JPH0590897U - Cold cathode tube lighting device - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to reduce the size of a backlight lighting device of a display device using liquid crystal and reduce the voltage thereof. [Configuration] First oscillation transformer 21, resonance capacitor 22
And a first oscillating circuit composed of transistors 23 and 24 connected thereto, a second oscillating transformer 25, and a resonance capacitor 2
2 and a second oscillating circuit composed of transistors 23 and 24 connected to the second oscillating circuit. They are connected to each other. A capacitor 26 is connected in series between each of the secondary windings and each of the electrodes.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a backlight lighting device such as a liquid crystal display panel of a display device.

[0002]

[Prior Art]

 In recent liquid crystal display devices, it is common practice to illuminate a liquid crystal display panel or the like from the back surface. FIG. 4 is a cross-sectional view of an example of this lighting device. In the figure, 1 is a light guide, 2 is a reflecting surface, 3 is a diffusing surface, 4 is a light source, and a cold cathode tube is generally used. 5 is a liquid crystal plate.

In the illumination device having such a configuration, the light from the tubular light source 4 propagates in the light guide body 1 as shown by the arrow in the figure, and the light propagated upward is directly diffused by the diffusion surface 3. The light propagating downward is reflected by the reflecting surface 2, passes through the light guide 1 again, is diffused by the diffusing surface 3, and in any case, is transmitted through the liquid crystal plate 5.

As a result, the transmittance varies depending on the liquid crystal pattern displayed on the liquid crystal plate 5, and the pattern can be recognized even in a dark place.

As an example of a lighting device of a lighting device in this case, a device having a configuration as shown in FIG. 3 is conventionally known. This is a oscillating circuit consisting of an oscillating transformer 11 consisting of a primary winding, a secondary winding and a feedback winding, a resonance capacitor 12, transistors 13 and 14, and generates a high frequency sinusoidal voltage from a DC voltage (+ DC) to the secondary winding. Let This frequency is generally 20 to 70 kHz.

One end of this secondary winding is grounded, and the other end is connected to one electrode of a cold cathode fluorescent lamp (CFL) 16 via a capacitor 15. The other electrode of the cold cathode fluorescent lamp (CFL) 16 is grounded.

In this case, the voltage applied to the cold cathode tube 16 needs to be, for example, 2 kV, although it depends on its length.

[0008]

[Problems to be solved by the device]

 However, it is difficult to reduce the size of the oscillation transformer 11 at a voltage of 2 kV due to insulation problems.

Further, in order to increase the size of the display surface, it is necessary to increase the length of the cold cathode tube 16, and inevitably it is necessary to increase the applied voltage accordingly. As a result, the problem of insulation becomes more serious and the size reduction of the oscillation transformer 11 becomes more difficult.

It is an object of the present invention to solve the above problems and provide a lighting device having a small oscillation transformer capable of lighting a long cold cathode fluorescent lamp 16.

[0011]

[Means for Solving the Problems]

 In order to solve the above-mentioned problem, in a lighting device that generates a high frequency voltage from a DC power supply by an oscillation circuit and lights a cold cathode tube 27, a first oscillation transformer 21 having a primary winding, a secondary winding and a feedback winding. And a second oscillating transformer 25 having a primary winding and a secondary winding, one end of each secondary winding is grounded, and the other end is in reverse phase. It is connected to the electrode of.

Further, capacitors 26 and 26 are connected in series between the other ends of the secondary windings of the first and second oscillation transformers 21 and 25 and the electrodes of the cold cathode tubes 27, respectively.

[0013]

【Example】

 FIG. 1 is a circuit diagram showing an example of a lighting device of the present invention. The first oscillating transformer 21, the resonance capacitor 22, and the transistors 23 and 24 are the same as in the case of FIG. 3, so the description of this part is omitted.

Usually, since the liquid crystal display device is often thin, the price of one transformer having a plurality of windings is lower than the cost of two transformers because of space limitations. The stage two-oscillation transformer 25 is designed so that one transformer has a plurality of windings, and the feedback voltage of the oscillation circuit on the second oscillation transformer 25 side is obtained from the feedback winding of the first oscillation transformer 21. There is.

Therefore, although the oscillation phases of the first and second oscillation transformers 21 and 25 are completely the same, their respective secondary windings are completely independent.

In this case, one end of each secondary winding is grounded, and the other end on the opposite phase side is connected to both electrodes of the cold cathode tube 27 via capacitors 26, 26, respectively. The voltage between both electrodes is the sum of the voltages generated in each secondary winding.

Therefore, when the generated voltage of each secondary winding is set to 1 kV, the voltage applied to the electrode of the cold cathode tube 27 becomes 2 kV, which is the same as the applied voltage of 2 kV in the case of FIG. Since the generated voltage is 1 kV, the withstand voltage of each winding is half that in the case of FIG.

That is, the lighting device only needs to generate a voltage that is half the voltage applied to the electrodes of the cold cathode tubes 27, and the withstand voltage can be suppressed to a low level. Therefore, the oscillation transformer can be downsized. It is possible to

Further, the capacitors 26, 26 connected between the respective secondary windings and the electrodes of the cold cathode tubes 27 can balance the discharge of the cold cathode tubes 27 and stabilize the lighting. The generated electric field is small because the voltage applied to the cold cathode tube 27 is low and the first and second oscillating transformers 21 and 25 have opposite polarities, so that they do not affect other circuits.

FIG. 2 is a circuit diagram showing another example of the lighting device of the present invention. In this case, by connecting the first oscillating transformer 21 and the second oscillating transformer 25 to the common transistors 23 and 24 and reversing the polarities of the first oscillating transformer 21 and the second oscillating transformer 25, the cold cathode tube 27 The phase of the terminal portion connected to the first oscillation transformer 21 and the phase of the terminal portion connected to the second oscillation transformer 25 are reversed.

Even if the oscillation transformer of the double bobbin structure in which the primary winding bobbin is arranged inside the iron core and the secondary winding bobbin is arranged concentrically outside the iron core is used as it is in the circuit of the device of the present application, Although there is no problem above, the shape becomes large and it is not possible to apply it to a thin lighting device.

Therefore, even if the primary winding bobbin and the secondary winding bobbin are arranged in series with respect to the iron core and the primary side and the secondary side are arranged side by side, in the case of the circuit of the present application, the secondary side Since the voltage generated by the winding is half the voltage applied to the cold-cathode tube 27, the withstand voltage structure can be simplified accordingly, dielectric breakdown does not occur between the primary and secondary windings, and the oscillation transformer itself can be made compact and thin. It is extremely effective as a lighting device.

[0023]

[Effect of the device]

 As described above, in the case of the cold cathode tube of the conventional length, the oscillation transformer can be downsized, and in the case of using the oscillation transformer of the conventional scale, the cold cathode tube of double the length can be turned on. .

Further, the capacitors 26 and 26 connected between the respective secondary windings and the respective electrodes of the cold cathode tubes 27 stabilize the discharge and stabilize the operation of the liquid crystal.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an example of a lighting device of the present invention.

FIG. 2 is a circuit diagram of another example of the lighting device of the present invention.

FIG. 3 is a circuit diagram of an example of a conventional lighting device.

FIG. 4 is a cross-sectional view of an example of a backlight of a liquid crystal display device of a display device.

[Explanation of symbols]

 21 First Oscillation Transformer 22 Resonant Capacitor 23 Transistor 24 Transistor 25 Second Oscillation Transformer 26 Capacitor 27 Cold Cathode Tube

Claims (4)

[Scope of utility model registration request] 1. A lighting device for generating a high frequency voltage from a direct current power source by an oscillation circuit to light a cold cathode tube, comprising:
It has a first oscillation transformer having a secondary winding, a secondary winding and a feedback winding, and a second oscillation transformer having a primary winding and a secondary winding, and grounds one end of each secondary winding and reverses the other end. A cold-cathode tube lighting device, which is connected to each electrode of a cold-cathode tube in a phase manner. 2. The cold cathode tube lighting according to claim 1, wherein a capacitor is connected in series between each of the other ends of the secondary windings of the first and second oscillation transformers and the electrodes of the cold cathode tube. apparatus. 3. A circuit for converting a direct current connected to the first oscillation transformer into an alternating current and a circuit for converting a direct current connected to the second oscillation transformer to an alternating current are separate circuits. 1 or 2 cold cathode tube lighting device. 4. The circuit for converting a direct current connected to the first oscillation transformer into an alternating current is also used as a circuit for converting a direct current connected to the second oscillation transformer into an alternating current. Cold cathode tube lighting device.