JPH0950894A - Lighting device for metal halide lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device for a metal halide lamp using a step-up transformer which is miniaturized while providing higher voltage. SOLUTION: Power supply is supplied from a variable DC power supply 1 to a capacitor 3 via a resistance 2 so that the high voltage is induced in the secondary side of the first step-up transformer 6 by charge and discharge by discharge action of a spark gap 5. Much higher voltage generates in the secondary side of the second step-up transformer 10 by the similar action. This high voltage is supplied in such a state as winding a trigger wire 13 around the outer tube of a metal halide lamp in several turns so as to generate a spark for discharging and lighting the metal halide lamp.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for a metal halide lamp used in a liquid crystal projector or the like.

[0003]

[0002]

[0004]

2. Description of the Related Art A conventional metal halide lamp lighting device used in a liquid crystal projector or the like has a circuit configuration as shown in FIG.

The lighting device of this metal halide lamp is
Variable DC power supply 1 to 250V by switching power supply, etc.
A DC voltage of a certain degree is supplied to the high voltage generation circuit 11, and a circuit element (not shown) provided inside the high voltage generation circuit 11 generates a sawtooth wave voltage due to charging and discharging. This sawtooth wave voltage is boosted by the boosting transformer 10, and a high voltage of about 15 kV to 30 kV is obtained at the output of the high voltage generating circuit 11.

The output of the high voltage generating circuit 11 is derived from the secondary winding 10b of the step-up transformer 10, one of which is a positive electrode of the variable DC power supply 1 and the other is via the metal halide lamp 4 and the variable DC power supply 1 is supplied. Is connected to the negative electrode of.

[0007]

Secondary winding 10b of the step-up transformer 10
When a high voltage is supplied to the metal halide lamp 4 through the metal halide lamp 4, the metal halide lamp 4 discharges and emits light.
A high voltage is required to discharge the metal halide lamp 4, but when it is discharged / lighted, the internal light emission potential becomes low and lighting is continued at 10V to 50V (a voltage that varies depending on the type of metal halide lamp). For this reason, it is general to provide a voltage detection circuit 12 at both ends of the metal halide lamp 4, detect a voltage fluctuation at the time of discharge / lighting, and change the voltage of the variable DC power supply 1 by this detection signal.

Further, a high DC voltage is required at the time of starting the metal halide lamp 4, but it is necessary to switch to a low voltage after starting the discharge and emitting light. Therefore, a high voltage is generated by utilizing the change in this voltage. The repetitive operation due to charge / discharge generated inside the circuit 11 is stopped.

As described above, the metal halide lamp 4
When activating, the high voltage signal is applied to the metal halide lamp 4, but after the discharge / lighting, the high voltage generation circuit 11
It is driven at a low voltage through the secondary winding 10b of the step-up transformer 10 to keep lighting and emitting light.

[0010]

[0004]

[0011]

However, when the metal halide lamp 4 continues to be lit, it is necessary to supply a current of about 5 A (ampere) from a DC power supply of about 50 V, so that the voltage of the step-up transformer 2 is increased. To prevent heat generation and voltage drop in the secondary winding, the secondary winding must be made of thick wire. As a result, when the wire rod is made thick, the step-up transformer itself becomes large, and it is inevitable that the entire high-voltage generating circuit 11 becomes large.

The present invention has been made in view of the above-mentioned problems. In a device used for lighting a metal halide lamp, a metal halide lamp using a step-up transformer capable of obtaining a higher voltage and being downsized can be provided. It is to provide a lighting device.

[0013]

[0005]

[0014]

In order to solve the above-mentioned problems, the present invention provides a high voltage generating circuit including a step-up transformer for stepping up a DC voltage to a predetermined voltage, and a high voltage obtained in a secondary winding of the step-up transformer. In a lighting device for a metal halide lamp having a metal halide lamp to which a voltage is applied as a starting voltage, both terminals of the metal halide lamp are connected to a DC voltage, and one end of a secondary winding of a step-up transformer is opened to connect the metal halide lamp. It is characterized by being wrapped around.

[0015]

The high voltage generating circuit used in the present invention is connected to a first step-up transformer in which a primary winding is connected to a capacitor via a first spark gap, and a secondary winding in the first step-up transformer. And a second step-up transformer to which the output from the rectifier circuit is applied to the primary winding through the second spark gap.
It is desirable that the high voltage obtained in the next winding is applied as the starting voltage of the metal halide lamp.

[0016]

[0007]

[0017]

In such a lighting device, one end of the secondary winding of the step-up transformer is wound around the metal halide lamp, and the metal halide lamp is lit by the high voltage generated in the secondary winding, and the metal halide lamp is lit after lighting. A current is supplied by a DC voltage connected to both terminals of the.

[0018]

[0008]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a structural diagram of a metal halide lamp used in the present invention. The metal halide lamp 4 is shown in FIG.
There is an arc tube 20 made of quartz glass in which a mixed gas of mercury and a metal halide is enclosed as shown in FIG.
A pair of tungsten electrodes 21 facing each other at a predetermined distance are provided at both ends of 0.

The arc tube 20 is an outer tube 22 having a hollow structure.
It is housed in (quartz glass) in a floating state and filled with a gas such as argon gas. The lead wires 23 provided at both ends of the arc tube 20 are drawn to the outside of the outer tube 22 via the fixing metal plate 24.

[0022]

When a voltage is applied to both ends of the metal halide lamp 4, the mixed gas consisting of mercury and a metal halide enclosed in the arc tube 20 is warmed to a vapor state, and a higher voltage is applied. And tungsten electrode 2
The discharge starts between 1 and 2. This discharge decomposes the metal and halogen, excites the metal atom, and emits light.

Now, an embodiment of the present invention using the metal halide lamp 4 will be described in detail with reference to FIG.
The same reference numerals used in the conventional example are assigned the same reference numerals.

As shown in FIG. 2, one of the lead wires 23 of the metal halide lamp 4 is connected to the plus side of the variable DC power supply 1 and the other is connected to the minus side.

[0025]

First, a DC voltage of about 250V is generated from the variable DC power supply 1, and the capacitor 3 is charged via the resistor 2. When the charge voltage gradually increases and exceeds the discharge voltage of the spark gap 5, the spark gap 5 is discharged. At this time, one of the spark gap 5 and the step-up transformer 6
A closed circuit is formed by the secondary winding 6a and the capacitor 3, the capacitor 3 is short-circuited by the primary winding 6a of the step-up transformer 6, and the charging voltage charged in the capacitor 3 is rapidly attenuated. Then, the spark gap 5 is opened, and the variable DC power supply 1 starts charging the capacitor 3 again. That is, when the spark gap 5 is switched, a sawtooth wave voltage is generated on the primary side of the step-up transformer 6 due to repeated charging and discharging determined by the constants of the resistor 2 and the capacitor 3.

[0026]

This sawtooth wave voltage is induced in the secondary winding 6b of the step-up transformer 6, but since the number of secondary windings of the step-up transformer 6 is larger than the number of primary windings, The voltage generated on the secondary side is boosted and induced in the secondary winding 6b. Next, the sawtooth wave voltage induced on the secondary side of the step-up transformer 6 is rectified by the diode 7 and charges the capacitor 8. When the charge voltage gradually increases and exceeds the discharge voltage of the newly provided spark gap 9, the spark gap 9 is discharged. Then, the spark gap 9, the primary side winding 10a of the second step-up transformer 10 and the capacitor 8 form a closed circuit, and the capacitor 8 is short-circuited at the primary side winding 10a of the second step-up transformer 10. Therefore, the charging voltage charged in the capacitor 8 is rapidly attenuated. That is, the charging / discharging phenomenon that occurs on the primary side of the first step-up transformer 6 also occurs on the primary side of the second step-up transformer 10.

[0027]

Then, the sawtooth wave voltage of the high voltage (25 to 30 kV) further boosted by the second boosting transformer 10 is generated in the secondary winding 10b. One of the secondary windings 10b of the step-up transformer 10 is connected to the variable DC power source 1
Of the trigger wire 13
Is arranged in a state of being wound several times on the surface of the outer tube 22 located on the arc tube 20 of the metal halide lamp 4.

Since a DC voltage of 250 V is directly applied from the variable DC power supply 1 to the lead wire 23 of the metal halide lamp 4, the mixed gas of mercury and metal halide in the arc tube 20 is warmed and discharged. Becomes critical. When a sawtooth wave voltage of high voltage (25 to 30 kV) is supplied from the trigger wire 13 connected to the secondary side of the step-up transformer 10, the trigger wire 13 is supplied.
A spark is generated between the tip of the wire and the portion of the tungsten terminal 21b closest to the minus terminal side.

[0029]

The arc tube 2 is triggered by this spark.
A discharge is started between the tungsten electrodes 21 inside 0, and the metal halide lamp 4 starts discharge / light emission.

A voltage detection circuit 12 is provided at both ends of the metal halide lamp 4, monitors the voltage at both ends of the metal halide lamp 4, generates a detection signal when the voltage drops, and outputs this signal to the variable DC power supply 1. It is supplied to the control terminal 1a. That is, the metal halide lamp 4 is discharged.
When light emission is started, the voltage across both ends is reduced to about 10V to 50V, so the voltage detection circuit 12 detects this voltage fluctuation and supplies a detection signal to the control terminal 1a of the variable DC power supply 1, whereby the variable DC power supply is supplied. 1 is the voltage (10V to 50V) required for the metal halide lamp 4 to discharge and emit light
Is controlled.

[0031]

As a result, the voltage supplied to the capacitor 3 is lowered, and the discharge voltage of the spark gap 5 cannot be reached, which is performed on the primary side of the step-up transformer 6.
Repeated charge / discharge operations stop. Then, since the sawtooth wave voltage is not induced on the secondary side of the step-up transformer 6, the high voltage of the trigger wire 13 is also stopped. However, the metal halide lamp 4 continues to emit light because the DC voltage necessary for discharging and emitting light is supplied from the variable DC power supply 1.

In the embodiment of the present invention, the double tube type in which the outer side of the arc tube is covered with the outer tube has been described in terms of safety against heat generation, but the trigger wire is directly attached to the arc tube having no outer tube. May be wrapped around.

[0033]

The variable DC power supply 1 is composed of, for example, a switching power supply circuit and changes the duty of a pulse signal for driving a switching element which is internally generated in accordance with a detection signal applied to the control terminal 1a. It controls the voltage.

In the embodiment of the present invention, the metal halide lamp in which a mixed gas of mercury and a metal halide is enclosed has been described. However, a metal halide lamp in which another mixed gas is enclosed depending on the use and emission color may be used.

In the embodiment of the present invention, the high-voltage generating circuit composed of the first and second step-up transformers has been described, but one step-up transformer may be formed to obtain a necessary high-voltage. You may comprise by 2 or more.

[0036]

[0016]

[0037]

As described above, according to the present invention, the DC power source is directly connected to both ends of the metal halide lamp, and the secondary side winding of the step-up transformer is drawn on the outer tube surface of the metal halide lamp in the critical state of discharge. Since the trigger wire is wound, a high-voltage current flows in the secondary winding of the step-up transformer for a moment during a spark that induces the discharge of a metal halide lamp, but then the current supply is cut off, so the step-up transformer is cut off. It is not necessary to thicken the wire rod of the secondary winding, and heat is not generated.

As a result, the step-up transformer and the high voltage generating circuit can be downsized.

[Brief description of drawings]

FIG. 1 is a structural diagram of a metal halide lamp according to an embodiment of the present invention.

FIG. 2 is a block diagram of a lighting device for a metal halide lamp according to an embodiment of the present invention.

FIG. 3 is a block diagram of a lighting device for a metal halide lamp in a conventional example.

[Explanation of symbols]

 1 ... Variable DC power supply 2 ... Resistor 3, 8 ... Capacitor 4 ... Metal halide lamp 5, 9 ... Spark gap 6, 10 ... Step-up transformer 7 ... Diode 11 ... High voltage Generator circuit 12 Voltage detector circuit 13 Trigger wire 20 Arc tube 21 Tungsten electrode 22 Outer tube 23 Lead wire 24 Metal plate

Claims (2)

[Claims] 1. A metal halide lamp comprising a high voltage generating circuit including a step-up transformer for stepping up a DC voltage to a predetermined voltage, and a metal halide lamp to which a high-voltage obtained at a secondary winding of the step-up transformer is applied as a starting voltage. In the lighting device, the both terminals of the metal halide lamp are connected to the DC voltage, one end of the secondary winding of the step-up transformer is opened, and the secondary winding is wound around the metal halide lamp. Lighting device for metal halide lamps. 2. The high-voltage generating circuit according to claim 1, wherein a first step-up transformer in which a primary winding is connected to a capacitor via a first spark gap, and a secondary winding in the first step-up transformer. A rectifier circuit connected to the rectifier circuit, and a second step-up transformer to which an output from the rectifier circuit is applied to the primary winding via a second spark gap. A lighting device for a metal halide lamp, wherein a high voltage to be applied is applied as a starting voltage of the metal halide lamp.