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 output voltage and current control of an 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), 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. With constant voltage control, the trigger current for the overcurrent protection must be somewhat higher than the full load current (e.g., 30%) to avoid false activation of the overcurrent protection. This requires a margin in the design of LED power supplies, but the UL Class 2 output requirement of 24V / 100W does not allow for an overcurrent protection design that is 1.3 times the rated current.

[0004] For this reason, existing LED power supplies use constant voltage / 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 greater than the rated load, the LED power supply operates in constant current control mode and outputs a fixed output current. This significantly reduces the margin that the LED power supply needs to maintain for overcurrent protection.

[0005] However, in recent years, there have been frequent LED lamp fires in Japan, most of which 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 decreases due to an increase in the short circuit level of the LED load, the LED power supply continues to supply a fixed output current. However, even if the LED lamp generates an arc due to a short circuit and ultimately smokes or catches fire, the LED power supply's short circuit protection function cannot be activated.

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

[0007] An object of the present invention is to provide an LED power supply that employs constant voltage and 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 the load), thereby protecting the LED power supply and the LED device it supplies power to. [Means for solving the problem]

[0008] To achieve the above-mentioned objectives, the present invention provides an LED power supply. The LED power supply employs constant voltage / constant current control and is configured to supply power to an LED device. It includes an input terminal, an output terminal, an isolated DC-DC conversion circuit, and a control module. The isolated DC-DC conversion circuit is electrically connected to the primary side and secondary side of the input terminal and output terminal, and is configured to receive an input voltage from the input terminal and output an output voltage from the output terminal. 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 electrically isolated signals 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 isolated DC-DC conversion circuit to stop operating. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows the voltage-current characteristic curves of various output control methods for an LED power supply. [Figure 2] 1 is a diagram showing the electrical circuit configuration of an LED power supply according to a first embodiment of the present invention. [Figure 3] Figure 2 shows the relationship between the output voltage and output current of the LED power supply. [Figure 4] The operation sequence of the LED power supply in Figure 2 is shown. [Figure 5] Figure 2 shows the experimental waveform of the LED power supply. [Figure 6] FIG. 10 is an electrical circuit diagram of an LED power supply according to a second embodiment of the present invention. [Figure 7] FIG. 10 is an electrical circuit diagram of an LED power supply according to a third embodiment of the present invention. [Figure 8] FIG. 10 is an electrical circuit diagram of an LED power supply according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[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 intended to illustrate the present invention and not to limit the scope of the present invention.

[0011] FIG. 2 is a schematic diagram of an LED power supply according to a first embodiment of the present invention. As shown in FIG. 2, the LED power supply 1 of the present invention employs constant-voltage / constant-current control (CV / CC) and is configured to supply power to an LED device (not shown). The LED power supply 1 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. 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 the output voltage Vo and 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 is configured to control the operation of the isolated DC-DC conversion circuit 11. 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 (a 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 electrically isolated signals 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 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, thereby causing the first control unit 121 to control the operation of the isolated DC-DC conversion circuit 11 according to the control signal.

[0013] Figure 3 shows the relationship between the output voltage and output current of the LED power supply in Figure 2. As shown in Figures 2 and 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 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 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 converter circuit 11. The threshold voltage V2 can be, for example, but is not limited to, 80% of the rated voltage V1, 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 is turned on, the supply voltage Vcc1 of the second control unit 122 is grounded, the optical coupler 123 is triggered, and a trigger signal is generated in the receiver 125. The trigger signal increases (raises) the voltage level (potential) of the feedback terminal FB of the first control unit 121, causing the first control unit 121 to activate the 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] See 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. A second terminal of the transmitter 124 is electrically connected to the anodes of the diodes D2 and D3, the cathodes of which 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 of the second control unit 122 is less than the rated load. The control signal is transmitted to the first control unit 121 via the constant voltage control terminal CV and the first optical coupler 123. The first control unit 121 controls the isolated DC-DC conversion circuit 11 to operate in the 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 the 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 node A and a first end of the resistor R2, respectively. Both ends of the resistor R3 are electrically connected to the output voltage Vo and a node B, respectively. The first end, second end, and third end of the first switch Q1 are electrically connected to node B, the anode of the diode D1, and the second end of the resistor R2, respectively. The both ends of the capacitor C1 are electrically connected to node B and a third end of the first switch Q1, respectively. The cathode and anode of the diode D4 are electrically connected to 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. 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 terminal, the second terminal, and the third terminal of the first switch Q1 are the collector, the base, and the emitter, respectively. The second switch Q2 is, for example, but not limited to, a field-effect transistor. The first terminal, the second terminal, and the third terminal of the second switch Q2 are the drain, the gate, and the source, respectively.

[0018] 2, the first, second, and third terminals 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 converter circuit 11 in 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, causing the first control unit 121 to activate a protection function and stop the operation of the isolated DC-DC converter circuit 11. The specific operating principle is as follows.

[0019] Please refer to Figures 2 and 4. Figure 4 is a schematic diagram of the operation sequence of the LED power supply shown in Figure 2. In Figure 4, FB is the voltage level at the feedback terminal FB, Va is the voltage at node A, and Vb is the voltage at node B. Since the voltage Va at node A is proportional to the output voltage Vo of the LED power supply 1, the voltage Va can reflect changes in the magnitude of the output voltage Vo. As shown in Figures 2 and 4, at the initial start-up of the LED power supply 1, the output voltage Vo gradually increases, and the supply voltage Vcc1 also begins to rise steadily. Because the output voltage Vo does not reach the preset constant voltage control threshold, the voltage level at the feedback terminal FB remains at a high potential. During the process of establishing a high potential, initially, both the first switch Q1 and the second switch Q2 are in an off state, and the voltage Va at node A gradually increases. When the voltage Va is less than the threshold Vtha, the RC circuit formed by resistor R3 and capacitor C1 is charged, and the voltage Vb at node B also gradually increases. The time it takes 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 on, the RC circuit discharges, and the voltage Vb drops to zero. If the output voltage Vo is greater than the threshold voltage V2, the voltage Va will correspondingly exceed the threshold Vtha. The first control unit 121 also includes a protection delay time when the feedback terminal FB first establishes a high potential to prevent malfunction of the protection function due to a high potential at the feedback terminal FB. When the output voltage Vo reaches the preset constant voltage control threshold, the second control unit 122 initiates feedback control, the voltage level at the feedback terminal FB returns to a low level, the first switch Q1 remains on, and the second switch Q2 remains off.

[0020] When the output voltage Vo gradually decreases due to an abnormality, the voltage Va also decreases. When the voltage Va falls below the threshold Vtha, the first switch Q1 switches off, the RC circuit charges, and the voltage Vb increases. When the voltage Vb increases to the threshold Vthb, the second switch Q2 switches on, the supply voltage Vcc1 is grounded, the second control unit 122 stops generating control signals, and the voltage level at the feedback terminal FB increases to a high potential. When the voltage level at the feedback terminal FB reaches an abnormally high potential for a predetermined time, the first control unit 121 activates a protection function and controls the isolated DC-DC converter circuit 11 to stop operating.

[0021] Figure 5 shows the experimental waveforms for the LED power supply in Figure 2. As shown in Figure 5, when the output LED load is micro-short or overpowered, LED power supply 1 operates in constant current control mode. As the LED micro-short or overpower condition worsens, the output voltage Vo decreases. When the output voltage Vo falls below the set threshold, the protection function immediately activates and stops the supply of power from LED power supply 1. This rapidly reduces the output current Io, preventing damage to LED power supply 1 and the LED devices it powers.

[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 first switch Q1 operate to turn on the second switch Q2, triggering the corresponding optocoupler and generating a trigger signal in the receiver. The first control unit 121 then controls the isolated DC-DC converter circuit 11 to stop operating based on the trigger signal, thereby achieving protection. Note that the specific embodiments of the optocoupler configuration, triggering method, and the first control unit 121 controlling the isolated DC-DC converter circuit 11 to stop operating based on the trigger signal are not limited to those shown in the first embodiment. Several possible embodiments are described below.

[0023] FIG. 6 is an electrical circuit diagram of an LED power supply according to a second embodiment of the present invention. Structures or components in FIG. 6 similar to those in FIG. 2 are designated by the same reference numerals and will not be described again. Unlike the power supply (power supply) 1 in FIG. 2, the LED power supply 1a in FIG. 6 further includes a second optocoupler in the optocoupler of the control module 12a. As shown in FIG. 6, the two 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 and third ends of the second switch Q2 are electrically connected to the anode of the diode D4 and the second end of the capacitor C2, respectively. The two ends of the receiver 127a of the second optocoupler are electrically connected to the supply voltage Vcc2 and the protection trigger terminal PT of the first control unit 121, respectively. 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 a feedback circuit (the operating principle of which is the same as in the first embodiment), triggering the second optocoupler. The second optocoupler receiver 127a generates a trigger signal, increasing the voltage level of the protection trigger terminal PT, thereby activating the protection function of the first control unit 121 and controlling the isolated DC-DC conversion circuit 11 to stop 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 second optocoupler receiver 127a 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. Thus, in the second embodiment, the first optocoupler 123 transmits a control signal for operating the isolated DC-DC conversion circuit 11 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. The first control unit 121 activates the protection function by increasing the voltage level of the protection trigger terminal PT, controlling the isolated DC-DC conversion circuit 11 to stop operation.

[0024] FIG. 7 is an electrical circuit diagram of an LED power supply according to a third embodiment of the present invention. The same structures or components as those in FIG. 6 are designated by the same reference numerals, and a repeated description will be omitted. The LED power supply 1b in FIG. 7 differs from the power supply (power supply) 1a in FIG. 6 in that the second optocoupler receiver in the control module 12b is installed at a different position. As shown in FIG. 6, in the third embodiment, both ends of the second optocoupler receiver 127b 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 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 operating principle is the same as in the first embodiment), triggering the second optocoupler. The second optocoupler receiver 127b generates a trigger signal, reducing the voltage level at the protection trigger terminal PT, causing the first control unit 121 to activate the protection function and shutting down 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 operating the isolated DC-DC conversion circuit 11 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 the protection function in response to a drop in the voltage level of the protection trigger terminal PT, thereby controlling the isolated DC-DC conversion circuit 11 to stop operation.

[0025] FIG. 8 is an electrical circuit diagram of an LED power supply according to a fourth embodiment of the present invention. Structures or components in FIG. 8 similar to those in FIG. 7 are designated by the same reference numerals, and a repeated description will be omitted. The LED power supply 1c in FIG. 8 differs from the power supply (power supply) 1b shown in FIG. 7 in that the position of the receiver of the second optical coupler in the control module 12c is different. The control module 12c also 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 for the first control unit 121. The first terminal of the second optical coupler receiver 127c is electrically connected to the supply voltage Vcc2 for the first control unit 121. The trigger circuit 15 is electrically connected to the second terminal of the second optical coupler receiver 127c and the sixth switch Q6. When the output voltage Vo is less than the threshold voltage V2, the second optocoupler is triggered by turning off the first switch Q1 and turning on the second switch Q2 based on a feedback circuit (the operating principle of which is the same as in the first embodiment). The receiver 127c of the second optocoupler generates a trigger signal, which the trigger circuit 15 receives and turns off the third switch Q3 and 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 operating the isolated DC-DC conversion circuit 11 in constant voltage or constant current control mode. The second optocoupler generates a trigger signal when the output voltage Vo is less than the threshold voltage V2, which causes the first control unit 121 to stop generating the control signal by grounding the supply voltage Vcc2, thereby stopping the operation of the isolated DC-DC conversion circuit 11 and achieving protection.

[0026] The trigger circuit 15 may be, for example, 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 that uses constant voltage and 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-described contents are merely preferred embodiments provided by the present invention, and 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 at node A Vb: voltage at node B Vtha, Vthb: threshold value 126:Transmitter 127a, 127b, 127c: Receivers 1a, 1b, 1c: LED power supply 12a, 12b, 12c: Control modules PT: Protective 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 employing constant voltage and 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 from the output terminal; the control module comprises a first control unit, a feedback circuit, a first switch, a second switch, a third resistor, a first capacitor, 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 comprises a first resistor, a first diode and a second resistor connected in series, both ends of the first resistor being electrically connected to the output voltage and a first node, respectively, and a cathode and an anode of the first diode being electrically connected to the first node and the second resistor, respectively; the first switch is electrically connected to the feedback circuit; the second switch is electrically connected to the first switch; both ends of the third resistor are electrically connected to the output voltage and a second node, respectively; both ends of the first capacitor are electrically connected to the second node and the first switch, respectively; the optical coupler is used for transmitting electrically isolated signals and includes a transmitter and a receiver electrically connected to the secondary side and the first control unit, respectively; During a protection delay time during which a high potential is established at the feedback end of the first control unit during an initial startup of the LED power supply, the first switch and the second switch are both in an off state, a first voltage at the first node increases with an increase in the output voltage, and an RC circuit formed by the third resistor and the first capacitor is charged by the output voltage, thereby increasing a second voltage at the second node, and when the first voltage increases to or above a first threshold, the first switch is switched on, the RC circuit is discharged, and the second voltage decreases to zero; and wherein after the protection delay time, if the output voltage is lower than a threshold voltage, the first switch is turned off, the RC circuit is charged, and the second voltage rises, thereby turning on the second switch, triggering the optical coupler to generate a trigger signal at the receiver, and the first control unit controls the isolated DC-DC conversion circuit to stop operating according to the trigger signal.

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, the 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 is 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 smaller 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 the feedback end of the first control unit via the first optical coupler, and the first control unit controls the 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 of claim 5, wherein the constant current control terminal is electrically connected to the transmitter of the first optical coupler and 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. 6. The LED power supply of claim 5, wherein the feedback circuit further comprises a fourth diode and a second capacitor, wherein 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, both 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, 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 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 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 the 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 of 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 smaller than the threshold voltage, the second switch is turned on, the supply voltage of the second control unit is grounded, the receiver of the first optical coupler generates the trigger signal to increase the 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 working.

11. 10. The LED power supply of claim 9, wherein the optocoupler further comprises a second optocoupler, wherein both ends of the transmitter of the second optocoupler are electrically connected to the output voltage and the first end of the second switch, respectively, and the second and third ends 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 optocoupler are electrically connected to the supply voltage and a protection trigger terminal of the first control unit, respectively, wherein when the output voltage is lower 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 to increase the voltage level of the protection trigger terminal, so that 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, and the second and third ends 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 the protection trigger terminal and the ground terminal of the first control unit, respectively, wherein 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 trigger terminal, and the first control unit activates a protection function and controls the isolated DC-DC conversion circuit to stop operating.

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, respectively, second and third ends of the second switch are electrically connected to the anode of the fourth diode and the second end of the second capacitor, respectively, and 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, wherein 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 a 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 the fourth switch, and 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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