LED display-oriented adaptive PWM backlight control method and backlight driving system

Abstract

The invention relates to the technical field of backlight control, in particular to an LED display-oriented adaptive PWM backlight control method and a backlight driving system, which are suitable for the backlight driving system comprising a boost converter, a brightness controller and an LED channel, and the method comprises the following steps: the brightness controller outputs a control voltage, a peak current control word and a duty ratio signal, and receives a state signal. Receiving brightness data, determining a nominal peak current and a duty ratio, and initializing the nominal peak current and the duty ratio; adjusting the control voltage to change the boost output, monitoring the state, locking the working point when all states are converted from the first state to the second state, and taking the final switching channel as a reference; a peak current word is increased for the non-reference channel under the working point, and when the state returns to the first state from the second state, an optimized peak current is taken back; and adjusting the duty ratio according to the ratio of the nominal peak current to the optimized peak current to enable the average current of each channel to be consistent. According to the invention, the problem that excessive voltage drop of a linear current regulator causes extra power consumption and heating and influences the brightness consistency between channels is solved.

Description

Technical Field

[0001] This invention relates to the field of backlight control technology, and in particular to an adaptive PWM backlight control method and backlight driving system for LED displays. Background Technology

[0002] LED displays on light poles are outdoor direct-view applications, typically composed of several display units / modules. Each module contains multiple light-emitting channels and needs to maintain consistent brightness and reliability under high brightness, wide temperature range, and long-term operation conditions. To achieve grayscale and brightness adjustment, a "constant current drive + PWM / time duty cycle control" driving method is commonly used in engineering. In the power supply and drive implementation of some light pole displays, to account for differences in forward voltage drops across different LED chains, cable voltage drops, temperature drift, and aging, the drive system is equipped with an adjustable power supply (such as a boost / adjustable output stage) to supply power to multiple channels, and a linear current regulator is used on the channel side for precise current control. Because the forward voltage drops of different LED chains are discrete, to ensure that the worst-performing channel still has sufficient voltage margin, the power supply output often reserves a higher voltage for the worst-performing channel. This causes the linear current regulators of other channels to bear additional voltage drops, generating excess power consumption and heat, resulting in decreased overall energy efficiency and affecting long-term outdoor reliability. Summary of the Invention

[0003] In view of the above technical problems, the present invention provides an adaptive PWM backlight control method and backlight driving system for LED displays. It aims to solve the problem that in the multi-channel driving of LED pole screen LED displays, the voltage requirements of each channel are inconsistent due to factors such as LED chain forward voltage drop dispersion, temperature / aging drift and cable voltage drop. This causes the power supply output to be set according to the worst channel, resulting in excessive voltage drop of some channel linear current regulators and causing additional power consumption and heat generation, while also affecting the brightness consistency between channels.

[0004] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part from practice of this disclosure.

[0005] According to one aspect of the present invention, an adaptive PWM backlight control method for LED displays is proposed, applied to a backlight driving system including a boost converter, a brightness controller, and several LED channels; the brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives a status signal for each of the LED channels, the status signal indicating whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state; the method includes: Receive brightness setting data, determine the nominal peak current setting value and the nominal duty cycle setting value, and initialize the peak current control word and the duty cycle control signal of each LED channel accordingly; The control voltage is adjusted to gradually change the output voltage of the boost converter, while monitoring each of the status signals; when all the status signals switch from the first state to the second state, the adjustment of the control voltage is stopped to lock the operating point, and the LED channel that last switched is determined as the reference channel. At the operating point, the peak current control word is increased by a preset step for each LED channel other than the reference channel to increase the peak current and the status signal of the LED channel is monitored; when the status signal switches from the second state back to the first state, the peak current control word is rolled back to the set value before the switching occurs to obtain the optimized peak current setting value of the LED channel; Duty cycle compensation is performed on each of the LED channels: the nominal duty cycle setting value is proportionally adjusted according to the ratio of the nominal peak current setting value to the corresponding optimized peak current setting value to obtain the target duty cycle, and the duty cycle control signal is updated accordingly to keep the average current of each of the LED channels consistent.

[0006] Furthermore, each of the LED channels is sequentially connected in series with an LED chain, a switching MOS transistor driven by the duty cycle control signal, and the linear current regulator. The output voltage of the boost converter is configured to cover the sum of the forward voltage drop of the LED chain, the on-state voltage drop of the switching MOS transistor, and the voltage drop of the linear current regulator. The operating point corresponds to a boundary state where the voltage drop of the linear current regulator of the reference channel is close to the minimum voltage margin, thereby limiting the minimum output voltage of the boost converter by the reference channel.

[0007] Furthermore, the brightness controller includes a resistive digital-to-analog converter, which outputs the control voltage according to the brightness setting data; the gradual adjustment of the control voltage includes: changing the control voltage in a discrete code step manner and using it as a feedback reference for the boost converter, so that the output voltage of the boost converter changes monotonically with the control voltage until each of the state signals completes the switch from the first state to the second state.

[0008] Furthermore, the reference channel is the LED channel that last switched from the first state to the second state, and the nominal peak current setting value of the reference channel remains unchanged; each non-reference channel is executed sequentially according to the preset channel order, and for any non-reference channel, the peak current control word is continuously increased and the peak current is synchronously increased while its state signal remains in the second state; when its state signal switches from the second state back to the first state, a rollback is performed and the peak current adaptive optimization of the non-reference channel ends; wherein, the peak current adaptive optimization increases the LED chain operating current of the non-reference channel to increase the forward voltage drop of the LED chain, thereby reducing the extra part of the voltage drop of the linear current regulator of the non-reference channel.

[0009] Furthermore, the target duty cycle is obtained according to the following rules: Based on the nominal duty cycle setting value, the target duty cycle is obtained by multiplying the nominal duty cycle setting value by the ratio of the nominal peak current setting value to the corresponding optimized peak current setting value; when the target duty cycle exceeds the allowable duty cycle range, the target duty cycle is limited to the allowable duty cycle range, and the duty cycle control signal is output based on the limited target duty cycle.

[0010] Furthermore, the peak current control word is a multi-bit control word, which, after decoding, controls the number of current mirror branches in the linear current regulator that are turned on. The peak current output by the linear current regulator is determined by the reference current, the preset current mirror magnification, and the number of current mirror branches that are turned on. Each current mirror branch includes a mirror transistor and a corresponding switching unit. The switching unit is used to switch between the common gate voltage and the off potential of the gate of the mirror transistor to enable or disable the current mirror branch independently.

[0011] Furthermore, the linear current regulator includes an output transistor for regulating the channel current and a comparator for generating the status signal. The comparator compares the control node voltage of the output transistor with a reference voltage. When the control node voltage crosses the reference voltage, the status signal switches between a first state and a second state to characterize whether the voltage margin of the linear current regulator crosses the preset threshold. The operating point is determined by the moment when the status signal switches from the first state to the second state, and the back-off moment of the peak current control word is determined by the moment when the status signal switches back from the second state to the first state.

[0012] Furthermore, the linear current regulator employs a current mirror structure and includes a reference transistor, multiple mirror transistors, a first operational amplifier, and a second operational amplifier. The second operational amplifier and the reference transistor form negative feedback to make the source-drain voltage of the reference transistor equal to the adjustable reference voltage, thereby controlling the operating regions of the reference transistor and the mirror transistors by adjusting the adjustable reference voltage. The first operational amplifier is used to keep the source-drain voltages of the reference transistor and each of the mirror transistors consistent to improve the accuracy of the current mirror. The adjustable reference voltage is set to keep the reference transistor and the mirror transistors in a low-dropout linear operating region to reduce current mismatch caused by device parameter drift and further reduce the voltage drop of the linear current regulator.

[0013] Furthermore, the method also includes: A soft start is performed on the boost converter, causing its output voltage to rise to an initial voltage level that enables each LED channel to enter a conduction state. After the soft start is completed, the brightness controller adjusts the control voltage in a monotonically discrete stepwise manner, causing the output voltage of the boost converter to decrease until all the status signals switch from the first state to the second state and lock the operating point.

[0014] According to another aspect of the present invention, a backlight driving system is provided, including a boost converter, a brightness controller, and a plurality of LED channels; the brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives a status signal of each of the LED channels, the status signal being used to indicate whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state; the brightness controller is used to execute the adaptive PWM backlight control method for LED displays as described above.

[0015] The technical solution of the present invention has the following beneficial effects: This invention addresses multi-channel driving scenarios for LED displays on light poles. By utilizing the voltage margin status signal of the linear current regulator for each channel, it adaptively determines the lowest available operating point of the power supply output. At this operating point, it performs adaptive optimization of the peak current for non-reference channels. Simultaneously, it incorporates PWM duty cycle compensation to minimize the additional voltage drop of the linear current regulator while maintaining consistent average current and brightness across all channels. This reduces channel power consumption and heat generation, improves system energy efficiency, and enhances the reliability and consistency of long-term outdoor operation. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating an adaptive PWM backlight control method for LED displays, as described in the embodiments of this specification. Figure 2 This is a schematic diagram of the backlight driver in the embodiments of this specification; Figure 3 This is a schematic diagram of the linear current regulator in the embodiments of this specification. Detailed Implementation

[0017] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, systems, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0018] Furthermore, the accompanying drawings are merely illustrative of this disclosure. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor systems and / or microcontroller systems.

[0019] This invention provides an adaptive PWM backlight control method for LED displays. (Refer to...) Figure 1 The diagram shown is a flowchart illustrating an adaptive PWM backlight control method for LED displays provided in an embodiment of the present invention. This method is applied to applications such as... Figure 2The illustrated backlight driving system includes a boost converter, a brightness controller, and several LED channels. The brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives status signals from each LED channel. These status signals indicate whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state. Specifically, after brightness data is input into the brightness controller, the controller outputs a control voltage VC as a feedback reference for the boost converter, causing the output voltage of the boost converter to change with VC and providing a common boost voltage for each channel. Simultaneously, the controller outputs PWMn and a peak current control word CM_SWn to each channel. PWMn drives the switching MOS transistor MPn within the channel to achieve PWM dimming, and CM_SWn is used to set the peak current of the channel's linear current regulator. Each LED channel can be connected in series between the boost voltage and ground in the order of LED chain, switching MOS transistor MPn, and linear current regulator LCR. The boost voltage covers the combined requirements of the LED chain forward voltage drop, MPn on-state voltage drop, and LCR voltage drop. Each channel can also output a status signal SENSEn to the brightness controller to reflect the voltage margin status of the channel linear current regulator, thereby providing a criterion for subsequent operating point locking and adaptive optimization.

[0020] like Figure 3 As shown, the linear current regulator can employ a current mirror structure to achieve programmable peak current and low voltage drop regulation. The reference branch consists of a negative feedback loop formed by reference transistor M0 and operational amplifier OP2. OP2 compares the reference voltage VREF and adjusts the control node Vcon to make the reference branch current form the reference current IREF, while simultaneously determining the operating region of the reference transistor. Operational amplifier OP1 is used to adjust the common gate node VG, ensuring that the source-drain voltage of reference branch node A matches that of mirror branch node D, thereby improving mirror accuracy and suppressing current deviations caused by device mismatch. The mirror branch consists of multiple mirror transistors M1, M2…MN. The decoder receives CM_SW and controls the number of enabled branches for each mirror branch, causing the output current to vary with the number of enabled branches, thus achieving digitally adjustable peak current. The output provides linear voltage drop regulation between the power supply and the mirror network through the regulating transistor MR. The comparator COMP compares the detected voltage VSENSE with the comparison reference VCOM and generates a status signal to indicate whether the MR regulation margin crosses the threshold, ensuring constant current output while minimizing the operating voltage drop and channel loss of the LCR.

[0021] The method performed may specifically include the following steps S101~S104: In step S101, brightness setting data is received, nominal peak current setting value and nominal duty cycle setting value are determined, and the peak current control word and duty cycle control signal of each LED channel are initialized accordingly.

[0022] Continue as Figure 2 As shown, each of the LED channels is connected in series with an LED chain, a switching MOS transistor driven by the duty cycle control signal, and a linear current regulator, and the output voltage of the boost converter is configured to cover the sum of the forward voltage drop of the LED chain, the on-state voltage drop of the switching MOS transistor, and the voltage drop of the linear current regulator.

[0023] After the brightness data is input into the brightness controller, the nominal peak current setting value Iset and the nominal duty cycle setting value δset are loaded into the brightness controller. Based on Iset, the output current of the linear current regulator of each channel is set to the corresponding nominal level through the CM_SW signal. At the same time, the PWM signal of each channel is initialized based on δset to form the duty cycle control start point. The brightness controller may include a 9-bit resistive digital-to-analog converter to generate a control voltage VC. VC is used as a voltage reference to determine the output voltage Vboost of the boost converter. At the same time, the brightness controller can monitor the status signal SENSE of each channel and generate control quantities such as VC, PWM and CM_SW according to a predetermined process, so that each channel enters a high-efficiency working preparation state that can be subsequently adaptively adjusted.

[0024] Continue to combine Figure 2 Each LED channel can adopt a series power path structure. The LED chain, the PWM-driven high-voltage MOS switch MP, and the linear current regulator LCR are connected sequentially between the boost output and ground. Vboost provides a common power supply for each channel and covers the superposition requirements of the LED chain forward voltage drop, the MOS switch on-state voltage drop, and the linear current regulator voltage drop. Taking channel n as an example, the voltage relationship is satisfied. ; in, This is the sum of the voltages across the LED chain or the forward voltage drops of each LED. This refers to the source-drain voltage of the high-voltage MOS switch MP. To reduce the voltage drop of the linear current regulator, the initialization of CM_SWn and PWMn is completed in stage S101, so that the above series path has a clear basis for current setting and duty cycle setting under nominal settings, providing a consistent starting condition for subsequent gradual adjustment of Vboost and channel adaptive optimization.

[0025] In step S102, the control voltage is adjusted to gradually change the output voltage of the boost converter, while monitoring each of the status signals; when all the status signals switch from the first state to the second state, the adjustment of the control voltage is stopped to lock the operating point, and the LED channel that last switched is determined as the reference channel.

[0026] Initially, a soft start is performed on the boost converter, causing its output voltage to rise to an initial voltage level sufficient to enable each LED channel to conduct. After the soft start, the brightness controller adjusts the control voltage in a monotonically stepped manner, causing the boost converter's output voltage to decrease until all state signals switch from the first state to the second state and lock the operating point. The operating point corresponds to a boundary state where the voltage drop of the linear current regulator of the reference channel is close to the minimum voltage margin, thereby limiting the minimum output voltage of the boost converter by the reference channel.

[0027] The brightness controller includes a resistive digital-to-analog converter (DAC), which outputs a control voltage based on the brightness setting data. The gradual adjustment of the control voltage includes: changing the control voltage in a discrete code step manner and using it as a feedback reference for the boost converter, causing the output voltage of the boost converter to change monotonically with the control voltage until each of the state signals completes the switch from the first state to the second state. The reference channel is the LED channel where the last switch from the first state to the second state occurs, and the nominal peak current setting value of the reference channel remains unchanged.

[0028] As an explanation, the boost converter enters a soft-start process, where the output voltage gradually rises to the initial voltage level, enabling each channel to conduct and enter a stable and controllable state. After the soft start, the brightness controller performs monotonic discrete step-wise adjustment of the control voltage VC. VC serves as the feedback reference quantity for the boost converter, causing the boost output voltage Vboost to change monotonically with VC and gradually converge in a decreasing direction. Simultaneously, the status signal SENSE of each channel is continuously sampled and evaluated. For any channel n, Vboost and the channel voltage distribution satisfy the above conditions. As Vboost decreases in discrete code steps, some channels... As the current gradually approaches the minimum margin range required to maintain constant current regulation, the status signal changes accordingly. When it is detected that all channels have switched from the first state to the second state, the stepping of VC stops and the current VC remains unchanged to lock the operating point at this moment. The channel that last completed the state switch is determined as the reference channel. This reference channel is in a boundary state, and its linear current regulator voltage drop is close to the minimum voltage margin. Therefore, this channel limits the minimum output voltage of Vboost. The nominal peak current setting corresponding to the reference channel remains unchanged to ensure the stability of the boundary reference.

[0029] The linear current regulator includes an output transistor for regulating the channel current and a comparator for generating the status signal. The comparator compares the control node voltage of the output transistor with a reference voltage. When the control node voltage crosses the reference voltage, the status signal switches between a first state and a second state to characterize whether the voltage margin of the linear current regulator crosses the preset threshold. The operating point is determined by the moment when the status signal switches from the first state to the second state, and the back-off moment of the peak current control word is determined by the moment when the status signal switches back from the second state to the first state.

[0030] Specifically, the linear current regulator employs a current mirror structure and includes a reference transistor, multiple mirror transistors, a first operational amplifier, and a second operational amplifier. The second operational amplifier and the reference transistor form negative feedback to make the source-drain voltage of the reference transistor equal to the adjustable reference voltage, thereby controlling the operating regions of the reference transistor and the mirror transistors by adjusting the adjustable reference voltage. The first operational amplifier is used to keep the source-drain voltage of the reference transistor and each of the mirror transistors consistent to improve the accuracy of the current mirror. Furthermore, the adjustable reference voltage is set to keep the reference transistor and the mirror transistors in a low-dropout linear operating region to reduce current mismatch caused by device parameter drift and further reduce the voltage drop of the linear current regulator.

[0031] As an explanation, the generation of the status signal can be achieved by a comparator inside the linear current regulator. The linear current regulator includes an output transistor MR for regulating the channel current and a comparator COMP, with COMP using a fixed comparison reference. Gate control voltage of MR Perform status monitoring: When Vboost is high and still provides sufficient voltage after deducting the LED chain voltage drop. When MR is in the effective regulation region, the channel current can reach or maintain the set value, and SENSE remains in a stable state; when Vboost continues to decrease or the channel current increases, causing an increase in the forward voltage drop of the LED chain, As the current decreases, an increase is needed to maintain a constant current. Provide compensation, if Cross The comparator output flips, and SENSE completes the switch from the first state to the second state, indicating that the voltage margin has exceeded the threshold and is approaching the boundary where the set current cannot be maintained. In the characterization of the voltage drop of a linear current regulator, the channel voltage drop can be decomposed into the minimum required portion and the excess portion: ; in Used to ensure that the linear current regulator regulates properly and maintains the accuracy of the output current. This represents the additional voltage drop corresponding to the excess margin. The channel loss can be written as: ; in Determined by peak current and current duty cycle; when the MOS on-resistance is sufficiently low, excessive losses are mainly caused by... Caused, which is defined as: ; By locking the operating point at the boundary state of the reference channel, Vboost can be reduced and suppressed while satisfying the requirements of dimmable and constant current regulation for each channel. The formation of this structure provides a low-loss power supply reference for subsequent channel-level adaptive optimization. In the implementation of the linear current regulator, a current mirror structure can be adopted, consisting of a reference transistor M0, multiple mirror transistors M1…MN, and two operational amplifier stages. The second operational amplifier forms negative feedback with the reference branch, making the source-drain voltage of the reference transistor equal to the adjustable reference voltage and constraining the operating region accordingly. The first operational amplifier is used to ensure that the source-drain voltages of the reference branch and the mirror branch are consistent to improve the accuracy of the current mirror, and to set the adjustable reference voltage in the low-dropout linear region to reduce mismatch and voltage drop. The number of mirror branches turned on is determined by the control word, and the channel current satisfies: ; Where N is the number of activated mirror transistors, and B is the mirror ratio. The reference current serves as the basis for the circuitry for the determination of state signals and the formation of boundary operating points, and provides a consistent detection interface for the subsequent determination of backoff time.

[0032] In step S103, at the operating point, the peak current control word is increased by a preset step for each LED channel other than the reference channel to increase the peak current and the status signal of the LED channel is monitored; when the status signal switches from the second state back to the first state, the peak current control word is rolled back to the set value before the switching occurs to obtain the optimized peak current setting value of the LED channel.

[0033] Furthermore, step S103 is executed sequentially for each non-reference channel according to a preset channel order, and for any non-reference channel, while its state signal remains in the second state, the peak current control word is continuously increased and the peak current is synchronously increased. When its state signal switches from the second state back to the first state, a rollback is performed and the peak current adaptive optimization of the non-reference channel is terminated. The peak current adaptive optimization increases the forward voltage drop of the LED chain by increasing the LED chain operating current of the non-reference channel, thereby reducing the extra part of the voltage drop of the linear current regulator of the non-reference channel.

[0034] After the operating point is locked, the reference channel retains its original peak current setting and does not participate in the adjustment. Peak current adaptive optimization is performed sequentially on each non-reference channel according to the preset channel order. The brightness controller attempts to increase the channel current of the current non-reference channel by writing a new peak current control word CM_SW. If the status signal SENSE of the channel remains in the second state, the current increase action continues. When it is detected that SENSE has switched from the second state back to the first state, the brightness controller rolls back the peak current control word to the previous setting value before the switch occurred and ends the adjustment process of the channel, so that the channel obtains a new peak current setting. Then, it enters the next non-reference channel and performs the same process.

[0035] The peak current control word can boost the channel peak current by changing the number of enabled branches in the current mirror. The decoder determines the number N of activated mirror transistors based on CM_SW, thereby changing the output current of the linear current regulator. The output current forms the channel peak current, and the relationship is as follows: ; Where B is the mirror magnification. For the reference current, N is determined by CM_SW. Increasing the peak current will increase the LED chain operating current and lead to an increase in the LED chain forward voltage drop, as well as the linear current regulator voltage drop. The corresponding decrease; while the output transistor MR remains active, the channel current remains set, and the status signal remains in the second state. To further reduce MR into the deep linear region, the gate voltage needs to be increased. Provide compensation when Exceeding the benchmark When the comparator output flips, SENSE switches back to the first state, indicating that the boundary condition of being unable to maintain the set current has been approached. Therefore, at this switching point, CM_SW is rolled back to the previous setting, which can fix the peak current at the maximum available setting that does not trigger the boundary, forming the optimized peak current setting value for this non-reference channel.

[0036] In step S104, duty cycle compensation is performed on each of the LED channels: the nominal duty cycle setting value is proportionally adjusted according to the ratio of the nominal peak current setting value to the corresponding optimized peak current setting value to obtain the target duty cycle, and the duty cycle control signal is updated accordingly to keep the average current of each of the LED channels consistent.

[0037] The target duty cycle is obtained according to the following rules: based on the nominal duty cycle setting value, the target duty cycle is obtained by multiplying the nominal duty cycle setting value by the ratio of the nominal peak current setting value and the corresponding optimized peak current setting value; when the target duty cycle exceeds the allowable duty cycle range, the target duty cycle is limited to the allowable duty cycle range, and the duty cycle control signal is output based on the limited target duty cycle.

[0038] Furthermore, the peak current control word is a multi-bit control word, which, after decoding, controls the number of current mirror branches in the linear current regulator that are turned on. The peak current output by the linear current regulator is determined by the reference current, the preset current mirror magnification, and the number of current mirror branches that are turned on. Each current mirror branch includes a mirror transistor and a corresponding switching unit. The switching unit is used to switch between the common gate voltage and the off potential of the gate of the mirror transistor to enable or disable the current mirror branch independently.

[0039] In the duty cycle compensation process, which revolves around the consistency of average current, after each channel completes peak current adaptation, the peak current has changed from its nominal value to its optimized value. The average current of each channel is determined by both the peak current and the PWM duty cycle. To ensure the average current returns to its nominal level, the PWM duty cycle needs to be proportionally adjusted so that the change in peak current is offset by the change in duty cycle. The duty cycle can be directly calculated using a proportional relationship: ; in, The nominal duty cycle setting value. This is the nominal peak current setting. The optimized peak current for the nth channel. The target duty cycle is compensated; when the target duty cycle exceeds the system's allowable range, it is limited to the allowable range for output to ensure that the PWM dimming timing and the operating constraints of the switching devices are not violated.

[0040] To facilitate duty cycle compensation, the peak current control word employs multi-bit digital control and a decoder drives a current mirror array to achieve quantized current regulation. The channel current is provided by the reference branch. The current mirror amplifies the signal by magnification B and then superimposes it. The decoder determines the number N of enabled mirror branches based on the binary control word CM_SW. When the gate of a certain mirror branch is connected to the common gate voltage... When the current branch is connected to ground, it is turned on; when connected to ground, it is turned off, thus changing the output peak current by changing N. The correspondence between the peak current and the control word can be written as: ; in That is, the output current of the channel linear regulator, which corresponds to the peak current of the channel under the PWM modulation framework. N is determined by CM_SW. This is provided by an external bias circuit. Thus, duty cycle compensation is achieved at the computational level through... To achieve average current normalization, the hardware layer uses CM_SW. Discrete controllability ensures that the compensation amount can be realized and repeated.

[0041] Finally, the tracking phase begins and each of the aforementioned status signals is periodically monitored. When any of the aforementioned status signals indicates that the corresponding LED channel deviates from the preset threshold, at least one of steps S102 to S104 is executed to update the control voltage VC, the peak current control word, and the duty cycle control signal, thereby reducing the additional power consumption caused by the difference in LED forward voltage drop and maintaining the consistent brightness of each of the aforementioned LED channels.

[0042] As can be seen from the above embodiments, the present invention is aimed at the multi-channel driving scenario of LED display on light pole screens. By utilizing the voltage margin state signal of the linear current regulator of each channel to adaptively determine the lowest available operating point of the power supply output, and at this operating point, the peak current of the non-reference channel is adaptively optimized. At the same time, with the cooperation of PWM duty cycle compensation, the additional voltage drop of the linear current regulator is minimized as much as possible while maintaining the consistency of average current and brightness of each channel. This reduces channel power consumption and heat generation, improves system energy efficiency, and is conducive to improving the reliability and consistency of long-term outdoor operation.

[0043] Based on reference Figure 2-3 Based on the same idea, a backlight driving system is provided, which includes a boost converter, a brightness controller, and several LED channels. The brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives a status signal of each LED channel. The status signal is used to indicate whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state. The brightness controller is used to execute the adaptive PWM backlight control method for LED displays as described above.

[0044] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0045] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. An adaptive PWM backlight control method for LED displays, characterized in that, The method is applied to a backlight driving system including a boost converter, a brightness controller, and several LED channels; the brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives a status signal for each LED channel, the status signal indicating whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state; the method includes: Receive brightness setting data, determine the nominal peak current setting value and the nominal duty cycle setting value, and initialize the peak current control word and the duty cycle control signal of each LED channel accordingly; The control voltage is adjusted to gradually change the output voltage of the boost converter, while monitoring each of the status signals; when all the status signals switch from the first state to the second state, the adjustment of the control voltage is stopped to lock the operating point, and the LED channel that last switched is determined as the reference channel. At the operating point, the peak current control word is increased by a preset step for each LED channel other than the reference channel to increase the peak current and the status signal of the LED channel is monitored; when the status signal switches from the second state back to the first state, the peak current control word is rolled back to the set value before the switching occurs to obtain the optimized peak current setting value of the LED channel; Duty cycle compensation is performed on each of the LED channels: the nominal duty cycle setting value is proportionally adjusted according to the ratio of the nominal peak current setting value to the corresponding optimized peak current setting value to obtain the target duty cycle, and the duty cycle control signal is updated accordingly to keep the average current of each of the LED channels consistent.

2. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, Each LED channel is connected in series with an LED chain, a switching MOS transistor driven by the duty cycle control signal, and the linear current regulator. The output voltage of the boost converter is configured to cover the sum of the forward voltage drop of the LED chain, the on-state voltage drop of the switching MOS transistor, and the voltage drop of the linear current regulator. The operating point corresponds to a boundary state where the voltage drop of the linear current regulator of the reference channel is close to the minimum voltage margin, thereby limiting the minimum output voltage of the boost converter by the reference channel.

3. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The brightness controller includes a resistive digital-to-analog converter, which outputs the control voltage according to the brightness setting data; The gradual adjustment of the control voltage includes: changing the control voltage in a discrete code step manner and using it as a feedback reference for the boost converter, so that the output voltage of the boost converter changes monotonically with the control voltage until each of the state signals completes the switch from the first state to the second state.

4. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The reference channel is the LED channel that last switched from the first state to the second state, and the nominal peak current setting value of the reference channel remains unchanged. Each non-reference channel is executed sequentially according to the preset channel order, and for any non-reference channel, the peak current control word is continuously increased and the peak current is synchronously increased while its state signal is in the second state. When its state signal switches from the second state back to the first state, a rollback is performed and the peak current adaptive optimization of the non-reference channel ends. The peak current adaptive optimization increases the forward voltage drop of the LED chain by increasing the LED chain operating current of the non-reference channel, thereby reducing the extra part of the voltage drop of the linear current regulator of the non-reference channel.

5. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The target duty cycle is obtained according to the following rules: The target duty cycle is obtained by multiplying the nominal duty cycle setting value by the ratio of the nominal peak current setting value to the corresponding optimized peak current setting value, based on the nominal duty cycle setting value. When the target duty cycle exceeds the allowable duty cycle range, the target duty cycle is limited to the allowable duty cycle range, and the duty cycle control signal is output based on the limited target duty cycle.

6. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The peak current control word is a multi-bit control word, which, after decoding, controls the number of current mirror branches in the linear current regulator that are turned on. The peak current output by the linear current regulator is determined by the reference current, the preset current mirror magnification, and the number of current mirror branches that are turned on. Each current mirror branch includes a mirror transistor and a corresponding switching unit. The switching unit is used to switch between the common gate voltage and the off potential of the gate of the mirror transistor to enable or disable the current mirror branch independently.

7. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The linear current regulator includes an output transistor for regulating the channel current and a comparator for generating the status signal. The comparator compares the control node voltage of the output transistor with a reference voltage. When the control node voltage crosses the reference voltage, the status signal switches between a first state and a second state to characterize whether the voltage margin of the linear current regulator crosses the preset threshold. The operating point is determined by the moment when the status signal switches from the first state to the second state, and the back-off moment of the peak current control word is determined by the moment when the status signal switches back from the second state to the first state.

8. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The linear current regulator adopts a current mirror structure and includes a reference transistor, multiple mirror transistors, a first operational amplifier, and a second operational amplifier; the second operational amplifier and the reference transistor form negative feedback so that the source-drain voltage of the reference transistor is equal to the adjustable reference voltage, thereby controlling the operating area of ​​the reference transistor and the mirror transistor by adjusting the adjustable reference voltage; The first operational amplifier is used to keep the source-drain voltage of the reference transistor consistent with that of each of the mirror transistors to improve the accuracy of the current mirror; Furthermore, the adjustable reference voltage is set to place the reference transistor and the mirror transistor in a low-dropout linear operating region to reduce current mismatch caused by device parameter drift and further reduce the voltage drop of the linear current regulator.

9. The adaptive PWM backlight control method for LED displays according to claim 1, characterized in that, The method further includes: A soft start is performed on the boost converter, causing its output voltage to rise to an initial voltage level that enables each LED channel to enter a conduction state. After the soft start is completed, the brightness controller adjusts the control voltage in a monotonically discrete stepwise manner, causing the output voltage of the boost converter to decrease until all the status signals switch from the first state to the second state and lock the operating point.

10. A backlight driving system, characterized in that, The device includes a boost converter, a brightness controller, and several LED channels. The brightness controller outputs a control voltage, a peak current control word, and a duty cycle control signal, and receives a status signal for each LED channel. The status signal is used to indicate whether the voltage margin of the corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state. The brightness controller is used to execute the adaptive PWM backlight control method for LED displays as described in any one of claims 1-9.

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