Linear constant-current LED power supply

Abstract

The invention provides a linear constant-current LED power supply. The LED power supply comprises an LED load unit, a first capacitor, a second capacitor, a first switch, a second switch and a third switch, a first end of the first capacitor is coupled to rectified input voltage of the LED power supply through a first diode and is coupled to the LED load unit through a third diode, and a second end of the second capacitor is coupled to the LED load unit through a second diode. The second end of the first capacitor is coupled to the ground through the first switch and the first resistor and is coupled to the first end of the second capacitor through the third switch; the first end of the second capacitor is further coupled to the rectified input voltage through a second diode, and the second end of the second capacitor is coupled to the ground through a second switch and a second resistor. According to the linear constant-current LED power supply, the conduction phase angle of input current is increased in a mode of charging the first capacitor and the second capacitor, the PF value of the LED power supply is increased, in addition, a load LED is discharged through a series circuit of the first capacitor and the second capacitor, the efficiency of the LED power supply is improved while the high PF value is achieved, and the linear constant-current LED power supply with the high PF value and high efficiency is achieved.

Description

Technical Field

[0001] The present application relates to the field of circuits, and in particular to a linear constant current light emitting diode (LED) power supply. Background Art

[0002] Linear constant current LED power supplies are widely used in the field of LED lighting due to their simple and reliable structure and low system cost. Figure 1 Figure 2 shows the topology of a traditional linear constant current LED power supply. Figure 1 As shown, in this LED power supply, the rectified input voltage V in The load LED is connected to the output capacitor Co in parallel through the discharge resistor Rb and the switch S2 and is coupled to the ground through the load switch S1 and the current sampling resistor Rcs. The current flowing through the load switch S1 coupled to the load LED is sampled through the current sampling resistor Rcs to generate a load current sampling voltage Vcs. Since the average current flowing through the output capacitor Co is 0 in the steady state, the average value of the current flowing through the load switch S1 is equal to the average value of the current flowing through the load LED. Therefore, the load switch S1 is controlled to work in a saturated conduction state through the load current sampling voltage Vcs, which can ensure the constant current output of the load LED. Only when the rectified input voltage V in When the output voltage Vo is higher than the load LED, current will flow through the load switch S1 and input current I will flow into the LED power supply. in The input current I in The conduction phase angle is small, so in order to achieve the requirement of high power factor PF value, it is necessary to add switch S2 and bleeder resistor Rb. in When the output voltage Vo of the load LED is lower than that of the load switch S1 (i.e., no current flows through the load switch S1), the switch S2 is turned on to form a discharge current on the discharge resistor Rb, so that the input current I in Follows input voltage V in And changes.

[0003] The key working waveform of this traditional linear constant current LED power supply is as follows Figure 2 Specifically, Figure 2 The output voltage Vo of the load LED and the rectified input voltage V in , load current sampling voltage Vcs and input current I in The working waveform diagram. Figure 2 As shown, the rectified input voltage V in When the input current I is less than the output voltage Vo on the load LED, inAll of this energy is provided by the branch where the bleeder resistor Rb is located. This part of the energy is completely lost in the bleeder resistor Rb and cannot be transmitted to the load LED, which seriously affects the efficiency of the linear constant current LED power supply. Summary of the invention

[0004] In view of the above problems, the present application proposes a new high-efficiency linear constant current LED power supply. The linear constant current LED power supply includes: an LED load unit, a first capacitor, a second capacitor, a first switch, a second switch and a third switch, wherein the first end of the first capacitor is coupled to the rectified input voltage of the LED power supply through a first diode and is coupled to the LED load unit through a third diode, the second end of the first capacitor is coupled to the ground through a first switch and a first resistor and is coupled to the first end of the second capacitor through a third switch; the first end of the second capacitor is also coupled to the rectified input voltage through a second diode, and the second end of the second capacitor is coupled to the ground through a second switch and a second resistor; the first switch, the second switch and the third switch are configured to: when the rectified input voltage is lower than the output voltage of the LED load unit but higher than the voltage on at least one of the first capacitor and the second capacitor, the rectified input voltage charges the parallel circuit of the first capacitor and the second capacitor or charges at least one of the first capacitor and the second capacitor; and when the rectified input voltage is lower than the output voltage of the LED load unit and lower than the voltage on the first capacitor and the second capacitor, the series circuit of the first capacitor and the second capacitor discharges to the LED load unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present application may be better understood according to the following description of the specific implementation modes of the present application in combination with the accompanying drawings, wherein:

[0006] Figure 1 The topology of the traditional linear constant current LED power supply is shown;

[0007] Figure 2 It shows that Figure 1 The key working waveform diagram of the traditional linear constant current power supply shown;

[0008] Figure 3 A schematic topology structure of a linear constant current LED power supply according to an exemplary embodiment of the present application is shown;

[0009] Figure 4 An exemplary key point operating waveform diagram of a linear constant current LED power supply according to an exemplary embodiment of the present application is shown;

[0010] Figure 5 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Figure 4 An equivalent circuit diagram during the first example time period shown;

[0011] Figure 6 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Figure 4 An equivalent circuit diagram during the second example time period shown;

[0012] Figure 7 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Figure 4 An equivalent circuit diagram during a third example time period is shown;

[0013] Figure 8 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Figure 4 An equivalent circuit diagram during a fourth example time period is shown;

[0014] Fig. 9 Another exemplary key point working waveform diagram of the linear constant current LED power supply according to the exemplary embodiment of the present application is shown;

[0015] Fig.10 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Fig. 9 An equivalent circuit diagram during the first example time period shown;

[0016] Fig.11 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Fig. 9 An equivalent circuit diagram during the second example time period shown;

[0017] Fig.12 The linear constant current LED power supply according to the exemplary embodiment of the present application is shown in FIG. Fig. 9 The equivalent circuit diagram during the third example time period is shown. DETAILED DESCRIPTION

[0018] The features and exemplary embodiments of various aspects of the application will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the application. However, it is obvious to those skilled in the art that the application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the application by illustrating the example of the application. The application is by no means limited to any specific configuration proposed below, but covers any modification, replacement and improvement of elements, parts and algorithms without departing from the spirit of the application. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid causing unnecessary ambiguity to the application.

[0019] The terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprises..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements. In addition, it should be noted that the term "A is coupled to B" used herein can mean "A is directly coupled to B" or "A is indirectly coupled to B via one or more other elements".

[0020] As mentioned above, in a traditional linear constant current LED power supply, the rectified input voltage V in When the input current I is less than the output voltage Vo on the load LED, in All of this energy is provided by the branch where the bleeder resistor Rb is located. This part of the energy is completely lost in the bleeder resistor Rb and cannot be transmitted to the load LED, which seriously affects the efficiency of the linear constant current LED power supply. In view of this, the present application proposes a new linear constant current LED power supply topology and control method thereof, which does not affect the power supply efficiency while meeting the power factor value requirements of the LED power supply, thereby realizing a high-efficiency linear constant current LED power supply. For example, PF>0.9 and power supply efficiency>81% can be achieved at the same time, or the power supply efficiency can be slightly reduced to achieve a smaller total harmonic distortion (for example, less than 20%).

[0021] Figure 1 FIG. 2 shows a schematic topological structure of a linear constant current LED power supply according to an exemplary embodiment of the present application. Figure 1 As shown, the linear constant current LED power supply includes: an LED load unit, a first capacitor C1, a second capacitor C2, a first switch Sa, a second switch Sb and a third switch Sc, wherein the first end of the first capacitor C1 is coupled to the rectified input voltage V of the LED power supply through a first diode D1. in The first end of the first capacitor C1 is coupled to the ground through the first switch Sa and the first resistor Rc1 and is coupled to the first end of the second capacitor C2 through the third switch Sc; the first end of the second capacitor C2 is also coupled to the rectified input voltage V through the second diode D2. in, the second end of the second capacitor C2 is coupled to the ground through the second switch Sb and the second resistor Rc2. The LED load unit may include a load LED, an output capacitor Co, a load switch S1 and a current sampling resistor Rcs, the output capacitor Co is connected in parallel with the load LED, and the load LED is coupled to the ground through the load switch S1 and the current sampling resistor Rcs. According to an embodiment of the present application, the first switch Sa, the second switch Sb and the third switch Sc may be configured as follows: when the rectified input voltage V in When the voltage is lower than the output voltage Vo of the LED load unit but higher than the voltage on at least one of the first capacitor C1 and the second capacitor C2, the rectified input voltage V in The parallel circuit of the first capacitor C1 and the second capacitor C2 is charged or at least one of the first capacitor C1 and the second capacitor C2 is charged; and when the rectified input voltage V in When the voltage is lower than the output voltage Vo of the LED load unit and lower than the voltage on the first capacitor C1 and the second capacitor C2, the series circuit of the first capacitor C1 and the second capacitor C2 discharges to the LED load unit, thereby increasing the input current I of the LED power supply. in The conduction phase angle can improve the PF value of the LED power supply.

[0022] The following will refer to Figures 4 to 12 The working process of the linear constant current LED power supply according to the embodiment of the present application is described.

[0023] According to an exemplary embodiment of the present application, in Figure 3 In the linear constant current LED power supply shown, the first capacitor C1 and the second capacitor C2 can be set to have equal capacitance values. When the charging currents of the first capacitor C1 and the second capacitor C2 are set to be unequal (for example, by setting the first resistor Rc1 and the second resistor Rc2 to have different resistance values), the voltages on the first capacitor C1 and the second capacitor C2 are different. For example, the resistance value of the first resistor Rc1 can be set to be greater than the resistance value of the second resistor Rc2, so that the charging current of the second capacitor C2 is greater than the charging current of the first capacitor C1, and the voltage on the second capacitor C2 is greater than the voltage on the first capacitor C1, then the charging time of the first capacitor C1 in one power frequency cycle is greater than the charging time of the second capacitor C2. In this case, the key point working waveform of the linear constant current LED power supply is as follows: Figure 4 shown. Figure 4 The output voltage Vo of the load LED and the rectified input voltage V in , load current sampling voltage Vcs, current I flowing through the first switch Sa and the second switch Sb Sa and I Sb 、Input current I in, the gate voltage Sa_gate of the first switch Sa, the gate voltage Sb_gate of the second switch Sb, and the gate voltage Sc_gate of the third switch Sc. The charging currents of the first capacitor C1 and the second capacitor C2 are not equal, that is, the current I flowing through the first switch Sa and the second switch Sb is Sa and I Sb The positive magnitudes are not equal.

[0024] like Figure 4 As shown, in the first exemplary time period (t0-t1), the rectified input voltage V in Higher than the output voltage Vo of the load LED, the LED current is now determined by the input voltage V in Provided that the current flowing through the load switch S1 is equal to the input current I in , the first switch Sa, the second switch Sb, and the third switch Sc are all in the off state. Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Figure 5 As shown, the current flow direction is shown by the arrow. Input voltage V in The output capacitor Co is charged while supplying current to the load LED, and then the input current I in The current flows into the ground through the load switch S1 and the current sampling resistor Rcs. The voltage Vcs on the current sampling resistor Rcs is used as feedback to control the current flowing through the load switch S1, that is, the average current of the load LED. At this stage, the load switch S1 works in a saturated conduction state.

[0025] like Figure 4 As shown, in the second exemplary time period (t1-t2 and t5-t6), the rectified input voltage V in is lower than the output voltage Vo of the load LED, and higher than both the voltage on the first capacitor C1 and the voltage on the second capacitor C2. At this time, the input voltage V in The first capacitor C1 is charged with a constant current through the first diode D1 and the first switch Sa, and the second capacitor C2 is charged with a constant current through the second diode D2 and the second switch Sb. The current on the load LED is provided by the output capacitor Co (that is, the output capacitor Co discharges to the load LED). The third switch Sc is in the off state, and the first switch Sa and the second switch Sb are both in the saturated conduction state. During this period, if Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Figure 6 As shown, the current flow direction is shown by the arrow. Input current I in Equal to the sum of the charging current of the first capacitor C1 and the charging current of the second capacitor C2. Input voltage V inThe first capacitor C1 is charged through the first diode D1 and the first switch Sa. The first resistor Rc1 detects the charging current of the first capacitor C1 and converts it into a voltage. The first switch Sa works in a saturated conduction state. The voltage on the first resistor Rc1 is used as feedback to control the first switch Sa to control the charging current of the first capacitor C1. Input voltage V in The second capacitor C2 is charged through the second diode D2 and the second switch Sb, the second resistor Rc2 detects the charging current of the second capacitor C2 and converts it into a voltage, the second switch Sb works in a saturated conduction state, the voltage on the second resistor Rc2 is used as feedback, and the second switch Sb is controlled to control the charging current of the second capacitor C2. The charging current of the second capacitor C2 is greater than the charging current of the first capacitor C1, so the voltage on the second capacitor C2 is greater than the voltage on the first capacitor C1.

[0026] like Figure 4 As shown, in the third example time period (t2-t3 and t4-t5), the rectified input voltage V in The input voltage V in The first capacitor C1 is charged with a constant current through the first diode D1 and the first switch Sa. The current on the load LED is provided by the output capacitor Co (i.e., the output capacitor Co discharges to the load LED). The second capacitor C2 is neither charged nor discharged, and its voltage remains unchanged. The third switch Sc is in the off state, the first switch Sa works in the saturated on state, and the second switch Sb does not affect the working state of the LED power supply whether it is in the on or off state. During this time period, if Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Figure 7 As shown, the current flow direction is shown by the arrow. Input current I in Equal to the charging current of the first capacitor C1. Input voltage V in The first capacitor C1 is charged through the first diode D1 and the first switch Sa. The first resistor Rc1 detects the charging current of the first capacitor C1 and converts it into a voltage. The first switch Sa works in a saturated conduction state. The voltage on the first resistor Rc1 is used as feedback to control the first switch Sa to control the charging current of the first capacitor C1.

[0027] like Figure 4 As shown, in the fourth example time period (t3-t4), the rectified input voltage V in The input voltage V in It can neither provide current to the load LED nor charge the first capacitor C1 and the second capacitor C2. The input current I inis zero. At this time, the series circuit of the first capacitor C1 and the second capacitor C2 discharges to the load LED and provides current. Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Figure 8 As shown, the current flow direction is shown by the arrow. The current sampling resistor Rcs of the load LED detects the discharge current of the first capacitor C1 and the second capacitor C2 and converts it into voltage. The second switch Sb and the third switch Sc work in a fully on state, the load switch S1 works in a saturated on state, and the first switch Sa is in an off state. The voltage on the current sampling resistor Rcs is used as feedback to control the load switch S1, and then control the discharge current of the first capacitor C1 and the second capacitor C2, that is, the average current of the load LED.

[0028] According to another exemplary embodiment of the present application, in the Figure 3 In the linear constant current LED power supply shown, the first capacitor C1 and the second capacitor C2 can be set to have equal capacitance values, and the charging currents of the first capacitor C1 and the second capacitor C2 are also set to be equal (for example, by setting the first resistor Rc1 and the second resistor Rc2 to have the same resistance value), the voltages on the first capacitor C1 and the second capacitor C2 are the same, and the charging time of the first capacitor C1 and the second capacitor C2 is the same in each power frequency cycle, and the first capacitor C1 and the second capacitor C2 are always in a parallel state when charging. In this case, the key working waveforms of the linear constant current LED power supply are as follows: Fig. 9 shown. Fig. 9 The output voltage Vo of the load LED and the rectified input voltage V in , load current sampling voltage Vcs, current I flowing through the first switch Sa and the second switch Sb Sa and I Sb 、Input current I in , a working waveform diagram of a gate voltage Sa_gate of the first switch Sa, a gate voltage Sb_gate of the second switch Sb, and a gate voltage Sc_gate of the third switch Sc.

[0029] like Fig. 9 As shown, in the first exemplary time period (t0-t1), the rectified input voltage V in Higher than the output voltage Vo of the load LED, the LED current is now determined by the input voltage V in Provided that the current flowing through the load switch S1 is equal to the input current I in , the first switch Sa, the second switch Sb, and the third switch Sc are all in the off state. Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Fig.10 As shown, the current flow direction is shown by the arrow. Input voltage Vin The output capacitor Co is charged while supplying current to the load LED, and then the input current I in The current flows into the ground through the load switch S1 and the current sampling resistor Rcs. The voltage Vcs on the current sampling resistor Rcs is used as feedback to control the current flowing through the load switch S1, that is, the average current of the load LED. At this stage, the load switch S1 works in a saturated conduction state.

[0030] like Fig. 9 As shown, in the second example time period (t1-t2 and t3-t4), the rectified input voltage V in The input voltage V in The first capacitor C1 is charged with a constant current through the first diode D1 and the first switch Sa, and the second capacitor C2 is charged with a constant current through the second diode D2 and the second switch Sb. The current on the load LED is provided by the output capacitor Co (that is, the output capacitor Co discharges to the load LED). The third switch Sc is in the off state, and the first switch Sa and the second switch Sb are both in the saturated conduction state. During this period, if Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Fig.11 As shown, the current flow direction is shown by the arrow. Input current I in Equal to the sum of the charging current of the first capacitor C1 and the charging current of the second capacitor C2. Input voltage V in The first capacitor C1 is charged through the first diode D1 and the first switch Sa. The first resistor Rc1 detects the charging current of the first capacitor C1 and converts it into a voltage. The first switch Sa works in a saturated conduction state. The voltage on the first resistor Rc1 is used as feedback to control the first switch Sa to control the charging current of the first capacitor C1. Input voltage V in The second capacitor C2 is charged through the second diode D2 and the second switch Sb, the second resistor Rc2 detects the charging current of the second capacitor C2 and converts it into a voltage, the second switch Sb works in a saturated conduction state, the voltage on the second resistor Rc2 is used as feedback, and the second switch Sb is controlled to control the charging current of the second capacitor C2. The charging current of the first capacitor C1 is equal to the charging current of the second capacitor C2, so the voltage on the first capacitor C1 is equal to the voltage on the second capacitor C2.

[0031] like Fig. 9 As shown, in the third example time period (t2-t3), the rectified input voltage V in Lower than the voltage on the first capacitor C1 and the second capacitor C2, the input voltage V inIt can neither provide current to the load LED nor charge the first capacitor C1 and the second capacitor C2. The input current I in is zero. At this time, the series circuit of the first capacitor C1 and the second capacitor C2 discharges to the load LED and provides current. Figure 3 The equivalent circuit diagram of the linear constant current LED power supply is shown in Fig.12 As shown, the current flow direction is shown by the arrow. The current sampling resistor Rcs of the load LED detects the discharge current of the first capacitor C1 and the second capacitor C2 and converts it into voltage. The second switch Sb and the third switch Sc work in a fully on state, the load switch S1 works in a saturated on state, and the first switch Sa is in an off state. The voltage on the current sampling resistor Rcs is used as feedback to control the load switch S1, and then control the discharge current of the first capacitor C1 and the second capacitor C2, that is, the average current of the load LED.

[0032] In summary, according to the embodiments of the present application, a new linear constant current LED power supply topology structure and control method thereof are provided. The input current I of the LED power supply is increased by charging the first capacitor C1 and the second capacitor C2. in The conduction phase angle increases the PF value of the LED power supply, and then the input voltage V in When the current is so low that it can neither provide current to the load LED nor charge the first capacitor C1 and the second capacitor C2, the first capacitor C1 and the second capacitor C2 are connected in series to discharge the load LED, and the previously charged energy is discharged to the load LED, so that the efficiency of the LED power supply can be improved while achieving a high PF value, and a linear constant current LED power supply with a high PF value and high efficiency can be achieved. The larger the charging current of the first capacitor C1 and the second capacitor C2, the higher the PF value of the LED power supply, the lower the total harmonic distortion, and the lower the power efficiency; the smaller the charging current of the first capacitor C1 and the second capacitor C2, the lower the PF value of the LED power supply, the higher the total harmonic distortion, and the higher the power efficiency. Therefore, in practice, the charging current of the first capacitor C1 and the second capacitor C2 can be configured as needed to achieve a high-efficiency linear constant current LED power supply with desired performance.

[0033] In the above text, "embodiment", "exemplary embodiment" and the like are mentioned, however, it should be understood that the features mentioned in each embodiment are not necessarily applicable only to the embodiment, but may be used in other embodiments. Features in one embodiment may be applied to another embodiment, or may be included in another embodiment.

[0034] In the above text, ordinal numbers such as "first", "second", etc. are mentioned. However, it should be understood that these expressions are only for the convenience of description and reference, and the objects defined do not have a sequential relationship.

[0035] The application can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in the specific embodiment can be modified, and the system architecture does not depart from the basic spirit of the application. Therefore, the current embodiment is regarded as exemplary and non-restrictive in all aspects, and the scope of the application is defined by the attached claims rather than the above description, and all changes falling within the meaning of the claims and the scope of equivalents are thereby included in the scope of the application.

Claims

1. A linear constant current LED power supply, comprising: LED load unit, a first capacitor, a second capacitor, a first switch, a second switch and a third switch, wherein: A first end of the first capacitor is coupled to the rectified input voltage of the LED power supply through a first diode and is coupled to the LED load unit through a third diode, and a second end of the first capacitor is coupled to ground through the first switch and a first resistor and is coupled to the first end of the second capacitor through the third switch; The first end of the second capacitor is also coupled to the rectified input voltage through a second diode, and the second end of the second capacitor is coupled to ground through the second switch and the second resistor; and The first switch, the second switch and the third switch are configured such that: when the rectified input voltage is lower than the output voltage of the LED load unit but higher than the voltage on at least one of the first capacitor and the second capacitor, the rectified input voltage charges the parallel circuit of the first capacitor and the second capacitor or charges at least one of the first capacitor and the second capacitor; and when the rectified input voltage is lower than the output voltage of the LED load unit and lower than the voltage on the first capacitor and the second capacitor, the series circuit of the first capacitor and the second capacitor discharges to the LED load unit.

2. The linear constant current LED power supply according to claim 1, wherein: The capacitance value of the first capacitor is equal to the capacitance value of the second capacitor, and the resistance value of the first resistor is greater than the resistance value of the second resistor.

3. The linear constant current LED power supply according to claim 2, wherein: When the rectified input voltage is higher than the output voltage of the LED load unit, the first switch, the second switch and the third switch are all configured to be in an off state, so that the rectified input voltage is coupled to the LED load unit through the first diode and the third diode to power the LED load unit.

4. The linear constant current LED power supply according to claim 2, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit but higher than the voltage on the first capacitor and the second capacitor, the third switch is configured to be in an off state, and the first switch and the second switch are configured to operate in a saturated conduction state, so that the rectified input voltage charges the parallel circuit of the first capacitor and the second capacitor.

5. The linear constant current LED power supply according to claim 2, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit and the voltage on the second capacitor but higher than the voltage on the first capacitor, the third switch is configured to be in an off state, and the first switch is configured to operate in a saturated on state, so that the rectified input voltage charges the first capacitor.

6. The linear constant current LED power supply according to claim 2, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit and lower than the voltage on the first capacitor and the second capacitor, the first switch is configured to be in an off state, and the second switch and the third switch are configured to operate in a fully on state, so that the series circuit of the first capacitor and the second capacitor is coupled to the LED load unit through the third diode to discharge to the LED load unit.

7. The linear constant current LED power supply according to claim 1, wherein: The capacitance value of the first capacitor is equal to the capacitance value of the second capacitor, and the resistance value of the first resistor is equal to the resistance value of the second resistor.

8. The linear constant current LED power supply according to claim 7, wherein: When the rectified input voltage is higher than the output voltage of the LED load unit, the first switch, the second switch and the third switch are all configured to be in an off state, so that the rectified input voltage is coupled to the LED load unit through the first diode and the third diode to power the LED load unit.

9. The linear constant current LED power supply according to claim 7, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit but higher than the voltage on the first capacitor and the second capacitor, the third switch is configured to be in an off state, and the first switch and the second switch are configured to operate in a saturated conduction state, so that the rectified input voltage charges the parallel circuit of the first capacitor and the second capacitor.

10. The linear constant current LED power supply according to claim 7, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit and lower than the voltage on the first capacitor and the second capacitor, the first switch is configured to be in an off state, and the second switch and the third switch are configured to operate in a fully on state, so that the series circuit of the first capacitor and the second capacitor is coupled to the LED load unit through the third diode to discharge to the LED load unit.

11. The linear constant current LED power supply according to any one of claims 1 to 10, wherein: The LED load unit includes a load LED, an output capacitor, a load switch and a current sampling resistor. The output capacitor is connected in parallel with the load LED, and the load LED is coupled to the ground through the load switch and the current sampling resistor.

12. The linear constant current LED power supply according to claim 11, wherein: When the rectified input voltage is lower than the output voltage of the LED load unit but higher than the voltage on at least one of the first capacitor and the second capacitor, the output capacitor discharges to the load LED.

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