JP2003217878A - Method of driving cold-cathode lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of driving a cold-cathode lamp capable of preventing the electric leakage in safety, and stably supplying the power. <P>SOLUTION: This method is applied to a cold-cathode lamp of a back light module in a liquid crystal monitor of a large size, and drives the cold-cathode lamps with the voltage of constant phase difference between the adjacent cold- cathode lamps, to drive a number of cold-cathode lamps under a predetermined power source, and to reduce troubles such as electric leakage. The constant phase difference is regularly generated between the adjacent cold-cathode lamps. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a cold cathode fluorescent lamp used for a liquid crystal backlight or the like, and more particularly to driving a large number of cathode fluorescent lamps simultaneously. About the method. 2. Description of the Related Art A liquid crystal monitor using a backlight module has an advantage that power consumption is small when compared with other monitors (CRT, PDP). Is large in size,
Therefore, in order to provide the necessary light source for the liquid crystal monitor, the total number of lumens of the light source provided by the backlight module must be increased. To solve this problem, the illuminance of the cold cathode lamp in the backlight module is increased. Or by increasing the number of cold cathode lamps. The backlight module has a type in which light enters from the side (see FIG. 1). In this type, a cold cathode lamp 2 is provided near the light guide plate 1, and a reflection plate 3 is attached to the bottom side of the light guide plate 1. A light diffusing film 4 having different optical characteristics is further provided on the surface of the light guide plate 3 from which light is emitted, and the light source of the cold cathode lamp 2 is a light source such as the light guide plate 1, the reflection plate 3, and the light diffusion film 4. After refraction of
By reflecting, the light source emits light toward the liquid crystal cell 5 aligned above. Another direct-type backlight module currently used by a manufacturer is that several cold cathode lamps 7 are provided in a cover 6 having a reflection function as shown in FIG. A light diffusing film 8 having different optical characteristics is provided between the lamp 7 and the liquid crystal cell 9, and when each of the cold cathode lamps 7 emits light, the light source irradiates the liquid crystal cell 9 directly through the light diffusing film 8. Provide a light source. [0004] However, in the backlight module according to the above-described system in which light enters from the side, the illuminance is about 2000 cd / cm ² , and the light source required for a large-sized liquid crystal monitor is A backlight module that allows light to enter from the side does not have much power. In the case of using a direct-type backlight module, since a large number of cold-cathode lamps are mounted and no light source input mediation is required by the light guide plate, there is no waste caused by the light source penetrating the light guide plate. Although a large amount of light sources are used and generally provide an illuminance of 10,000 cd / cm ² , a disadvantage is that when each of the CCFLs is installed at a short distance, the CCFL has a high voltage and a high frequency, so that an electric leakage occurs. And the problem of power supply occurs, and such a problem is dealt with by controlling the voltage phase of the power supply, but the phases of the adjacent cold cathode lamps are not always the same, A large earth leakage may occur naturally. In addition, the irregular phase difference has a disadvantage that an electric leakage phenomenon occurs irregularly and the whole becomes unstable. Such a problem is dealt with by a driving circuit (inverter) of the cold cathode lamp. Therefore, various vendors designed the inverter drive circuit to be synchronous,
Although this simultaneous circuit design can overcome situations such as earth leakage caused by interference due to phase mismatch between loads at startup,
There is a drawback that the power supply becomes unstable at the time of start-up because it requires a maximum power on the power supply, and furthermore, the voltage suddenly increases or decreases, so the life of each part is shortened, and of course the liquid crystal It also affects monitor quality. Therefore, a cold cathode lamp driving method according to the present invention is provided so as to provide a safe and stable power supply by preventing electric leakage. [0005] A method of driving a cold cathode lamp with a voltage having a constant phase difference is used to generate a constant phase difference between adjacent cold cathode lamps. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driving method in which a large number of cold cathode tubes (T) are mounted is applied to a driving method of a cold cathode tube of a direct type backlight module for monitoring a liquid crystal having a particularly large size. Rather than having the drive inverter circuit be a synchronous circuit as in the structure, the drive inverter was designed to drive each load by a constant phase difference voltage method, and each inverter 10 was mounted. When driving the cold cathode lamp (T), a constant phase difference appears between each adjacent cold cathode lamp (T), and various choices are provided in the circuit design of the constant phase difference. For example, when applying a D-type inverter (see Fig. 4) or other digital control methods, and supplying a power supply with a certain phase difference to each cold cathode lamp (T), it is formed from the design stage. As can be seen from the waveform representing the phase difference (see FIG. 5), it is possible to know the position where the appropriate inverter 10 and the cold cathode etc. (T) match each other, and between each adjacent cold cathode lamp (T). In the situation where all the phase differences occur, and each phase difference is the same value, the cold cathode lamp (T) greatly reduces the power required at the time of starting, thereby driving successfully (see FIG. 6), Also, the occurrence rate of electric leakage and the like can be greatly reduced. According to the present invention, the rate of occurrence of electric leakage and the like is greatly reduced, and the waveform suddenly becomes maximum at the time of startup even when a large power supply is required for the application of the synchronous circuit. Therefore, it was possible to avoid the shortening of the life caused by such a problem.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural explanatory view of a side light type backlight module having a known structure. FIG. 2 is a structural explanatory view of a direct-type backlight module in a known structure. FIG. 3 is a diagram showing the power of a synchronous circuit in a known structure. FIG. 4 is a circuit diagram using a D-type inverter according to the present invention. FIG. 5 is an explanatory view of an embodiment of the present invention. FIG. 6 is a diagram showing power output from a power supply according to the present invention. [Description of Signs] 1 Light guide plate 2 Cold cathode lamp (CCFT) 3 Reflector (reflective sheet) 4 Light diffusion film (light diffusion sheet) 5 Liquid crystal cell 6 Cover 7 Cold cathode lamp 8 Light diffusion film 9 Liquid crystal cell

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Claims (1)

The present invention is used for a cold cathode lamp of a backlight module in a large-sized liquid crystal monitor, and drives a large number of cold cathode lamps under a predetermined power supply. A method of driving a cold cathode lamp, wherein a constant phase difference is provided between each adjacent cold cathode lamp in order to reduce the light emission.