LED drive circuit and LED drive chip

Abstract

An LED drive circuit and an LED drive chip. The LED drive circuit comprises a sampling module, a voltage conversion module and a control module. The voltage conversion module converts an input voltage into an output voltage and provides the output voltage to an LED load. When a PWM control signal is a high-level signal, the sampling module samples an output feedback voltage, which is positively correlated with the output voltage, to obtain an output feedback sampled voltage and stores the output feedback sampled voltage. When the PWM control signal is a low-level signal, the control module receives the output feedback sampled voltage and the output feedback voltage, and controls, on the basis of the output feedback sampled voltage and the output feedback voltage, the voltage conversion module to stabilize the output voltage.

Description

LED driving circuit and LED driving chip

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202411128323.9, filed on August 16, 2024, and entitled “LED driving circuit and LED driving chip”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of integrated circuits, and in particular, to an LED driving circuit and an LED driving chip. BACKGROUND

[0004] In a light-emitting diode (LED) driving device, a boost output and a current source for controlling the brightness of an LED lamp are included. In a pulse width modulation (PWM) dimming mode, when a PWM signal is at a high level, the current source is turned on to make the LED work, and when the PWM signal is at a low level, the current source is turned off to make the LED stop working. Since the human eye recognizes the average brightness of the LED within a period of time, the PWM dimming mode is widely used in the driving device of the LED.

[0005] In the prior art, when the PWM signal is at a low level, the stability of the internal voltage of the device can be maintained by a capacitor. However, the voltage of the capacitor will continue to decrease over time, and the output voltage of the LED driving device will also decrease, resulting in insufficient load. The problem of insufficient load can be solved by increasing the deep dimming mode. However, when the dimming is changed by changing the duty cycle of the PWM signal, the LED will flicker. SUMMARY

[0006] The embodiments described in the present disclosure provide an LED driving circuit and an LED driving chip.

[0007] According to a first aspect of the present disclosure, an LED driving circuit is provided, comprising a sampling module, a voltage conversion module, and a control module.

[0008] The voltage conversion module is configured to convert an input voltage into an output voltage and provide to an LED load. The sampling module is configured to sample an output feedback voltage to obtain an output feedback sampling voltage and store when the PWM control signal is a high level signal; wherein the output feedback voltage is positively correlated with the output voltage. The control module is configured to receive the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low level signal, and control the voltage conversion module to stabilize the output voltage according to the output feedback sampling voltage and the output feedback voltage.

[0009] In some embodiments of the present disclosure, the control module is further configured to receive a reference voltage and a minimum LED feedback voltage when the PWM control signal is a high level signal, and control the voltage conversion module to stabilize the output voltage according to the reference voltage and the minimum LED feedback voltage.

[0010] In some embodiments of the present disclosure, the sampling module includes a digital-to-analog converter and an analog-to-digital converter. An input end of the analog-to-digital converter is connected to a feedback end of the voltage conversion module and a second input end of the control module, an output end of the analog-to-digital converter is connected to an input end of the digital-to-analog converter, and an output end of the digital-to-analog converter is connected to a first input end of the control module.

[0011] In some embodiments of the present disclosure, the control module includes a selection unit and a control unit. A first input end of the selection unit is connected to an output end of the sampling module, a second input end of the selection unit is connected to a feedback end of the voltage conversion module and an input end of the sampling module, a third input end of the selection unit is connected to the reference voltage, a fourth input end of the selection unit is connected to the minimum LED feedback voltage, and a control end of the selection unit is connected to the PWM control signal. An input end of the control unit is connected to an output end of the selection unit, and an output end of the control unit is connected to a control end of the voltage conversion module.

[0012] The selection unit is configured to select the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low-level signal, and select the reference voltage and the minimum LED feedback voltage when the PWM control signal is a high-level signal. The control unit is configured to determine an error amplification voltage according to the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low-level signal, and determine the error amplification voltage according to the reference voltage and the minimum LED feedback voltage when the PWM control signal is a high-level signal. The control unit is further configured to convert the error amplification voltage into a clock signal, and control a duty cycle of the voltage conversion module according to the clock signal to stabilize the output voltage.

[0013] In some embodiments of the present disclosure, the selection unit includes a first selector and a second selector. A first input terminal of the first selector is connected to an output terminal of the sampling module, a second input terminal of the first selector is connected to the reference voltage, a control terminal of the first selector is connected to the PWM control signal, and an output terminal of the first selector is connected to a first input terminal of the control unit. A first input terminal of the second selector is connected to a feedback terminal of the voltage conversion module and an input terminal of the sampling module, a second input terminal of the second selector is connected to the minimum LED feedback voltage, a control terminal of the second selector is connected to the PWM control signal, and an output terminal of the second selector is connected to a second input terminal of the control unit.

[0014] The first selector is configured to select the output feedback sampling voltage when the PWM control signal is a low-level signal, and select the reference voltage when the PWM control signal is a high-level signal. The second selector is configured to select the output feedback voltage when the PWM control signal is a low-level signal, and select the minimum LED feedback voltage when the PWM control signal is a high-level signal.

[0015] In some embodiments of the present disclosure, the selection unit includes a four-to-two selector. A first input terminal of the four-to-two selector is connected to an output terminal of the sampling module, a second input terminal of the four-to-two selector is connected to a feedback terminal of the voltage conversion module, a control terminal of the four-to-two selector is connected to the PWM control signal, a third input terminal of the four-to-two selector is connected to the reference voltage, a fourth input terminal of the four-to-two selector is connected to the minimum LED feedback voltage, a first output terminal of the four-to-two selector is connected to a first input terminal of the control unit, and a second output terminal of the four-to-two selector is connected to a second input terminal of the control unit.

[0016] The four-to-two selector is configured to turn on the first input end of the four-to-two selector and the first output end of the four-to-two selector, the second input end of the four-to-two selector and the second output end of the four-to-two selector when the PWM control signal is a low-level signal; and turn on the third input end of the four-to-two selector and the first output end of the four-to-two selector, the fourth input end of the four-to-two selector and the second output end of the four-to-two selector when the PWM control signal is a high-level signal.

[0017] In some embodiments of the present disclosure, the control unit is further configured to increase the charging duration of the voltage conversion module to increase the duty cycle of the voltage conversion module when the PWM control signal is a low-level signal and the output feedback voltage is lower than the output feedback sampling voltage.

[0018] In some embodiments of the present disclosure, the control unit is further configured to increase the charging duration of the voltage conversion module to increase the duty cycle of the voltage conversion module when the PWM control signal is a high-level signal and the minimum LED feedback voltage is lower than the reference voltage; and decrease the charging duration of the voltage conversion module to decrease the duty cycle of the voltage conversion module when the PWM control signal is a high-level signal and the minimum LED feedback voltage is higher than the reference voltage.

[0019] In some embodiments of the present disclosure, the control unit includes an error amplifier, a comparator, a flip-flop, a NAND gate, a driver, a first resistor, and a first capacitor. The non-inverting input end of the error amplifier is connected to the first output end of the selection unit, the inverting input end of the error amplifier is connected to the second output end of the selection unit, the output end of the error amplifier is connected to the inverting input end of the comparator and the first end of the first resistor, the non-inverting input end of the comparator is connected to a ramp signal, the output end of the comparator is connected to the input end of the flip-flop, the output end of the flip-flop is connected to the control end of the voltage conversion module through the NAND gate and the driver in sequence, and the second end of the first resistor is connected to ground through the first capacitor.

[0020] In some embodiments of the present disclosure, when the PWM control signal is a low-level signal and the output feedback voltage is lower than the output feedback sampling voltage, the error amplifier voltage increases, so that the duration of the low-level signal output by the comparator increases, thereby increasing the charging duration.

[0021] In some embodiments of the present disclosure, when the PWM control signal is a high signal and the minimum LED feedback voltage is lower than the reference voltage, the error amplification voltage is increased to increase the duration of the low signal output by the comparator, so as to increase the charging duration; when the PWM control signal is a high signal and the minimum LED feedback voltage is higher than the reference voltage, the error amplification voltage is decreased to decrease the duration of the low signal output by the comparator, so as to decrease the charging duration.

[0022] In some embodiments of the present disclosure, the analog-to-digital converter is configured to sample the output feedback voltage at a preset time after the PWM control signal jumps to a high signal, the preset time being less than the difference between the PWM control signal pulse width and the sampling time of the analog-to-digital converter.

[0023] In some embodiments of the present disclosure, the LED driving circuit further comprises a minimum voltage detection module, and the LED load comprises a plurality of LED load branches in parallel. A plurality of inputs of the minimum voltage detection module are connected to feedback ends of the plurality of LED load branches one by one, and an output of the minimum voltage detection module is connected to a fourth input of the selection unit.

[0024] The minimum voltage detection module is configured to receive LED feedback voltages of the plurality of LED load branches respectively, and determine the minimum LED feedback voltage according to the plurality of LED feedback voltages.

[0025] In some embodiments of the present disclosure, the voltage conversion module comprises an inductor, a diode, a control tube, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a second capacitor and a third capacitor. The input voltage is connected to the anode of the diode and the second end of the control tube through the inductor, the first end of the control tube is grounded, and the control end of the control tube is connected to the output end of the control module. The cathode of the diode is connected to the first end of the second resistor, the first end of the fourth resistor, the first end of the fifth resistor and the input end of the LED load, the second end of the second resistor is connected to the first end of the third resistor, the second input end of the control module and the input end of the sampling module, and the second end of the third resistor is grounded. The second end of the fourth resistor is grounded through the second capacitor, and the second end of the fifth resistor is grounded through the third capacitor.

[0026] According to a second aspect of the present disclosure, an LED driving chip is provided, comprising the LED driving circuit according to the first aspect of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present disclosure or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or the related description. Obviously, the drawings in the following description are some embodiments of the present disclosure, rather than all the embodiments of the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the present disclosure.

[0028] FIG. 1 is a circuit schematic diagram of an LED driving device provided by the prior art.

[0029] FIG. 2 is a circuit schematic diagram of another LED driving device provided by the prior art.

[0030] FIG. 3 is a structural schematic diagram of an LED driving circuit provided by an embodiment of the present disclosure.

[0031] FIG. 4 is a structural schematic diagram of another LED driving circuit provided by an embodiment of the present disclosure.

[0032] FIG. 5 is a circuit schematic diagram of an LED driving circuit provided by an embodiment of the present disclosure.

[0033] FIG. 6 is a sampling timing diagram of an analog-to-digital converter provided by an embodiment of the present disclosure.

[0034] FIG. 7 is a circuit schematic diagram of another LED driving circuit provided by an embodiment of the present disclosure.

[0035] FIG. 8 is a simulation schematic diagram of an output current of an LED driving circuit and an LED driving device provided by an embodiment of the present disclosure.

[0036] In the drawings, the same reference signs correspond to the same elements. It should be noted that the elements in the drawings are schematic, and are not drawn to scale. DETAILED DESCRIPTION

[0037] In order to make the purposes, technical solutions and advantages of the embodiments of the present disclosure clearer, the following will combine the drawings to make a clear and complete description of the technical solutions of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the present disclosure.

[0038] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. As used herein, the statement that two or more parts or components are "coupled" or "connected" together shall mean that the parts are joined or operate together either directly or through one or more intermediate parts or components.

[0039] FIG. 1 is a circuit schematic diagram of an LED driving device provided by the prior art, as shown in FIG. 1, the LED driving device comprises a Boost circuit 10, a current source 20 for controlling the brightness of the LED, and a control circuit 30. Wherein, the input end of the Boost circuit 10 is connected with an input voltage Vin, the output end of the Boost circuit 10 is connected with the input end of an LED load 40, the output end of the LED load is connected with the ground through the current source 20, two input ends of the control circuit 30 are connected with a reference voltage Vref and a minimum LED feedback voltage V_ledx_min respectively, and the output end of the control circuit 30 is connected with the control end of the Boost circuit 10.

[0040] For example, as shown in FIG. 1, the control circuit 30 comprises an error amplifier EA, a comparator CMP, a flip-flop RS, an inverter INV, a driver DRV, a first resistor R1 and a first capacitor C1. Wherein, the non-inverting input end of the error amplifier EA is connected with the reference voltage Vref, the inverting input end of the error amplifier EA is connected with the minimum LED feedback voltage V_ledx_min, the output end of the error amplifier EA is connected with the inverting input end of the comparator CMP, the non-inverting input end of the comparator CMP is connected with a ramp signal VRAMP, the output end of the comparator CMP is connected with the input end of the flip-flop RS, the output end of the flip-flop RS is connected with the input end of the inverter INV, and the output end of the inverter INV is connected with the input end of the driver DRV.

[0041] The boost circuit 10 comprises a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a second capacitor C2, a third capacitor C3, an inductor L, a diode D and a power transistor NM1, wherein the gate of the power transistor NM1 is connected to the output of the driver DRV, the first end of the power transistor NM1 is connected to the ground, and the second end of the power transistor NM1 is connected to the second end of the inductor L and the anode of the diode D. The first end of the inductor L is connected to the input voltage Vin, and the cathode of the diode D is connected to the first end of the second resistor R2, the first end of the fourth resistor R4, the first end of the fifth resistor R5 and the input end of the LED load 40. The second end of the fourth resistor R4 is connected to the ground through the second capacitor C2, the second end of the fifth resistor R5 is connected to the ground through the third capacitor C3, and the second end of the second resistor R2 is connected to the ground through the third resistor R3.

[0042] The boost circuit 10 can boost the input voltage Vin to obtain an output voltage Vout, and provide the output voltage Vout to the LED load 40.

[0043] The current source 20 comprises an operational amplifier AMP, a switch transistor NM2 and a sixth resistor R6, wherein the non-inverting input of the operational amplifier AMP is connected to the LED reference voltage Vref_led, the inverting input of the operational amplifier AMP is connected to the first end of the sixth resistor R6 and the first end of the switch transistor NM2, the output of the operational amplifier AMP is connected to the gate of the switch transistor NM2, the second end of the switch transistor NM2 is connected to the output end of the LED load 40, and the second end of the sixth resistor R6 is connected to the ground.

[0044] In the PWM dimming mode, when the PWM signal is at a high level, the operational amplifier AMP controls the switch transistor NM2 to be turned on, i.e. the current source 20 is turned on, so that the current flows from the input end of the LED load 40, through the LED load 40, and then to the ground potential. When the PWM signal is at a low level, the gate voltage of the switch transistor NM2 is pulled to the ground, which is equivalent to the current source 20 being turned off, so that no current flows through the LED load 40. The human eye recognizes the average brightness in a period of time, so the PWM dimming mode is widely used in the driving control mode of the LED.

[0045] Specifically, when the LED load 40 comprises a plurality of LED load branches in parallel, the voltage at the output end of each LED load branch is the LED feedback voltage V_ledx of the LED load branch, and the minimum LED feedback voltage V_ledx_min is the minimum one among the LED feedback voltages V_ledx of all the LED load branches. When the LED load 40 comprises one LED load branch, as shown in FIG. 1, the LED feedback voltage V_ledx of the LED load branch is the minimum LED feedback voltage V_ledx_min.

[0046] When the PWM signal is low, it is equivalent to that the Boost circuit 10 has no load, and the minimum LED feedback voltage V_ledx_min is easy to rise to the output voltage Vout, that is, the voltage at the inverting input terminal of the error amplifier EA is raised, and then the output voltage of the error amplifier EA is lowered, which brings great difficulty to the establishment of the circuit when the PWM signal jumps to high.

[0047] In order to solve the above problems, an LED driving device as shown in FIG. 2 is provided, which is a circuit schematic diagram of another LED driving device provided by the prior art. As shown in FIG. 2, the control circuit 30 includes an error amplifier EA, a comparator CMP, a flip-flop RS, a first inverter INV1, a second inverter INV2, a NAND gate, a first resistor R1 and a first capacitor C1.

[0048] Among them, the non-inverting input terminal of the error amplifier EA is connected with the reference voltage Vref, the inverting input terminal of the error amplifier EA is connected with the minimum LED feedback voltage V_ledx_min, the output terminal of the error amplifier EA is connected with the inverting input terminal of the comparator CMP, the non-inverting input terminal of the comparator CMP is connected with the ramp signal VRAMP, and the output terminal of the comparator CMP is connected with the input terminal of the flip-flop RS. The output terminal of the flip-flop RS is connected with the input terminal of the first inverter INV1, the output terminal of the first inverter INV1 is connected with the first input terminal of the NAND gate, the second input terminal of the NAND gate is connected with the PWM signal, the output terminal of the NAND gate is connected with the input terminal of the second inverter INV2, and the output terminal of the second inverter INV2 is connected with the gate of the power transistor NM1.

[0049] Specifically, when the PWM signal is low, the error amplifier EA is controlled not to output, that is, the connection between the output terminal of the error amplifier EA and the inverting input terminal of the comparator CMP is disconnected, and the voltage at the inverting input terminal of the comparator CMP is maintained by the electric quantity stored by the first capacitor C1 when the PWM signal is a high signal. At this time, the power transistor NM1 is in an off state, and the output voltage Vout is maintained by the electric quantity stored by the second capacitor C2 and the third capacitor C3 when the PWM signal is a high signal.

[0050] Generally, the frequency of the PWM signal is 20KHz to 100HZ. When the frequency of the PWM signal is low, for example, the frequency of the PWM signal is 100HZ, the voltage at the inverting input of the comparator CMP and the output voltage Vout continuously decrease over time due to the leakage of the devices connected at the inverting input of the comparator CMP and the output of the Boost circuit 10, and the energy is replenished only when the PWM signal jumps to high level, which causes the output of the LED driving device to fluctuate. In actual applications, it is necessary to stabilize the output voltage Vout as much as possible to ensure that the LED lamp can have a comfortable brightness for the human eye in any mode.

[0051] If the duty cycle of the PWM signal is low, the energy may not be replenished before the Boost circuit 10 is in the off state, that is, the energy consumed by the LED driving device when the PWM signal is low is greater than the energy replenished when the PWM signal is high, which results in poor load capacity of the LED driving device.

[0052] To solve the problem of poor load capacity of the LED driving device caused by the decrease of the output voltage of the LED driving device, a deep dimming mode is added to divide the LED dimming mode into two sections. When the duty cycle of the PWM signal is low, for example, the pulse width of the PWM signal is 7μs, the PWM dimming mode is switched to the deep dimming mode. In the deep dimming mode, the non-inverting input of the error amplifier EA is switched to a fixed voltage, the inverting input of the error amplifier EA is switched to the feedback end of the Boost circuit 10, that is, the connection point of the second resistor R2 and the third resistor R3, and the second input of the NAND gate is switched to high level.

[0053] In the deep dimming mode, the Boost circuit 10 works in closed loop, which can solve the problem of the decrease of the output voltage Vout caused by the leakage in open loop control, maintain the stability of the output of the LED driving device, and also solve the problem of insufficient load capacity. However, the PWM signal clock is uncertain and the capacitance values of the first capacitor C1, the second capacitor C2 and the third capacitor C3 are uncertain. When the frequency of the PWM signal is low, the capacitor leakage in the PWM dimming mode has not had time to replenish energy before switching to the deep dimming mode, and the output voltage Vout rises in the deep dimming mode. The closed loop operation of the whole loop makes the LED feedback voltage V_ledx not be suppressed, so the current is larger than that in the PWM dimming mode, which causes the human eye to see LED flicker when the PWM signal duty cycle is changed to dim.

[0054] Therefore, the present disclosure provides an LED driving circuit, which comprises a sampling module, a voltage conversion module and a control module. The voltage conversion module can convert an input voltage into an output voltage and provide the output voltage to an LED load. When a PWM control signal is a high-level signal, the sampling module can sample an output feedback voltage positively correlated with the output voltage to obtain an output feedback sampling voltage and store the output feedback sampling voltage. When the PWM control signal is a low-level signal, the control module can receive the output feedback sampling voltage and the output feedback voltage, and control the voltage conversion module to stabilize the output voltage according to the output feedback sampling voltage and the output feedback voltage. In this way, the output voltage can be stabilized when the PWM control signal is a low-level signal, so as to ensure the load capacity, and LED flickering can be avoided when the duty cycle of the PWM control signal is adjusted.

[0055] The technical solutions provided by the present disclosure will be described in detail below with reference to several specific embodiments.

[0056] FIG. 3 is a structural schematic diagram of an LED driving circuit according to an embodiment of the present disclosure. As shown in FIG. 3, the LED driving circuit 100 comprises a sampling module 110, a voltage conversion module 120 and a control module 130.

[0057] The first input end of the control module 130 is connected to the output end of the sampling module 110, the second input end of the control module 130 is connected to the feedback end of the voltage conversion module 120 and the input end of the sampling module 110, the control end of the control module 130 is connected to a PWM control signal, the output end of the control module 130 is connected to the control end of the voltage conversion module 120, the input end of the voltage conversion module 120 is connected to an input voltage Vin, and the output end of the voltage conversion module 120 is connected to the input end of an LED load 40.

[0058] The voltage conversion module 120 is configured to convert the input voltage Vin into an output voltage Vout and provide the output voltage Vout to the LED load 40. The sampling module 110 is configured to sample the output feedback voltage V_out when the PWM control signal is a high-level signal to obtain an output feedback sampling voltage V_out_s and store the output feedback sampling voltage V_out_s, wherein the output feedback voltage V_out is positively correlated with the output voltage Vout. The control module 130 is configured to receive the output feedback sampling voltage V_out_s and the output feedback voltage V_out when the PWM control signal is a low-level signal, and control the voltage conversion module 120 to stabilize the output voltage Vout according to the output feedback sampling voltage V_out_s and the output feedback voltage V_out.

[0059] For example, FIG. 4 is a structural schematic diagram of another LED driving circuit according to an embodiment of the present disclosure. As shown in FIG. 4, the sampling module 110 comprises a digital-to-analog converter DAC and an analog-to-digital converter ADC.

[0060] The input end of the analog-to-digital converter ADC is connected to the feedback end of the voltage conversion module 120 and the second input end of the control module 130, the output end of the analog-to-digital converter ADC is connected to the input end of the digital-to-analog converter DAC, and the output end of the digital-to-analog converter DAC is connected to the first input end of the control module 130.

[0061] Specifically, the analog-to-digital converter ADC is an 8-bit analog-to-digital converter ADC. After the PWM control signal jumps to a high-level signal, the analog-to-digital converter ADC samples the output feedback voltage V_out to obtain an 8-bit binary code value, and transmits the 8-bit binary code value to the digital-to-analog converter DAC to write the 8-bit binary code value into the digital-to-analog converter DAC for latching, until the next time the PWM control signal jumps to a high-level signal, the next time the converted 8-bit binary code value is written into the digital-to-analog converter DAC.

[0062] The digital-to-analog converter DAC is an 8-bit digital-to-analog converter DAC, and the digital-to-analog converter DAC outputs a corresponding output feedback sampling voltage V_out_s according to the received 8-bit binary code value.

[0063] It should be noted that the present embodiment only takes 8 bits as an example to exemplarily illustrate the bits of the digital-to-analog converter DAC and the analog-to-digital converter ADC, and in actual application, the digital-to-analog converter DAC and the analog-to-digital converter ADC can be of other bits, and the present disclosure does not specifically limit this, but only limits that the bits of the digital-to-analog converter DAC and the analog-to-digital converter ADC are the same.

[0064] Continuing to refer to FIG. 4, the control module 130 includes a selection unit 131 and a control unit 132. The first input end of the selection unit 131 is connected to the output end of the sampling module 110, the second input end of the selection unit 131 is connected to the feedback end of the voltage conversion module 120 and the output end of the sampling module 110, and the control end of the selection unit 131 is connected to the PWM control signal. The input end of the control unit 132 is connected to the output end of the selection unit 131, and the output end of the control unit 132 is connected to the control end of the voltage conversion module 120.

[0065] Exemplarily, the selection unit 131 includes two selectors. As shown in FIG. 4, the selection unit 131 includes a first selector MUX1 and a second selector MUX2. The first input end of the first selector MUX1 is connected to the output end of the sampling module 110, the control end of the first selector MUX1 is connected to the PWM control signal, and the output end of the first selector MUX1 is connected to the first input end of the control unit 132.

[0066] The first input terminal of the second selector MUX2 is connected with the feedback terminal of the voltage conversion module 120 and the input terminal of the sampling module 110, the control terminal of the second selector MUX2 is connected with the PWM control signal, and the output terminal of the second selector MUX2 is connected with the second input terminal of the control unit 132.

[0067] When the PWM control signal is a low-level signal, the first selector MUX1 turns on the first input terminal of the first selector MUX1 and the output terminal of the first selector MUX1, so that the first selector MUX1 selects the output feedback sampling voltage V_out_s as the output and provides the output feedback sampling voltage V_out_s to the first input terminal of the control unit 132. At the same time, the second selector MUX2 turns on the first input terminal of the second selector MUX2 and the output terminal of the second selector MUX2, so that the second selector MUX2 selects the output feedback voltage V_out as the output and provides the output feedback voltage V_out to the second input terminal of the control unit 132.

[0068] In other embodiments, the selection unit 131 includes a four-to-two selector. The first input terminal of the selector is connected with the output terminal of the sampling module 110, the second input terminal of the selector is connected with the feedback terminal of the voltage conversion module 120 and the input terminal of the sampling module 110, the control terminal of the selector is connected with the PWM control signal, the first output terminal of the selector is connected with the first input terminal of the control unit 132, and the second output terminal of the selector is connected with the second input terminal of the control unit 132.

[0069] When the PWM control signal is a low-level signal, the selector turns on the first input terminal of the selector and the first output terminal of the selector, the second input terminal of the selector and the second output terminal of the selector, so that the selector selects the output feedback sampling voltage V_out_s and the output feedback voltage V_out as the output and provides the output feedback sampling voltage V_out_s to the first input terminal of the control unit 132 and the output feedback voltage V_out to the second input terminal of the control unit 132.

[0070] In this way, when the PWM control signal is a low-level signal, the selection unit 131 selects the output feedback sampling voltage V_out_s and the output feedback voltage V_out as the output.

[0071] When the PWM control signal is a low-level signal, the control unit 132 can receive the output feedback sampling voltage V_out_s and the output feedback voltage V_out output by the selection unit 131, determine the error amplification voltage of the output feedback sampling voltage V_out_s and the output feedback voltage V_out, convert the error amplification voltage into a clock signal, and control the charge and discharge duration of the voltage conversion module 120 according to the clock signal.

[0072] Since the output voltage Vout is positively correlated with the output feedback voltage V_out, the output feedback voltage V_out starts to decrease when the output voltage Vout starts to decrease. When the PWM control signal is a low signal, if the output feedback voltage V_out decreases to be lower than the output feedback sampling voltage V_out_s, the error amplification voltage increases. At this time, the control unit 132 controls the charging time length of the voltage conversion module 120 to increase, that is, controls the duty cycle of the voltage conversion module 120 to increase, so as to make the output voltage Vout increase, thereby maintaining the stability of the output voltage Vout and ensuring the load capacity.

[0073] In addition, when the PWM control signal is a low signal, the output voltage Vout is stable, so that the output current is relatively stable when the PWM control signal is switched from a low signal to a high signal, and therefore, when the duty cycle of the PWM control signal is adjusted, the phenomenon of LED flickering does not occur.

[0074] Therefore, when the PWM control signal is a low signal, the control unit 132 determines the error amplification voltage according to the output feedback sampling voltage V_out_s and the output feedback voltage V_out, converts the error amplification voltage into a clock signal, and controls the duty cycle of the voltage conversion module 120 according to the clock signal, so as to stabilize the output voltage Vout.

[0075] In summary, in the embodiment of the present disclosure, the LED driving circuit includes a sampling module, a voltage conversion module and a control module. The voltage conversion module can convert an input voltage into an output voltage and provide the output voltage to an LED load. When the PWM control signal is a high signal, the sampling module can sample an output feedback voltage positively correlated with the output voltage, obtain an output feedback sampling voltage and store the output feedback sampling voltage. When the PWM control signal is a low signal, the control module can receive the output feedback sampling voltage and the output feedback voltage, and control the voltage conversion module according to the output feedback sampling voltage and the output feedback voltage to stabilize the output voltage. In this way, the output voltage can be stabilized when the PWM control signal is a low signal, so as to ensure the load capacity, and the phenomenon of LED flickering can be avoided when the duty cycle of the PWM control signal is adjusted.

[0076] In some embodiments, continuing to refer to FIG. 3 and FIG. 4, a third input end of the control module 130 is connected with a reference voltage Vref, and a fourth input end of the control module 130 is connected with a minimum LED feedback voltage V_ledx_min.

[0077] The control module 130 is further configured to, when the PWM control signal is a high signal, receive the reference voltage Vref and the minimum LED feedback voltage V_ledx_min, and control the voltage conversion module 120 according to the reference voltage Vref and the minimum LED feedback voltage V_ledx_min to stabilize the output voltage Vout.

[0078] As shown in FIG. 4, the third input terminal of the selection unit 131 is connected to the reference voltage Vref, and the fourth input terminal of the selection unit 131 is connected to the minimum LED feedback voltage V_ledx_min.

[0079] As shown in FIG. 4, the second input terminal of the first selector MUX1 is connected to the reference voltage Vref, and the second input terminal of the second selector MUX2 is connected to the minimum LED feedback voltage V_ledx_min.

[0080] When the PWM control signal is a high-level signal, the second input terminal and the output terminal of the first selector MUX1 are turned on, the first selector MUX1 selects the reference voltage Vref, and the reference voltage Vref is provided to the first input terminal of the control unit 132. At the same time, the second input terminal and the output terminal of the second selector MUX2 are turned on, the second selector MUX2 selects the minimum LED feedback voltage V_ledx_min, and the minimum LED feedback voltage V_ledx_min is provided to the second input terminal of the control unit 132.

[0081] As shown in FIG. 4, the third input terminal of the selection unit 131 is connected to the reference voltage Vref, and the fourth input terminal of the selection unit 131 is connected to the minimum LED feedback voltage V_ledx_min.

[0082] When the PWM control signal is a high-level signal, the third input terminal and the first output terminal of the selector are turned on, the fourth input terminal and the second output terminal of the selector are turned on, the selector selects the reference voltage Vref and the minimum LED feedback voltage V_ledx_min, the reference voltage Vref is provided to the first input terminal of the control unit 132, and the minimum LED feedback voltage V_ledx_min is provided to the second input terminal of the control unit 132.

[0083] Thus, when the PWM control signal is a high-level signal, the selection unit 131 selects the reference voltage Vref and the minimum LED feedback voltage V_ledx_min.

[0084] When the PWM control signal is a high-level signal, the control unit 132 can receive the reference voltage Vref and the minimum LED feedback voltage V_ledx_min output by the selection unit 131, determine an error amplification voltage of the reference voltage Vref and the minimum LED feedback voltage V_ledx_min, convert the error amplification voltage into a clock signal, and control the charging and discharging duration of the voltage conversion module 120 according to the clock signal.

[0085] When the PWM control signal is a high-level signal, if the output minimum LED feedback voltage V_ledx_min is lower than the reference voltage Vref, the error amplification voltage increases. At this time, the control unit 132 controls the charging duration of the voltage conversion module 120 to increase, i.e., controls the duty cycle of the voltage conversion module 120 to increase, so as to make the output voltage Vout rise and thereby maintain the output voltage Vout stable, and further make the minimum LED feedback voltage V_ledx_min rise to the reference voltage Vref.

[0086] On the contrary, if the output minimum LED feedback voltage V_ledx_min is higher than the reference voltage Vref, the error amplification voltage decreases. At this time, the control unit 132 controls the charging duration of the voltage conversion module 120 to decrease, i.e., controls the duty cycle of the voltage conversion module 120 to decrease, so as to make the output voltage Vout decrease and thereby maintain the output voltage Vout stable, and further make the minimum LED feedback voltage V_ledx_min decrease to the reference voltage Vref.

[0087] In this way, when the PWM control signal is a high-level signal, the control unit 132 determines the error amplification voltage according to the reference voltage Vref and the minimum LED feedback voltage V_ledx_min, converts the error amplification voltage into a clock signal, and controls the duty cycle of the voltage conversion module 120 according to the clock signal, so as to stabilize the output voltage Vout.

[0088] In the embodiments of the present disclosure, no matter whether the PWM control signal is a high-level signal or a low-level signal, the LED driving circuit 100 has a stable output voltage Vout, further improving the output stability thereof. In addition, the PWM control signal is used to control the input of the switching control module 130, and is not used to control the duty cycle of the voltage conversion module 120, so that the control mode is relatively simple.

[0089] In some embodiments, continuing to refer to FIG. 3 and FIG. 4, the LED driving circuit 100 further includes a current source 20, and the LED load 40 is grounded through the current source 20.

[0090] For example, when the PWM control signal is a high-level signal, the current source 20 is turned on, and the current flows through the LED load 40 and then flows to the ground potential. When the PWM signal is a low-level signal, the current source 20 is turned off, and no current flows through the LED load 40.

[0091] In this way, the duty cycle of the PWM control signal can be adjusted to control the brightness of the LEDs in the LED load 40.

[0092] In some embodiments, FIG. 5 is a circuit schematic diagram of an LED driving circuit according to an embodiment of the present disclosure. As shown in FIG. 5, the control unit 132 includes an error amplifier EA, a comparator CMP, a flip-flop RS, a NAND gate, a driver DRV, a first resistor R1, and a first capacitor C1.

[0093] The non-inverting input terminal of the error amplifier EA is connected to the first output terminal of the selection unit 131, the inverting input terminal of the error amplifier EA is connected to the second output terminal of the selection unit 131, the output terminal of the error amplifier EA is connected to the inverting input terminal of the comparator CMP and the first terminal of the first resistor R1, and the non-inverting input terminal of the comparator CMP is connected to the ramp signal VRAMP.

[0094] The output terminal of the comparator CMP is connected to the input terminal of the flip-flop RS, the output terminal of the flip-flop RS is connected to the control terminal of the voltage conversion module 120 through the NAND gate and the driver DRV in sequence, and the second terminal of the first resistor R1 is connected to the ground through the first capacitor C1.

[0095] For example, when the PWM control signal is a high-level signal, the non-inverting input terminal of the error amplifier EA receives the reference voltage Vref, the inverting input terminal of the error amplifier EA receives the minimum LED feedback voltage V_ledx_min, and the error amplifier EA can determine the error amplification voltage of the reference voltage Vref and the minimum LED feedback voltage V_ledx_min.

[0096] When the minimum LED feedback voltage V_ledx_min is lower than the reference voltage Vref, the error amplification voltage output by the error amplifier EA increases, that is, the voltage at the inverting input terminal of the comparator CMP increases, the duration of the low-level signal output by the comparator CMP increases, and the control unit 132 controls the charging duration of the voltage conversion module 120 to increase.

[0097] When the minimum LED feedback voltage V_ledx_min is higher than the reference voltage Vref, the error amplification voltage output by the error amplifier EA decreases, that is, the voltage at the inverting input terminal of the comparator CMP decreases, the duration of the low-level signal output by the comparator CMP decreases, and the control unit 132 controls the charging duration of the voltage conversion module 120 to decrease.

[0098] When the PWM control signal is a low signal, the non-inverting input terminal of the error amplifier EA receives the output feedback sampling voltage V_out_s, and the inverting input terminal of the error amplifier EA receives the output feedback voltage V_out, and the error amplifier EA can determine the error amplification voltage of the output feedback sampling voltage V_out_s and the output feedback voltage V_out.

[0099] When the output feedback voltage V_out is lower than the output feedback sampling voltage V_out_s, the error amplification voltage output by the error amplifier EA increases, that is, the voltage of the inverting input terminal of the comparator CMP increases, the duration of the low signal output by the comparator CMP increases, and the control unit 132 controls the charging duration of the voltage conversion module 120 to increase.

[0100] In some embodiments, the analog-to-digital converter ADC is configured to sample the output feedback voltage V_out at a preset time after the PWM control signal jumps to a high signal, and the preset time is less than the difference between the pulse width of the PWM control signal and the sampling time of the analog-to-digital converter ADC.

[0101] For example, the sampling timing diagram of the analog-to-digital converter provided by the embodiment of the present disclosure is shown in FIG. 6. As shown in FIG. 6, the analog-to-digital converter ADC starts sampling at a preset time T after the PWM control signal jumps from a low signal to a high signal, and the sampling time of the analog-to-digital converter ADC is t. When T+t is less than the time during which the PWM control signal maintains a high signal, that is, less than the pulse width of the PWM control signal, the accuracy of the sampling of the analog-to-digital converter ADC can be ensured.

[0102] For example, when the speed of the analog-to-digital converter ADC is 2M clock, the sampling time t of the analog-to-digital converter ADC is 4μs, and the preset time T is 1μs.

[0103] In the embodiment of the present disclosure, the output feedback voltage V_out tends to be stable at a preset time after the PWM control signal jumps to a high signal, and the analog-to-digital converter ADC starts sampling the output feedback voltage V_out, which can ensure the accuracy of the sampling. In addition, the preset time is less than the difference between the pulse width of the PWM control signal and the sampling time of the analog-to-digital converter ADC, and the PWM control signal still maintains a high signal when the sampling of the analog-to-digital converter ADC is completed, which further ensures the accuracy of the sampling.

[0104] In some embodiments, continuing to refer to FIG. 5, the voltage conversion module 120 includes an inductor L, a diode D, a power tube NM1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a second capacitor C2, and a third capacitor C3.

[0105] The input voltage Vin is connected to the anode of the diode D and the second end of the power transistor NM1 through the inductor L, the first end of the power transistor NM1 is grounded, and the control end of the power transistor NM1 is connected to the output end of the control module 130. The cathode of the diode D is connected to the first end of the second resistor R2, the first end of the fourth resistor R4, the first end of the fifth resistor R5, and the input end of the LED load 40, and the second end of the second resistor R2 is connected to the first end of the third resistor R3, the second input end of the control module 130, and the input end of the sampling module 110. The second end of the third resistor R3 is grounded, the second end of the fourth resistor R4 is grounded through the second capacitor C2, and the second end of the fifth resistor R5 is grounded through the third capacitor C3.

[0106] For example, when the PWM control signal is a high-level signal, if the minimum LED feedback voltage V_ledx_min is lower than the reference voltage Vref, the duration of the low-level signal output by the comparator CMP increases, the driver DRV controls the on duration of the power transistor NM1 to increase, thereby increasing the charging duration of the voltage conversion module 120, that is, increasing the duty cycle of the voltage conversion module 120.

[0107] When the minimum LED feedback voltage V_ledx_min is higher than the reference voltage Vref, the duration of the low-level signal output by the comparator CMP decreases, the driver DRV controls the on duration of the power transistor NM1 to decrease, thereby decreasing the charging duration of the voltage conversion module 120, that is, decreasing the duty cycle of the voltage conversion module 120.

[0108] When the PWM control signal is a low-level signal, if the output feedback voltage V_out is lower than the output feedback sampling voltage V_out_s, the duration of the low-level signal output by the comparator CMP increases, the driver DRV controls the on duration of the power transistor NM1 to increase, thereby increasing the charging duration of the voltage conversion module 120, that is, increasing the duty cycle of the voltage conversion module 120.

[0109] In some embodiments, FIG. 7 is a structural schematic diagram of another LED driving circuit provided by the embodiments of the present disclosure, as shown in FIG. 7, the LED driving circuit 100 further includes a minimum voltage detection module 140, and the LED load 40 includes a plurality of LED load branches 41 connected in parallel.

[0110] The plurality of input ends of the minimum voltage detection module 140 are connected to the feedback ends of the plurality of LED load branches 41 one by one, and the output end of the minimum voltage detection module 140 is connected to the fourth input end of the selection unit 131.

[0111] The minimum voltage detection module 140 is configured to receive the LED feedback voltages V_ledx of the plurality of LED load branches 21, and determine the minimum LED feedback voltage V_ledx_min according to the plurality of LED feedback voltages V_ledx.

[0112] For example, as shown in FIG. 7, the LED load 40 includes a first LED load branch 411 and a second LED load branch 412 in parallel, and the LED driving circuit 100 further includes two current sources 20, i.e., a first current source 21 and a second current source 22. The input ends of the first LED load branch 411 and the second LED load branch 412 are connected to the output end of the voltage conversion module 120, the output end of the first LED load branch 411 is connected to the ground through the first current source 21, and the output end of the second LED load branch 412 is connected to the ground through the second current source 22.

[0113] The minimum voltage detection module 140 includes a first input end and a second input end. The output end of each LED load branch is the feedback end of the LED load branch. Therefore, the feedback end of the first LED load branch 411 is connected to the first input end of the minimum voltage detection module 140, and the feedback end of the second LED load branch 412 is connected to the second input end of the minimum voltage detection module 140.

[0114] The minimum voltage detection module 140 can receive the LED feedback voltage V_ledx of the first LED load branch 411 and the LED feedback voltage V_ledx of the second LED load branch 412, compare the two LED feedback voltages V_ledx, and determine the smaller one as the minimum LED feedback voltage V_ledx_min.

[0115] For example, if the LED feedback voltage V_ledx of the first LED load branch 411 is greater than the LED feedback voltage V_ledx of the second LED load branch 412, the minimum LED feedback voltage V_ledx_min is the LED feedback voltage V_ledx of the second LED load branch 412. If the LED feedback voltage V_ledx of the first LED load branch 411 is less than the LED feedback voltage V_ledx of the second LED load branch 412, the minimum LED feedback voltage V_ledx_min is determined as the LED feedback voltage V_ledx of the first LED load branch 411.

[0116] The first current source 21 can control the brightness of the LEDs on the first LED load branch 411, and the second current source 22 can control the brightness of the LEDs on the second LED load branch 412.

[0117] It should be noted that FIG. 7 only exemplarily shows that the LED load 40 includes two LED load branches 41, the corresponding minimum voltage detection module 140 includes two input terminals, and the LED driving circuit 100 includes two current sources 20. In actual applications, the LED load 40 can also include three or more than three LED load branches 41, the corresponding minimum voltage detection module 140 also includes three or more than three input terminals, and the LED driving circuit 100 can also include three or more than three current sources 20, and the number of the LED load branches 41, the number of the input terminals of the minimum voltage detection module 140 and the number of the current sources 20 are equal.

[0118] FIG. 8 is a simulation diagram of the output current of the LED driving circuit and the LED driving device provided by the embodiment of the present disclosure. As shown in FIG. 8, when the PWM control signal is a low-level signal, the output current of the LED driving device near the deep dimming mode is only 96.81355 mA. With the decrease of the duty ratio of the PWM control signal, the LED driving device switches to the deep dimming mode, at this time, the output voltage Vout of the LED driving device is raised, and the output current can reach 145.1886 mA. Obviously, when adjusting the duty ratio of the PWM control signal to dim, the output current changes suddenly before and after the mode switching, and therefore the human eye can observe that the LED suddenly becomes bright, that is, the LED flickers.

[0119] As shown in FIG. 8, when the PWM control signal is a low-level signal, the output current of the LED driving circuit 100 is maintained near 145.1886 mA, and when adjusting the duty ratio of the PWM control signal to dim, there is no sudden change in the output current, and therefore the human eye cannot see the LED flicker.

[0120] The embodiment of the present disclosure also provides an LED driving chip, which includes the LED driving circuit 100 provided by any one of the above embodiments.

[0121] The LED driving chip provided by the embodiment of the present disclosure includes the LED driving circuit 100 provided by any one of the above embodiments, has the same functional modules and beneficial effects as the LED driving circuit 100, and will not be described here.

[0122] Unless the context clearly indicates otherwise, the singular form of a word includes the plural, and vice versa, as the word is used in this text and the attached claims. Thus, when referring to the singular, the plural of the corresponding term is generally included. Similarly, the words "comprise" and "include" are to be interpreted as inclusive rather than exclusive. Likewise, the terms "include" and "or" should be interpreted as inclusive, unless expressly prohibited from such an interpretation in this text. Where the term "example" is used in this text, especially when it follows a list of terms, the "example" is merely an example and is illustrative, and should not be considered exclusive or exhaustive.

[0123] Further aspects and ranges of adaptation become apparent from the description provided herein. It should be understood that the various aspects of the disclosure can be implemented alone or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended to be illustrative only and are not intended to limit the scope of the present disclosure.

[0124] The above detailed description of several embodiments of the disclosure has been presented for the purposes of illustration and description. It is apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the disclosure without departing from the spirit and scope of the disclosure. The scope of the disclosure is defined by the appended claims.

Claims

1. An LED driving circuit comprising: The sampling module, the voltage conversion module and the control module; The voltage conversion module is configured to convert an input voltage into an output voltage and provide to an LED load; The sampling module is configured to sample an output feedback voltage when the PWM control signal is a high-level signal to obtain an output feedback sampling voltage and store the output feedback sampling voltage; wherein the output feedback voltage is positively correlated with the output voltage; The control module is configured to receive the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low-level signal, and control the voltage conversion module to stabilize the output voltage according to the output feedback sampling voltage and the output feedback voltage.

2. The LED driving circuit of claim 1, wherein, The control module is further configured to receive a reference voltage and a minimum LED feedback voltage when the PWM control signal is a high-level signal, and control the voltage conversion module to stabilize the output voltage according to the reference voltage and the minimum LED feedback voltage.

3. The LED driving circuit of claim 2, wherein, The sampling module comprises a digital-to-analog converter and an analog-to-digital converter; An input end of the analog-to-digital converter is connected to a feedback end of the voltage conversion module and a second input end of the control module, an output end of the analog-to-digital converter is connected to an input end of the digital-to-analog converter, and an output end of the digital-to-analog converter is connected to a first input end of the control module.

4. The LED driving circuit of claim 2, wherein, The control module comprises a selection unit and a control unit; A first input end of the selection unit is connected to an output end of the sampling module, a second input end of the selection unit is connected to a feedback end of the voltage conversion module and an input end of the sampling module, a third input end of the selection unit is connected to the reference voltage, a fourth input end of the selection unit is connected to the minimum LED feedback voltage, and a control end of the selection unit is connected to the PWM control signal; An input end of the control unit is connected to an output end of the selection unit, and an output end of the control unit is connected to a control end of the voltage conversion module; The selection unit is configured to select to output the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low-level signal, and select to output the reference voltage and the minimum LED feedback voltage when the PWM control signal is a high-level signal; The control unit is configured to determine an error amplification voltage according to the output feedback sampling voltage and the output feedback voltage when the PWM control signal is a low-level signal, and determine the error amplification voltage according to the reference voltage and the minimum LED feedback voltage when the PWM control signal is a high-level signal; The control unit is further configured to convert the error amplification voltage into a clock signal, and control a duty cycle of the voltage conversion module according to the clock signal to stabilize the output voltage.

5. The LED driving circuit of claim 4, wherein, The selection unit comprises a first selector and a second selector; The first input end of the first selector is connected with the output end of the sampling module, the second input end of the first selector is connected with the reference voltage, the control end of the first selector is connected with the PWM control signal, and the output end of the first selector is connected with the first input end of the control unit; The first input end of the second selector is connected with the feedback end of the voltage conversion module and the input end of the sampling module, the second input end of the second selector is connected with the minimum LED feedback voltage, the control end of the second selector is connected with the PWM control signal, and the output end of the second selector is connected with the second input end of the control unit; The first selector is configured to output the output feedback sampling voltage when the PWM control signal is a low-level signal, and output the reference voltage when the PWM control signal is a high-level signal. The second selector is configured to output the output feedback voltage when the PWM control signal is a low-level signal, and output the minimum LED feedback voltage when the PWM control signal is a high-level signal.

6. The LED driving circuit of claim 4, wherein, The selection unit comprises a four-to-two selector; The first input end of the four-to-two selector is connected with the output end of the sampling module, the second input end of the four-to-two selector is connected with the feedback end of the voltage conversion module, the control end of the four-to-two selector is connected with the PWM control signal, the third input end of the four-to-two selector is connected with the reference voltage, the fourth input end of the four-to-two selector is connected with the minimum LED feedback voltage, the first output end of the four-to-two selector is connected with the first input end of the control unit, and the second output end of the four-to-two selector is connected with the second input end of the control unit; The four-to-two selector is configured to turn on the first input end and the first output end of the four-to-two selector, the second input end and the second output end of the four-to-two selector when the PWM control signal is a low-level signal, and turn on the third input end and the first output end of the four-to-two selector, the fourth input end and the second output end of the four-to-two selector when the PWM control signal is a high-level signal.

7. The LED driving circuit of claim 4, wherein, The control unit is further configured to increase the charging duration of the voltage conversion module to increase the duty cycle of the voltage conversion module when the PWM control signal is a low-level signal and the output feedback voltage is lower than the output feedback sampling voltage.

8. The LED driving circuit of claim 7, wherein, The control unit is further configured to, when the PWM control signal is a high-level signal and the minimum LED feedback voltage is lower than the reference voltage, control the charging duration of the voltage conversion module to increase, so as to increase the duty cycle of the voltage conversion module; when the PWM control signal is a high-level signal and the minimum LED feedback voltage is higher than the reference voltage, control the charging duration of the voltage conversion module to decrease, so as to decrease the duty cycle of the voltage conversion module.

9. The LED driving circuit of claim 8, wherein, The control unit comprises an error amplifier, a comparator, a flip-flop, a NAND gate, a driver, a first resistor and a first capacitor. The non-inverting input terminal of the error amplifier is connected to the first output terminal of the selection unit, the inverting input terminal of the error amplifier is connected to the second output terminal of the selection unit, the output terminal of the error amplifier is connected to the inverting input terminal of the comparator and the first terminal of the first resistor, the non-inverting input terminal of the comparator is connected to a ramp signal, the output terminal of the comparator is connected to the input terminal of the flip-flop, the output terminal of the flip-flop is connected to the control terminal of the voltage conversion module through the NAND gate and the driver in sequence, and the second terminal of the first resistor is connected to the ground through the first capacitor.

10. The LED driving circuit of claim 9, wherein, When the PWM control signal is a low-level signal and the output feedback voltage is lower than the output feedback sampling voltage, the error amplification voltage is increased, so that the duration of the low-level signal output by the comparator is increased, so as to increase the charging duration.

11. The LED driving circuit of claim 9, wherein, When the PWM control signal is a high-level signal and the minimum LED feedback voltage is lower than the reference voltage, the error amplification voltage is increased, so that the duration of the low-level signal output by the comparator is increased, so as to increase the charging duration; when the PWM control signal is a high-level signal and the minimum LED feedback voltage is higher than the reference voltage, the error amplification voltage is decreased, so that the duration of the low-level signal output by the comparator is decreased, so as to decrease the charging duration.

12. The LED driving circuit of claim 3, wherein, The analog-to-digital converter is configured to sample the output feedback voltage at a preset time after the PWM control signal jumps to a high-level signal, and the preset time is less than the difference between the PWM control signal pulse width and the sampling time of the analog-to-digital converter.

13. The LED driving circuit according to any one of claims 4 to 11, wherein, The LED driving circuit further comprises a minimum voltage detection module, and the LED load comprises a plurality of LED load branches in parallel. A plurality of input terminals of the minimum voltage detection module are connected to feedback terminals of a plurality of the LED load branches in one-to-one correspondence, and an output terminal of the minimum voltage detection module is connected to a fourth input terminal of the selection unit. The minimum voltage detection module is configured to receive LED feedback voltages of a plurality of the LED load branches respectively, and determine the minimum LED feedback voltage according to a plurality of the LED feedback voltages.

14. The LED driving circuit according to any one of claims 2 to 12, wherein, The voltage conversion module comprises an inductor, a diode, a control tube, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a second capacitor and a third capacitor. The input voltage is connected to the positive electrode of the diode and the second end of the control tube through the inductor, the first end of the control tube is grounded, and the control end of the control tube is connected to the output end of the control module; The negative electrode of the diode is connected to the first end of the second resistor, the first end of the fourth resistor, the first end of the fifth resistor and the input end of the LED load, the second end of the second resistor is connected to the first end of the third resistor, the second input end of the control module and the input end of the sampling module, and the second end of the third resistor is grounded; The second end of the fourth resistor is grounded through the second capacitor, and the second end of the fifth resistor is grounded through the third capacitor.

15. An LED driving chip comprising the LED driving circuit according to any one of claims 1 to 14.

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