CN102708804B - Backlight dimming method and backlight driving circuit - Google Patents
Backlight dimming method and backlight driving circuit Download PDFInfo
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Abstract
The invention discloses a backlight dimming method, which comprises the following steps that: a determination module of a main control unit acquires a pulse signal duty ratio according to a gray scale value of a picture to be displayed and compares the duty ratio with a set duty ratio threshold value; when the duty ratio acquired by the determination module is greater than the duty ratio threshold value, a pulse width modulation (PWM) signal generation module of the main control unit generates a PWM signal and outputs the signal to a light dimming controller; when the duty ratio acquired by the determination module is smaller than the duty ratio threshold value, a pulse frequency modulation (PFM) signal generation module of the main control unit generates a PFM signal and outputs the signal to the light dimming controller; and the light dimming controller performs light dimming according to the input PWM signal or the input PFM signal. The invention also discloses a corresponding backlight driving circuit. When required output backlight current is relatively low, the working efficiency of the system can be effectively improved; the power consumption is reduced, the electromagnetic interference (EMI) is reduced, and the color temperature consistency of a light emitting diode (LED) backlight source during working at low current is improved; and when the backlight dimming method is applied to 1D dimming and 2D dimming, an effect is relatively good.
Description
Technical Field
The present invention relates to a liquid crystal display technology, and more particularly, to a backlight dimming method and a backlight driving circuit.
Background
Currently, Light Emitting Diodes (LEDs) are increasingly widely used in the field of liquid crystal display backlights, liquid crystal television products using LED backlights conquer many users with their Light, thin and environmental protection concepts, and LED lamps are becoming the main application products of backlights.
Currently, the LED backlight driving circuit generally adopts the following two ways when adjusting the brightness of an LED lamp tube as a backlight: the method comprises the following steps of simulating dimming and Pulse Width Modulation (PWM), wherein a constant current driving circuit is adopted in a dimming simulating mode, the brightness of an LED backlight source is changed by changing the backlight current of the LED backlight source, the adjusting range of the backlight current is limited to be between a maximum value and about 10% of the maximum value (namely 10: 1 dimming range), the color spectrum of an LED is related to the current, and the color temperature and the color coordinate of the LED are different when the backlight current is changed, so that the display effect is influenced; the PWM changes the effective value of the backlight current by controlling the on-off time ratio of the backlight current, so as to achieve the purpose of changing the brightness of the LED lamp tube, namely, the backlight current is either at the maximum value or is switched off, when the duty ratio of a PWM signal is adjusted within 100% -10%, the linearity is good, the efficiency can be improved compared with an analog dimming mode, and the color cast can be avoided when the current changes; when the duty ratio of the PWM signal is adjusted within 10% -1%, the backlight current is very small, the Rising time (Rising time) and the Falling time (Falling time) of the PWM signal are fixed, the linearity of Dimming (Dimming) is poor, and meanwhile, the efficiency of backlight driving is sharply reduced; when the duty ratio of the PWM is small and the on-time of the backlight driving circuit is short, the maximum value of the backlight current output by the backlight driving circuit changes along with the change of the PWM duty ratio, so that the color temperature consistency of the LED backlight source is influenced, and the display effect is influenced.
Disclosure of Invention
In view of the above, the present invention provides a backlight dimming method and a backlight driving circuit to solve the problems of low backlight driving efficiency and influence on color temperature uniformity of an LED backlight source caused by the existing backlight dimming method.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention provides a dimming method of backlight, which comprises the following steps:
the determining module of the main control unit obtains the duty ratio of the pulse signal according to the gray value of the picture to be displayed and compares the duty ratio value with a set duty ratio threshold value;
when the duty ratio obtained by the determining module is higher than the duty ratio threshold value, a PWM signal generating module of the main control unit generates a PWM signal and outputs the PWM signal to the dimming controller;
when the duty ratio obtained by the determining module is lower than the duty ratio threshold value, a PFM signal generating module of the main control unit generates a PFM signal and outputs the PFM signal to a dimming controller;
the dimming controller performs dimming through the input PWM signal or PFM signal.
In the above scheme, the duty threshold is 10%.
In the above scheme, the obtaining of the duty ratio of the pulse signal according to the gray value of the picture to be displayed is as follows: and inquiring the duty ratio corresponding to the gray value of the image to be displayed from the stored corresponding relation table between the gray value of the image and the duty ratio of the pulse signal.
In the above scheme, the generating a PFM signal further includes: the PFM signal generating module of the main control unit generates the PFM signal according to the pulse signal duty ratio obtained by the determining module and the time interval of the PFM signal.
In the above scheme, the determining module of the main control unit obtains the time interval of the PFM signal according to the gray-level value of the picture to be displayed, where the time interval is: and the determining module of the main control unit inquires the time interval of the PFM signal corresponding to the gray value of the picture to be displayed from the stored corresponding relation table between the gray value of the picture and the time interval of the pulse signal.
The invention also provides a backlight dimming method, which comprises the following steps:
the determining module of the main control unit obtains the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputs the pulse signal to the PWM signal generating module and the PFM signal generating module of the dimming controller;
according to the input pulse signal, a PWM signal generating module of the dimming controller generates a PWM signal, or a PFM signal generating module of the dimming controller generates a PFM signal;
the dimming module of the dimming controller performs dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module.
In the above solution, the PFM signal generating module of the dimming controller generates a PFM signal, which is:
the PFM signal generating module of the dimming controller obtains a backlight current target value to be output to the backlight source according to the input pulse signal; and detecting the backlight current currently output to the backlight source, and generating a PFM signal when detecting that the backlight current is lower than the backlight current target value.
In the above solution, the PFM signal generating module of the dimming controller generates a PFM signal, including:
generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value;
or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
The invention also provides a backlight driving circuit, which comprises a main control unit and a dimming controller; wherein, the main control unit includes: the device comprises a determining module, a PWM signal generating module and a PFM signal generating module, wherein the determining module is used for obtaining the duty ratio of a pulse signal according to the gray value of a picture to be displayed and comparing the duty ratio value with a set duty ratio threshold value; the PWM signal generating module is used for generating a PWM signal and outputting the PWM signal to the dimming controller when the duty ratio obtained by the determining module is higher than a preset duty ratio threshold value; the PFM signal generating module is used for generating a PFM signal and outputting the PFM signal to the dimming controller when the duty ratio obtained by the determining module is lower than a preset duty ratio threshold;
and the dimming controller is used for dimming through the input PWM signal or PFM signal.
In the above scheme, the determining module is further configured to obtain a time interval of the PFM signal according to a gray value of a picture to be displayed; the PFM signal generating module is further configured to generate a PFM signal according to the duty ratio of the pulse signal obtained by the determining module and the time interval of the PFM signal, and output the PFM signal to the dimming controller.
In the above scheme, the determining module is further configured to query the PFM signal time interval corresponding to the gray value of the picture to be displayed from the stored correspondence table between the gray value of the picture and the pulse signal time interval.
The invention also provides a backlight driving circuit, which comprises a main control unit and a dimming controller, wherein the main control unit comprises a determination module, and the dimming controller comprises a PWM signal generation module, a PFM signal generation module and a dimming module; wherein,
the determining module is used for obtaining the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputting the pulse signal to the PWM signal generating module and the PFM signal generating module of the dimming controller;
the PWM signal generating module is used for generating a PWM signal according to the input pulse signal;
the PFM signal generating module is used for generating a PFM signal according to the input pulse signal;
and the dimming module is used for dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module.
In the above scheme, the PFM signal generating module is further configured to obtain a backlight current target value to be output to the backlight source according to the input pulse signal; and detecting the backlight current currently output to the backlight source, and generating a PFM signal when the backlight current currently output to the backlight source is lower than the backlight current target value.
In the foregoing solution, the PFM signal generating module is further configured to: generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value; or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
According to the invention, through a mixed Dimming mode combining PWM and Pulse Frequency Modulation (PFM), when the duty ratio is lower than a certain value, a PFM signal is generated and Dimming is carried out based on the PFM signal, when the backlight current required to be output is lower, the working efficiency of the system can be effectively improved, the power consumption is reduced, the EMI is reduced, the color temperature consistency of the LED backlight source during low-current working is improved, and the effect is better when the LED backlight source is applied to 1D Dimming and 2D Dimming.
Drawings
FIG. 1 is a flowchart illustrating an implementation of a backlight dimming method according to the present invention;
FIG. 2 is a flowchart illustrating another method for dimming a backlight according to the present invention;
FIG. 3 is a waveform diagram of the PFM signal;
FIG. 4 is a schematic diagram of a corresponding relationship between duty ratio values and output backlight current values in a PWM mode;
FIG. 5 is a schematic diagram showing a comparison of backlight power consumption for displaying different pictures under 1D-Dimming;
FIG. 6 is a schematic diagram showing a comparison of the power consumption of Global Dimming (Global Dimming) and 1D-Dimming for the same screen;
fig. 7 is a schematic structural diagram of a backlight driving circuit according to an embodiment of the invention.
Detailed Description
The basic idea of the invention is: by means of the Dimming mode combining PFM and PWM, different Dimming modes are selected according to different load conditions, namely the brightness degree of a picture to be displayed, backlight adjustment during liquid crystal display is achieved, backlight driving efficiency during liquid crystal display can be improved, power consumption is reduced, electromagnetic Interference (EMI) is reduced, meanwhile, color temperature consistency of an LED backlight source during low current is improved, and the effect is better when the LED backlight source is applied to one-dimensional Dimming (1D-Dimming) and two-dimensional Dimming (2D-Dimming).
The specific implementation process of the method can include the following two modes:
firstly, the main control unit obtains the duty ratio of a pulse signal according to the gray value of a picture to be displayed, and generates a PWM signal or a PFM signal according to the obtained duty ratio of the pulse signal and outputs the PWM signal or the PFM signal to the dimming controller; the dimming controller performs dimming through an input PWM signal or PFM signal.
Here, the main control unit may obtain a time interval of the PFM signal according to a gray scale value of a picture to be displayed, generate the PFM signal according to the obtained duty ratio of the pulse signal and the time interval of the PFM signal, and output the PFM signal to the dimming controller. Specifically, the main control unit queries the PFM signal time interval corresponding to the gray value of the picture to be displayed from the stored correspondence table between the gray value of the picture and the pulse signal time interval.
Secondly, the main control unit obtains the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputs the pulse signal to the dimming controller; the dimming controller generates a PWM signal or a PFM signal according to the input pulse signal, and performs dimming through the generated PWM signal or PFM signal.
Here, the dimming controller obtains a backlight current target value to be output to the backlight source according to the input pulse signal; and detecting the backlight current currently output to the backlight source, and generating and outputting a PFM signal when detecting that the backlight current is lower than the backlight current target value.
Specifically, the dimming controller generates a PFM signal with a duty ratio higher than the duty ratio threshold, and adjusts a time interval of the PFM signal in real time according to the current backlight current output to the backlight source and outputs the PFM signal until the current backlight current output to the backlight source reaches the backlight current target value; or the dimming controller generates a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusts the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source and outputs the PFM signal until the backlight current currently output to the backlight source reaches the backlight current target value.
The duty ratio of the PFM signal output by the dimming controller is higher than a preset duty ratio threshold, for example, when the duty ratio threshold is 10%, the duty ratio of the PFM signal generated by the dimming controller may be within 20% -30%. The waveform of the PFM signal is shown in fig. 3, wherein in an Active state, the PFM signal is a pulse signal; in the Inactive (Inactive) state, the output PFM signal is a low level signal. In practical application, when the PFM signal is in an Active state, the dimming controller controls the power switch to operate, and when the PFM signal is in an Inactive state, the dimming controller controls the power switch to stop operating.
In the specific implementation process of the two modes, the generation of the PWM signal is the same as that in the existing PWM mode, and is not described herein again.
Specifically, the dimming method for backlight provided by the present invention, which is used for adjusting the brightness of an LED backlight during liquid crystal display, as shown in fig. 1, may mainly include the following steps:
step 101: the determining module of the main control unit obtains the duty ratio of the pulse signal according to the gray value of the picture to be displayed and compares the duty ratio value with a set duty ratio threshold value;
specifically, the determining module of the main control unit may query the duty ratio corresponding to the gray value of the image to be displayed from the stored correspondence table between the gray value of the image and the duty ratio of the pulse signal.
Step 102: when the duty ratio obtained by the determining module is higher than the duty ratio threshold value, a PWM signal generating module of the main control unit generates a PWM signal and outputs the PWM signal to the dimming controller; when the duty ratio obtained by the determining module is lower than the duty ratio threshold value, a PFM signal generating module of the main control unit generates a PFM signal and outputs the PFM signal to a dimming controller;
here, generating the PFM signal may include: the PFM signal generating module of the main control unit generates the PFM signal according to the pulse signal duty ratio obtained by the determining module and the time interval of the PFM signal.
Step 103: the dimming controller performs dimming through the input PWM signal or PFM signal.
In practical applications, since the PWM method has poor linearity of Dimming (Dimming) when the duty ratio is lower than 10%, and the efficiency of backlight driving is reduced sharply, and the color temperature uniformity of the LED backlight is affected, so as to affect the display effect, the duty ratio threshold may be preferably 10%.
Specifically, another dimming method for backlight provided by the present invention realizes brightness adjustment of an LED backlight source during liquid crystal display, as shown in fig. 2, the method mainly includes the following steps:
step 201: the determining module of the main control unit obtains the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputs the pulse signal to the PWM signal generating module and the PFM signal generating module of the dimming controller;
step 202: according to the input pulse signal, a PWM signal generating module of the dimming controller generates a PWM signal, or a PFM signal generating module of the dimming controller generates a PFM signal;
step 203: the dimming module of the dimming controller performs dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module.
Here, the PFM signal generating module of the dimming controller generates a PFM signal as follows: the PFM signal generating module of the dimming controller obtains a backlight current target value to be output to the backlight source according to the input pulse signal; and detecting the backlight current currently output to the backlight source, and generating a PFM signal when detecting that the backlight current is lower than the backlight current target value.
Specifically, the PFM signal generating module of the dimming controller generates a PFM signal, including: generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value; or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
Table 1 is a table of correspondence between duty ratio values of Dimming and values of backlight Current output to the LED backlight when a duty ratio of an LED driving circuit (Driver) designed based on TI DDA009IC is 10% -100%, and fig. 4 is a schematic diagram of correspondence between backlight Current and duty ratio obtained based on table 1, where a typical value of LED Current (Current) is 60 mA.
TABLE 1
As can be seen from FIG. 4, the duty ratio is between 10% and 100%, the PWM mode is adopted, the linearity is good, the efficiency is about 70% to 92% through calculation, the adjusting effect is good, the efficiency is high, and meanwhile, the difference between the color temperature and the color coordinate can be avoided.
FIG. 5 shows the comparison of backlight power consumption of different pictures under 1D-Dimming, and the maximum power consumption in full white mode is 4.07W, and FIG. 6 shows the comparison of Global Dimming and 1D-Dimming power consumption of the same picture. From fig. 5 and fig. 6, it can be obtained that in 1D-Dimming or 2D-Dimming, the duty ratio is between 10% and 100% in Dimming, which can better save the backlight power consumption and improve the efficiency.
However, under a light load condition, the PWM dimming effect is not ideal. When the backlight current required to be output is very small, namely the duty ratio is lower than 10%, under the influence of the Rising time and the Falling time, the linearity of Dimming is very poor, and a very sharp current waveform can be generated, so that not only is noise easily generated and EMI (electro-magnetic interference) increased, but also the efficiency of the whole backlight is very poor. At this time, the PFM mode is selected for dimming, and the PFM signal with the duty ratio higher than the duty ratio threshold is output, and pulses are skipped when needed, so that the problems that the PWM signal causes the reduction of the backlight driving efficiency when the duty ratio is low and influences the color temperature consistency of the LED backlight source are avoided, and the backlight driving efficiency is improved, and the color temperature consistency of the LED backlight source is improved.
Correspondingly, the invention also provides a backlight driving circuit, which comprises a main control unit and a dimming controller; wherein, the main control unit includes: the device comprises a determining module, a PWM signal generating module and a PFM signal generating module, wherein the determining module is used for obtaining the duty ratio of a pulse signal according to the gray value of a picture to be displayed and comparing the duty ratio value with a set duty ratio threshold value; the PWM signal generating module is used for generating a PWM signal and outputting the PWM signal to the dimming controller when the duty ratio obtained by the determining module is higher than a preset duty ratio threshold value; the PFM signal generating module is used for generating a PFM signal and outputting the PFM signal to the dimming controller when the duty ratio obtained by the determining module is lower than a preset duty ratio threshold; and the dimming controller is used for dimming through the input PWM signal or PFM signal.
The determining module is further configured to obtain a time interval of the PFM signal according to a gray value of a picture to be displayed; the PFM signal generating module is further configured to generate a PFM signal according to the duty ratio of the pulse signal obtained by the determining module and the time interval of the PFM signal, and output the PFM signal to the dimming controller.
Here, the determining module is further configured to query the PFM signal time interval corresponding to the gray value of the picture to be displayed from the stored correspondence table between the gray value of the picture and the pulse signal time interval.
The invention also provides another backlight driving circuit, which comprises a main control unit and a dimming controller, wherein the main control unit comprises a determination module, and the dimming controller comprises a PWM signal generation module, a PFM signal generation module and a dimming module; the device comprises a determining module, a PWM signal generating module and a PFM signal generating module, wherein the determining module is used for obtaining the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputting the pulse signal to a dimming controller; the PWM signal generating module is used for generating a PWM signal according to the input pulse signal; the PFM signal generating module is used for generating a PFM signal according to the input pulse signal; and the dimming module is used for dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module.
The PFM signal generating module is further used for obtaining a backlight current target value to be output to the backlight source according to the input pulse signal; and detecting the backlight current currently output to the backlight source, and generating a PFM signal when the backlight current currently output to the backlight source is lower than the backlight current target value.
Here, the PFM signal generating module is further configured to: generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value; or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
In practical applications, both the PWM signal generating module and the PFM signal generating module can be implemented by one square wave generator, and the specific process is the prior art and is not described herein again. The dimming module is a module with a dimming function, and may be the dimming controller in fig. 7.
In practical applications, the structure of the backlight driving circuit is shown in fig. 7, and may specifically include: the LED backlight control circuit comprises an input filter, a power switch, an inductor or a transformer, an output rectifier or a filter, a dimming controller and a main control unit, wherein an input end Vin is connected with a power supply, an output end Vout outputs backlight current and backlight voltage to an LED backlight source, the output end Vout is connected with the dimming controller, and the output backlight current is fed back to the dimming controller. In practical applications, the LED backlight source may be an LED light Bar (Bar). The main control module may specifically include the determination module, the PWM signal generation module, and the PFM signal generation module.
Specifically, when a picture to be displayed is dark, the duty ratio is required to be lower than 10%, and at this time, the backlight driving circuit may perform dimming and output a backlight current in the following two ways:
firstly, a main control unit generates a PFM signal according to the brightness degree of a picture to be displayed and outputs the PFM signal to a dimming controller, the dimming controller works in an intermittent mode according to the PFM signal, and backlight current output to an LED backlight source by a backlight driving circuit is maintained at a required level;
in this case, the PFM signal is generated according to the gray scale of the picture to be displayed, the duty ratio and the Inactive time length are determined, and the PFM signal is directly output to the dimming controller for dimming.
Specifically, when the gray level of a picture to be displayed is high, that is, when the picture with high brightness is required to be displayed, the PFM signal is in an Active state, the dimming controller is in a working state, and controls the power switch to work, and the power switch controls the input power supply, the input filter, the inductor or the transformer, and the output rectifier or the filter to integrally output the backlight voltage to the LED backlight source.
When the gray scale of the image to be displayed is low, namely the image with high brightness is required to be displayed, the PFM signal is in an Inactive state, the dimming controller is in a state of stopping working, the power switch is controlled to be turned off, at the moment, the backlight voltage on the LED backlight source can be maintained only by the discharge of an inductor or a transformer, at the moment, the backlight current on the LED backlight source is small, the brightness of the LED backlight source is dark, and the image with low brightness can be displayed on the display.
In this working mode, the dimming controller only needs to work according to the received signal, and the dimming controller can also collect the backlight current in real time in a working state to determine whether the backlight current value is within the range of the set value, and dynamically adjust the backlight current.
Secondly, the main control unit generates a pulse signal according to the brightness degree of a picture to be displayed and outputs the pulse signal to the dimming controller, wherein the duty ratio of the pulse signal generated by the main control unit is lower than 10%; the dimming controller generates a PFM signal with a duty ratio higher than 10%, obtains a target value of a backlight current to be output according to a pulse signal output by the main control unit, and adjusts a time interval of the generated PFM signal or adjusts the time interval and the duty ratio of the generated PFM signal (the duty ratio of the PFM signal is always above 10% during adjustment) according to the backlight current fed back by the output terminal Vout and the target value of the backlight current to be output until the output backlight current reaches the target value of the backlight current to be output.
Specifically, the dimming controller receives a PWM signal with a duty ratio below 10% sent by the main control chip, the dimming controller converts the PWM signal into a PFM adjustment mode to generate a PFM signal with a certain duty ratio (greater than 10%, for example, 50%) and, at the same time, the dimming controller receives a backlight current fed back by the LED backlight source to determine whether the backlight current reaches a backlight current target value, if the backlight current is smaller than the backlight current target value, a PFM signal in an Active state is generated, and if the backlight current is larger than the backlight current target value, a PFM signal in an Inactive state is generated.
When the PFM signal is in an Active state, the dimming controller generates a control signal with a certain duty ratio to the power switch, the power switch works, the power switch controls the voltage of the input end Vin, the input filter, the inductor or the transformer and the output rectifier or the filter to work, the voltage is output to the LED backlight source through the output end Vout, and the backlight current on the LED backlight source is controlled to rise until the backlight current rises to a backlight current target value;
when the PFM signal is in an Inactive state, the dimming controller stops generating the control signal to the power switch, the power switch stops working, and at the moment, the backlight voltage on the LED backlight source is supplied only by discharging of energy storage elements such as capacitance or inductance, so that the backlight current on the LED backlight source is controlled to be reduced until the backlight current is reduced to a backlight current target value.
The duty ratio coefficient can be automatically switched according to the magnitude of the backlight current required to be output, so that the dynamic power consumption of the dimming controller is reduced under the condition of light load, and the conversion efficiency is improved. Specifically, for closed-loop dynamic control, a currently common mode is proportional-integral-derivative (PID) control, and the adjustment control is dynamically performed by acquiring the difference between a control target and a set target in real time, or by some other existing control algorithm.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.
Claims (10)
1. A method of dimming a backlight, the method comprising:
the determining module of the main control unit obtains the duty ratio of the pulse signal and the time interval of the PFM signal according to the gray value of a picture to be displayed, and compares the duty ratio with a set duty ratio threshold value;
when the duty ratio obtained by the determining module is higher than the duty ratio threshold value, a PWM signal generating module of the main control unit generates a PWM signal and outputs the PWM signal to the dimming controller;
when the duty ratio obtained by the determining module is lower than the duty ratio threshold, a PFM signal generating module of the main control unit generates a PFM signal according to the duty ratio of the pulse signal obtained by the determining module and the time interval of the PFM signal and outputs the PFM signal to a dimming controller;
the dimming controller performs dimming through the input PWM signal or PFM signal.
2. The method of claim 1, wherein the duty cycle threshold is 10%.
3. A method for dimming a backlight according to claim 1, wherein the duty ratio of the pulse signal is obtained according to the gray-level value of the picture to be displayed, and is as follows: and inquiring the duty ratio corresponding to the gray value of the image to be displayed from the stored corresponding relation table between the gray value of the image and the duty ratio of the pulse signal.
4. The method of claim 1, wherein the determining module of the main control unit obtains a time interval of the PFM signal according to the gray-level value of the picture to be displayed, the time interval being: and the determining module of the main control unit inquires the time interval of the PFM signal corresponding to the gray value of the picture to be displayed from the stored corresponding relation table between the gray value of the picture and the time interval of the pulse signal.
5. A method of dimming a backlight, the method comprising:
the determining module of the main control unit obtains the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputs the pulse signal to the PWM signal generating module and the PFM signal generating module of the dimming controller;
according to the input pulse signal, a PWM signal generating module of the dimming controller generates a PWM signal, or a PFM signal generating module of the dimming controller generates a PFM signal;
the dimming module of the dimming controller performs dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module;
the PFM signal generating module of the dimming controller obtains a backlight current target value to be output to the backlight source according to an input pulse signal; and detecting the backlight current currently output to the backlight source, and generating a PFM signal when detecting that the backlight current is lower than the backlight current target value.
6. The method of claim 5, wherein the PFM signal generating module of the dimming controller generates the PFM signal, comprising:
generating a PFM signal with duty ratio higher than a duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value;
or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
7. A backlight driving circuit is characterized by comprising a main control unit and a dimming controller; wherein, the main control unit includes: the device comprises a determining module, a PWM signal generating module and a PFM signal generating module, wherein the determining module is used for obtaining the duty ratio of a pulse signal and the time interval of a PFM signal according to the gray value of a picture to be displayed and comparing the duty ratio with a set duty ratio threshold; the PWM signal generating module is used for generating a PWM signal and outputting the PWM signal to the dimming controller when the duty ratio obtained by the determining module is higher than a preset duty ratio threshold value; the PFM signal generating module is used for generating a PFM signal according to the duty ratio of the pulse signal obtained by the determining module and the time interval of the PFM signal to generate the PFM signal and outputting the PFM signal to the dimming controller when the duty ratio obtained by the determining module is lower than a preset duty ratio threshold;
and the dimming controller is used for dimming through the input PWM signal or PFM signal.
8. The backlight driving circuit of claim 7, wherein the determining module is further configured to query the PFM signal time interval corresponding to the gray value of the picture to be displayed from the stored correspondence table between the gray value of the picture and the pulse signal time interval.
9. The backlight driving circuit is characterized by comprising a main control unit and a dimming controller, wherein the main control unit comprises a determination module, and the dimming controller comprises a PWM signal generation module, a PFM signal generation module and a dimming module; wherein,
the determining module is used for obtaining the duty ratio of a pulse signal according to the gray value of a picture to be displayed and outputting the pulse signal to the PWM signal generating module and the PFM signal generating module of the dimming controller;
the PWM signal generating module is used for generating a PWM signal according to the input pulse signal;
the PFM signal generating module is used for obtaining a backlight current target value to be output to the backlight source according to the input pulse signal; detecting the backlight current currently output to the backlight source, and generating a PFM signal when the backlight current currently output to the backlight source is lower than the backlight current target value;
and the dimming module is used for dimming through the PWM signal generated by the PWM signal generation module or the PFM signal generated by the PFM signal generation module.
10. The backlight driving circuit of claim 9, wherein the PFM signal generating module is further configured to: generating a PFM signal with duty ratio higher than a duty ratio threshold, and adjusting the time interval of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value; or generating a PFM signal with the duty ratio higher than the duty ratio threshold, and adjusting the time interval and the duty ratio of the PFM signal in real time according to the backlight current currently output to the backlight source until the backlight current currently output to the backlight source reaches the backlight current target value.
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