TWI245150B - Programmable distributed multiple lamps CCFL inverter system - Google Patents

Abstract

A CCFL inverter system for multiple lamps in LCD display is provided. The system is consisting of a controller and multiple drivers. The controller senses the current of each lamp and provides PWM signals for each driver. Each driver drives a transformer and delivers power to the lamps. The controller provides phase shift of lamp current as well as burst dimming pulse to reduce the power supply current ripple. The programming capability provides versatile brightness control and lamp failure management.

Description

1245150 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a backlight tube driving system, particularly a programmable decentralized multi-lamp liquid crystal display backlight driving system. [Previous Technology] As the application of liquid crystal displays gradually expands, its size also gradually increases, so the number of cold cathode tubes used in backlight sources must also be increased to maintain the same or higher brightness. Based on the brightness distribution average sentence and the requirements for extending the lamp's life, the absolute value and relative difference of the lamp current should be carefully controlled. The increase in the number of lamps also greatly increases the probability of damage to a single lamp of the display. There are three types of conventional multi-lamp modules, according to the circuit structure of pushing / controlling the lamps. Please refer to "Figure 1 1 A" to "Figure 1 1 C". As shown in the "Figure 1A", each backlight tube 400 and its control / driving circuit 500 are a set of independent circuits, and include diodes 401 and 402 and a ninth resistor R 9. The multi-lamp module is to repeat this circuit multiple times. The disadvantage is that the module cost increases linearly in proportion to the number of lamps. "Figure 1 1B" shows that multiple backlight tubes 400 are driven by a single control / push circuit 500. The current difference between the backlight tubes 400 is compensated by a capacitor 403 connected in series to the high voltage end of the tube. The disadvantage is that to make the capacitor 403 have the effect of the balance tube current, the capacitor impedance must be close to the lamp impedance. In this way, the working voltage of the secondary side of the transformer is greatly increased, which causes the transformer 300 cost to rise, the reliability of the module to decline, and the power efficiency of the module to be reduced accordingly. As shown in "Figure 1 1C", the current difference between the lamps is compensated by a passive balance network 600 connected in series to the high-voltage side and the low-voltage side. Its disadvantages

1245150 V. Description of the invention (2) Yes, the balanced network 6 0 0 is suitable for dual lamp groups. A single PWM can drive up to four lamps. There is no phase difference between the lamp currents of the same group of lamps. If a single lamp fails, the remaining lamp currents must be switched off when they are out of balance. From the above description of the prior art, with the current increase in the size of LCD screens, there are more and more backlight lamps. Therefore, the current balance and failure management of the lamps have become a very important technical topic. [Summary of the Invention]

In view of the above problems, the main object of the present invention is to provide a programmable decentralized multi-lamp liquid crystal display backlight driving system, so as to solve the technical problems existing in the prior art.

Therefore, in order to achieve the above object, the programmable decentralized multi-lamp liquid crystal display backlight driving system disclosed in the present invention is used to drive more than one backlight tube / group. The backlight tube is output by a transformer according to a driver. The driving signal is promoted. The system includes: a controller that detects the current of the backlight tube to generate a corresponding pulse width modulation signal and a dimming pulse wave, and outputs a pulse width modulation driving signal according to which Each pulse width modulation driving signal can freely combine the pulse width modulation signal and the dimming pulse wave; and more than one driver receives the corresponding pulse width modulation driving signal to drive the corresponding driver. , So that the driver pushes the corresponding backlight tube / group to emit light. The programmable decentralized multi-lamp liquid crystal display backlight driving system disclosed in the present invention is a multi-lamp backlight driving system using control and driving circuits separated. This system can meet the low cost of four or more lamps,

Page 7 1245150 V. Description of the invention (4) 4 0 0 and a current detection circuit 7 0 0, in which a plurality of passive components are coupled. The driver 200 drives the transformer 300 according to the corresponding PWM drive signal output terminal. A primary capacitor C 1 is connected in series on one end of the primary side, and a backlight tube 4 0 is coupled on one end of the secondary side. The backlight tube 400 is connected in parallel with a second capacitor C2 and a third capacitor C3, and the second capacitor C2 and the third capacitor C3 are coupled to the driver 2000. Transformer 300 is used to output high voltage to drive backlight backlight tube 400. The current detection circuit 700 detects the output current of the transformer 300 and the output current of the backlight tube 400 respectively.

The controller 1 0 0 detects a single lamp current to generate a corresponding PWM driving signal to the driver 2 0 0. The driver 2 0 0 provides a high voltage to illuminate the backlight tube 4 through a transformer 3 0 0. 0. The PWM drive signals and dimming pulses generated by the controller 100 have phase shifts to reduce power supply current fluctuations, and linear dimming or pulse dimming are used. In addition, the controller 100 can feedback the lamp voltage when the lamp current feedback signal is low. The driver 200 detects the lamp current and the secondary current of the transformer. If each exceeds a predetermined value, the driver 200 will automatically shorten the driving pulse width of the PWM driving signal.

The controller 100 is divided into five basic blocks. As shown in the "Figure 2", it is composed of the central processing unit 110, the multi-phase PWM time base generation module 120, and the multi-phase dimming pulse wave generation mode. Group 1 3 0, pulse width modulation module 1 40, and multiplexer 1 50. The CPU 1 1 0 executes a control program to set the multi-phase PWM time base

Page 9 1245150 V. Description of the invention (5) Generate module 1 2 0, multi-phase dimming pulse group 1 4 0 and multiplex cry, ^ Λ branch, and 1 30, pulse width modulation mode 7 states 1 5 0 function fish parameters. Qianshi from the bus of data & data. The central processor 110 writes the internal registers of the four modules to the female furnace 4 Central Lu Sou cry · η η There is a program in the six states of heart suppression processing mode 110 Cunjie saves the preset program, the program is stored in memory (ROM), the important uncle Ding, the cat π storage state can be a read-only memory , Can be crying from external storage ^ / 1 can be sighed in the program memory (ROM) program can also be provided by the outer shirt & — μ σ * 〒 funeral ”face k. The control interface interface to provide for 1, work storage 15 read The central processor 110 provides detailed information about the operating status of this system to the group via the terminal k. The detailed operation process is explained in the following paragraphs. The core current of the invention = phase shift of the lamp current can reduce the power supply current Npple. Refer to "Figure 3", which is a multi-phase pwM time base generation mode, a block diagram of 120, which is composed of a PWM divider 121 and the Yeh group shift record state 1 22, each shift The bit recorder i 22 generates a PWM time base. Yau has the Npwm group. The PWM divider 121 operates with reference to the system clock. ^ The multi-phase PWM time base generation module ι20 provides the pwM time base. The CPU 1 1 0 sets the PWM divider 1 2 1 to get the PWM time base. The shift register 122 sets the Npwm group time base Take four lamps as an example. For example, if the phase of the lamp current is divided into four groups (Npwm =: 4) in equal proportion, that is, the phase shift of each group is 90 degrees. Taking eight lamps as an example, It can be divided into four groups of lamp current phases, one phase is shared by two lamps, or it is divided into eight groups of current phases, one for each lamp. I. The present invention provides a lamp that can adjust its current magnitude and Grouping dimming pulses to adjust the brightness of the lamps. Grouping the dimming pulses of multiple lamps as a phase shift can avoid the instantaneous high current generated by the power supply when the backlight system is started, and it can reduce

Page 10 1245150, description of the invention (6) Source current fluctuation map [Paragraph 4] is a block of a multi-phase dimming pulse wave generating module 1 3 0, which generates Nburst dimming pulse wave phases. The frequency of the dimming pulse is determined by the setting value of the dimming wave divider 1 3 1 according to the lamp operating frequency Fp ·. The width of the dimming pulse is determined by the setting value of the dimming pulse width register 1 32. Medium 2 The processor 1 1 0 reads the brightness control input voltage value through the multiplexer 1 50 to externally adjust the light pulse wave divider 131 to obtain the corresponding backlight brightness. The dimming pulse width is stored again. The 1 and 1 series are temporarily stored with a dimming pulse width on-period. The dimming pulse wave divider 131 is commonly input to: connection = comparison? The output of 134 and the dimming pulse wave divider 131 have the -pulse wave; setting two: the bit recorder 135 generates the-dimming pulse wave, each group example bitmap ^ four lamps as an example,

In place: Every two lamps share the -J π V group dimming pulse wave phase, one for each lamp. [Figure 5] is a pulse width modulation (PWM) mode

In this case, the output of the variable group 140 corresponds to the driving signal of 422, to provide the PWM no. Of each lamp, which is read into the lamp current processor via the multiplexer 150. The turn-on cycle adjusts the direction and number. And threshold comparison

The pulse width modulation (PWM) module 140 is composed of a corresponding on-period counting module 141, and each PWM signal 141 outputs a PWM driving signal. Lai ¥ cycle counting module 1245150 V. Description of the invention (7) Enter the Pw central processing unit U0 and write the preset value of the MM duty cycle to pm, / register 1411. At the beginning of the PWM on period, this preset value is loaded into the temporary ¥ on period register 1 4 1 2. Comparator 1 4 1 4 compares the PWM on period ::: 1412 and the output value of divider 1413 with? The $ elbow time base and the dimming pulse λ ++ corresponding on-period are used as the pWM drive signal output. The derivation of the Γ :: base determines the phase & of the lamp current, and the dimming pulse determines the lamp wave i ^ The total number of lamps Nlamp and PWM time base, and the dimming pulse ^ base and dimming pulse. For example, when eight lamps are divided into four groups of pwM, "M (Npwm 2 4)" and eight groups of dimming pulses (Nburst = 8) are used. The controller 1 00 needs to convert the linear signal to a digital signal to perform the calculation. CPU n. Selection via 15 multiplexers: signal. Please refer to "Figure 6". For the block diagram of the multiplexer 15, the signal = 151 is used to convert the input linear signal to a digital signal for use in the evening D conversion 1 50. The central processing unit i 丨 〇 converts the brightness control voltage to. The pulse width of the Xigong device, and then read in the current of each tube in sequence, after comparing the predetermined dimming tube turn-on period. Each CPU 1 1 0 has a soft start, soft start, and function. Soft start (SOU start) is to increase the pulse width of the backlight system to start the dithering until the lamp current reaches a predetermined value, which is fast or slow ... Step by step, the soft on is at the beginning of each dimming pulse. . The tube current is gradually increased to avoid the audible noise generated by the transformer. The lamp system must be started initially and the dimming pulse wave must be started. The second adjustment of the lamp current pulse width is to gradually increase the lamp pulse width. 7 ~ or more pulses of modulation signal

1245150 V. Description of the invention (8) A small difference in the pulse width arrangement of adjacent signals. The working principle is similar to soft start. At the beginning of the system startup, the frequency of the lamp's current pulse width modulation signal is raised, and the set value is restored after the lamp is lit. The anti-jitter (a η ΐ i f 1 i c k e r i n g) is due to the strong negative resistance of the lamp at low temperature, which causes the lamp current to jitter and the temperature of the lamp to rise. At the beginning of the backlight system, the pulse width modulation is periodically adjusted within a predetermined period of time. For example, the lamp current is inconsistent with the positive and negative half cycles or the interval period pulse width is not the same, which can suppress the lamp current jitter.

"Figure 7" shows a schematic diagram of the central processing unit 1 10 responsible for executing control programs to set and maintain the functions of each module. The processor 1 10 is used to connect with other modules to control the operation of other modules And operates according to the system clock. The program memory 111 is used to store the required programs, and communicates with the central processing unit 110 through a data bus (external data bus and external address bus).

The central processing unit 1 10 reads the backlight backlight current values (such as brightness control and lamp current) and transmits the system via a serial bus (such as a system management bus (SM bus) or an I 2C bus) and external communication. Status information (such as lamp failure). The system clock (systemc 1 ock) of the central processing unit 1 10 can take the shadow clock (dot / pixe 1 c 1 ock) of the image (vide ο) system, so that the lamp current and the dimming pulse can be related to the image The signal is synchronized to avoid the interference of the backlight system on the image. In addition, the central processing unit 100 can also synchronize with the synchronization signal (horizontal synchronization signal H-Sync, vertical synchronization signal V-Sync) in the video signal. The lamp current pulse width modulation signal and dimming pulse wave are synchronized with the system clock.

Page 13 1245150 V. Description of the invention (9) The controller 1 0 0 generates a PWM driving signal for each / each group of lamps to drive a high power driver 2 0 0. The driver 200 shifts the low-voltage PWM driving signal through a voltage shifter 210 to drive the power crystal. The driver 2000 uses a power transistor to drive the transformer. It can use a full-bridge type (as shown in Figure 8A), a half-bridge type (as shown in Figure 8B), and a push-pull type (such as [Shown in Figure 8C].

In the "Figure 8A", the first transistor Q1 and the second transistor Q2 are connected in series and coupled to a voltage shifter 2 1 0. Similarly, the third transistor Q3 is connected in series with the fourth transistor Q4 , And is coupled to the voltage shifter 210. One end of the transformer 3 0 0 primary side is coupled between the first transistor Q1 and the second transistor Q2 through a first capacitor C 1, and the other end is coupled to the third transistor Q3 and the fourth transistor Q 4. between. The voltage shifter 210 obtains a first comparison signal from a first comparator CMP1, and obtains a second comparison signal from a second comparator CMP2. The first comparison signal is the result after comparing the current on the secondary side of the transformer 300 with a reference value, and the second comparison signal is the result after comparing the current on the backlight tube 400 with a reference value.

The half-bridge connection shown in "Figure 8B" is a series connection of the first transistor Q1 and the second transistor Q2, and one end of the primary side of the transformer 300 is coupled to the first transistor Q1. In the middle of the second transistor Q2, the other end is connected to the ground terminal through a capacitor C4. The "push-pull" connection system shown in "Figure 8C" couples the first transistor Q 1 and the second transistor Q 2 to the two ends of the transformer 300 primary side, respectively. The driver 2000 can also monitor the voltage and current on the secondary side of the transformer to provide protection. If the lamp fails, the driver will automatically shorten the conduction period to maintain

Page 14 1245150 5. Within the spirit and scope of the invention description (π), some modifications and retouching can be made. Therefore, the scope of patent protection of the present invention shall be determined by the scope of the patent application attached to this specification.

Page 1245150 Brief description of the diagram. The first diagram is the system architecture diagram of the programmable decentralized multi-lamp liquid crystal display backlight drive system disclosed in the present invention. The second diagram is the controller of the drive system in the first diagram. Block diagram; Figure 3 is a block diagram of a multi-phase PWM time base generating module; Figure 4 is a block diagram of a multi-phase dimming pulse wave generating module; Figure 5 is a pulse width modulation (PWM) ) Module block diagram; Figure 6 is a block diagram of brightness adjustment and lamp current feedback multiplexer; Figure 7 is a relationship diagram between the central processing unit and each module executing the program; Figure 8 A Figure 8B is the driver of the full bridge connection method; Figure 8B is the driver of the half-bridge connection method; Figure 8C is the driver of the push-pull connection method; Figure 9 is the lamp current and voltage shared feedback Schematic diagram of the circuit; Figures 10A to 10B are examples of the current detection circuit; Figure 1A is the circuit structure of the dual-lamp module disclosed in the prior art, Figure 1 1B The figure is the second of the dual-lamp module circuit structure disclosed in the prior art; and FIG. 1 1 C Three pairs of the lamp module circuit configuration disclosed prior art. [Illustration of Symbols] 100 controller 2 0 0 driver 3 0 0 transformer 4 0 0 backlight tube 5 0 0 control / push circuit

1245150 on page 17 Brief description of the diagram 6 0 0 Balanced network 7 0 0 Current detection circuit 110 CPU 120 Multi-phase PWM time base generation module 130 Multi-phase dimming pulse wave generation module 140 Pulse width modulation module 150 Multiplexer 111 Program memory 121 PWM divider

122 Shift recorder 131 Dimming pulse wave divider 132 Dimming pulse width register 133 Dimming pulse width on period register 13 4 Comparator 135 Shift register 141 PWM on period counting module 1411 PWM temporary storage 1412 PWM on-cycle register 1413 Divider

1414 Comparator 151 A / D converter 210 Voltage shifter 401 Diode 40 2 Diode

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Claims (1)

1245150 _Case No. 92130785_ Year Month__ VI. Scope of patent application Light tube / group connection is used to detect the current of the one or more backlight tubes / groups and the current of the transformer. 2. The programmable decentralized multi-lamp liquid crystal display backlight driving system according to item 1 of the scope of patent application, wherein the multi-phase PWM time base generation module further includes: a PWM divider, according to the central processor's Set to generate a PWM time base; and The complex array shift recorder shifts the PWM time base as the pulse width modulation signal. 3. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the multi-phase dimming pulse wave generating module further includes: a dimming pulse width register, which To store a set value to determine the pulse width of the dimming pulse; a dimming pulse width on-period register, which outputs a on-period according to the set value; A dimming pulse wave divider, the central processor reads a brightness control input voltage value through the multiplexer to set the dimming pulse wave divider to obtain the corresponding backlight brightness; a comparator, according to the on period and The backlight brightness outputs a dimming pulse wave; and a complex array shift register for phase shifting the dimming pulse wave. 4. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the pulse width modulation module further includes: Page 21 1245150 _Case No. 92130785_Year Month Day__ VI. Scope of patent application The complex array PWM on-cycle counting module is used to output the PWM driving signal. 5. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 4 of the scope of patent application, wherein the PWM on-cycle counting module further includes: a PWM register, storing a PWM on-cycle preset Value; a PWM on-period register, used to load the preset value at the beginning of the PWM on-period; A comparator is used to compare the output values of the PWM on-period register and a divider, the PWM time base and the dimming pulse wave to generate corresponding on-periods as the PWM drive signal output. 6. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the system clock of the controller is obtained from the shadow clock. 7. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, the lamp current pulse width modulation signal and dimming pulse are synchronized with the system clock. 8. Programmable dispersed multi-lamp liquid crystal as described in item 1 of the scope of patent application The display backlight driving system, wherein the current detection circuit includes a fifth resistor for sampling the transformer current; and a sixth resistor for sampling the backlight tube current. 9. The programmable decentralized multi-lamp liquid crystal display backlight driving system as described in item 1 of the scope of patent application, wherein the current detection circuit includes a seventh resistor for sampling the transformer current; and an eighth resistor connected in parallel with each other. Page 22 1245150 _Case No. 92130785_ Year Month__ VI. Patent Application Range The resistor and the fourth capacitor are coupled between the seventh resistor and the ground terminal to sample the current of the backlight tube. 10. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein a secondary impedance and a secondary impedance are connected in series between the secondary side of the transformer and the ground terminal. 11. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 9 of the scope of patent application, which further includes a zener diode coupled to the lamp current feedback output terminal of the current detection circuit. Between the first impedance and the second impedance. 12. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the controller obtains system setting parameters and provides system working status via a serial bus. 1 3. According to the programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, during the initial period of system startup, the lamp current pulse width modulation signal is changed every two or more There is a small difference in the pulse width of adjacent signals. 14. The programmable decentralized multi-lamp liquid crystal display backlight driving system as described in item 1 of the scope of patent application, wherein the lamp current pulse width modulates the pulse width of the lamp at the start of the system and the start of the dimming pulse. Department is rising gradually. 15. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the lamp current pulse width modulation signal frequency is raised at the start of the system, and the lamp is After lighting, the setting value will be restored. 16. Programmable dispersed multi-lamp liquid crystal as described in item 1 of the scope of patent application Page 23 1245150 _Case No. 92130785_Year_Month__ VI. Patent application scope Display backlight driving system, in which the controller feedbacks the lamp voltage when the lamp current feedback signal is low. 17. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the dimming method of the controller is linear dimming or pulse dimming. 18. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the driver is a full bridge type. 19. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the driver is a half-bridge type. 20. The programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the driver is a push-pull type. 2 1. The back programmable decentralized multi-lamp liquid crystal display backlight driving system described in item 1 of the scope of patent application, wherein the driver detects the lamp voltage and the secondary current of the transformer, if each exceeds a predetermined value , The driver automatically shortens the driving pulse width of the PWM driving signal.