JPH04253187A - Power source device for metal halide lamp - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the light color and intensity of a metal halide lamp and the reduction of the lamp life, make the structure simpler than that of a conventional device of an AC feed system at a lower cost, and prevent flickers of light while the lamp is lighted. CONSTITUTION:The DC power of a DC power circuit 30 is fed to a metal halide lamp 7 to turn the lamp 7 on by a DC feed system, a complex and expensive inverter circuit for AC conversion used in a conventional device is omitted, the structure is simplified at a low cost, and flickers of light are prevented while the lamp 7 is lighted. Transfer switches 28, 29 are interlockingly transferred by the reverse action of a keep relay 27 each time the power source of the DC power circuit 30 is turned on, the applied polarity of the power of the lamp 7 is automatically reversed, and the deterioration of the light color and intensity and the reduction of the lamp life due to the continuous DC feed for a long period are prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for a metal halide lamp, which is used to supply power to a metal halide lamp.

0002

[Prior Art] Conventionally, metal halide lamps are formed by enclosing a metal halide in a lamp tube, and when the lamp is turned on and the enclosed metal vaporizes, the pressure inside the tube increases and it emits high-intensity light. Since a light color close to daylight can be obtained by adjusting the encapsulated metal, it is used as a projection light source for an overhead projector (OHP) and various other illumination light sources.

[0003] If a metal halide lamp is used instead of a halogen lamp, 2 to 2.5 times the brightness of a halogen lamp can be obtained with the same electric power.

By the way, when this kind of metal halide lamp is turned on with DC power supply, the vaporized metal inside the tube becomes positive (
The halogen is ionized to be negative (+) and drawn to the negative electrode, and the halogen is ionized to negative (-) and drawn to the positive electrode.

If the product is used in this state for a long period of time, from tens to hundreds of hours, metal ions will adhere only to the negative electrode, degrading the light color and brightness, and furthermore, the positive electrode will be extremely worn out by the halogen. , the lamp life will be shortened.

[0006] Therefore, a power supply device for a metal halide lamp has conventionally been formed by an AC power supply type power supply device for a metal halide lamp.

[0007] A conventional AC power supply type power supply device that controls supplied power to a constant level by chopper control of transistors is constructed as shown in FIG.

Then, when the power switch 1 is turned on and the normally open automatic return type start operation push button switch 2 is pressed, the AC power at the input terminals 3 and 4 turns on the switch 2 and the normally closed relay switch 5. The starter 6 is supplied to the starter 6 through the starter 6, and the high voltage for starting generated by boosting the voltage of the starter 6 is supplied to the metal halide lamp 7.

[0009]Also, the AC power supplied through the power switch 1 is converted into a DC power by rectification by a rectifier 8 having a diode bridge configuration and smoothing by a smoothing capacitor 9, and then converted to a DC power by a chopper transistor 10, a freewheel diode 11, and a smoothing reactor 12. Transistors 13, 14, 15 through
, 16 inverter circuits 17.

This inverter circuit 17 is connected to pairs of transistors 13 and 16, 14 and 1 by an inverter drive circuit 18.
5 are reversely switched and driven at about 50 to 250 Hz to generate alternating current for sustaining lighting between the connection point of transistors 13 and 14 and the connection point of transistors 15 and 16,
This alternating current is harmonic bypass capacitor 19, starter 6
It is supplied to the lamp 7 via.

[0011] Then, the lamp 7 is activated by the high voltage for starting.
When the inverter circuit 17 is discharged, a voltage drop corresponding to the current flowing through the lamp 7 occurs in the current detection resistor 20 provided on the input side of the inverter circuit 17, and this voltage drop is supplied to the control circuit 21 as a current detection signal.

The control circuit 21 has an output control function for controlling the electric power supplied from the inverter circuit 17 to the lamp 7 at a constant level, and a function for automatically stopping the starter 6.

When a current detection signal begins to be supplied from the resistor 20 due to discharge of the lamp 7, the automatic stop function immediately energizes the current detection relay 22, turns off the relay switch 5, and stops power supply to the starter 6. , the high voltage output of the starter 6 is automatically stopped.

Further, the input voltage of the inverter circuit 17 is divided by voltage dividing resistors 23 and 24 provided on the input side of the inverter circuit 17, and this divided voltage is used as a voltage detection signal corresponding to the voltage applied to the lamp 7. The signal is supplied to the control circuit 21 as a signal.

Then, the output control function of the control circuit 21 adds and synthesizes the absolute value voltage detection signal and current detection signal to form a positive level power detection signal. An error signal is formed with the signal.

This error signal is supplied as an output control signal to the chopper drive circuit 26, which controls the chopper operation of the transistor 10 and controls the power supplied to the lamp 7 to a constant power based on the reference signal.

At this time, the direct current of the lamp 7 becomes an alternating current with a rectangular wave as shown in FIG.

Furthermore, if the switch 1 is turned off while the lamp 7 is lit, the lamp 7 will be turned off due to the power supply being stopped, and
The relay 22 is de-energized and the relay switch 5 returns to the on state.

When the power switch 1 is turned on at time ta and turned off at time tb, switches 1 and 2 and relay 22
, the starter 6 is turned on and off at timings a, b, c, and d in FIG. 5, and the current flowing through the lamp 7 is as shown in e in the figure.

[0020]

In the case of the conventional power supply device for metal halide lamps shown in FIG. 3, an inverter circuit 17 must be provided in order to supply AC power, which has the problem of complicating the configuration and increasing the cost. be.

[0021] There is also the problem that flicker of light occurs during lighting due to AC power supply.

[0022] By the way, in OHPs and the like, the lighting light source is normally used for about 1 to 5 hours each time, and this is a period during which the light color and brightness deteriorate and the lamp life decreases due to long-term continuous DC power supply. Much shorter.

The present invention provides a power supply device for metal halide lamps that prevents deterioration of light color and brightness and shortens lamp life, has a simple and inexpensive configuration, and does not cause flickering of light during lighting. The purpose is to

[0024]

[Means for Solving the Problems] In order to achieve the above object, the power supply device for metal halide lamps of the present invention rectifies and smoothes AC power to convert it into DC power, and the output power is used to power the metal halide lamp. The lamp includes a DC power supply circuit for supplying and maintaining lighting, and a polarity reversing means for reversing the polarity of the DC power applied to the metal halide lamp each time the DC power supply circuit is powered on.

[0025]

[Operation] In the case of the power supply device of the present invention configured as described above, the DC power of the DC power supply circuit is supplied to the metal halide lamp, and the metal halide lamp is lit by the DC power supply method. A complicated and expensive inverter circuit for conversion can be omitted, and there is no flicker of light during lighting.

[0026] Since the polarity of the DC power applied to the metal halide lamp is reversed each time the power is turned on by the polarity reversing means, deterioration of light color and brightness and reduction of lamp life due to long-term continuation of DC power supply with fixed applied polarity occur. is prevented.

[0027]

Embodiment One embodiment will be described with reference to FIGS. 1 and 2.

In FIG. 1, the same reference numerals as those in FIG. 3 indicate the same or equivalent elements, and 27 is a keep relay (latching relay) for polarity switching provided on the input side of the rectifier 8, which is reversed every time a voltage is applied. It consists of a working mechanical relay. 28 and 29 are linked by relay 27 and have two contacts A and B.
These are two output changeover switches that are selectively switched to , and together with the relay 27, form a polarity reversal means.

Reference numeral 30 denotes a DC power supply circuit having a configuration similar to that of the conventional device shown in FIG. 3, except that the inverter circuit 17 is omitted.

Then, the changeover switches 28 and 29 are inserted at the position of the inverter circuit 17, and the changeover switches 28 and 29 are inserted into the inverter circuit 17.
The switching piece of the switch 29 is connected to the positive pole point P formed by the connection point of the reactor 12 and the resistor 23, and the switching piece of the switch 29 is connected to the positive pole point P formed by the connecting point of the reactor 12 and the resistor 23.
0, is connected to the negative pole point N formed by the connection point of the resistor 24.

Further, contact A of the changeover switch 28 and contact B of the changeover switch 29 are connected to the lamp 7 via the starter 6.
is connected to one electrode X of the switch 28, and the contact B of the changeover switch 28
and the contact A of the changeover switch 29 are connected to the other electrode Y of the lamp 7.

It is assumed that the two states of the keep relay 27 are a forward state and a reverse state, and that the keep relay 27 is in the reverse state and the changeover switches 28 and 29 are held at the contact B before the power is turned on.

In this state, when the power switch 1 is turned on at time t1 as shown in FIG. The relay 27 is reversed to the normal state as shown in FIG. 2b, and the changeover switch 28 is
, 29 are immediately switched to contact A, and a DC voltage of polarity is applied to the lamp 7, with the electrode X being positive and the electrode Y being negative.

When the push button switch 2 is pressed immediately after time t1 as shown in FIG. 2c and the starter 6 is turned on as shown in FIG. A forward current begins to flow through 7 in the direction from electrode X to electrode Y.

Based on this forward current, the current detection signal of the resistor 20 is supplied to the control circuit 21, and the automatic stop function of this circuit 21 immediately energizes the current detection relay 22, and this energization causes the state shown in FIG. After the relay switch 5 is turned off, the lamp 7 continues to be lit by the DC power supply current from the power supply circuit 30 shown in FIG.

During DC power supply, the chopper operation of the transistor 10 is controlled by drive control of the chopper drive circuit 26 based on the output control function of the control circuit 21, and the power supplied to the lamp 7 is maintained constant.

[0037] Next, for example, due to the end of use of OHP,
When the power switch 1 is turned off at time t2, which is about 1 to 5 hours after time t1, the DC power supply of the power supply circuit 30 is stopped, the lamp 7 is turned off, the current detection relay 22 is turned off, and the relay switch 5 is reset. .

Further, the keep relay 27 maintains the normal state even when the voltage application is stopped, and the changeover switches 28 and 29 are held at contact A.

Next, when the power switch 1 is turned on again at time t3, the keep relay 27 is reversed by voltage application, the changeover switches 28 and 29 are immediately switched to the contact B, and the lamp 7 is switched from the power supply circuit 30. The polarity of the voltage applied to the lamp 7 is reversed from that at time t1, and a DC voltage with a polarity such that the electrode X is negative and the electrode Y is positive is applied to the lamp 7.

Furthermore, when the push button switch 2 is pressed to turn on the starter 6, the lamp 7 is discharged and a reverse current in the direction from the electrode Y to the electrode The light flows and the lamp 7 continues to be lit.

Thereafter, each time the lamp 7 is turned on, the changeover switches 28 and 29 are switched in conjunction with each other due to the reversal operation of the keep relay 27 based on the turning on of the power switch 1, and the polarity of the DC power supply to the power supply circuit 30 is automatically changed. This prevents deterioration of light color and brightness and shortening of lamp life due to long-term continuation of DC power supply.

[0042] Also, during lighting, based on stable DC power supply,
No brightness flicker occurs.

In the case of FIG. 1, constant power control is performed by chopper driving the transistor 10, but it goes without saying that constant power control can be performed using various control methods such as series control and parallel control.

Note that when one lighting time is long, the polarity of the DC power supply to the lamp 7 may be reversed every predetermined period of time using a timer.

[0045]

[Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

Since DC power from the DC power supply circuit is supplied to the metal halide lamp and the metal halide lamp is lit using the DC power supply method, the complicated and expensive inverter circuit for AC conversion of the conventional device can be omitted.
The structure is simplified and the cost is reduced, and flickering does not occur during lighting.

Furthermore, since the polarity reversing means reverses the applied polarity of the metal halide lamp each time the DC power supply circuit is powered on, deterioration of light color and brightness and shortening of lamp life due to long-term continuation of DC power supply is prevented.

Therefore, it is possible to light a metal halide lamp with a simple and inexpensive configuration without deteriorating the lighting characteristics or lamp life, and without causing flicker of light during lighting. It is extremely effective as a power supply device for a relatively short light source, such as a projection light source, which is used for a relatively short time of one to several hours.

[Brief explanation of the drawing]

[Figure 1] 1 of the power supply device for metal halide lamps of the present invention
It is a wiring diagram of an example.

2A, b, c, d, e, and f are timing charts for explaining the operation of FIG. 1; FIG.

FIG. 3 is a wiring diagram of a conventional device.

FIG. 4 is a waveform diagram of the lighting current in FIG. 3;

5A, b, c, d, and e are timing charts for explaining the operation of FIG. 3; FIG.

[Explanation of symbols]

7 Metal halide lamp 27 Keep relay 28, 29 Selector switch 30 DC power supply circuit

Claims (1)

[Claims] 1. A DC power supply circuit that rectifies and smoothes an AC power supply to convert it into a DC power supply, and supplies the DC power to a metal halide lamp to keep it lit; A power supply device for a metal halide lamp, comprising a polarity reversing means for reversing the polarity applied to the metal halide lamp.