Anti-flickering LED driving circuit and driving control method thereof

Abstract

An LED driving circuit is used to drive LED load and improve the stroboscopic effect caused by the ripple in the mains. The driving circuit includes at least a rectifier bridge group with a set of output ports for rectifying the mains, allowing the formation of two different current paths of load branches, including LED load and LED constant current control circuit, and at least a capacitive branch including an input capacitor. The load branch has a threshold value of its conduction voltage, and selects the power supply source in the rectified mains and the input capacitor. The LED driving circuit has simple structure and high reliability, can optimize the input current harmonic performance while preventing stroboscopic effect, and meets various standard requirements.

Description

Technical Field

[0001] This invention relates to electronic circuits, and more specifically to a flicker-free LED driving circuit and its driving control method. Background Technology

[0002] LED lighting is a green, energy-saving, and environmentally friendly lighting method, and it has now become the most mainstream lighting method. Since the LED diodes used in LED lighting require direct current (DC) to drive them, and the current flowing through the LED load is directly related to the brightness of the LED load, an LED driver circuit is needed between the AC mains power and the LED load to convert the AC power into DC power and ensure that the current flowing through the LED load remains constant, thereby guaranteeing constant brightness of the LED lighting.

[0003] However, during LED driver control, low-frequency ripple from the input AC mains power is often introduced into the DC output. This low-frequency ripple produces flickering perceptible to the human eye in LED lighting equipment, and therefore needs to be avoided as much as possible. For example... Figure 1 As shown, typically, an LED driver circuit receives rectified mains power, filters it, and then converts the DC current on the input capacitor C1 to drive the LED load. The magnitude of the low-frequency ripple output by the driver circuit largely depends on the filtering capability of the input capacitor C1. If the input capacitor value is small, a large voltage ripple will be generated in each half-cycle, and excessive low-frequency ripple will be reflected in the LED current, causing flickering. A larger input capacitor C1 value can reduce the impact of low-frequency ripple, thereby eliminating flickering. However, when the input capacitor C1 value is large, a very large current distortion will be generated at the input terminal in each half-wave of mains power, reducing the power factor and failing to meet the subharmonic requirements in various environmental certifications.

[0004] Figure 2 This illustrates a prior art design for a flicker-free LED driver circuit, such as... Figure 2 As shown, existing flicker-free LED driver circuits reduce input current distortion and improve subharmonic performance to meet standards by setting a constant current circuit on the input capacitor branch to control the charging current of the input capacitor. However, to meet the power supply needs of the input capacitor to the LED load during the half-wave trough, the high-voltage constant current circuit connected in series with the input capacitor requires a large current capability to provide sufficient input power, resulting in high cost. Furthermore, since the input capacitor is not directly connected to the input terminal, its input impedance is relatively high, and it lacks the ability to absorb the high voltage on the DC bus after rectification of the mains input. When voltage fluctuations cause voltage spikes and surges at the input terminal, the constant current circuit is easily damaged, resulting in poor reliability. Higher voltage-rated power devices are needed to improve system reliability.

[0005] Therefore, it is necessary to develop simpler and more reliable flicker-free LED driver circuits that also meet the input current harmonic requirements. Summary of the Invention

[0006] To address various problems existing in conventional LED driver circuits and flicker-reducing LED driver circuits in the prior art, a new LED driver circuit is proposed. This LED driver circuit receives and converts mains power to drive an LED load and reduces flicker caused by ripple in the mains power. The LED driver circuit includes: a rectifier bridge with one set of input ports and at least one set of output ports for receiving and rectifying the mains power, and outputting power at the output ports; a capacitive branch connected between the output ports of the rectifier bridge and including at least one input capacitor; and a load branch including an LED load and an LED constant current control circuit. During each half-cycle of the mains power, when the mains voltage rectified by the rectifier bridge is less than the forward voltage of the load branch, the input capacitor supplies power to the load branch. When the mains voltage rectified by the rectifier bridge is greater than or equal to the forward voltage of the load branch, the load branch directly draws power from the output ports of the rectifier bridge, and the input capacitor stops supplying power to the load branch.

[0007] In one embodiment, the capacitive branch and the load branch are connected to the same set of output ports of the rectifier bridge group, and the capacitive branch further includes an isolation device configured to allow a charging loop to be formed between the output port of the rectifier bridge group and the input capacitor, and to prevent the formation of a discharging loop.

[0008] In one embodiment, the isolation device may be a diode.

[0009] In one embodiment, the rectifier bridge group has two sets of output ports, the capacitive branch is connected to the first set of output ports of the rectifier bridge group, and the load branch is connected to the second set of output ports of the rectifier bridge group. The first set of output ports and the second set of output ports of the rectifier bridge group are independent of each other.

[0010] In one embodiment, the first group of output ports and the second group of output ports have a common output terminal. The rectifier bridge group includes six diodes. The first group of output ports uses the first, second, third, and fourth diodes to form a first rectifier bridge structure. The second group of output ports reuses the third and fourth diodes and forms a second rectifier bridge structure with the fifth and sixth diodes. The third and fourth diodes are connected to the common output terminal.

[0011] In one embodiment, within each half-cycle of the mains power, the moment when the mains voltage rectified by the rectifier bridge rises to a level greater than the load branch turn-on voltage is earlier than the moment when the input capacitor begins charging from the rectifier bridge through the output port.

[0012] In one embodiment, two different circuit paths are allowed in the load branch: a first current path is used when the input capacitor supplies power to the load branch, and a second current path is used when the output port of the rectifier bridge supplies power to the load branch.

[0013] In one embodiment, the load branch has three ports, the first current path is established through the first port and the second port, and the second current path is established through the first port and the third port.

[0014] In one embodiment, the LED constant current control circuit includes a first constant current source circuit and a second constant current source circuit, wherein the first constant current source circuit is used to control the current flowing from a set of output ports of the rectifier bridge group to the LED load, and the second constant current source circuit is used to control the current flowing from the input capacitor to the LED load.

[0015] In one embodiment, the negative terminals of a set of output ports of the rectifier bridge are simultaneously connected to the negative terminal of the input capacitor, the first constant current source circuit is located before the LED load on the path of current flowing from a set of output ports of the rectifier bridge to the LED load, and the second constant current source circuit is located before the LED load on the path of current flowing from the input capacitor to the LED load.

[0016] In one embodiment, the first constant current source circuit and the second constant current source circuit share the same current feedback signal.

[0017] In one embodiment, the first constant current source circuit has a first current reference value, the second constant current source circuit has a second current reference value, and the first current reference value is greater than the second current reference value.

[0018] In one embodiment, the positive terminals of a set of output ports of the rectifier bridge are simultaneously connected to the positive terminal of the input capacitor. The first constant current source circuit is located after the LED load in the path of current flowing from the set of output ports of the rectifier bridge to the LED load, and the second constant current source circuit is located after the LED load in the path of current flowing from the input capacitor to the LED load.

[0019] In one embodiment, the first constant current source circuit and the second constant current source circuit each use their own independent feedback signals, and the first constant current source circuit and the second constant current source circuit have different ground terminals.

[0020] In one embodiment, the current reference values ​​of the first constant current source circuit and the second constant current source circuit are the same.

[0021] In one embodiment, the driving circuit further includes a discharge branch connected between the mains input terminals or between a set of output ports of the rectifier bridge group, the discharge branch being used to generate a controllable discharge current at the mains input terminals.

[0022] In one embodiment, the discharge branch begins discharging at a time no later than the moment when the rectified mains voltage rises to the on-state voltage of the load branch.

[0023] In one embodiment, the discharge branch stops discharging at a time no earlier than the time when the rectified mains voltage drops to the on-state voltage of the load branch.

[0024] In one embodiment, the drive circuit is configured such that, within each half-wave of mains power, the position at which the input current of the drive circuit rises to 5% of the peak input current is no greater than 60 degrees.

[0025] In one embodiment, the drive circuit is configured such that, within each half-wave of the mains power, the position at which the input current of the drive circuit drops to 5% of the peak input current is not less than 90 degrees.

[0026] On the other hand, an LED driving circuit is proposed, which rectifies and transforms the mains power to drive an LED load and improves the flicker caused by ripple in the mains power. The LED circuit includes an input capacitor that can receive rectified mains power for charging, a rectifier bridge group for rectifying the mains power, and an LED load. In each half-wave of the mains power, the LED load switches the power supply source between the input capacitor and the rectified mains power with the on-state voltage of its branch as the threshold.

[0027] In one embodiment, when the rectified mains voltage is lower than the on-state voltage of the branch where the LED load is located, the LED load and the input capacitor form a first current loop. When the rectified mains voltage is greater than or equal to the on-state voltage of the branch where the LED load is located, the first current loop is disconnected, and a set of output ports of the rectifier bridge and the LED load together form a second current loop.

[0028] In one embodiment, during the first half-cycle of each mains half-wave, when the rectified mains voltage rises to the voltage across the input capacitor, a set of output ports of the rectifier bridge further forms a third current loop with the input capacitor to charge the input capacitor.

[0029] In one embodiment, during the first half-cycle of each mains half-wave, the formation time of the second current loop is earlier than the formation time of the third circuit loop.

[0030] In one embodiment, during the second half of each mains half-wave, when the rectified mains voltage is less than the voltage across the input capacitor, the third current loop is disconnected.

[0031] In one embodiment, the drive circuit includes an isolation device for controlling the formation and disconnection of the third current loop.

[0032] In one embodiment, the isolation device is a diode connected to the input capacitor.

[0033] In one embodiment, the rectifier bridge group has two independent sets of output ports, the first set of output ports is used to form the second current loop, and the second set of output ports is used to form the third current loop.

[0034] In one embodiment, the first set of output ports and the second set of output ports have a common terminal, which is used in both the second current loop and the third current loop.

[0035] In one embodiment, the loop currents of the first current loop and the second current loop are constant during conduction.

[0036] In one embodiment, the first current loop and the second current loop share a current feedback signal, which is used to control the current values ​​of the first current loop and the second current loop to remain constant during conduction.

[0037] In one embodiment, the negative terminals of a set of output ports of the rectifier bridge are simultaneously connected to the negative terminals of the input capacitor, serving as the ground terminals of the first current loop and the second current loop. The first current loop performs feedback constant current control based on a first reference current value, and the second current loop performs feedback constant current control based on a second reference current value.

[0038] In one embodiment, the second reference value is configured to be greater than the first reference value, so as to shut down the first current loop by making the current feedback signal continuously greater than the first reference value after the second current loop is turned on.

[0039] In one embodiment, the positive terminals of a set of output ports of the rectifier bridge are simultaneously connected to the positive terminals of the input capacitor, serving as the positive input terminals of the first current loop and the second current loop. The first current loop and the second current loop each have their own independent current feedback signal and ground terminal, which are used to control the current values ​​of the first current loop and the second current loop to remain constant during conduction after comparing them with a first reference current value and a second reference current value, respectively.

[0040] In one embodiment, the first reference current value is equal to the second reference current value.

[0041] In one embodiment, the drive circuit further includes a fourth current loop formed by a bleed branch between the mains input terminals or between a set of output ports of the rectifier bridge, the fourth current loop being used to controllably generate a bleed current in the presence of a silicon controlled rectifier dimmer in the circuit environment.

[0042] In one embodiment, within each mains half-wave, the formation time of the fourth current loop is no later than the formation time of the second current loop.

[0043] In one embodiment, within each mains half-wave, the disconnection time of the fourth current loop is no earlier than the disconnection time of the second current loop.

[0044] In one embodiment, the drive circuit is configured such that, within each half-wave of mains power, the position at which the input current of the drive circuit rises to 5% of the peak input current is no greater than 60 degrees.

[0045] In one embodiment, the drive circuit is configured such that within each half-wave of the mains power, the input current of the drive circuit drops to a position of not less than 90 degrees where it reaches 5% of the peak value of the input current.

[0046] In another aspect, a method for controlling an LED driver circuit to improve flicker problems is proposed. The method includes: rectifying the mains power and outputting it at a rectified output port; charging an input capacitor through one of the rectified output ports; and supplying power to an LED load through one of the rectified output ports or the input capacitor. The LED load switches its power source between the input capacitor and one of the rectified output ports, using the on-state voltage of its branch as a threshold.

[0047] In one embodiment, the LED load switches its power supply source between the input capacitor and the rectified output port using the on-state voltage of its branch as a threshold. This includes: when the rectified mains voltage is lower than the on-state voltage of the branch where the LED load is located, a first current loop is formed by the LED load and the input capacitor; and when the rectified mains voltage is greater than or equal to the on-state voltage of the branch where the LED load is located, the first current loop is disconnected, and a second current loop is formed by the rectified output port and the LED load.

[0048] In one embodiment, within each half-wave of the mains power, when the rectified mains voltage is greater than the voltage across the input capacitor, a third current loop is formed between one of the rectified output ports and the input capacitor to charge the input capacitor.

[0049] The LED driver circuit and control method proposed in this invention, by setting the on-state voltage of the branch containing the LED load as a threshold, switches the power supply between the rectifier bridge output and the mains power, successfully reducing the ripple caused by the mains power and simultaneously correcting the waveform of the input current. This not only prevents flicker but also optimizes the harmonic performance of the input current, meeting standard requirements. Furthermore, this driver circuit has the advantages of simple structure, low cost, and high reliability. Attached Figure Description

[0050] In all the following figures, the same reference numerals indicate that the same, similar or corresponding features or functions are present.

[0051] Figure 1 A schematic diagram of the structure of an LED driver circuit in the prior art is shown;

[0052] Figure 2 A schematic diagram of a flicker-free LED driving circuit in the prior art is shown;

[0053] Figure 3 A schematic diagram of an LED driving circuit 100 according to an embodiment of the present invention is shown;

[0054] Figure 4 It shows the use of Figure 3 The LED driving circuit 100 of the embodiment shown is the same Figure 1 The diagram shows a comparison of the waveforms of the LED driving circuit in the conventional solution of the prior art within the half-wave period of the mains power.

[0055] Figure 5 A schematic diagram of an LED driving circuit 500 according to an embodiment of the present invention is shown;

[0056] Figure 6A schematic diagram of the structure of an LED driving circuit 600 according to another embodiment of the present invention is shown;

[0057] Figure 7 A schematic diagram of the structure of an LED driving circuit 700 according to yet another embodiment of the present invention is shown;

[0058] Figure 8 A schematic diagram of the structure of an LED driving circuit 800 according to another embodiment of the present invention is shown;

[0059] Figure 9 A schematic diagram of the structure of a load branch 102 according to an embodiment of the present invention is shown;

[0060] Figure 10 A schematic diagram of the structure of a load branch 102 according to another embodiment of the present invention is shown;

[0061] Figure 11 A schematic diagram of the structure of an LED driving circuit 1100 according to another embodiment of the present invention is shown;

[0062] Figure 12 A flowchart of a method for controlling an LED driving circuit according to an embodiment of the present invention is shown; Detailed Implementation

[0063] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0064] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “in an embodiment,” “in an embodiment,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes only and are not necessarily drawn to scale. It should be understood that when an element is referred to as “connected to” or “coupled” to another element, it can be a direct connection or coupling to the other element or there may be intermediate elements. Conversely, when an element is referred to as “directly connected to” or “directly coupled to” another element, there are no intermediate elements. The same reference numerals indicate the same elements. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0065] It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, such elements should not be limited by these terms. These terms are used to distinguish one element from another. Therefore, the first element discussed below may be referred to as the second element without departing from the teachings of the concept of the invention. As used herein, the term "and / or" includes any and all combinations of any one or more of the associated listed items.

[0066] Figure 3 A schematic diagram of an LED driving circuit 100 according to an embodiment of the present invention is shown. Figure 3As shown, the LED driver circuit 100 is used in an AC power environment and includes a rectifier bridge group Z1, a capacitive branch 101 containing an input capacitor C1, and a load branch 102 containing an LED load LED1 and an LED constant current control circuit 103. The sinusoidal AC power, after passing through the rectifier bridge Z1, is rectified into a DC half-wave with a dome-shaped periodic waveform, which is then output at the output port of the rectifier bridge group Z1. The rectifier bridge group Z1 includes at least one set of output ports; that is, it can have only one set of output ports or more than one set (e.g., two sets). The LED driver circuit 100 further transforms the rectified AC power VBUS output from the rectifier bridge group Z1 to drive the LED load LED1. The capacitive branch 101 can be connected to a set of output ports of the rectifier bridge group Z1. During each half-wave cycle, the rectified AC mains power VBUS is fed into the capacitive branch 101 through this set of input ports, and the input capacitor C1 is charged by the rectified AC mains power. Furthermore, the load branch 102 can be connected to a set of output ports of the rectifier bridge group Z1. The rectified AC mains power VBUS is further fed into the load branch 102 through this set of output ports to drive the LED load. It should be noted that the rectifier bridge group Z1 can use the same set of output ports to connect to both the capacitive branch 101 and the load branch 102, or it can be connected through two different sets of output ports. For ease of understanding, it is assumed here and in this specification that when each set of output ports of the rectifier bridge group outputs the rectified AC mains power, the output difference between the output ports is ignored, and all have the same value, uniformly labeled as VBUS.

[0067] Within each half-wave of the mains power supply, the LED load LED1 switches its power source between the input capacitor C1 and the rectified mains power, using the conduction voltage of its branch 101 as a threshold. Specifically, within each half-cycle of the mains power supply, when the mains voltage rectified by the rectifier bridge group Z1 is less than the conduction voltage of the load branch 102, the input capacitor C1 supplies power to the load branch 102. When the mains voltage rectified by the rectifier bridge group Z1 is greater than or equal to the conduction voltage of the load branch 102, the load branch 102 directly draws power from the output port of the rectifier bridge group Z1, and the input capacitor C1 stops supplying power to the load branch 102. In this context and in this application, "the input capacitor C1 supplies power to the load branch 102" and "the input capacitor C1 serves as the power source for the LED load LED1" should be understood as the load branch 102 obtaining power from both ends of the input capacitor C1. The power supply energy comes from the electrical energy stored in the input capacitor C1 itself, excluding external electrical energy supplied to the load branch 102 via the two ends of the input capacitor C1.

[0068] Specifically, such as Figure 3As shown in the embodiment, when the rectified mains voltage VBUS is lower than the turn-on voltage of the LED load branch 102, the LED load LED and the input capacitor C1 form a first current loop L1. When the rectified mains voltage VBUS is greater than or equal to the turn-on voltage of the LED load branch 102, the first current loop is disconnected, and a set of output ports of the rectifier bridge group Z1 and the LED load LED1 together form a second current loop L3.

[0069] In one embodiment, during the first half-cycle of each mains half-wave, when the rectified mains voltage VBUS rises to the voltage across the input capacitor C1, a set of output ports of the rectifier bridge Z1 further forms a third current loop L3 with the input capacitor C1 to charge the input capacitor C1, thereby replenishing the energy consumed by the input capacitor C1 in supplying power to the LED load LED1. This configuration allows the LED driver circuit 100 to utilize the simple charging control method for the input capacitor C1 in the prior art, while preventing the third current loop from occurring simultaneously with the first current loop, thus avoiding a decrease in the charging effect of the input capacitor C1.

[0070] In one embodiment, during the second half of each mains half-wave, when the rectified mains voltage VBUS drops to the voltage across the input capacitor C1, the third current loop is disconnected, preventing the input capacitor C1 from passing through the third current loop, or allowing it to discharge to the LED load LED1 through the output port of the rectifier bridge Z1, thereby reducing energy loss on the input capacitor C1.

[0071] Figure 4 It shows the use of Figure 3 The LED driving circuit 100 of the embodiment shown is the same Figure 1 The diagram shows a waveform comparison of a conventional LED driver circuit within a half-wave cycle of the mains power supply, comparing changes in voltage across input capacitor C1 and changes in input current. This differs from, for example... Figure 1 In the conventional solution shown, the power supply source is determined by comparing the voltage across the input capacitor C1 with the rectified mains voltage. For example... Figure 4 As shown, to ensure that the LED load is continuously turned on without flickering, the voltage on the input capacitor C1 must not be less than the threshold voltage for the branch where the LED load is located to be turned on while the input capacitor C1 is supplying power to the LED load. Figure 1 In the existing technical solution shown, when the input voltage VBUS reaches its peak in half a mains power cycle, as VBUS stops charging the input capacitor C1, the input capacitor C1 begins to act as a power source for the LED load, and the voltage VC1 on the input capacitor C1 decreases until VBUS rises to a level greater than the voltage across the input capacitor C1 (threshold Vt1) in the next cycle. (Comparison) Figure 1The existing technical solution shown is Figure 3 In the illustrated embodiment, by using the on-state voltage of load branch 102 as the threshold for switching the power supply source (at threshold Vt2), in each half-wave of the mains power, the rectified voltage is supplied to load branch 102 by the mains power supply for at least the first delay time Td1 in the second half-cycle after the peak arrives. During this time, the voltage VC1 on the output capacitor C1 remains unchanged. In this way, the rectified mains power VBUS prolongs the time when the mains power is used as the power supply source, while shortening the time when the input capacitor C1 is powered in each half-cycle of the mains power, reducing the voltage ripple of the input capacitor C1 in each cycle. This helps to improve the flicker problem caused by the mains ripple when the input capacitor C1 is a small value, allowing the capacitance value of the input capacitor C1 to be set smaller to improve the power factor.

[0072] Furthermore, in some embodiments, by reasonably setting the capacitance value of the input capacitor C1 and the conduction voltage value of the LED load branch, the moment when the rectified mains voltage VBUS rises to a value greater than the conduction voltage of the load branch within each half-cycle of the mains power supply is earlier than the moment when the self-rectifying bridge group Z1 starts charging the input capacitor C1 through the output port. That is, the formation time of the second current loop is earlier than that of the third current loop. In this way, in the first half-cycle, after VBUS rises to the conduction threshold of the LED load branch, the second delay time Td2 is advanced to start supplying power to the LED load branch. At this time, the voltage VC1 on the input capacitor stops falling, without waiting for VBUS to continue rising to a position where charging of the input capacitor C1 can begin. This further shortens the time for the input capacitor C1 to supply power to the LED load within each half-cycle of the mains power supply, thereby further reducing mains ripple and improving flicker performance.

[0073] at the same time, Figure 3 The design of the illustrated embodiment helps to further improve input current harmonic performance to meet harmonic standards. Taking the ErP standard as an example, within each half-wave of the mains power supply, the input current must rise to 5% of the peak input current at an angle no greater than 60 degrees within each half-wave cycle (180 degrees). Furthermore, the peak input current must be located before a 65-degree angle, and the input current must decrease to 5% of the peak input current at an angle no less than 90 degrees. Figure 1 The existing technology shown presents difficulties in achieving this standard, primarily because the input current relies entirely on the charging current of the input capacitor C1, making it difficult to control. However, as... Figure 4As shown, when the second current loop forms earlier than the third current loop, a current step is generated on the input current Iin waveform, allowing the input current to supply power to the LED load branch 102 via the second current loop. This step helps to meet the requirement that the position where the input current rises to 5% of the peak input current is no greater than 60 degrees. Furthermore, the existence of the second current loop itself contributes to meeting harmonic standards. After the 90-degree position of the mains half-wave cycle, the voltage of the input capacitor C1 reaches its peak, causing the third current loop to disconnect and the charging current for the input capacitor C1 to disappear. However, the input current Iin can still continue to exist relying on the LED load power supply current in the second current loop, making it easier to meet the requirement that the position where the input current drops to 5% of the peak input current is no less than 90 degrees.

[0074] On the other hand, compared to Figure 2 The existing LED driver circuit solution shown is as follows: Figure 3 In the illustrated embodiment, the LED driver circuit 100 does not require a constant current source with high current load capacity to charge the input capacitor C1. Instead, the rectified mains power directly charges the input capacitor C1 within each half-wave cycle. Furthermore, the power supply time of the input capacitor C1 to the LED load branch within each half-wave cycle is relatively short compared to... Figure 2 The LED driver circuit shown is shorter, resulting in less energy loss. This eliminates the need for a dedicated constant current circuit for charging the input capacitor and for matching a large charging current to that circuit, simplifying the structure and reducing cost.

[0075] Figure 5 A schematic diagram of an LED driving circuit 500 according to an embodiment of the present invention is shown. Figure 5 In the illustrated embodiment, the rectifier bridge group Z1 has one set of output ports, so the capacitive branch 101 and the load branch 102 are connected to the same set of output ports of the rectifier bridge group Z1. The capacitive branch 101 also includes an isolation device D1 for controlling the formation and disconnection of the third current loop. The isolation device D1 is configured to allow the formation of a charging loop between the output port of the rectifier bridge group Z1 and the input capacitor C1, and to prevent the formation of a discharging loop. In one embodiment, the isolation device D1 can be a diode connected between the input capacitor C1 and the output port. In other embodiments, other common combinations of devices and control circuits with isolation functions in the prior art can be used as the isolation device D1 to achieve switching control of the third current loop. For example, a controlled switch can be used, controlled by detecting the voltage value across the isolation device; this invention does not limit this.

[0076] exist Figure 5In the illustrated embodiment, the load branch 102 has three terminals. The negative terminal of the output port of the rectifier bridge group Z1 and one terminal of the output capacitor C1 are connected to the third terminal of the load branch 102. The positive terminal of the output port of the rectifier bridge group Z1 is connected to the second terminal of the load branch 102. Specifically, the isolation device D1 is a diode, with its anode connected to the positive terminal of the output port of the rectifier bridge group Z1 and its cathode connected to the first terminal of the input capacitor C1. The second terminal of the input capacitor C1 is connected to the negative terminal of the output port of the rectifier bridge group. The first terminal of the input capacitor C1 is further connected to the first terminal of the load branch 102. In this way, the two ends of the input capacitor C1, together with the first and third terminals of the load branch 102, form a first current loop for supplying power to the LED load branch.

[0077] Figure 6 A schematic diagram of an LED driving circuit 600 according to another embodiment of the present invention is shown. Figure 5 The embodiments shown are the same, in Figure 6 In the illustrated embodiment, the isolation device D1 is also a diode. Compared to Figure 5 The embodiment shown, Figure 6 The main difference in the illustrated embodiment lies in the position of the common terminal of the input capacitor and the output port of the rectifier bridge group. The positive terminal of the output port of the rectifier bridge group Z1 and one end of the output capacitor C1 are connected to the first terminal of the load branch 102, and the negative terminal of the output port of the rectifier bridge group Z1 is connected to the third terminal of the load branch 102. Specifically, the anode of the isolation diode D1 is connected to the second terminal of the input capacitor C1, and the cathode is connected to the negative terminal of the output port of the rectifier bridge group Z1. The first terminal of the output capacitor C1 is connected to the positive terminal of the output port of the rectifier bridge group Z1 and the first terminal of the load branch 102. The second terminal of the input capacitor C1 is further connected to the second terminal of the load branch 102. In this way, the two ends of the input capacitor C1 and the load branch 102 can form a first current loop for supplying power to the LED load branch.

[0078] Compared to Figure 2 The prior art LED driver circuit shown is Figure 5 , Figure 6 The LED driver circuits 500 and 600 shown can improve the flicker problem caused by mains ripple, meet the input current harmonic standard, and improve the power factor, while maintaining the absorption capacity of the input capacitor C1 for abnormal fluctuations such as voltage spikes and glitches on the rectified mains power. This reduces the requirements for power components in the LED driver circuit and improves reliability.

[0079] Figure 7 A schematic diagram of the structure of an LED driving circuit 700 according to another embodiment of the present invention is shown, as follows: Figure 7As shown, the rectifier bridge group Z1 has two sets of output ports. The capacitive branch 101 is connected to the first set of output ports P1 of the rectifier bridge group Z1, and the load branch 102 is connected to the second set of output ports P2 of the rectifier bridge group Z1. The first set of output ports P1 and the second set of output ports P2 are independent of each other. The term "independent" here and in this application means that the first set of output ports P1 and the second set of output ports P2 each output independently through a rectifier bridge structure, and the output signals do not interfere with each other. Thus, the first set of output ports P1, together with the load branch 102, forms a second current loop, while the second set of output ports P2, together with the capacitive branch 101, forms a third current loop.

[0080] exist Figure 7 In the illustrated embodiment, since the capacitive branch 101 and the load branch 102 are no longer connected in parallel, the capacitive branch 101 may contain only the input capacitor C1. Because the first and second output ports of the rectifier bridge group Z1 are independent of each other, when the rectified mains power finishes charging the input capacitor C1, a discharge circuit cannot be formed between the input capacitor and the first output port of the rectifier bridge group Z1; therefore, no additional isolation components are required.

[0081] The first and second output ports of the rectifier bridge Z1 share a common output terminal, which is used in both the second and third current loops. In the illustrated embodiment, the negative terminals of the first and second output ports are set as the common output terminal. In other embodiments, the negative terminals of the first and second output ports may also be set as the common output terminal, as will be discussed below. Figure 8 The illustrated embodiment will be described in detail. The rectifier bridge group Z1 includes six diodes. The first set of output ports utilizes diodes DR1-DR4 to form a first rectifier bridge structure. The second set of output ports reuses diodes DR3 and DR4, together with diodes DR5 and DR6, to form a second rectifier bridge structure. Diodes DR3 and DR4 are connected to a common output terminal, i.e., the negative terminals of the first and second output ports. Specifically, the negative terminals of the first and second output ports are connected to the anodes of diodes DR3 and DR4.

[0082] Figure 8 A schematic diagram of an LED driving circuit 800 according to another embodiment of the present invention is shown, compared to Figure 7The illustrated embodiment differs in that the positive terminals of the first and second output ports are set as a common output terminal. The rectifier bridge group Z1 includes six diodes. The first set of output ports utilizes diodes DR1-DR4 to form a first rectifier bridge structure. The second set of output ports reuses diodes DR3 and DR4, together with diodes DR5 and DR6, to form a second rectifier bridge structure. Diodes DR3 and DR4 are connected to the common output terminal, i.e., the positive terminals of the first and second output ports. Specifically, the positive terminals of the first and second output ports are connected to the cathodes of diodes DR3 and DR4.

[0083] Similar to LED driver circuit 700, the design of LED driver circuit 800 allows capacitive branch 101 to include only capacitor C1, thus eliminating the need for isolation devices.

[0084] Figure 9 A schematic diagram of the structure of a load branch 102 according to an embodiment of the present invention is shown, as follows: Figure 9 As shown, load branch 102 allows for the establishment of two different current paths. When the input capacitor C1 supplies power to the load branch, a first current path is used, making the first current path part of a first current loop. When the output port of the rectifier bridge group supplies power to the load branch, a second current path is used, making the second current path part of a second current loop. Load branch 102 may have three ports, such that the first current path is established through the first and second ports, and the second current path is established through the first and third ports. In other embodiments, load branch 102 may also implement two different current paths using a conventional four-port configuration, which will not be detailed here. In load branch 102, the LED constant current control circuit 103 includes a first constant current source circuit IC1 and a second constant current source circuit IC2. The second constant current source circuit IC2 is used to control the current flowing from a set of output ports of the rectifier bridge group Z1 to the LED load LED1, i.e., the current in the second current loop. The first constant current source circuit IC1 is used to control the current flowing from the input capacitor C1 to the LED load LED1, i.e., the current in the first current loop. This ensures that the current in the first and second current loops remains constant during conduction, thereby guaranteeing that the current flowing through the LED load LED1 remains constant in each half-wave cycle.

[0085] In the illustrated embodiment, the load branch is designed for the case where the input capacitor C1 and a set of output ports of the rectifier bridge group Z1 share a common negative terminal (common ground), adaptable to, for example... Figure 5 and Figure 7The circuit structure of the rectifier bridge group Z1 and capacitive branch 101 shown in the embodiment. In this case, the negative terminal of one set of output ports of the rectifier bridge group Z1 is simultaneously connected to the negative terminal of the input capacitor C1, and then connected to the first port of the load branch 102, serving as the ground terminal for the first current loop and the second current loop. The second constant current source circuit IC2 is located before the LED load LED1 in the current path from one set of output ports of the rectifier bridge group Z1 to the LED load LED1, and the first constant current source circuit IC1 is located before the LED load LED1 in the current path from the input capacitor C1 to the LED load LED1. In the illustrated embodiment, the input terminal of the first constant current source IC1 serves as the second port of the load branch 102, and the input terminal of the second constant current source circuit IC2 serves as the third port of the load branch 102. This allows for separate control of the power supply to the LED load LED1 by the first current loop and the second current loop under common ground conditions.

[0086] In the illustrated embodiment, since the first current loop and the second current loop share a common ground, the first constant current source circuit IC1 and the second constant current source circuit IC2 can share the same current feedback signal VCS for feedback control. In the illustrated embodiment, the current feedback signal VCS is generated by a feedback resistor RCS. Regarding the reference, the first current loop performs feedback constant current control based on a first reference current value REF1, and the second current loop performs feedback constant current control based on a second reference current value REF2. The first constant current source circuit IC1 generates a first current control signal AMP1 by comparing the first reference current value REF1 with the current feedback signal VCS, controlling the on-state of the power switch Q1 to maintain a constant current value in the first loop. The second constant current source circuit IC2 generates a second current control signal AMP2 by comparing the second reference current value REF1 with the current feedback signal RCS, controlling the on-state of the power switch Q2 to maintain a constant current value in the second loop.

[0087] Preferably, the second reference value REF2 is configured to be greater than the first reference value REF1. This is used to ensure that, after the second current loop is turned on, the current feedback signal RCS remains consistently greater than the first reference value REF1. This allows AMP1 to continuously reduce the current in the first current loop through a negative feedback mechanism, ultimately turning off the first current loop. In this way, without configuring additional control circuitry, it is possible to switch the power supply between the rectified mains power and the input capacitor C1 in a very simple manner, using the conduction voltage of the load branch 102 as a threshold.

[0088] Figure 10 A schematic diagram of the load branch 102 according to another embodiment of the present invention is shown. Compared to Figure 9The embodiment shown has a load branch designed for the case where the input capacitor C1 and a set of output ports of the rectifier bridge Z1 share a common positive terminal (common high side), adaptable to, for example... Figure 6 and Figure 8 The circuit structure of the rectifier bridge group Z1 and capacitive branch 101 shown in the embodiment. In this case, the positive terminals of one set of output ports of the rectifier bridge group Z1 are simultaneously connected to the positive terminal of the input capacitor C1, and then connected to the first port of the load branch 102. This serves as the positive terminal (high-side terminal) of both the first and second current loops. The second constant current source circuit IC2 is located after the LED load LED1 in the current path from one set of output ports of the rectifier bridge group Z1 to the LED load LED1, and the first constant current source circuit IC1 is located after the LED load LED1 in the current path from the input capacitor C1 to the LED load LED1. In the illustrated embodiment, the ground terminal GND1 of the first constant current source IC1 serves as the second port of the load branch 102, and the ground terminal GND2 of the second constant current source IC2 serves as the third port of the load branch 102. This allows for separate control of the power supply to the LED load LED1 by the first and second current loops under common high-side conditions.

[0089] In the illustrated embodiment, since the first current loop and the second current loop share a common high-side terminal, the first constant current source circuit IC1 and the second constant current source circuit IC2 use their respective independent feedback signals VCS1 and VCS2 for feedback control. VCS1 and VCS2 are generated by feedback resistors RCS1 and RCS2, respectively. Furthermore, the first constant current source circuit IC1 and the second constant current source circuit IC2 have different ground terminals GND1 and GND2. Regarding the reference aspect, the same... Figure 9 The embodiments shown are the same, with the first current loop performing feedback constant current control based on a first reference current value REF1, and the second current loop performing feedback constant current control based on a second reference current value REF2.

[0090] Preferably, the first reference current value REF1 and the second reference current value REF2 are the same. Figure 9 In the illustrated embodiment, due to the difference in the two reference current values, a small low-frequency ripple will be generated in the LED current during the switching process of the power supply circuit (i.e., the power source) in each half-wave cycle. This is in response to... Figure 10 In the embodiment shown, the first reference current value REF1 and the second reference current value REF2 are the same, which eliminates this tiny low-frequency ripple and further optimizes the anti-flicker performance.

[0091] Figure 10 The illustrated embodiment further provides another control circuit for switching power sources, such as... Figure 10As shown, the feedback signal VCS2 of the second constant current source circuit is further used to control the switching of the power supply source. VCS2 is fed into a comparator CMP1 and compared with a current threshold REF3. The output of CMP1 is connected to the enable terminal EN of the first constant current source circuit IC1. During each half-wave cycle, when the feedback signal on VCS2 is greater than REF3, it is considered that the rectified mains voltage is greater than the conduction voltage of the load branch 102. At this time, the output of CMP1 causes the first constant current source circuit IC1 to turn off, cutting off the first current loop. When the feedback signal on VCS2 is less than REF3, it is considered that the rectified mains voltage has dropped to less than the conduction voltage of the load branch 102, and the second current loop is disconnected. At this time, the output of CMP1 re-enables the first constant current source circuit IC1, opening the first current loop.

[0092] Those skilled in the art will understand that the above-described control circuit for switching power sources is exemplary and not limiting. Any prior art circuit implementation that switches the power supply loop according to given conditions can be used in the above control circuit, and this invention will not elaborate further on this.

[0093] exist Figure 9 and Figure 10 In the illustrated embodiment, the first constant current source circuit IC1 and the second constant current source circuit IC2 can be linear constant current circuits. Those skilled in the art will understand that in other embodiments, switching constant current circuits, charge pumps, or other suitable circuits with constant current source functionality can also be used to achieve constant current control of the loop current; this invention does not limit such applications.

[0094] Figure 11 A schematic diagram of the structure of an LED driving circuit 1100 according to another embodiment of the present invention is shown, compared to Figure 3 The embodiment shown, Figure 11 A bleed branch 110 is further added, which can be connected between the mains input terminals or between a set of output ports of the rectifier bridge group Z1. The bleed branch 110 can form a fourth current loop between the mains input terminals or between a set of output ports of the rectifier bridge group. The fourth current loop is used to controllably generate bleed current when a silicon controlled rectifier dimmer is present in the circuit environment.

[0095] In one embodiment, preferably, the discharge branch 110 is configured to begin discharging at a time no later than the time when the rectified mains voltage rises to the load branch conduction voltage, so that within each mains half-wave, the formation time of the fourth current loop is no later than the formation time of the second current loop. This provides, on the one hand, a holding current and a sustaining current to the SCR dimmer when the edge of the SCR dimmer has arrived, maintaining the SCR dimmer's conduction during this period and preventing accidental shutdown due to insufficient input current; on the other hand, it further optimizes the harmonic performance of the input current, particularly benefiting the requirement that the position where the input current rises to 5% of the peak input current is no greater than 60 degrees.

[0096] In another embodiment, the discharge branch 110 is further configured to stop discharging at a time no earlier than the time when the rectified mains voltage drops to the load branch's on-state voltage in each half-wave cycle, so that the turn-off time of the fourth current loop is no earlier than the turn-off time of the second current loop within each mains half-wave. Besides preventing accidental turn-off and maintaining the SCR dimmer's conduction, this further optimizes the harmonic performance of the input current, particularly benefiting the requirement that the input current drops to at least 90 degrees when the position is not less than 5% of the peak input current. Here, "stop" should be understood as stopping discharging at any point in the remaining time period of the current cycle.

[0097] Figure 12 A flowchart of a method for controlling an LED driving circuit according to an embodiment of the present invention is shown, the method comprising:

[0098] Step 1201: After rectifying the mains power, output it at the rectified output port;

[0099] Step 1202: Charge an input capacitor C1 through one of the rectifier output ports;

[0100] Step 1203: Power LED1 to the LED load through one of the rectifier output ports or the input capacitor C1;

[0101] Among them, the LED load LED1 switches its power supply source between the input capacitor C1 and one of the rectifier output ports, using the conduction voltage of its branch as the threshold.

[0102] In one embodiment, the LED load LED1 switches its power supply between the input capacitor C1 and one of the rectified output ports using the on-state voltage of its branch as a threshold.

[0103] When the rectified mains voltage is lower than the forward voltage of the branch containing the LED load LED1, the first current loop is formed by the LED load LED1 and the input capacitor C1; and

[0104] When the rectified mains voltage is greater than or equal to the conduction voltage of the branch where the LED load LED1 is located, the first current loop is disconnected, and the second current loop is formed by the rectified output port and the LED load LED1.

[0105] In particular, the above control method also includes, within each half-wave of the mains power, when the rectified mains voltage is greater than the voltage across the input capacitor C1, a third current loop is formed between one of the rectified output ports and the input capacitor C1 to charge the input capacitor.

[0106] The above description of the control methods and steps according to embodiments of the present invention is merely exemplary and is not intended to limit the present invention. Furthermore, some well-known control steps and control parameters used are not given or described in detail to make the present invention clear, concise, and easy to understand. Those skilled in the art should understand that the step numbers used in the above description of the control methods and steps according to embodiments of the present invention are not intended to indicate the absolute order of the steps. These steps are not implemented in the order of their step numbers, but may be implemented in different orders, or may be implemented simultaneously and in parallel, and are not limited to the described embodiments.

[0107] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. An LED driving circuit, wherein the LED driving circuit rectifies and converts mains power to drive an LED load and improves flicker caused by ripple in the mains power, wherein, The LED circuit includes an input capacitor that can receive rectified mains power for charging, a rectifier bridge group that rectifies the mains power, and an LED load. In each half-wave of the mains power, the rectified mains power directly charges the input capacitor. The LED load switches its power source between the input capacitor and the rectified mains power with the on-state voltage of its branch as a threshold. The LED driving circuit includes The rectifier bridge group has a set of input ports and at least a set of output ports for receiving the mains power and rectifying the mains power, and outputting the power at the output ports; A capacitive branch, connected between a set of output ports of the rectifier bridge group, includes at least the input capacitor; The load branch includes the LED load and the LED constant current control circuit; The rectifier bridge has a set of output ports. The capacitive branch and the load branch are connected to the same set of output ports of the rectifier bridge. The capacitive branch also includes an isolation device. The common terminal of the isolation device and the input capacitor are connected to the load branch. The isolation device is configured to allow a charging circuit to form between the output port of the rectifier bridge and the input capacitor, and to prevent a discharging circuit from forming; or The rectifier bridge group has two sets of output ports. The capacitive branch is connected to the first set of output ports of the rectifier bridge group, and the load branch is connected to the second set of output ports of the rectifier bridge group. The first set of output ports and the second set of output ports of the rectifier bridge group are independent of each other. The load branch allows for two different circuit paths. When the input capacitor supplies power to the load branch, a first current path is used. When the output port of the rectifier bridge supplies power to the load branch, a second current path is used. The load branch has three ports. The first current path is established through the first port and the second port, and the second current path is established through the first port and the third port.

2. The LED driving circuit as described in claim 1, wherein, During each half-cycle of the mains power, when the mains voltage after rectification by the rectifier bridge group is less than the conduction voltage of the load branch, the input capacitor supplies power to the load branch. When the mains voltage after rectification by the rectifier bridge group is greater than or equal to the conduction voltage of the load branch, the load branch directly draws power from the output port of the rectifier bridge group, and the input capacitor stops supplying power to the load branch.

3. The LED driving circuit as described in claim 1, wherein, The rectifier bridge has a set of output ports, the capacitive branch and the load branch are connected to the same set of output ports of the rectifier bridge, and the isolation device is a diode.

4. The LED driving circuit as described in claim 1, wherein, The rectifier bridge group has two sets of output ports. The first set of output ports and the second set of output ports have a common output terminal. The rectifier bridge group includes six diodes. The first set of output ports uses the first, second, third, and fourth diodes to form a first rectifier bridge structure. The second set of output ports reuses the third and fourth diodes and forms a second rectifier bridge structure with the fifth and sixth diodes. The third and fourth diodes are connected to the common output terminal.

5. The LED driving circuit as described in claim 1, wherein, Within each half-cycle of the mains power, the moment when the mains voltage rectified by the rectifier bridge rises to a level greater than the on-state voltage of the load branch is earlier than the moment when the input capacitor begins to charge from the output port of the rectifier bridge.

6. The LED driving circuit as described in claim 1, wherein, The LED constant current control circuit includes a first constant current source circuit and a second constant current source circuit. The first constant current source circuit is used to control the current flowing from a set of output ports of the rectifier bridge group to the LED load, and the second constant current source circuit is used to control the current flowing from the input capacitor to the LED load.

7. The LED driving circuit as described in claim 6, wherein, The negative terminals of a set of output ports of the rectifier bridge are simultaneously connected to the negative terminal of the input capacitor. The first constant current source circuit is located before the LED load in the path of current flowing from a set of output ports of the rectifier bridge to the LED load, and the second constant current source circuit is located before the LED load in the path of current flowing from the input capacitor to the LED load.

8. The LED driving circuit as described in claim 7, wherein, The first constant current source circuit and the second constant current source circuit share the same current feedback signal.

9. The LED driving circuit as described in claim 7, wherein, The first constant current source circuit has a first current reference value, the second constant current source circuit has a second current reference value, and the first current reference value is greater than the second current reference value.

10. The LED driving circuit as described in claim 6, wherein, The positive terminals of a set of output ports of the rectifier bridge are simultaneously connected to the positive terminal of the input capacitor. The first constant current source circuit is located after the LED load on the path of current flowing from a set of output ports of the rectifier bridge to the LED load, and the second constant current source circuit is located after the LED load on the path of current flowing from the input capacitor to the LED load.

11. The LED driving circuit as described in claim 10, wherein, The first constant current source circuit and the second constant current source circuit each use their own independent feedback signals, and the first constant current source circuit and the second constant current source circuit have different ground terminals.

12. The LED driving circuit as described in claim 10, wherein, The first constant current source circuit and the second constant current source circuit have the same current reference value.

13. The LED driving circuit as described in claim 1, wherein, The driving circuit further includes a discharge branch connected between the mains input terminals or between a set of output ports of the rectifier bridge group. The discharge branch is used to generate a controllable discharge current at the mains input terminals.

14. The LED driving circuit as described in claim 13, wherein, The discharge branch begins discharging at a time no later than the moment when the rectified mains voltage rises to the on-state voltage of the load branch.

15. The LED driving circuit as described in claim 13, wherein, The discharge branch stops discharging at a time no earlier than the moment when the rectified mains voltage drops to the on-state voltage of the load branch in each half-wave cycle.

16. The LED driving circuit according to any one of claims 1-15, wherein, The drive circuit is configured such that, within each half-wave of the mains power, the position at which the input current of the drive circuit rises to 5% of the peak input current is no greater than 60 degrees.

17. The LED driving circuit according to any one of claims 1-15, wherein, The drive circuit is configured such that, within each half-wave of the mains power, the position at which the input current of the drive circuit drops to 5% of the peak input current is not less than 90 degrees.

18. The LED driving circuit as described in claim 1, wherein, When the rectified mains voltage is lower than the on-state voltage of the branch where the LED load is located, the LED load and the input capacitor form a first current loop. When the rectified mains voltage is greater than or equal to the on-state voltage of the branch where the LED load is located, the first current loop is disconnected, and a set of output ports of the rectifier bridge and the LED load together form a second current loop.

19. The LED driving circuit as described in claim 18, wherein, During the first half-cycle of each mains half-wave, when the rectified mains voltage rises to the voltage across the input capacitor, a set of output ports of the rectifier bridge further forms a third current loop with the input capacitor to charge the input capacitor. During the second half-cycle of each mains half-wave, when the rectified mains voltage is less than the voltage across the input capacitor, the third current loop is disconnected.

20. A method for controlling an LED driving circuit as described in any one of claims 1-19 to improve flicker problems, the method comprising: The mains power is rectified and then output at the rectified output port; An input capacitor is charged through one of the rectified output ports; The LED load is powered through one of the rectified output ports or the input capacitor; The LED load uses the on-state voltage of its branch as a threshold to switch power sources between the input capacitor and the rectified output port, and the rectified mains power directly charges the input capacitor.

21. The method for controlling an LED driving circuit as described in claim 20, wherein, The LED load switches its power supply source between the input capacitor and the rectified output port using the on-state voltage of its branch as a threshold. When the rectified mains voltage is lower than the on-state voltage of the branch containing the LED load, a first current loop is formed by the LED load and the input capacitor; and When the rectified mains voltage is greater than or equal to the on-state voltage of the branch where the LED load is located, the first current loop is disconnected, and the second current loop is formed by the rectified output port and the LED load.

22. The method for controlling an LED driving circuit as described in claim 21, wherein, Within each half-wave of the mains power, when the rectified mains voltage is greater than the voltage across the input capacitor, a third current loop is formed between one of the rectified output ports and the input capacitor to charge the input capacitor.

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