Patent Application
20070024209
The present invention relates to a protection control circuit for discharge lamps and particularly to a protection control circuit adopted for used on a plurality of discharge lamp driving lines to provide independent protection control.
Electricity control techniques for inverters are known in the art. U.S. Pat. No. 6,791,239 proposed by the Applicant is such an example. That technique focuses on the conventional inverter circuit and includes an individual pulse-width modulation (PWM) control unit, a driving unit, and a voltage boosting unit to drive an individual discharge lamp (CCFL or EEFL). As the size of display panels increases gradually, the number of the discharge lamps also increases. The required electricity increases too. Hence the size of circuit board to accommodate the configuration of the PWM control unit, driving unit and voltage boosting unit made according to the number of discharge lamps is larger, and circuit layout and production are more difficult. Illumination and electric field interference among the discharge lamps also increases. As a result, luminance uniformity suffers. While the aforesaid technique provides a solution, it mainly aims to provide, through a single PWM control unit, synchronous driving signals of the same phase and same frequency according to the driving units and voltage boosting units that are required to drive the discharge lamps on the rear end. Thereby each driving unit, voltage boosting unit and discharge lamp can be driven synchronously to achieve the uniform luminance.
U.S. Pat. No. 6,867,955 and U.S. Patent Publication Ser. No. 2005/0122066 A1 disclose other techniques to address the arc discharge phenomenon occurred to an inverter at a high voltage output zone in abnormal conditions. They provide a protection device which generates a protection signal which is fed back to a control unit to stop high voltage output in the high voltage zone.
However, with the size of the display panel increased constantly, the number of the discharge lamps increases even more. The driving lines for the driving units, voltage boosting units and discharge lamps also increase. If one of the lines is abnormal (not necessary malfunctions, could be an irregular voltage for a short period of time), the control unit receives the signal and stops all driving signals. If this situation occurs to the upper discharge lamps where heat concentrates, the display panel will be shut down and cannot display. Moreover, as the display panel becomes larger, if merely one discharge lamp is abnormal, it does not seriously effect user's viewing of the display panel. Hence the existing techniques that provide a single protection control mode are troublesome and undesirable.
Therefore the primary object of the present invention is to solve the aforesaid problems. The invention provides a protection control circuit that controls each driving line independently. In the event that one of the lines is abnormal, electricity output is suspended or temporarily halted only on that abnormal line. Hence the driving line of each discharge lamp can be protected and controlled independently.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
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The first electricity condition is an electric conductive condition and the second electricity condition is an electric interrupt or idle condition. The switch device 20 may be an analog switch, relay, micro-controller or an electronic element capable of distributing multiple signals. As shown in the drawing, the control unit 11 converts the first voltage distribution signal through the switch device 20 to a plurality of second voltage distribution signals to the driving lines L1-L4. It is to be noted that, depending on different electric characteristics of electronic elements, the multiple second voltage distribution signals may have same phase and same frequency as taught in U.S. Pat. No. 6,791,239. Thereby uniform luminance can be achieved on the discharge lamps 141-144. For the switch device 20 made of a micro-controller, in the event that an abnormal condition occurred to each of the driving lines L1-L4 (such as the voltage alters due to increasing of line resistance), the second voltage distribution signals of the abnormal driving lines L1-L4 can be regulated according to the feedback protection signals A, B, C and D to enhance the uniform luminance of the discharge lamps 141-144. The invention mainly aims to feed back the protection signals A, B, C and D of the driving lines L1-L4 to the switch device 20. The feedback approach can adopt, but not limited to, the direct feedback as shown in the drawing, or the ones adopted in U.S. Pat. No. 6,867,955 and U.S. Patent Publication Ser. No. 2005/0122066A1. Whatever the feedback approach, in the event that one of the driving lines L1-L4 is abnormal (say L1), the protection signal A fed back on the abnormal circuit L1 is detected by the switch device 20, and the abnormal circuit L1 is switched to the second electricity condition. The rest driving lines L2-L4 are not affected and can function continuously.
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While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
