in FIG. 6 are indicated by the same reference numerals, and the description will not be repeated. The LED power supply 1b in FIG. 7 is different from the power supply (power supply) 1a in FIG. 6 in that the installation position of the receiver of the second optical coupler of the control module 12b is different. As shown in FIG. 6, in the third embodiment, both 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. Thus, when the output voltage Vo is less than the threshold voltage V2, the first switch Q1 is turned off and the second switch Q2 is turned on based on the feedback circuit (the operation principle is the same as in the first embodiment), to trigger the second optical coupler. The receiver 127b of the second optical coupler generates a trigger signal, reduces the voltage level of the protection trigger terminal PT, causes the first control unit 121 to activate the protection function, and stops the operation of the isolated DC-DC conversion circuit 11. In another embodiment, the control module 12b further includes a capacitor C5, which is connected in parallel to the receiver 127b of the second optical coupler. Thus, in the third embodiment, the first optical coupler 123 transmits a control signal for the isolated DC-DC conversion circuit 11 to operate in a constant voltage or constant current control mode, the second optical coupler generates a trigger signal when the output voltage Vo is less than the threshold voltage V2, and the first control unit 121 activates a protection function due to a drop in the voltage level of the protection trigger terminal PT, and controls the isolated DC-DC conversion circuit 11 to stop operating.

[0025] FIG. 8 is an electrical circuit diagram of an LED power supply according to a fourth embodiment of the present invention. The structures or components of FIG. 8 similar to those of FIG. 7 are indicated by the same reference numerals, and will not be described again. The LED power supply 1c of FIG. 8 is different from the power supply (power supply) 1b shown in FIG. 7 in that the installation position of the receiver of the second optical coupler of the control module 12c is different, and the control module 12c includes a third switch Q3, a fourth switch Q4, and a trigger circuit 15. As shown in FIG. 8, in the fourth embodiment, the third switch Q3 and the fourth switch Q4 are configured to rectify the input voltage Vin to provide the 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 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 less than the threshold voltage V2, the first switch Q1 is turned off and the second switch Q2 is turned on based on the feedback circuit (the operation principle is the same as that of the first embodiment), so that the second optocoupler is triggered. The receiver 127c of the second optocoupler generates a trigger signal, and the trigger circuit 15 receives the trigger signal and turns off the third switch Q3 and turns off the fourth switch Q4. At this time, the supply voltage Vcc2 of the first control unit 121 is grounded, and the first control unit 121 controls the isolated DC-DC conversion circuit 11 to stop operating. Thus, in the fourth embodiment, the first optocoupler 123 is used to transmit a control signal for the isolated DC-DC conversion circuit 11 to operate in a constant voltage or constant current control mode, and the second optocoupler generates a trigger signal when the output voltage Vo is less than the threshold voltage V2, and the first control unit 121 stops generating the control signal by grounding the supply voltage Vcc2, thereby stopping the operation of the isolated DC-DC conversion circuit 11 and realizing protection.

[0026] The trigger circuit 15 may be, but is not limited to, a latch circuit including a fifth switch Q5 and a sixth switch Q6 shown in Fig. 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 is not limited to this.

[0027] As described above, the present invention provides an LED power supply, which adopts constant voltage constant current control, and can immediately activate a protection function to stop operation when the output voltage is below a threshold voltage. In this way, the LED power supply of the present invention can immediately stop operation when the output voltage is abnormal, thereby protecting the LED power supply and the LED device it supplies power to.

[0028] It should be noted that the above-mentioned contents are merely preferred embodiments provided by the present invention, the present invention is not limited to the described embodiments, and the scope of the present invention is determined by the scope of the attached patent application. In addition, the present invention can be modified in various ways by those skilled in the art, and all such modifications are included in the scope of the attached patent application. [Explanation of symbols]

[0029] 1:LED power supply 11: Isolated DC-DC conversion circuit 12: Control module 13: Input terminal 14: Output terminal Vin: Input voltage Vo: Output voltage Io: Output current 121: First control unit 122: second control unit 123: First optical coupler Q1: First switch FB: Feedback end 124: Transmitter 125: Receiver Vcc1, Vcc2: Supply voltage I1: Threshold current V1: Rated voltage V2: Threshold voltage CV: Constant voltage control terminal CC: Constant current control terminal D1, D2, D3, D4: Diodes R1, R2, R3, R4, R5: Resistance Q2: Second switch C1, C2, C3, C4, C5: Capacitors A, B: Node Va: Voltage of node A Vb: voltage at node B Vtha, Vthb: Threshold 126: Transmitter 127a, 127b, 127c: Receiver 1a, 1b, 1c: LED power supply 12a, 12b, 12c: Control module PT: Protection trigger end Q3: The third switch Q4: The fourth switch 15: Trigger circuit Q5: The fifth switch Q6: The sixth switch

Claims

1. An LED power supply adopting constant voltage constant current control is configured to supply power to an LED device, the LED power supply comprising: an input terminal, an output terminal, an isolated DC-DC conversion circuit, and a control module; the isolated DC-DC conversion circuit includes a primary side and a secondary side electrically connected to the input terminal and the output terminal, respectively, and is configured to receive an input voltage from the input terminal and to output an output voltage to the output terminal; 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 configured to control an 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 transmitting an electrically isolated signal and includes a transmitter and a receiver electrically connected to the secondary side and the first control unit, respectively; when the output voltage is less than a threshold voltage, the first switch is turned off, the second switch is turned on, and 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 operating.

2. 2. The LED power supply according to claim 1, wherein, when an 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, an output current of the isolated DC-DC conversion circuit is smaller than a threshold current, and the output voltage is fixed to a rated voltage.

3. 3. The LED power supply according to claim 2, wherein when the output load is equal to or greater than the rated load, the isolated DC-DC conversion circuit operates in a constant current control mode, and in the constant current control mode, when the output voltage becomes greater than the threshold voltage, the first switch is turned on and the second switch is turned off, and when the output current is equal to the threshold current and the output voltage is less than the threshold voltage, the first switch is turned off and the second switch is turned on, and the first control unit controls to stop operation of the isolated DC-DC conversion circuit.

4. 4. The LED power supply of claim 3, wherein the threshold voltage is 80% of the rated voltage.

5. the optical coupler comprises a first optical coupler; 4. The LED power supply of claim 3, wherein the control module further comprises a second control unit, the second control unit is electrically connected to the secondary side and the transmitter of the first optical coupler, and is configured to sense the output voltage and the output current to generate a control signal, the control signal is transmitted to a feedback end of the first control unit through the first optical coupler, and the first control unit controls an operation of the isolated DC-DC conversion circuit according to the control signal.

6. The control module further includes a constant voltage control terminal and a constant current control terminal; the constant voltage control terminal 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 less than the rated load, the control signal is transmitted to the first control unit via the constant voltage control terminal and the first optical coupler, and the first control unit controls the isolated DC-DC conversion circuit to operate in the constant voltage control mode based on the control signal; 6. The LED power supply according to claim 5, wherein the constant current control terminal 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 equal to or greater than 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 terminal and the first optical coupler, and the first control unit controls the isolated DC-DC conversion circuit to operate in the constant current control mode based on the control signal.

7. 7. The LED power supply of claim 6, wherein the control module further comprises: a second diode and a third diode, the second diode is electrically connected between the transmitter and the constant voltage control end of the first optical coupler, and an anode and a cathode of the second diode are electrically connected to the transmitter and the constant voltage control end of the first optical coupler, respectively; the third diode is electrically connected between the transmitter and the constant current control end of the first optical coupler, and an anode and a cathode of the third diode are electrically connected to the transmitter and the constant current control end of the first optical coupler, respectively.

8. The feedback circuit further comprises a third resistor, a first capacitor, a fourth diode and a second capacitor, both 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 a first end of the second resistor, respectively, both 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, 6. The LED power supply of claim 5, wherein a first end of the first switch is electrically connected to the third end of the first switch, 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, the second switch is electrically connected to the anode of the fourth diode and the second capacitor, the control module comprises a fourth resistor and a third capacitor connected in series between the output voltage and a ground end, the fourth resistor and the third capacitor are electrically connected to the output voltage and the ground end, respectively, and a connection point between the fourth resistor and the third capacitor is electrically connected to the second control unit.

9. 9. The LED power supply of claim 8, wherein a first voltage at the first node is proportional to the output voltage, and when the output voltage is greater than the threshold voltage, the first voltage is correspondingly greater than a first threshold and the first switch is in an ON state, a second voltage at 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 and the first switch is in an OFF state, the second voltage rises and the second switch is switched to an ON state.

10. 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, and when the output voltage is smaller than the threshold voltage, the second switch is turned on, a supply voltage of the second control unit is grounded, the receiver of the first optical coupler generates the trigger signal to increase a voltage level of the feedback end, and the first control unit activates a protection function and controls the isolated DC-DC conversion circuit to stop operating.

11. 10. The LED power supply of claim 9, wherein the optical coupler further comprises a second optical coupler, wherein both ends of the transmitter of the second optical coupler are electrically connected to the output voltage and the first end of the second switch, respectively, the second end and the third end of the second switch are electrically connected to the anode of the fourth diode and the second end of the second capacitor, respectively, and both ends of the receiver of the second optical coupler are electrically connected to a supply voltage and a protection trigger end of the first control unit, respectively, wherein when the output voltage is smaller 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, and the first control unit activates a protection function and controls the isolated DC-DC conversion circuit to stop operating.

12. 10. The LED power supply of claim 9, wherein the optical coupler further comprises a second optical coupler, wherein both ends of the transmitter of the second optical coupler are electrically connected to the output voltage and the first end of the second switch, respectively, the second end and the third end of the second switch are electrically connected to the anode of the fourth diode and the second end of the second capacitor, respectively, and both ends of the receiver of the second optical coupler are electrically connected to a protection trigger end and the ground end of the first control unit, respectively, wherein when the output voltage is smaller 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 trigger end, and the first control unit activates a protection function and controls to stop the operation of the isolated DC-DC conversion circuit.

13. The optical coupler further comprises a second optical coupler, both ends of the transmitter of the second optical coupler are electrically connected to the output voltage and a first end of the second switch, the second end and the third end of the second switch are electrically connected to the anode of the fourth diode and the second end of the second capacitor, respectively, the first end of the receiver of the second optical coupler is electrically connected to a supply voltage of the first control unit, and 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 an input voltage to provide the supply voltage of the first control unit.

10. The LED power supply according to claim 9, wherein the trigger circuit is electrically connected to a second end of the receiver of the second optocoupler and the sixth switch, and when the output voltage is smaller than the threshold voltage, the second switch is turned on to trigger the second optocoupler, and the receiver of the second optocoupler generates the trigger signal, and when the trigger circuit receives the trigger signal, it turns off the third switch and turns off the fourth switch, at this time, the supply voltage of the first control unit is grounded, and the first control unit controls the isolated DC-DC conversion circuit to stop operating.

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