JP2002359092A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in a conventional discharge lamp lighting device wherein a difference is made in voltages applied to the electrodes 21, 22 of the discharge lamp 20 due to different stray capacitance of cables 31, 32 connected to the discharge lamp 20, causing early deterioration of the discharge lamp 20. SOLUTION: This lighting device is provided with secondary windings 2a, 2b connected at one end in common having the same specifications, a discharge lamp 20 having electrodes at both ends, a cable 31, and a cable 32 having a shorter straight line between its both ends than that of the cable 31. The other end of the secondary winding 2a is connected to one electrode 21 of the discharge lamp 20 through a first wiring passage including the cable 31, and the other end of the secondary winding 2b to the other electrode 22 through a second wiring passage including the cable 32. A capacitive component is added between the second wiring passage and the earth, and the capacitance between the earth and the first wiring passage is equalized to that between the earth and the second wiring passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting apparatus suitable for a direct type small liquid crystal monitor in which a discharge lamp is mounted on the back of a liquid crystal display panel.

[0002]

2. Description of the Related Art As a method of lighting a discharge lamp, there are two types: a direct type in which a discharge lamp is attached to the back of a liquid crystal display panel; Are mainly used. In this direct type, a discharge lamp in which an elongated tube is bent in a U-shape or the like is used instead of a straight tube type discharge lamp.

In order to light such a long U-shaped discharge lamp 20, a higher kick-off (open output) voltage is required. For this purpose, for example, an inverter circuit having two secondary windings 2a and 2b as shown in FIG. 3 is used. The secondary windings 2a and 2b have the same number of turns, and the primary winding 1
Are electromagnetically coupled with the same degree of coupling. Q1 and Q2 are push-pull switching transistors, R is a bias resistor, C is a resonance capacitor connected in parallel with the primary winding 1, and an intermediate tap of the primary winding 1 is an input terminal via a choke coil L. 3 is connected.

[0004] Reference numeral 4a denotes a connector serving as a contact between the cable 31 and the secondary winding 2a, and reference numeral 4b denotes a connector serving as a contact between the cable 32 and the secondary winding 2b. One ends of the two secondary windings 2a and 2b of the inverter transformer T are both grounded.
The other end of the secondary winding 2a is connected to the electrode 21 of the discharge lamp 20 via a wiring path including the connector 4a and the cable 31. The other end of the secondary winding 2b is connected to the electrode 22 via a wiring path including the connector 4b and the cable 32. When a DC voltage is applied to the input terminal 3, a high-frequency sine wave is output to the secondary windings 2a and 2b of the inverter transformer T, and the discharge lamp 20 is turned on with a double voltage.

FIG. 4 is a diagram showing a schematic configuration of a liquid crystal display panel. Reference numeral 20 denotes a U-shaped discharge lamp mounted on the back of the liquid crystal display panel 10. Space constraints in the liquid crystal display panel 10 and a high-voltage inverter transformer T
Cause secondary noise 2a, 2b
Is connected to the end of the liquid crystal display panel 10 as shown in the figure. Therefore, one electrode 21 of the discharge lamp 20 is connected to the connector 4 via the long cable 31, and the other electrode 22 is connected to the connector 4 via the short cable 32. The secondary windings 2a and 2b (FIG. 3) of the inverter transformer T are connected to the connector 4.

[0006]

SUMMARY OF THE INVENTION Two cables 31, 32
Since the lengths of the cables 31 and 32 are different from each other, a difference occurs in the magnitude of the stray capacity generated in each of the cables 31 and 32. As a result, there is a problem that a difference occurs in the output voltage applied to each of the electrodes 21 and 22 of the discharge lamp 20, and the deterioration of the discharge lamp 20 is accelerated. An object of the present invention is to eliminate imbalance of voltages applied to both electrodes 21 and 22 and to prevent early deterioration of the discharge lamp 20.

[0007]

SUMMARY OF THE INVENTION The present invention provides a secondary winding 2a, 2b having the same specifications, one end of which is commonly connected, a discharge lamp 20 having electrodes at both ends, a cable 31, and both ends of the cable 31. A cable 32 having a short linear distance between the other ends of the secondary winding 2a connected to one electrode of the discharge lamp 20 via a first wiring path including the cable 31; In the discharge lamp lighting device in which the other end of the secondary winding 2b is connected to the other end of the secondary winding 2b via the second wiring path including the cable 32, a capacitance component is added between the second wiring path and the ground, It is characterized in that the capacitance between the ground and the second wiring path is equalized.

[0008]

FIG. 1 is an inverter circuit diagram showing one embodiment of the present invention. Parts common to the conventional inverter circuit of FIG. 3 are denoted by the same reference numerals in FIG. This inverter circuit is different from the conventional one in that a capacitor 5 is inserted between a ground line, which is connected between one electrode 22 of the discharge lamp 20 and the secondary winding 2b and includes a cable 32 and a connector 4b, and ground. It is in the point which did.

That is, as compared with the wiring path including the longer cable 31 connected to the other electrode 21 side of the discharge lamp 20, the stray capacity of the wiring path on the shorter cable 32 side is smaller than the capacitance of the capacitor 5. Is supplemented by By inserting the capacitor 5, the capacitance between the grounds of the wiring path on the long cable 31 side and the wiring path on the short cable 32 side is made substantially the same.

On the other hand, FIG. 2 shows another embodiment of the present invention, in which a cable 32 having a shorter linear distance X between both ends is deformed to have a meandering shape. In this example, the cable 32 is formed by a conductor pattern provided on the printed circuit board 6. The meandering of the cable increases the stray capacity. Therefore, without adding the capacitor 5 as in the above-described embodiment, the two cables 3 are used.
The stray capacity of 1, 32 can be made about the same size.

As described above, one electrode of the discharge lamp 20
A secondary winding 2 via a first wiring path including a cable 31 to 21
a, the secondary winding 2b is connected to the other electrode 22 via the second wiring path including the cable 32, and the capacitance between the grounds of the first and second wiring paths in the discharge lamp lighting device. Are equal, so both electrodes of the discharge lamp 20 at the time of lighting are
Voltages of the same level are applied to 21 and 22 in a well-balanced manner. Note that, although the description has been given of the example of the inverter circuit in which the secondary windings 2a and 2b are provided in one inverter transformer T,
The present invention can be applied to an inverter circuit having two inverter transformers Ta and Tb of the same specification as shown in FIG. Parts corresponding to the inverter circuit in FIG. 3 are denoted by the same reference numerals in FIG.

[0012]

According to the present invention, the imbalance of the voltage applied to the electrodes at both ends of the discharge lamp can be eliminated by a simple process of simply adding a capacitance component to the wiring path side of the shorter cable, and the discharge can be prevented. The durability of the lamp can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is an enlarged plan view showing a modified example of the cable.

FIG. 3 is a circuit diagram illustrating an example of an inverter circuit.

FIG. 4 is a schematic configuration diagram of a liquid crystal display panel.

FIG. 5 is a circuit diagram showing another configuration example of the inverter circuit.

[Explanation of symbols]

 2a Secondary winding 2b Secondary winding 20 Discharge lamp 31 Cable 32 Cable

Continued on the front page F term (reference) 3K014 AA02 BA00 3K072 AA01 BA03 BC02 CA16 GA01 GB14 GC03 HA09 5H007 AA07 BB03 CA01 CB03 CB06 CC32 EA08 FA14 FA16 HA03

Claims (3)

[Claims] 1. A first of the same specification having one end commonly connected.
A second secondary winding, a discharge lamp having electrodes at both ends,
A first cable and a second cable having a shorter linear distance between both ends than the first cable, the first cable being connected to one electrode of the discharge lamp via a first wiring path including the first cable;
Discharge lamp lighting device in which the other end of the secondary winding is connected and the other end of the second secondary winding is connected to the other electrode of the discharge lamp via a second wiring path including a second cable. 3. The discharge lamp lighting device according to claim 1, wherein a capacitance component is added between the second wiring path and the ground, and the first wiring path and the second wiring path have the same capacitance between the grounds. 2. The discharge lamp lighting device according to claim 1, wherein the added capacitance component is a capacitor element inserted between the second wiring path and the ground. 3. The discharge lamp lighting device according to claim 1, wherein the added capacity component is a stray capacity increased by meandering the second cable.