TWI282533B - Brightness-adjustable power transformation circuit for backlight module of display device - Google Patents

Abstract

The present invention relates to a brightness-adjustable power transformation circuit for backlight module of display device, which includes a transformer, a switch driver, a modulation control device, a burst mode control module and a linear mode control module. A center tap of a primary coil of the transformer receives a DC power, and a secondary coil generates an AC output voltage. A first switch device and a second switch device of the switch driver are connected with both ends of the primary coil, respectively. The first and second switch devices convert DC power into AC output voltage by using a push-pull method. The modulation control device provides a first modulation signal and a second modulation signal controlling the first and the second switch devices, respectively. The burst mode control module provides a burst signal to the modulation control device to output and limit the first and the second modulation signals. In addition, the linear mode control module provides a DC voltage such that the modulation control device modulates the first and the second modulation signals in accordance with the DC voltage.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of display devices, and more particularly to an adjustable brightness substation circuit suitable for use in a display device. Backlight module. ° Prior Crystal Display (LCD) panels are increasingly being used in many electronic devices, such as display screens for notebook computers, personal digital assistants (PDAs), and even information products. The flying instrument display system uses LCD technology. This type of product is usually used in different shades of the environment. In order to make the image displayed on the LCD screen more visible, the LCD display device needs a backlight source, that is, a back surface of the LCD panel. light source. In addition to providing a backlight to the LCD panel, it is also necessary to be able to adjust the intensity of the backlight so that the image on the LCD screen is clearly visible in different shades. Figure 1 shows the lamp inverter used in a conventional LCD backlight module. As shown in the figure, the converter 1〇{) includes a variable piezoelectric circuit, a buck power conversion circuit, and a Pulse Width Modulation (PWM). Among them, the primary side coil of the variable piezoelectric routing transformer T1, the transistor q2, the transistor Q3 and the related resistors R3, R4, and the inductance LI, the diode D1 and the transistor Q1 and the related resistors Rl, R2 constitute a drop. The step-d〇wn buck converter 'and the DC power input to the buck power conversion circuit. The transformer τι is connected to the transistor Q2 and the two ends of the primary side (the first and third legs) respectively.

[282533 _ V. Invention description (2) The extreme set of crystal Q3, while the flute 4 of the secondary side of the basin T1 is stolen, the central tap is connected to the inductor L1, the transformer end, and the second-underside flute R, To the fluorescent tube (LP) one of the LPs of the LP: another; 5: l^ change the circuit to control. And the S-shell can be increased by adjusting the demand of the buck-type power supply, and the manufacturing of the converter is reduced. The power U is not high, but the step-down electric diode D1 and the transistor qi shown in Fig. 1 are composed of: ίίΐΐΐ!路' is still a burden on the manufacturing cost. As a backlight, ^0 port used on both sides of the LCD panel with a light tube Tian Jiyao Yuyuan 'in view of this, this ancient road, available - transformer drive two lights ^ out - kind of redundancy Degree... The content of the invention is adjustable. The second type is suitable for the backlight module of the display device. The second and the second electric circuit have adjustable brightness and brightness ratio (dimming rat io) l〇〇: 1 〇色 for another purpose The invention provides an adjustable brightness substation circuit capable of driving a lamp in two LCD backlight modules in a left-handed manner. In order to achieve the purpose, the present invention provides an adjustable brightness substation circuit, which is used to display a backlight module. The adjustable brightness substation circuit according to the present invention includes a transformer, a switching drive device, a modulation control device, a burst mode control module, and a

1282533 V. Description of the invention (3) wherein the transformer has a primary side (sec nd ndary) line DC power supply for the linear mode control module c primary side and secondary side coils, The centertap end of the circle receives one and the electromyogram pair, and /tj generates an AC output voltage from the secondary side coil and supplies it to the display device backlight module. The switching drive device has a first switching device connected to one end of the primary side coil and a second switching device connected to the other end of the primary side coil, the first switching device and the second switching device being in a push-pul 1 manner The transformer converts the DC power to an AC output voltage. The modulation control device provides a first modulation signal and a second modulation signal for respectively controlling the first and second switching devices, and the first and second modulation signals have a first duty cycle to be turned on in turn. And closing the first and second switching devices. Furthermore, the 'pulse train control module provides _pulse signal to modulation control to modulate the first and second modulation signals, and the pulse signal has a second period to output and suppress the first and the second -1 material μ咕制楳接# Ancient 1 brother one tone change signal. Linear mode control voltage to modulation control device f, so that modulation and modulation: installed: according to DC adjustment voltage to adjust the first and second modulation = control module 'change the transmission frequency according to a start signal and the second adjustment The oscillating frequency of the variable signal can be: display: when the device is turned on, the AC output voltage is raised to - start the electric power. After the backlight module of the body light module device is turned on, the adjustment is adjusted after the display = signal Frequency, AC wheel and second pressure value. After w main hanging power

1282533

BRIEF DESCRIPTION OF THE DRAWINGS The objects, features, and advantages of the present invention can be more clearly understood from the following description. LCJ) Circuit 20 0 includes pretty crying T1 ^ 丄 〜 保 、 、 、 、 、 、 、 、 、 冗 冗 冗 冗 冗 〇 〇 〇 〇 〇 〇 〇 〇 〇 〇 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换 切换The linear mode control module 24〇C10 is applied to the iron-back control module 250. DC power supply Vdc via a bypass capacitor is also σ 坚 Τ 1 0 The center tap of the primary side coil (2nd foot), cut

The first switching device S10 and the second switching device S20 of the switching device 210 are respectively connected to the two ends (the jth and the third legs) of the primary winding of the transformer Τ10, and the first switching device S10 and the second switching device S20 are pushed and pulled by one. The method is turned on and off in turn so that the transformer T1 is turned on the secondary side coil to convert the DC power source I into an AC output voltage. Both ends (fourth and fifth legs) of the secondary side coil of the transformer 11 () drive the lamps LP1, LP2 and a capacitor C20 in parallel as a filter capacitor. The diodes D10, D20 and D30, D40 act as voltage rectifying circuits on LP1, LP2 to protect the lamp from being damaged by excessive output voltage. The feedback circuit 270 returns the signal of the contact F to the modulation control device 2 2 〇. The modulation control device 220 provides a first modulation signal 222 and a second modulation signal 224 for respectively controlling the first and second switching devices si, S20, so that the jth and second switching devices are turned on in a push-pull manner. And off. The modulation control device 22 0 is preferably a PWM control circuit, and the first and second switching devices S1 0, S 2 0 may be any switching device such as a transistor. Due to the magnitude of the AC output voltage generated by the transformer T1 0 on the secondary side coil and the primary side

1282533 V. Description of the invention (5) The length of the DC power supply VDC application time of the coil is approximately proportional to the frequency, for example, controlling the first and second modulation signals 222 of the first and second switching devices slS, S2〇 The higher the 224 frequency is, the larger the AC output voltage is, and the first and second modulation signals 222, 224 of 80% duty cycle control the AC output generated by the first and first switching devices S1 0, S 2 0 . The voltage, which is greater than the first and second modulation signals 222, 224 at 30% duty cycle, controls the AC output voltage produced by the first and second switching devices S10, S20.

The burst mode control module 203 provides a burst signal 2 3 2 to the P WM control circuit 220 to modulate the first and second modulation signals 222, 2 24, and the burst signal 2 3 2 is a periodic Pulses can output and suppress the first and second modulation signals 2 2 2, 2 2 4 . The linear mode control module 24 4 provides a DC regulation voltage 242 to the PWM control circuit 22 0. The PWM control circuit 22 0 can adjust the first and second modulation signals 2 2 according to the DC adjustment voltage 2 4 2 . 224 work cycle. In addition, since the illuminating lamp requires a high starting voltage, the adjustable brightness substation circuit 200 further includes a starting frequency control module 25 〇 that receives the start signal 2 6 2 provided by the optical subtraction circuit 260. . When the backlight module of the display device is turned on, since the light sensing circuit 260 does not sense sufficient brightness, the start signal 2 62 is sent, and the startup frequency control module 250 raises the PWM control according to the start signal 262 ' The frequency of the first and second modulation signals 222, 224 provided by the circuit 220 increases the AC output voltage to a startup voltage value to illuminate the lamps LP1, LP2. Then, after the backlight of the display device is lit, the light sensing circuit 206 picks up the start signal 2 6 2 , and the start frequency control module 250 adjusts the frequencies of the first and second modulated signals 2 22 , 224 . Make communication,

1282533 The output voltage returns to the normal operating voltage value. 3, with reference to 4a~4 (1, 5a~5c and 仏~"" to improve the brightness of the variable brightness substation circuit 2 〇〇. ρ · control circuit 220 The PWM generating circuit 226 and the driving transistor (31(), Q2〇 and the related resistors R10 and R20, and the bases of the driving transistors Q10 and Q2 are respectively connected to the output terminals 322 and 324 of the PWM generating circuit 226 to drive the transistor. The emitters of qi〇 and Q2〇 output first and second modulation signals 222 and 224 to respectively control the first and first switching devices S1 〇, s 2 0. As shown in the preferred embodiment of FIG. 3, PWM The generating circuit 226 receives the feedback signals provided by the feedback circuit 270 composed of the resistors R30 R R38 and C30 to C34 to adjust the pulse signals on the output terminals 322 and 324. Since the PWM control circuit 220 is familiar with the art. person

As is known, the detailed principles thereof will not be described again here. The DC regulation voltage 2 4 2 provided by the linear mode control module 2 4 可以 can be generated by dividing the supply voltage Vcc by the resistor R4 〇 and the variable resistor vr as shown in FIG. 3 . Referring to FIG. 4a, the PWM generating circuit 2 26 compares the result of the internally generated triangular wave 400 with the level of the DC adjusting voltage 242, and generates a pulse 42 at the base of the driving transistor Q10 (also driving the transistor Q2〇). The base generates another pulse wave. As shown in FIG. 4b, the pulse wave 420 is a Pulse-Width Modulation (PWM), and the duty cycle of the pulse wave 420 is in accordance with the DC adjustment voltage 242. And change. The pulse waves 43 0 and 440 in the 4C and 4d diagrams are used to illustrate the first and second modulation signals 222 respectively having 40% duty cycles on the emitters of the driving transistors q1() and Q2 0,

224, and the pulse waves 430, 440 in the 4e, 4f diagrams are used to illustrate the first and second modulation signals 222, 224 having a 10% duty cycle. User desire

0798-A20505TWF(Nl); C90020; MFLIN.ptd Page 10 1282533 V. Description of the invention (7) When adjusting the brightness of the LCD backlight module, the variable resistance VR can be adjusted to change the DC adjustment voltage 242, and then linearly adjust The duty cycle of the first and second modulation signals 222, 2 24 is changed. In this embodiment, the frequency ranges of the first and second modulation signals 222, 224 are between 40 KHz and 60 KHz.

In Fig. 4a, the frequency of the triangular wave 400 generated inside the PWM generating circuit 226 can be determined by the externally connected resistance value and capacitance value of the PWM generating circuit 226. Therefore, as shown in the preferred embodiment of FIG. 3, the startup frequency control module 250 can be composed of a switching device S50, a capacitor C50, and resistors R50 and R52. Since a high starting voltage is required when the lamp is started, it is required. The startup frequency of the PWM is increased. Therefore, when the startup signal 262 is issued, turning off the switching device S50 causes the resistor R50 to be connected in parallel with the resistor R52, and reduces the external resistance of the PWM generating circuit 226. As a result, the frequency of the triangular wave 410 generated inside the PWM generating circuit 226 is increased. Therefore, the frequencies of the first and second modulation signals 2 22, 224 are also increased. When the start signal 262 is retracted, the switch is turned on to install the iS50, so that the resistance value and the capacitance value of the external circuit of the pwM generating circuit 226 return to normal, thereby adjusting the first and third 's week change signals 222, 224 to return to the normal frequency.

The burst mode control module 230 can include a comparator 330. Referring to FIG. 5a, the 'burst mode control module 23 〇 is based on the triangular wave 50 〇 and the DC input voltage level on the two inputs 332, 334 of the comparator 33 〇. The pulse signal 232 is generated 51. The waveform 520 of the pulse signal 232 shown in FIG. 5b changes its duty cycle with the DC level 51〇, and the waveform 530 in FIG. 5c is used to illustrate that there are 5〇. Pulse train signal 232 of % duty cycle. The user can change the triangular wave frequency or the DC input voltage level on the two input terminals 332, 334 of the comparator 33 to adjust the brightness of the LCD backlight module.

0798-A20505TW(Nl); C90020; MFLIN.ptd Page 11 1282533 V. Description of invention (8) Degree. FIG. 6a illustrates a schematic diagram of the PWM generation circuit 226 outputting and suppressing the modulated signal waveform applied to the switching drive device 21 by the pulse train signal 232. The waveform 6〇〇 in the 6a and 6b diagrams represents the burst signal 232, 6a. In the figure 6c, the waveform 6 1 0 represents the first (second) modulation signal without the pulse train 2 3 2 modulation 2 2 2 (2 2 4) 'the waveform 6 2 0 in the 6th and 6th diagrams It represents the result of the pulse signal 232 modulation, as shown, when the pulse signal 232 is at a high level, the PWM generation circuit 226 can make the driving transistor Q1 〇 (Q2 〇) output first (second The modulation signal 222 (224) is switched to the switching device 21A, and when the pulse signal 232 is at the low level, the PWM generating circuit 226 causes the driving transistor Q10 (Q20) to suppress the first (second) modulation signal. 222 (224). In this way, according to the adjustable brightness substation circuit of the present invention, the adjustable brightness ratio of the brightness can be at least 100:1, and the frequency range of the pulse signal 232 is not caused by the flashing of the lamp. Between 2 〇〇 Hz and 400 Hz. In summary, the present invention discloses an adjustable brightness substation circuit suitable for a display device module, which can drive the lamps in the two LCD backlight modules in an economical manner and has at least 1 〇〇 1 and 4. Although the present invention has been disclosed above with reference to a specific embodiment, it is easy to explain the technical contents of the present invention, and the present invention is not intended to be used in the embodiment of the present invention. In the scope of this issue, the scope of the spirit of the day is subject to the definition of the patent application scope. ^The protection of the Ming

❶

1282533

The first diagram of the conventional substation circuit used in the lamp is a schematic diagram of the middle of the backlight module; the second diagram is a simple schematic diagram of the LCD back according to the present invention; the third embodiment of the adjustable brightness substation circuit of the optical module is according to the present 4A~4f is a schematic diagram illustrating the waveform of the modulation signal of the modulation control wave and the output; the circuit diagram of the example; the triangle 5a~5c generated by the internal oscillation is a description of the pulse mode control module A triangular wave. - a schematic diagram of the burst signal waveform output by the DC voltage;

Figures 6a to 6d are diagrams illustrating the modulation signal of the modulation control device by pulse train signal output and suppression applied to the switching drive device. DESCRIPTION OF REFERENCE NUMERALS 1 0 0~ conventional lamp tube converter; 11 0~PWM controller; 210~switching drive device; 220~modulation control device (pwM control circuit); 222~first modulation signal; 224~ Two modulation signals; 226~PWM generation circuit; 230~burst mode control module; 2 3 2~pulse signal; 240~ linear mode control module; 2 4 2~DC adjustment voltage;

1282533 Schematic description 250~ start frequency control module; 2 6 0~ light sensing circuit; 2 6 2~ start signal; 270~ feedback circuit; 322~PWM generation circuit one output; 324~PWM generation circuit Another output terminal of 226; 3 3 0~ comparator; 3 3 2~ one input terminal of comparator; 334~ another input terminal of comparator; 40 0~ triangular waveform generated inside PWM generating circuit 226; 41 0 ~ DC adjustment voltage level waveform; 4 2 0 ~ pulse waveform; 430~50% duty cycle first modulation signal waveform; 440~5 0% duty cycle second modulation signal waveform; 4 5 0~ The triangular waveform on the input of the comparator; 4 6 0~the DC input voltage level waveform on the other input of the comparator; 4 7 0~pulse signal waveform; 4 8 0~5 0 % duty cycle pulse train Signal waveform; 4 9 0~ waveform of the pulse signal modulation; 492~pulse signal waveform; 494~ waveform without pulse signal modulation; T1, T10~ transformer;

Dl, D10, D20 > D30, D40 ~ diode; U ~ inductance;

0798-A20505TWF(Nl);C90020;MFLIN.ptd Page 14 1282533 Schematic description LP, LP1, LP2~ lamp;

Ql, Q2, Q3, Q10, Q20~ transistor; CIO, C20, C30, C32, C34, C50~ capacitor;

Rl, R2, R3, R4, RIO, R20R, 30, R32, R34, R36, R38, R40, R50, R52~ resistance; S10, S20~ switching device; VR~variable resistor.

0798 - A20505TW( N1); C90020; MFLIN. p t d第15页

Claims (1)

1282533 VI. Application Patent Range ^ -- 1 · Adjustable brightness substation circuit suitable for backlight module of display device, including i ε device, with secondary side coil and one secondary side coil, the one receiving constant current power supply, For pressing on the secondary side and providing the backlight module to the display device; having a first switching device connected to the primary switching device connected to the secondary side coil and the second switching device in a push-pull manner Converting the source into the AC wheel-out voltage; the central tap-end coil of the secondary side coil generates an AC output power-switching drive device, one end of the side coil and a second end, and the first switching device has a tone change The variable control is configured to respectively provide the DC power generating device with the second first pulse-changing device, and the first device for controlling the first switching signal has a signal and the first string mode control device has a signal number and The second modulation-linear mode control device is configured such that the first application specifically includes a start-up frequency signal to change the first change. The control mode adjusts the second-tone variable range control mode to control the first modulation signal and a second modulation signal off device and the second switching device, the first first working cycle is turned on and off in turn a switching device; a module that provides a pulse train signal to the modulation. The Zhouliang signal and the second modulation signal, the pulse period is to output and suppress the first modulation signal, and the group 'provides a constant current adjustment voltage to the modulation control device according to the DC adjustment voltage to adjust the signal The first work cycle. . The adjustable brightness power-changing circuit of the first item is further configured to: the first frequency and the first rate provided by the start-up frequency control module for the backlight of the display device to be modulated by the backlight One shock frequency 1282533 VI. _ Please patent range When opening, increase the above-mentioned AC output voltage to - start voltage 3. As described in item 2 of the patent application scope. The startup frequency control module adjusts the oscillation frequency of the second seventh and fruit group lighting signals of the modulation control device after the display of the electrical circuit, and the second modulation of the alternating current is constantly working. Voltage value. ^Output voltage returns to a positive 4·If you apply for a patent range! The above-mentioned modulation control device is a pulse width modulation control. The adjustable brightness power conversion % as described in claim 4 of the patent application. The pulse width modulation control circuit changes the first duty cycle of the first modulation signal according to the level of the DC adjustment voltage provided by the linear mode group to adjust the above-mentioned The pulse width of the second modulation signal is described. The adjustable brightness substation circuit of claim 5, wherein the first and the last modulation signals provided by the pulse width modulation control circuit have a periodicity of one of the periodic oscillation frequencies. 7. The adjustable brightness substation circuit of claim 6, wherein the first and second modulation signals have an oscillation frequency range of 40 KHz to 60 KHz. 8. The adjustable brightness power-changing circuit of claim 1, wherein the pulse train mode control module adjusts the second duty cycle of the pulse train signal to modulate a pulse width of the pulse train signal The length of time for outputting and suppressing the first modulation signal and the second modulation signal is controlled. I face 0798-A20505TWF (Nl); C90020; MFLIN.ptd Page 17 1282533 9 · If applying for a patent, one of the above pulse train modes is a pulse frequency. The adjustable brightness substation circuit of the range 8th, the pulse signal provided by the control module has a period of 11; as in the first application of the patent scope, wherein the above-mentioned switching drive device is above the adjustable brightness substation circuit , transistor. The first and upper second switching devices are 0798-A20505TW(Nl);C90020;MFLIN.ptd第18页