JPH0689788A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To reduce the ripple current of a smoother capacitor and prevent discharge lamp from flickering by alternately switching the switching elements of a plurality of inverter circuits connected in parallel with a DC power supply. CONSTITUTION:Using a drive pulse generating circuit 13, drive pulses S1, S2 are impressed to the gates of switching elements 6, 10. If therein the period of the drive pulses is represented by T, the pulses S1, S2 are emitted alternately at the interval T/2, and the switching elements 6, 10 are turned on and off alternately. Accordingly ripples on the discharge current (i) to a smoother capacitor 2 can be made smaller than when the switching elements 6, 10 are turned on and off simultaneously. This allows reducing noises on the power supply line, preventing discharge lamps FL1, FL2 from flickering, and suppressing self-heating of the smoother capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight for lighting a back light of a liquid crystal display used for office automation equipment (OA equipment) or a back light for meters of automobiles. The present invention relates to a lighting device.

[0002]

2. Description of the Related Art Conventionally, fluorescent lamps have been used for backlighting liquid crystal displays and the like, but external electrode type discharge lamps having no filament are being developed for backlights. In this discharge lamp, a rare gas such as xenon (Xe) is sealed in the lamp tube at about 100 torr, and a high frequency high voltage of about 30 kHz is applied to a pair of external electrodes provided on the tube wall of the lamp tube. Is lit. This discharge lamp has the advantage that it is brighter than the case where a fluorescent lamp is used as a backlight, since it serves as a light emitting surface except for the electrode attachment portion. Further, it is possible to easily construct a lamp tube that is arbitrarily curved in accordance with the curved shape of the portion to be back-illuminated, and there is an advantage that it can be illuminated from the back without waste. In order to light two such discharge lamps in parallel, two sets of inverter circuits are connected in parallel to a DC power source in which smoothing capacitors are connected in parallel, and a current limiting capacitor is connected to the secondary side of the oscillation transformer of each inverter circuit. Connect the discharge lamp via. A switching element is connected in series to the primary winding of the oscillation transformer. Conventionally, a drive pulse is applied simultaneously to the gate terminals of the switching elements of the inverter circuit to light two discharge lamps.

[0003]

In the conventional lighting device,
Since the switching elements of the inverter circuit are turned on / off at the same time, there is a problem that a large ripple current flows in the smoothing capacitor, and the line noise caused by this ripple current causes a problem that the discharge lamp flickers. In addition, when a large ripple current flows in, the smoothing capacitor self-heats, which is a factor that shortens the life of the capacitor.

The present invention has been proposed in order to solve the problems of the prior art, and the ripple current flowing into the smoothing capacitor can be reduced, so that self-heating of the capacitor and flicker of the discharge lamp can be prevented. An object is to provide a discharge lamp lighting device that can be prevented.

[0005]

To achieve this object, a discharge lamp lighting device according to the present invention comprises a DC power supply, a smoothing capacitor connected in parallel to the DC power supply, and one end of a primary winding. A plurality of oscillating transformers connected to the DC power supply, a plurality of switching elements connected between the other end of the primary winding of each oscillating transformer and ground, and a lamp tube wall filled with a discharge gas. A plurality of discharge lamps, each of which has a pair of external electrodes connected to the output winding of each oscillation transformer via a current limiting capacitor, and a plurality of switching elements are alternately turned on and off at fixed time intervals. As described above, a drive pulse generating circuit for alternately inputting a drive pulse for switching is provided to the control terminal of each switching element.

[0006]

According to the above-mentioned structure, since the switching elements are alternately switched, the charging / discharging current to the smoothing capacitor only sees a ripple current for one set of the lighting circuit in a certain time, and the switching elements are switched. Ripple current can be made smaller than when both are turned on and off at the same time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the discharge lamp lighting device according to the present invention will be described in detail below with reference to the drawings. An example of this lighting device is shown in the block diagram of FIG. In this figure, a smoothing capacitor 2 is connected in parallel to a DC power supply 1 having a power supply voltage of 12V, for example. One end of the primary winding 5a of the oscillation transformer 5 that constitutes the inverter circuit 3 is connected to the positive terminal of the DC power supply 1, and
One end of a primary winding 9a of an oscillating transformer 9 that constitutes another inverter circuit 4 is connected. Each oscillation transformer 5,
Between the other ends of the primary windings 5a, 9a of the DC power supply 9 and the negative terminal of the DC power supply 1, the switching elements 6, 1 composed of FETs
0 is connected respectively. Each switching element 6,
The gate terminals (control terminals) of 10 are connected to the output terminals 13a and 13b of the drive pulse generating circuit 13 via resistors 7 and 11, respectively. This pulse generation circuit 13
Is supplied with power from the DC power supply 1. Resistors 8 and 12 are connected between the gate terminals of the switching elements 6 and 10 and the negative terminal of the power source 1, respectively. Further, the external electrodes 15a, 15b and 17a, 17b of the discharge lamps FL1, FL2 are respectively connected to the secondary windings (output windings) 5b, 9b of the oscillation transformers 5, 9 via the current limiting capacitors 14, 16. It is connected. here,
Noble gases such as xenon (Xe) and argon (Ag) are enclosed in the lamp tubes 15 and 17 of the discharge lamps FL1 and FL2 in an amount of 100 to 120 torr, and the external electrodes 15a and 15b and 17a and 17b are used as the lamp tubes. A pair is attached to the pipe walls of 15 and 17. Secondary winding 5 of oscillation transformers 5 and 9 of each inverter circuit 3 and 4
A high-voltage high-frequency power source boosted to about 3 to 4 kV can be taken out from b and 9b, and the discharge lamp is turned on by applying the high-frequency power source between the electrodes of the lamp.

In the discharge lamp lighting device configured as described above, the drive pulse generating circuit 13 outputs drive pulses S1 and S2 of about 30 kHz as shown in FIGS. 2 (a) and 2 (b) to the gates of the switching elements 6 and 10. It is applied to each terminal. Here, assuming that the cycle of the drive pulses S1 and S2 is T, the drive pulses S1 and S2 are alternately output after a fixed time T / 2, so that the gate pulses shown in FIGS.
The switching elements 6 and 10 are alternately turned on and off as shown by the waveforms of the source-to-source voltages VGS1 and VGS2. Therefore, when the charging / discharging current i to the smoothing capacitor 2 only sees one set of the inverter circuit 3 or 4 and the ripple current for the lamp load in a certain time, when the switching elements 6 and 10 are turned on / off at the same time. The ripple current flowing into the smoothing capacitor 2 can be made smaller than that. The voltage C across the smoothing capacitor 2 (the electrostatic capacity is C)
The waveform of i is shown in FIG. As a result, noise on the power supply lines 18, 19 is reduced, and the discharge lamps FL1, F
Flickering of L2 can be prevented. Further, the self-heating of the smoothing capacitor 2 can be reduced.

[0009]

As described above, according to the present invention, since the switching elements of the plurality of inverter circuits connected in parallel to the DC power source are alternately switched,
The ripple current flowing into the smoothing capacitor connected in parallel with the DC power supply can be reduced, and line noise can be suppressed. As a result, the flicker of the discharge lamp connected to each inverter circuit can be prevented. Also, by reducing the ripple current, self-heating of the smoothing capacitor can be suppressed,
The life of the capacitor can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a discharge lamp lighting device according to the present invention.

FIG. 2 is an operation waveform diagram of this lighting device.

[Explanation of symbols]

 1 DC power supply 2 Smoothing capacitor 3,4 Inverter circuit 5,9 Oscillation transformer 6,10 Switching element 13 Drive pulse generating circuit 14,16 Current limiting capacitor 15a, 15b, 17a, 17b Electrode FL1, FL2 Discharge lamp

Claims (1)

[Claims] 1. A DC power supply, a smoothing capacitor connected in parallel to the DC power supply, a plurality of oscillation transformers each having one end of a primary winding connected to one pole of the DC power supply, and each of the oscillation transformers. A plurality of switching elements respectively connected between the other end of the primary winding and the other pole of the DC power supply, and a pair of external electrodes attached to the tube wall of the lamp tube in which a discharge gas is enclosed are provided in each oscillation transformer. A plurality of discharge lamps are connected to the output winding via current limiting capacitors, and a switching terminal is used to control the switching terminals so that the switching elements are alternately turned on and off at fixed time intervals. A discharge lamp lighting device, comprising: a drive pulse generation circuit for alternately inputting drive pulses.