JP2008262866A - Lighting circuit for discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting circuit for a discharge lamp that can improve the lighting performance according to the characteristics of the discharge lamp in a simple circuit configuration. <P>SOLUTION: A lighting circuit 1 for a discharge lamp includes an NTC thermistor 6 connected in series with a discharge lamp L between a power supply circuit 2 for supplying DC current to the discharge lamp L and an ignitor 3 for starting to light the discharge lamp L in a lighting circuit for the discharge lamp that performs DC drive of the discharge lamp L. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting circuit for driving a discharge lamp in a direct current.

As lighting circuits for lighting a discharge lamp such as a metal halide lamp, those described in the following Patent Documents 1 to 3 are known. The lighting circuits described in Patent Documents 1 to 3 include a power supply circuit for obtaining a DC voltage necessary for lighting the discharge lamp, and a lighting start circuit for generating a high-pressure pulse to start the discharge lamp. Yes. As such a lighting circuit, a smoothing capacitor in the power supply circuit is used in order to prevent a line loss after starting and maintain a stable lighting state while suppressing the inrush current of the discharge lamp at the time of starting from becoming high. There are those in which a negative characteristic thermistor is connected in series, and those in which both ends of a resistor connected in series to a smoothing capacitor in a power supply circuit can be short-circuited by a relay circuit.
Japanese Patent Laid-Open No. 10-241875 JP 2001-155888 A JP 2006-302540 A

  However, in the lighting circuit including the negative characteristic thermistor described above, since the negative characteristic thermistor is connected in series to the smoothing capacitor in the power supply circuit, it is possible to stabilize the lighting according to the performance variation such as the impedance of the discharge lamp to be used. It was difficult to maintain the sex. In addition, in a lighting circuit including a resistor and a relay circuit, it is necessary to use a highly reliable relay circuit in order to realize stable lighting, which tends to increase the scale and cost of the circuit. there were.

  Accordingly, the present invention has been made in view of such problems, and an object thereof is to provide a discharge lamp lighting circuit capable of improving lighting performance according to the characteristics of the discharge lamp with a simple circuit configuration. And

  In order to solve the above-mentioned problems, a discharge lamp lighting circuit according to the present invention is a discharge lamp lighting circuit for driving a discharge lamp in a direct current, a power supply circuit for supplying a direct current to the discharge lamp, and a high voltage for starting the discharge lamp. An NTC thermistor connected in series with the discharge lamp is provided between the voltage generation circuit and the voltage generation circuit. An NTC (Negative Temperature Coefficient) thermistor is a thermistor having a negative temperature characteristic in which resistance decreases as the element temperature increases.

  According to such a discharge lamp lighting circuit, even when the characteristics of the discharge lamp vary due to the NTC thermistor connected in series with the discharge lamp between the power supply circuit and the high voltage generation circuit, Since it becomes easy to select an element in accordance with the characteristics, an inrush current at the start of the discharge lamp is surely prevented, and after starting, a current is stably supplied to the discharge lamp to improve the lighting stability. In addition, since the degree of freedom of arrangement of elements is increased as compared with the case where an NTC thermistor is provided in parallel with the discharge lamp in the power supply circuit, it is easy to maintain the lighting stability of the discharge lamp.

  The power supply circuit preferably includes an inrush current reduction circuit including a resistance element connected in parallel with the discharge lamp between the output terminals, and a switch element connected to both ends of the resistance element. In this case, the inrush current at the start of the discharge lamp can be further reduced, and damage to the discharge lamp at the start can be prevented.

  According to the present invention, lighting performance can be improved according to the characteristics of the discharge lamp with a simple circuit configuration.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a discharge lamp lighting circuit according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic configuration diagram of a discharge lamp lighting circuit 1 according to a preferred embodiment of the present invention. A discharge lamp lighting circuit 1 shown in the figure is a circuit for lighting a high-pressure discharge lamp mounted in a light source device and maintained at atmospheric pressure or higher when the mercury xenon lamp, xenon lamp or the like is not lit. The power supply circuit 2, an igniter (high voltage generation circuit) 3, an open / close control circuit 4, a constant current control circuit 5, an NTC thermistor 6, and a detection resistor 7 are provided.

The power supply circuit 2 is connected to an external power supply 8 that is an AC power supply or a DC power supply, and an alternating current or a direct current is supplied from the external power supply 8. When the current supplied from the external power supply 8 is an alternating current, the switching power supply 9 of the power supply circuit 2 converts the alternating current into a direct current, further converts the direct current into a high frequency pulse current, and then converts the high frequency pulse current. Take out using the built-in transformer. The extracted high-frequency pulse signal is rectified and smoothed by a circuit subsequent to the switching power supply 9 and then supplied to the discharge lamp L as a driving current for DC driving. In this case, the switching power supply 9, on the basis of the control signal C _P from the constant current control circuit 5 changes the pulse width of the high frequency pulsed current (switching pulse width) to be generated.

  Specifically, in the power supply circuit 2, a rectifier circuit 10 including two diodes for rectifying a high-frequency pulse current is connected to the output side of the switching power supply 9, and the high-frequency pulse current is again converted into a direct current by the rectifier circuit 10. And is supplied to the discharge lamp L side. An electrolytic capacitor 11 is connected between the output terminals of the power supply circuit 2 at the subsequent stage of the rectifier circuit 10 in parallel with the discharge lamp L as viewed from the switching power supply 9. Since the current output from the rectifier circuit 10 includes a ripple current component corresponding to the frequency (switching frequency) of the high-frequency pulse current of the switching power supply 9, the electrolytic capacitor 11 has a current in the current output from the rectifier circuit 10. The ripple current component is reduced and output to the igniter 3. Furthermore, the electrolytic capacitor 11 also has a function of supplying a current for starting the discharge lamp L via the igniter 3 immediately after the discharge lamp L starts to be lit.

Further, a series resistor 12 is connected to the cathode of the electrolytic capacitor 11 between the output terminals in the power supply circuit 2 so as to be in parallel with the discharge lamp L. Mechanical relays, semiconductor switches, etc. are connected to both ends of the series resistor 12. The relay circuit (switch element) 13 is connected. Relay circuit 13 is for short-circuiting and opening between the two ends of the series resistor 12, having a function of switching ON / OFF by the control signal C _R of the switching control circuit 4. The series resistor 12 and the relay circuit 13 constitute an inrush current reduction circuit that reduces the inrush current at the start of the discharge lamp L.

  The output of the power supply circuit 2 is connected to the input of an igniter 3 for starting the discharge lamp L. The igniter 3 applies a high-pressure pulse to both ends of the discharge lamp L at the start of lighting of the discharge lamp L. A discharge lamp L such as a xenon lamp or a mercury xenon lamp is connected between the output terminal To of the igniter 3, and an initial arc discharge inside the discharge lamp L is started and maintained by the igniter 3.

Between the input terminal Ti on the cathode side of the discharge lamp L of the igniter 3 and the output of the power supply circuit 2, a detection resistor 7 for detecting a discharge current flowing through the discharge lamp L is connected in series with the discharge lamp L. Yes. Furthermore, a constant current control circuit 5 is connected to both ends of the detection resistor 7. The constant current control circuit 5 flows through the discharge lamp L when a potential difference between both ends of the detection resistor 7 is input and current is continuously supplied to the discharge lamp L after the discharge lamp L starts to be lit. A control signal _CP is generated so that the discharge current becomes a constant value, and the switching pulse width is controlled. The detection resistor 7 preferably has a resistance value sufficiently smaller than that of the series resistor 12. As a result, the characteristics of the discharge current supplied to the discharge lamp L are not affected by the detection resistor 7. For example, the resistance value of the detection resistor 7 is 10 mΩ to 100 mΩ with respect to the resistance value 2.2Ω to 10Ω of the series resistor 12.

An opening / closing control circuit 4 for controlling opening / closing of the relay circuit 13 is also connected to both ends of the detection resistor 7. Switching control circuit 4 includes an operational amplifier, is constituted by a capacitor or the like, is a potential difference E _L is input corresponding to the discharge current I _L flowing through the discharge lamp L, which is detected by the detecting resistor 7, the low-frequency component E _L of the potential difference And a predetermined threshold value E _LTH . In order to compare the low-frequency component E _{L of the} potential difference with the threshold value E _LTH , the switching control circuit 4 is configured to respond only to the low-frequency component E _L of the potential difference. Specifically, the open / close control circuit 4 turns off the relay circuit 13 when the potential difference E _L corresponding to the discharge current I _L is smaller than the threshold value E _LTH , and turns off the relay circuit 13 when the potential difference E _L is equal to or _larger than the threshold value E _LTH. The circuit 13 is turned on. This threshold value E _LTH is set as a value smaller than a value corresponding to a discharge current when the discharge lamp L is in an arc discharge state and discharge is stabilized. Then, switching control circuit 4 is operated to turn off the relay circuit 13 outputs a switching control signal C _R of the high level to the relay circuit 13, when turning on the relay circuit 13, the low level to the relay circuit 13 Open / close control signal _CR is output.

  Further, an NTC thermistor 6 is connected in series with the discharge lamp L between the anode-side input terminal Ti of the discharge lamp L of the igniter 3 and the output of the power supply circuit 2. This NTC thermistor 6 is an element having a negative temperature characteristic in which the resistance value decreases as the element temperature rises due to self-heating due to energization. A metal oxide such as nickel, manganese, cobalt, iron or the like is mixed and sintered. It has been done. When the discharge lamp lighting circuit 1 including the NTC thermistor 6 is mounted on the light source device, the NTC thermistor 6 uses the cooling air for the discharge lamp L in the light source device to prevent the heat generation of the discharge lamp L. It arrange | positions in a flow path (it mentions later for details).

  Hereinafter, the structure of the light source device 21 on which the discharge lamp lighting circuit 1 is mounted will be described in detail with reference to FIG.

  A light source device 21 shown in the figure is a vertical type light source device that emits ultraviolet rays downward. For example, in a photolithography process when manufacturing a semiconductor device, a photoresist on a wafer is exposed. Used for. The light source device 21 includes a rectangular parallelepiped housing 22, and a front region and a rear region are formed in the housing 22 by a partition plate 22a.

  The front region of the housing 22 accommodates a discharge lamp L, which is a mercury xenon lamp that irradiates ultraviolet rays, and a reflection mirror 24 that reflects the ultraviolet rays emitted from the discharge lamp L by the reflecting surface 24a and emits them downward. Yes. The reflection surface 24a of the reflection mirror 24 is formed to be an elliptical condensing mirror surface, for example. The discharge lamp L is attached to a rectangular support plate 25 located above the reflection mirror 24, and is supported in the reflection mirror 24 while being inserted through the opening 24 b of the reflection mirror 24.

  An exit 22c for emitting ultraviolet rays to the outside is formed at a position facing the discharge lamp L in the vertical direction on the bottom surface side of the housing 22. Between the exit port 22c and the discharge lamp L, a diaphragm part 26 for adjusting the amount of ultraviolet light passing therethrough is provided, and between the exit port 22c and the diaphragm part 26, the exit port 22c is connected to the exit lamp 22c. A shutter 27 for turning on / off the emission of ultraviolet rays is provided.

  The rear region of the housing 22 accommodates a discharge lamp lighting circuit 1 as a circuit unit and a fan 28 for discharging the cooling air A flowing through the housing 22 to the outside of the housing 22. Each part of the housing 22 is formed with an air intake, and an air intake 29 for mainly cooling the discharge lamp lighting circuit 1 is formed on the rear surface of the housing 22 as a part of the air intake. Is formed. Here, the NTC thermistor 6 is disposed on the flow path of the cooling air A between the fan 28 and the air intake port 29 on the rear surface of the main unit 1 a of the discharge lamp lighting circuit 1.

  According to the discharge lamp lighting circuit 1 described above, the characteristics of the discharge lamp L vary due to the NTC thermistor 6 connected in series with the discharge lamp L between the power supply circuit 2 and the igniter 3. However, since it is easy to select an element in accordance with the characteristics, an inrush current at the start of the discharge lamp L is surely prevented, and a stable current is supplied to the discharge lamp L after the start to stabilize the lighting. Improves. That is, immediately after the start of the discharge lamp L, the element temperature of the NTC thermistor 6 is low, so the resistance value of the NTC thermistor 6 is increased and the inrush current is reduced. After the discharge lamp is started, the element temperature gradually increases due to energization. The resistance value of the NTC thermistor 6 becomes low, and power loss in the lighting circuit 1 can be prevented.

  In particular, by inserting a thermistor in series with the lamp between the power supply circuit 2 and the discharge lamp L, the negative characteristics (relationship between current and voltage) of the discharge lamp L are improved. It can be operated. In addition, the degree of freedom of element arrangement is increased as compared with the case where the power supply circuit 2 includes the NTC thermistor 6 in parallel with the discharge lamp L. As a result, it is possible to prevent a situation in which the element temperature is excessively increased due to the heat of the discharge lamp and cannot be lowered to an appropriate resistance value at the time of relighting start. Accordingly, it is easy to reduce the inrush current of the discharge lamp L and maintain the lighting stability. More specifically, it becomes easy to arrange the thermistor in a temperature environment that matches the lighting characteristics of the discharge lamp L.

  Also, if lighting performance is poor due to variations in lamp characteristics, re-lighting control is often performed. As a result of repeated lighting start-up retries, excessive load is applied to the lamp electrodes (especially the cathode) and lamp malfunctions occur. There is a possibility that it will develop. According to the present embodiment, since lighting stability is improved, such a risk can be reduced.

  Further, by using the NTC thermistor, it is easy to reduce the circuit scale while maintaining high resistance value control reliability as compared with the case of using a switching element such as a relay circuit.

  Further, the discharge lamp includes a series resistor 12 connected in parallel with the discharge lamp L between the output terminals of the power supply circuit 2 and a relay circuit 13 connected to both ends of the series resistor 12, thereby providing a discharge lamp. The inrush current at the start of L can be further reduced, and damage to the discharge lamp at the start can be prevented.

  In addition, this invention is not limited to embodiment mentioned above. For example, a semiconductor power switch using SiC instead of the NTC thermistor may be used.

1 is a schematic configuration diagram of a discharge lamp lighting circuit according to a preferred embodiment of the present invention. It is a side view which shows the inside of the light source device with which the lighting circuit for discharge lamps of FIG. 1 was mounted.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lighting circuit for discharge lamps, 2 ... Power supply circuit, 3 ... Igniter (high voltage generation circuit), 6 ... NTC thermistor, 12 ... Series resistance, 13 ... Relay circuit (switching element), L ... Discharge lamp.

Claims (2)

In the discharge lamp lighting circuit for direct current driving of the discharge lamp,
An NTC thermistor connected in series to the discharge lamp is provided between a power supply circuit for supplying a direct current to the discharge lamp and a high voltage generation circuit for starting the discharge lamp.
A lighting circuit for a discharge lamp. The power supply circuit has a rush current reduction circuit including a resistance element connected in parallel with the discharge lamp between output terminals, and a switch element connected to both ends of the resistance element.
The discharge lamp lighting circuit according to claim 1.

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