LED drive circuit and lighting circuit

Abstract

The utility model provides an LED drive circuit and a lighting circuit, comprising a first capacitor and a first switch tube, the first end of the first capacitor receives the bus voltage, and the first capacitor is grounded through the first switch tube; a second capacitor and a second switch tube, a first end of the second capacitor receives the bus voltage and is connected with an anode of an LED load, and a second end of the second capacitor is grounded through the second switch tube; the first end of the switch connection circuit is connected with the first end of the first capacitor, and the second end of the switch connection circuit is connected with the second end of the second capacitor; wherein on-off of the switch connection circuit, the first switch tube and the second switch tube is controlled according to the magnitude of the bus voltage. According to the utility model, the power factor of the system can be improved, THD is reduced, and the purposes of reducing loss and improving efficiency are achieved.

Description

Technical Field

[0001] The utility model relates to the field of power electronics, in particular to an LED drive circuit and a lighting circuit. Background Art

[0002] In the lighting field, many customers now hope to adopt a DOB solution, that is, the driver power supply and LED lamp beads are placed on an aluminum substrate for heat dissipation. Therefore, a linear drive solution for the LED driver circuit is more suitable for the DOB solution. It has EMI problems, fewer power devices, and it is easier to integrate the LED driver circuit with the lamp beads on the PCB board. If the LED driver circuit adopts a switch drive solution, not only more power devices are required, but when the driver circuit is placed on an aluminum substrate, it is more difficult to pass relevant regulations on electromagnetic compatibility and conducted radiation.

[0003] Generally, there are no inductors or capacitors at the front end of the linear LED driver circuit that affect the phase, so the phase shift φ of the input voltage and input current can be considered close to 0, that is, cosφ≈1. λ represents the PF value. Therefore, when the system THD is designed to be less than 0.25, the system PF can be close to or greater than 0.97. In linear drive solutions, many customers desire high PF (PF>0.95) and THDi <25% @120Vac for single-segment LEDs. However, traditional single-segment solutions struggle to meet these requirements. Currently, multi-segment LED control is predominant, with options including 2-segment, 3-segment, and 4-segment LEDs. Multi-segment LEDs are more expensive to handle flicker. For filament lamps, which require only two output lines (LED+ and LED-), single-segment LEDs are typically the only option; multi-segment LEDs are rarely used. In dimming applications, single-segment LED drivers are easier to design due to optical design limitations. Summary of the Invention

[0004] The purpose of the utility model is to provide a simple and efficient LED drive circuit and lighting circuit, which are used to solve the problems of low power factor and complex LED drive circuit structure in the prior art.

[0005] The utility model proposes an LED driving circuit for driving LED loads. The AC input voltage is rectified by a rectifier circuit to obtain a bus voltage.

[0006] a first capacitor and a first switch tube, wherein a first end of the first capacitor receives the bus voltage, and a second end of the first capacitor is grounded through the first switch tube;

[0007] a second capacitor and a second switch tube, wherein a first end of the second capacitor receives the bus voltage and is connected to the anode of the LED load, and a second end of the second capacitor is grounded through the second switch tube;

[0008] a switch connection circuit, a first end of which is connected to the first end of the first capacitor, and a second end of which is connected to the second end of the second capacitor;

[0009] The switching circuit, the first switching tube and the second switching tube are controlled to be on and off according to the magnitude of the bus voltage.

[0010] Optionally, when the bus voltage is less than a set threshold, the switch connection circuit is turned on, the first switch tube and the second switch tube are turned off, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor supply power to the LED load.

[0011] Optionally, when the bus voltage is greater than a set threshold and less than the turn-on voltage of the LED load, the switch connection circuit is turned off, the first switch tube and the second switch tube are turned on, the first capacitor and the second capacitor are connected in parallel, and the bus voltage charges the first capacitor and the second capacitor.

[0012] Optionally, when the bus voltage is greater than the turn-on voltage of the LED load, the switch connection circuit, the first switch tube and the second switch tube are turned off, the first capacitor and the second capacitor are connected in parallel, and the bus voltage supplies power to the LED load.

[0013] Optionally, a third capacitor is further included, and the third capacitor is connected in parallel with the LED load.

[0014] Optionally, a third switch tube is further included, and the cathode of the LED load is grounded through the third switch tube;

[0015] When the bus voltage is less than a set threshold, or when the bus voltage is greater than the turn-on voltage of the LED load, the third switch tube is turned on.

[0016] Optionally, a first operational amplifier is configured to operationally amplify the first reference voltage and the first sampling signal representing the first capacitor current, and an output end of the first operational amplifier is connected to the control end of the first switching tube;

[0017] a second operational amplifier, operable to amplify the second reference voltage and the second sampling signal representing the second capacitor current, wherein the output end of the second operational amplifier is connected to the control end of the second switch tube;

[0018] The third operational amplifier performs operational amplification on the third reference voltage and the third sampling signal representing the LED load current, and the output end of the third operational amplifier is connected to the control end of the third switching tube.

[0019] Optionally, the switch connection circuit includes a third diode and a fourth switch tube, and the third diode and the fourth switch tube are connected in series;

[0020] When the bus voltage is less than a set threshold, the fourth switch tube is turned on;

[0021] When the bus voltage is greater than a set threshold, the fourth switch tube is turned off.

[0022] Optionally, the switch connection circuit further includes a first resistor, a first voltage-stabilizing diode, and a first switch, wherein a first end of the first resistor is connected to a high-potential end of the first capacitor, and a second end of the first resistor is connected to a control end of the fourth switching diode; a cathode of the first voltage-stabilizing diode is connected to the control end of the fourth switching diode, and an anode of the first voltage-stabilizing diode is connected to a low-potential end of the second capacitor;

[0023] The control end of the fourth switch tube is grounded through the first switch. When the bus voltage is less than a set threshold, the first switch is turned off. When the bus voltage is greater than the set threshold, the first switch is turned on.

[0024] Optionally, the switch connection circuit further includes a fourth operational amplifier and a first switch, the fourth operational amplifier performing operational amplification on the third reference voltage and a fourth sampling signal representing the fourth switch current, and the output end of the third operational amplifier is connected to the control end of the fourth switch tube;

[0025] The control end of the fourth switch tube is also grounded through the first switch. When the bus voltage is less than a set threshold, the first switch is turned off. When the bus voltage is greater than the set threshold, the first switch is turned on.

[0026] Optionally, a first diode and a second diode are further included, the first end of the first capacitor receives the bus voltage through the first diode, and the first end of the second capacitor receives the bus voltage through the second diode.

[0027] Optionally, the capacitance of the first capacitor is equal to the capacitance of the second capacitor.

[0028] Optionally, the voltage of the first capacitor and the voltage of the second capacitor are both greater than half of the turn-on voltage of the LED load and less than the turn-on voltage of the LED load.

[0029] A lighting circuit is also provided, comprising an LED load and any one of the above-mentioned LED driving circuits.

[0030] Compared with existing technologies, the present invention has the following advantages: The first and second capacitors are each connected to the output of the rectifier circuit via a unidirectional conducting element, and the series-parallel switching of the first and second capacitors is controlled according to the bus voltage output by the rectifier circuit to drive a single-stage LED load. The present LED driver circuit has a simple structure, a high system power factor, low THD, and high output efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the principle diagram of embodiment 1 of the LED driving circuit of the utility model;

[0032] Figure 2 This is the principle diagram of embodiment 2 of the LED driving circuit of the present utility model;

[0033] Figure 3 This is a working timing diagram of the LED driving circuit of the utility model. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and solution made within the spirit and scope of the present invention.

[0035] In order to enable the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0036] The following paragraphs describe the present invention in more detail by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and not to exact proportions, in order to facilitate and clearly illustrate the embodiments of the present invention.

[0037] Reference Figure 1, illustrates a schematic diagram of Embodiment 1 of the LED driver circuit of the present invention. The AC input voltage AC is rectified by a bridge rectifier to generate a bus voltage Vbus. The LED driver circuit of the present invention includes a first capacitor C1, a second capacitor C2, and a third capacitor C3. Depending on the magnitude of the bus voltage Vbus, the first and second capacitors C1 and C2 are connected in series or in parallel to drive the LED load. The third capacitor C3 is connected in parallel with the LED load. Furthermore, when the bus voltage Vbus is less than a set threshold (representing the maximum voltage on the capacitors C1 / C2), the first capacitor C1 and the second capacitor C2 are connected in series, the LED load is turned on, and the first capacitor C1 and the second capacitor C1 discharge to the LED load and the third capacitor C3; when the bus voltage Vbus is greater than the set threshold and less than the turn-on voltage VF of the LED load, the first capacitor C1 and the second capacitor C2 are connected in parallel, the bus voltage Vbus charges the first capacitor C1 and the second capacitor C2, and the third capacitor C3 supplies power to the LED load; when the bus voltage Vbus is greater than the turn-on voltage VF, the first capacitor C1 and the second capacitor C2 are connected in parallel, the first capacitor C1 and the second capacitor C2 are neither charged nor discharged, the LED load is turned on, the bus voltage Vbus supplies power to the LED load, and at the same time charges the third capacitor C3.

[0038] Specifically, the LED driving circuit of the present invention also includes a switch connection circuit 01, a switch tube Q1, a switch tube Q2 and a switch tube Q3. The first end of the first capacitor C1 receives the bus voltage Vbus, the second end of the first capacitor C1 is grounded through the switch tube Q1, the first end of the second capacitor C2 receives the bus voltage Vbus, the second end of the second capacitor C2 is grounded through the switch tube Q2 and connected to the anode of the LED load, and the cathode of the LED load is grounded through the switch tube Q3; the switch connection circuit 01 is connected between the first end of the first capacitor C1 and the second end of the second capacitor C2, and the on and off states of the switch connection circuit 01, the first switch tube Q1, the switch tube Q2 and the switch tube Q3 are controlled according to the size of the bus voltage Vbus to drive the LED load. Specifically, when the bus voltage Vbus is less than a set threshold, the switch connection circuit O1 is turned on, the switches Q1 and Q2 are turned off, and the switch Q3 is turned on. The first capacitor C1 and the second capacitor C2 are connected in series, and the first capacitor C1 and the second capacitor C2 discharge to the LED load. The first capacitor C1, the second capacitor C2, the LED load, the switch Q3, and the body diode of the switch Q1 form a discharge loop. When the bus voltage Vbus is greater than the set threshold and less than the forward voltage VF of the LED load, the switch connection circuit O1 is turned off, the switches Q1 and Q2 are turned on, and the switch Q3 is turned off. The first capacitor C1 and the second capacitor C2 are connected in parallel, and the bus voltage Vbus charges the first capacitor C1 and the second capacitor C2. The third capacitor C3 discharges to the LED load, and the third capacitor C3 and the LED load form a discharge loop. When the bus voltage Vbus is greater than the turn-on voltage VF of the LED load, the switch connection circuit O1 is turned off, the switch tubes Q1 and Q2 are turned off, the switch tube Q3 is turned on, the first capacitor C1 and the second capacitor C2 are neither charged nor discharged, and the bus voltage Vbus supplies power to the LED load and charges the third capacitor C3.

[0039] The LED driving circuit of the present invention also includes a sampling resistor Rcs1 and an operational amplifier U1. The sampling resistor Rcs1 is connected between the switch tube Q1 and the ground terminal. The sampling voltage Vcs1 on the sampling resistor Rcs1 represents the current flowing through the capacitor C1. The operational amplifier U1 performs operational amplification on the first reference voltage Vref1 and the sampling voltage Vcs1. The output end of the operational amplifier U1 is connected to the control end of the switch tube Q1. When the bus voltage Vbus is greater than the set threshold and less than the turn-on voltage VF of the LED load, the operational amplifier U1 drives the switch tube Q1 to turn on and controls the current flowing through the switch tube Q1. The circuit further includes a sampling resistor Rcs2, an operational amplifier U2, and a switch S2. The sampling resistor Rcs2 is connected between the switch tube Q2 and the ground terminal. The sampled voltage Vcs2 on the sampling resistor Rcs2 represents the current flowing through the capacitor C2. The operational amplifier U2 performs operational amplification on the second reference voltage Vref2 and the sampled voltage Vcs2. The output terminal of the operational amplifier U2 is connected to the control terminal of the switch tube Q2. The switch S2 is also connected between the gate of the switch tube Q2 and the ground terminal. When the bus voltage Vbus is less than a set threshold or the bus voltage Vbus is greater than the turn-on voltage VF of the LED load, the switch S2 is controlled to be turned on to pull the gate of the switch tube Q2 to the ground terminal to turn off the switch tube Q2. When the bus voltage Vbus is greater than the set threshold and less than the turn-on voltage VF of the LED load, the switch S2 is controlled to be turned off, and the operational amplifier U2 drives the switch tube Q2 to turn on and controls the current flowing through the switch tube Q2. It also includes a sampling resistor Rcs3 and an operational amplifier U3. The switch tube Q3 and the sampling resistor Rcs3 are connected in series between the LED and the ground terminal. The sampling voltage Vcs3 on the sampling resistor Rcs3 represents the current of the LED. The operational amplifier U3 performs operational amplification on the third reference voltage Vref3 and the sampling voltage Vcs3. The output end of the operational amplifier U3 is connected to the control end of the switch tube Q3. When the bus voltage Vbus is less than the set threshold or greater than the conduction voltage VF of the LED load, the operational amplifier U3 drives the switch tube Q3 to turn on and controls the current flowing through the LED. The LED driving circuit of the present invention also includes a first unidirectional conducting element and a second unidirectional conducting element. The first capacitor C1 receives the bus voltage Vbus through the first unidirectional conducting element, and the second capacitor C2 receives the bus voltage through the second unidirectional conducting element. The first unidirectional conducting element and the second unidirectional conducting element are preferably diodes D1 and diodes D2, respectively. Specifically, the first capacitor C1 receives the bus voltage Vbus through the diode D1, the anode of the diode D1 receives the bus voltage Vbus, and the cathode of the diode D1 is connected to the common connection end of the first capacitor C1 and the switch connection circuit 01; the anode of the diode D2 receives the bus voltage Vbus, and the cathode of the diode D2 is connected to the common connection end of the second capacitor C2 and the LED load, so as to prevent the capacitors C1 and C2 from discharging to the parasitic capacitance of the rectifier bridge.

[0040] In this embodiment of the present invention, the switch connection circuit 01 includes a diode D3 and a switch tube Q4 connected in series, the anode of the diode D3 is connected to the common connection terminal of the cathode of the diode D1 and the capacitor C1, and the cathode of the diode D3 is connected to the common connection terminal of the second capacitor C2 and the switch tube Q2; further, the switch connection circuit 01 also includes a resistor R1 and a voltage regulator tube Dz, the resistor R1 is connected between the gate of the switch tube Q4 and the common connection terminal of the cathode of the diode D1 and the capacitor C1, and the voltage regulator tube Dz is connected between the gate of the switch tube Q4 and the second capacitor Between C2 and the common connection terminal of the switch tube Q2, when the bus voltage Vbus is less than the set threshold, the gate-source voltage Vgs of the switch tube Q4 automatically reaches the starting threshold, so that the switch tube Q4 is self-turned on. The resistor R1 is selected to have a large value, which can be set to be greater than a certain threshold, to prevent a large amount of discharge current generated when the first capacitor C1 discharges from flowing into the gate of the switch tube Q4; further, the switch connection circuit 01 also includes a switch S1. When the bus voltage Vbus is greater than the set threshold, the switch S1 is turned on, the gate of the switch tube Q4 is pulled to ground, and the switch tube Q4 is turned off.

[0041] In the present invention, preferably, the capacitance of the first capacitor C1 and the second capacitor C2 are equal. After the first capacitor C1 and the second capacitor C2 are charged, the sum of the voltage VC1 of the first capacitor C1 and the voltage VC2 of the second capacitor C2 is less than 2VF, and the ranges of VC1 and VC2 are respectively between 1 / 2VF and VF. When the capacitors C1 and C2 are connected in series, the voltage on the capacitors C1 and C2 is sufficient to drive the LED to turn on, while preventing the voltages VC1 and VC2 on the capacitors C1 and C2 from being too large. If VC1+VC2 is greater than 2VF, the conduction angle of the LED will be too small, resulting in poor PF and THD, which will not meet the expected requirements.

[0042] The LED drive circuit of the present invention only requires three power switching tubes and three capacitors, and all three power switching tubes can be NMOS tubes. Each power switching tube does not need floating control, and the control circuits of the three power switching tubes can be integrated into the same chip. In addition, the switch connection circuit can adopt a self-conducting circuit, which is simple to control and has a fast response. The drive circuit of the present invention can meet the requirements of high PF and low THDi, for example, it can meet the requirements of PF>0.95 and THDi<25%. At the same time, it is easy to eliminate flicker in single-segment lamp beads, and it is easy to meet the requirement of low flicker.

[0043] Reference Figure 2 , illustrates the principle diagram of embodiment 2 of the LED driving circuit of the utility model, the principle Figure 2 and Figure 1 The difference lies in the different implementation methods of the switch connection circuit 01. Figure 2 and Figure 1The same parts will not be repeated. The switch connection circuit 01 in this embodiment also includes a switch tube Q4, a diode D3 and a switch S1, and also includes an operational amplifier U4 and a sampling resistor Rcs4. The switch tube Q4 and the diode D3 are connected in series, the anode of the diode D3 is connected to the cathode of the diode D1 and the common connection end of the capacitor C1, and the cathode of the diode D3 is connected to the common connection end of the second capacitor C2 and the switch tube Q2. The switch S1 is used to turn on when Vbus is greater than the set threshold to turn off the switch tube Q4. The sampling resistor Rcs4 is connected in series with the switch tube Q4 to sample the current flowing through the switch tube Q4. The sampling resistor Rcs4 is selected to be smaller and can be set to be less than a certain threshold. The operational amplifier U4 performs operational amplification on the fourth reference voltage Vref4 and the sampling voltage Vcs4 at the connection end of the resistor Rcs4 and the switch tube Q4. The output end of the operational amplifier U4 is connected to the gate of the switch tube Q4 to drive the switch tube Q4 to control the current flowing through the switch tube Q4. Compared to Figure 1 , Figure 2 Optimized Figure 1 The loss caused by the middle resistor R1 further improves the efficiency.

[0044] Reference Figure 3 , which illustrates the working timing diagram of the LED driver circuit of the present invention. At time t0, the bus voltage Vbus rises to the set threshold. At t0-t1, the bus voltage Vbus is greater than the set threshold VC and less than the LED conduction voltage VF. The switch tube Q4 is turned off, and the capacitors C1 and C2 are connected in parallel. An input current Iin is generated on the bus to charge the capacitors C1 and C2, and the capacitor C3 supplies power to the LED load. At t1-t2, the bus voltage Vbus is greater than the LED conduction voltage VF, the LED is turned on, the bus voltage supplies power to the LED and charges the third capacitor C3, and the input current Iin increases to the sum of the LED load current and the charging current of the third capacitor C3. At t2-t3, the working state is the same as that at t0-t1 and will not be repeated. At t3-t4, the bus voltage Vbus is less than the set threshold VC, and the capacitors C1 and C2 are connected in series and discharge the LED. At this time, there is no current on the bus, that is, the input current Iin is zero. It should be noted that the working state is the same at the points symmetrically on both sides of the peak of the bus voltage Vbus.

[0045] The utility model improves the PF of the LED driving circuit and reduces THDi. At the same time, when the bus voltage Vbus is low, the LED can be powered by the capacitors C1 and C2 connected in series, thereby improving the driving efficiency. In addition, the utility model has a small number of power switch tubes and a simple structure.

[0046] Furthermore, the present invention also provides a lighting circuit, including the LED driving circuit introduced above, for driving an LED load to improve the lighting efficiency of the lighting circuit, optimize the THDi of the lighting circuit, reduce the flicker of the lamp beads, and make the lighting circuit meet relevant standards.

[0047] Although the embodiments are described and explained separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that they can be replaced and integrated between the embodiments. If there is anything not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0048] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. An LED drive circuit, wherein an AC input voltage is rectified to obtain a bus voltage, characterized in that: a first capacitor and a first switch tube, wherein a first end of the first capacitor receives the bus voltage, and a second end of the first capacitor is grounded through the first switch tube; a second capacitor and a second switch tube, wherein a first end of the second capacitor receives the bus voltage and is connected to the anode of the LED load, and a second end of the second capacitor is grounded through the second switch tube; a switch connection circuit, a first end of which is connected to the first end of the first capacitor, and a second end of which is connected to the second end of the second capacitor; The switching circuit, the first switching tube and the second switching tube are controlled to be on and off according to the magnitude of the bus voltage.

2. The LED driving circuit according to claim 1, wherein: When the bus voltage is less than a set threshold, the switch connection circuit is turned on, the first switch tube and the second switch tube are turned off, the first capacitor and the second capacitor are connected in series, and the first capacitor and the second capacitor supply power to the LED load.

3. The LED driving circuit according to claim 1, wherein: When the bus voltage is greater than a set threshold and less than the turn-on voltage of the LED load, the switch connection circuit is turned off, the first switch tube and the second switch tube are turned on, the first capacitor and the second capacitor are connected in parallel, and the bus voltage charges the first capacitor and the second capacitor.

4. The LED driving circuit according to claim 1, wherein: When the bus voltage is greater than the conduction voltage of the LED load, the switch connection circuit, the first switch tube and the second switch tube are all turned off, the first capacitor and the second capacitor are connected in parallel, and the bus voltage supplies power to the LED load.

5. The LED driving circuit according to claim 1, wherein: A third capacitor is also included, and the third capacitor is connected in parallel with the LED load.

6. The LED driving circuit according to claim 1, wherein: It also includes a third switch tube, and the cathode of the LED load is grounded through the third switch tube; When the bus voltage is less than a set threshold, or when the bus voltage is greater than the turn-on voltage of the LED load, the third switch tube is turned on.

7. The LED driving circuit according to claim 6, wherein: Also includes, a first operational amplifier, operable to amplify a first reference voltage and a first sampling signal representing the first capacitor current, wherein an output end of the first operational amplifier is connected to a control end of the first switching tube; a second operational amplifier, operable to amplify the second reference voltage and the second sampling signal representing the second capacitor current, wherein the output end of the second operational amplifier is connected to the control end of the second switch tube; The third operational amplifier performs operational amplification on the third reference voltage and the third sampling signal representing the LED load current, and the output end of the third operational amplifier is connected to the control end of the third switching tube.

8. The LED driving circuit according to claim 4, wherein: The switch connection circuit includes a third diode and a fourth switch tube, and the third diode and the fourth switch tube are connected in series; When the bus voltage is less than a set threshold, the fourth switch tube is turned on; When the bus voltage is greater than a set threshold, the fourth switch tube is turned off.

9. The LED driving circuit according to claim 8, wherein: The switch connection circuit further includes a first resistor, a first voltage-stabilizing diode, and a first switch, wherein a first end of the first resistor is connected to a high-potential end of the first capacitor, and a second end of the first resistor is connected to a control end of the fourth switch transistor; a cathode of the first voltage-stabilizing diode is connected to the control end of the fourth switch transistor, and an anode of the first voltage-stabilizing diode is connected to a low-potential end of the second capacitor; The control end of the fourth switch tube is grounded through the first switch.

10. The LED driving circuit according to claim 8, wherein: The switch connection circuit further includes a fourth operational amplifier and a first switch, wherein the fourth operational amplifier performs operational amplification on a third reference voltage and a fourth sampling signal representing the fourth switch current, and an output end of the third operational amplifier is connected to a control end of the fourth switch tube; The control end of the fourth switch tube is also grounded through the first switch.

11. The LED driving circuit according to claim 1, wherein: It also includes a first diode and a second diode, the first end of the first capacitor receives the bus voltage through the first diode, and the first end of the second capacitor receives the bus voltage through the second diode.

12. The LED driving circuit according to claim 1, wherein: The capacitance of the first capacitor is equal to the capacitance of the second capacitor.

13. The LED driving circuit according to claim 1, wherein: The maximum value of the first capacitor voltage and the maximum value of the second capacitor voltage are both greater than half of the turn-on voltage of the LED load and less than the turn-on voltage of the LED load.

14. A lighting circuit, comprising an LED load, characterized in that: It also includes the LED driving circuit according to any one of claims 1 to 13, used to drive an LED load.

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