LED driving device and driving method

Abstract

The LED driver includes a main converter stage and a power commutation stage in parallel with an LED unit. An energy diversion mode of operation is used, during which a set current is supplied to the LED unit and the main converter stage is used to supply a current greater than the set current. The power commutation stage is used to divert energy from the LED unit and return the diverted energy to the input to the main converter. The remaining set current is supplied to the LED unit. This allows for deeper dimming than the dimming level applied to the main converter stage, but does not require an additional switch-mode power converter.

Description

[Technical Field]

[0001] The present invention relates to an LED driver, and more particularly to an LED driver that implements a dimming function. [Background technology]

[0002] It is well known to provide LED drivers with dimming capabilities for smart lighting systems, e.g., for indoor and outdoor applications, which aim to provide pleasant lighting with rich and vibrant colors and the ability to create a wide range of desired colors or color temperatures.

[0003] The most important and fundamental element for achieving this controllability is the ability to implement deep dimming functions (for various colors). Deep dimming is therefore a key parameter for meeting the desired optical performance of a smart lighting system. For example, there is a large difference between the color and color temperature range that can be achieved, such as between 5% dimming and 0.1% dimming.

[0004] Conventional driver systems typically allow brightness dimming down to a minimum brightness level such as 5%. So-called "deep dimming" below this minimum brightness level is difficult to achieve with existing driver architectures, especially those based on switch-mode power conversion circuits.

[0005] Improving the dimming function to enable dimming below this lower limit, for example, below 5% brightness, such as down to 0.1% brightness, is a major challenge for conventional driver circuits, especially in the low power output region. The problem is that single-stage topology switched-mode power supply systems cannot reach deep dimming below 5% due to the driver architecture, for example, as a result of dynamic characteristics or control loop limitations. Therefore, it is the hardware design that makes it difficult to achieve the desired deep dimming. Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional solutions include adding one or more additional switch-mode power topology structures. However, this increases the complexity and cost of the overall architecture. Therefore, there is a need for a driver that allows for reduced current drive (and therefore deep dimming) while reducing circuit complexity. Another conventional solution is to add a resistive bleeder in parallel with the LED, but the resistive bleeder typically dissipates power and results in high losses.

[0007] US9538601B1 discloses a bypass switch 22 for bypassing current to the LED 12. [Means for solving the problem]

[0008] The invention is defined by the claims.

[0009] The concept of the present invention is to provide a main power converter that performs dimming down to a first brightness level (i.e., first dimming depth), and to enable dimming to a lower brightness level (second, deeper dimming depth) by using a power commutation stage to divert energy from the LED load and return it to the input. Thus, deep dimming is possible with a simple architecture and is power efficient because diverted power is reused instead of being dissipated. Preferably, the main power converter is maintained above its minimum output for stable operation.

[0010] According to an example according to an aspect of the present invention, there is provided an LED driving device, Input and an output of the LED driver adapted to connect an LED unit; a main converter stage adapted to convert power at the input and output a converter current to the LED unit at an output of the main converter stage; a power commutation stage coupled to the output of the main converter stage; a controller adapted to implement an energy divert mode of operation upon receiving a signal to set a current to the LED unit to a set current, wherein during the energy divert mode, the controller: operating a main converter stage to output the converter current at a current greater than the set current; At the same time, an LED driving device is provided that is adapted to operate the power commutation stage to divert energy from the converter current that is greater than the set current, return the diverted energy to the input of the main converter stage, and allow the remaining current to the LED unit through the output of the LED driving device, and the controller is adapted to divert the energy in an amount corresponding to the current difference between the converter current of the main converter stage that is greater than the set current and the set current, thereby causing the remaining current to the LED unit to be equal to the set current.

[0011] By diverting current from the LED unit and returning the energy to the input rather than to the LED unit, the driver can reduce the current supplied to the LED unit, for example, to a set current below a threshold current for deep dimming. In this manner, the dimming function is performed by the power commutation stage. This means that the dimming level that needs to be reached by the main converter stage can be mitigated (i.e., dimmed less deeply) by maintaining its output current higher than the threshold current. This relaxes the requirements on the main converter stage while allowing the entire driver to achieve the desired overall dimming level. Because the output current is diverted, the overall achieved dimming level (corresponding to the set current) is, for example, less than 1% (of the nominal LED unit current), e.g., as low as 0.1%. And, because the diverted current / energy is returned to the main converter stage, deep dimming is possible with improved efficiency compared to existing solutions.

[0012] The present invention may use existing hardware. The main converter stage may comprise a resonant converter. This is a known type of converter for use as a main converter stage in LED lighting drivers. For example, a driver architecture (Signify's Xitanium driver) is known that includes a half-bridge (LLC / LCC) topology in the main converter stage and a power commutation stage based on a flyback topology. The present invention can also utilize this flyback topology for the auxiliary power supply (described below).

[0013] In alternative embodiments, the main converter stage may comprise an isolated converter, such as a flyback converter, or a non-isolated converter, such as a boost converter.

[0014] In some embodiments, the power commutation stage is adapted to be electrically in parallel with the LED unit, while in other examples, the power commutation stage is adapted to be magnetically coupled to the main converter stage.

[0015] The controller is adapted, for example, to implement the energy diversion mode to provide the remaining current to the LED unit when the set current is less than a threshold dimming current, and the main converter stage operates sub-normally when the main converter stage is adapted to directly output the set current less than the threshold dimming current.

[0016] The threshold dimming level is then the level that can be achieved by the main converter stage with desired performance, such as desired efficiency, stability, power factor correction level, total harmonic distortion level, etc. (i.e., any desired or rated parameter). For dimming levels below this threshold level (i.e., deeper dimming), the power commutation stage is used.

[0017] The controller may be adapted to implement a normal dimming mode, distinct from the energy diversion mode, upon receiving a signal to set a current to the LED unit to the set current that is greater than the threshold dimming current.

[0018] The main converter stage operates normally when the main converter stage is adapted to directly output the set current above the threshold dimming level. The normal dimming mode can be implemented by the main converter stage without using the power commutation stage. Thus, during the normal dimming mode, the controller is adapted to operate the main converter stage to directly output the set current to the LED unit and to deactivate the power commutation stage to prevent energy from being diverted from the converter current. In this manner, the power commutation stage does not impair the normal operation of the main converter stage when the main converter stage is operating within its intended operating range, and the power commutation stage is not involved in normal operation. In another example, as described below, the power commutation stage can also operate to divert power for an auxiliary power source, which can reduce the size or rating of a dedicated auxiliary power supply unit.

[0019] The threshold dimming current may include a minimum design dimming current normally provided by a control loop and components of the main converter stage, for example, within a range of 1% to 5% of the nominal current of the main converter stage.

[0020] For example, the main converter stage may not be able to operate at a desired efficiency or stability level when controlled to provide an output below the threshold dimming level, but may operate above the threshold dimming level at or above the desired efficiency or stability level.

[0021] The power diversion stage may further include a winding for supplying an auxiliary power signal to a non-light-emitting component from a portion of the diverted energy, and the power diversion stage returns a remaining portion of the diverted energy to the input.

[0022] When the LED unit is on, this diverted energy usage contributes to powering non-light-emitting components (such as a control IC), and therefore contributes to the peak energy demand of the non-light-emitting components.

[0023] The driver preferably further comprises an auxiliary power supply circuit (in addition to the auxiliary power signal described above) for supplying alternative auxiliary power used by the non-light-emitting components. This can have a reduced size as a result of using part of the diverted energy to generate another auxiliary power supply signal. Therefore, the separate auxiliary power supply for standby power can be made smaller (because when the LED unit is off, the control IC requires much less energy, and therefore the separate auxiliary power supply can be designed with a smaller power rating).

[0024] The auxiliary power supply circuit, for example, said input, and It is connected to any one of the power components of the main converter stage.

[0025] The above are two known implementations of the auxiliary power circuit, such as the VCC power supply. This connection provides power to the auxiliary power circuit. The winding used to generate the auxiliary power signal provides an alternative auxiliary power source.

[0026] The power commutation stage may, for example, comprise a flyback converter having a primary flyback winding electrically connected in parallel with the output of the main converter stage and adapted to be connected in parallel with the LED unit, and a secondary flyback winding magnetically coupled to the primary flyback winding and electrically connected to the input.

[0027] The flyback converter is a known device for implementing an auxiliary power supply: besides the winding (one secondary winding that provides the auxiliary power supply), a further winding (the secondary flyback winding) is added that couples energy back to the input.

[0028] The secondary flyback winding is connected to the input via a buffer circuit, which may be a diode or a diode-capacitor circuit.

[0029] The power commutation stage may include a switch in series with the primary flyback winding, the controller being adapted to activate and deactivate the power commutation stage by controlling the switch, which also provides high frequency flyback commutation.

[0030] The switch thus opens or closes a diversion current path for the converter current from the main converter stage.

[0031] The present invention provides a drive unit as defined above; A lighting circuit including the LED unit is also provided.

[0032] The present invention is a driving method for driving an LED unit, using a main converter stage to convert power at an input, thereby outputting a converter current to the LED unit at an output of the main converter stage; and performing an energy diversion mode of operation upon receiving a signal to set a current to the LED unit to a set current that is less than a threshold dimming current, wherein if the main converter stage is adapted to directly output the set current that is less than the threshold dimming current, the main converter stage will operate subnormally, and the energy diversion mode of operation is: operating a main converter stage to output a converter current at a current greater than the set current; A driving method is also provided, which includes operating a power commutation stage coupled to the output of the main converter stage and coupled in parallel with the LED unit to divert energy from the converter current and return the diverted energy to the input of the main converter stage, while simultaneously supplying a remaining current to the LED unit, diverting the energy in an amount corresponding to a current difference between the converter current of the main converter stage, which is greater than the set current, and the set current, thereby making the remaining current to the LED unit equal to the set current.

[0033] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief explanation of the drawings]

[0034] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: [Figure 1] 1 shows a first example of an LED driving device connected to an LED unit. [Figure 2] 2 shows a second example of an LED driving device. [Figure 3] 1 shows a third example of an LED driving device. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be described with reference to the drawings.

[0036] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

[0037] The present invention provides an LED driver having a main converter stage and a power diversion stage in parallel with an LED unit. An energy diversion mode of operation is used, during which a set current is supplied to the LED unit and the main converter stage is used to supply a current greater than the set current. The power diversion stage is used to divert energy from the LED unit and return the diverted energy to the input to the main converter. The remaining set current is supplied to the LED unit. This allows for deeper dimming than the dimming level applied to the main converter stage, still keeping the main converter stage within a comfortable operating range and improving the efficiency of energy diversion without dissipating its energy.

[0038] Figure 1 shows a first example of an LED driver 10 connected to an LED unit 50, which together form a lighting circuit such as part of a luminaire. The driver has an input 12, which in the example shown is a mains AC input. The input is rectified by a bridge rectifier 14 and supplied as input 15 to a mains converter stage.

[0039] The main converter stage comprises a switched-mode power converter. The example shown has a half-bridge formed by switches S1 and S2 and an LLC resonant tank connected to the node between the switches. LLC is a well-known technology, and therefore will not be further described here unless necessary. The converter output is formed by a transformer with a primary winding Tprim and a secondary winding Tsec.

[0040] The switches S1 and S2 are controlled by a control circuit 18.

[0041] The LED unit 50 is connected to the secondary side of the transformer via rectifier diodes D1 and D2.

[0042] The main converter stage is adapted to convert power at an input 12 and output a converter current to the LED unit at an output 16 of the main converter stage. Other types of resonant converters may be used, such as an LCC converter. As an alternative to a resonant converter, the main converter stage may be an isolated converter, such as a flyback converter, or a non-isolated converter, such as a boost converter.

[0043] In an embodiment in which a power commutation stage is coupled to output 16, the power commutation stage is electrically in parallel with LED unit 50 and therefore functions as an electrical energy diversion and returning system. In an alternative embodiment, the power commutation stage may be magnetically coupled to secondary winding Tsec to form a magnetic energy diversion system. In the following description, electrical energy diversion is taken as an example to explain the present invention. Those skilled in the art will understand that magnetic energy diversion and returning is similar in concept and implementation. Therefore, this alternative will not be described in further detail.

[0044] The power commutation stage includes a flyback converter having a primary flyback winding L1 electrically connected in parallel with the LED unit 50 and a secondary flyback winding L2 magnetically coupled to the primary flyback winding and electrically connected to the input 15 of the main converter stage.

[0045] The coupling to the input 15 is via diode D3 back to the half bridge S1, S2. Diode D3 acts as a blocking circuit. There may be a buffer capacitor to buffer the returned energy. Thus, when a fluctuating current is generated in inductor L1, there is an induced magnetic field and an induced current in L2, and by this mechanism the energy delivered to the output is returned to the input 15 of the main converter stage.

[0046] In the preferred embodiment, in addition to the energy return function, a flyback converter is a known device for implementing auxiliary power. Thus, the diverted energy may be used for auxiliary power for non-lighting components such as the MCU / IC. An additional winding L3 (described below) is provided for this purpose.

[0047] The power commutation stage includes a switch S in series with the primary flyback winding L1.

[0048] The controller 20 activates and deactivates the power commutation stage by controlling the switch S. The switch S opens or closes a bypass current path for the converter current from the main converter stage. In this manner, the controller 20 implements an energy diversion mode of operation.

[0049] This diversion mode is used when the set current at which the LED units should be driven is too low for the main converter stage to achieve the desired efficiency and / or accuracy and / or stability and / or acceptable PFC / THD, etc. During this diversion mode, the converter current of the main converter stage is maintained at a current greater than the set current, so that the converter current can be supplied with the desired accuracy, efficiency, etc. However, the power commutation stage is operated to divert energy from the converter current and return the divert energy to the input 15. As a result, the desired set current is still supplied to the LED units 50.

[0050] Thus, the current supplied to the LED unit is reduced to a set current that is below the threshold current. The threshold current corresponds to a threshold dimming level, which is the dimming level that can be achieved with the desired efficiency by the main converter stage. For dimming levels below this threshold level (i.e., deeper dimming), a power commutation stage is used.

[0051] Deep dimming is therefore achieved by diverting current away from the LED units using a power commutation stage. This relaxes the requirements on the main converter stage so that the entire driver can achieve the desired overall dimming level. The overall achieved dimming level (corresponding to the set current) is, for example, less than 1% (of the nominal LED unit current), e.g., as low as 0.1%.

[0052] For brightness levels above this threshold level, normal dimming mode is used, which can be implemented by the main converter stage without requiring the use of the power commutation stage. Thus, during normal dimming mode, the main converter stage is used to output the converter current as a set current directly to the LED units, and the power commutation stage is disabled (to prevent energy from being diverted from the converter current).

[0053] The invention can use existing hardware, for example driver architectures with a half-bridge (LLC or LCC) topology in the main circuit as shown (Signify's Xitanium driver) are known.

[0054] The auxiliary power supply using a flyback topology is shown as inductor L3. As shown, inductor L3 has two taps for generating two different auxiliary supply voltages that are stored on respective capacitors C1 and C2. These may be, for example, two or more of 3V, 5V, 12V, and 24V.

[0055] The auxiliary power supply using coil L3 is operational only when the main converter is providing an output and is therefore not operational during standby. Winding L3 provides the auxiliary power signal from a portion of the diverted energy. The diverted energy is therefore based on the current through coil L3, which is used to induce currents in both L2 and L3, each of which therefore forms part of the diverted energy. The portion of the diverted energy induced in coil L3 is used, for example, to power a non-light-emitting component, which may be, for example, controller 18 or other control circuitry or a sensor.

[0056] In both the dimming and normal modes described above, the main converter stage may output even more energy, allowing the auxiliary power supply using coil L3 to divert energy for auxiliary power.

[0057] There is also a separate auxiliary power circuit 30 which functions during standby (when no energy is supplied to the LED unit and therefore no inductive signal is generated by the flyback converter).

[0058] Conventionally, this dedicated auxiliary power circuit 30 must cover a large range of output power. During standby, the output power required is small, but when the LED unit is on, the control circuit 18 requires a larger amount of power, and therefore the auxiliary power supply must output more power. Therefore, although the rated power of the auxiliary power supply is sufficient to meet the greatest demand, this capacity is redundant most of the time.

[0059] In this invention, since inductor L3 can provide auxiliary power when the LEDs are on (even if the LEDs are not deeply dimmed), the coupling between L1 and L3 can be used to divert energy for peak auxiliary power. The main converter stage can be set to output a current greater than the desired LED current, so that a portion is diverted to provide energy transfer from L1 to L3.

[0060] In this manner, auxiliary power circuit 30 does not need to be designed with such a high power rating because it only needs to provide a small output power during standby mode or to supplement inductor L3, and therefore auxiliary power circuit 30 can be smaller than existing designs.

[0061] The auxiliary power circuit 30 is a dedicated auxiliary power supply. The auxiliary power circuit 30 may be directly connected to the bus after a rectifier, or may derive power from the inductor of a switch-mode converter or from transformers Tprim, Tsec. The auxiliary power circuit 30 may include, for example, a buck converter and a linear regulator. Those skilled in the art will understand that typical auxiliary power circuits 30 are well known, and therefore, further details will not be provided herein.

[0062] In light output mode, if there is energy to be diverted, the energy stored in inductor L3 may or may not be sufficient for non-lighting loads (e.g., controller 18). If it is sufficient, the original auxiliary power circuitry is not needed and therefore the power rating can be lower. If it is not sufficient, the original auxiliary power circuitry may be used to supply the remainder.

[0063] In the lights-off mode, the original auxiliary power supply circuit 30 operates independently.

[0064] In extreme situations during the lights-out mode, if the auxiliary power circuit 30 is still not sufficient, the half-bridges S1, S2 can be started up and the coupling between the inductors L1 and L3 can be used to divert all the output power to the non-lighting loads.

[0065] Therefore, the dedicated auxiliary power supply circuit 30 and the power diversion circuit have their own operation and function. When in deep dimming stage, they cooperate to achieve the desired deep dimming level, so that LED color temperature adjustment can be more accurate and RGBW color mixing can be used to enable a wider range of desired colors.

[0066] The present invention further utilizes existing circuits, in particular reusing auxiliary power sources by providing interaction with a half-bridge circuit. The flyback topology operates in two functions: different dimming levels.

[0067] A second example of an LED driver is shown in Figure 2. Figure 2 differs from Figure 1 in that a full-bridge topology S1 to S4 is used by the main converter.

[0068] FIG. 3 shows a third example of an LED driving device.

[0069] The main converter is simply represented by block 40. In this example, diode D3 is coupled back to the main bus, i.e., the output of the rectifier. The primary flyback winding L1 has a connection back to the output of the half-bridge, i.e., LLC converter stage. This is simply an alternative topology.

[0070] The present invention also provides a driving method for driving an LED unit, the driving method comprising the steps of using a main converter stage to convert power at an input, thereby outputting a converter current to the LED unit at the output of the main converter stage. Upon receiving a signal to set the current to the LED unit to a set current less than a threshold dimming current, an energy diversion mode of operation is implemented, and the main converter stage would operate below normal if the main converter stage were adapted to directly output a set current less than the threshold dimming current. The energy diversion mode of operation comprises: Maintaining a converter current in the main converter stage at a current greater than a set current; A power commutation stage coupled to the output and coupled in parallel with the LED unit is operated to divert energy from the converter current and return the diverted energy to the input, while simultaneously supplying the remaining current to the LED unit, diverting energy in an amount corresponding to the current difference between the converter current of the main converter stage, which is greater than the set current, and the set current, thereby making the remaining current to the LED unit equal to the set current.

[0071] Those skilled in the art can understand and effect variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0072] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0073] It should be noted that when the term "adapted to" is used in the claims or specification, the term "adapted to" is intended to be equivalent to the term "configured to."

[0074] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An LED driver, Input and an output of the LED driver adapted to connect an LED unit; a main converter stage adapted to convert power at the input and output a converter current to the LED unit at an output of the main converter stage; a power commutation stage coupled to the output and coupled to the input of the main converter stage; a controller adapted to implement an energy diversion mode of operation upon receiving a signal to set a current to the LED unit to a set current, wherein during the energy diversion mode, the controller: operating a main converter stage to output the converter current at a current greater than the set current; and a controller adapted to operate the power commutation stage to simultaneously divert electrical energy in an amount corresponding to a current difference between the converter current of the main converter stage, which is greater than the set current, and the set current, return the diverted electrical energy to the input of the main converter stage, and provide the remaining current to the LED unit through the output of the LED driver, whereby the remaining current to the LED unit becomes equal to the set current.

2. an input of the power commutation stage coupled to the output of the LED driver, an output of the power commutation stage coupled to the input of the LED driver, the power commutation stage adapted to be electrically in parallel with the LED unit, and the controller: adapted to implement the energy diversion mode to provide the remaining current to the LED unit when the set current is less than a threshold dimming current; 2. The driving device of claim 1, wherein the main converter stage operates abnormally when the main converter stage is adapted to directly output the set current that is less than the threshold dimming current.

3. 3. The driving device of claim 2, wherein the controller is adapted to implement a normal dimming mode different from the energy diversion mode when the controller receives a signal to set the current to the LED unit to the set current that is greater than the threshold dimming current.

4. when the main converter stage is adapted to directly output the set current that is greater than the threshold dimming current, the main converter stage operates normally; The controller, during the normal dimming mode: operating the main converter stage to output the converter current directly to the LED unit at the set current; 4. The drive arrangement of claim 3, adapted to disable the power commutation stage to prevent the electrical energy from being diverted from the converter current.

5. 5. The drive arrangement of claim 2, wherein the threshold dimming current comprises a minimum design dimming current normally provided by a control loop and components of the main converter stage.

6. 6. A drive arrangement according to any one of claims 2 to 5, wherein the threshold dimming current is in the range of 1% to 5% of the nominal current of the main converter stage.

7. 7. The drive device of claim 1, wherein the power diversion stage further comprises a winding for supplying an auxiliary power signal to a non-light-emitting component from a portion of the diverted electrical energy, and the power diversion stage returns a remaining portion of the diverted electrical energy to the input.

8. 8. The driving device of claim 7, further comprising an auxiliary power supply circuit for providing alternative auxiliary power for use by the non-light emitting components.

9. The auxiliary power supply circuit said input, and 9. The drive arrangement of claim 8, connected to any one of the power supply components of the main converter stage.

10. 10. A drive arrangement as claimed in any preceding claim, wherein the main converter stage comprises a resonant converter.

11. 11. The drive arrangement of claim 1, wherein the power commutation stage comprises a flyback converter comprising: a primary flyback winding electrically connected in parallel with the output of the main converter stage and adapted for connection in parallel with the LED unit; and a secondary flyback winding magnetically coupled to the primary flyback winding and electrically connected to the input.

12. 12. The drive arrangement of claim 11, wherein the secondary flyback winding is connected to the main converter stage and the input through a buffer circuit.

13. 13. A drive arrangement according to claim 11 or 12, wherein the power commutation stage comprises a switch in series with the primary flyback winding, and wherein the controller is adapted to activate and deactivate the power commutation stage by controlling the switch.

14. A drive device according to any one of claims 1 to 13; and a lighting circuit comprising the LED unit.

15. A driving method for driving an LED unit, using a main converter stage to convert power at an input, thereby outputting a converter current to the LED unit at an output of the main converter stage; and performing an energy diversion mode of operation upon receiving a signal to set a current to the LED unit to a set current that is less than a threshold dimming current, wherein if the main converter stage is adapted to directly output the set current that is less than the threshold dimming current, the main converter stage will operate abnormally, and the energy diversion mode of operation is: operating a main converter stage to output a converter current at a current greater than the set current; a power commutation stage coupled to the output of the main converter stage, coupled in parallel with the LED unit, and coupled to the input of the main converter stage to divert electrical energy in an amount corresponding to a current difference between the converter current of the main converter stage and the set current, which is greater than the set current, and return the diverted electrical energy to the input of the main converter stage, and at the same time supply a remaining current to the LED unit, thereby making the remaining current to the LED unit equal to the set current.

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