CN-122024657-A - LED display-oriented self-adaptive PWM backlight control method and backlight driving system

CN122024657ACN 122024657 ACN122024657 ACN 122024657ACN-122024657-A

Abstract

The invention relates to the technical field of backlight control, in particular to an LED display-oriented self-adaptive PWM backlight control method and a backlight driving system, which are suitable for a backlight driving system comprising a boost converter, a brightness controller and an LED channel. The method comprises the steps of receiving brightness data, determining nominal peak current and duty ratio, initializing, adjusting control voltage to enable boost output to change, monitoring state, locking working points when all the first state is changed from the second state, taking a last switching channel as a reference, increasing peak current words for non-reference channels under the working points, retracting to obtain optimized peak current when the state is changed from the second state to the first state, and adjusting the duty ratio according to the ratio of the nominal peak current to the optimized peak current to enable average currents of all channels to be consistent. The invention solves the problems that excessive voltage drop occurs in the linear current regulator, extra power consumption and heat are caused, and meanwhile, the brightness consistency among channels is affected.

Inventors

HAO GUANGJUN
QIN DAN
XIAO XUEQIANG
Yang Xiuya

Assignees

太龙智显科技（深圳）有限公司

Dates

Publication Date: 20260512
Application Date: 20260313

Claims (10)

1. The self-adaptive PWM backlight control method for LED display is characterized by being applied to a backlight driving system comprising a boost converter, a brightness controller and a plurality of LED channels, wherein the brightness controller outputs control voltage, a peak current control word and a duty ratio control signal and receives state signals of the LED channels, the state signals are used for indicating whether voltage margin of a corresponding linear current regulator crosses a preset threshold value and is switched between a first state and a second state, and the method comprises the following steps: Receiving brightness setting data, determining a nominal peak current set value and a nominal duty cycle set value, and initializing the peak current control word and the duty cycle control signal of each LED channel according to the nominal peak current set value and the nominal duty cycle set value; When all the state signals are switched from the first state to the second state, stopping adjusting the control voltage to lock the working point, and determining the last switched LED channel as a reference channel; Increasing the peak current control word for each of the LED channels except the reference channel by a preset step at the operating point to boost peak current and monitor the status signal of the LED channel; when the state signal is switched from the second state to the first state, the peak current control word is retracted to a set value before switching occurs, so that an optimized peak current set value of the LED channel is obtained; and carrying out duty cycle compensation on each LED channel, namely carrying out proportional adjustment on the nominal duty cycle set value according to the ratio of the nominal peak current set value to the optimized peak current set value to obtain a target duty cycle, and updating the duty cycle control signal according to the target duty cycle so as to keep the average current of each LED channel consistent.
2. The method according to claim 1, wherein each of the LED channels is sequentially connected in series with an LED chain, a switching MOS transistor driven by the duty control signal, and the linear current regulator, and the output voltage of the boost converter is configured to cover a sum of a forward voltage drop of the LED chain, a turn-on voltage drop of the switching MOS transistor, and a voltage drop of the linear current regulator, the operating point corresponding to a boundary state where the linear current regulator voltage drop of the reference channel is close to a minimum voltage margin, thereby defining a minimum output voltage of the boost converter by the reference channel.
3. The method of claim 1, wherein the brightness controller comprises a resistive digital-to-analog converter outputting the control voltage according to the brightness setting data, and wherein the step-wise adjusting the control voltage comprises changing the control voltage in discrete code steps 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 status signals completes switching from the first state to the second state.
4. The method according to claim 1, wherein the reference channel is the LED channel in which the switching from the first state to the second state occurs last, the nominal peak current setting value of the reference channel is kept unchanged, the method is performed sequentially for each non-reference channel in a preset channel order, and the peak current control word is continuously increased and the peak current is synchronously raised for any non-reference channel when the state signal of the non-reference channel is kept in the second state, and the peak current adaptive optimization of the non-reference channel is performed after the state signal of the non-reference channel is switched from the second state back to the first state, wherein 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 LED-oriented adaptive PWM backlight control method according to claim 1, wherein the target duty cycle is obtained according to the following rule: Multiplying the nominal duty cycle set value by the ratio of the nominal peak current set value to the optimized peak current set value by taking the nominal duty cycle set value as a reference to obtain the target duty cycle; and when the target duty ratio exceeds an allowable duty ratio range, limiting the target duty ratio within the allowable duty ratio range, and outputting the duty ratio control signal on the basis of the limited target duty ratio.
6. The method for controlling the self-adaptive PWM backlight of the LED display according to claim 1, wherein the peak current control word is a multi-bit control word, the number of the turned-on current mirror branches in the linear current regulator is controlled after decoding, the peak current output by the linear current regulator is determined by the reference current, the preset current mirror multiplying power and the number of the turned-on current mirror branches together, each current mirror branch comprises a mirror transistor and a switching unit corresponding to the mirror transistor, and the switching unit is used for switching between the common gate voltage and the turned-off potential of the gate connection of the mirror transistor so as to enable or disable the current mirror branches independently.
7. The method of claim 1, wherein the linear current regulator comprises an output transistor for regulating a channel current and a comparator for generating the state signal, the comparator comparing a control node voltage of the output transistor with a reference voltage, the state signal switching between the first state and the second state when the control node voltage crosses the reference voltage to characterize whether a voltage margin of the linear current regulator crosses the preset threshold, and determining the operating point at a time when the state signal is switched from the first state to the second state, and determining a backoff time of the peak current control word at a time when the state signal is switched from the second state back to the first state.
8. The method of claim 1, wherein the linear current regulator is of a current mirror structure and comprises a reference transistor, a plurality of mirror transistors, a first operational amplifier and a second operational amplifier, wherein the second operational amplifier and the reference transistor form negative feedback so that source-drain voltages of the reference transistor are equal to adjustable reference voltages, the adjustable reference voltages are adjusted to control the operating areas of the reference transistor and the mirror transistors, the first operational amplifier is used for keeping source-drain voltages of the reference transistor and the mirror transistors consistent to improve current mirror precision, and the adjustable reference voltages are set to enable the reference transistor and the mirror transistors to be in a low-drop linear operating area so as to reduce current mismatch caused by device parameter drift and further reduce voltage drop of the linear current regulator.
9. The method of adaptive PWM backlight control for LED-oriented displays of claim 1, further comprising: after the soft start is completed, the brightness controller adjusts the control voltage in a monotonic discrete stepping mode, so that the output voltage of the boost converter changes towards a reducing direction until each state signal is switched from the first state to the second state and the working point is locked.
10. A backlight driving system, comprising a boost converter, a brightness controller and a plurality of LED channels, wherein 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 for indicating whether a voltage margin of a corresponding linear current regulator crosses a preset threshold and switches between a first state and a second state, and the brightness controller is used for executing the adaptive PWM backlight control method for LED-oriented display according to any one of claims 1-9.

Description

LED display-oriented self-adaptive PWM backlight control method and backlight driving system Technical Field The invention relates to the technical field of backlight control, in particular to an LED display-oriented self-adaptive PWM backlight control method and a backlight driving system. Background The lamp post screen LED display belongs to outdoor direct display application, and is generally composed of a plurality of display units/modules, wherein the modules comprise multiple paths of luminous channels and the brightness consistency and reliability are required to be kept under the conditions of high brightness, wide temperature and long-term operation. In order to realize gray scale and brightness adjustment, a driving mode of constant current driving and PWM/time duty control is generally adopted in engineering, and in the power supply and driving realization of part of lamp post screens, in order to consider factors such as forward voltage drop difference, cable voltage drop, temperature drift, aging and the like of LED chains of different channels, an adjustable power supply (such as a boosting/adjustable output stage) is configured for the driving system to supply power to multiple channels, and a linear current regulator is adopted at the channel side to accurately control current. Because the forward voltage drops of the LED chains of different channels are discrete, in order to ensure that the worst channel still has enough voltage margin, the power supply output always reserves higher voltage according to the worst channel, so that the linear current regulators of other channels bear extra voltage drops and generate redundant power consumption and heat, thereby reducing the overall energy efficiency and affecting the long-term reliability outdoors. Disclosure of Invention In view of the above technical problems, the invention provides a self-adaptive PWM backlight control method and a backlight driving system for LED display, which aim to solve the problems that in the multi-channel driving of the lamp post screen LED display, the voltage requirements of all channels are inconsistent due to factors such as discrete forward voltage drop of an LED chain, temperature/aging drift, cable voltage drop and the like, so that power supply output is set according to a worst channel, excessive voltage drop is caused to a part of channel linear current regulators, extra power consumption and heat are caused, and meanwhile, the brightness consistency among channels is influenced. Other features and advantages of the present disclosure will be apparent from the following detailed description, or may be learned in part by the practice of the disclosure. According to one aspect of the invention, an adaptive PWM backlight control method for LED display is provided, which is applied to a backlight driving system comprising a boost converter, a brightness controller and a plurality of LED channels, wherein the brightness controller outputs control voltage, a peak current control word and a duty ratio control signal, and receives status signals of the LED channels, and the status signals are used for indicating whether voltage margin of a corresponding linear current regulator crosses a preset threshold value and is switched between a first state and a second state, and the method comprises the following steps: Receiving brightness setting data, determining a nominal peak current set value and a nominal duty cycle set value, and initializing the peak current control word and the duty cycle control signal of each LED channel according to the nominal peak current set value and the nominal duty cycle set value; When all the state signals are switched from the first state to the second state, stopping adjusting the control voltage to lock the working point, and determining the last switched LED channel as a reference channel; Increasing the peak current control word for each of the LED channels except the reference channel by a preset step at the operating point to boost peak current and monitor the status signal of the LED channel; when the state signal is switched from the second state to the first state, the peak current control word is retracted to a set value before switching occurs, so that an optimized peak current set value of the LED channel is obtained; and carrying out duty cycle compensation on each LED channel, namely carrying out proportional adjustment on the nominal duty cycle set value according to the ratio of the nominal peak current set value to the optimized peak current set value to obtain a target duty cycle, and updating the duty cycle control signal according to the target duty cycle so as to keep the average current of each LED channel consistent. Further, each LED channel is sequentially connected with an LED chain, a switching MOS transistor driven by the duty ratio control signal and the linear current regulator in series, and the output voltage of the boost converter is configured to c