LED backlight control circuit

Abstract

An LED backlight control circuit is provided, which is configured to, in a case that the LED backlight control circuit is in a high-frequency dimming state under control of a low-frequency dimming signal and a high-frequency dimming signal or in a high-low-frequency hybrid dimming state under control of a high-low-frequency hybrid dimming signal: generate a dimming synchronization signal based on the low-frequency dimming signal and the high-frequency dimming signal or based on the high-low-frequency hybrid dimming signal; generate a system clock enable signal based on a period count of a system clock signal or based on an output voltage representation signal representing a system output voltage of the LED backlight control circuit; generate a dimming clock signal based on the system clock signal and the system clock enable signal; and generate an on control signal for controlling a switch tube in the LED backlight control circuit to change from an off state to an on state based on the dimming synchronization signal and the dimming clock signal.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to an LED backlight control circuit. Background Technology

[0002] Currently, LED backlight switching power supplies used in light-emitting diode (LED) display devices can meet the requirements of low-frequency pulse width dimming (e.g., within the 100Hz to 10kHz frequency range) and analog dimming. As people place higher demands on the image clarity, contrast, and system energy efficiency of LED display devices, the technical requirements for LED backlight switching power supplies are also increasing. However, traditional LED backlight switching power supplies can only meet the requirements of low-frequency, high-precision dimming. When applied to LED display devices with higher display requirements, such as high-frequency or high-low frequency mixed dimming at frequencies of tens or even hundreds of kHz, voltage drops in the LED lamps under the control of the high-frequency or high-low frequency mixed dimming signal may occur, leading to abnormal lamp current. This results in the inability to meet the requirements of high-precision dimming and high contrast for LED backlighting. Summary of the Invention

[0003] According to an embodiment of the present invention, an LED backlight control circuit is configured to, under the control of a low-frequency dimming signal and a high-frequency dimming signal, be in a high-frequency dimming state, or under the control of a high-low-frequency mixed dimming signal, be in a high-low-frequency mixed dimming state: generating a dimming synchronization signal based on the low-frequency dimming signal and the high-frequency dimming signal, or based on the high-low-frequency mixed dimming signal; generating a system clock enable signal based on a cycle count of a system clock signal, or based on an output voltage characterization signal characterizing the system output voltage of the LED backlight control circuit; generating a dimming clock signal based on the system clock signal and the system clock enable signal; and generating a turn-on control signal based on the dimming synchronization signal and the dimming clock signal to control the switching transistor in the LED backlight control circuit to change from an off state to a turn-on state. Attached Figure Description

[0004] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0005] Figure 1 A schematic diagram of the logic structure of a traditional LED backlight control circuit for single-channel constant current control is shown.

[0006] Figure 2 A schematic diagram of the logic structure of a traditional LED backlight control circuit for multi-channel constant current control is shown.

[0007] Figure 3 and Figure 4 It shows Figure 1 or Figure 2The waveform diagrams of multiple signals in the LED backlight control circuit are shown.

[0008] Figure 5 A schematic diagram of the logic structure of an LED backlight control circuit according to an embodiment of the present invention is shown.

[0009] Figure 6 and Figure 7 It shows Figure 5 The waveform diagrams of multiple signals in the LED backlight control circuit are shown.

[0010] Figure 8 A schematic diagram of the logic structure of another LED backlight control circuit according to an embodiment of the present invention is shown.

[0011] Figure 9 It shows Figure 8 The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Detailed Implementation

[0012] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configuration and algorithm presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention. Furthermore, it should be noted that the term "A connected to B" as used herein can mean "A and B are directly connected" or "A and B are indirectly connected via one or more other elements."

[0013] Figure 1 A schematic diagram of the logic structure of a traditional LED backlight control circuit for single-channel constant current control is shown. (For example...) Figure 1As shown, under the control of at least one of the high-frequency dimming signal HPWM, low-frequency dimming signal LPWM, and high-low frequency mixed dimming signal LHPWM provided by the video control processor of the LED display device, the LED backlight control circuit 100 is in any one of the following states: non-dimming state, high-frequency dimming state, low-frequency dimming state, and high-low frequency mixed dimming state. When the high-frequency dimming signal HPWM, the low-frequency dimming signal LPWM, and the high-low frequency mixed dimming signal LHPWM are all at a high level, the switch Q2 and the switch S1 remain in the on state, and the LED backlight control circuit 100 is in the non-dimming state. When the high-frequency dimming signal HPWM switches between high and low levels, the low-frequency dimming signal LPWM is at a high level, and there is no high-low frequency mixed dimming signal LHPWM, the switch Q2 and the switch S1 switch with the high-frequency dimming signal HPWM switching between high and low levels. Instead, the LED backlight control circuit 100 switches between the on and off states, and is in a high-frequency dimming state. When the high-frequency dimming signal HPWM is high, the low-frequency dimming signal LPWM switches between high and low levels, and there is no high-low frequency mixed dimming signal LHPWM, the switching transistor Q2 and the switch S1 switch between the on and off states as the low-frequency dimming signal LPWM switches between high and low levels, and the LED backlight control circuit 100 is in a low-frequency dimming state. When the high-low frequency mixed dimming signal LHPWM switches between high and low levels, and there is no high-frequency dimming signal HPWM or low-frequency dimming signal LPWM, the switching transistor Q2 and the switch S1 switch between the on and off states as the high-low frequency mixed dimming signal LHPWM switches between high and low levels, and the LED backlight control circuit 100 is in a high-low frequency mixed dimming state. It should be noted that the LED backlight control circuit 100 can be integrated with the video control processor of the LED display device or can be independent of the video control processor.

[0014] like Figure 1As shown, when the LED backlight control circuit 100 is in a non-dimming state or a high-frequency or high-low-frequency mixed dimming state: when the switching transistor Q1 is in the on state, the DC input voltage Vin charges the output inductor L1 and the output capacitor Cout; when the switching transistor Q1 is in the off state, the energy stored in the output inductor L1 and the energy stored in the output capacitor Cout simultaneously power the LED string; when the system output voltage Vout exceeds the predetermined output voltage, a lamp current iLED begins to flow through the LED string; as the system output voltage Vout gradually increases, the lamp current iLED gradually increases; the lamp current iLED generates a lamp current characterization signal FB on the constant current setting resistor Rset; resistor Rf An RC filter composed of capacitor Cf filters the lamp current characterization signal FB to generate a filtered lamp current characterization signal FBf; the transconductance amplifier U1, based on the filtered lamp current characterization signal FBf and the constant current control reference voltage Vref1, generates a lamp current deviation characterization signal Vcomp, which represents the deviation between the lamp current iLED and the preset lamp current iLED_ref, through loop compensation of compensation resistor Rcomp1 and compensation capacitor Ccomp1; the voltage detection and proportional current conversion module generates an inductor magnetization characterization current Icsp based on the current sensing signal Vcs generated by the input current i1 flowing through the output inductor L when the switch Q1 is in the on state and the current sensing resistor Rs; the clock generation... The generation module generates a system clock signal Clk and a maximum duty cycle characterization signal Max_duty based on the PWM switching control signal used to control the on and off of the switching transistor Q1. The continuous conduction mode (CCM) subharmonic compensation module generates a subharmonic compensation current Icomp based on the system clock signal Clk and the maximum duty cycle characterization signal Max_duty. The inductor magnetization characterization current Icsp and the subharmonic compensation current Icomp are superimposed on the current sensing resistor Rsense to generate a current sensing signal Vsense. Comparator 1 generates a lamp current deviation characterization signal Vcomp by comparing the current sensing signal Vsense. The turn-off control signal Tri_off is used to control the switching transistor Q1 from the on state to the off state; the dimming synchronization signal generation module generates the dimming synchronization signal Syn_dim based on the high-frequency dimming signal HPWM and the low-frequency dimming signal LPWM or based on the high-low frequency mixed dimming signal LHPWM; the logic AND gate generates the dimming clock signal Clk_r by performing a logical AND operation on the system clock signal Clk and the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM; the logic OR gate generates the turn-on control signal Tri_on used to control the switching transistor Q1 from the off state to the on state by performing a logical OR operation on the dimming synchronization signal Syn_dim and the dimming clock signal Clk_r.The switching control logic module generates the PWM switching control signal by performing logical operations on the turn-off control signal Tri_off and the turn-on control signal Tri_on.

[0015] like Figure 1 As shown, during the period when the LED backlight control circuit 100 is in the non-dimming state, the lamp current iLED flowing through the LED string is maintained at the preset lamp current iLED_ref, which can be represented by the following equation (1).

[0016] (Equation 1)

[0017] like Figure 1 As shown, during the period when the LED backlight control circuit 100 is in the high-frequency or high-low frequency mixed dimming state, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is at a high level, the lamp current iLED flowing through the LED string is the preset lamp current iLED_ref, and when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is at a low level, the lamp current iLED flowing through the LED string is 0. That is, during the period when the LED backlight control circuit 100 is in the high-frequency or high-low frequency mixed dimming state, the lamp current iLED_dim flowing through the LED string can be represented by the following equation (2), where D is the duty cycle of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM.

[0018] (Equation 2)

[0019] Figure 2 This diagram illustrates the logic structure of a traditional LED backlight control circuit for multi-channel constant current control. Combined with... Figure 1 and Figure 2It can be seen that the difference between LED backlight control circuit 200 and LED backlight control circuit 100 lies in the addition of a constant current control module and a minimum value module. Specifically, the constant current control module is configured to, for any LED string LEDn among multiple LED strings LED1 to LEDX (X is an integer greater than or equal to 2), achieve adaptive constant current control of the lamp current iLEDn based on the lamp current characterization signal CC_FB generated on the constant current setting resistor Rset and the constant current control reference voltage Cc_vref. The minimum value module is configured to, based on the characterization signal iLEDn, achieve adaptive constant current control of the lamp current iLEDn. The voltage difference characterization signal VLED1 to VLEDX, representing the voltage difference across each LED string (LED1 to LEDX), generates a minimum difference characterization signal VLED_min. This allows the transconductance amplifier U1, based on the minimum difference characterization signal VLED_min and the constant current control reference voltage Vref2, to generate a lamp current deviation characterization signal Vcomp, representing the deviation between the lamp currents iLED1 to iLEDX flowing through the LED strings LED1 to LEDX and the preset lamp current iLED_ref, through loop compensation via compensation resistor Rcomp1 and compensation capacitor Ccomp1. It should be noted that, assuming the on-state voltage of each LED is equal, the lamp currents iLED1 to iLEDX are typically also equal.

[0020] Figure 3 It shows Figure 1 or Figure 2 The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Figure 3 As shown, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM switches between high and low levels and the high-level duration is relatively long, the number of PWM pulses used to control the on / off state of the switching transistor Q1 during each high-level period of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is relatively large. Therefore, the system output voltage Vout can be effectively regulated during the high-level period of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM, fluctuating around the preset output voltage with a small amplitude. The lamp current deviation characterization signal Vcomp will not open-loop, and the lamp current iLED flowing through the LED string conforms to the theoretical calculation value of Equation 2. Therefore, high-precision dimming of the LED string can be achieved. It should be noted that for... Figure 2 The LED backlight control circuit 200 shown here, iLED represents the lamp current flowing through any one of the LED strings LED1 to LEDX.

[0021] Figure 4 It shows Figure 1 or Figure 2The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Figure 4 As shown, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM switches between high and low levels and the duration of the high level is short, the dimming clock signal Clk_r, which enables the output of the switch control signal PWM, only has one or two pulses during each high-level period. Therefore, the number of pulses of the switch control signal PWM, which controls the on and off of the switch Q1, is also only one or two. Moreover, the duty cycle of the switch control signal PWM is very large, and the demagnetization time of the output inductor L1 in each switching cycle of the switch Q1 is very short. This causes the system output voltage Vout to be unable to obtain more energy within 1 to 2 switching cycles of the switch Q1, thus continuously decreasing. The lamp current deviation characterization signal Vcomp continuously increases and eventually opens the loop. The lamp current iLED flowing through the LED string is much smaller than the theoretical calculated value in Equation 2, thus triggering the system open-loop protection and causing the dimming of the LED string to fail. It should be noted that for Figure 2 The LED backlight control circuit 200 shown here, iLED represents the lamp current flowing through any one of the LED strings LED1 to LEDX.

[0022] In view of the above, an LED backlight control circuit according to an embodiment of the present invention is proposed, configured to be in a high-frequency dimming state under the control of a low-frequency dimming signal and a high-frequency dimming signal, or in a high-low frequency mixed dimming state under the control of a high-low frequency mixed dimming signal: generating a dimming synchronization signal based on the low-frequency dimming signal and the high-frequency dimming signal or based on the high-low frequency mixed dimming signal; generating a system clock enable signal based on the cycle count of the system clock signal or based on an output voltage characterization signal characterizing the system output voltage of the LED backlight control circuit; generating a dimming clock signal based on the system clock signal and the system clock enable signal; and generating a turn-on control signal based on the dimming synchronization signal and the dimming clock signal for controlling the switching transistor in the LED backlight control circuit to change from an off state to a turn-on state.

[0023] According to embodiments of the present invention, when the LED backlight control circuit is in a high-frequency or high-low-frequency mixed dimming state, it generates a system clock enable signal based on a cycle count of the system clock signal or an output voltage characterization signal characterizing the system output voltage of the LED backlight control circuit. Based on the system clock enable signal, it generates a turn-on control signal to control the switching transistors in the LED backlight control circuit from an off state to a turn-on state. This allows control over the number of cycles of the switching control signal output when the high-frequency or high-low-frequency mixed dimming signal is low, thus solving the problem of combining... Figure 1and Figure 2 The problem of dimming failure caused by system open-loop operation when the LED backlight control circuit is in a high-frequency or high-low frequency mixed dimming state.

[0024] It should be understood that the LED backlight control circuit according to embodiments of the present invention can be implemented as an LED backlight control circuit for single-channel constant current control, or it can be implemented as an LED backlight control circuit for multi-channel constant current control. When the LED backlight control circuit according to embodiments of the present invention is implemented as an LED backlight control circuit for single-channel constant current control, it can employ a method similar to... Figure 1 The logic structure shown can be similar when implemented as a multi-channel constant current control LED backlight control circuit. Figure 2 The logical structure shown.

[0025] Figure 5 A schematic diagram of the logic structure of an LED backlight control circuit according to an embodiment of the present invention is shown. (Combined with...) Figure 1 / 2 and Figure 5 It can be seen that the difference between the LED backlight control circuit 500 and the LED backlight control circuits 100 / 200 lies in the addition of a dimming signal pulse width / frequency detection module 502 and a high-frequency dimming enhancement module 504. Specifically, the dimming signal pulse width / frequency detection module 502 is configured to generate a dimming enhancement enable signal EN1 based on the pulse width or frequency of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM. The high-frequency dimming enhancement module 504 is configured to generate a system clock enable signal Clock_EN based on the cycle count of the system clock signal clk when the dimming enhancement enable signal EN1 is in the dimming enhancement enabled state, after the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from low to high or from high to low. In this case, a logic AND gate generates a dimming clock signal Clk_r by performing a logical AND operation on the system clock signal Clk and the system clock enable signal Clock_EN.

[0026] like Figure 5 As shown, in some embodiments, when the pulse width of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is less than a predetermined duration or the frequency is greater than a predetermined frequency, the dimming enhancement enable signal EN1 changes from a dimming enhancement disabled state to a dimming enhancement enabled state (e.g., from a low level to a high level).

[0027] like Figure 5As shown, in some embodiments, the high-frequency dimming enhancement module 504 can be configured to generate a cycle count control signal P_min based on the cycle count of the system clock signal Clk, which is used to control the number of cycles of the switching control signal PWM that controls the on and off of the switching transistor Q1 when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is at a low level, and to generate a system clock enable signal Clock_EN based on the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM and the cycle count control signal P_min.

[0028] like Figure 5 As shown, in some embodiments, the high-frequency dimming enhancement module 504 includes a multi-cycle counting unit and a logic OR gate, wherein: the multi-cycle counting unit is configured to generate a cycle number control signal P_min by performing a multi-cycle count of N (N is an integer greater than or equal to 2) cycles on the system clock signal Clk after the high-frequency dimming signal HPWM changes from a low level to a high level or from a high level to a low level when the dimming enhancement enable signal EN1 is in the dimming enhancement enabled state; the logic OR gate is configured to generate a system clock enable signal Clock_EN by performing a logical OR operation on the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM and the cycle number control signal P_min. In this scenario, if the pulse width of the high-frequency or high-low frequency mixed dimming signal HWPM / LHPWM is less than the pulse width of the cycle number control signal P_min, then the system clock enable signal Clock_EN is equal to the cycle number control signal P_min; if the pulse width of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is greater than the pulse width of the cycle number control signal P_min, then the system clock enable signal Clock_EN is equal to the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM. When the system clock enable signal Clock_EN is high, the dimming clock signal Clk_r is equal to the system clock signal clk; when the system clock enable signal Clock_EN is low, the dimming clock signal Clk_r is low.

[0029] Figure 6 It shows Figure 5 The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Figure 6As shown, the high-frequency dimming enhancement module 504 generates a cycle count control signal P_min by starting multi-cycle counting of the system clock signal Clk when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from low to high. In this case, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from low to high, the system clock enable signal Clock_EN changes from low to high; and when the cycle count of the system clock signal Clk reaches a predetermined number, the system clock enable signal Clock_EN changes from high to low.

[0030] Figure 7 It shows Figure 5 The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Figure 7 As shown, the high-frequency dimming enhancement module 504 generates a cycle count control signal P_min by starting multi-cycle counting of the system clock signal Clk when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from a high level to a low level. In this case, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from a high level to a low level, the cycle count control signal P_min changes from a low level to a high level; and when the cycle count of the system clock signal Clk reaches a predetermined number, the clock count control signal P_min changes from a high level to a low level.

[0031] from Figure 6 and Figure 7 It can be seen that when the pulse width of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is less than the predetermined duration or the frequency is greater than the predetermined frequency (i.e., during the period when the dimming enhancement enable signal EN1 is at a high level), regardless of whether the pulse width of the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is wide or narrow, the switching control signal PWM for N (N≥1) cycles will be output when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is at a low level. This ensures that the system output voltage Vout will not drop much during the period when the LED backlight control circuit 500 is in the high-frequency or high-low frequency mixed dimming state, thereby keeping the lamp current deviation characterization signal Vcomp in a closed-loop adjustment state. Therefore, high-precision dimming of LED strings can be achieved.

[0032] Figure 8 A schematic diagram of the logic structure of another LED backlight control circuit according to an embodiment of the present invention is shown. (In conjunction with...) Figure 1 / 2 and Figure 8It can be seen that the difference between the LED backlight control circuit 800 and the LED backlight control circuits 100 / 200 lies in the addition of a high-frequency dimming enhancement module 802 and a voltage divider network 804. Specifically, the voltage divider network 804 is configured to generate an output voltage characterization signal VFBO by dividing the system output voltage Vout. The high-frequency dimming enhancement module 802 is configured to generate a system clock enable signal Clock_EN1 based on the comparison relationship between the output voltage characterization signal VFBO, the first voltage threshold Vth1, and the second voltage threshold Vth2 after the LED backlight control system 800 enters the high-frequency or high-low frequency mixed dimming state and the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM changes from low to high for the first time. In this case, a logic AND gate generates a dimming clock signal Clk_r by performing a logical AND operation on the system clock signal Clk and the system clock enable signal Clock_EN1.

[0033] like Figure 8 As shown, in some embodiments, the high-frequency dimming enhancement module 802 is configured to generate a first comparison result signal OP1 based on the comparison relationship between the output voltage characterization signal VFBO and the first voltage threshold Vth1; generate a second comparison result signal OP2 based on the comparison relationship between the output voltage characterization signal VFBO and the second voltage threshold Vth2; after the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM enters a state of switching between high and low levels and changes from low level to high level for the first time, generate an output voltage judgment signal OVJ based on the first comparison result signal OP1 and the second comparison result signal OP2; and generate a system clock enable signal Clock_EN1 based on the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM and the output voltage judgment signal OVJ.

[0034] like Figure 8As shown, in some embodiments, the high-frequency dimming enhancement module 802 includes a comparator 2, a comparator 3, threshold judgment control logic, and an OR gate, wherein: the comparator 2 is configured to generate a first comparison result signal OP1 by comparing the output voltage characterization signal VFBO with a first voltage threshold Vth1; the comparator 3 is configured to generate a second comparison result signal OP2 by comparing the output voltage characterization signal VFBO with a second voltage threshold Vth2; the threshold judgment control logic is configured to generate an output voltage judgment signal OVJ by performing a logical operation on the first comparison result signal OP1 and the second comparison result signal OP2 after the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM enters a state switching between high and low levels and changes from low level to high level for the first time; the OR gate is configured to generate a system clock enable signal Clock_EN1 by performing a logical OR operation on the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM and the output voltage judgment signal OVJ.

[0035] Figure 9 It shows Figure 8 The waveform diagrams of multiple signals in the LED backlight control circuit are shown. Figure 9 As shown, when the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM enters a state of switching between high and low levels and changes from low to high for the first time, the output voltage judgment signal OVJ changes from low to high, and the system clock enable signal Clock_EN1 changes from low to high; when the output voltage characterization signal VFBO is higher than the second voltage threshold Vth2, the output voltage judgment signal OVJ changes from high to low, and the system clock enable signal Clock_EN1 changes from high to low; when the output voltage characterization signal VFBO is lower than the first voltage threshold Vth1, the output voltage judgment signal OVJ changes from high to low. When J changes from low to high, the system clock enable signal Clock_EN1 changes from low to high. When the output voltage judgment signal OVJ is high but the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is low, the system clock enable signal Clock_EN1 is high, and the switch control signal PWM switches between high and low levels. When the output voltage judgment signal OVJ is low and the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM is low, the system clock enable signal Clock_EN1 is low, and the switch control signal PWM is continuously low.

[0036] from Figure 9It can be seen that regardless of whether the high-frequency or high-low frequency mixed dimming signal HPWM / LHPWM has a high duty cycle or a low duty cycle, the system output voltage Vout can be maintained at a high voltage level through the above control method. Therefore, it can be ensured that the lamp current flowing through the LED string always remains between the preset lamp current iLED_ref or 0 when in the high-frequency or high-low frequency mixed dimming state, thereby achieving high-precision dimming of the LED string in the high-frequency or high-low frequency mixed dimming state.

[0037] It should be understood that the LED backlight control circuit according to the embodiments of the present invention can be applied not only to boost backlight system topologies, but also to various backlight system topologies including buck, buck-boost, flyback, forward, and asymmetric half-bridge (AHB).

[0038] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. An LED backlight control circuit, configured to be in a high-frequency dimming state under the control of a low-frequency dimming signal and a high-frequency dimming signal, or in a high-low frequency mixed dimming state under the control of a high-low frequency mixed dimming signal: A dimming synchronization signal is generated based on the low-frequency dimming signal and the high-frequency dimming signal or based on the high-low frequency mixed dimming signal; A system clock enable signal is generated based on the cycle count of the system clock signal or based on the output voltage characterization signal that characterizes the system output voltage of the LED backlight control circuit. A dimming clock signal is generated based on the system clock signal and the system clock enable signal; as well as Based on the dimming synchronization signal and the dimming clock signal, a turn-on control signal is generated to control the switching transistor in the LED backlight control circuit to change from the off state to the on state. The generation of the system clock enable signal based on the cycle count of the system clock signal includes: generating a dimming enhancement enable signal based on the pulse width or frequency of the high-frequency dimming signal or the high-low frequency mixed dimming signal; when the dimming enhancement enable signal is in the dimming enhancement enabled state, generating a cycle count control signal based on the cycle count of the system clock signal to control the number of cycles of the switch control signal output when the high-frequency dimming signal or the high-low frequency mixed dimming signal is at a low level, which is used to control the on and off of the switch transistor; and generating the system clock enable signal based on the high-frequency dimming signal or the high-low frequency mixed dimming signal and the cycle count control signal, wherein when the high-frequency dimming signal or the high-low frequency mixed dimming signal changes from a low level to a high level or from a high level to a low level, the cycle count control signal changes from a low level to a high level, and when the cycle count of the system clock signal reaches a predetermined number, the cycle count control signal changes from a high level to a low level.

2. The LED backlight control circuit according to claim 1, wherein, The LED backlight control circuit is in a non-dimming state under the control of the low-frequency dimming signal, the high-frequency dimming signal, and the high-low frequency mixed dimming signal, or in a low-frequency dimming state or a high-frequency dimming state under the control of the low-frequency dimming signal and the high-frequency dimming signal, wherein: When the high-frequency dimming signal, the low-frequency dimming signal, and the high-low frequency mixed dimming signal are all at a high level, the LED backlight control circuit is in the non-dimming state. When the high-frequency dimming signal is at a high level and the low-frequency dimming signal switches between high and low levels, the LED backlight control circuit is in the low-frequency dimming state; and When the high-frequency dimming signal switches between high and low levels and the low-frequency dimming signal is at a high level, the LED backlight control circuit is in the high-frequency dimming state.

3. The LED backlight control circuit according to claim 1 is further configured as follows: After the high-frequency dimming signal or the high-low frequency mixed dimming signal changes from low level to high level or from high level to low level, the system clock enable signal is generated based on the period count of the system clock signal.

4. The LED backlight control circuit according to claim 1 is further configured as follows: The system clock enable signal is generated by performing a logical OR operation on the high-frequency dimming signal or the high-low frequency mixed dimming signal and the cycle number control signal.

5. The LED backlight control circuit according to claim 1, wherein, Generating the system clock enable signal based on the output voltage characterization signal includes: After the LED backlight control system enters the high-frequency dimming state or the high-low frequency mixed dimming state, and after the high-frequency dimming signal or the high-low frequency mixed dimming signal changes from low level to high level for the first time, the system clock enable signal is generated based on the comparison relationship between the output voltage characterization signal, the first voltage threshold, and the second voltage threshold.

6. The LED backlight control circuit according to claim 5 is further configured as follows: A first comparison result signal is generated based on the comparison relationship between the output voltage characterization signal and the first voltage threshold; A second comparison result signal is generated based on the comparison relationship between the output voltage characterization signal and the second voltage threshold; An output voltage judgment signal is generated based on the first comparison result signal and the second comparison result signal; as well as The system clock enable signal is generated based on the high-frequency dimming signal or the high-low frequency mixed dimming signal and the output voltage judgment signal.

7. The LED backlight control circuit according to claim 6 is further configured as follows: The system clock enable signal is generated by performing a logical OR operation on the high-frequency dimming signal or the high-low frequency mixed dimming signal and the output voltage judgment signal.

8. The LED backlight control circuit according to claim 5, wherein: When the output voltage characterization signal is lower than the first voltage threshold, the system clock enable signal changes from low to high; and When the output voltage characterization signal is higher than the second voltage threshold, the system clock enable signal changes from high level to low level.

9. The LED backlight control circuit according to claim 8, wherein: When the high-frequency dimming signal or the high-low frequency mixed dimming signal changes from low level to high level for the first time after the LED backlight control system enters the high-frequency dimming state or the high-low frequency mixed dimming state, the system clock enable signal changes from low level to high level.

10. The LED backlight control circuit according to claim 1, further configured as follows: The dimming clock signal is generated by performing a logical AND operation on the system clock signal and the system clock enable signal.

11. The LED backlight control circuit according to claim 1, further configured as follows: The conduction control signal is generated by performing a logical OR operation on the dimming synchronization signal and the dimming clock signal.

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