LED Driving Circuit and Method

Abstract

Disclosed is an LED driving circuit, comprising: a power converter for converting an input voltage into a driving voltage, the driving voltage being used to drive at least one LED string connected in series therewith; a channel controller for adjusting the peak current of a corresponding LED string according to a current level signal and for turning on or off the corresponding LED string according to a pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; the peak current of the LED string changes following the change of the driving voltage; the integration period includes at least one sub-period, and each sub-period includes at least one period of the pulse width modulation signal. The present application further provides an LED driving method, which adjusts the peak current of the LED string to follow the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value and reduce power consumption.

Description

Technical Field

[0001] The present invention relates to the field of electronic technologies, and particularly to an LED driving circuit and method. Background Art

[0002] Compared with traditional light sources such as incandescent lamps and fluorescent lamps, light-emitting diodes (LEDs) have significant advantages, including high efficiency, good directivity, color stability, high reliability, long life, small size, and environmental safety.

[0003] LEDs are current-driven devices, and regulating the current passing through the LEDs is an important control technology. To drive a large array of LEDs from a direct current (DC) voltage source, a DC-DC switching power converter such as a boost-type or buck-boost type power converter is typically used to provide a supply voltage to multiple LED strings. In liquid crystal display (LCD) applications using LED backlighting, a controller needs to control multiple LED strings, and each LED string has an independent current setting, so that the brightness of different parts of the LCD can be independently controlled. In addition, the controller can turn on or off different parts of the LCD in a timed manner.

[0004] Figure 1 The schematic diagram of an LED driving circuit 100 in the prior art is shown. As Figure 1 shown, the LED driving circuit 100 in the prior art includes a power converter 101 connected between a DC input voltage Vin and multiple LED strings 102. The power converter 101 converts the input voltage Vin into a driving voltage Vdrive for driving the LED strings 102. The first end A of each LED string is connected to the driving voltage Vdrive, and the second end B is connected to a channel controller 103 for controlling the LED string. Among them, the first end of each LED string is the anode of the first LED, and the second end of each LED string is the cathode of the last LED in each LED string. Each channel controller 103 at least includes a channel switch Qm connected in series with the LED string. The channel controller 103 adjusts the current of the corresponding LED string 102 according to a current level signal Code, so as to control the illuminance output of the corresponding LED string. The channel switch Qm1 of each channel controller 103 independently controls the brightness of the corresponding LED string 102 according to a pulse width modulation signal (PWM signal).

[0005] When the PWM signal is at an effective level (for example, high level), the channel controller 103 starts to work and outputs a constant current; when the PWM signal is at an invalid level (for example, low level), the channel controller 103 stops working, and the current on the LED string is 0.

[0006] See Figure 2, when the current ILED1 on the first LED string 102 is a square wave, a periodic perturbation will be generated on the power converter 101, resulting in a low-amplitude periodic oscillation of the driving voltage Vdrive. See Figure 3 , within each period of the PWM signal, the peak current ILED of the LED string is the same, so the voltage difference VLED across the LED string remains constant, and the periodic oscillation of the driving voltage Vdrive will also cause the voltage Vk at the second end B of the LED string to oscillate periodically.

[0007] When the channel controller 103 is working, the voltage Vk at the second end B of the LED string will drop to a set value, which should be as small as possible to minimize power consumption on the premise of meeting normal operation. However, when the driving voltage Vdrive oscillates and is transmitted to the second end B of the LED string, the voltage Vk at point B may drop below the set value at the low point of the oscillation, resulting in abnormal operation of the system. To avoid the voltage Vk at point B from dropping below the set value, the set value needs to be increased. To further offset the oscillation effect of the driving voltage Vdrive, the set value will be further increased, resulting in a significant increase in power consumption. Summary of the Invention

[0008] In view of the above problems, an object of the present invention is to provide an LED driving method and circuit, which can reduce the influence of the voltage oscillation at the cathode of the LED string caused by the driving voltage oscillation and reduce power consumption at the same time.

[0009] According to a first aspect of the present invention, there is provided an LED driving circuit, including: a power converter for converting an input voltage into a driving voltage, the driving voltage being used to drive at least one LED string connected in series therewith; a channel controller for adjusting the peak current of the corresponding LED string according to a current level signal and turning on or off the corresponding LED string according to a pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; wherein, the peak current of the LED string changes following the change of the driving voltage; the first end of the LED string is connected to the driving voltage, and the second end is connected to the channel controller; the integration period includes at least one sub-period, and each sub-period includes at least one period of the pulse width modulation signal.

[0010] Preferably, the integration period includes a plurality of sub-periods, and the peak current of the LED string is different within each sub-period, and the duty cycle of the peak current is different.

[0011] Preferably, the average current of the LED string in each sub-period is the product of the peak current of the LED string and the duty cycle of the peak current in each sub-period, and the average current of the LED string within an integration period is the sum of the average currents of the LED string in a plurality of sub-periods.

[0012] Preferably, the peak current and the duty cycle of the LED string are inversely proportional within each sub-cycle. Among them, when the peak current of the LED string increases, the duty cycle for adjusting the peak current of the LED string decreases, so that the average current within the sub-cycle remains constant.

[0013] Preferably, the current level signal is a digital signal and is used to control the current level of the corresponding LED string.

[0014] Preferably, each LED string corresponds to a corresponding channel controller, and each channel controller receives a current level signal and a pulse width modulation signal to adjust the average current of the corresponding LED string.

[0015] Preferably, the LED driving circuit has only one channel controller, and multiple LED strings are all connected to the channel controller; among them, the LED driving circuit further includes a plurality of driving switches, and each driving switch is connected between the driving voltage and the corresponding LED string, and controls the conduction and cutoff of the driving switch according to a driving signal to drive or turn off the corresponding LED string.

[0016] Preferably, each sub-cycle includes a plurality of working intervals. Within one working interval, one of the plurality of driving switches is turned on to drive the corresponding LED string, and the remaining driving switches are turned off.

[0017] Preferably, within one working interval, the driving signal turns on one of the driving switches to drive the corresponding LED string, and the channel controller receives the current level signal and the pulse width modulation signal of the corresponding LED string.

[0018] Preferably, the channel controller includes a channel switch, a sampling resistor, and a channel regulator. The channel regulator includes a digital-to-analog converter, a comparator, a first switch, a second switch, and an inverter; among them, the channel switch and the sampling resistor are connected in series between the second end of the LED string and the ground terminal, and a node between the channel switch and the sampling resistor outputs a current sampling signal; the digital-to-analog converter is used to receive the current level signal and convert the current level signal into a reference voltage; the input terminal of the inverter receives the pulse width modulation signal, and the output terminal outputs a reverse pulse width modulation signal; the comparator, its first terminal receives the reference voltage, its second terminal receives the current sampling signal, and its output terminal is connected to the control terminal of the channel switch via the first switch; the control terminal of the channel switch is also connected to the ground terminal via the second switch; the control terminal of the first switch receives the pulse width modulation signal; the control terminal of the second switch receives the reverse pulse width modulation signal.

[0019] Preferably, the LED driving circuit further includes: a clamping switch, connected between the second end of the LED string and the channel switch; the control terminal of the clamping switch receives the power supply voltage.

[0020] According to another aspect of the present invention, there is provided an LED driving method, including: converting an input voltage into a driving voltage for driving at least one LED string connected in series therewith; connecting a plurality of LED strings in series between the driving voltage and a channel controller; adjusting the peak current of a corresponding LED string according to a current level signal and turning on or off the corresponding LED string according to a pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; wherein, the peak current of the LED string changes following the change of the driving voltage; the integration period includes at least one sub-period, and each sub-period includes at least one period of the pulse width modulation signal.

[0021] Preferably, the integration period includes a plurality of sub-periods, and the peak current of the LED string is different in each sub-period, and the duty cycle of the peak current is different.

[0022] Preferably, the average current of the LED string in each sub-period is the product of the peak current of the LED string and the duty cycle of the peak current in each sub-period, and the average current of the LED string within an integration period is the sum of the average currents of the LED string in a plurality of sub-periods.

[0023] Preferably, the peak current and the duty cycle of the LED string in each sub-period are inversely proportional, wherein when the peak current of the LED string becomes larger, the duty cycle of the peak current of the LED string is adjusted to be smaller so that the average current in this sub-period remains constant.

[0024] Preferably, the current level signal is a digital signal for controlling the current level of a corresponding LED string.

[0025] Preferably, connecting a plurality of LED strings in series between the driving voltage and a channel controller includes: connecting each LED string in series between the driving voltage and a corresponding channel controller respectively.

[0026] Preferably, connecting a plurality of LED strings in series between the driving voltage and a channel controller includes: connecting each LED string and a corresponding driving switch in series between the driving voltage and the same channel controller; controlling the conduction and cut-off of the driving switch according to a driving signal to drive or turn off the corresponding LED string.

[0027] Preferably, each sub-period includes a plurality of working intervals, and in one working interval, one of the plurality of driving switches is controlled to conduct to drive the corresponding LED string, and the remaining driving switches are controlled to be cut off.

[0028] Preferably, in one working interval, the average current of the corresponding LED string is adjusted according to the current level signal and the pulse width modulation signal of the LED string conducted by the driving switch.

[0029] The LED driving circuit and method provided by the present invention adjust the peak current of the corresponding LED string according to the current level signal and turn on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period. The peak current of the LED string follows the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value, reducing power consumption.

[0030] Furthermore, the duty cycle of the peak current is adjusted according to the pulse width modulation signal so that the average current of the corresponding LED string remains constant within an integration period, improving the working efficiency of the LED string and enabling precise control of the average current of the LED.

[0031] Furthermore, multiple driving switches are used to drive the LED strings in a time-sharing manner, which can reduce the number of channel controllers, reduce circuit components, reduce costs, and reduce power consumption.

[0032] Furthermore, a clamping switch is provided between the second end of the LED string and the channel switch to clamp the node voltage between the clamping switch and the channel switch to the power supply voltage, and this power supply voltage does not exceed 5V, which can prevent the channel switch from being broken down by high voltage. Description of the Drawings

[0033] Through the following description of the embodiments of the present invention with reference to the drawings, the above and other objects, features, and advantages of the present invention will become clearer. In the drawings:

[0034] Figure 1 The structural schematic diagram of the LED driving circuit in the prior art is shown;

[0035] Figure 2 The waveform schematic diagrams of the driving voltage, the current of the LED string, and the voltage at the cathode end of the LED string in the prior art are shown;

[0036] Figure 3 The waveform schematic diagram of the peak currents of multiple LED strings in the prior art is shown;

[0037] Figure 4 The schematic diagram of the LED driving circuit provided by the first embodiment of the present invention is shown;

[0038] Figure 5 The waveform schematic diagrams of the driving voltage, the current of the LED string, and the voltage at the cathode end of the LED string provided by the embodiments of the present invention are shown;

[0039] Figure 6 The waveform schematic diagram of the peak currents of multiple LED strings provided by the embodiments of the present invention is shown;

[0040] Figure 7Shows a schematic diagram of the LED driving circuit provided by the second embodiment of the present invention;

[0041] Figure 8 Shows a schematic diagram of the LED driving circuit provided by the third embodiment of the present invention;

[0042] Figure 9 Shows a flowchart of the LED driving method provided by the embodiment of the present invention. Detailed Description of the Invention

[0043] The various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the drawings, the same elements are denoted by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0044] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0045] Figure 4 Shows a schematic diagram of the LED driving circuit provided by the embodiment of the present invention. As Figure 4 shown, the LED driving circuit 100 includes a power converter 101, a channel controller 103, and a plurality of LED strings 102 connected between the power converter 101 and the channel controller 103.

[0046] Among them, the power converter 101 converts the DC input voltage Vin into a driving voltage Vdrive, and the driving voltage Vdrive is used to drive the LED string 102 connected in series therewith.

[0047] Specifically, the first end (anode end) of each LED string is connected to the driving voltage Vdrive; the second end (cathode end) is connected to the channel controller 103. Among them, the first end of each LED string is the anode of the first LED, and the second end of each LED string is the cathode of the last LED of each LED string.

[0048] The channel controller 103 adjusts the peak current Ipk of the corresponding LED string according to the current level signal Code, so that the peak current Ipk of the LED string changes with the change of the driving voltage Vdrive. The channel controller 103 also turns on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period.

[0049] In this embodiment, each LED string is serially connected with a corresponding channel controller 103. That is, the first LED string is connected between the driving voltage Vdrive and the first channel controller 1031, the second LED string is connected between the driving voltage Vdrive and the second channel controller 1032, and the m-th LED string is connected between the driving voltage Vdrive and the m-th channel controller 103m.

[0050] In this embodiment, the current level signal Code is, for example, a digital signal. When the driving voltage Vdrive oscillates periodically, the peak current Ipk of the LED string is adjusted to change following Vdrive to cancel the oscillation influence of the driving voltage Vdrive. Thus, the voltage Vk at the second end of the LED string can be kept at the lowest to reduce power consumption.

[0051] While adjusting the peak current Ipk of the LED string, the duty cycle of the peak current Ipk of the LED string is adjusted according to the pulse width modulation signal to keep the average current Iav of the LED string constant within an integration period.

[0052] The integration period includes a plurality of sub-periods. The peak current of the LED string is different within each sub-period, and the duty cycle of the peak current is also different. The peak current and the duty cycle of the LED string are inversely proportional within each sub-period. That is, when the peak current of the LED string becomes larger, the duty cycle of the peak current of the LED string is adjusted to become smaller, so that the average current within this sub-period remains constant.

[0053] See Figure 5 , taking the first LED string and the integration period as an example of the period of a pulse width modulation signal of the first LED string for illustration. Within the first period T1, the peak current of the first LED string is Ipk1, the duty cycle D1 = t1 / T1, and the average current Iav1 = Ipk1*D1 = Ipk1*t1 / T1; within the second period T2, the peak current of the first LED string is Ipk2, the duty cycle D2 = t2 / T2, and the average current Iav2 = Ipk2*D2 = Ipk2*t2 / T2; within the third period T3, the peak current of the first LED string is Ipk3, the duty cycle D3 = t3 / T3, and the average current Iav3 = Ipk3*D3 = Ipk3*t3 / T3. The first period T1, the second period T2, and the third period T3 are all the periods of the pulse width modulation signal PWM1 of the first LED string. Since Vdrive becomes smaller within the second period T2, the corresponding peak current Ipk2 becomes smaller and the duty cycle becomes larger, so that Iav1 = Iav2 = Iav3.

[0054] The integration period is, for example, the period of a pulse width modulation signal corresponding to an LED string, or the sum of the periods of the pulse width modulation signals corresponding to all LED strings, or a frame period, etc.

[0055] See Figure 6 , and taking the time-division operation of multiple LED strings as an example for illustration. The integration period includes multiple sub-periods, and each sub-period is the sum of the periods of the pulse-width modulation signals of m LED strings.

[0056] The peak current of the first LED string in the first sub-period is different from the peak current of the first LED string in the second sub-period, and the duty cycle is also different, but the average current of the first LED string remains constant within one integration period.

[0057] Wherein, the average current of the LED string in each sub-period is the product of the peak current of the LED string in each sub-period and the duty cycle of the peak current. The average current of the LED string within one integration period is the sum of the average currents of the LED string in multiple sub-periods. That is, the average current of the LED string within one integration period

[0058] See Figure 4 , the channel controller 103 includes a channel switch Qm1, a sampling resistor Rs, and a channel regulator 104. Among them, the channel switch Qm1 and the sampling resistor Rs are connected in series between the second end of each LED string and the ground terminal, and a node between the channel switch Qm1 and the sampling resistor Rs outputs a current sampling signal Vs. The channel regulator 104 adjusts the peak current of the corresponding LED string 102 according to the current level signal Code, so as to control the illuminance output of the corresponding LED string. Each channel switch Qm1 controls the brightness of the corresponding LED string 102 according to the pulse-width modulation signal.

[0059] The channel regulator 104 includes a digital-to-analog converter 1041, a comparator 1042, a first switch S1, a second switch S2, and an inverter 1043. The digital-to-analog converter 1041 is used to receive the current level signal Codem and convert the current level signal Codem into a reference voltage Vrefm; the input end of the inverter 1043 receives the pulse-width modulation signal PWMm, and the output end outputs a reverse pulse-width modulation signal PWMm-r; the first end of the comparator 1042 receives the reference voltage Vrefm, the second end receives the current sampling signal Vs, and its output end is connected to the control end of the channel switch Qm1 via the first switch S1; the control end of the channel switch Qm1 is also connected to the ground terminal via the second switch S2; the control end of the first switch S1 receives the pulse-width modulation signal PWMm; the control end of the second switch receives the reverse pulse-width modulation signal PWMm-r.

[0060] The LED driving circuit provided by the embodiment of the present invention adjusts the peak current of the corresponding LED string according to the current level signal and turns on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period. The peak current of the LED string follows the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value and reduce the power consumption.

[0061] Further, the duty cycle of the peak current is adjusted according to the pulse width modulation signal so that the average current of the corresponding LED string remains constant within an integration period, improving the working efficiency of the LED string and enabling the average current of the LED to be accurately controlled.

[0062] Figure 7 The schematic diagram of the LED driving circuit provided by the second embodiment of the present invention is shown. Compared with the first embodiment, there is only one channel controller 103 in this embodiment, and the second ends of all LED strings are connected to the same channel controller 103.

[0063] The LED driving circuit further includes a plurality of driving switches (K1-Km), which are respectively connected between the driving voltage Vdrive and the first ends of the corresponding LED strings. The driving switches are turned on and off according to the corresponding driving signals to drive the corresponding LED strings.

[0064] Specifically, the first driving switch K1 is connected between the driving voltage Vdrive and the first LED string; the second driving switch K2 is connected between the driving voltage Vdrive and the second LED string;...; the mth driving switch Km is connected between the driving voltage Vdrive and the mth LED string.

[0065] Each sub-period includes a plurality of working intervals. Within one working interval, one of the plurality of driving switches is turned on to drive the corresponding LED string, and the rest of the driving switches are turned off.

[0066] Within one working interval, the driving signal turns on one of the driving switches to drive the corresponding LED string, and the channel controller 103 receives the current level signal and the pulse width modulation signal of the corresponding LED string. For example, when the first driving switch K1 is turned on, the rest of the driving switches are turned off, and the channel controller 103 receives the current level signal Code1 and the pulse width modulation signal PWM1 of the first LED string; when the mth driving switch Km is turned on, the rest of the driving switches are turned off, and the channel controller 103 receives the current level signal Codem and the pulse width modulation signal PWMm of the mth LED string.

[0067] The rest of this embodiment is the same as that of the first embodiment and will not be described in detail here.

[0068] The LED driving circuit provided by the embodiment of the present invention adjusts the peak current of the corresponding LED string according to the current level signal and turns on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period. The peak current of the LED string follows the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value and reduce the power consumption.

[0069] Further, the duty cycle of the peak current is adjusted according to the pulse width modulation signal so that the average current of the corresponding LED string remains constant within an integration period, improving the working efficiency of the LED string and enabling the average current of the LED to be accurately controlled.

[0070] Further, multiple driving switches are used to drive the LED strings in a time-sharing manner, which can reduce the number of channel controllers, reduce circuit components, reduce costs and reduce power consumption.

[0071] Figure 8 The schematic diagram of the LED driving circuit provided by the third embodiment of the present invention is shown. Compared with the second embodiment, the channel controller 103 further includes a clamping switch Q2, which is connected between the second end of the LED string and the channel switch Q1, and its control terminal receives the power supply voltage VDD.

[0072] In this embodiment, the drain of the clamping switch Q2 is connected to the second end of the LED string, and the source is connected to the channel switch Q1, and is used to clamp its source voltage (i.e., the node voltage between the clamping switch Q2 and the channel switch Q1) to the power supply voltage VDD. Generally, the power supply voltage VDD does not exceed 5V.

[0073] When the voltage at the second end of the LED string is too high, the clamping switch Q2 can clamp the node voltage between the clamping switch Q2 and the channel switch Q1 to the power supply voltage, thereby preventing the channel switch Q1 from being broken down by high voltage.

[0074] The LED driving circuit provided by the embodiment of the present invention adjusts the peak current of the corresponding LED string according to the current level signal and turns on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period. The peak current of the LED string follows the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value and reduce the power consumption.

[0075] Further, the duty cycle of the peak current is adjusted according to the pulse width modulation signal so that the average current of the corresponding LED string remains constant within an integration period, improving the working efficiency of the LED string and enabling the average current of the LED to be accurately controlled.

[0076] Further, by using multiple driving switches to drive the LED strings in a time-sharing manner, the number of channel controllers can be reduced, the circuit components can be decreased, the cost can be lowered, and the power consumption can be reduced.

[0077] Further, a clamping switch is arranged between the second end of the LED string and the channel switch, and the node voltage between the clamping switch and the channel switch is clamped to the power supply voltage, which does not exceed 5V, so as to prevent the channel switch from being broken down by high voltage.

[0078] Figure 9 The flowchart showing the LED driving method provided by the embodiment of the present invention is shown. Refer to Figure 9 , and the LED driving method includes the following steps.

[0079] In step S01, the input voltage is converted into a driving voltage, and the driving voltage is used to drive at least one LED string connected in series therewith.

[0080] In step S02, a plurality of LED strings are connected in series between the driving voltage and the channel controller.

[0081] In this embodiment, the first end (anode end) of each LED string is connected to the driving voltage Vdrive; the second end (cathode end) is connected to the channel controller 103. Among them, the first end of each LED string is the anode of the first LED, and the second end of each LED string is the cathode of the last LED of each LED string.

[0082] In a preferred embodiment, each LED string is connected in series with a corresponding channel controller 103, that is, the first LED string is connected between the driving voltage Vdrive and the first channel controller 1031, the second LED string is connected between the driving voltage Vdrive and the second channel controller 1032, and the mth LED string is connected between the driving voltage Vdrive and the mth channel controller 103m.

[0083] In a preferred embodiment, each LED string and the corresponding driving switch are connected in series between the driving voltage Vdrive and the same channel controller; the driving or closing of the corresponding LED string is controlled according to the driving signal to control the on and off of the driving switch.

[0084] In step S03, the peak current of the corresponding LED string is adjusted according to the current level signal, and the corresponding LED string is turned on or off according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; wherein, the peak current of the LED string changes following the change of the driving voltage.

[0085] In this embodiment, the current level signal Code is, for example, a digital signal. When the driving voltage Vdrive oscillates periodically, the peak current Ipk of the LED string is adjusted to follow the change of Vdrive to cancel the oscillation effect of the driving voltage Vdrive, so that the voltage Vk at the second end of the LED string can be kept at the lowest level to reduce power consumption.

[0086] While adjusting the peak current Ipk of the LED string, the duty cycle of the peak current Ipk of the LED string is adjusted according to the pulse width modulation signal to keep the average current Iav of the LED string constant within an integration period.

[0087] The integration period includes multiple sub-periods. The peak current of the LED string is different in each sub-period, and the duty cycle of the peak current is also different. The peak current and the duty cycle of the LED string are inversely proportional in each sub-period. That is, when the peak current of the LED string becomes larger, the duty cycle of the peak current of the LED string is adjusted to become smaller, so that the average current within the sub-period remains constant.

[0088] See Figure 5 , taking the first LED string and the integration period as an example of the period of a pulse width modulation signal of the first LED string for illustration. In the first period T1, the peak current of the first LED string is Ipk1, the duty cycle D1 = t1 / T1, and the average current Iav1 = Ipk1*D1 = Ipk1*t1 / T1; in the second period T2, the peak current of the first LED string is Ipk2, the duty cycle D2 = t2 / T2, and the average current Iav2 = Ipk2*D2 = Ipk2*t2 / T2; in the third period T3, the peak current of the first LED string is Ipk3, the duty cycle D3 = t3 / T3, and the average current Iav3 = Ipk3*D3 = Ipk3*t3 / T3. The first period T1, the second period T2, and the third period T3 are all the periods of the pulse width modulation signal PWM1 of the first LED string. Since Vdrive becomes smaller in the second period T2, the corresponding peak current Ipk2 becomes smaller and the duty cycle becomes larger, so that Iav1 = Iav2 = Iav3.

[0089] The integration period is, for example, the period of the pulse width modulation signal corresponding to an LED string, or the sum of the periods of the pulse width modulation signals corresponding to all LED strings, or the frame period, etc.

[0090] See Figure 6 , taking the time-division operation of multiple LED strings as an example for illustration. The integration period includes multiple sub-periods, and each sub-period is the sum of the periods of the pulse width modulation signals of m LED strings.

[0091] The peak current of the first LED string in the first sub-period is different from that in the second sub-period, and the duty cycle is also different. However, the average current of the first LED string remains constant within an integration period.

[0092] Among them, the average current of the LED string in each sub-period is the product of the peak current of the LED string in each sub-period and the duty cycle of the peak current. The average current of the LED string within an integration period is the sum of the average currents of the LED string in multiple sub-periods. That is, the average current of the LED string within an integration period

[0093] When using multiple driving switches and a channel controller to adjust the peak current and the duty cycle of the peak current of the LED string, each sub-period includes multiple working intervals. Within one working interval, one of the multiple driving switches is controlled to conduct to drive the corresponding LED string, and the remaining driving switches are controlled to turn off. Within one working interval, the average current of the corresponding LED string is adjusted according to the current level signal and the pulse width modulation signal of the LED string conducted by the driving switch.

[0094] The LED driving method provided by the embodiments of the present invention adjusts the peak current of the corresponding LED string according to the current level signal and turns on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period. The peak current of the LED string follows the change of the driving voltage to offset the oscillation influence of the driving voltage, so as to ensure that the voltage at the second end of the LED string remains at the minimum value and reduce power consumption.

[0095] Furthermore, adjusting the duty cycle of the peak current according to the pulse width modulation signal enables the average current of the corresponding LED string to remain constant within an integration period, improves the working efficiency of the LED string, and enables the average current of the LED to be accurately controlled.

[0096] Furthermore, using multiple driving switches to drive the LED string in a time-sharing manner can reduce the number of channel controllers, reduce circuit components, and reduce costs and power consumption.

[0097] As described above in accordance with the embodiments of the present invention, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and its modified use based on the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. An LED driving circuit, characterized in that, it includes: A power converter for converting an input voltage into a driving voltage, and the driving voltage is used to drive at least one LED string connected in series therewith; A channel controller for adjusting the peak current of the corresponding LED string according to the current level signal and turning on or off the corresponding LED string according to the pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; Wherein, the peak current of the LED string changes with the change of the driving voltage; the first end of the LED string is connected to the driving voltage, and the second end is connected to the channel controller; The integration period includes a plurality of sub-periods, each sub-period includes at least one period of the pulse width modulation signal, and the peak current of the LED string is different in each sub-period, and the duty cycle of the peak current is different.

2. The LED driving circuit according to claim 1, characterized in that, The average current of the LED string in each sub-period is the product of the peak current of the LED string and the duty cycle of the peak current in each sub-period, and the average current of the LED string in an integration period is the sum of the average currents of the LED string in a plurality of sub-periods.

3. The LED driving circuit according to claim 1, characterized in that, The peak current and the duty cycle of the LED string in each sub-period are inversely proportional. Wherein, when the peak current of the LED string becomes larger, the duty cycle of the peak current of the LED string is adjusted to become smaller so that the average current in this sub-period remains constant.

4. The LED driving circuit according to claim 1, characterized in that, The current level signal is a digital signal for controlling the current level of the corresponding LED string.

5. The LED driving circuit according to claim 1, characterized in that, Each LED string corresponds to a corresponding channel controller, and each channel controller receives the current level signal and the pulse width modulation signal to adjust the average current of the corresponding LED string.

6. The LED driving circuit according to claim 1, characterized in that, The LED driving circuit has only one channel controller, and multiple LED strings are all connected to the channel controller; Wherein, the LED driving circuit further includes a plurality of driving switches, each driving switch is connected between the driving voltage and the corresponding LED string, and the conduction and cutoff of the driving switch are controlled according to the driving signal to drive or turn off the corresponding LED string.

7. The LED driving circuit according to claim 6, characterized in that, Each sub-period includes a plurality of working intervals, and in one working interval, one of the plurality of driving switches is turned on to drive the corresponding LED string, and the remaining driving switches are turned off.

8. The LED driving circuit according to claim 7, characterized in that, In one working interval, the driving signal turns on one of the driving switches to drive the corresponding LED string, and the channel controller receives the current level signal and the pulse width modulation signal of the corresponding LED string.

9. The LED driving circuit according to claim 5 or 6, characterized in that, The channel controller includes a channel switch, a sampling resistor, and a channel regulator. The channel regulator includes a digital-to-analog converter, a comparator, a first switch, a second switch, and an inverter; Wherein, the channel switch and the sampling resistor are connected in series between the second end of the LED string and the ground terminal, and a node between the channel switch and the sampling resistor outputs a current sampling signal; The digital-to-analog converter is configured to receive a current level signal and convert the current level signal into a reference voltage; The input terminal of the inverter receives a pulse width modulation signal, and the output terminal outputs an inverted pulse width modulation signal; A comparator, whose first terminal receives the reference voltage, second terminal receives the current sampling signal, and whose output terminal is connected to the control terminal of the channel switch via the first switch; The control terminal of the channel switch is also connected to the ground terminal via the second switch; The control terminal of the first switch receives the pulse width modulation signal; The control terminal of the second switch receives the inverted pulse width modulation signal.

10. The LED driving circuit according to claim 9, characterized in that, further comprising: A clamping switch connected between the second end of the LED string and the channel switch; The control terminal of the clamping switch receives a power supply voltage.

11. An LED driving method, characterized in that, comprising: Converting an input voltage into a driving voltage, the driving voltage being used to drive at least one LED string connected in series therewith; Connecting a plurality of LED strings in series between the driving voltage and the channel controller; Adjusting the peak current of the corresponding LED string according to a current level signal and turning on or off the corresponding LED string according to a pulse width modulation signal to adjust the duty cycle of the peak current so that the average current of the corresponding LED string remains constant within an integration period; Wherein, the peak current of the LED string changes following the change of the driving voltage; The integration period includes a plurality of sub-periods, each sub-period includes at least one period of the pulse width modulation signal, and the peak current of the LED string is different within each sub-period, and the duty cycle of the peak current is different.

12. The LED driving method according to claim 11, characterized in that, The average current of the LED string in each sub-period is the product of the peak current of the LED string and the duty cycle of the peak current within each sub-period, and the average current of the LED string within an integration period is the sum of the average currents of the LED string in a plurality of sub-periods.

13. The LED driving method according to claim 11, characterized in that, The peak current and the duty cycle of the LED string are inversely proportional within each sub-period. Wherein, when the peak current of the LED string becomes larger, the duty cycle of the peak current of the LED string is adjusted to become smaller so that the average current within the sub-period remains constant.

14. The LED driving method according to claim 11, characterized in that, The current level signal is a digital signal and is used to control the current level of the corresponding LED string.

15. The LED driving method according to claim 11, characterized in that, Connecting a plurality of LED strings in series between the driving voltage and the channel controller includes: Connecting each LED string in series between the driving voltage and the corresponding channel controller.

16. The LED driving method according to claim 11, characterized in that, Connecting a plurality of LED strings in series between a driving voltage and a channel controller includes: Connecting each LED string and a corresponding driving switch in series between the driving voltage and the same channel controller; Controlling the conduction and cutoff of the driving switch according to a driving signal to drive or turn off the corresponding LED string.

17. The LED driving method according to claim 16, wherein, Each sub-period includes a plurality of working intervals. In one working interval, one of the plurality of driving switches is controlled to conduct to drive the corresponding LED string, and the remaining driving switches are controlled to cutoff.

18. The LED driving method according to claim 17, wherein, In one working interval, the average current of the corresponding LED string is adjusted according to the current level signal and the pulse width modulation signal of the LED string for which the driving switch conducts.

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