JP3839760B2 - Backlight for LCD - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cold cathode tube control circuit, and more particularly to a cold cathode tube control circuit applicable to a liquid crystal display.
[0002]
[Prior art]
In recent years, color liquid crystal displays have been used as color display devices for notebook personal computers and small liquid crystal televisions.
[0003]
A color filter system is used for colorization of color liquid crystal displays except for a few special systems.
[0004]
In a liquid crystal display device that enables color display in combination with a color filter, color display is performed by combining dots of three colors of red, green, and blue.
[0005]
This color filter is very expensive, and high accuracy is required for the work of attaching to the panel.
[0006]
Furthermore, using a color filter requires three times the number of dots in order to achieve the same resolution as a monochrome liquid crystal display panel, so the number of horizontal drive circuits in a normal liquid crystal panel is tripled. Thus, the cost is increased, and the number of connection points between the panel and the drive circuit is tripled, so that the connection work becomes difficult.
[0007]
Therefore, as a method of performing color display using a liquid crystal panel, a method using a color filter has many elements that are expensive in terms of cost, and is difficult to manufacture at a low cost. Further, since the light transmittance of the color filter is only about 20%, and the brightness is reduced to about 1/5 by using the color filter, the power consumption of the backlight becomes very large. was there.
[0008]
As a color liquid crystal display device that does not use a color filter, as a field sequential method, a method of performing color display by combining a monochrome liquid crystal panel and a three-color backlight is proposed as disclosed in JP-A-1-179914. Compared with the method, high-definition color display can be realized at low cost. As for the three-color backlight, as in Japanese Patent Application No. 7-271994 and Japanese Patent Application No. 8-49476, three cold cathode tubes that emit red, green, and blue are used. And a method of fitting in a space equivalent to a thin backlight using a light guide plate.
[0009]
However, the part of the inverter circuit that generates a high voltage to light the cold cathode tube is difficult to switch by an inexpensive semiconductor switch, and an inverter is connected to each cold cathode tube, and the output of the three inverters is output. By controlling, lighting of the three cold cathode tubes was controlled. In addition, regarding the size of the inverter, although the lighting time is one third or less, the peak current does not change so much, so the coil and other parts cannot be reduced in size. Therefore, three inverters having the same size as the conventional one are required, which is a serious problem for use in notebook personal computers. In addition, the inverter is a problem because the inverter is many times more expensive than the cold cathode tube.
[0010]
Further, as shown in FIG. 3, for example, three cold cathode tubes 5, 6 and 7 that generate red, green, and blue are generally easily available and inexpensive in a high withstand voltage bidirectional current. connected in series to switches 8, 9 and 10 made of bi-directional thyristors flown respectively, means that the voltage from the high voltage generating means 4a made of the DC power source 1 and the inverter 3 which these indicia pressurized contemplated.
[0011]
However, when the voltage from the high voltage generating means 4a and marked pressure, under the condition where the switches 8, 9 and 10 of all of the bidirectional thyristor in the OFF state, the breakdown voltage of these switches 8, 9 and 10 is not sufficient , Any one of the cold-cathode tubes 5, 6 or 7 is discharged, and is not completely extinguished.
[0012]
Therefore, it is considered difficult to control the lighting of the cold cathode tube by the bidirectional thyristor. In the prior art, as shown in FIG. 4, independent inverters 3a and 3b are provided for the cold cathode tubes 5, 6 and 7, respectively. And 3c are connected, and the input power supply of each of the inverters 3a, 3b and 3c is controlled by the switches 2a, 2b and 2c, so that the lighting of the cold cathode tubes 5, 6 and 7 is controlled. It cannot be solved.
[0013]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and a problem to be solved by the present invention is to provide a cold cathode tube control circuit that controls lighting of a plurality of cold cathode tubes with a single inverter. It is.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a high voltage generating means (4) whose output is controllable , and a plurality of cold cathode tubes (5, 6, 7) connected in parallel to each other, in parallel with each other. A plurality of switch means (8, 9, 10) connected in series to the plurality of cold cathode tubes (5, 6, 7), and receiving a high voltage from the high voltage generating means (4). One of the switching means (8, 9, 10) is turned on before application, and then the high voltage is applied to connect one cooling means connected to the one switching means (8, 9, 10). There is provided a control circuit for a cold cathode tube, wherein only the cathode tube (5, 6, 7) is turned on.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[0016]
FIG. 1 shows a block diagram of a preferred embodiment of the present invention, in which a high voltage generating means 4 whose output can be controlled by a DC power source 1, a semiconductor switch 2 using a transistor and an inverter 3 is constructed. The
[0017]
The high voltage generating means 4 capable of controlling the output is connected in parallel with three cold cathode tubes 5, 6 and 7 for developing red, green and blue colors, The cathode tubes 5, 6 and 7 are connected in series with switch means 8, 9 and 10 each consisting of a bidirectional thyristor which is easy to obtain and inexpensive and which allows a current to flow in both directions with high withstand voltage.
[0018]
In the embodiment of the present invention, the power source of the inverter 3 in the high voltage generating means 4 is controlled in addition to the switch means 8, 9 and 10 which are bidirectional thyristors connected in series to the cold cathode tubes 5, 6 and 7, respectively. By providing the switch 2 to be operated and controlling the switch 2 and the switch means 8, 9 and 10 in combination, the discharge of the cold cathode tubes 5, 6 and 7 can be controlled stably.
[0019]
In more detail, the switching means 8, 9 and 10 made of bi-directional thyristor is in the OFF state, a high voltage from the high voltage generating means 4 are marked pressurized discharge either of the cold-cathode tube 5, 6 or 7 Will happen. In order to solve this problem, when it is not desired to discharge the cold cathode fluorescent lamp 5, 6 or 7, the switch 2 constituting the high voltage generating means 4 is turned off so that the output voltage of the inverter 3 is lower than the discharge start voltage. This makes it possible to stop the discharge of all the cold cathode tubes 5, 6 and 7.
[0020]
Regarding the selection of the cold cathode tubes 5, 6 and 7 to be lit, in the field sequential method, the cold cathode tubes 5, 6 and 7 to be lit simultaneously are always one of red, green and blue. In addition, it is necessary to leave several milliseconds after one cold cathode tube 5, 6 or 7 is turned off until another cold cathode tube 5, 6 or 7 is turned on next time.
[0021]
Accordingly, as shown in FIG. 2, when the switch 2 is a high voltage from the inverter 3 in the ON state is marked pressurized, only one sure of the switching means 8, 9 and 10 can be turned ON is there. In this case, if the discharge start voltages of the cold cathode fluorescent lamps 5, 6 and 7 are the same, only one of the cold cathode fluorescent lamps 5, 6 or 7 connected in series with the ON switch is turned on.
[0022]
Further, since one of the cold cathode tubes 5, 6 or 7 is lit, the output voltage of the inverter 3 is lowered, so that the cold cathode tube connected in series with the other switch means 8, 9 or 10 in the OFF state. No discharge occurs in 5, 6 or 7. Therefore, it is possible to reliably light only the selected one of the cold cathode tubes 5, 6 or 7 and not cause the other cold cathode tubes 5, 6 or 7 to discharge.
[0023]
It is switch 2 to the ON state in FIG. 2, before the high voltage is marked pressurized from the inverter 3, one of the switching means 8, 9 and 10 has become ON state. This is for lighting the cold cathode fluorescent lamp 5, 6 or 7 connected in series to the switch means 8, 9 or 10 which is surely turned on, but normally the switch 2 is turned on and the inverter 3 is turned on. Since the time from when the power is turned on to when the high voltage is output is longer than the time until the switch means 8, 9 or 10 is turned on, it may be simultaneously performed. In addition, a certain period of time is allowed after the switch 2 is turned off until all the switch means 8, 9 and 10 are turned off. This takes into account the time difference until the output of the inverter 3 in the high voltage generating means 4 becomes equal to or lower than the discharge start voltage of the cold cathode tubes 5, 6 or 7, and may be necessary depending on the type of the inverter. . By controlling as described above, lighting of the cold cathode fluorescent lamps 5, 6 and 7 can be stably controlled.
[0024]
【The invention's effect】
In the embodiment of the present invention, lighting of three cold cathode fluorescent lamps can be controlled by one inverter, the number of inverters can be reduced to one third, and the cost can be greatly reduced and the size can be reduced. It becomes. In addition, depending on the arrangement of the switch means connected in series to each cold cathode tube, it is possible to reduce the size by integrating a single route for high voltage wiring.
[0025]
Further, when the cold cathode tube is not lit, the inverter input power supply is in the OFF state, so that useless power consumption can be prevented.
[0026]
Furthermore, as an application range of the present invention, not only a field sequential type backlight but also a wide range of applications can be applied to a system that is used while switching the lighting of a plurality of discharge tubes.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a timing chart of the embodiment of the present invention.
FIG. 3 is a block diagram of the prior art.
FIG. 4 is a block diagram of a different prior art.
[Explanation of symbols]
4 High voltage generating means 5 Cold cathode tube 6 Cold cathode tube 7 Cold cathode tube 8 Switch means 9 Switch means 10 Switch means

Claims (1)

High voltage generating means (4) whose output can be controlled, a plurality of cold cathode tubes (5, 6, 7) connected in parallel to each other, and a plurality of cold cathode tubes (parallel to each other) A plurality of switch means (8, 9, 10) connected in series to 5, 6, 7),
Before applying a high voltage from the high voltage generating means (4), one of the switch means (8, 9, 10) is turned on, and then the high voltage is applied to the one switch means (8, 9). 10) A control circuit for a cold-cathode tube, wherein only one cold-cathode tube (5, 6, 7) connected to 10) is turned on.

Images