Backlight driver and control method thereof

Abstract

The invention discloses a backlight driver which is used for driving a light emitting diode (LED) lamp string through a driving transistor in a load path. The LED lamp string, the driving transistor and the electric load are sequentially coupled to form a load path. The backlight driver comprises a current stabilizer and a margin detection circuit. The current stabilizer is coupled to the driving transistor and the first end of the electric load so as to control the driving current flowing through the load path at least according to the feedback voltage from the first end of the electric load. The margin detection circuit is coupled to the first end of the electric load and the voltage stabilizer so as to control the voltage stabilizer to adjust the power supply voltage of the first end of the LED lamp string at least according to the feedback voltage from the first end of the electric load.

Description

Technical Field

[0001] The invention relates to an electronic circuit, and more particularly to a backlight driver capable of reducing heat consumption and a control method thereof. Background Art

[0002] Light-emitting diode (LED) backlight module is a light source used to illuminate various display devices such as televisions, computer monitors, and smart phones. Compared with traditional backlight sources, LED backlight modules are more energy-efficient, more durable, and have a longer service life.

[0003] The LED backlight module uses a driving transistor to drive the LED light string to generate the required brightness. In the related art, the LED backlight module uses the gate voltage of the gate terminal of the driving transistor to adjust the power supply voltage of the LED light string. During operation, the gate voltage of the driving transistor is negatively correlated with the drain voltage of the driving transistor. Therefore, the LED backlight module estimates the drain voltage by monitoring the gate voltage, estimates the headroom voltage of the driving transistor based on the drain voltage, and adjusts the supply voltage based on the headroom voltage, thereby saving power and reducing heat consumption. However, since the characteristics of the driving transistor will generate differences between components due to process differences, and the operating range of the gate voltage of the driving transistor is relatively large, it is not easy to accurately estimate the headroom voltage, resulting in power waste and increased heat consumption.

[0004] In another method of LED backlight module, the LED backlight module uses the drain voltage of the drain of the driving transistor to adjust the power supply voltage of the LED light string. However, this method will increase the number of pins in the LED backlight module and increase the manufacturing cost. Summary of the invention

[0005] An embodiment of the present invention discloses a backlight driver that drives a light-emitting diode (LED) light string through a driving transistor in a load path. The LED light string, the driving transistor, and an electrical load are coupled in sequence to form a load path, the electrical load includes a first end and a second end coupled to a ground end, and the backlight driver includes a current stabilizer and a residual detection circuit. The current stabilizer is coupled to the driving transistor and the first end of the electrical load to control the driving current flowing through the load path at least based on a feedback voltage from the first end of the electrical load. The residual detection circuit is coupled to the first end of the electrical load and a voltage stabilizer to control the voltage stabilizer to adjust the supply voltage of the first end of the LED light string at least based on the feedback voltage from the first end of the electrical load.

[0006] The embodiment of the present invention discloses a control method for controlling a backlight driver to drive a light emitting diode (LED) light string through a driving transistor in a load path. The LED light string, the driving transistor and the electric load are coupled in sequence to form a load path, the electric load includes a first end and a second end coupled to a ground end, the backlight driver includes a current stabilizer and a residual detection circuit, the current stabilizer is coupled to the first end of the electric load and the driving transistor, and the residual detection circuit is coupled to the first end of the electric load and a voltage stabilizer. The method includes the current stabilizer controlling the driving current flowing through the load path at least according to a feedback voltage from the first end of the electric load, and the residual detection circuit controlling the voltage stabilizer to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electric load. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a circuit diagram of a light-emitting diode (LED) backlight module in an embodiment of the present invention.

[0008] Figure 2 Department Figure 1 Flow chart of the control method of the backlight driver.

[0009] Figure 3 Department Figure 1 The timing diagram of the LED backlight module.

[0010] Figure 4 It is a circuit diagram of another LED backlight module in an embodiment of the present invention.

[0011] The reference numerals are described as follows:

[0012] 1,4: LED backlight module

[0013] 10,40: Backlight driver

[0014] 11: Residual detection circuit

[0015] 116: First comparator

[0016] 118: Filter

[0017] 114: Second comparator

[0018] 112: margin controller

[0019] 12,42: Flow stabilizer

[0020] 122: Flow controller

[0021] 124: Voltage Generator

[0022] 126: Switch

[0023] 128: Operational Amplifier

[0024] 13: LED light string

[0025] 14: Electrical load

[0026] 15: Voltage stabilizer

[0027] 200: Control Method

[0028] S202 and S204: Steps

[0029] D1 to DN: Light Emitting Diode

[0030] Id: driving current

[0031] Id1 to Id4: Level

[0032] P1 to P5: Ports

[0033] Pb: boost pulse

[0034] Pnc, Pnn: normal pulse

[0035] R1 and R2: resistors

[0036] Sm: amplitude control signal

[0037] Sr: Adjustment signal

[0038] Sw: Width control signal

[0039] t1 to t6: time

[0040] Tframe: frame period

[0041] Td: driving transistor

[0042] Vac: AC reference voltage

[0043] Vdc: DC reference voltage

[0044] Vfb: Feedback voltage

[0045] VOUT: supply voltage

[0046] Vp: voltage pulse

[0047] Vpref: Control reference voltage

[0048] Vsync: vertical synchronization signal DETAILED DESCRIPTION

[0049] Figure 1The circuit diagram of a light-emitting diode (LED) backlight module 1 in an embodiment of the present invention is shown. The LED backlight module 1 can be used in a display device, and an LED light string can be used to illuminate the display device. Furthermore, the LED backlight module 1 can control the power supply voltage VOUT supplied to the LED light string to provide sufficient brightness, save energy and reduce heat consumption.

[0050] The LED backlight module 1 may include a backlight driver 10, an LED light string 13, a driving transistor Td, an electric load 14, a voltage regulator 15, and resistors R1 and R2. The LED light string 13, the driving transistor Td, and the electric load 14 may be coupled in sequence to form a load path. Specifically, the LED light string 13 includes a first end coupled to the voltage regulator 15; and a second end. The driving transistor Td includes a control end coupled to the backlight driver 10; a first end coupled to the second end of the LED light string 13; and a second end. The electric load 14 includes a first end coupled to the second end of the driving transistor Td; and a second end coupled to a ground end. The ground end may provide a ground voltage, such as 0V. The backlight driver 10 may be coupled to the first end of the electric load 14 and the voltage regulator 15. The LED light string 13 may include LEDD1 to LED DN coupled to each other in sequence, where N may be a positive integer greater than 1. For example, N may be 3, LED D1 to LED D3 may be coupled to each other in sequence, the anode of LED D1 is the first end of LED light string 13, and the cathode of LED D3 is the second end of LED light string 13. The driving transistor Td may be an N-type metal-oxide-semiconductor field-effect transistor (MOSFET). The electric load 14 may be a fixed resistor for sensing the feedback voltage Vfb. For example, the electric load 14 may be a 100 ohm resistor. The resistors R1 and R2 may be fixed resistors for forming a voltage divider.

[0051] During operation, the LED light string 13 can receive the power supply voltage VOUT and emit light when the driving current Id passes through it. The backlight driver 10 can adjust the power supply voltage VOUT through the voltage regulator 15, and can make the driving current Id pass through the driving transistor Td to drive the LED light string 13. The driving current Id can include multiple pulses, and the amplitude and pulse width of each pulse can be the same or different. Generally speaking, the higher the average level of the driving current Id, the brighter the brightness of the LED light string 13. When the driving current Id flows through the driving transistor Td, a voltage drop will be formed between the first end and the second end of the driving transistor Td, which is called the residual voltage. If the residual voltage is too high, power will be wasted in the driving transistor Td, causing heat consumption. If the residual voltage is insufficient, the driving transistor Td will not be able to generate enough driving current Id, resulting in insufficient brightness. Therefore, the backlight driver 10 can adjust the power supply voltage VOUT to a suitable level to ensure sufficient brightness while saving energy and reducing heat consumption.

[0052] The backlight driver 10 may be implemented as an integrated circuit and may include a current stabilizer 12, a residual detection circuit 11, and connection ports P3 to P5. The voltage stabilizer 15 may be a DC-to-DC regulator and may include connection ports P1 and P2. The current stabilizer 12 is coupled to the control end of the driving transistor Td through the connection port P4. The residual detection circuit 11 is coupled to the first end of the electric load 14 through the connection port P5, and is coupled to the voltage stabilizer 15 through the connection ports P3 and P2. The voltage stabilizer 15 may also be coupled to the first end of the LED light string 13 through the connection port P1.

[0053] The current regulator 12 may include a current regulator controller 122, a voltage generator 124, a switch 126 and an operational amplifier 128. The current regulator controller 122, the voltage generator 124 and the switch 126 may generate a voltage pulse Vp to control the pulse in the driving current Id. The operational amplifier 128 and the driving transistor Td may form a feedback loop to detect a feedback voltage Vfb.

[0054] The current regulating controller 122 can generate an amplitude control signal Sm and a width control signal Sw to control the amplitude and pulse width of the pulse respectively.

[0055] The voltage generator 124 is coupled to the current regulating controller 122 to receive the amplitude control signal Sm, controls the amplitude of the control reference voltage Vpref according to the amplitude control signal Sm, and outputs the control reference voltage Vpref. In other words, the amplitude of the control reference voltage Vpref is adjustable. In some embodiments, the amplitude control signal Sm may be a voltage signal, and the voltage generator 124 may be a voltage-controlled voltage source. In other embodiments, the amplitude control signal Sm may be a current signal, and the voltage generator 124 may be a current-controlled voltage source. The amplitude of the amplitude control signal Sm may be positively correlated with the amplitude of the control reference voltage Vpref. For example, the amplitude of the amplitude control signal Sm may be increased to increase the amplitude of the control reference voltage Vpref.

[0056] The switch 126 includes a control end coupled to the current regulating controller 122 to receive the width control signal Sw; a second end coupled to the voltage generator 124 to receive the first end of the control reference voltage Vpref and control the voltage pulse Vp according to the control reference voltage Vpref and the width control signal Sw. The switch 126 can adjust the pulse width of the voltage pulse Vp according to the width control signal Sw, and adjust the amplitude of the voltage pulse Vp according to the control reference voltage Vpref. The width control signal Sw can be a pulse width modulation (PWM) voltage. In some embodiments, the pulse width of the voltage pulse Vp can be equal to the pulse width of the width control signal Sw, and the amplitude of the voltage pulse Vp can be equal to the amplitude of the control reference voltage Vpref.

[0057] The operational amplifier 128 includes an inverting input terminal coupled to the first terminal of the electric load 14 to receive the feedback voltage Vfb; a non-inverting input terminal coupled to the second terminal of the switch 126 to receive the voltage pulse Vp; and an output terminal coupled to the control terminal of the driving transistor Td. The operational amplifier 128 can control the pulses in the driving current Id according to the feedback voltage Vfb and the voltage pulse Vp. Since the non-inverting input terminal and the inverting input terminal of the operational amplifier 128 can be regarded as virtual short circuits in a steady state, the operational amplifier 128 can adjust the control voltage of the control terminal of the driving transistor Td so that the feedback voltage Vfb matches the voltage pulse Vp. The control voltage can be negatively correlated with the voltage of the first terminal of the driving transistor Td, and positively correlated with the driving current Id. If the voltage pulse Vp significantly exceeds the feedback voltage Vfb, the operational amplifier 128 can increase the control voltage to increase the driving current Id, so that the feedback voltage Vfb increases until the feedback voltage Vfb is equal to the voltage pulse Vp. However, if the supply voltage VOUT is insufficient to provide the driving current Id in the load path, the feedback voltage Vfb will be less than the voltage pulse Vp despite the large control voltage. For example, if the supply voltage VOUT is 8.1V and the driving current Id is 1mA, the voltage drop across the LED string 13 may be 7V, the headroom voltage of the driving transistor Td may be 1V, and the feedback voltage Vfb across the electrical load 14 may be 0.1V. Since the voltage drop on the load path is 8.1V (=7+1+0.1), the voltage drop on the load path is equal to the supply voltage VOUT, and therefore the supply voltage VOUT is sufficient to provide 1 mA as the driving current Id. If the driving current Id increases from 1mA to 2mA, in an ideal case, the voltage drop across the LED light string 13 may need to be about 7V or greater than 7V (such as 7.3V), the margin voltage of the driving transistor Td may become less than or equal to 1.3V (if the power supply voltage VOUT remains unchanged, the margin voltage of the driving transistor Td will be suppressed and become smaller), and the feedback voltage Vfb across the electrical load 14 may become 0.2V or greater. However, at this time, the required voltage drop on the load path is 8.8V (=7.3+1.3+0.2), which exceeds the power supply voltage VOUT (8.8>8.1), so the power supply voltage VOUT is insufficient to provide a driving current Id of 2mA, so the driving current Id will be adjusted to between 1mA and 2mA, resulting in a feedback voltage Vfb between 0.1V and 0.2V, and a margin voltage of the driving transistor Td between 1V and 1.3V. In other words, the margin voltage is insufficient.

[0058] The margin detection circuit 11 may include a first comparator 116, a filter 118, a second comparator 114, and a margin controller 112. In some embodiments, the margin detection circuit 11 may be enabled during the adjustment period of the supply voltage VOUT, and disabled during the normal period when the supply voltage VOUT is not adjusted. The feedback voltage Vfb may include a direct current (DC) component and an alternating current (AC) component. The first comparator 116 may detect insufficient margin voltage based on the DC component in the feedback voltage Vfb. The filter 118 and the second comparator 114 may detect insufficient margin voltage based on the AC component in the feedback voltage Vfb. The margin controller 112 may control the regulator 15 to adjust the supply voltage VOUT based on the detection results of the first comparator 116 and the second comparator 114.

[0059] The first comparator 116 includes a first input terminal coupled to the first terminal of the electric load 14 to receive the feedback voltage Vfb; a second input terminal to receive the DC reference voltage Vdc, and an output terminal to output a first comparison result according to the feedback voltage Vfb and the DC reference voltage Vdc. The first input terminal of the first comparator 116 may be an inverting input terminal, and the second input terminal of the first comparator 116 may be a non-inverting input terminal. The DC reference voltage Vdc may be generated by a first voltage source and may be set to a fixed level, such as 0.2V. The first comparator 116 may compare the feedback voltage Vfb and the DC reference voltage Vdc to generate a first comparison result. In some embodiments, if the feedback voltage Vfb is less than the DC reference voltage Vdc, the first comparator 116 may set the first comparison result to a logic high level (e.g., 1.8V), indicating that insufficient headroom voltage is detected. If the feedback voltage Vfb is equal to or exceeds the DC reference voltage Vdc, the first comparator 116 may set the first comparison result to a logic low level (eg, 0V), indicating that sufficient headroom voltage is detected.

[0060] The filter 118 may be coupled to a first terminal of the electric load 14 to generate a filter voltage according to the feedback voltage Vfb. The second comparator 114 includes a first input terminal coupled to the filter 118 to receive the filter voltage; a second input terminal to receive the AC reference voltage Vac; and an output terminal to output a second comparison result according to the filter voltage and the AC reference voltage Vac. The first input terminal of the second comparator 114 may be an inverting input terminal, and the second input terminal of the second comparator 114 may be a non-inverting input terminal. The AC reference voltage Vac may be generated by a second voltage source and may be set to a fixed level equal to or different from the DC reference voltage Vdc. For example, the AC reference voltage Vac may be 0.1V. The second comparator 114 may compare the filter voltage with the AC reference voltage Vac to generate a second comparison result. In some embodiments, if the filter voltage is less than the AC reference voltage Vac, the second comparator 114 may set the second comparison result to a logic high level, indicating that insufficient headroom voltage is detected. If the filtered voltage is equal to or exceeds the AC reference voltage Vac, the second comparator 114 may set the second comparison result to a logic low level, indicating that the headroom voltage is detected to be sufficient.

[0061] The margin controller 112 may be coupled to the output terminal of the first comparator 116, the output terminal of the second comparator 114, and the regulator 15, so as to control the regulator 15 to adjust the supply voltage VOUT according to the first comparison result and the second comparison result. If the first comparison result and the second comparison result indicate that the feedback voltage Vfb is less than the DC reference voltage Vdc and / or the filter voltage is less than the AC reference voltage Vac, the margin detection circuit 11 may control the regulator 15 to increase the supply voltage VOUT. If the first comparison result and the second comparison result indicate that the feedback voltage Vfb exceeds the DC reference voltage Vdc and the filter voltage exceeds the AC reference voltage Vac, the margin detection circuit 11 may control the regulator 15 to reduce the supply voltage VOUT. In some embodiments, the margin controller 112 may include an OR gate, wherein the OR gate has a first end coupled to the output terminal of the first comparator 116 to receive the first comparison result; a second end coupled to the output terminal of the second comparator 114 to receive the second comparison result; and an output end to output a bitwise OR operation result of the first comparison result and the second comparison result. The margin controller 112 may generate an adjustment signal Sr according to the result of the bit OR operation. If the result of the bit OR operation is a logic high level, the margin controller 112 may reduce the value of the adjustment signal Sr, thereby increasing the supply voltage VOUT; if the result of the bit OR operation is a logic low level, the margin controller 112 may increase the value of the adjustment signal Sr, thereby reducing the supply voltage VOUT.

[0062] In some embodiments, the margin detection circuit 11 may omit the filter 118 and the second comparator 114, and the margin controller 112 may be coupled to the output terminal of the first comparator 116 to adjust the supply voltage VOUT according to the first comparison result. If the first comparison result indicates that the feedback voltage Vfb is less than the DC reference voltage Vdc, the margin detection circuit 11 may control the regulator 15 to increase the supply voltage VOUT. If the first comparison result indicates that the feedback voltage Vfb exceeds the DC reference voltage Vdc, the margin detection circuit 11 may control the regulator 15 to reduce the supply voltage VOUT.

[0063] Figure 2 It is a flow chart of a control method 200 of the backlight driver 10. The method 200 includes steps S202 and S204, and controls the driving current Id and the supply voltage VOUT according to the feedback voltage Vfb. Any reasonable technical changes or step adjustments belong to the scope disclosed by the present invention. Steps S202 and S204 are as follows:

[0064] Step S202: The current regulator 12 is based on at least a feedback voltage Vfb from a first terminal of the electrical load 14.

[0065] To control the driving current Id flowing through the load path;

[0066] Step S204 : The residual power detection circuit 11 controls the regulator 15 at least according to the feedback voltage Vfb from the first end of the electric load 14 , so as to adjust the supply voltage VOUT of the first end of the LED light string 13 .

[0067] In step S202, the current regulator 12 adjusts the driving current Id until the feedback voltage Vfb is equal to the voltage pulse Vp. The current regulator 12 can generate a boost pulse and a plurality of normal pulses of the driving current Id in one frame according to the amplitude control signal Sm and the width control signal Sw. Figure 3 As shown, the driving current Id may include a boost pulse and a plurality of normal pulses in a frame to achieve efficient margin voltage control. Figure 3An explanation will be provided in subsequent paragraphs. Multiple normal pulses may have equal amplitudes and equal pulse widths. The amplitude of the boost pulse may exceed the amplitude of the normal pulse, and the pulse width of the boost pulse may be less than the amplitude of the normal pulse. The product of the amplitude and pulse width of the boost pulse in the drive current may be equal to the product of the amplitude and pulse width of the normal pulse. The current regulator 12 may adjust the amplitude of the normal pulse and the amplitude of the boost pulse according to the amplitude control signal Sm, and adjust the pulse width of the normal pulse and the pulse width of the boost pulse according to the width control signal Sw. In this way, the current regulator 12 controls the generation of the boost pulse and the normal pulse in the drive current Id to reduce screen flicker and enhance the user experience. In some embodiments, the current regulator 12 may adjust the amplitude of the normal pulse and the amplitude of the boost pulse according to the amplitude control signal Sm and the feedback voltage Vfb, and adjust the pulse width of the normal pulse and the pulse width of the boost pulse according to the width control signal Sw and the feedback voltage Vfb.

[0068] In step S204, if the feedback voltage Vfb is less than the DC reference voltage Vdc and / or the filter voltage is less than the AC reference voltage Vac, the margin detection circuit 11 controls the regulator 15 to increase the supply voltage VOUT; if the feedback voltage Vfb exceeds the DC reference voltage Vdc and the filter voltage exceeds the AC reference voltage Vac, the margin detection circuit 11 controls the regulator 15 to reduce the supply voltage VOUT. In this way, the margin detection circuit 11 can control the regulator 15 to adjust the supply voltage VOUT.

[0069] The LED backlight module 1 adopts method 200 to simultaneously control the driving current Id and the power supply voltage VOUT according to the feedback voltage Vfb. Compared with the traditional method of adjusting the power supply voltage according to the drain voltage of the driving transistor, the LED backlight module 1 can save the number of pins and reduce the manufacturing cost of the backlight driver 10. Compared with the traditional method of using the gate voltage of the driving transistor to estimate the margin voltage to adjust the power supply voltage, the LED backlight module 1 can use the feedback voltage Vfb to adjust the power supply voltage VOUT. Since the feedback voltage Vfb directly reflects the driving current Id, the LED backlight module 1 can accurately adjust the power supply voltage, thereby accurately adjusting the driving current Id to the required level, achieving efficient energy saving and heat dissipation. In addition, the current stabilizer 12 uses a boost pulse in the driving current Id to reduce screen flicker and enhance user experience, while achieving effective margin voltage control.

[0070] Figure 3It is a timing diagram of the LED backlight module 1, wherein the horizontal axis represents time, and the vertical axis represents the voltage of the vertical synchronization signal Vsync, the conventional driving current Id without a boost pulse, and the driving current Id of the present case with a boost pulse. The vertical synchronization signal Vsync indicates the start of the image frame, and the time interval between the corresponding edges (e.g., rising edges) of two consecutive pulses in the vertical synchronization signal Vsync is called the frame period Tframe. For example, the rising edges of the two consecutive pulses appear at time t0 and time t6, respectively, so the time interval between time t0 and time t6 is called the frame period Tframe. The dashed waveforms in the conventional driving current Id and the driving current Id of the present case represent the waveforms using the unregulated power supply VOUT, and the solid waveforms in the conventional driving current Id and the driving current Id of the present case represent the waveforms using the regulated power supply VOUT. The conventional driving current Id includes normal pulses Pnc with equal amplitude and pulse width. The driving current Id of the present case includes a boost pulse Pb (e.g., between time t1 and time t2) and multiple normal pulses Pnn (e.g., between time t4 and time t5). In an example, the driving current Id in this embodiment includes 1 boost pulse Pb and 1000 normal pulses Pnn in a frame period Tframe.

[0071] For the conventional driving current Id, the supply voltage VOUT can be adjusted during each normal pulse Pnc. Therefore, the time interval between time t1 and time t6 can be called an adjustment period. Figure 3 As shown, the conventional driving current Id decreases from level Id1 to level Id2 during the regulation period. Figure 1 and Figure 3 Since the feedback loop in the LED backlight module 1 has sufficient gain, the feedback voltage Vfb will not have insufficient margin voltage. Therefore, the margin detection circuit 11 continues to reduce the supply voltage VOUT until the voltage at the first end of the voltage driving transistor Td is less than the minimum margin voltage of the driving transistor Td. The minimum margin voltage is a voltage that causes the driving current Id to drop from the ideal value by a predetermined percentage. For example, if the ideal value of the driving current Id is 1mA and the predetermined percentage is 1%, the minimum margin voltage is a voltage that causes the driving current Id to drop from the ideal value to 0.99mA. Therefore, when insufficient margin voltage is detected, the traditional driving current Id may be too low, causing the LED light string 13 to be unable to generate the required brightness, thereby causing the screen to flicker. Further, when the margin detection circuit 11 detects insufficient margin, the supply voltage VOUT can be increased through the regulator 15, but due to the slow feedback response of the regulator 15 and the lengthy recovery time, the brightness is insufficient for a long time, thereby reducing the user experience.

[0072] For the driving current Id of the present case, the supply voltage VOUT can be adjusted during the boost pulse Pb period rather than during the normal pulse Pnn period. Therefore, the time interval between time t1 and time t4 can be called the adjustment period, and the time interval between time t4 and time t6 can be called the normal period. In the present embodiment, the driving current Id of the present case decreases from level Id3 to level Id4 during the adjustment period. Therefore, since the product of the amplitude and pulse width of the boost pulse Pb is equal to the product of the amplitude and pulse width of the normal pulse Pnn, for the unregulated supply voltage VOUT (the dotted waveform in the driving current Id of the present case), the boost pulse Pb and the normal pulse Pnn in the driving current Id of the present case can generate a constant average level within the frame period Tframe. Therefore, although the driving current Id of the present case decreases from level Id3 to level Id4 during the boost pulse Pb period, since the number of boost pulses Pb (=1) is significantly less than the number of normal pulses Pnn (=1000), the human eye can hardly perceive the brightness reduction, thereby reducing screen flicker and improving user experience.

[0073] Although the driving current Id in this embodiment only includes one boost pulse Pb, the present invention is not limited thereto, and those skilled in the art should understand that the driving current Id in this embodiment may include more than one boost pulse Pb to meet design requirements.

[0074] Figure 4 This is a circuit diagram of another LED backlight module 4 in an embodiment of the present invention. The difference between the LED backlight module 4 and the LED backlight module 1 is that the current stabilizer 12 in the backlight driver 10 is replaced by the current stabilizer 42 in the backlight driver 40. The other components in the LED backlight module 4 are similar to those in the LED backlight module 1, and their descriptions can be found in the previous text, which will not be repeated here. The following discussion will focus on the current stabilizer 42.

[0075] The current regulator 42 may include a current regulator controller 122, a voltage generator 124, a switch 126, and an operational amplifier 128. The current regulator controller 122, the voltage generator 124, the operational amplifier 128, and the switch 126 may generate a voltage pulse Vp to change the pulse in the driving current Id. The operational amplifier 128 and the driving transistor Td may form a feedback loop to detect a feedback voltage Vfb.

[0076] The operational amplifier 128 comprises an inverting input terminal coupled to the first terminal of the electric load 14 to receive the feedback voltage Vfb, a non-inverting input terminal coupled to the voltage generator 124 to receive the control reference voltage Vpref, and an output terminal for generating a driving voltage according to the feedback voltage Vfb and the control reference voltage Vpref.

[0077] The switch 126 includes a control end coupled to the current regulating controller 122 to receive the width control signal Sw; a first end coupled to the voltage generator 124 to receive the driving voltage; and a second end coupled to the control end of the driving transistor Td to generate a voltage pulse Vp according to the driving voltage and the width control signal Sw, and control the pulse in the driving current Id according to the voltage pulse Vp.

[0078] The arrangement of other components in the flow stabilizer 42 and the operation of the flow stabilizer 42 may be similar to those of the flow stabilizer 12 , and the description thereof may refer to the foregoing text, which will not be repeated here for the sake of brevity.

[0079] Similar to the LED backlight module 1, the LED backlight module 4 can use the method 200 to simultaneously control the driving current Id and the supply voltage VOUT according to the feedback voltage Vfb. Compared with the conventional method of adjusting the supply voltage VOUT according to the drain voltage of the driving transistor Td, the backlight driver 40 can save the number of pins and reduce the manufacturing cost. In addition, the current regulator 42 uses a boost pulse in the driving current Id to reduce screen flicker and enhance the user experience, while achieving effective margin voltage control.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A backlight driver, driving a light-emitting diode (LED) lamp string through a driving transistor in a load path, wherein the LED lamp string, the driving transistor and an electric load are coupled in sequence to form the load path, wherein the electric load comprises a first terminal and a second terminal coupled to a ground terminal, wherein: The backlight driver comprises: a current stabilizer coupled to the driving transistor and the first end of the electric load to control a driving current flowing through the load path according to at least a feedback voltage from the first end of the electric load; and A margin detection circuit is coupled to the first end of the electrical load and a regulator to control the regulator to adjust a supply voltage of a first end of the LED light string at least according to the feedback voltage from the first end of the electrical load.

2. The backlight driver according to claim 1, wherein: The current stabilizer generates a boost pulse and multiple normal pulses of the driving current in a signal frame, wherein an amplitude of the boost pulse exceeds an amplitude of each of the multiple normal pulses, and a pulse width of the boost pulse is smaller than a pulse width of each of the multiple normal pulses.

3. The backlight driver according to claim 2, wherein: A product of the amplitude and the pulse width of the boost pulse is equal to a product of the amplitude and the pulse width of each normal pulse.

4. The backlight driver according to claim 1, wherein: The driving transistor comprises a control end, a first end coupled to a second end of the LED light string, and a second end coupled to the first end of the electrical load; and The current stabilizer comprises: A constant current controller for generating an amplitude control signal and a width control signal; a voltage generator coupled to the current regulating controller to control an amplitude of a control reference voltage according to the amplitude control signal and output the control reference voltage; a switch, comprising a control terminal coupled to the current regulating controller to receive the width control signal; a first terminal coupled to the voltage generator to receive the control reference voltage; and a second terminal generating a voltage pulse according to the control reference voltage and the width control signal; and an operational amplifier having an inverting input terminal coupled to the first terminal of the electrical load to receive the feedback voltage; and a non-inverting input terminal coupled to the second terminal of the switch to receive the voltage pulse; and an output terminal coupled to the control terminal of the driving transistor to control a pulse in the driving current according to the feedback voltage and the voltage pulse.

5. The backlight driver according to claim 1, wherein: The driving transistor comprises a control end, a first end coupled to a second end of the LED light string, and a second end coupled to the first end of the electrical load; and The current stabilizer comprises: A constant current controller for generating an amplitude control signal and a width control signal; a voltage generator coupled to the current regulating controller to control an amplitude of a control reference voltage according to the amplitude control signal and output the control reference voltage; an operational amplifier having an inverting input terminal coupled to the first terminal of the electric load to receive the feedback voltage; a non-inverting input terminal coupled to the voltage generator to receive the control reference voltage; and an output terminal for generating a driving voltage according to the feedback voltage and the control reference voltage; and A switch, comprising a control terminal coupled to the current regulating controller to receive the width control signal; a first terminal coupled to the voltage generator to receive the driving voltage; and a second terminal coupled to the control terminal of the driving transistor to generate a voltage pulse according to the driving voltage and the width control signal, and to control a pulse in the driving current according to the voltage pulse.

6. The backlight driver according to claim 1, wherein: The residual detection circuit comprises: a first comparator, comprising a first input terminal coupled to the first terminal of the electric load to receive the feedback voltage; a second input terminal to receive a direct current (DC) reference voltage; and an output terminal to output a first comparison result according to the feedback voltage and the DC reference voltage; a filter coupled to the first end of the electric load to generate a filtered voltage according to the feedback voltage; a second comparator, comprising a first input terminal coupled to the filter to receive the filter voltage; a second input terminal to receive an alternating current (AC) reference voltage; and an output terminal to output a second comparison result according to the filter voltage and the AC reference voltage; and A margin controller is coupled to the output terminal of the first comparator, the output terminal of the second comparator and the voltage regulator to control the voltage regulator to adjust the supply voltage according to the first comparison result and the second comparison result.

7. The backlight driver according to claim 6, wherein: If the first comparison result and the second comparison result indicate that the feedback voltage is less than the DC reference voltage and / or the filter voltage is less than the AC reference voltage, the margin detection circuit controls the regulator to increase the supply voltage.

8. The backlight driver according to claim 6, wherein: If the first comparison result and the second comparison result indicate that the feedback voltage exceeds the DC reference voltage and the filter voltage exceeds the AC reference voltage, the margin detection circuit controls the regulator to reduce the supply voltage.

9. The backlight driver according to claim 1, wherein: The residual detection circuit comprises: The first comparator comprises a first input terminal coupled to the first terminal of the electric load to receive the feedback voltage; a second input terminal to receive a DC reference voltage; and an output terminal, outputting a first comparison result according to the feedback voltage and the DC reference voltage; A margin controller is coupled to the output terminal of the first comparator and the voltage regulator to control the voltage regulator to adjust the supply voltage according to the first comparison result.

10. The backlight driver according to claim 9, wherein: If the first comparison result indicates that the feedback voltage is less than the DC reference voltage, the margin detection circuit controls the regulator to increase the supply voltage.

11. The backlight driver according to claim 9, wherein: If the first comparison result indicates that the feedback voltage exceeds the DC reference voltage, the margin detection circuit controls the regulator to reduce the supply voltage.

12. A control method for controlling a backlight driver to drive a light emitting diode (LED) lamp string through a driving transistor in a load path, wherein the LED lamp string, the driving transistor and the electric load are coupled in sequence to form the load path, and the electric load comprises a first terminal, and a second end coupled to a ground end, the backlight driver comprising a current stabilizer and a residual detection circuit, the current stabilizer coupled to the first end of the electric load and the driving transistor, the residual detection circuit coupled to the first end of the electric load and a voltage stabilizer, characterized in that: The method comprises: The current regulator controls a driving current flowing through the load path according to at least a feedback voltage from the first end of the electrical load; and The residual power detection circuit controls the voltage regulator to adjust a supply voltage of a first end of the LED light string at least according to the feedback voltage from the first end of the electric load.

13. The method according to claim 12, characterized in that: The current regulator controls the driving current flowing through the load path according to at least the feedback voltage from the first end of the electric load, including: The current stabilizer adjusts an amplitude of a boost pulse in the driving current according to an amplitude control signal and the feedback voltage; and The current stabilizer adjusts a pulse width of the boost pulse according to a width control signal and the feedback voltage; The method further includes filtering the feedback voltage by the margin detection circuit to generate a filtered voltage; and The residual power detection circuit controls the voltage regulator to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electrical load, including: The margin detection circuit controls the voltage regulator to adjust the supply voltage at least according to the feedback voltage and the filter voltage.

14. The method according to claim 13, characterized in that The residual power detection circuit controls the voltage regulator to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electrical load, including: If the feedback voltage is less than a DC reference voltage and / or the filter voltage is less than an AC reference voltage, the margin detection circuit controls the regulator to increase the supply voltage.

15. The method according to claim 13, characterized in that The residual power detection circuit controls the voltage regulator to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electrical load, including: If the feedback voltage exceeds a DC reference voltage and the filter voltage exceeds an AC reference voltage, the margin detection circuit controls the regulator to reduce the supply voltage.

16. The method according to claim 13, characterized in that A product of the amplitude and the pulse width in the boost pulse is equal to a product of an amplitude and a pulse width of a normal pulse in the driving current.

17. The method according to claim 13, characterized in that The driving current includes a boost pulse and a plurality of normal pulses in one frame.

18. The method according to claim 12, characterized in that The current regulator controls the driving current flowing through the load path according to at least the feedback voltage from the first end of the electric load, including: The current stabilizer adjusts an amplitude of a boost pulse in the driving current according to an amplitude control signal and the feedback voltage; and The current regulator adjusts a pulse width of the boost pulse according to a width control signal and the feedback voltage.

19. The method according to claim 18, characterized in that The residual power detection circuit controls the voltage regulator to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electric load, including: If the feedback voltage is less than a DC reference voltage, the margin detection circuit controls the regulator to increase the supply voltage.

20. The method of claim 18, wherein: The residual power detection circuit controls the voltage regulator to adjust the supply voltage of the first end of the LED light string at least according to the feedback voltage from the first end of the electric load, including: If the feedback voltage exceeds a DC reference voltage, the margin detection circuit controls the regulator to reduce the supply voltage.

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