CN102006696A - Light-emitting diode backlight drive circuit, method and constant current source thereof - Google Patents
Light-emitting diode backlight drive circuit, method and constant current source thereof Download PDFInfo
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Abstract
The invention relates to a light-emitting diode backlight drive circuit, a method and a constant current source thereof. The light-emitting diode backlight drive circuit comprises a frequency multiplier, a counter, a comparator and the constant current source, wherein the frequency multiplier is connected with the counter and used for receiving a reference clock signal, carrying out frequency multiplication treatment and outputting a clock signal input as a counter clock; the counter is connected with the frequency multiplier and used for counting according to the clock signal and outputting a counter output signal; the comparator is connected with the counter and used for receiving and comparing gray scale data and the counter output signal and generating a chip selecting signal used for controlling the constant current source; and the constant current source is connected with the comparator and a LED and used for outputting a PWM (Pulse Width Modulation) current to the LED according to the received current data and chip selecting signal. The invention can satisfy the control requirement of LED backlight, has the advantage of simple circuit and is easy for realization.
Description
Technical field
The present invention relates to a kind of backlight driving method, particularly a kind of light-emitting diode (light-emittingdiode is hereinafter to be referred as LED) backlight drive circuit, method and constant-current source thereof.
Background technology
Along with the development of technology, LCD TV has become the main flow of panel TV gradually.Wherein, the light emitting source of LED-backlit LCD TV adopts LED, and along with improving constantly of LED efficient, the continuous decline of price makes the LED-backlit LCD TV progressively enter common people house.
Along with LED more and more plays a role as display device, driving and the control technology of LED also just show more and more importantly, and the LED type of drive of prior art mainly contains two kinds: constant voltage drives and constant current driven.Because the brightness of LED is along with the increase of electric current by self strengthens, the internal resistance of LED also can have small variation in lighting the process of heating, so constant current driven drives more useful and more stable than constant voltage.
At present, constant current driven generally adopts pulse width modulation (Pulse Width Modulation is hereinafter to be referred as PWM) current signal that LED is carried out light emitting control.In order to reach environmental protection and requirements of saving energy, realize the abundant and low-power consumption of color simultaneously, need accurately control, promptly accurately control duty ratio and the current amplitude of PWM LED, this just needs the LED driving method and the drive circuit of simple possible, thereby obtains more stable PWM current signal.And the LED driving method of prior art, be by the core of microprocessor as the LCD display system, display image is handled, produce the required clock signal of led drive circuit, the control led drive circuit carries out work, need extra controller and control circuit that the LED chip for driving is controlled, its circuit complexity, control inconvenience.
Summary of the invention
The purpose of this invention is to provide a kind of LED backlight drive circuit, method and constant-current source thereof, effectively solve prior art and the LED chip for driving is controlled, technological deficiencies such as circuit complexity, control inconvenience because of needs extra controller and control circuit.
To achieve these goals, the invention provides a kind of LED backlight drive circuit, comprising: frequency multiplier, counter, comparator and constant-current source, wherein
Frequency multiplier is connected with described counter, is used to receive reference clock signal and carries out process of frequency multiplication, and output is as the clock signal of described counter clock input;
Counter is connected with described frequency multiplier, is used for according to described clock signal counting and output counter output signal;
Comparator is connected with described counter, is used for receiving and comparing luma data and described counter output signal, produces the chip selection signal of control constant-current source;
Constant-current source is connected with described comparator, and is connected with light-emitting diode, is used for according to the current data that receives and described chip selection signal to described light-emitting diode output pulse width modulated current.
Described reference clock signal is vertical synchronizing signal or horizontal-drive signal.
For achieving the above object, the present invention also provides a kind of LED backlight driving method, comprising:
Receive reference clock signal and carry out process of frequency multiplication, output is as the clock signal of counter clock input;
According to described clock signal counting and output counter output signal;
More described counter output signal and the luma data that in the time that anti-interference spacing wave exists, imports, the chip selection signal and the output that produce the control constant-current source;
According to described chip selection signal and the current data that in the time that anti-interference spacing wave exists, imports with to light-emitting diode output pulse width modulated current.
Described reception reference clock signal also carries out process of frequency multiplication, and also comprises before the clock signal of output as described counter clock input:
Described reference clock signal is set, makes described anti-interference spacing wave start from the rising edge of described reference clock signal, and make and in the time that described anti-interference spacing wave exists, import luma data and current data.
Describedly comprise according to described chip selection signal and the current data that in the time that anti-interference spacing wave exists, imports with to light-emitting diode output pulse width modulated current:
If chip selection signal is 0, then carry out constant-current source output according to described current data;
If chip selection signal is 1, then do not carry out constant-current source output.
Described reference clock signal is a vertical synchronizing signal.
Described reference clock signal is a horizontal-drive signal.
For achieving the above object, the present invention also provides a kind of constant-current source, comprising: first selector switch, second selector switch, first resistance, several control leakage resistances, second resistance, first triode and second triode, wherein,
First selector switch, its control end is connected with the output of comparator, and the selecting side connects constant voltage or ground connection, and output is connected with the source electrode of described first resistance, several control leakage resistances and first triode;
Second selector switch, its control end receives the input current data of light-emitting diode, the selecting side with described several control in leakage resistances any one be connected, output is connected with the grid of described first resistance, first triode and the source electrode of second triode;
Second triode, its source electrode is connected with drain electrode, second resistance of described first triode, and its drain electrode is connected with light-emitting diode;
Second resistance, the drain electrode of described first triode of one termination and the grid of second triode, other end ground connection.
The LED backlight drive circuit that the present invention proposes, method and constant-current source thereof, adopted the structure of frequency multiplier and constant-current source, by obtaining luma data (Gray Data) and current data (Current Data) in the time that exists in anti-interference spacing wave (Dummy), reference clock signal is carried out process of frequency multiplication, then obtain the clock signal compare with luma data (Gray Data), clock signal less than the time of luma data (Gray Data) in output PWM current signal, promptly utilize the duty ratio of luma data (Gray Data) control PWM current signal and the amplitude that current data (Current Data) is controlled the high level of PWM current signal, thereby obtain PWM constant current output, and then realization is to the control of LED, this circuit is easy to realize that reliability is higher.
Description of drawings
In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, to do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below, apparently, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.
Fig. 1 is a LCD panel picture signal schematic diagram of the present invention;
Fig. 2 is the structural representation of LED-backlit drive circuit of the present invention;
Fig. 3 is the flow chart of LED-backlit driving method of the present invention;
Fig. 4 is the flow chart of LED-backlit driving method embodiment one of the present invention;
Fig. 5 is the sequential chart of LED-backlit driving method embodiment one of the present invention;
Fig. 6 is the flow chart of LED-backlit driving method embodiment two of the present invention;
Fig. 7 is the sequential chart of LED-backlit driving method embodiment two of the present invention;
Fig. 8 is the structural representation of constant-current source of the present invention.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that is obtained under the creative work prerequisite.
Fig. 1 is a LCD panel picture signal schematic diagram of the present invention, and as shown in Figure 1, the picture signal of LCD panel has Vsyc, Hsyc, DENB and DCK several.Wherein, Vsyc is a vertical synchronizing signal, and its frequency is exactly usually said refreshing frequency, and it is the image control signal of LCD plate, when Vsyc comes an effective impulse, just shows a frame picture on the LCD panel.Hsyc is a horizontal-drive signal, and when Hsyc comes an effective impulse, Source Driver just sends data to row of liquid crystal display screen.DENB is a data enable signal, when DENB is effective, under Vsyc and the effective prerequisite of Hsyc, just has data and is shown to the LCD panel.DCK is a data transfer clock, is the reference clock that transfer of data arrives the LCD panel.
With 60Hz, 1920 * 1080 vision signals are example, and the picture signal of LCD panel is specifically described.FHD (Full High Definition, full HD) 1920 * 1080 true resolution is 2200 * 1125 (according to the VESA standard, usually the resolution of sign is effective resolution, and the data of in fact giving screen be by total resolution come to, for example 1920 * 1080 total resolution is 2200 * 1125), wherein, for Vsyc, the individual anti-interference spacing waves of 45 (1125-1080) (Dummy) are arranged; For Hsyc, the individual anti-interference spacing waves of 280 (2200-1920) (Dummy) are arranged.Wherein, the position of anti-interference spacing wave (Dummy) can be provided with in data source.The frequency of Vsyc is 60Hz, in a Vsyc cycle (16.67ms), the pulse (cycle is 14.82us) of 1125 Hsyc is arranged.Promptly under the effective situation of DENB high level, each Vsyc transmits 1125 circuit-switched data in the cycle.
Fig. 2 is the structural representation of LED-backlit drive circuit of the present invention, as shown in Figure 2, LED-backlit drive circuit agent structure of the present invention comprises: frequency multiplier, counter, comparator and constant-current source. wherein, frequency multiplier, be connected with counter, be used to receive reference clock signal and carry out process of frequency multiplication, output is as the clock signal (CCCLK) of counter clock input; Counter is connected with frequency multiplier, is used for according to clock signal (CCCLK) counting and output counter output signal (COUT); Comparator is connected with counter, is used for receiving and luma data (Gray Data) sum counter output signal (COUT), produces the chip selection signal (CCOUT) of control constant-current source; Constant-current source is connected with comparator, and is connected with LED, is used for exporting the PWM current signal according to current data (Current Data) that receives and chip selection signal (CCOUT) to LED.
Above-mentioned frequency multiplier, counter, comparator and constant-current source all have (Reset) signal that resets.This reset signal all is connected with Vsyc or Hsyc, that is to say, when the effective saltus step of the rising edge of each Vsyc or Hsyc produced, above-mentioned frequency multiplier, counter, comparator and constant-current source all will upgrade once.Therefore, the comparison frequency of luma data (Gray Data) sum counter output signal (COUT) the also period frequency with Vsyc or Hsyc is identical, also is that the cycle is identical, i.e. the cycle that adjustment cycle is a Vsyc or Hsyc.
Luma data (Gray Data) can be controlled the duty ratio (ratio of pulse high level and low level in the one-period) of PWM current signal.Current data (Current Data) can be controlled the amplitude of the high level of PWM current signal.Luma data (Gray Data) and current data (Current Data) are for to obtain from display image, and the binary digital signal of process microprocessor processes, be that control core microprocessors in the LED-backlit source obtains the data analysis of wanting display image, its method has multiple, does not repeat them here.Simultaneously, also can adopt low price schemes such as adding single-chip microcomputer, control luma data (Gray Data) and current data (Current Data) are to the led drive circuit transmission timing.The LED drive controlling mode of simple possible has been proposed according to the concrete property of luma data (Gray Data) and current data (Current Data) in the present embodiment.
The course of work is specific as follows:
Input signal in the native system has: as Vsyc or Hsyc and the luma data (Gray Data) and the current data (Current Data) of reference clock signal.
One-period with Vsyc is an example as a regulating cycle, Vsyc is as the input of frequency multiplier, through N (even-multiple that N equals 8) times frequency multiplication, output is as the clock signal (CCCLK) of counter clock input, this clock signal (CCCLK) equals N times of Vsyc frequency, and Vsyc is the rising edge useful signal.
The output of frequency multiplier links to each other with the input of counter, and the output of frequency multiplier is as the input clock of counter, and counter is to clock signal (CCCLK) counting, output counter output signal (COUT).Simultaneously, Vsyc or Hsyc be again as (Reset) signal that resets of counter, and when the rising edge of Vsyc arrives, the output signal (COUT) of counter is reset to 0, restarts counting.
The output of counter links to each other with the input of comparator, the output of counter, be counter output signal (COUT) and luma data (Gray Data) two inputs of device as a comparison, compare, wherein, luma data (Gray Data) imports in the time that anti-interference spacing wave (Dummy) exists and is stored in the comparator, and this anti-interference spacing wave (Dummy) starts from the rising edge of Vsyc.When counter output signal (COUT) during less than luma data (Gray Data), the output chip selection signal (CCOUT) of comparator is " 0 ", when counter output signal (COUT) was equal to, or greater than luma data (GrayData), the output chip selection signal (CCOUT) of comparator was " 1 ".Simultaneously, Vsyc is (Reset) signal that resets of device as a comparison again, when the rising edge of Vsyc arrives, the output chip selection signal (CCOUT) of comparator is reset to 0, restarts comparison.
Comparator is connected with constant-current source, and the output chip selection signal (CCOUT) of comparator is selected as the input of constant-current source circuit.When chip selection signal (CCOUT) is " 0 ", constant source flowing system work, and according to the current data of importing (Current Data), output pwm signal.Wherein, current data (Current Data) imports in the time that anti-interference spacing wave (Dummy) exists and is stored in the comparator, and this anti-interference spacing wave (Dummy) starts from the rising edge of Vsyc.When chip selection signal (CCOUT) was " 1 ", constant source flowing system was not worked, and does not have output current, and electric current is zero.Simultaneously, in order to keep needing Vsyc (Reset) signal that resets synchronously as constant-current source with aforementioned each several part (frequency multiplier, counter and comparator).
In said process, by the time of luma data (Gray Data) control CCOUT output " 0 ", control the time of pwm signal output current, can change the duty ratio of pwm signal.
By current data (Current Data), in constant-current source, can change pwm signal output current amplitude.Promptly,, obtain the required duty ratio and the pwm signal of current amplitude by predefined luma data (Gray Data) and current data (Current Data) by circuit of the present invention.
After pwm signal produces, control LED.The duty ratio of PWM and current amplitude can change the luminous intensity of LED.When arbitrary in duty ratio and the current amplitude or the two increase simultaneously, so long as within the working range of the requirement of LED, just can increase the brightness of LED.For the adjusting of color, can only be that the LED of corresponding multiple color uses when working together.Existing main coloured LED has the LED of three kinds of colors of RGB.These three kinds of LED by certain positional alignment, be can be as accurate as the luminosity of each LED of control by this method.The LED of many different colours, mixed light under the brightness of accurately being controlled can produce abundant more color, to reach the accurate control to color.
The LED-backlit drive circuit that present embodiment provides can change according to the LED of different model, and is simple.
The LED-backlit drive circuit that the embodiment of the invention provides has adopted the structure of frequency multiplier and constant-current source, by obtaining luma data (Gray Data) and current data (Current Data) in the time that exists in anti-interference spacing wave (Dummy), reference clock signal is carried out process of frequency multiplication, then obtain the clock signal compare with luma data (Gray Data), clock signal less than the time of luma data (GrayData) in output PWM current signal, promptly utilize the duty ratio of luma data (Gray Data) control PWM current signal and the amplitude that current data (Current Data) is controlled the high level of PWM current signal, thereby obtain PWM constant current output, and then realization is to the control of LED, this circuit is easy to realize that reliability is higher.
Fig. 3 is the flow chart of LED-backlit driving method of the present invention, and as shown in Figure 3, present embodiment LED-backlit driving method comprises:
Wherein, luma data (Gray Data) imports in the time that anti-interference spacing wave (Dummy) exists and is stored in the comparator, and this anti-interference spacing wave (Dummy) starts from the rising edge of Vsyc.
Wherein, current data (Current Data) imports in the time that anti-interference spacing wave (Dummy) exists and is stored in the comparator, and this anti-interference spacing wave (Dummy) starts from the rising edge of Vsyc.
Need to prove that luma data (Gray Data) is the gradation data of the LED that controls after Video processing, current data (Current Data) is the control data of the constant-current source output current after the Video processing.Luma data (Gray Data) and current data (Current Data) import in anti-interference spacing wave (Dummy) life period, have guaranteed the normal demonstration of image, simultaneously, have improved the treatment effeciency that shows.Present interfaces technology, for example I
2C, SPI or the like, message transmission rate can satisfy the requirement of high-speed transfer fully.
Fig. 4 is the flow chart of LED-backlit driving method embodiment one of the present invention; Fig. 5 is the sequential chart of LED-backlit driving method embodiment one of the present invention, and as shown in Figure 4 and Figure 5, particularly, in the present embodiment, reference clock signal is Vsyc, with the one-period of Vsyc as an adjustment cycle.
The LED-backlit driving method of present embodiment comprises:
Because luma data (Gray Data) and current data (Current Data) are to import in the time that anti-interference spacing wave (Dummy) exists and store, the rising edge that anti-interference spacing wave (Dummy) starts from Vsyc is set, i.e. initial at an adjustment cycle, just import and storage luma data (Gray Data) and current data (Current Data).
After the system start-up, earlier Vsyc is carried out process of frequency multiplication.Multiple is 8 integral multiple.Commonly used is the GTG of 8bit or 10bit now, perhaps higher so multiple selects 256 or 1024, so that realize the more accurate control to LED.Through the clock input of doubled clock (CCCLK) as counter.
Counter output signal (COUT) and luma data (Gray Data) be two inputs of device as a comparison, compare.Wherein, luma data (Gray Data) is that (beginning to the time the pulse 1 of Hsyc from the rising edge of Vsyc) imports in the time that anti-interference spacing wave exists.When counter output signal (COUT) during less than luma data (Gray Data), the output chip selection signal (CCOUT) of comparator is " 0 ", when counter output signal (COUT) was equal to, or greater than luma data (GrayData), the output chip selection signal (CCOUT) of comparator was " 1 ".For example, if luma data (GrayData)=2000, then rolling counters forward to 1～1999 during this period of time, the chip selection signal (CCOUT) of comparator output all is " 0 ", after rolling counters forward to 2000, the chip selection signal (CCOUT) of comparator output all is " 1 ".The chip selection signal (CCOUT) of comparator output is connected to the control end (CS) of controlled constant-current source circuit.
For controlled constant-current source, when chip selection signal (CCOUT) is " 0 ", keep constant-current source output, promptly output current (OUTPUT) is a high level; When chip selection signal (CCOUT) is " 1 ", turn-off constant-current source, promptly output current (OUTPUT) is 0.If luma data (Gray Data)=2000, then rolling counters forward to 1～1999 during this period of time, the chip selection signal (CCOUT) of comparator output all be " 0 ", keeps constant-current source to export, promptly output current (OUTPUT) is a high level; After rolling counters forward to 2000, the chip selection signal (CCOUT) of comparator output all is " 1 ", turn-offs constant-current source, and promptly output current (OUTPUT) is 0.
Wherein, the value of output current (OUTPUT) is by current data (Current Data) decision, and current data (Current Data) (beginning to the time the pulse 1 of Hsyc from the rising edge of Vsyc) in the time that anti-interference spacing wave exists imports and keeps.
Simultaneously, for each above-mentioned part, when Vsyc refreshed again, all devices all will reset, and the output current of constant-current source (OUTPUT) is reset to 0, and chip selection signal (CCOUT) is reset to 0.In an adjustment cycle, luma data (Gray Data) and current data (Current Data) import in the time that anti-interference spacing wave exists and keep, to next adjustment cycle, luma data (Gray Data) and current data (Current Data) will import again.
The LED-backlit driving method that the embodiment of the invention provides is by obtaining luma data (Gray Data) and current data (Current Data) in the time that exists in anti-interference spacing wave (Dummy), and Vsyc carried out process of frequency multiplication, the clock signal that acquisition is compared with luma data (Gray Data), clock signal less than the time of luma data (Gray Data) in output PWM current signal, promptly utilize the duty ratio of luma data (Gray Data) control PWM current signal and the amplitude that current data (CurrentData) is controlled the high level of PWM current signal, thereby obtain constant current PWM output, and then realization is to the control of LED, this method can accurately be controlled the working condition of each LED, Region control for existing LED-backlit source, and the multidimensional in following color space is handled, created condition, be easy to realize that reliability is higher.
Fig. 6 is the flow chart of LED-backlit driving method embodiment two of the present invention; Fig. 7 is the sequential chart of LED-backlit driving method embodiment two of the present invention, as shown in Figure 6 and Figure 7, particularly, in the present embodiment, reference clock signal is Hsyc, with the one-period of Hsyc as an adjustment cycle, make luma data (Gray Data) and current data (Current Data) anti-interference spacing wave (Dummy) exist during in importing.
The LED-backlit driving method of present embodiment comprises:
Step 31, Hsyc is set, makes anti-interference spacing wave (Dummy) start from the rising edge of Hsyc, and make importing luma data (GrayData) and current data (Current Data) in the time that anti-interference spacing wave (Dummy) exists;
Because luma data (Gray Data) and current data (Current Data) are to import in the time that anti-interference spacing wave (Dummy) exists and store, the rising edge that anti-interference spacing wave (Dummy) starts from Hsyc is set, i.e. initial at an adjustment cycle, just import and storage luma data (Gray Data) and current data (Current Data).
Step 32, receive Hsyc and carry out process of frequency multiplication, output is as the clock signal (CCCLK) of counter clock input;
After the system start-up, earlier Hsyc is carried out process of frequency multiplication, multiple is 8 integral multiple.Commonly used is the GTG of 8bit or 10bit now, perhaps higher so multiple selects 256 or 1024, so that realize the more accurate control to LED.Through the clock input of doubled clock (CCCLK) as counter.
Step 33, according to described clock signal (CCCLK) counting and output counter output signal (COUT);
Step 34, the luma data (Gray Data) that compares counter output signal (COUT) and in the time that anti-interference spacing wave exists, import, the chip selection signal (CCOUT) that produces the control constant-current source is also exported;
Counter output signal (COUT) and luma data (Gray Data) be two inputs of device as a comparison, compare.Wherein, luma data (Gray Data) is to import in the time that anti-interference spacing wave exists, when counter output signal (COUT) is equal to, or greater than luma data (Gray Data), the output chip selection signal (CCOUT) of comparator is " 1 ", when counter output signal (COUT) during less than luma data (Gray Data), the output chip selection signal (CCOUT) of comparator is " 0 ".For example, if luma data (Gray Data)=2000, then rolling counters forward to 1～1999 during this period of time, the chip selection signal (CCOUT) of comparator output all is " 0 ", after rolling counters forward to 2000, the chip selection signal (CCOUT) of comparator output all is " 1 ".The chip selection signal (CCOUT) of comparator output is connected to the control end (CS) of controlled constant-current source circuit.
Step 35, according to chip selection signal (CCOUT) and the current data (Current Data) that in the time that anti-interference spacing wave exists, imports, to LED output PWM electric current.
For controlled constant-current source, when chip selection signal (CCOUT) is " 0 ", keep constant-current source output, and output current (OUTPUT) is a high level; When chip selection signal (CCOUT) is " 1 ", turn-off constant-current source, promptly output current (OUTPUT) is 0.If luma data (Gray Data)=2000, then rolling counters forward to 1～1999 during this period of time, the chip selection signal (CCOUT) of comparator output all be " 0 ", keeps constant-current source to export, promptly output current (OUTPUT) is a high level; After rolling counters forward to 2000, the chip selection signal (CCOUT) of comparator output all is " 1 ", turn-offs constant-current source, and promptly output current (OUTPUT) is 0.
Wherein, the value of output current (OUTPUT) is by current data (Current Data) decision, and current data (Current Data) imports in the time that anti-interference spacing wave exists and keeps.
Simultaneously, for each above-mentioned part, when Hsyc refreshed again, all devices all will reset.The output current of constant-current source (OUTPUT) is reset to 0, and chip selection signal (CCOUT) is reset to 0.In an adjustment cycle, luma data (Gray Data) and current data (Current Data) import in the time that anti-interference spacing wave exists and keep, to next adjustment cycle, luma data (Gray Data) and current data (Current Data) will import again.
The LED-backlit driving method that the embodiment of the invention provides is by obtaining luma data (Gray DATA) and current data (Current Data) in the time that exists in anti-interference spacing wave (Dummy), and Hsyc carried out process of frequency multiplication, then obtain the clock signal compare with luma data (Gray Data), clock signal less than the time of luma data (Gray Data) in output PWM current signal, promptly utilize the duty ratio of luma data (Gray Data) control PWM current signal and the amplitude that current data (Current Data) is controlled the high level of PWM current signal, thereby obtain PWM constant current output, and then realization is to the control of LED, this method is easy to realize, reliability is higher, this method can accurately be controlled the working condition of each LED, Region control for existing LED-backlit source, and the multidimensional in following color space is handled, created condition, be easy to realize that reliability is higher.
Need to prove that because the cycle of Hsyc is littler, as reference clock signal, promptly the one-period with Hsyc is preferred scheme as an adjustment cycle with Hsyc.
Fig. 8 is the structural representation of constant-current source of the present invention, as shown in Figure 8, the constant-current source of the embodiment of the invention comprises: first selector switch 1, second selector switch 2, first resistance 3 (R1), several control leakage resistances 4 (R3, R4......Rn), second resistance 5 (R2), first triode 6 and second triode 7, wherein, first selector switch 1, its control end is connected with the output (CCOUT) of comparator, the selecting side connects constant voltage or ground connection, and output is connected with the source electrode of described first resistance 3, several control leakage resistances 4 and first triode 6; Second selector switch 2, its control end receives the input current data (Current Data) of LED, the selecting side is connected with described several controls any one in leakage resistances 4, and output is connected with the grid of described first resistance 3, first triode 6 and the source electrode of second triode 7; Second triode 7, its source electrode is connected with drain electrode, second resistance 5 of described first triode 6, and its drain electrode is connected with LED; Second resistance 5, the drain electrode of described first triode 6 of one termination and the grid of second triode 7, other end ground connection.
When CCOUT=0, the selecting side of first selector switch 1 connects VCC, this constant-current source circuit work.When CCOUT=1, the selecting side of first selector switch 1 connects GND, and this constant-current source circuit is not worked.
Current data (Current Data) determines which is in parallel in first resistance 3 (R1) and several control leakage resistances 4 (R3, R4......Rn).
Constant-current source output current I is approximately equal to VCC/ (R1||Rx), X=3 wherein, and 4 ... n.Output current I utilizes the current characteristics control LED of LED luminous.Because the output of I is periodic, this has just formed a kind of PWM and has produced circuit, by the control of PWM electric current realization to LED.
The constant-current source that the embodiment of the invention provides is exported periodic electric current, form a kind of PWM and produced circuit, and then realization is to the control of LED, this circuit can accurately be controlled the working condition of each LED, be the Region control in existing LED-backlit source, and the processing of the multidimensional in following color space, condition created, be easy to realize that reliability is higher.
It should be noted that at last: above embodiment only in order to technical scheme of the present invention to be described, is not intended to limit; Although with reference to previous embodiment the present invention is had been described in detail, those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that aforementioned each embodiment put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of various embodiments of the present invention technical scheme.
Claims (8)
1. a LED backlight drive circuit is characterized in that, comprising: frequency multiplier, counter, comparator and constant-current source, wherein,
Frequency multiplier is connected with described counter, is used to receive reference clock signal and carries out process of frequency multiplication, and output is as the clock signal of described counter clock input;
Counter is connected with described frequency multiplier, is used for according to described clock signal counting and output counter output signal;
Comparator is connected with described counter, is used for receiving and comparing luma data and described counter output signal, produces the chip selection signal of control constant-current source;
Constant-current source is connected with described comparator, and is connected with light-emitting diode, is used for according to the current data that receives and described chip selection signal to described light-emitting diode output pulse width modulated current.
2. LED backlight drive circuit according to claim 1 is characterized in that, described reference clock signal is vertical synchronizing signal or horizontal-drive signal.
3. a LED backlight driving method is characterized in that, comprising:
Receive reference clock signal and carry out process of frequency multiplication, output is as the clock signal of counter clock input;
According to described clock signal counting and output counter output signal;
More described counter output signal and the luma data that in the time that anti-interference spacing wave exists, imports, the chip selection signal and the output that produce the control constant-current source;
According to described chip selection signal and the current data that in the time that anti-interference spacing wave exists, imports with to light-emitting diode output pulse width modulated current.
4. LED backlight driving method according to claim 3 is characterized in that, described reception reference clock signal also carries out process of frequency multiplication, and also comprises before the clock signal of output as described counter clock input:
Described reference clock signal is set, makes described anti-interference spacing wave start from the rising edge of described reference clock signal, and make and in the time that described anti-interference spacing wave exists, import luma data and current data.
5. LED backlight driving method according to claim 3 is characterized in that, describedly comprises according to described chip selection signal and the current data that imports in the time that anti-interference spacing wave exists with to light-emitting diode output pulse width modulated current:
If chip selection signal is 0, then carry out constant-current source output according to described current data;
If chip selection signal is 1, then do not carry out constant-current source output.
6. according to claim 3,4 or 5 described LED backlight driving methods, it is characterized in that,
Described reference clock signal is a vertical synchronizing signal.
7. according to claim 3,4 or 5 described LED backlight driving methods, it is characterized in that,
Described reference clock signal is a horizontal-drive signal.
8. a constant-current source is characterized in that, comprising: first selector switch, second selector switch, first resistance, several control leakage resistances, second resistance, first triode and second triode, wherein,
First selector switch, its control end is connected with the output of comparator, and the selecting side connects constant voltage or ground connection, and output is connected with the source electrode of described first resistance, several control leakage resistances and first triode;
Second selector switch, its control end receives the input current data of light-emitting diode, the selecting side with described several control in leakage resistances any one be connected, output is connected with the grid of described first resistance, first triode and the source electrode of second triode;
Second triode, its source electrode is connected with drain electrode, second resistance of described first triode, and its drain electrode is connected with light-emitting diode;
Second resistance, the drain electrode of described first triode of one termination and the grid of second triode, other end ground connection.
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