CN201349354Y

CN201349354Y - Analogy and digital dimming backlight source drive device

Info

Publication number: CN201349354Y
Application number: CNU2009200015783U
Authority: CN
Inventors: 王舜弘
Original assignee: TPV Investment Co Ltd
Current assignee: Top Victory Investments Ltd; TPV Investment Co Ltd
Priority date: 2009-01-19
Filing date: 2009-01-19
Publication date: 2009-11-18
Anticipated expiration: 2019-01-19

Abstract

The utility model provides an analogy and digital dimming backlight source drive device. A switch inverter is used for changing the input direct current voltage into the output alternative current voltage to turn on the backlight source in the enable period of the pulse width modulation dimming signal and the energy is not transferred to turn off the backlight source in the disable period of the pulse width modulation dimming signal. When the duty period of the pulse width modulation dimming signal is larger than the critical duty period, the strip lamp current output from the backlight source is used as the first current value in the enable period and when the duty period of the pulse width modulation dimming signal is smaller than or equal to the critical duty period, the strip lamp current output from the backlight source is used as the second current value in the enable period and the second current value is smaller than the first current value. Thus the backlight source drive device uses the digital dimming as the basis, the average brightness is reduced to a degree and furthermore the strip lamp current is reduced using the analogy dimming, thus the average brightness is furthermore reduced to increase the brightness contrast value.

Description

Backlight driving device in conjunction with simulation and digital dimming

Technical field

The utility model relates to a kind of backlight driving device, and is particularly related to a kind of backlight driving device in conjunction with simulation and digital dimming.

Background technology

Because liquid crystal itself is not had a characteristics of luminescence, LCD must add that in the liquid crystal panel back backlight provides light, can reach the function of demonstration.LCD adopts cold-cathode fluorescence lamp (ColdCathode Fluorescent Lamp abbreviates CCFL as) as backlight more at present.CCFL has some properties, consider maximization its efficient, life-span and practicality, need a drive unit power source conversion to be become the interchange string ripple of frequency 40kHz to 80kHz to drive CCFL, and after the CCFL startup enters normal operating conditions, the operating voltage of CCFL is at 400Vrms to 1000Vrms, and the lamp current that flows through CCFL is at 3mArms to 7mArms.Lamp current is big more, the brighter display of CCFL.

Please refer to Fig. 1, it is a kind of calcspar of existing C CFL drive unit.CCFL drive unit 1 comprises suitching type inverter (switching inverter) 11, step-up transformer 12, resonant circuit 13, feedback circuit 14 and control circuit 15.Suitching type inverter 11 for example is semibridge system, full-bridge type or push-pull dc-to-ac, and it utilizes the switching of power switch input direct voltage Vdc to be converted to the alternating voltage Vac1 of square wave form.After the alternating voltage Vac1 of square wave form boosts through step-up transformer 12, be filtered into the output AC voltage Vac2 of approximate string waveshape again through resonant circuit 13, to drive CCFL 2.The lamp current Ilamp of CCFL 2 is flow through in feedback circuit 14 detectings, and exports feedback voltage Vfb according to this.Control circuit 15 with the switching of control suitching type inverter 11 power switchs, makes the brightness stability of CCFL 2 according to feedback voltage Vfb output control signal Vctrl.Control circuit 15 also receives dim signal Vdim, and the user can adjust the brightness of CCFL 2 by dim signal Vdim.The mode of existing adjustment CCFL 2 brightness can be divided into two kinds of simulation light modulation and digital dimmings, wherein digital dimming generally is called burst mode (burst mode) light modulation or low frequency pulse-width modulation (Pulse Width Modulation again, be called for short PWM) light modulation, its with the dimming scope broadness, the light modulation linearity is good and circuit is realized advantage such as easy and be present modal dimming mode.

When CCFL drive unit 1 adopted the simulation light modulation, its dim signal Vdim was the signal of direct current form, changed the lamp current Ilamp size of CCFL 2 by the DC level that changes dim signal Vdim, and reached the dimming function of adjusting CCFL2 brightness.Actually, a kind of mode is the fixing switching frequency of suitching type inverter 11 power switchs, but the DC level according to dim signal Vdim changes its responsibility cycle (duty cycle), and then change is sent to the energy number of CCFL2 to change lamp current Ilamp size.Also having a kind of mode is the switching frequency that changes suitching type inverter 11 power switchs according to the DC level of dim signal Vdim, and then the impedance of change resonant circuit 13 is to change lamp current Ilamp size.

Please refer to Fig. 2 (A) and Fig. 2 (B), it is the lamp current waveform schematic diagram of existing simulation light modulation.In this example, when Fig. 2 (A), lamp current Ilamp is 7mArms; When Fig. 2 (B), lamp current Ilamp is 3mArms.Therefore, the brightness of CCFL2 is when Fig. 2 (A) than at Fig. 2 (B) Shi Weigao.

When CCFL drive unit 1 adopts digital dimming, its dim signal Vdim is the signal of PWM form, and because its frequency far below the interchange string ripple of the frequency 40kHz to 80kHz that drives CCFL 2, so this dim signal of title Vdim is a low frequency PWM dim signal, or abbreviates the PWM dim signal as.PWM dim signal Vdim in one-period, comprise one enable during and a forbidden energy during, opening CCFL 2 in the time of during enabling makes it bright, during forbidden energy, close CCFL 2 and make it dark, other define its responsibility cycle be one enable during divided by one-period, and represent with percentage.Because the frequency of PWM dim signal Vdim is usually more than 100Hz, the imperceptible CCFL 2 of human eye is bright once dark once under the influence that human vision persists, can only feel the mean value (being mean flow rate) of this variation, therefore, the lamp current Ilamp size of fixation of C CFL 2, change the bright and dark ratio of CCFL 2 by the responsibility cycle that changes PWM dim signal Vdim, and then change the average current size of CCFL 2, reach the dimming function of adjustment CCFL 2 brightness.

Please refer to Fig. 3 (A) to Fig. 3 (C), it is the lamp current waveform schematic diagram of existing digital dimming.In this example, fixed lamp tube electric current I lamp is rated value 7mArms, but the PWM dim signal Vdim that utilizes frequency 200Hz, different responsibility cycle changes the average current size of CCFL 2, as when Fig. 3 (A), PWM dim signal Vdim responsibility cycle is 80%, and lamp current Ilamp mean value is 7mArms * 80%=5.6mArms; When Fig. 3 (B), PWM dim signal Vdim responsibility cycle is 40%, and lamp current Ilamp mean value is 7mArms * 40%=2.8mArms; When Fig. 3 (C), PWM dim signal Vdim responsibility cycle is 30%, and lamp current Ilamp mean value is 7mArms * 30%=2.1mArms.Therefore, the mean flow rate of CCFL 2 when Fig. 3 (A) than at Fig. 3 (B) Shi Weigao, and when Fig. 3 (B) than at Fig. 3 (C) Shi Weigao.

The brightness contrast value that an important parameter of display performance quality is exactly a picture, brightness contrast value refer to the ratio that transfers to maximum brightness and following the data that measure out of minimum brightness when brightness.The parent that the display of high brightness contrast often attracts clients looks at, because it allows the GTG level can be fine and smooth more, and can bring the user sharper keen, vision imaging clearly.For needing backlight that the display (as LCD) of light to reach Presentation Function is provided, the brightness of adjusting picture promptly is to adjust the brightness that backlight provided.So, the existing backlight light-adjusting mode of the improvement of needs is arranged to obtain higher brightness contrast value.

Summary of the invention

The purpose of this utility model is exactly to be to propose a kind of backlight driving device in conjunction with simulation and digital dimming, and it has higher brightness contrast value.

In order to reach above-mentioned purpose and other purpose, the utility model proposes a kind of backlight driving device in conjunction with simulation and digital dimming, it comprises a suitching type inverter, a feedback circuit, a control circuit and a responsibility cycle detector, suitching type inverter coupled to a backlight wherein, feedback circuit is coupled to backlight, control circuit is coupled to feedback circuit and suitching type inverter, and the responsibility cycle detector is coupled to feedback circuit; In addition, the suitching type inverter receives an input direct voltage, and control circuit and responsibility cycle detector all receive an impulse width modulation and light adjusting signal.

The suitching type inverter converts input direct voltage to output AC voltage to open backlight during the impulse width modulation and light adjusting signal enables, do not transmit energy to close backlight during impulse width modulation and light adjusting signal forbidden energy.Feedback circuit receives the lamp current of backlight output.In impulse width modulation and light adjusting signal responsibility cycle during greater than a critical responsibility cycle, feedback circuit is exported one first feedback voltage according to lamp current, and control circuit then makes lamp current be fixed on one first current value according to first feedback voltage control suitching type inverter during the impulse width modulation and light adjusting signal enables.When impulse width modulation and light adjusting signal responsibility cycle is less than or equal to critical responsibility cycle, the impedance that the responsibility cycle detector is adjusted feedback circuit makes feedback circuit export one second feedback voltage according to lamp current, control circuit then makes lamp current be fixed on one second current value according to second feedback voltage control suitching type inverter during the impulse width modulation and light adjusting signal enables, and second current value is less than first current value.

The beneficial effects of the utility model are: the utility model is based on digital dimming, utilize the responsibility cycle detector detecting impulse width modulation and light adjusting signal responsibility cycle when being less than or equal to critical responsibility cycle, the impedance of change feedback circuit reduces the lamp current size with the simulation dimming mode, and mean flow rate is further reduced and raising brightness contrast value.

Description of drawings

Fig. 1 is a kind of calcspar of existing C CFL drive unit;

Fig. 2 (A)～Fig. 2 (B) is the lamp current waveform schematic diagram of existing simulation light modulation;

Fig. 3 (A)～Fig. 3 (C) is the lamp current waveform schematic diagram of existing digital dimming;

Fig. 4 (A)～Fig. 4 (C) is the lamp current waveform schematic diagram in conjunction with simulation and digital dimming according to the utility model one embodiment;

Fig. 5 is that it can realize lamp current waveform schematic diagram shown in Fig. 4 (A)～Fig. 4 (C) according to the calcspar of the CCFL drive unit of the combination simulation of the utility model one embodiment and digital dimming;

Fig. 6 is a concrete circuit diagram of implementing of CCFL drive unit 5 calcspars shown in Figure 5;

Fig. 7 is the circuit diagram of another embodiment of responsibility cycle detector 66 shown in Figure 6.

Description of reference numerals: 1-CCFL drive unit; 11-suitching type inverter; The 12-step-up transformer; The 13-resonant circuit; The 14-feedback circuit; The 15-control circuit; 2-cold-cathode fluorescence lamp (CCFL); The 5-CCFL drive unit; 51,61-suitching type inverter; 52,62-step-up transformer; 53,63-resonant circuit; 54,64-feedback circuit; 55,65-control circuit; 56,66,76-responsibility cycle detector; 651-error amplifier (EA); 652-comparator (CMP); The 653-oscillator; The 654-output driver; 761-comparator (CMP); C1, C2-capacitor; Cd, Cf-filtering capacitor; The Cp-resonant capacitor; Db, Dd-diode; Dr1, Dr2-rectifier diode; Dm1, Dm2-body diode; I1-first current value; I2-second current value; The Ilamp-lamp current; The Llk-resonant inductor; Mn1, Mn2-power switch; The Mn3-switch; Rd1, Rd2-voltage grading resistor; Rf1, Rf2, Rf3-feedback resistor; Rsen1, Rsen2-detect resistor; V1-first feedback voltage; V2-second feedback voltage; The Vac1-alternating voltage; The Vac2-output AC voltage; Vctrl, Vg1, Vg2-control signal; The Vdc-input direct voltage; The Vdim-dim signal; The Verror-error voltage; The Vfb-feedback voltage; Vpwm-pulse-width modulation (PWM) dim signal; The Vramp-ramp voltage; The Vref-reference voltage; Vth-critical reference voltage.

Embodiment

For above-mentioned and other purposes, feature and advantage of the present utility model can be become apparent, preferred embodiment cited below particularly, and cooperate appended graphicly, be described in detail below:

The brightness contrast value of display picture refers to the ratio that transfers to maximum brightness and following the data that measure out of minimum brightness when brightness.For needing backlight that the display (as LCD) of light to reach Presentation Function is provided, its maximum brightness will be subject to the high-high brightness that backlight can provide (be rated value and PWM dim signal responsibility cycle is adjusted into 100% as fixed lamp tube electric current under at digital dimming), and it is infeasible improving maximum brightness.Therefore, the utility model is based on digital dimming, mean flow rate low to certain degree after (as when PWM dim signal responsibility cycle is less than or equal to a critical responsibility cycle) further utilize the simulation light modulation to reduce lamp current size, make mean flow rate further fall ground and raising brightness contrast value.

Please refer to Fig. 4 (A) to Fig. 4 (C), it is the lamp current waveform schematic diagram in conjunction with simulation and digital dimming according to the utility model one embodiment.In this example, critical responsibility cycle is 30%.In PWM dim signal responsibility cycle during greater than critical responsibility cycle (30%), shown in Fig. 4 (A) and Fig. 4 (B), fixed lamp tube electric current I lamp is rated value 7mArms, but utilizes the PWM dim signal of frequency 200Hz, different responsibility cycle to change the average current size of backlight.When PWM dim signal responsibility cycle is less than or equal to critical responsibility cycle (30%), shown in Fig. 4 (C), utilize the simulation light modulation to reduce and fixed lamp tube electric current I lamp is 3mArms, utilize the PWM dim signal Vdim of frequency 200Hz, different responsibility cycle to change the average current size of CCFL 2 again.

When Fig. 4 (A), PWM dim signal responsibility cycle is 80%, and lamp current Ilamp mean value is 7mArms * 80%=5.6mArms; When Fig. 4 (B), PWM dim signal responsibility cycle is 40%, and lamp current Ilamp mean value is 7mArms * 40%=2.8mArms; When Fig. 4 (C), PWM dim signal responsibility cycle is 30%, and lamp current Ilamp mean value is 3mArms * 30%=0.9mArms.Therefore, the mean flow rate of backlight when Fig. 4 (A) than at Fig. 4 (B) Shi Weigao, and when Fig. 4 (B) than at Fig. 4 (C) Shi Weigao.In addition, existing digital dimming shown in dimming mode of the present utility model and Fig. 3 (A)～Fig. 3 (C) shown in comparison diagram 4 (A)～Fig. 4 (C), when PWM dim signal responsibility cycle was less than or equal to critical responsibility cycle (30%), the mean flow rate of dimming mode of the present utility model was low than the mean flow rate of existing digital dimming; For example, the fluorescent tube average current is 0.9mArms shown in Fig. 4 (C), and the fluorescent tube average current is 2.1mArms shown in Fig. 3 (C).

Please refer to Fig. 5, it is that it can realize lamp current waveform schematic diagram shown in Fig. 4 (A)～Fig. 4 (C) according to the calcspar of the backlight driving device of the combination simulation of the utility model one embodiment and digital dimming.In this example, backlight 2 is an example with CCFL, and CCFL drive unit 5 comprises suitching type inverter 51, step-up transformer 52, resonant circuit 53, feedback circuit 54, control circuit 55 and responsibility cycle detector 56.Control circuit 55 receives PWM dim signal Vpwm, and during PWM dim signal Vpwm enables output control signal Vctrl, control suitching type inverter 51 converts input direct voltage Vdc to the alternating voltage Vac1 of square wave form, alternating voltage Vac1 is filtered into the output AC voltage Vac2 that is similar to the string waveshape through resonant circuit 53 again and makes it bright to open CCFL 2 after then boosting through step-up transformer 52.Control circuit 55 is exported control signal Vctrl during PWM dim signal Vpwm forbidden energy, control suitching type inverter 51 does not transmit energy makes it dark to close CCFL 2.

In addition, utilize responsibility cycle detector 56 to receive PWM dim signal Vpwm and detect its responsibility cycle, so that when PWM dim signal Vpwm responsibility cycle is less than or equal to critical responsibility cycle, the further simulation light modulation reduction lamp current size of utilizing makes mean flow rate further fall ground and raising brightness contrast value.In PWM dim signal Vpwm responsibility cycle during greater than critical responsibility cycle, as Fig. 4 (A) and Fig. 4 (B), feedback circuit 54 receiving light current I lamp and generation value according to this are the feedback voltage Vfb of first feedback voltage V 1, control circuit 55 then makes lamp current Ilamp be fixed on first current value I 1 according to first feedback voltage V, 1 control suitching type inverter 51 during PWM dim signal Vpwm enables, as 7mArms.When PWM dim signal Vpwm responsibility cycle is less than or equal to critical responsibility cycle, as Fig. 4 (C), it is the feedback voltage Vfb of second feedback voltage V 2 according to lamp current Ilamp generation value that the impedance that responsibility cycle detector 56 is adjusted feedback circuit 54 makes feedback circuit 54, control circuit then makes lamp current Ilamp be fixed on second current value I 2 according to second feedback voltage V, 2 control suitching type inverters 51 during PWM dim signal Vpwm enables, as 3mArms.Wherein, second current value I 2 is less than first current value I 1, and generally design first current value I 1 for the lamp current rated value so that CCFL 2 can provide high-high brightness.

Please refer to Fig. 6, it is a concrete circuit diagram of implementing of CCFL drive unit 5 calcspars shown in Figure 5, be applicable to the effectively PWM dim signal Vpwm of (low active) of low level, promptly PWM dim signal Vpwm when low level for during enabling, be forbidden energy when high level during.Suitching type inverter 61 is a kind of semi-bridge type inverters, it comprises two the power switch Mn1 and the Mn2 that are realized by N channel mos field-effect transistor (MOSFET), and power switch Mn1 and Mn2 exist body diode (body diode) Dm1 and Dm2 anti-and that connect at the drain-source interpolar, and the reverse circulated path can be provided.Whether two power switch Mn1 and Mn2 control its conducting by the control signal Vctrl (it comprises Vg1 and Vg2) that its grid received, during PWM dim signal Vpwm enables alternately conducting so that convert input direct voltage Vdc the alternating voltage Vac1 of square wave form to, but all not conductings and do not allow input direct voltage Vdc energy pass through during PWM dim signal Vpwm forbidden energy.Step-up transformer 62 primary sides receive alternating voltage Vac1, and the alternating voltage Vac1 after the secondary side generation is boosted.Resonant circuit 63 is a series resonance shunt load form, and resonant inductor L1k and resonant capacitor Cp coupled in series and cross-over connection be in step-up transformer 62 secondary side two ends, and resonant capacitor Cp two ends are couple to load, and promptly CCFL 2.

Feedback circuit 64 comprises that electric current changes potential circuit (being realized by detecting resistor R sen1 and Rsen2), rectification circuit (being realized by rectifier diode Dr1 and Dr2), the first feedback resistor Rf1, the second feedback resistor Rf2 and the first filtering capacitor Cf, wherein, the first feedback resistor Rf1, first end is coupled to the output of rectification circuit, the first feedback resistor Rf1, second end is coupled to the second feedback resistor Rf2, first end and the first filtering capacitor Cf, first end, and the second feedback resistor Rf2, second end and the first filtering capacitor Cf, second end all are coupled to earth terminal.Detecting resistor R sen1 and Rsen2 respectively with corresponding C CFL 2 coupled in series, with the lamp current Ilamp of reception CCFL 2 outputs, and produce a voltage signal corresponding to lamp current Ilamp, wherein, when lamp current Ilamp was big more, voltage signal was big more.This voltage signal is followed the voltage signal that produces the pulse direct current form through the full-wave rectification of rectifier diode Dr1 and Dr2, this pulsed dc voltage signal then through after the dividing potential drop of the first feedback resistor Rf1 and the second feedback resistor Rf2 again through the filtering of the first filtering capacitor Cf, and the generation value is the feedback voltage Vfb of first feedback voltage V 1 on the first filtering capacitor Cf, first end.

Responsibility cycle detector 66 comprises diode Dd, the first voltage grading resistor Rd1, the second voltage grading resistor Rd2, the second filtering capacitor Cd, switch Mn3 (being realized by N passage MOSFET) and the 3rd feedback resistor Rf3, wherein, the first voltage grading resistor Rd1, first end is coupled to diode Dd cathode terminal, the first voltage grading resistor Rd1, second end is coupled to the second voltage grading resistor Rd2, first end, the second filtering capacitor Cd, first end and switch Mn3 control end, and the second voltage grading resistor Rd2, second end and the second filtering capacitor Cd, second end all are coupled to earth terminal; In addition, the 3rd feedback resistor Rf3 first end is coupled to the first feedback resistor Rf1, first end, and the 3rd feedback resistor Rf3 second end is coupled to switch Mn3 first end, and switch Mn3 second end is coupled to the first feedback resistor Rf1, second end.Diode Dd anode tap receives PWM dim signal Vpwm, this PWM dim signal Vpwm through the dividing potential drop of the first voltage grading resistor Rd1 and the second voltage grading resistor Rd2 after again through the filtering of the second filtering capacitor Cd, and go up generation one control voltage signal corresponding to PWM dim signal Vpwm responsibility cycle at the second filtering capacitor Cd, first end (or switch Mn3 control end), wherein, when PWM dim signal Vpwm responsibility cycle more hour, the control voltage signal is big more.Therefore, can design when PWM dim signal Vpwm responsibility cycle is less than or equal to critical responsibility cycle, the control voltage signal can make the conducting greater than critical voltage (threshold voltage) of switch Mn3 gate-source voltage.In case switch Mn3 conducting, then the 3rd feedback resistor Rf3 and the first feedback resistor Rf1 coupled in parallel, this moment, generation value on the first filtering capacitor Cf, first end was the feedback voltage Vfb of second feedback voltage V 2, and second feedback voltage V 2 is greater than first feedback voltage V 1.

Control circuit 65 comprises error amplifier 651, comparator 652, oscillator 653 and output driver 654.Error amplifier 651 positive input terminals are coupled to the output of feedback circuit 64 to receive feedback voltage Vfb, also receive simultaneously PWM dim signal Vpwm, error amplifier 651 negative input ends receive reference voltage Vref, so error amplifier 651 is according to the difference output error voltage Verror of feedback voltage Vfb and reference voltage Vref.Comparator 652 positive input terminals are coupled to the output of error amplifier 651 to receive error voltage Verror, comparator 652 negative input ends are coupled to the ramp voltage Vramp (it comprise the voltage signal of sawtooth waveforms or triangular wave form) of oscillator 653 with reception oscillator 653 outputs, so comparator 652 relative error voltage Verror and ramp voltage Vramp, and

output logic

1 or 0 according to this.Output driver 654 is coupled to comparator 652, according to the output generation control signal Vctrl of comparator 652.When PWM dim signal Vpwm is high level, diode Db conducting, the feedback voltage Vfb value is about the voltage of aforementioned high level and is more much bigger than reference voltage Vref, make error voltage Verror bigger than ramp voltage Vramp always, so comparator 652 output logic 1 always, all not conductings and do not allow input direct voltage Vdc energy pass through of this moment output driver 654 output control signal Vg1 and Vg2 power controlling switch Mn1 and Mn2.When PWM dim signal Vpwm is low level, not conducting of diode Db, the feedback voltage Vfb value will be first feedback voltage V 1 or second feedback voltage V 2 by feedback circuit 64 impedances decision, make error voltage Verror size between ramp voltage Vramp maximum and minimum value and the signal of comparator 652 output PWM forms, this moment output driver 654 output PWM forms control signal Vg1 and Vg2 power controlling switch Mn1 and Mn2 alternately conducting so that input direct voltage Vdc is converted to the alternating voltage Vac1 of square wave form.

Please refer to Fig. 7, it is the circuit diagram of another embodiment of responsibility cycle detector 66 shown in Figure 6.Its critical voltage of switch Mn3 of being realized by N passage MOSFET might make the and then drift of critical responsibility cycle because factors such as temperature produce drift.Drift about along with switch Mn3 threshold voltage shift for fear of critical responsibility cycle, therefore, form responsibility cycle detector 76 as shown in Figure 7 at the preceding adding comparator 761 of the switch Mn3 of responsibility cycle detector 66 control end.Comparator 761 compares control voltage signal on the second filtering capacitor Cd, first end and critical reference voltage Vth, and according to this

output logic

1 or 0 control switch Mn3 conducting whether, wherein logical one for example is a 5V voltage and logical zero for example is a 0V voltage, so can not be subjected to the influence of switch Mn3 threshold voltage shift.

In sum, the utility model is based on digital dimming, utilize the responsibility cycle detector detecting impulse width modulation and light adjusting signal responsibility cycle when being less than or equal to critical responsibility cycle (be equivalent to mean flow rate low to a certain degree), the impedance of change feedback circuit reduces the lamp current size with the simulation dimming mode, and mean flow rate is further reduced and raising brightness contrast value.

More than explanation is just illustrative for the utility model; and it is nonrestrictive; those of ordinary skills understand; under the situation of the spirit and scope that do not break away from following claims and limited; can make many modifications; change, or equivalence, but all will fall in the protection range of the present utility model.

Claims

1. one kind in conjunction with the simulation and the backlight driving device of digital dimming, it is characterized in that it comprises:

One suitching type inverter, be coupled to a backlight, during an impulse width modulation and light adjusting signal enables, convert an input direct voltage to an output AC voltage to open described backlight, during described impulse width modulation and light adjusting signal forbidden energy, do not transmit energy to close described backlight;

One feedback circuit is coupled to described backlight, receives a lamp current of described backlight output;

One responsibility cycle detector, be coupled to described feedback circuit, receive described impulse width modulation and light adjusting signal, in described impulse width modulation and light adjusting signal responsibility cycle during greater than a critical responsibility cycle, described feedback circuit is exported one first feedback voltage according to described lamp current, when described impulse width modulation and light adjusting signal responsibility cycle was less than or equal to described critical responsibility cycle, the impedance that described responsibility cycle detector is adjusted described feedback circuit made described feedback circuit export one second feedback voltage according to described lamp current; And

One control circuit, be coupled to described feedback circuit and described suitching type inverter, receive described impulse width modulation and light adjusting signal, when described impulse width modulation and light adjusting signal responsibility cycle is greater than described critical responsibility cycle and during enabling, controlling described suitching type inverter according to described first feedback voltage makes described lamp current be fixed on one first current value, in the time of during described impulse width modulation and light adjusting signal responsibility cycle is less than or equal to described critical responsibility cycle and is enabling, control described suitching type inverter according to described second feedback voltage and make described lamp current be fixed on one second current value, wherein said second current value is less than described first current value.

2. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described feedback circuit comprises:

One electric current changes potential circuit, receives described lamp current and converts a voltage signal according to this to;

One rectification circuit, being coupled to described electric current changes potential circuit, and described voltage signal is carried out rectification to produce a pulsed dc voltage signal;

One first feedback resistor, its first end are coupled to described rectification circuit to receive described pulsed dc voltage signal;

One second feedback resistor, its first end are coupled to described first feedback resistor, second end, and its second end is coupled to an earth terminal; And

One first filtering capacitor, its first end are coupled to described first feedback resistor, second end and described second feedback resistor, first end and export described first feedback voltage, and its second end is coupled to described earth terminal.

3. the backlight driving device in conjunction with simulation and digital dimming according to claim 2 is characterized in that described responsibility cycle detector comprises:

One diode, its anode tap receive described impulse width modulation and light adjusting signal;

One first voltage grading resistor, its first end is coupled to described diode cathode end;

One second voltage grading resistor, its first end are coupled to described first voltage grading resistor, second end, and its second end is coupled to described earth terminal;

One second filtering capacitor, its first end are coupled to described first voltage grading resistor, second end and described second voltage grading resistor, first end, and its second end is coupled to described earth terminal;

One the 3rd feedback resistor, its first end are coupled to described first feedback resistor, first end; And

One switch, its first end are coupled to described the 3rd feedback resistor second end, and its second end is coupled to described first feedback resistor, second end, and its control end is coupled to described second filtering capacitor, first end.

4. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described control circuit comprises:

One error amplifier is coupled to described feedback circuit, exports an error voltage according to the difference of a described feedback voltage and a reference voltage;

One oscillator is exported a ramp voltage;

One comparator is coupled to described error amplifier and described oscillator, more described error voltage and described ramp voltage, and output logic 1 or 0 according to this; And

One output driver is coupled to described comparator, and the output of the described comparator of foundation produces described control signal.

5. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described suitching type inverter comprises a full-bridge type inverter.

6. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described suitching type inverter comprises a semi-bridge type inverter.

7. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described suitching type inverter comprises a push-pull dc-to-ac.

8. the backlight driving device in conjunction with simulation and digital dimming according to claim 1 is characterized in that described backlight comprises a cold-cathode fluorescence lamp.