A circuit and method for reducing the frequency of multi-segment linearly driven LEDs

Abstract

The application discloses a circuit and method for reducing stroboscopic of multi-section linear driving LED, and the technical scheme is as follows: the circuit comprises an energy storage element and multi-section light emitting units; each section of the light emitting units comprises at least one or more LED lamp beads connected in series; the multi-section controlled conduction elements are arranged correspondingly with the multi-section light emitting units, and are sequentially turned on and turned off along with the change of the DC bus voltage in the power frequency cycle, so that each section of the light emitting units is sequentially turned on and turned off according to the predetermined time sequence along with the change of the DC bus voltage; the plurality of unidirectional conduction elements are electrically connected with the multi-section controlled conduction elements, and form a plurality of directional conduction paths; the energy storage element is charged in the rising stage of the DC bus voltage; and the energy storage element discharges to the section of the light emitting units through the unidirectional conduction element when the DC bus voltage decreases. According to the application, only an energy storage capacitor and a small amount of diodes need to be added to the existing circuit, so that at least one section of the light emitting units can be kept current conduction in the whole power frequency cycle, and the stroboscopic is reduced.

Description

Technical Field

[0001] This invention relates to the field of LED lighting driving technology, and in particular to a circuit and method for reducing flicker in multi-segment linear driven LEDs. Background Technology

[0002] Existing low-power LED lighting solutions typically employ inductorless, multi-segment linear drive to meet harmonic distortion, power factor, and constant power requirements, such as... Figure 1 As shown, a commonly used three-segment linear LED driver circuit includes three LED strings, three linear switches, and a current-limiting resistor. The three LED strings are connected in series between the DC bus voltage and ground. The three linear switches correspond to each LED string segment and are set with different on-current conditions, such as... Figure 2 As shown, three linear switches sequentially turn on and off according to the DC bus voltage changes within the power frequency cycle. This allows the bus current to follow the bus voltage changes, resulting in a high power factor. Within each half-power frequency cycle, each string of LEDs lights up and turns off once, causing significant periodic fluctuations in light output at the power frequency, with measured SVM values ​​typically greater than 3.0. While connecting capacitors in parallel to each string of LEDs can reduce flicker by continuing to power the LEDs when the input voltage drops, this requires individual capacitors, resistors, and isolation diodes for each string of LEDs, leading to a large number of capacitors, high cost, and the large capacitors connected in parallel with the LEDs making it difficult to pass high-level input surge tests. Connecting independent flicker-eliminating switch circuits in series with the LEDs to eliminate power frequency current ripple can also reduce flicker, but it requires additional independent filter circuits and constant current devices outside the existing circuit, resulting in a complex circuit structure, low integration, and increased cost, hindering large-scale application in cost-sensitive LED lighting products. While using a multiplier to detect input power can reduce flicker, the control logic is complex and the cost is also high.

[0003] In summary, existing solutions for reducing flicker in multi-segment linear drive LEDs all suffer from problems such as high cost, complex circuitry, or poor surge tolerance, making them difficult to apply on a large scale in cost-sensitive LED lighting products. Summary of the Invention

[0004] To address the problems of severe flicker in existing multi-segment linearly driven LEDs and the high cost and complex circuitry of existing flicker reduction solutions, the first objective of this invention is to provide a circuit for reducing flicker in multi-segment linearly driven LEDs. Its feature is that it only adds an energy storage element and a few unidirectional conducting elements to the existing multi-segment linearly driven circuit, without changing the basic architecture of the existing circuit, so that at least one light-emitting unit can maintain current conduction throughout the entire power frequency cycle, thereby reducing flicker.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a circuit for reducing the flicker of multi-segment linearly driven LEDs, the input of which is a DC bus voltage, comprising: multiple light-emitting units, including at least a first light-emitting unit and a second light-emitting unit connected in series; each light-emitting unit includes at least one or more LED beads connected in series; multiple controlled conducting elements, corresponding to the multiple light-emitting units, which are sequentially turned on and off as the DC bus voltage changes within the power frequency cycle, so that each light-emitting unit is sequentially turned on and off according to a predetermined timing sequence as the DC bus voltage changes; multiple unidirectional conducting elements, electrically connected to the multiple controlled conducting elements, forming multiple directional conducting paths; and an energy storage element, electrically connected to the multiple light-emitting units, and connected to at least one light-emitting unit through the multiple unidirectional conducting elements. A directional charging and discharging path is formed. During the DC bus voltage rise phase, when the controlled conducting element corresponding to the highest voltage segment is turned on, the DC bus voltage charges the energy storage element through at least one light-emitting unit. The voltage across the energy storage element is limited to not exceeding the difference between the DC bus voltage and the total forward voltage drop of the turned-on light-emitting unit. During the DC bus voltage fall phase, each controlled conducting element is turned off sequentially in the reverse order of the rise phase. The controlled conducting elements that are still in the conducting state continue to drive the corresponding light-emitting unit to emit light, and the voltage of the energy storage element is maintained. When the DC bus voltage drops below the operating voltage of at least one light-emitting unit, the energy storage element discharges to that light-emitting unit through a unidirectional conducting element, so that the at least one light-emitting unit maintains a current conducting state throughout the entire power frequency cycle.

[0006] Specifically, the multi-segment light-emitting unit includes a first light-emitting unit and a second light-emitting unit connected in series; the multi-segment controlled conducting element includes a first switch, a second switch, and a third switch, wherein the first and second switches respectively drive the light-emitting units at different voltage segments to conduct, and the third switch is connected in series with an energy storage element at the output terminal of the second light-emitting unit, establishing an energy storage charging path when the highest voltage segment is conducted; the energy storage element is an energy storage capacitor; during the DC bus voltage rise phase, when the DC bus voltage rises above the forward conduction voltage of the first light-emitting unit, the first switch turns on first, and the first light-emitting unit lights up; as the DC bus voltage continues to rise, the first switch turns off and the second switch turns on, and the first and second light-emitting units light up simultaneously; when the DC bus voltage continues to rise to the highest segment, the first and second switches turn off and the third switch turns on. When the first and second light-emitting units are lit, the DC bus voltage charges the energy storage capacitor through them. The charging voltage of the energy storage capacitor does not exceed the DC bus voltage minus the total forward voltage drop of the first and second light-emitting units. During the DC bus voltage drop phase, the third switch is turned off first, and the second switch is turned on. The first and second light-emitting units continue to light up, and the energy storage capacitor voltage remains unchanged. The second switch is then turned off, and the first switch is turned on. Only the first light-emitting unit lights up, and the energy storage capacitor voltage remains unchanged. When the DC bus voltage drops below the operating voltage of the first light-emitting unit, the energy storage capacitor discharges directionally to the first light-emitting unit through a unidirectional conducting element, maintaining the current conduction of the first light-emitting unit until the DC bus voltage exceeds the operating voltage of the first light-emitting unit again in the next rising phase, at which point the energy storage capacitor discharges.

[0007] Specifically, during the discharge phase, the energy storage element discharges directionally to both the first and second light-emitting units simultaneously through a unidirectional conducting element, so that both the first and second light-emitting units maintain current conduction during the period when the DC bus voltage is lower than their respective operating voltages.

[0008] Specifically, the multi-segment controlled conduction element also includes a controlled conduction element for establishing an energy storage charging path. When the controlled conduction element for establishing the energy storage charging path is turned on at the highest voltage segment of the DC bus voltage, the DC bus voltage charges the energy storage element through all the preceding light-emitting units.

[0009] Specifically, the energy storage capacitor forms a discharge path to the first light-emitting unit through at least one of the parasitic parallel diodes of the third switch or one of the diodes connected in parallel outside the third switch.

[0010] Specifically, a ground-limiting resistor is provided on the source side of the first switching transistor and / or the second switching transistor. During the discharge of the energy storage capacitor through the parasitic parallel diode of the third switching transistor, the current-limiting resistor enables the discharge circuit to form a complete circuit through the ground wire, thereby enabling the corresponding constant current control circuit to limit the discharge current.

[0011] Specifically, the controlled conduction element is a MOSFET or a transistor; the energy storage element is an electrolytic capacitor or a ceramic capacitor.

[0012] Another objective of this invention is to provide a method for reducing flicker in multi-segment linearly driven LEDs. The method is characterized by the ability to reduce flicker by simply adding an energy storage element and a few unidirectional conduction elements to the existing multi-segment linearly driven circuit without changing the basic architecture of the existing circuit. This allows at least one segment of the light-emitting unit to maintain current conduction throughout the entire power frequency cycle.

[0013] To achieve the above objectives, the technical solution adopted by the present invention includes the following steps: S1: During the rising phase of the DC bus voltage, as the bus voltage increases, each controlled conducting element is turned on sequentially from the low voltage section to the high voltage section, driving the corresponding light-emitting unit to light up step by step. S2: When the controlled conducting element corresponding to the highest voltage segment is turned on, the bus voltage charges the energy storage element through the already turned-on multi-segment light-emitting unit. The charging voltage of the energy storage element is limited to not exceeding the difference between the bus voltage and the total forward voltage drop of the already turned-on light-emitting unit. S3: During the DC bus voltage drop phase, each controlled conducting element is turned off sequentially from the high voltage section to the low voltage section. During each turn-off phase, the controlled conducting elements that are still in the conducting state continue to drive the corresponding light-emitting unit to emit light, and the energy storage element voltage is maintained. S4: When the bus voltage drops below the operating voltage threshold of at least one section of the light-emitting unit, the energy storage element discharges directionally to the at least one section of the light-emitting unit through a unidirectional conducting element to maintain its current conduction. S5: When the bus voltage rises again to a level higher than the operating voltage threshold of the light-emitting unit, the discharge terminates and the normal power supply to the light-emitting unit is restored by the bus voltage.

[0014] Specifically, in step S4, the energy storage element simultaneously discharges directionally to m segments of the n light-emitting units, where 1≤m≤n and n≥2.

[0015] Specifically, in step S4, the energy storage element forms a discharge path through the parasitic parallel diode of the controlled conduction element. When the corresponding controlled conduction element is in the off state, it completes the discharge to the target light-emitting unit by utilizing the unidirectional conduction characteristic of its inherent parasitic parallel diode, or forms a discharge path through an external parallel diode.

[0016] Specifically, by adjusting the number of LED elements connected in series in each light-emitting unit and the capacitance of the energy storage element, the charging voltage amplitude in step S2 and the discharge duration in step S4 are changed, thereby controlling the balance between the stroboscopic visibility (SVM) and the power factor (PF).

[0017] Another objective of this invention is to provide an LED driving circuit, characterized in that it can maintain current conduction in at least one segment of the light-emitting unit throughout the entire power frequency cycle by simply adding an energy storage element and a small number of unidirectional conducting elements to the existing multi-segment linear driving circuit without changing the basic architecture of the existing circuit, thereby reducing flicker.

[0018] To achieve the above objectives, the technical solution adopted by the present invention is as follows: it includes a rectifier circuit and the above-mentioned circuit for reducing the flicker of multi-segment linear driven LEDs; the output terminal of the rectifier circuit is connected to the DC bus voltage input terminal of the circuit for reducing the flicker of multi-segment linear driven LEDs, so as to provide it with DC bus voltage.

[0019] Another objective of this invention is to provide an LED driver chip, characterized in that it can maintain current conduction in at least one segment of the light-emitting unit throughout the entire power frequency cycle by simply adding an energy storage element and a small number of unidirectional conduction elements to the existing multi-segment linear drive circuit without changing the basic architecture of the existing circuit, thereby reducing flicker.

[0020] To achieve the above objectives, the technical solution adopted by the present invention is: an LED driver chip that integrates some or all of the unidirectional conduction elements of the circuit for reducing the flicker of multi-segment linear driven LEDs, and integrates the drive control logic of the controlled conduction elements in the same package.

[0021] Another objective of this invention is to provide an LED lighting device characterized by the ability to maintain current conduction in at least one segment of the light-emitting unit throughout the entire power frequency cycle by simply adding an energy storage element and a small number of unidirectional conduction elements to the existing multi-segment linear drive circuit without changing the basic architecture of the existing circuit, thereby reducing flicker.

[0022] To achieve the above objectives, the technical solution adopted by the present invention is: an LED lighting device including the above-mentioned circuit for reducing the flicker of multi-segment linear drive LEDs.

[0023] The circuit and method for reducing flicker in multi-segment linear driven LEDs provided by this invention have the following advantages compared to existing technologies: First, the cost is extremely low, requiring only the addition of one energy storage capacitor and a few diodes, while existing technologies require multiple sets of capacitors or independent filter control circuits; Second, it does not change the basic architecture of existing multi-segment linear drive circuits, and existing production lines only need to add a few components to complete the upgrade, without redesigning the PCB or replacing the driver IC; Third, it utilizes the natural switching timing of multi-segment drive to achieve charging and discharging control of the energy storage element, without the need for additional control logic circuits; Fourth, the SVM can be reduced from greater than 3.0 to below 1.0, meeting the latest flicker standard requirements of major markets such as China and India; Fifth, the balance between SVM and power factor (PF) can be flexibly adjusted by adjusting the number of LEDs in each segment and the capacitance value of the energy storage element; Sixth, some or all unidirectional conduction elements can be integrated into the driver chip, further reducing system cost and PCB area. Attached Figure Description

[0024] Figure 1 Here is a schematic diagram of an existing multi-segment linear drive LED circuit; Figure 2 shows the bus voltage and current waveforms of the existing three-segment linearly driven LED; Figure 3 This is a circuit schematic diagram of Embodiment 1 of the present invention; Figure 4 This is another circuit schematic diagram of Embodiment 1 of the present invention; Figure 5 In Embodiment 1 of the present invention Figure 4 Waveform diagram corresponding to the embodiment; Figure 6 This is another circuit schematic diagram of Embodiment 1 of the present invention; Figure 7 In Embodiment 1 of the present invention Figure 3 , 6 Waveform diagram corresponding to the embodiment; Figure 8 This is a diagram of the n-segment generalized circuit architecture of Embodiment 1 of the present invention; Figure 9 This is a flowchart of a method for reducing flicker in multi-segment linearly driven LEDs according to Embodiment 3 of the present invention.

[0025] Reference numerals: LED1, first light-emitting unit; LED2, second light-emitting unit; Q1, first switching transistor; Q2, second switching transistor; Q3, third switching transistor; C1, energy storage capacitor; D1, first diode; D2, second diode; D3, third diode; D4, fourth diode; D5, fifth diode; D6, sixth diode; D7, seventh diode; VBUS, DC bus voltage; R1, first resistor; R2, second resistor; R3, third resistor; R4, fourth resistor; AMP1, first operational amplifier; AMP2, second operational amplifier; AMP3, third operational amplifier; Vref, reference voltage. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] Example 1: A circuit for reducing flicker in multi-segment linearly driven LEDs, such as... Figure 3 As shown, the input of the circuit is the DC bus voltage VBUS. The circuit includes: a first light-emitting unit LED1, a second light-emitting unit LED2, a first switch Q1, a second switch Q2, a third switch Q3, an energy storage capacitor C1, and multiple diodes, including a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4.

[0029] The first light-emitting unit LED1 and the second light-emitting unit LED2 are connected in series between the DC bus voltage VBUS and each switching transistor. Each light-emitting unit consists of one or more LEDs connected in series. Specifically, the anode of the first light-emitting unit LED1 is connected to the positive terminal of the DC bus voltage VBUS, and the cathode of the first light-emitting unit LED1 is directly connected to the anode of the second light-emitting unit LED2. This series connection node is the output node of the first light-emitting unit LED1, and the cathode of the second light-emitting unit LED2 constitutes the output node of the second light-emitting unit LED2 in this embodiment.

[0030] A first diode D1 is connected in series between the output terminal of the second light-emitting unit LED2 and the positive terminal of the energy storage capacitor C1. Its anode is connected to the cathode of the second light-emitting unit LED2, and its cathode is connected to the positive terminal of the energy storage capacitor C1. During normal charging, the first diode D1 allows current to flow from the second light-emitting unit LED2 through itself to the positive terminal of the energy storage capacitor C1. At the same time, during the non-charging phase of the energy storage capacitor C1, it prevents the charge stored in the energy storage capacitor C1 from flowing back into the second light-emitting unit LED2 through this path.

[0031] The drain of the first switching transistor Q1 is connected to the output terminal of the first light-emitting unit LED1 (i.e., the series node between the cathode of the first light-emitting unit LED1 and the anode of the second light-emitting unit LED2), and the source is connected to node A. The drain of the second switching transistor Q2 is connected to the output terminal of the second light-emitting unit LED2, and the source is connected to node B. Node A and node B are connected by a third resistor R3, which limits current. The first switching transistor Q1 and the second switching transistor Q2 respectively drive the light-emitting units under different voltage ranges to conduct.

[0032] The positive terminal of the energy storage capacitor C1 is connected to the negative terminal of the first diode D1. The third diode D3 is connected in series between the energy storage capacitor C1 and the drain of the third switching transistor Q3, with its anode connected to the negative terminal of the energy storage capacitor C1 and its cathode connected to the drain of the third switching transistor Q3. The source of the third switching transistor Q3 is connected to node C, which is then grounded via the first resistor R1. Node B and node C are connected via the second resistor R2, which limits current; the first resistor R1 also limits current. Thus, the third resistor R3, the second resistor R2, and the first resistor R1 are connected in series between node A and ground, forming a stepped grounding sampling network: the branch of the first switching transistor Q1 is grounded via node A, the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1; the branch of the second switching transistor Q2 is grounded via node B, the second resistor R2, node C, and the first resistor R1; and the branch of the third switching transistor Q3 is grounded via node C and the first resistor R1. That is, the first diode D1, the energy storage capacitor C1, the third diode D3, the third switch Q3, the node C and the first resistor R1 are connected in sequence between the output terminal of the second light-emitting unit LED2 and ground, and are used to establish an energy storage charging path when the highest voltage segment is turned on.

[0033] The second diode D2 is connected between the positive terminal of the energy storage capacitor C1 and the positive terminal of the DC bus voltage VBUS. Its anode is connected to the positive terminal of the energy storage capacitor C1, and its cathode is connected to the positive terminal of the DC bus voltage VBUS, forming a directional discharge path from the energy storage capacitor C1 to the first light-emitting unit LED1. The conduction direction of the second diode D2 is the same as the discharge direction of the energy storage capacitor C1, that is, the discharge current flows from the positive terminal of the energy storage capacitor C1 through the second diode D2 to the anode of the first light-emitting unit LED1. At the same time, it plays an isolation role during the charging and non-discharging phases of the energy storage capacitor C1, preventing the DC bus voltage VBUS from leaking into the energy storage capacitor C1 in the reverse direction through the second diode D2.

[0034] The fourth diode D4 is connected between the negative terminal of the energy storage capacitor C1 and ground, with its anode grounded and its cathode connected to the negative terminal of the energy storage capacitor C1, forming the return path during the discharge phase of the energy storage capacitor C1. When the energy storage capacitor C1 discharges directionally to the first light-emitting unit LED1, the discharge current flows from the source of the first switching transistor Q1 to ground, and then flows back to the negative terminal of the energy storage capacitor C1 through the forward conduction of the fourth diode D4, forming a complete discharge circuit. At the same time, during the charging phase of the energy storage capacitor C1, the fourth diode D4 is in the reverse cutoff state and does not affect the charging process.

[0035] That is, in the above circuit structure, the multiple light-emitting units are the first light-emitting unit LED1 and the second light-emitting unit LED2 connected in series, and each light-emitting unit includes at least one or more LED beads connected in series; the multiple controlled conducting elements are the first switching transistor Q1, the second switching transistor Q2, and the third switching transistor Q3, which are arranged corresponding to the multiple light-emitting units and are turned on and off sequentially according to the change of the DC bus voltage VBUS within the power frequency cycle, so that each light-emitting unit is turned on and off sequentially according to the change of the DC bus voltage VBUS in a predetermined time sequence; the multiple unidirectional conducting elements are the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4, which are electrically connected to the multiple controlled conducting elements. The circuit forms multiple directional conduction paths. The first diode D1 and the third diode D3 are respectively located on the bus between the output terminal of the second light-emitting unit LED2 and the positive terminal of the energy storage capacitor C1, and between the negative terminal of the energy storage capacitor C1 and the drain of the third switch Q3. These are used for inter-segment isolation and reverse blocking of the energy storage charging path. The second diode D2 forms a directional discharge path from the energy storage capacitor C1 to the first light-emitting unit LED1. The fourth diode D4 forms a return path during the discharge stage of the energy storage capacitor C1. The energy storage element is the energy storage capacitor C1, which is electrically connected to multiple light-emitting units and forms a directional charging and discharging path with the first light-emitting unit LED1 through the second diode D2 and the fourth diode D4.

[0036] Specifically, such as Figure 3As shown, the circuit is divided into an upper power path section and a lower drive control section by the dashed line. The upper power path section includes a first light-emitting unit LED1, a second light-emitting unit LED2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an energy storage capacitor C1; the lower drive control section includes a first switch Q1, a second switch Q2, a third switch Q3, and their respective operational amplifiers, resistors, and a reference voltage source.

[0037] Specifically, the first switch Q1, the second switch Q2, and the third switch Q3 are all MOSFETs, and the gates of each switch are driven and controlled by corresponding operational amplifiers. The output of the first operational amplifier AMP1 is connected to the gate of the first switch Q1, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the first switch Q1 (i.e., node A). The output of the second operational amplifier AMP2 is connected to the gate of the second switch Q2, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the second switch Q2 (i.e., node B). The output of the third operational amplifier AMP3 is connected to the gate of the third switch Q3, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the third switch Q3 (i.e., node C). The positive terminal of the energy storage capacitor C1 is connected to the cathode of the first diode D1 and the anode of the second diode D2, and the negative terminal of the energy storage capacitor C1 is grounded through the fourth diode D4.

[0038] It is readily understood by those skilled in the art that the aforementioned operational amplifiers, reference voltage Vref, and resistors together constitute a closed-loop linear constant current regulation circuit for the branch containing the corresponding switching transistor. Taking the branch containing the first switching transistor Q1 as an example, when the first switching transistor Q1 is turned on (at this time, the second switching transistor Q2 and the third switching transistor Q3 are both turned off), the current flowing through the first switching transistor Q1 flows out from node A, sequentially through the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1 to ground. A sampling voltage is generated on the series combination of the third resistor R3, the second resistor R2, and the first resistor R1. This sampling voltage is fed back to the inverting input terminal of the first operational amplifier AMP1 (connected to node A) and compared with the reference voltage Vref at the non-inverting input terminal. The first operational amplifier AMP1 adjusts its output voltage according to the comparison result, thereby adjusting the gate voltage of the first switching transistor Q1, so that the potential of node A is clamped to the reference voltage Vref, thereby stabilizing the current flowing through the branch containing the first switching transistor Q1 at around I=Vref / (R3+R2+R1). Taking the branch containing the second switch Q2 as an example, when the second switch Q2 is turned on (at this time, the first switch Q1 and the third switch Q3 are both turned off), the current flowing through the second switch Q2 flows out from node B, passes through the second resistor R2, node C, and the first resistor R1 in sequence to ground. A sampling voltage is generated on the series combination of the second resistor R2 and the first resistor R1. This sampling voltage is fed back to the inverting input terminal of the second operational amplifier AMP2 (connected to node B), and compared with the reference voltage Vref at the non-inverting input terminal, so that the potential of node B is clamped to the reference voltage Vref, thereby stabilizing the current flowing through the branch containing the second switch Q2 at around I=Vref / (R2+R1). The constant current regulation principle of the branch containing the third switch Q3 is the same. When the third switch Q3 is turned on (at this time, the first switch Q1 and the second switch Q2 are both turned off), the current flowing through the third switch Q3 flows out from node C, through the first resistor R1 to ground, and generates a sampling voltage on the first resistor R1. This sampling voltage is fed back to the inverting input terminal of the third operational amplifier AMP3 (connected to node C), and compared with the reference voltage Vref at the non-inverting input terminal, so that the potential of node C is clamped to the reference voltage Vref, thereby stabilizing the current flowing through the branch containing the third switch Q3 at around I=Vref / R1. As can be seen, the above-mentioned stepped grounding sampling network results in the low-voltage branch (Q1 branch) having the largest equivalent sampling resistance (R3+R2+R1) and the smallest corresponding current, while the high-voltage branch (Q3 branch) has the smallest equivalent sampling resistance (R1 only) and the largest corresponding current. This naturally forms a current distribution that matches the "low current in the low segment and high current in the high segment" requirement of multi-segment linear drive, which is beneficial to improving the sinusoidal nature of the input current waveform and increasing the power factor PF.Furthermore, by independently adjusting the resistance values ​​of the third resistor R3, the second resistor R2, and the first resistor R1, the driving current amplitude of the corresponding branch under each voltage segment can be set to match the optimal operating current required for the charging process of the light-emitting unit and the energy storage capacitor C1 under different voltage segments.

[0039] The working process of the low-frequency lightning circuit provided in this embodiment is as follows: When the DC bus voltage VBUS rises above the forward conduction voltage of the first light-emitting unit LED1, the first switch Q1 turns on. Current flows from the DC bus voltage VBUS through the first light-emitting unit LED1, the first switch Q1, node A, the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1 to ground, illuminating the first light-emitting unit LED1. At this time, the second switch Q2 and the third switch Q3 are both in the off state, the second light-emitting unit LED2 does not conduct, and the voltage of the energy storage capacitor C1 remains unchanged.

[0040] When the DC bus voltage VBUS continues to rise and exceeds the total forward voltage drop of the first LED1 and the second LED2, the first switch Q1 turns off and the second switch Q2 turns on. Current flows from the DC bus voltage VBUS sequentially through the first LED1, the second LED2, the second switch Q2, node B, the second resistor R2, node C, and the first resistor R1 to ground, simultaneously illuminating the first LED1 and the second LED2. At this time, the third switch Q3 remains off, and the voltage of the energy storage capacitor C1 remains unchanged.

[0041] When the DC bus voltage VBUS continues to rise above the total forward voltage drop of the first light-emitting unit LED1, the second light-emitting unit LED2, and the energy storage capacitor C1, the first switch Q1 and the second switch Q2 turn off, and the third switch Q3 turns on. Current flows from the DC bus voltage VBUS sequentially through the first light-emitting unit LED1, the second light-emitting unit LED2, and the first diode D1 to the positive terminal of the energy storage capacitor C1, then through the energy storage capacitor C1, the third diode D3, the third switch Q3, node C, and the first resistor R1 to ground. The first light-emitting unit LED1 and the second light-emitting unit LED2 light up, and simultaneously, the DC bus voltage VBUS charges the energy storage capacitor C1 through the first light-emitting unit LED1 and the second light-emitting unit LED2. The voltage across the energy storage capacitor C1 is limited to not exceeding the difference between the DC bus voltage VBUS and the total forward voltage drop of the turned-on light-emitting units.

[0042] It will be readily understood by those skilled in the art that the aforementioned limiting relationship of the charging voltage originates from Kirchhoff's voltage law: in the charging circuit, the DC bus voltage VBUS is equal to the sum of the forward voltage drop of the first light-emitting unit LED1, the forward voltage drop of the second light-emitting unit LED2, the on-state voltage drop of the third switch Q3, and the voltage across the energy storage capacitor C1. Since the on-state voltage drop of the third switch Q3 is relatively small and negligible, the charging voltage of the energy storage capacitor C1 is naturally clamped near the difference between the bus voltage and the total forward voltage drop of the two light-emitting units, achieving self-limitation of the charging voltage without the need for additional voltage regulation circuitry. Furthermore, when the voltage across the energy storage capacitor C1 approaches this difference, the charging current automatically tends to zero, and the charging process naturally terminates, preventing overcharging of the energy storage capacitor C1.

[0043] During the decreasing phase of the DC bus voltage VBUS, each controlled conducting element is turned off sequentially in the reverse order of the increasing phase. Specifically, when the DC bus voltage VBUS begins to decrease, and falls below the total voltage drop of the first light-emitting unit LED1, the second light-emitting unit LED2, and the energy storage capacitor C1, the third switch Q3 turns off first, and the second switch Q2 turns on. Current flows from the DC bus voltage VBUS sequentially through the first light-emitting unit LED1, the second light-emitting unit LED2, the second switch Q2, node B, the second resistor R2, node C, and the first resistor R1 to ground, and the first light-emitting unit LED1 and the second light-emitting unit LED2 continue to light up. Due to the isolation effect of the first diode D1, the third diode D3, and the second diode D2, the bus voltage is still higher than the potential of node M (i.e., the positive terminal node of energy storage capacitor C1), and the second diode D2 is reverse-biased and cut off; the path from node N (i.e., the negative terminal node of energy storage capacitor C1) to ground is also isolated due to the reverse-biased cutoff of the fourth diode D4, and the voltage of energy storage capacitor C1 remains unchanged and does not discharge.

[0044] When the DC bus voltage VBUS continues to drop, becoming insufficient to simultaneously drive the first LED1 and the second LED2, the second switch Q2 turns off, and the first switch Q1 turns on. Current flows from the DC bus voltage VBUS through the first LED1, the first switch Q1, node A, the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1 to ground, illuminating only the first LED1. The voltage of the energy storage capacitor C1 remains unchanged.

[0045] When the DC bus voltage VBUS continues to drop below the operating voltage of the first light-emitting unit LED1, the DC bus voltage VBUS is insufficient to directly drive the first light-emitting unit LED1. At this time, the energy storage capacitor C1 discharges directionally to the first light-emitting unit LED1 through the second diode D2 and the fourth diode D4. The specific discharge circuit is as follows: the discharge current flows out from the positive terminal of the energy storage capacitor C1, through the second diode D2 to the anode terminal of the first light-emitting unit LED1, i.e., the positive terminal of the DC bus voltage VBUS, then through the first light-emitting unit LED1 to the cathode terminal, through the first switch Q1, node A, the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1 to ground, and then returns to the negative terminal of the energy storage capacitor C1 through the fourth diode D4, forming a complete discharge circuit. The discharge current maintains the current conduction of the first light-emitting unit LED1, allowing the first light-emitting unit LED1 to continue emitting light. The discharge process continues until the DC bus voltage VBUS rises again to a level higher than the operating voltage of the first light-emitting unit LED1 in the next rising phase. At this point, the discharge terminates and the bus voltage restores normal power supply to the first light-emitting unit LED1.

[0046] Therefore, throughout the entire power frequency cycle, the first light-emitting unit LED1 remains in a current-conducting state, and its light output does not have a period of complete interruption, thereby reducing the visibility of flicker effect (SVM).

[0047] It is readily understood by those skilled in the art that the SVM (Spotlight Visibility Variation) is closely related to the modulation depth of the light output waveform within the power frequency cycle. In existing multi-segment linearly driven LED circuits, when the DC bus voltage VBUS drops below the operating voltage of the lowest-segment light-emitting unit, all light-emitting units are turned off, and the light output drops to zero during this period, with the modulation depth approaching 100%, which is the fundamental reason for the high SVM value. In this embodiment, the energy storage capacitor C1 discharges directionally to the first light-emitting unit LED1 during the low-voltage period, so that the minimum value of the light output is no longer zero, but is maintained at a certain level, thereby significantly reducing the modulation depth of the light output waveform and thus reducing the SVM. Even if the current amplitude during the discharge phase is lower than that during the normal conduction phase, as long as the light output is not completely interrupted, the SVM can be significantly improved.

[0048] Those skilled in the art will readily understand that the discharge current of the aforementioned energy storage capacitor C1 will gradually decrease during the discharge process, and the brightness of the first light-emitting unit LED1 will also gradually decrease during the discharge phase. However, since the human eye's perception of brightness is logarithmic, as long as the current of the first light-emitting unit LED1 does not drop to zero during the discharge period, the flicker effect perceived by the human eye can be significantly reduced.

[0049] Figure 7 This embodiment (i.e.) is shown Figure 3 The simulation waveform diagram of the corresponding embodiment includes the input current Iin waveform of the DC bus voltage VBUS, the voltage waveform of the energy storage capacitor C1, the current waveform of the first light-emitting unit LED1, the current waveform of the second light-emitting unit LED2, and the current waveforms of the first switch Q1, the second switch Q2, and the third switch Q3 (which shares a branch with the first diode D1 and the third diode D3, so they are labeled as Q3 / D1 / D3 current). In addition, it also includes the current waveforms of the second diode D2 and the fourth diode D4 (labeled as D2 / D4 current). As can be seen from the simulation waveform, during the rising phase of the DC bus voltage VBUS, Q1 first turns on to light up LED1, followed by Q2, which then turns on to light up both LED1 and LED2. Finally, Q3 turns on and charges C1 through the preceding LED1 and LED2, causing the voltage of C1 to gradually rise to its peak value. During the falling phase of the bus voltage, Q3 and Q2 turn off in sequence, and LED2 turns off. Only Q1 continues to conduct, keeping LED1 lit. When the bus voltage is lower than the operating voltage of LED1, D2 and D4 turn on, and C1 discharges to LED1 through D2 and returns through D4, maintaining the current of LED1 until the bus voltage rises again in the next power frequency cycle. Throughout the entire power frequency cycle, the current waveform of LED1 remains continuous and uninterrupted.

[0050] It should be noted that the first switch Q1, the second switch Q2, and the third switch Q3 in the above embodiments can be implemented using MOSFETs or transistors. This application is not limited in this regard, as long as each switch can be turned on and off sequentially with changes in the DC bus voltage. The energy storage capacitor C1 can be an electrolytic capacitor or a ceramic capacitor.

[0051] Furthermore, in the circuit structure of Embodiment 1 above, by adjusting the number of LED elements (i.e., LED beads) connected in series in each light-emitting unit and the capacitance value of the energy storage capacitor C1, the visibility of the flicker effect (SVM) and the power factor (PF) can be flexibly adjusted. The principle is as follows: The forward voltage drop of each light-emitting unit is equal to the sum of the forward voltage drops of all the LEDs connected in series within that unit. When the number of LEDs connected in series in a certain light-emitting unit is changed, the forward voltage drop of that unit changes accordingly, which in turn affects the on-start and off times of that unit within the power frequency cycle, i.e., the on-time window of that unit changes.

[0052] Specifically, reducing the number of LEDs connected in series in a certain light-emitting unit will decrease its forward voltage drop, causing that unit to turn on earlier and turn off later. This widens the time window for direct drive by the bus voltage, shortening the discharge time required for the energy storage capacitor C1, which helps reduce SVM. However, the reduced forward voltage drop in this segment will cause the input current waveform to deviate from a sine wave, leading to a decrease in the power factor (PF). Conversely, increasing the number of LEDs connected in series will increase the forward voltage drop and narrow the conduction time window, which helps increase PF. However, the discharge time required for the energy storage capacitor C1 will be longer, potentially increasing SVM. Furthermore, the sum of the number of LEDs connected in series in each light-emitting unit segment determines the charging voltage of the energy storage capacitor C1 in the highest voltage segment (equal to the peak bus voltage minus the total forward voltage drop across all segments), thus affecting the stored energy and discharge duration of the energy storage capacitor C1. The capacitance value of the energy storage capacitor C1 directly determines its stored energy at a given charging voltage: increasing the capacitance value can extend the discharge duration and reduce SVM, but the peak current during the charging phase will cause a decrease in PF; decreasing the capacitance value has the opposite effect. Therefore, in practical design, a balance between SVM and PF can be achieved by comprehensively adjusting the number of LEDs connected in series in each light-emitting unit and the capacitance value of the energy storage capacitor C1. For example, when a strict flicker requirement of SVM≤1.0 needs to be met, the number of LEDs connected in series can be appropriately reduced and the capacitance value of the energy storage capacitor C1 can be increased; in scenarios where a high PF needs to be considered, the number of LEDs connected in series can be increased and a smaller capacitance value of the energy storage capacitor C1 can be selected.

[0053] In one specific embodiment Figure 4 This illustrates another specific circuit structure for the frequency reduction lightning circuit of this application. In this embodiment, the energy storage capacitor C1 discharges simultaneously to the first light-emitting unit LED1 and the second light-emitting unit LED2 through a diode during the discharge phase. Figure 3 Compared to the illustrated embodiment, this embodiment adds a sixth diode D6 to the series bus between the first light-emitting unit LED1 and the second light-emitting unit LED2 to achieve inter-segment reverse blocking, and adds a fifth diode D5 between the positive terminal of the energy storage capacitor C1 and the anode terminal of the second light-emitting unit LED2 to form an independent directional discharge path from the energy storage capacitor C1 to the second light-emitting unit LED2; simultaneously, Figure 3 The unidirectional conducting element located between the negative terminal of the energy storage capacitor C1 and the drain of the third switching transistor Q3 is still retained in this embodiment and is represented by the third diode D3. The circuit of this embodiment includes six diodes: the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, and the sixth diode D6.

[0054] Specifically, the sixth diode D6 is connected in series on the bus between the output terminal of the first light-emitting unit LED1 and the input terminal of the second light-emitting unit LED2. Its anode is connected to the cathode of the first light-emitting unit LED1, and its cathode is connected to the anode of the second light-emitting unit LED2. During normal operation, it allows current to flow from the first light-emitting unit LED1 to the second light-emitting unit LED2, while preventing the discharge current from flowing back into the node where the first light-emitting unit LED1 is located when the energy storage capacitor C1 discharges to the second light-emitting unit LED2. The first diode D1 is connected in series between the output terminal of the second light-emitting unit LED2 and the positive terminal of the energy storage capacitor C1. Its anode is connected to the cathode of the second light-emitting unit LED2, and its cathode is connected to the positive terminal of the energy storage capacitor C1, forming a reverse blocking element for the energy storage charging path.

[0055] The second diode D2 is connected between the positive terminal of the energy storage capacitor C1 and the anode of the first light-emitting unit LED1. Its anode is connected to the positive terminal of the energy storage capacitor C1, and its cathode is connected to the anode of the first light-emitting unit LED1, forming a directional discharge path from the energy storage capacitor C1 to the first light-emitting unit LED1. The fifth diode D5 is connected between the positive terminal of the energy storage capacitor C1 and the anode of the second light-emitting unit LED2. Its anode is connected to the positive terminal of the energy storage capacitor C1, and its cathode is connected to the anode of the second light-emitting unit LED2, forming a directional discharge path from the energy storage capacitor C1 to the second light-emitting unit LED2. The third diode D3 is connected in series between the negative terminal of the energy storage capacitor C1 and the drain of the third switching transistor Q3. Its anode is connected to the negative terminal of the energy storage capacitor C1, and its cathode is connected to the drain of the third switching transistor Q3, establishing an energy storage charging path in the highest voltage range. The fourth diode D4 is connected between the negative terminal of the energy storage capacitor C1 and ground. Its anode is grounded, and its cathode is connected to the negative terminal of the energy storage capacitor C1, forming a return path during the discharge phase of the energy storage capacitor C1.

[0056] like Figure 4 As shown, the connection method of each operational amplifier, resistor and reference voltage in this embodiment is the same as... Figure 3 The embodiment shown is the same: the source of the first switch Q1 is connected to node A, the source of the second switch Q2 is connected to node B, and the source of the third switch Q3 is connected to node C; node A and node B are connected through the third resistor R3, node B and node C are connected through the second resistor R2, and node C is grounded through the first resistor R1. Thus, the third resistor R3, the second resistor R2, and the first resistor R1 are connected in series to form a stepped grounding sampling network. Each operational amplifier and resistor forms a closed-loop linear constant current regulation circuit. The specific constant current control method is the same as... Figure 3 The embodiments shown are the same and will not be repeated here. Figure 3The difference is that the positive terminal of the energy storage capacitor C1 is connected to the negative terminal of the first diode D1, the positive terminal of the second diode D2, and the positive terminal of the fifth diode D5; a sixth diode D6 is set on the series bus between LED1 and LED2.

[0057] When the DC bus voltage VBUS drops below the operating voltage of the first light-emitting unit LED1 and the second light-emitting unit LED2, the energy storage capacitor C1 discharges directionally to the first light-emitting unit LED1 through the second diode D2 and the fourth diode D4: the discharge current flows from the positive terminal of the energy storage capacitor C1 through the second diode D2 into the anode terminal of the first light-emitting unit LED1, then through the first light-emitting unit LED1, the first switch Q1, node A, the third resistor R3, node B, the second resistor R2, node C, and the first resistor R1 to ground, and then returns to the negative terminal of the energy storage capacitor C1 through the fourth diode D4. A complete discharge circuit is formed. Simultaneously, the energy storage capacitor C1 discharges directionally to the second light-emitting unit LED2 through the fifth diode D5 and the fourth diode D4: the discharge current flows from the positive terminal of the energy storage capacitor C1 through the fifth diode D5 into the anode terminal of the second light-emitting unit LED2, then through the second light-emitting unit LED2, the second switch Q2, node B, the second resistor R2, node C, and the first resistor R1 to ground, and then flows back to the negative terminal of the energy storage capacitor C1 through the fourth diode D4, forming another complete discharge circuit. This ensures that both circuits maintain current conduction when the DC bus voltage is lower than their respective operating voltages. During this process, due to the presence of the sixth diode D6, the two discharge circuits are effectively isolated at the series node between the first light-emitting unit LED1 and the second light-emitting unit LED2, preventing crosstalk between the discharge currents.

[0058] Those skilled in the art should pay particular attention to the fact that the inter-segment reverse blocking function of the aforementioned sixth diode D6 is a key design feature of this embodiment for achieving the "simultaneous directional discharge to the first light-emitting unit LED1 and the second light-emitting unit LED2". Specifically, during the discharge phase, the second diode D2 leads the positive terminal potential of the energy storage capacitor C1 to the anode of the first light-emitting unit LED1, i.e., the positive terminal of the DC bus voltage VBUS, and the fifth diode D5 leads the positive terminal potential of the energy storage capacitor C1 to the anode of the second light-emitting unit LED2, i.e., the cathode of the sixth diode D6. Since both the fifth diode D5 and the second diode D2 are drawn from the same positive terminal of the energy storage capacitor C1, and the cathode potential of the fifth diode D5 is lower than that of the second diode D2, a reverse bias voltage is formed between the anode and cathode of the sixth diode D6, and the sixth diode D6 is reliably cut off, thereby effectively isolating the discharge circuit containing LED1 from the discharge circuit containing LED2 at the LED1 / LED2 series node.

[0059] Assuming the sixth diode D6 is not installed, during the discharge phase, the discharge current injected into the energy storage capacitor C1 through the second diode D2 and the discharge current injected through the fifth diode D5 will couple at the LED1 / LED2 series node. On the one hand, the discharge current flowing into the anode of LED1 through the second diode D2 will not only flow through LED1 to Q1 and then to ground, but may also be shunted to the LED2 and Q2 branches through the LED1 series node. On the other hand, the discharge current flowing into the anode of LED2 through the fifth diode D5 may also flow in reverse into the LED1 series node, causing the two discharge circuits to crosstalk each other and the discharge current distribution to be chaotic, thus making it impossible to independently control the discharge current amplitude of each light-emitting unit. After setting the sixth diode D6, the aforementioned crosstalk is completely blocked: During normal operation, D6 is forward-biased, and current can flow from LED1 to LED2; during the discharge phase, D6 is reverse-biased and cut off, and the discharge circuit of LED1 and the discharge circuit of LED2 remain electrically independent. The discharge current of the two circuits is independently determined by the terminal voltage of the energy storage capacitor C1, the equivalent impedance of each branch, and the volt-ampere characteristics of the corresponding light-emitting unit, thereby enabling the technical solution of "simultaneous directional discharge to LED1 and LED2" to be reliably realized.

[0060] Figure 5 This embodiment (i.e.) is shown Figure 4 The simulation waveform diagram of the corresponding embodiment includes the bus voltage waveform corresponding to the AC peak value, the total forward voltage drop threshold line of each light-emitting unit (including the line corresponding to the total voltage drop of LED1+LED2, the line corresponding to the voltage drop of LED1, etc.), the current of the first switch Q1, the current of the second switch Q2, the current of the third switch Q3 (labeled as Q3 / D1 / D3 current since it shares a branch with D1 / D3), the input current Iin, the current of the first light-emitting unit LED1, the current of the second light-emitting unit LED2, the voltage waveform of the energy storage capacitor C1, the current waveform of the second diode D2, the current waveform of the fifth diode D5, and the current waveform of the sixth diode D6. Figure 5 As can be seen from the simulation waveform, the energy storage capacitor C1 is charged by the bus voltage through the preceding light-emitting unit during the highest voltage segment. After the voltage of C1 reaches its peak, Q3 and Q2 are turned off sequentially during the bus voltage drop phase. When the bus voltage drops below the operating voltage of LED1 and LED2, D2 and D5 are turned on simultaneously, and C1 discharges directionally to LED1 and LED2 respectively. The fourth diode D4 carries the total return current of the two discharge circuits, so that the current waveforms of LED1 and LED2 remain continuous throughout the entire power frequency cycle. D6 carries the forward conduction current from LED1 to LED2 during the normal conduction phase and plays an inter-segment reverse blocking role during the discharge phase.

[0061] It should be noted that in this embodiment, the discharge load of the energy storage capacitor C1 is increased, and the discharge time is correspondingly shortened, but the number of light-emitting units that are kept on increases. In practical applications, the energy storage capacitor C1 can be selected to discharge to one or more strings of light-emitting units according to the balance requirements of SVM and power factor PF.

[0062] It is readily understood by those skilled in the art that when the energy storage capacitor C1 discharges simultaneously to the first light-emitting unit LED1 and the second light-emitting unit LED2—that is, when discharging to the first light-emitting unit LED1 through the second diode D2 and to the second light-emitting unit LED2 through the fifth diode D5—the return current of both discharge circuits returns to the negative terminal of the energy storage capacitor C1 via the fourth diode D4. Both light-emitting units simultaneously consume the charge stored in the energy storage capacitor C1, accelerating the discharge rate and causing the voltage of the energy storage capacitor C1 to drop more rapidly, thus shortening the complete discharge time. In practical designs, if simultaneous discharge to both light-emitting units is chosen, the capacitance of the energy storage capacitor C1 can be increased accordingly to compensate for the shortened discharge time. Alternatively, based on the different weights of each light-emitting unit's contribution to flicker, discharge can be selectively directed only to the segment or several segments that contribute the most to flicker, thereby reducing SVM while minimizing the impact on the power factor PF.

[0063] In one specific embodiment, see details. Figure 6 This illustrates yet another specific circuit structure for the frequency reduction lightning circuit of this application. (Compared to...) Figure 3 Unlike the embodiment shown in the previous one, which used an externally discrete fourth diode D4 to form the discharge return path of the energy storage capacitor C1, in this embodiment, the energy storage capacitor C1 forms a discharge path to the first light-emitting unit LED1 through the second diode D2 and the parasitic parallel body diode of the third switch Q3. The inherent parasitic body diode of the third switch Q3 is used instead of... Figure 3 The fourth diode D4 used for discharge return current is removed. Figure 3 The third diode D3 is located between the negative terminal of the energy storage capacitor C1 and the drain of the third switching transistor Q3, so that the negative terminal of the energy storage capacitor C1 is directly connected to the drain of the third switching transistor Q3, thereby simplifying the circuit structure.

[0064] Specifically, in this embodiment, the third switch Q3 is a MOSFET, and it has a parasitic parallel body diode, namely the seventh diode D7. The anode of this parasitic parallel body diode is located on the source side of the third switch Q3, and the cathode is located on the drain side of the third switch Q3. The circuit structure of this embodiment is similar to... Figure 3The main difference in the illustrated embodiment is that: the first light-emitting unit LED1 and the second light-emitting unit LED2 are still directly connected in series between the DC bus voltage VBUS and each switching transistor; the first diode D1 is connected in series between the output terminal of the second light-emitting unit LED2 and the positive terminal of the energy storage capacitor C1, with its anode connected to the cathode of the second light-emitting unit LED2 and its cathode connected to the positive terminal of the energy storage capacitor C1; the negative terminal of the energy storage capacitor C1 is directly connected to the drain of the third switching transistor Q3; the source of the third switching transistor Q3 is connected to node C, and node C is grounded through the first resistor R1 (the first resistor R1 acts as a current limiter and serves as the grounding sampling resistor for the charging branch where the third switching transistor Q3 is located); that is, the energy storage capacitor C1, the third switching transistor Q3, node C, and the first resistor R1 are connected in series between the cathode of the first diode D1 and ground. The second diode D2 is connected between the positive terminal of the energy storage capacitor C1 and the positive terminal of the DC bus voltage VBUS. Its anode is connected to the positive terminal of the energy storage capacitor C1, and its cathode is connected to the positive terminal of the DC bus voltage VBUS, thus forming a directional discharge path from the energy storage capacitor C1 to the first light-emitting unit LED1 between the positive terminals of the energy storage capacitor C1 and the DC bus voltage VBUS. The drain of the first switch Q1 is connected to the series node of the first light-emitting unit LED1 and the second light-emitting unit LED2 (i.e., the output terminal of the first light-emitting unit LED1), and its source is connected to node A; the drain of the second switch Q2 is connected to the output terminal of the second light-emitting unit LED2, and its source is connected to node B; node A and node B are connected through the third resistor R3 (the third resistor R3 limits current), and node B is grounded through the fourth resistor R4 (the fourth resistor R4 limits current). Therefore, the third resistor R3 and the fourth resistor R4 are connected in series between node A and ground, forming a stepped grounding sampling network for the branch containing the first switch Q1 and the branch containing the second switch Q2: the branch containing the first switch Q1 is grounded through node A, the third resistor R3, node B, and the fourth resistor R4; the branch containing the second switch Q2 is grounded through node B and the fourth resistor R4. The charging branch containing the third switch Q3 is independently grounded through node C and the first resistor R1, connecting to the grounding sampling branches of the branches containing the first and second switches Q1.

[0065] During the peak of the rising phase of the DC bus voltage VBUS, the third switch Q3 is turned on. The charging current flows from the positive terminal of the DC bus voltage VBUS through the first light-emitting unit LED1, the second light-emitting unit LED2, and the first diode D1 to the positive terminal of the energy storage capacitor C1. Then, it flows through the energy storage capacitor C1, the drain of the third switch Q3, the channel of the third switch Q3, the source of the third switch Q3, node C, and the first resistor R1 to ground, completing the charging of the energy storage capacitor C1. The voltage across the energy storage capacitor C1 is charged to the difference between the DC bus voltage VBUS, the total forward voltage drop of the first light-emitting unit LED1 and the second light-emitting unit LED2, and the forward voltage drop of the first diode D1 and the third switch Q3. During this charging process, because the potential of the positive terminal of the energy storage capacitor C1 is lower than the potential of the positive terminal of the DC bus voltage VBUS, the second diode D2 is in a reverse cutoff state and does not participate in the charging.

[0066] When the DC bus voltage VBUS drops below the operating voltage of the first light-emitting unit LED1, the channels of the first switch Q1, the second switch Q2, and the third switch Q3 are all turned off successively. However, the charge stored in the energy storage capacitor C1 keeps the potential at the positive terminal of the energy storage capacitor C1 at a higher level, which is higher than the potential at the positive terminal of the DC bus voltage VBUS at this time. The second diode D2 then conducts forward. The charge stored in the energy storage capacitor C1 discharges directionally to the first light-emitting unit LED1 through the second diode D2, and discharges back through the parasitic parallel diode of the third switch Q3 (i.e., the seventh diode D7). The specific discharge circuit is as follows: The discharge current flows out from the positive terminal of the energy storage capacitor C1, through the second diode D2, to the positive terminal of the DC bus voltage VBUS, then through the first light-emitting unit LED1 to its output terminal, through the first switch Q1, node A, the third resistor R3, node B, and the fourth resistor R4 to ground, then through the first resistor R1 to node C, the source of the third switch Q3, through the parasitic parallel diode D7 of the third switch Q3 to its drain, and finally to the negative terminal of the energy storage capacitor C1, forming a complete discharge circuit. The discharge current maintains the conduction of the first light-emitting unit LED1, allowing it to continue emitting light during this period, until the DC bus voltage VBUS rises again to a level higher than the operating voltage of the first light-emitting unit LED1 in the next rising phase. At this point, the discharge terminates, and the bus voltage resumes normal power supply to the first light-emitting unit LED1. In other words, the energy storage capacitor C1, together with the second diode D2 and the parasitic parallel diode of the third switch Q3, forms the discharge path to the first light-emitting unit LED1.

[0067] It should be noted that the unidirectional conduction function in the above-mentioned discharge return path is not limited to being implemented using the inherent parasitic parallel diode D7 of the third switch Q3. It can also be implemented by connecting an independent diode in parallel with the source and drain of the third switch Q3, or by using at least one of the parasitic parallel diode D7 and the external parallel diode to form the discharge return path. When the third switch Q3 itself does not have a parasitic parallel diode (e.g., using a transistor or a MOSFET with certain special processes), or when the conduction characteristics of the parasitic parallel diode (such as forward voltage drop, reverse recovery time, etc.) do not meet the requirements of the discharge current, an external parallel diode can be used to replace or supplement the parasitic parallel diode to form a discharge path to the first light-emitting unit LED1. The anode of the external parallel diode is connected to the source of the third switch Q3, and the cathode is connected to the drain of the third switch Q3. Its conduction direction is the same as that of the parasitic parallel diode D7. During the discharge stage, the discharge current is allowed to flow from ground through node C and the first resistor R1 to the source of the third switch Q3, then through the external parallel diode to the drain of the third switch Q3, and finally back to the negative terminal of the energy storage capacitor C1.

[0068] This embodiment utilizes the inherent parasitic structure of the MOSFET as a unidirectional conducting element in the discharge return path, thereby reducing the number of external discrete diodes; and Figure 3 Compared to the illustrated embodiment, in this embodiment, the discharge return path of the energy storage capacitor C1 does not need to be set. Figure 3 The fourth diode D4 in the middle was also removed. Figure 3 The third diode D3 is located between the negative terminal of the energy storage capacitor C1 and the drain of the third switch Q3. The energy storage capacitor C1 is directly connected between the cathode of the first diode D1 and the drain of the third switch Q3. Only the external second diode D2 is retained as a discharge injection path to form a complete directional charging and discharging circuit.

[0069] Specifically, such as Figure 6As shown, in this embodiment, the gates of the first switch Q1, the second switch Q2, and the third switch Q3 are all driven and controlled by their respective operational amplifiers. Specifically, the output of the first operational amplifier AMP1 is connected to the gate of the first switch Q1, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the first switch Q1. The output of the second operational amplifier AMP2 is connected to the gate of the second switch Q2, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the second switch Q2. The output of the third operational amplifier AMP3 is connected to the gate of the third switch Q3, its non-inverting input is connected to the reference voltage Vref, and its inverting input is connected to the source of the third switch Q3. Therefore, the equivalent sampling resistance of the branch containing the first switch Q1 is the series connection of the third resistor R3 and the fourth resistor R4 (i.e., R3+R4), with a corresponding current I=Vref / (R3+R4); the equivalent sampling resistance of the branch containing the second switch Q2 is the fourth resistor R4, with a corresponding current I=Vref / R4; and the equivalent sampling resistance of the independent charging branch containing the third switch Q3 is the first resistor R1, with a corresponding charging current I=Vref / R1. By independently adjusting the resistance values ​​of the first resistor R1 and the fourth resistor R4, the charging current amplitude of the energy storage capacitor C1 and the driving current amplitude of each light-emitting unit can be set respectively.

[0070] It is readily understood by those skilled in the art that in this embodiment, the ground sampling resistor (first resistor R1) of the charging branch where the third switch Q3 is located is independently set with respect to the ground sampling resistor (fourth resistor R4) of the branches where the first switch Q1 and the second switch Q2 are located. That is, the Q3 branch is independently grounded through node C and the first resistor R1, while the Q1 / Q2 branch is independently grounded through node B and the fourth resistor R4. The design principle is as follows: if the fourth resistor R4 is not set and the third resistor R3 is directly connected to the first resistor R1 (that is, the Q1 / Q2 branch and the Q3 branch share the same ground sampling resistor R1), then the discharge circuit of the energy storage capacitor C1 will not pass through the ground wire GND, but will form a closed loop between node A and node C. At this time, the first operational amplifier AMP1 cannot sense the discharge current flowing through the first light-emitting unit LED1 through its feedback terminal, and therefore cannot limit the discharge current. By setting an independent fourth resistor R4 to make the Q1 / Q2 branch independently grounded, the discharge circuit of the energy storage capacitor C1 must return to the negative terminal of C1 through the ground line GND and then through the parasitic parallel diode D7 of the third switch Q3. This forces the discharge current to flow through the path from the source of Q1 to ground. The first operational amplifier AMP1 can sense the discharge current through node A and achieve current limiting control of the discharge current by adjusting the gate voltage of Q1.

[0071] It should be noted that during the discharge of the energy storage capacitor C1 to the first light-emitting unit LED1 through the parasitic parallel diode of the second diode D2 and the third switch Q3, a current-limiting resistor to ground is set on the source side of the first switch Q1 and / or the second switch Q2. This allows the discharge circuit of the energy storage capacitor C1 to form a complete closed loop through the ground line GND, thereby enabling the corresponding constant current control circuit (i.e., the closed-loop constant current regulation circuit where the first operational amplifier AMP1 is located) to sense the discharge current and perform current-limiting control on it.

[0072] Specifically, in this embodiment, the fourth resistor R4 is a ground current-limiting resistor located between the source side (node ​​B) of the second switch Q2 and ground. It ensures that the discharge circuit of the energy storage capacitor C1 must flow back to the negative terminal of the energy storage capacitor C1 through node B, the fourth resistor R4, ground GND, the first resistor R1, node C, and the parasitic parallel diode D7 of the third switch Q3. This allows the first operational amplifier AMP1 to sense the discharge current through node A and perform current-limiting control on it.

[0073] It will be readily understood by those skilled in the art that the aforementioned ground current-limiting resistor is not limited to being disposed only on the source side of the second switching transistor Q2, but can also be disposed on the source side of the first switching transistor Q1, or simultaneously on the source sides of the first switching transistor Q1 and the second switching transistor Q2. For example, as an equivalent variation of this embodiment, the third resistor R3 can be replaced with a ground current-limiting resistor directly connected between the source of the first switching transistor Q1 (node ​​A) and ground (in this case, node B and node A can be directly connected by a wire or by other components with smaller resistance values), which can also enable the discharge circuit of the energy storage capacitor C1 to form a complete circuit through the ground wire GND; as another example, independent ground current-limiting resistors can be disposed between the source of the first switching transistor Q1 and ground, and between the source of the second switching transistor Q2 and ground (i.e., Q1 and Q2 are each grounded through independent resistors), which can also achieve the above-mentioned technical effect of forming a complete discharge circuit through the ground wire. All the above variations are within the protection scope of this invention.

[0074] Furthermore, during the discharge phase, since the forward voltage drop of the first light-emitting unit LED1 is less than the total forward voltage drop of the first light-emitting unit LED1 and the second light-emitting unit LED2 connected in series, the discharge current will preferentially be conducted through the discharge path where the first light-emitting unit LED1 with the smaller voltage drop is located, and will not be diverted through the branch where the second switch Q2 is located, thereby ensuring that the discharge current mainly flows through the first light-emitting unit LED1.

[0075] It is also readily understood by those skilled in the art that Figure 6 The simulation waveforms of the illustrated embodiment can also be referred to Figure 7 The waveform shown is used for illustration. Although... Figure 7 Based on Figure 3The diagram was drawn based on the corresponding embodiment (i.e., the discharge return path of the energy storage capacitor C1 uses an external discrete fourth diode D4), but because... Figure 6 The illustrated embodiments and Figure 3 The fundamental working principle of the embodiments shown is the same—both use the first light-emitting unit LED1 as the discharge target and utilize the natural switching timing of multi-segment driving to control the charging and discharging of the energy storage capacitor C1. The only difference is that... Figure 6 The return path in the circuit is replaced by the parasitic parallel diode D7 of the third switch Q3. Figure 3 The external fourth diode D4 in the middle - therefore Figure 7 The bus voltage waveform, Q1 current, Q2 current, Q3 current, input current Iin, LED1 current, LED2 current, and C1 voltage waveform shown are for... Figure 6 The illustrated embodiments are also applicable. Specifically, in the description Figure 6 When the waveform of the embodiment shown is displayed, Figure 7 The "Q3 / D1 / D3 current" marked in the text corresponds to Figure 6 The current waveform of the charging branch where the third switch Q3 is located ( Figure 6 This branch consists of the third switch Q3 and the first diode D1 (excluding the third diode D3). Figure 7 The "D2 / D4 current" marked in the text corresponds to Figure 6 The discharge path current waveform is shown in the figure, where the current in the second diode D2 is the discharge injection current waveform. Figure 7 The return current originally carried by the fourth diode D4 is now... Figure 6 In the illustrated embodiment, the parasitic parallel diode D7 of the third switch Q3 is used instead, therefore, in the description Figure 6 In the illustrated embodiment, it should be Figure 7 The "D4 current" part should be understood as the "D7 current" (i.e., the parasitic parallel diode current of the third switching transistor Q3). Based on the above explanation, Figure 7 The waveform diagram shown can also be used to illustrate... Figure 6 The working process of the illustrated embodiment is as follows: throughout the entire power frequency cycle, the current of the first light-emitting unit LED1 remains continuous and uninterrupted. Those skilled in the art will understand that the first diode D1, second diode D2, third diode D3, fourth diode D4, fifth diode D5, and sixth diode D6 in the above embodiments can also be implemented using other types of unidirectional conducting devices. This application does not limit this, as long as the conduction direction of the unidirectional conducting device is consistent with the charging and discharging direction of the energy storage capacitor C1.

[0076] In one specific embodiment, see details. Figure 8This embodiment illustrates the generalized n-segment architecture of the frequency reduction lightning circuit of this application. This embodiment extends the frequency reduction lightning circuit to a general structure for n-segment light-emitting units.

[0077] like Figure 8 As shown, the circuit includes n series-connected light-emitting units and n+1 controlled conducting elements, where n≥2.

[0078] n light-emitting units are connected in series between the DC bus voltage VBUS and each linear switch. Of the n+1 linear switches, the first to nth linear switches are respectively configured to correspond to the n light-emitting units, and are sequentially turned on and off according to the change of the DC bus voltage within the power frequency cycle; the (n+1)th linear switch is used to establish an energy storage charging path when it is turned on during the highest voltage segment. That is, the aforementioned multi-segment controlled conducting element includes controlled conducting elements (the first to nth linear switches) corresponding to each light-emitting unit and a controlled conducting element (the (n+1)th linear switch) used to establish the energy storage charging path. The energy storage capacitor is connected in series with the (n+1)th linear switch. When the (n+1)th linear switch is turned on, the DC bus voltage charges the energy storage capacitor through the preceding n light-emitting units; that is, the energy storage element is charged through the preceding light-emitting unit when the controlled conducting element corresponding to the highest voltage segment is turned on.

[0079] Multiple unidirectional conducting elements constitute m directional discharge paths between the energy storage capacitor and m of the n light-emitting units, where 1≤m≤n and n≥2. When the DC bus voltage drops below the operating voltage of the m light-emitting units, the energy storage element discharges directionally to the m light-emitting units simultaneously through the unidirectional conducting elements during the discharge phase, maintaining its current conduction.

[0080] Specifically, such as Figure 8 As shown, the above m directional discharge paths are labeled as discharge path 1, discharge path 2, ..., discharge path m, respectively. Each discharge path consists of one or more unidirectional conducting elements connected in series. One end is connected to the positive terminal of the energy storage capacitor, and the other end is connected to the anode terminal of the corresponding light-emitting unit being discharged. The conduction direction of the unidirectional conducting elements is consistent with the discharge direction of the energy storage capacitor, and they also serve as isolation during the charging and non-discharging phases. When the DC bus voltage drops below the operating voltage of the above m light-emitting units, the energy storage capacitor simultaneously discharges directionally to the corresponding m light-emitting units through the m discharge paths, maintaining current conduction during the voltage trough. In practical design, the number of light-emitting unit segments m (1≤m≤n) that need to be kept conducting and the corresponding discharge path configuration can be flexibly selected according to the balance requirements of SVM and PF.

[0081] It should be noted that the number of discharge lamp strings, *m*, and their specific selection can be flexibly configured based on the actual target values ​​of SVM and PF. Furthermore, by adjusting the number of LEDs connected in series in each light-emitting unit, the forward voltage drop and conduction time window of each unit can be changed; by changing the capacitance of the energy storage element, the charging voltage amplitude and discharge duration can be altered. In practical designs, the balance between flicker visibility (SVM) and power factor (PF) can be controlled by comprehensively adjusting the number of LEDs connected in series in each light-emitting unit and the capacitance of the energy storage element.

[0082] It will be readily understood by those skilled in the art that the number of segments n in the above-described generalized n-segment architecture is not limited to a specific value; the choice of the number of segments depends on the product's power rating, input voltage range, and the number of channels in the driver chip. Increasing the number of segments n results in an input current waveform closer to a sine wave, improving power factor (PF), but also increasing circuit complexity. Furthermore, the energy storage charging path can also be located at the output of other intermediate segment light-emitting units. In this case, the charging voltage of the energy storage capacitor is equal to the bus voltage minus the total forward voltage drop of that segment and all preceding light-emitting units, potentially achieving a better balance between signal strength (SVM) and power factor (PF) under specific conditions.

[0083] The correspondence between the above-mentioned n-segment generalized architecture and the aforementioned specific embodiments is as follows: Figure 3 The embodiment shown corresponds to the case of n=2 and m=1, that is, the two light-emitting units and the energy storage capacitor only discharge to the first light-emitting unit LED1, and the discharge return path adopts the external fourth diode D4; Figure 4 The embodiment shown corresponds to the case of n=2 and m=2, that is, the two light-emitting units and the energy storage capacitor simultaneously discharge to the first light-emitting unit LED1 and the second light-emitting unit LED2, and the discharge return path still uses the external fourth diode D4. Figure 6 The illustrated embodiment corresponds to the case where n=2 and m=1, but the discharge return path is replaced by the parasitic parallel diode D7 of the third switch Q3 instead of the external fourth diode D4, or an external parallel diode is used. Those skilled in the art can flexibly select the number of light-emitting unit segments n, the number of discharge segments m, and the implementation method of the discharge return path based on the n-segment generalized architecture, according to actual needs.

[0084] Furthermore, it will be readily understood by those skilled in the art that the energy storage element in the above embodiments is not limited to a single energy storage capacitor; multiple capacitors may be connected in parallel to increase the total capacitance, or multiple capacitors may be connected in series to improve the voltage rating. In applications requiring greater energy storage, supercapacitors may also be used as energy storage elements. The equivalent series resistance of the energy storage element affects the efficiency of the discharge circuit; low-ESR ceramic capacitors or high-quality aluminum electrolytic capacitors are beneficial for improving discharge efficiency.

[0085] Example 2: An LED driver chip, which integrates some or all of the unidirectional conducting elements of the circuit for reducing flicker of multi-segment linear driven LEDs as described in any specific embodiment of Example 1, and integrates them with the driving control logic of the controlled conducting elements in the same package. Some or all of the unidirectional conducting elements in Example 1 are integrated inside the LED driver chip, and are integrated with the driving control logic of the controlled conducting elements in the same package.

[0086] Specifically, since diodes are standard semiconductor devices, they can be fabricated on the same silicon chip as the switching logic in the driver chip. After integration, only an energy storage capacitor and an LED string need to be configured externally to achieve complete low-frequency flicker multi-segment linear drive functionality. Furthermore, when a MOSFET is used as the controlled conduction element, its parasitic parallel diode itself can serve as part of the discharge path, further reducing the number of additional diodes that need to be integrated.

[0087] The circuit working principle of this embodiment is the same as that of Embodiment 1, and will not be repeated here.

[0088] Example 3: A method for reducing flicker in multi-segment linearly driven LEDs, applicable to circuits as described in Example 1 or Example 2.

[0089] like Figure 9 As shown, the method includes the following steps: S1, during the rising phase of the DC bus voltage, as the bus voltage increases, each controlled conducting element is turned on sequentially from the low-voltage section to the high-voltage section, driving the corresponding light-emitting unit to light up step by step.

[0090] S2, when the controlled conducting element corresponding to the highest voltage segment is turned on, the bus voltage charges the energy storage element through the already turned-on multi-segment light-emitting unit. The charging voltage of the energy storage element is limited to not exceeding the difference between the bus voltage and the total forward voltage drop of the already turned-on light-emitting unit.

[0091] S3, during the decreasing phase of the DC bus voltage, each controlled conducting element is turned off sequentially from the high voltage section to the low voltage section. During each turn-off phase, the controlled conducting elements that are still in the conducting state continue to drive the corresponding light-emitting unit to emit light, and the voltage of the energy storage element is maintained.

[0092] S4, when the bus voltage drops below the operating voltage threshold of at least one section of the light-emitting unit, the energy storage element discharges directionally to the at least one section of the light-emitting unit through a unidirectional conducting element to maintain its current conduction.

[0093] S5, when the bus voltage rises again to a level higher than the operating voltage threshold of the light-emitting unit, the discharge terminates and the normal power supply to the light-emitting unit is restored by the bus voltage.

[0094] Through the cycle of steps S1 to S5 above, at least one light-emitting unit is continuously turned on throughout the entire power frequency cycle, thereby reducing the visibility of the flicker effect (SVM).

[0095] It should be noted that in step S4 above, the energy storage element can discharge to only one segment of the light-emitting unit, or it can simultaneously discharge directionally to m segments out of n light-emitting units, where 1≤m≤n and n≥2. Furthermore, in step S4, the energy storage element can form a discharge path via the parasitic parallel diode of the controlled conducting element or via an external parallel diode. When the corresponding controlled conducting element is in the off state, it utilizes the inherent unidirectional conduction characteristic of its parasitic parallel diode to complete the discharge to the target light-emitting unit, or it can form a discharge path through an external parallel diode. By adjusting the number of LEDs connected in series in each segment of the light-emitting unit and the capacitance value of the energy storage element, the charging voltage amplitude in step S2 and the discharge duration in step S4 can be changed, thereby controlling the balance between the flicker effect visibility (SVM) and the power factor (PF).

[0096] Example 4: An LED driver circuit, differing from Example 1 in that a rectifier circuit is added to the front stage of the low-frequency flicker circuit, forming a complete LED driver circuit. Specifically, this LED driver circuit includes a rectifier circuit and the circuit for reducing the flicker of multi-segment linear driven LEDs as described in Example 1. The output terminal of the rectifier circuit is connected to the DC bus voltage input terminal of the low-frequency flicker circuit, used to convert AC mains power into a pulsating DC bus voltage VBUS, which is then supplied to the multi-segment linear drive circuit. The rectifier circuit can be a bridge rectifier circuit.

[0097] It will be readily understood by those skilled in the art that, in addition to a full-bridge rectifier circuit, the above-mentioned rectifier circuit can also employ other common rectifier topologies such as a half-bridge rectifier circuit and a voltage doubler rectifier circuit. Different rectifier topologies produce output pulsating DC bus voltage VBUS with different waveform shapes and peak values, but as long as the output DC bus voltage VBUS exhibits periodic changes, the frequency reduction lightning circuit described in this application is applicable. Furthermore, a filter circuit (such as a small-value filter capacitor) can be added between the rectifier circuit and the frequency reduction lightning circuit as needed to reduce the high-frequency ripple of the bus voltage. However, care should be taken not to use excessively large filter capacitor values, otherwise, spike pulses may appear in the input current waveform, reducing the power factor PF. In some application scenarios, a fuse, varistor, or other protective components can be connected in series at the input of the rectifier circuit to improve the circuit's surge withstand capability and safety.

[0098] The working principle of the low-frequency lightning circuit section in this embodiment is the same as that in Embodiment 1, and will not be repeated here.

[0099] Example 5: An LED lighting device comprising the circuit described in Example 1 for reducing flicker of multi-segment linear drive LEDs.

[0100] The LED lighting device includes, but is not limited to, LED bulbs, LED tubes, LED panel lights, and other lighting products with a power of up to 25W. Since the solution in this application does not change the basic architecture of existing multi-segment linear drive circuits, existing lighting product production lines only need to add an energy storage capacitor and a few diodes to the existing circuit to complete the upgrade, without redesigning the PCB or replacing the driver IC.

[0101] The working principle of the low-frequency lightning circuit section in this embodiment is the same as that in Embodiment 1, and will not be repeated here.

[0102] In summary, the circuit and method for reducing flicker in multi-segment linearly driven LEDs provided by this invention add an energy storage element and a few unidirectional conducting elements to the existing multi-segment linearly driven LED circuit. The charging and discharging of the energy storage element is achieved by utilizing the natural switching timing of the multi-segment drive, ensuring that at least one light-emitting unit maintains current conduction throughout the entire power frequency cycle, thereby reducing the visible flicker effect (SVM). This solution does not change the basic architecture of the existing circuit and requires no additional control logic, thus possessing practical value.

[0103] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the invention without departing from the scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A circuit for reducing flicker in multi-segment linearly driven LEDs, wherein the input is a DC bus voltage, characterized in that, include: The multi-segment light-emitting unit includes at least a first light-emitting unit and a second light-emitting unit connected in series; each segment light-emitting unit includes at least one or more LED beads connected in series. Multiple controlled conducting elements are arranged corresponding to the multiple light-emitting units. They are turned on and off sequentially as the DC bus voltage changes within the power frequency cycle, so that each light-emitting unit is turned on and off sequentially according to a predetermined timing sequence as the DC bus voltage changes. Multiple unidirectional conducting elements are electrically connected to the multiple controlled conducting elements to form multiple directional conducting paths; An energy storage element is electrically connected to the multiple light-emitting units and forms a directional charging and discharging path with at least one light-emitting unit through the multiple unidirectional conducting elements; During the DC bus voltage rise phase, when the controlled conducting element corresponding to the highest voltage segment is turned on, the DC bus voltage charges the energy storage element through at least one light-emitting unit. The voltage across the energy storage element is limited to not exceeding the difference between the DC bus voltage and the total forward voltage drop of the turned-on light-emitting unit. During the DC bus voltage drop phase, each controlled conducting element is turned off sequentially in the reverse order of the rise phase. The controlled conducting elements that are still in the conducting state continue to drive the corresponding light-emitting unit to emit light, and the voltage of the energy storage element is maintained. When the DC bus voltage drops below the operating voltage of at least one section of light-emitting unit, the energy storage element discharges to that section of light-emitting unit through the unidirectional conducting element, so that the at least one section of light-emitting unit maintains the current conducting state throughout the entire power frequency cycle.

2. The circuit according to claim 1, characterized in that, The multi-segment light-emitting unit includes a first light-emitting unit and a second light-emitting unit connected in series; the multi-segment controlled conduction element includes a first switch, a second switch, and a third switch, wherein the first switch and the second switch respectively drive the light-emitting unit to conduct under different voltage segments, and the third switch is connected in series with the energy storage element at the output terminal of the second light-emitting unit to establish an energy storage charging path when the highest voltage segment is turned on; the energy storage element is an energy storage capacitor; During the rising phase of the DC bus voltage, when the DC bus voltage rises above the forward conduction voltage of the first light-emitting unit, the first switch transistor turns on first, and the first light-emitting unit lights up; as the DC bus voltage continues to rise, the first switch transistor turns off and the second switch transistor turns on, and the first and second light-emitting units light up simultaneously; when the DC bus voltage continues to rise to the highest level, the first and second switch transistors turn off and the third switch transistor turns on, and the first and second light-emitting units light up. At the same time, the DC bus voltage charges the energy storage capacitor through the first and second light-emitting units, and the charging voltage of the energy storage capacitor does not exceed the DC bus voltage minus the total forward voltage drop of the first and second light-emitting units. During the DC bus voltage drop phase, the third switch is turned off first, the second switch is turned on, the first and second light-emitting units continue to light up, and the energy storage capacitor voltage remains unchanged. The second switch is then turned off, and the first switch is turned on, so only the first light-emitting unit is lit, and the voltage of the energy storage capacitor remains unchanged. When the DC bus voltage drops below the operating voltage of the first light-emitting unit, the energy storage capacitor discharges directionally to the first light-emitting unit through a unidirectional conducting element, maintaining the current of the first light-emitting unit until the DC bus voltage exceeds the operating voltage of the first light-emitting unit again in the next rising stage, at which point the discharge of the energy storage capacitor terminates.

3. The circuit according to claim 1 or 2, characterized in that, During the discharge phase, the energy storage element discharges directionally to both the first and second light-emitting units simultaneously through the unidirectional conducting element, so that both the first and second light-emitting units maintain current conduction during the period when the DC bus voltage is lower than their respective operating voltages.

4. The circuit according to claim 1, characterized in that, The multi-segment controlled conduction element also includes a controlled conduction element for establishing an energy storage charging path. When the controlled conduction element for establishing the energy storage charging path is turned on at the highest voltage segment of the DC bus voltage, the DC bus voltage charges the energy storage element through all preceding light-emitting units.

5. The circuit according to claim 2, characterized in that, The energy storage capacitor forms a discharge path to the first light-emitting unit through at least one of the parasitic parallel diodes of the third switch or one of the diodes connected in parallel outside the third switch.

6. The circuit according to claim 5, characterized in that, A ground-limiting resistor is provided on the source side of the first switching transistor and / or the second switching transistor. The current-limiting resistor enables the discharge circuit to form a complete circuit through the ground wire during the discharge of the energy storage capacitor through the parasitic parallel diode of the third switching transistor, thereby enabling the corresponding constant current control circuit to limit the discharge current.

7. The circuit according to claim 1, characterized in that, The controlled conduction element is a MOSFET or a transistor; the energy storage element is an electrolytic capacitor or a ceramic capacitor.

8. A method for reducing flicker in multi-segment linearly driven LEDs, characterized in that, Applied to a circuit that receives DC bus voltage as input and includes multiple series-connected light-emitting units, multiple controlled conduction elements, energy storage elements, and multiple unidirectional conduction elements, the circuit includes the following steps: S1: During the rising phase of the DC bus voltage, as the bus voltage increases, each controlled conducting element is turned on sequentially from the low voltage section to the high voltage section, driving the corresponding light-emitting unit to light up step by step. S2: When the controlled conducting element corresponding to the highest voltage segment is turned on, the bus voltage charges the energy storage element through the already turned-on multi-segment light-emitting unit. The charging voltage of the energy storage element is limited to not exceeding the difference between the bus voltage and the total forward voltage drop of the already turned-on light-emitting unit. S3: During the DC bus voltage drop phase, each controlled conducting element is turned off sequentially from the high voltage section to the low voltage section. During each turn-off phase, the controlled conducting elements that are still in the conducting state continue to drive the corresponding light-emitting unit to emit light, and the energy storage element voltage is maintained. S4: When the bus voltage drops below the operating voltage threshold of at least one section of the light-emitting unit, the energy storage element discharges directionally to the at least one section of the light-emitting unit through a unidirectional conducting element to maintain its current conduction. S5: When the bus voltage rises again to a level higher than the operating voltage threshold of the light-emitting unit, the discharge terminates and the normal power supply to the light-emitting unit is restored by the bus voltage.

9. The method according to claim 8, characterized in that, In step S4, the energy storage element simultaneously discharges directionally to m segments of the n-segment light-emitting unit, where 1≤m≤n and n≥2.

10. The method according to claim 8, characterized in that, In step S4, the energy storage element forms a discharge path through the parasitic parallel diode of the controlled conduction element. When the corresponding controlled conduction element is in the off state, it completes the discharge to the target light-emitting unit by utilizing the unidirectional conduction characteristic of its inherent parasitic parallel diode, or forms a discharge path through an external parallel diode.

11. The method according to claim 8, characterized in that, By adjusting the number of LEDs connected in series in each light-emitting unit and the capacitance of the energy storage element, the charging voltage amplitude in step S2 and the discharge duration in step S4 are changed, thereby controlling the balance between the stroboscopic visibility (SVM) and the power factor (PF).

12. An LED driving circuit, characterized in that, It includes a rectifier circuit and a circuit for reducing the flicker of multi-segment linear drive LEDs as described in any one of claims 1 to 7; the output terminal of the rectifier circuit is connected to the DC bus voltage input terminal of the circuit for reducing the flicker of multi-segment linear drive LEDs, and provides it with a DC bus voltage.

13. An LED driver chip, characterized in that, The circuit integrates some or all of the unidirectional conduction elements of the circuit for reducing the flicker of multi-segment linear drive LEDs as described in any one of claims 1 to 7, and is integrated with the drive control logic of the controlled conduction elements in the same package.

14. An LED lighting device, characterized in that, A circuit comprising reducing flicker of a multi-segment linearly driven LED as described in any one of claims 1 to 7.

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