TWI239223B - Driving of discharge lamp tube and apparatus for controlling light adjustment - Google Patents

Abstract

Driving of the discharge lamp tube and apparatus for controlling light adjustment include a switching voltage regulator, a D/A converter, and a level-changing circuit. The switching voltage regulator has a switch apparatus for adjusting the mean value of the low-voltage DC signal. The D/A converter can increase the low-voltage DC signal to a high-voltage AC signal that is applied to the discharge lamp tube. The invented apparatus also includes a brightness controller, which has a brightness table defined by the relationship between the work cycle of the light-adjustment control signal and the current flow of lamp tube. Thus, it is capable of changing the work cycle of the light-adjustment control signal according to the corresponding lamp-tube current in the brightness table. The level-changing circuit is connected between the output terminal of the brightness controller and the control terminal of the switch apparatus provided for the switching voltage regulator, and is used for changing the light-adjustment control signal to the required voltage level of the turning-on switch apparatus.

Description

1239223 V. Description of the invention (1) The present invention relates to a circuit for driving a discharge lamp, and particularly to a backlight inverter of a liquid crystal display (LCD) device. In recent years, more and more information, communication and consumer electronics products use L · CD screens to display messages. Generally speaking, LCD panels use a backlight module that includes a discharge lamp to provide light to the panel. The displayed image is currently the cold-cathode fluorescent lamp (CCFL) in various types of discharge lamps to best meet the needs of LCD backlight modules. Since the CCFL requires a high AC voltage to operate properly ', a high efficiency DC / AC conversion circuit is indispensable for the backlight module. Figure 1 is a simplified circuit diagram of a traditional inverter of an LCD backlight module. As shown in the figure, a well-known Royer circuit is used to convert a low DC input voltage to drive a cold cathode fluorescent lamp. High AC output voltage of CCFL 102. The Royer circuit 11 includes a pair of transistors Qn and Q12, a step-up transformer n, and a resonant capacitor C11. The capacitor C11 is connected across the primary winding WP of the transformer T1. The secondary coil ^ is coupled to a ballast capacitor C12 and is connected in series with the lamp tube 102. The bases of the transistors Qn and Qn are driven by the feedback coil WF of the transformer τ1, so they are turned on and off in turn: a center tap on the primary winding Wp of the transformer Ti is coupled to a step-down ( buck) inductor L1, and the DC voltage source ^ is applied to = said, type switching device Q13 'The step-down inductor L1 between the center tap and the switching device Q13 can convert the input DC voltage into a DC current. In addition, the connection

Page 4 1239223 V. Description of the invention (2) The diode Dl 1 between the ground and the output of the switching device Q1 3 limits the voltage variation on the inductor L1. Continuing to refer to FIG. 1, the backlight module converter 100 also includes a pulse width modulation (PWM) circuit 120 for dimming control of the lamp tube 102. Due to the brightness of the lamp tube and the lamp current The size is directly proportional, so adjusting the current flowing through the lamp tube 102 can control the brightness of the LCD backlight module. Generally speaking, the lamp current can be sensed from the resistor R1 connected in series with the lamp 102, and the lamp current can be adjusted by changing the voltage on the inductor L1. The PWM circuit 120 detects a sensing signal from the feedback circuit. The feedback circuit is composed of a resistor R1 diode D1 2 and the ρψM circuit 120 also receives a brightness control signal 可变 with a variable DC level, so that A PWM signal is provided to the switching device Q13. The brightness control signal BR is generally supplied by an LCD panel controller (not shown), where the DC level represents the amount of current that is desired to flow through the lamp. As a result, the pwM circuit 12 changes the duty cycle of the PWM signal output to the switching device Q1 3 according to the brightness control signal BR and the feedback sensing signal, which enables the transistor-type switching device Q13 to change the inductance L1 The average voltage is used to control the lamp current and control the luminous brightness of the lamp 102. However, the traditional converter 100 only got the dimming control function at the cost of a feedback circuit outside the pWM circuit 120. However, it also caused a high number of parts and costs, especially large The manufacturing cost of each LCD backlight module is spent on the pwM circuit 120. There is a great need for a dimming control device that can abandon the rain circuit and can also be used by the LC. , And easy to use

1239223 V. Description of the invention ⑶ The present invention can invent the dimming control at a lower cost without the present system-type voltage regulator, a change-over voltage regulator connected with a switch to open the rush, because the road is accurate Bit. The alternating current supply and flow period can be used to do the variable control between the closed lamp working week and shut down. The DC lamp can be adjusted to discharge the lamp according to the industrialization. The purpose of the device is to provide a set current and fewer parts. The other purpose is to provide a device that requires a PWM circuit. ≪ For a drive discharge level conversion circuit and a DC voltage source, According to a dimming, the input DC power can be adjusted to adjust the low-voltage DC signal. The light control signal is converted to an AC converter to increase the voltage applied to the discharge lamp, and the lamp tube current is used as the period and the lamp current. The driver has this brightness table controlled by the dimming control. The brightness generates a dimming control signal setting, compared to traditional designs, to drive a discharge lamp. A kind of device suitable for the lamp tube of the LCD backlight module has been used to transfer the low voltage direct control signal to the voltage source to cut the average amount of the switch. The switch is equipped with the voltage and DC signal. In this high voltage, the relationship between the dimming control and the discharge lamp The tube-loaded signal work week controller is shaped according to and changes the tone, including the flow change flow signal work cycle. Position the required signal to an AC signal. The defined reset period and lamp brightness table light control a switch. The operating brightness table of the high-voltage signal that can be periodically pulsed and converted to electricity includes the corresponding signal in a bright tube current. On the other hand, the present invention also discloses a dimming control device for a discharge lamp, including an exchange Voltage regulator, DC-to-AC converter, a brightness controller and a level conversion circuit. Switching regulator receives a DC voltage source and generates a low-voltage DC signal. The switching regulator has a power switch

0535-7751TWF (N); A91038; mflin.ptd

1239223

The device ’can be turned on and off periodically according to the duty cycle of the dimming control signal to chop the input DC and L voltage sources to form pulses, so as to adjust the average amount of the low-voltage DC signal. The DC-to-AC converter can boost this low-voltage DC signal to high-voltage AC signal, & high-voltage AC signal application = discharge lamp, which can provide the lamp current flowing through the discharge lamp. The brightness controller has a brightness table that defines the relationship between the duty cycle of the dimming control signal and the lamp current; the brightness controller generates a dimming control signal and changes the dimming control signal according to the corresponding lamp current in the brightness table. Working period. In addition, a level conversion circuit is coupled between the output terminal of the brightness controller and the control terminal of the power switching device, and is used to convert the dimming control signal to the voltage level required to turn on the power switching device. [Example] Figure 2A is a block diagram of an LCD backlight module converter according to the present invention. In the figure, the switching regulator 230 receives a DC voltage source Vdc and generates a low-voltage DC signal DC1qw; the switching voltage regulator The converter 230 includes a switching device Q23, which can periodically turn on and off according to the duty cycle (duty cyc 1 e) of the dimming control signal dm to chop the input DC voltage source L to form a pulse, so that it can adjust the low voltage DC Signal DCi. · The average amount. The level conversion circuit 220 is coupled between the LCD panel controller 240 and the switching device Q23 to change the dimming control signal DM to a voltage level required to turn on the switching device. The DC-to-AC converter 2 1 0 can enhance the low-voltage DC signal DClc) w to convert to a high-voltage AC signal AChigh. In this way, the high-voltage AC signal AChigh is applied to the discharge lamp 202 to provide flow through

0535-7751TWF (N); A91038; mflin.ptd Page 7 1239223

The lamp current il of the discharge lamp officer 202. Among them, the LCD panel controller 240 has two brightness tables determined by the relationship between the duty cycle of the light control signal DM and the lamp current. In fact, the LCD panel controller 24 can be used as a shell controller. Therefore, the brightness controller (LCD panel controller) 240 f dimming control signal DM as an output, and the duty cycle of the dimming control signal is changed according to the corresponding lamp current in the brightness table. Figure 2B is a schematic circuit diagram of the present invention. In the embodiment, the switching regulator 230 is a step-down converter, the DC-to-AC converter 21 is a resonant push-pull converter, and the switching device q23 represents A transistor type = power switching device. The DC-to-AC converter 2 丨 〇 is composed of a step-up transformer T2 ′, a pair of transistors Q2i and Q22, and a capacitor C2i. The capacitor C21 is connected across the primary winding of the transformer T2. The transformer τ2's = secondary coil ^ is coupled to another capacitor C22 and connected in series to the lamp tube 202. The tube 202 represents a cold cathode fluorescent lamp f (CCFL), and the capacitor C22 can stabilize the lamp current. IL is used for output ballasting. Transformer D1 The center tap on the primary coil is coupled to inductor L2, and a DC voltage source Vdc is applied to the power switch Q23. The inductor L2 is connected to the center tap and power switching device Q23. In other words, as a current source, the DC-to-AC converter 210 is basically a current-fed resonant push-pull converter due to the presence of the inductor L2. In addition, the two connected between the ground and the output of the power switching device Q23 The polar body D21 is used as a cl ipping diode.… If the converter of the present invention is used in a battery-powered system, the DC voltage source VDC power supply range is 7 to 20 volts, and the rating is General DC battery with a voltage of about 12 volts. Step-up transformer T2 uses its feedback coil% control

1239223 V. Description of the invention (6) The transistors Q21 and Q22 are turned on and off in turn, while the inductor L2 and capacitor C21 force the DC-to-AC converter 2 1 0 to perform a sine-wave operation to provide the driving waveform of the car. Give the lamp tube 2 02, and the voltage increase can be achieved by increasing the coil ratio Ws of the transformer T2: (WP + WF). As a result, the low-voltage DC signal DClow can be raised to a relatively high level by the step-up transformer T2. AC voltage, for example, the starting voltage required to increase from 12 volts to CCFL lamps is about 1 500 volts. In order to achieve the effect of dimming control, the power j supplied by the buck converter 23 must be changed. Under the control of the dimming control signal DM, the power switching device Q23 connected in series with the direct current = VDC is turned on and off to prevent Lian Miao :: two supply 'so the voltage on the input terminal of the inductor L2 is chopped and two Therefore, the average amount of the DC to AC converter 2 10 input is adjusted to control the large lamp current lL. Brightness controller 2: Qianyi light control signal DM, which is essentially the same as the right. Steal, X, has a continuous pulse with a dimmable duty cycle, however, the dimming control signal DM still needs to be turned on to turn on the power switch. Among them, the quasi-promote switching 1: circuit 220 is coupled between the control terminals of the brightness control unit Q23. The output end of the port and the power switch The brightness table previously described can be obtained by testing. According to the invention, the experiment of the module and the duty cycle and lamp current! 1 week light control signal ⑽ One is shown ... W your degree table, as shown below

I $ 9 pages of 0535-775nW (N); A91038; mflin.ptd 1239223 V. Description of the invention (7) Table 1_Working period lamp current 56.8% 12_4 mA (maximum) 51.6% 11.2 mA 49.7% 9.94 mA 48.6% 8.70 mA 46.4% 7.40 mA 45.0% 6.05 mA (minimum value) Those who are familiar with this technology should be clear: For the sake of brevity, Table 1 only lists six brightness settings, and Table 1 is adjusting two Redundancy table under the condition of the brightness of the discharge lamp. Since the brightness of the lamp tube changes directly with the lamp current IL, the shell controller 240 changes the duty cycle of the dimming control signal DM based on the brightness meter to provide the desired amount of current flowing through the lamp tube. For example, 'If the dimming control signal DM output by the brightness controller 240 has a duty cycle of 56 · 8%', then according to Table 1, the converter of the present invention will generate the maximum lamp current and cause the lamp 202 to emit the maximum Of brightness. To sum up, the present invention realizes the function of variable dimming without the need of a PWM circuit and a feedback circuit. Furthermore, the LCD backlight module converter of the present invention simplifies the number of parts required for a conventional converter and reduces the number of parts. product

In fact, the use of the present invention can reduce 42.7% of parts, M. 25.7%. "Although the present invention has been disclosed as above with a specific embodiment, the bran is easy to explain the technical content of the present invention, but it is not intended to mean: in this embodiment, anyone skilled in this art will not depart from the present invention and target Within this range, some changes and retouching can be made, so the invention of this invention ": 0535-7751TiVF (N); A91038; mflin.ptd Page 10 1239223 V. Description of the invention (8) Scope of application The ones defined shall prevail. Pg. 11535-7751TWF (N); A91038; mflin.ptd 11 ^ 1239223 The diagram is briefly explained in order to make the above-mentioned objects, features, and advantages of the present invention more obvious and understandable. A preferred embodiment is given below in cooperation with The attached drawings are described in detail as follows: FIG. 1 is a schematic circuit diagram of a conventional LCD backlight module converter; FIG. 2A is a block schematic diagram of an LCD backlight module converter according to the present invention; Circuit diagram of the LCD backlight module converter invented. [Label description] 1 0 0 ~ traditional converter 102 ~ cold cathode fluorescent tube 11 0 ~ Royer circuit 120 ~ PWM circuit 202 ~ cold cathode fluorescent tube 2 1 0 ~ DC to AC converter 2 2 0 ~ Level conversion circuit 230 to switching regulator 240 to brightness controller C11 to resonance capacitor C12 to ballast capacitor C21 to capacitor C22 to capacitor D12 and D21 to diode L1 to step-down inductor

0535-7751TWF (N); A91038; mflin.ptd Page 12 1239223 Brief description of the diagram L2 ~ Inductor Q11, Q1 2 ~ Transistor Q21, Q22 ~ Transistor Q1 3 ~ Transistor Switching Device Q23 ~ Transistor Switch Device R, resistor D1 ~ step-up transformer T2 ~ step-up transformer m 0535-7751TWF (N); A91038; mflin.ptd page 13

Claims (1)

1239223 VI. Scope of patent application 1. A device for driving a discharge lamp includes: a switching voltage regulator that receives a DC voltage source and generates a low-voltage DC signal, and has a switching device according to a dimming control signal. A duty cycle is periodically turned on and off to chop the input DC voltage source to form a pulse, which is used to adjust the average amount of the low voltage DC signal; a level conversion circuit is used to change the dimming control signal To a voltage level required to turn on the switching device; and a DC-to-AC converter to boost the low-voltage DC signal to a high-voltage AC signal to be applied to a discharge lamp. The high-voltage AC signal can provide current A lamp current through the discharge lamp; wherein the duty cycle of the dimming control signal can be changed according to a brightness table defined by the relationship between the duty cycle and the lamp current. … 2 · The device for driving a discharge lamp as described in item 1 of the scope of patent application, further comprising a party controller with the above-mentioned dimming control signal duty cycle and the above-mentioned brightness table defined by the relationship between the lamp current and the lamp current. To generate the dimming control signal and change the duty cycle of the dimming control signal according to the corresponding lamp current in the exemption table. 3. The device for driving a discharge lamp as described in item 2 of Shenyan's patent scope, wherein the above-mentioned lamp current flowing through the above-mentioned discharge lamp is directly changed with the above-mentioned duty cycle of the dimming control signal. 4 · The device for driving a discharge lamp as described in item 1 of the patent scope of the patent, the above-mentioned switching device of the switching voltage regulator-a transistor type switch 5 · The device for driving the discharge lamp as described in the scope of the patent application of Shen Qiao Tube device, 1239223 6. Scope of application for patent among which the above-mentioned exchange type 6 · If applying for the above-mentioned DC conversion 7 ·-a type of discharge switching type, with periodic formation of pulse-AC and DC signals chopped in one working week; voltage regulator system A buck converter. For the device for driving a discharge lamp as described in the first item of the scope of interest, the parent current converter is a resonant push-pull converter. The dimming control device of the lamp tube includes a voltage regulator that receives a DC voltage source and generates a low voltage and a power switch device, and inputs and inputs the DC voltage source according to a place where the dimming control signal is turned on and off. 'To adjust the average of the low-voltage DC signal, a high-voltage signal can provide a quasi-power switch that lights up the corresponding light control signal in the tube meter to turn on the 8. If set, of which dimming control 9. If set, Among them, the power of the bit conversion device that transmits the AC signal flowing through the lamp number between the control flow of the degree is opened for application. The application of the above AC conversion number is used to apply the discharge signal to the discharge lamp, which is related to the current. The circuit, which controls the switching device, discharges the above-mentioned working range switching regulator 'to boost the low-voltage DC signal to a lamp current added to a discharge lamp, one of the high-voltage AC signal tubes; A brightness table of the duty cycle and definition of the light control signal, used to generate the dimming control signal and change the dimming period according to the brightness, and to consume The output of the brightness between the controllers and to the dimming control signal required for one voltage level transition. The dimming control of the discharge lamp described in item 7 above, the lamp current of the lamp changes directly with the above-mentioned different operating cycles. The power switching device of the dimming control device for the discharge lamp described in item 7 is a transistor 0535-7751TWF (N); A91〇38; mf1in.ptd Page 15 1239223 Six-patent application range Body-type switchgear placed in the lower room 10 · As in the patent application range No. 71 above, the above-mentioned exchange pressure regulator system-22] ：： The dimming control device 11 · Such as the 7th step of the patent application. Among them, the above-mentioned DC-to-AC conversion is mixed with the dimming control of the discharge lamp 1 2. If the seventh scope of the patent application is applied, the device is a resonant push-pull converter. In the above brightness table, the dimming control device of the discharge lamp is described in the above table. ^ ^ The brightness of the two discharge lamps is between 45.0% and 56.8%. 〇535-7751TWF (N); A91038; mflin.ptd