LED linear driving circuit and LED linear driving method

Abstract

This application discloses an LED linear driving circuit and a linear driving method. The LED linear driving circuit includes a parallel LED load and an output capacitor, and multiple LED current branches connected to the cathode of the LED load. Each LED current branch includes a transistor and an operational amplifier that controls its conduction level. The LED linear driving circuit also includes: a voltage sampling circuit that generates a feedforward voltage that varies with the voltage difference across the output capacitor; and a reference signal generation circuit that generates multiple reference signals corresponding to each LED current branch based on the feedforward voltage, multiple current feedback signals from the multiple LED current branches, an error amplification signal obtained from the pull-up reference voltage, and the input voltage. Each operational amplifier adjusts the current on the transistor according to the corresponding current feedback signal and the reference signal. This reduces the current on the transistor when each LED current branch is turned on during startup, reduces losses, and improves system efficiency.

Description

Technical Field

[0001] This application relates to the field of LED driving technology, specifically to an LED linear driving circuit and an LED linear driving method. Background Technology

[0002] Light-emitting diodes (LEDs) have advantages over traditional light sources, such as high efficiency, energy saving, environmental protection, and good color rendering. As a result, LEDs are increasingly replacing traditional light sources and are widely used in the lighting field, and linear LED drivers have also made great strides.

[0003] In power systems, to improve power supply efficiency, reduce losses, ensure stable grid operation, and meet economic and regulatory requirements, many countries / regions require specific electrical equipment to have a power factor higher than 0.9. To meet this requirement, the equipment needs a wide input current range that is in phase with the input voltage, resulting in a lower output voltage in LED linear drive solutions. The efficiency of a linear LED driver depends on the voltage difference between the input and output voltages. While lowering the output voltage can increase the power factor to above 0.9, the input-output conversion efficiency is typically below 75%. When the voltage difference is large, the system efficiency struggles to meet operational requirements, making it difficult for most LED linear drive solutions to achieve a power factor of 0.9 or higher. To simultaneously meet the demands of high power factor and high efficiency, electrolytic capacitors are added to the LED linear drive circuit. When the input voltage is low, these electrolytic capacitors are connected in series to power the LED load. Utilizing the lossless nature of electrolytic capacitors, they can be combined and controlled in different input voltage ranges to achieve a wide input current range for a single load within the power frequency half-wave, thereby improving the power factor.

[0004] However, in this approach, since the output capacitors across the LED load are approximately short-circuited during startup, the output voltage in each LED current branch connected to the LED load cathode is approximately the input voltage. Consequently, during the transient startup process, the output voltage of each LED current branch is very high, resulting in significant transistor losses and severely impacting system efficiency. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides an LED linear driving circuit and an LED linear driving method.

[0006] According to one aspect of the present invention, an LED linear driving circuit is provided, comprising an LED load and an output capacitor connected in parallel. The anode of the LED load receives a half-wave input voltage of the power frequency output by a rectifier circuit. Multiple LED current branches are connected between the cathode and a reference ground. Each LED current branch includes a transistor and an operational amplifier that controls the conduction level of the transistor. The LED linear driving circuit further includes: a voltage sampling circuit that acquires a sampled voltage characterizing the voltage difference across the output capacitor and outputs a feedforward voltage that varies with the sampled voltage; and a reference signal generation circuit that obtains an error amplification signal based on the feedforward voltage, multiple current feedback signals of the multiple LED current branches, and a set pull-up reference voltage, and generates multiple reference signals corresponding to the multiple LED current branches based on the error amplification signal and the input voltage. Each operational amplifier adjusts the current on the corresponding transistor according to the current feedback signal on its LED current branch and the corresponding reference signal.

[0007] Optionally, after startup, the feedforward voltage decreases as the sampling voltage decreases, and the feedforward voltage is zero in steady state. In steady state, the error amplification signal is unrelated to the feedforward voltage.

[0008] Optionally, the feedforward voltage is the difference between the product of the sampled voltage and the first coefficient and a set threshold, wherein the set threshold is greater than zero and the first coefficient is greater than 0 and less than 1.

[0009] Optionally, the reference signal generation circuit generates a pull-up current based on the pull-up reference voltage, generates a first pull-down current based on the feedforward voltage, generates at least a second pull-down current and a third pull-down current based on the plurality of current feedback signals, and obtains the error amplification signal based on the pull-up current, the first pull-down current to the third pull-down current.

[0010] Optionally, the reference signal generation circuit includes a capacitor, which charges the capacitor based on the pull-up current and discharges the capacitor based on the first pull-down current to the third pull-down current, so as to use the voltage across the capacitor as the error amplification signal.

[0011] Optionally, the plurality of LED current branches include at least a first LED current branch, a second LED current branch, and a third LED current branch. The second LED current branch and the third LED current branch have the same structure but are different from the first LED current branch. The reference signal generation circuit obtains the second pull-down current based on the first current feedback signal of the first LED current branch and obtains the third pull-down current based on the second current feedback signal of the second LED current branch and the third current feedback signal of the third LED current branch.

[0012] Optionally, the first LED current branch includes a first transistor and a first sampling resistor connected in series, and a first operational amplifier connected to the control terminal of the first transistor. The second LED current branch includes a first diode, a first electrolytic capacitor, a second transistor, and a second sampling resistor connected in series, and a second operational amplifier connected to the control terminal of the second transistor. The third LED current branch includes a second diode, a second electrolytic capacitor, a third transistor, and a third sampling resistor connected in series, and a third operational amplifier connected to the control terminal of the third transistor. A fourth transistor is also connected between the common node of the second electrolytic capacitor and the third transistor and the cathode of the first diode. A fourth sampling resistor is connected between the control terminal of the fourth transistor and the cathode of the first diode. When the fourth transistor is turned on, the first electrolytic capacitor and the second electrolytic capacitor are connected in series. The sampling voltage includes a first output voltage obtained from the common node of the first transistor and the output capacitor, a second output voltage obtained from the common node of the first electrolytic capacitor and the second transistor, a third output voltage obtained from the common node of the second electrolytic capacitor and the third transistor, or the gate voltage signal of the control terminal to ground obtained from the control terminal of the fourth transistor.

[0013] Optionally, a fifth transistor is connected between the output terminal and the ground terminal of the rectifier circuit. The control terminal of the fifth transistor is connected to the output terminal of the fourth operational amplifier. The reference signal generation circuit also generates a fourth reference signal based on the error amplification signal and the input voltage. The fourth operational amplifier controls the conduction degree of the fifth transistor based on the fourth current feedback signal obtained from the fifth transistor and the fourth reference signal, so as to control the current flowing through the fifth transistor.

[0014] Optionally, the reference signal generation circuit includes: a multiplier that calculates the ratio of the error amplification signal and the sampled value of the input voltage to obtain a reference voltage; and a ratio adjustment unit that multiplies the reference voltage by different coefficients to obtain multiple reference signals and a fourth reference signal corresponding to multiple LED current branches.

[0015] According to another aspect of the present invention, an LED linear driving method is provided, applied in an LED linear driving circuit, the LED linear driving circuit including a parallel LED load and an output capacitor, the anode of the LED load receiving a power frequency half-wave input voltage output by a rectifier circuit, and multiple LED current branches connected between the cathode and a reference ground, each LED current branch including a transistor and an operational amplifier controlling the conduction degree of the transistor, wherein the LED linear driving method includes: acquiring a sampled voltage characterizing the voltage difference across the output capacitor, and outputting a feedforward voltage that varies with the sampled voltage; obtaining an error amplification signal based on the feedforward voltage, multiple current feedback signals of the multiple LED current branches, and a set pull-up reference voltage, and generating multiple reference signals corresponding to the multiple LED current branches based on the error amplification signal and the input voltage; and each operational amplifier adjusting the current on the corresponding transistor based on the current feedback signal on its respective LED current branch and the corresponding reference signal.

[0016] The embodiments of the present invention have at least the following beneficial effects:

[0017] The LED linear driving circuit and method provided by this invention obtain a feedforward voltage that varies with the sampling voltage by acquiring a sampling voltage characterizing the voltage difference across the output capacitor. An error amplification signal is generated jointly by the feedforward voltage, the current feedback signal on each LED current branch, and a preset pull-up reference voltage, thereby generating a reference signal for the error amplifier of each LED current branch. By incorporating the influence of the feedforward voltage into the adjustment of the reference signal, the reference signal can be adjusted according to the voltage difference across the output capacitor. During startup, a larger sampling voltage and feedforward voltage result in a smaller error amplification signal, allowing the transistors on the LED current branches to be started with a smaller reference signal, reducing the current on the transistors and thus reducing transistor startup losses and improving system efficiency.

[0018] Furthermore, a pull-up current is generated based on the pull-up reference voltage, and a first pull-down current is generated based on the feedforward voltage. A second and third pull-down current are generated based on multiple current feedback signals. The capacitor is charged via the pull-up current, the first pull-down current, and the third pull-down current to obtain the error amplification signal. This ensures that when the feedforward voltage is not zero, the error amplification signal changes negatively with the feedforward voltage, while the reference signal changes positively with the error amplification signal. Therefore, during startup, the presence of the first pull-down current generated by the feedforward voltage reduces the error amplification signal provided by the reference signal generation circuit, reduces the transistor current during the transient turn-on of each LED current branch, and the magnitude of the first pull-down current is adjustable, allowing for precise control of the current magnitude.

[0019] Furthermore, the feedforward voltage is the difference between the product of the sampled voltage and the first coefficient and a set threshold. By adjusting the first coefficient and the set threshold, the feedforward voltage can be made to decrease as the sampled voltage decreases after startup, and it is zero in steady state. Therefore, the error amplification signal is unrelated to the feedforward voltage in steady state. Thus, the feedforward voltage is only used to reduce the error amplification signal during startup, and it will not affect the generation of the error amplification signal after steady state, nor will it affect the normal operation of the LED linear drive circuit.

[0020] Furthermore, after processing the error amplification signal and the input voltage, a reference voltage is obtained. The product of the reference voltage and a certain coefficient yields the fourth reference signal controlling the fifth transistor. Thus, the startup of the fifth transistor is simultaneously influenced by both the input voltage and the error amplification signal. When the input voltage remains constant but the system power decreases, the current on the fifth transistor can be reduced, thereby reducing the transistor's losses and improving system efficiency.

[0021] It should be noted that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the present invention. Attached Figure Description

[0022] Figure 1 A schematic circuit diagram of an LED linear driving circuit according to an embodiment of the present invention is shown;

[0023] Figure 2 The diagram shows the current path of the LED linear driving circuit during operation according to the first embodiment of the present invention;

[0024] Figure 3 The diagram shows the current path of the LED linear driving circuit during operation according to the second embodiment of the present invention;

[0025] Figure 4 A schematic circuit block diagram of the signal control circuit in an LED linear drive circuit according to an embodiment of the present invention is shown.

[0026] Figure 5 A schematic circuit diagram of a reference signal generation circuit according to an embodiment of the present invention is shown;

[0027] Figure 6 A schematic diagram showing the variation of sampling voltage over time in an LED linear driving circuit according to an embodiment of the present invention is shown;

[0028] Figure 7 A schematic flowchart of an LED linear driving method according to an embodiment of the present invention is shown. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in various forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0030] Figure 1 A schematic circuit diagram of an LED linear driving circuit according to an embodiment of the present invention is shown.

[0031] like Figure 1 As shown, the LED linear drive circuit 100 of this embodiment includes a rectifier circuit BD, an LED load and an output capacitor Cout connected in parallel, and multiple LED current branches. The anode of the LED load is connected to the output terminal of the rectifier circuit BD and receives the input voltage Vin of the power frequency half-wave. Multiple LED current branches are connected between the cathode of the LED load and ground. Each LED current branch includes a transistor and an operational amplifier that controls the conduction level of the transistor.

[0032] Specifically, in Figure 1In this embodiment, the multiple LED current branches include a first LED current branch, a second LED current branch, and a third LED current branch. The first LED current branch includes a first transistor M1 and a first sampling resistor R1 connected in series, and a first operational amplifier OP1 connected to the control terminal of the first transistor M1. The second LED current branch includes a first diode D1, a first electrolytic capacitor CE1, a second transistor M2, and a second sampling resistor R2 connected in series, and a second operational amplifier OP2 connected to the control terminal of the second transistor M2. The third LED current branch includes a second diode D2, a second electrolytic capacitor CE2, a third transistor M3, and a third sampling resistor R3 connected in series, and a third operational amplifier OP3 connected to the control terminal of the third transistor M3. The circuit structures of the second and third LED current branches are the same but different from those of the first LED current branch. The operational amplifier amplifies the error between the current feedback signal and the corresponding reference signal of each LED current branch, and controls the operating current of the corresponding branch based on the result of the error amplification, thereby achieving constant current control of the LED load. For example, the first operational amplifier OP1 controls the operating current of the first LED current branch based on the error amplification result of the first current feedback signal VR1 and the first reference signal Vref1 of the first LED current branch, which is to say, it controls the first current Iout1 on the first transistor M1. Similarly, the second operational amplifier OP2 controls the operating current of the second LED current branch based on the error amplification result of the second current feedback signal VR2 and the second reference signal Vref2 of the second LED current branch, which is to say, it controls the second current Iout2 on the second transistor M2. The third operational amplifier OP3 controls the operating current of the third LED current branch based on the error amplification result of the third current feedback signal VR3 and the third reference signal Vref3 of the third LED current branch, which is to say, it controls the third current Iout3 on the third transistor M3. The voltages on each LED current branch are the first output voltage Vout1, the second output voltage Vout2, and the third output voltage Vout3, respectively.

[0033] Furthermore, a fourth transistor M4 is connected between the common node of the second electrolytic capacitor CE2 and the third transistor M3 and the cathode of the first diode D1. A fourth sampling resistor R4 is connected between the control terminal of the fourth transistor M4 and the cathode of the first diode D1. A third diode D3 is connected between the common node of the cathodes of the second electrolytic capacitor CE2 and the second diode D2 and the anode of the LED load. A fourth diode D4 is also connected between the output terminal of the rectifier circuit BD and the anode of the LED load. The control terminal of the fourth transistor M4 receives voltage from the voltage comparison circuit (…). Figure 1The series-parallel switching signal VGS (not shown) is generated to control the on and off states of the fourth transistor M4. When the series-parallel switching signal VGS controls the fourth transistor M4 to turn on, the first electrolytic capacitor CE1 and the second electrolytic capacitor CE2 are connected in series. The operating state of each LED current branch will be determined by... Figure 2 and Figure 3 This will be introduced in the middle.

[0034] When the circuit is powered on, the output capacitor Cout is not yet charged and is approximately short-circuited. Due to the presence of the first diode D1 and the second diode D2, the first output voltage Vout1, the second output voltage Vout2, and the third output voltage Vout3 are all approximately equal to the input voltage Vin. The turn-on loss of the first transistor M1 is the product of the first current Iout1 and the first output voltage Vout1; the turn-on loss of the second transistor M2 is the product of the second current Iout2 and the second output voltage Vout2; and the turn-on loss of the third transistor M3 is the product of the third current Iout3 and the third output voltage Vout3. Because the output voltage of each LED current branch is large during power-on, the losses of the three transistors are all very large, which will affect the system efficiency. Therefore, this embodiment of the application uses the signal control circuit in the LED linear drive circuit 100 ( Figure 1 The reference signal generation circuit 220 (not shown) inside adjusts the reference signal received by each LED current branch to adjust the current magnitude of each transistor when it is turned on during startup, thereby reducing the loss on each transistor and improving system efficiency.

[0035] Therefore, the LED linear driving circuit in this embodiment also includes a signal control circuit, which includes a voltage sampling circuit 210 and a reference signal generation circuit 220. The voltage sampling circuit 210 acquires a sampled voltage representing the voltage difference across the output capacitor Cout and outputs a feedforward voltage Vsft that varies with the sampled voltage. The reference signal generation circuit 220 obtains an error amplification signal Vcomp based on the feedforward voltage Vsft, multiple current feedback signals (first current feedback signal VR1, second current feedback signal VR2, and third current feedback signal VR3) from multiple LED current branches, and a set pull-up reference voltage Vref0. Based on the error amplification signal Vcomp and the input voltage Vin, it generates multiple reference signals Vref1 / Vref2 / Vref3 corresponding to the multiple LED current branches. Then, each operational amplifier adjusts the current on the corresponding transistor according to the current feedback signal on its LED current branch and the corresponding reference signal.

[0036] The voltage sampling circuit 210 acquires sampling voltages including a first output voltage Vout1 obtained from the common node of the first transistor M1 and the output capacitor Cout, a second output voltage Vout2 obtained from the common node of the first electrolytic capacitor CE1 and the second transistor M2, a third output voltage Vout3 obtained from the common node of the second electrolytic capacitor CE2 and the third transistor M3, or the gate voltage signal VGT of the control terminal to ground obtained from the control terminal of the fourth transistor M4. The first output voltage Vout1, the second output voltage Vout2, and the third output voltage Vout3 can all characterize the voltage of the LED load cathode to ground, and the sum of the gate voltage signal VGT and the voltage drop across the fourth sampling resistor R4 can also characterize the voltage of the LED load cathode to ground, and thus characterize the voltage difference across the output capacitor Cout. The voltage sampling circuit 210 selects at least one of these sampling voltages to obtain the feedforward voltage Vsft, for example, obtaining the feedforward voltage Vsft only from the gate voltage signal VGT. In this embodiment, when the feedforward voltage Vsft is not zero, it changes positively with the sampling voltage, while the error amplification signal Vcomp changes negatively with it. Therefore, during startup, the sampling voltage is higher, resulting in a larger feedforward voltage Vsft, which in turn leads to a smaller error amplification signal Vcomp, and consequently, a smaller reference signal. This results in smaller currents in each LED current branch, and a smaller product of transient current and output voltage when each transistor is turned on, thus reducing startup losses. Furthermore, after startup, the feedforward voltage Vsft decreases as the sampling voltage decreases, and reaches zero in steady state. Therefore, in steady state, the error amplification signal Vcomp is uncorrelated with the feedforward voltage Vsft. In other words, after entering steady state, the feedforward voltage Vsft does not affect the generation of the error amplification signal Vcomp, and thus does not affect the generation of the reference signal. Under steady state, the reference signal generation circuit 220 generates an error amplification signal Vcomp based on the current feedback signals (VR1, VR2 and VR3) of each LED current branch, the feedforward voltage Vsft (which is basically zero), and the pull-up reference voltage Vref0. Then, combined with the input voltage Vin, multiple reference signals (Vref1, Vref2 and Vref3 and even Vref4) of each LED current branch are obtained.

[0037] See also Figure 1A fifth transistor M5 is connected between the output of the rectifier circuit BD and the ground terminal. The control terminal of the fifth transistor M5 is connected to the output of the fourth operational amplifier OP4. The fifth transistor M5 is also connected to the fourth operational amplifier OP4 through the fifth sampling resistor R5. The fourth operational amplifier OP4 controls the conduction state of the fifth transistor M5 based on the error amplification result of the fourth current feedback signal VR4 and the fourth reference signal Vref4 obtained from the fifth sampling resistor R5. When the input voltage is relatively low, the fifth transistor M5 needs to be turned on to ensure that current can be drawn from the grid, thereby improving the power factor and reducing harmonic distortion. Currently, the generation of the fourth reference signal Vref4 is related to the input voltage Vin. For example, the voltage obtained by dividing the input voltage Vin through a series resistor network is used to calculate the fourth reference signal Vref4. However, since the fourth reference signal Vref4 is generated only based on the input voltage, under the same input voltage, when the system power decreases, the loss of the fifth transistor M5 is large and remains unchanged, resulting in a significant decrease in system efficiency. Therefore, in this embodiment, the reference signal generation circuit 220 also generates a fourth reference signal Vref4 based on the error amplification signal Vcomp and the input voltage Vin. Then, the fourth operational amplifier OP4 controls the conduction level of the fifth transistor M5 based on the fourth current feedback signal VR4 and the fourth reference signal Vref4 to control the current flowing through the fifth transistor M5, thereby reducing the loss on the transistor. When the input voltage remains unchanged but the power decreases, the loss is reduced and the system efficiency is improved.

[0038] Figure 2 A current path diagram of an LED linear driving circuit according to a first embodiment of the present invention is shown during operation.

[0039] like Figure 2As shown, in this embodiment, when the input voltage Vin is greater than the first threshold voltage VF and less than the second threshold voltage VCAP, taking the first threshold voltage VF being less than or equal to the load operating voltage as an example, the input voltage Vin is sufficient to power the LED load but insufficient to charge the electrolytic capacitor. The series-parallel switching signal VGS controls the fourth transistor M4 to turn off. This controls the first transistor M1 to turn on, while the second transistor M2 and the third transistor M3 are both turned off. The input voltage Vin powers the LED load, and current flows through the first LED current branch where the first transistor M1 is located, forming the first current path ①. When the input voltage Vin exceeds the second threshold voltage VCAP, the first transistor M1 is turned off. The series-parallel switching signal VGS still controls the fourth transistor M4 to turn off, while the second transistor M2 and the third transistor M3 are turned on. The first LED current branch containing the first transistor M1 is turned off, and the second LED current branch containing the second transistor M2 and the third LED current branch containing the third transistor M3 are both turned on. The second and third LED current branches are connected in parallel, forming current paths ② and ③. The input voltage Vin supplies power to the LED load and charges the first electrolytic capacitor CE1 and the second electrolytic capacitor CE2. The second threshold voltage VCAP is, for example, greater than or equal to the operating voltage of the LED load and the sum of the voltages across the two electrolytic capacitors.

[0040] In this embodiment, the circuit structures of the second LED current branch and the third LED current branch are the same, and the current flowing through the second transistor M2 and the third transistor M3 is controlled to be approximately half the current flowing through the first transistor M1. This can be achieved by making the resistance values ​​of the first sampling resistor R1, the second sampling resistor R2, and the third sampling resistor R3 the same, while the values ​​of the first reference signal Vref1, the second reference signal Vref2, and the third reference signal Vref3 are different, such as Vref1 = 2 * Vref2 = 2 * Vref3, and the values ​​of the second reference signal Vref2 and the third reference signal Vref3 are the same. In another example, the resistance values ​​of the first sampling resistor R1, the second sampling resistor R2, and the sampling resistor R3 are different, such as R1 = 0.5R2 = 0.5R3, while the values ​​of the first reference signal Vref1, the second reference signal Vref2, and the third reference signal Vref3 are the same, that is, the resistance values ​​of the second sampling resistor R2 and the third sampling resistor R3 are the same. Both combinations allow for current feedback signal sampling from current paths ② and ③ even after current path ① is turned off, enabling closed-loop control of the output current. The second and third LED current branches share the same circuit structure and component parameters. Therefore, by designing the reference signal or resistor values, accurate sampling and feedback of the load current can be achieved, thereby controlling the LED load to operate at a constant current.

[0041] Figure 3 A current path diagram of an LED linear driving circuit according to a second embodiment of the present invention is shown during operation.

[0042] like Figure 3 As shown, since the input voltage Vin is a dome wave, when the input voltage Vin is less than the first threshold voltage VF, the fifth transistor M5 turns on. The fifth transistor M5 and the rectifier circuit BD form a conduction loop, i.e., current path ⑤ is formed. The series-parallel switching signal VGS controls the fourth transistor M4 to turn on, so the second electrolytic capacitor CE2 and the first electrolytic capacitor CE1 can form a series path. The two electrolytic capacitors form a discharge loop through the fourth transistor M4 and the first transistor M1 to supply power to the LED load, forming... Figure 3 Current path ④. The fourth diode D4 prevents current from flowing back into the input terminal from the electrolytic capacitor. Current path ⑤ ensures that current can still be drawn from the grid when the input voltage Vin is relatively low, thereby improving the power factor and reducing harmonic distortion. In this embodiment, the input voltage Vin is sampled and used as the reference envelope signal for each constant current control, thereby controlling the input current to have a sinusoidal or quasi-sinusoidal envelope, achieving power factor correction.

[0043] Figure 4 A schematic circuit block diagram of the signal control circuit in an LED linear drive circuit according to an embodiment of the present invention is shown. Figure 5 A schematic circuit diagram of a reference signal generation circuit according to an embodiment of the present invention is shown.

[0044] like Figure 4 As shown, the signal control circuit 200 in this embodiment includes, for example, a voltage sampling circuit 210, a reference signal generation circuit 220, and a voltage comparison circuit 230.

[0045] like Figure 4 As shown, the voltage comparator circuit 230 receives the input voltage Vin and the first threshold voltage VF. When the input voltage Vin is less than (or less than or equal to) the first threshold voltage VF, the series-parallel switching signal VGS output by the voltage comparator circuit 230 is used to control the fourth transistor M4 to turn on, and the two electrolytic capacitors are connected in series. When the input voltage Vin is greater than (or greater than or equal to) the first threshold voltage VF, the series-parallel switching signal VGS output by the voltage comparator circuit 230 is used to control the fourth transistor M4 to turn off, and the two electrolytic capacitors are connected in parallel. This series-parallel switching signal VGS is generated by the voltage comparator circuit 230 and is a different signal from the gate voltage signal VGT. The voltage sampling circuit 210 and... Figure 1 As described in the embodiment, it obtains a feedforward voltage Vsft that varies with the sampling voltage by acquiring the sampling voltage, and outputs the feedforward voltage Vsft to the reference signal generation circuit 220.

[0046] Combination Figure 4 and Figure 5 The reference signal generation circuit 220 generates a pull-up current Iu1 based on the pull-up reference voltage Vref0, a second pull-down current Id2 and a third pull-down current Id3 based on multiple current feedback signals VR1, VR2 and VR3, and a first pull-down current Id1 based on the feedforward voltage Vsft. The circuit charges or discharges the capacitor C1 inside the reference signal generation circuit 220 based on the pull-up current Iu1, the first pull-down current Id1 to the third pull-down current Id3 to obtain the error amplification signal Vcomp. Specifically, the reference signal generation circuit 220 includes, for example, voltage-controlled current sources A1, A2, A3, and A4, and capacitor C1. Voltage-controlled current source A1 receives the pull-up reference voltage Vref0 and generates a pull-up current Iu1 to charge capacitor C1; voltage-controlled current source A2 receives the feedforward voltage Vsft and generates a first pull-down current Id1 to discharge capacitor C1; voltage-controlled current source A3 receives the first current feedback signal VR1 and generates a second pull-down current Id2 to discharge capacitor C1; a selection voltage VRS is obtained based on the second current feedback signal VR2 and the third current feedback signal VR3, and voltage-controlled current source A4 generates a third pull-down current Id3 based on the selection voltage VRS to discharge capacitor C1. That is, by combining the pull-up current with multiple pull-down currents to charge and discharge capacitor C1, the error amplification signal Vcomp is obtained. During startup, the feedforward voltage Vsft reduces the error amplification signal Vcomp, decreasing the first reference signal Vref1 to the third reference signal Vref3, thereby reducing the current flowing through the first transistor M1, the second transistor M2, and the third transistor M3, thus reducing startup losses and improving system efficiency.

[0047] Furthermore, the reference voltage generation circuit 220 also includes a multiplexer 224 and an adder. The second current feedback signal VR2 and the third current feedback signal VR3 are first superimposed by the adder, and the superposition result is input to the multiplexer 224 (MUX). The multiplexer 224 is also connected to a reference ground. The multiplexer 224 selects to output the superposition result of the second current feedback signal VR2 and the third current feedback signal VR3 or a ground signal as the selection voltage VRS based on the series-parallel switching signal VGS. When the series-parallel selection signal VGS is invalid, causing the fourth transistor M4 to turn off, the second LED current branch and the third LED current branch are connected in parallel, and the multiplexer 224 uses the positive current from the superposition result of the second current feedback signal VR2 and the third current feedback signal VR3 as the selection voltage VRS. When the series-parallel selection signal VGS is valid, causing the fourth transistor M4 to turn on, the first electrolytic capacitor CE1 and the second electrolytic capacitor CE2 are connected in series, and the multiplexer 224 outputs a ground signal as the selection voltage VRS. When the series-parallel selection voltage VGS is invalid, the selection voltage VRS is obtained through the positive current portion of VR2 and VR3, which generates a third pull-down current Id3 via the voltage-controlled current source A4. Both the second pull-down current Id2 and the third pull-down current Id3 serve as the discharge current for capacitor C1. Furthermore, the second pull-down current Id2 is generated after the first transistor M1 is turned on, and the third pull-down current Id3 is generated after the second transistor M2 and the third transistor M3 are turned on. Therefore, the error amplification signal Vcomp is obtained by charging and discharging capacitor C1 through multiple currents. In steady state, the feedforward voltage Vsft is zero, and the first pull-down current Id1 is zero, which does not affect the magnitudes of the second and third pull-down currents Id2 and Id3.

[0048] The reference signal generation circuit 220 also includes a multiplier 221, which calculates the proportional value of the error amplified signal Vcomp after proportional adjustment and the sampled value MULT of the input voltage Vin to obtain the reference voltage VREF. The sampled value MULT of the input voltage Vin is obtained, for example, through a voltage divider unit 225, which includes a series resistor Rup and a resistor Rdn to divide the input voltage Vin and provide the sampled value MULT from the midpoint between the two resistors. The error amplified signal Vcomp after proportional adjustment and the sampled value MULT are combined and processed by the multiplier 221 and then by the clamping circuit 222 to obtain the reference voltage VREF. The reference signal generation circuit 220 also includes a proportional adjustment unit 223, which multiplies the reference voltage VREF by different coefficients (e.g., k1, k2, k3, and k4) to obtain multiple reference signals (Vref1, Vref2, and Vref3) corresponding to multiple LED current branches and a fourth reference signal Vref4.

[0049] Furthermore, in this embodiment, the voltage sampling circuit 210 processes the sampled voltage to obtain the feedforward voltage Vsft. The feedforward voltage Vsft is, for example, the difference between the product of the sampled voltage and a first coefficient kx and a set threshold Voffset. The set threshold Voffset is greater than zero, and the first coefficient kx is greater than 0 and less than 1. For example, taking the gate voltage signal VGT as the sampled voltage, the expression for the feedforward voltage Vsft is: Vsft = kx × VGT - Voffset.

[0050] Figure 6 A schematic diagram illustrating the variation of the sampled voltage over time in an LED linear driving circuit according to an embodiment of the present invention is shown.

[0051] Combination Figure 6 As can be seen, the sampling voltage can be Vout1, Vout2, Vout3, or VGT, or it can be the result of calculations on two or more sampling voltages. The peak value of the sampling voltage gradually decreases and then stabilizes after startup. The feedforward voltage Vsft decreases as the peak value of the sampling voltage decreases, and in steady state, the peak value of the sampling voltage remains essentially unchanged, while the feedforward voltage Vsft is almost zero. In steady state, the error amplification signal Vcomp is uncorrelated with the feedforward voltage Vsft. Therefore, the existence of the threshold Voffset ensures that the value of the feedforward voltage Vsft can be zero in steady state. By adjusting the first coefficient kx and the value of the threshold Voffset, the initial value and steady-state value of the feedforward voltage Vsft can be adjusted, thereby adjusting the error amplification signal Vcomp.

[0052] Figure 7 A schematic flowchart of an LED linear driving circuit according to an embodiment of the present invention is shown.

[0053] This LED linear driving method is applied to the aforementioned LED linear driving circuit. (See attached image) Figure 7 The LED linear driving method in this embodiment includes, for example, the following steps:

[0054] In step S101, a sampled voltage representing the voltage difference across the output capacitor is obtained, and a feedforward voltage that varies with the sampled voltage is output.

[0055] In step S102, an error amplification signal is obtained based on the feedforward voltage, multiple current feedback signals of multiple LED current branches, and a set pull-up reference voltage. Multiple reference signals corresponding to the multiple LED current branches are generated based on the error amplification signal and the input voltage.

[0056] In step S103, each operational amplifier adjusts the current on the corresponding transistor according to the current feedback signal on the LED current branch and the corresponding reference signal.

[0057] The LED linear driving method in this embodiment is based on the LED linear driving circuit described above. The specific circuit principle, structure and working process have been described above and will not be repeated here.

[0058] It should be noted that the numerical values ​​in this article are for illustrative purposes only. In other embodiments of the present invention, other numerical values ​​may be sampled to implement this solution. The specific values ​​should be reasonably set according to the actual situation, and the present invention does not limit them.

[0059] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

[0060] It should also be understood that the terminology and expressions used herein are for descriptive purposes only, and one or more embodiments described herein should not be limited to these terms and expressions. The use of these terms and expressions does not exclude any illustrative and descriptive equivalent features (or parts thereof), and it should be recognized that various modifications that may exist should also be included within the scope of the claims. Other modifications, variations, and substitutions may also exist. Accordingly, the claims should be considered to cover all such equivalents.

Claims

1. An LED linear driving circuit, comprising a parallel LED load and an output capacitor, wherein the anode of the LED load receives a power frequency half-wave input voltage output from a rectifier circuit, and multiple LED current branches are connected between the cathode and a reference ground, each LED current branch including a transistor and an operational amplifier controlling the conduction level of the transistor, wherein, The LED linear driving circuit further includes: A voltage sampling circuit acquires a sampled voltage representing the voltage difference across the output capacitor and outputs a feedforward voltage that varies with the sampled voltage; and The reference signal generation circuit obtains an error amplification signal based on the feedforward voltage, multiple current feedback signals from the multiple LED current branches, and a set pull-up reference voltage. It then generates multiple reference signals corresponding to the multiple LED current branches based on the error amplification signal and the input voltage. Each operational amplifier adjusts the current on the corresponding transistor based on the current feedback signal on its LED current branch and the corresponding reference signal.

2. The LED linear driving circuit according to claim 1, wherein, After startup, the feedforward voltage decreases as the sampling voltage decreases, and the feedforward voltage is zero in steady state. In steady state, the error amplification signal is unrelated to the feedforward voltage.

3. The LED linear driving circuit according to claim 2, wherein, The feedforward voltage is the difference between the product of the sampled voltage and the first coefficient and a set threshold, wherein the set threshold is greater than zero and the first coefficient is greater than 0 but less than 1.

4. The LED linear driving circuit according to claim 1, wherein, The reference signal generation circuit generates a pull-up current based on the pull-up reference voltage, generates a first pull-down current based on the feedforward voltage, generates at least a second pull-down current and a third pull-down current based on the plurality of current feedback signals, and obtains the error amplification signal based on the pull-up current, the first pull-down current to the third pull-down current.

5. The LED linear driving circuit according to claim 4, wherein, The reference signal generation circuit includes a capacitor. The reference signal generation circuit charges the capacitor based on the pull-up current and discharges the capacitor based on the first pull-down current to the third pull-down current, so as to use the voltage across the capacitor as the error amplification signal.

6. The LED linear driving circuit according to claim 4, wherein, The plurality of LED current branches include at least a first LED current branch, a second LED current branch, and a third LED current branch. The second LED current branch and the third LED current branch have the same structure, but are different from the first LED current branch. The reference signal generation circuit obtains the second pull-down current based on the first current feedback signal of the first LED current branch, and obtains the third pull-down current based on the second current feedback signal of the second LED current branch and the third current feedback signal of the third LED current branch.

7. The LED linear driving circuit according to claim 6, wherein, The first LED current branch includes a first transistor and a first sampling resistor connected in series, and a first operational amplifier connected to the control terminal of the first transistor. The second LED current branch includes a first diode, a first electrolytic capacitor, a second transistor, and a second sampling resistor connected in series, and a second operational amplifier connected to the control terminal of the second transistor. The third LED current branch includes a second diode, a second electrolytic capacitor, a third transistor, and a third sampling resistor connected in series, and a third operational amplifier connected to the control terminal of the third transistor. A fourth transistor is connected between the common node of the second electrolytic capacitor and the third transistor and the cathode of the first diode. A fourth sampling resistor is connected between the control terminal of the fourth transistor and the cathode of the first diode. When the fourth transistor is turned on, the first electrolytic capacitor and the second electrolytic capacitor are connected in series. The sampling voltage includes a first output voltage obtained from the common node of the first transistor and the output capacitor, a second output voltage obtained from the common node of the first electrolytic capacitor and the second transistor, a third output voltage obtained from the common node of the second electrolytic capacitor and the third transistor, or the gate voltage signal of the control terminal to ground obtained from the control terminal of the fourth transistor.

8. The LED linear driving circuit according to claim 1, wherein, A fifth transistor is also connected between the output terminal and the ground terminal of the rectifier circuit. The control terminal of the fifth transistor is connected to the output terminal of the fourth operational amplifier. The reference signal generation circuit further generates a fourth reference signal based on the error amplification signal and the input voltage. The fourth operational amplifier controls the conduction level of the fifth transistor based on the fourth current feedback signal obtained from the fifth transistor and the fourth reference signal, so as to control the current flowing through the fifth transistor.

9. The LED linear driving circuit according to claim 8, wherein, The reference signal generation circuit includes: The multiplier calculates the reference voltage by combining the proportional value of the error amplification signal with the sampled value of the input voltage. The proportional adjustment unit multiplies the reference voltage by different coefficients to obtain multiple reference signals and the fourth reference signal corresponding to the multiple LED current branches.

10. An LED linear driving method, applied in an LED linear driving circuit, the LED linear driving circuit including a parallel LED load and an output capacitor, wherein the anode of the LED load receives a power frequency half-wave input voltage output from a rectifier circuit, and multiple LED current branches are connected between the cathode and a reference ground, each LED current branch including a transistor and an operational amplifier controlling the conduction level of the transistor, wherein... The LED linear driving method includes: Acquire a sampled voltage representing the voltage difference across the output capacitor, and output a feedforward voltage that varies with the sampled voltage; An error amplification signal is obtained based on the feedforward voltage, multiple current feedback signals from the multiple LED current branches, and a set pull-up reference voltage. Multiple reference signals corresponding to the multiple LED current branches are then generated based on the error amplification signal and the input voltage. Each operational amplifier adjusts the current on its corresponding transistor based on the current feedback signal on its LED current branch and the corresponding reference signal.

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