JP2002117990A - Feeder system for discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence probability of a flame failure when a discharge lamp such as a high-pressure mercury vapor discharge lamp or a metal halide lamp is returned to a glow discharge after it is once shifted to an arc discharge. SOLUTION: This feeder system for the discharge lamp is provided with a variable DC power supply 18 controlling the power of the discharge lamp 1, smoothing capacitors 12 and 13 connected in parallel with the discharge lamp 1 at the output end of the variable DC power supply, and a starter 19 applying a high voltage to the discharge lamp 1 at the start of lighting. The electrostatic capacities of the smoothing capacitors 12 and 13 are set to a small value (12) immediately after the lighting state of the discharge lamp 1 is shifted to the arc discharge from the glow discharge. The electrostatic capacities of the smoothing capacitors 12 and 13 are changed to large values (12, 13) when the arc discharge is stably maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for a discharge lamp, and more particularly to a power supply for a discharge lamp for lighting a high-intensity high-pressure mercury vapor lamp used as a light source for a projector.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a power supply device for lighting a discharge lamp such as a high-pressure mercury vapor discharge lamp or a metal halide lamp. The power supply device for a discharge lamp includes a DC power supply for supplying power to the discharge lamp, a switch element (Q1) using an FET or the like, a choke coil (L1), a flywheel diode (D1), and a smoothing capacitor (C).
It comprises a DC lamp power supply circuit including a step-down chopper, a lamp voltage detection circuit, and a lamp current detection circuit, each of which is a constituent element of 1), a starter that operates when the discharge lamp is started, a discharge lamp, and the like. The discharge lamp power supply circuit controls the lamp voltage and the lamp current based on the signals detected by the lamp voltage detection circuit and the lamp current detection circuit so that the product of the lamp voltage and the lamp current is substantially constant. The power is controlled to be constant.

FIGS. 2 (a) and 2 (b) show lamp voltage characteristics and lamp current characteristics from the start of the discharge lamp to the steady lighting state when such a power supply device for a discharge lamp is used. It is. As shown in the figure, the initial arc discharge at the start-up has a low lamp voltage, so when trying to input the rated power to the discharge lamp, a large lamp current has to flow and the loss of circuit elements increases. In addition, since an element having a large current rating must be used, constant current control is often performed so as not to exceed a certain upper limit current. When the arc discharge continues and the temperature of the discharge lamp rises, that is, when the heat arc discharge occurs, the lamp voltage rises and it becomes possible to supply power specified below the upper limit current to the discharge lamp. Transition.

FIGS. 3 (a) and 3 (b) correspond to FIGS.
FIG. 4 is an enlarged view of a lamp voltage characteristic and a lamp current characteristic when the discharge lamp shown in FIG. As shown in the figure, when the discharge lamp is started, a starter (or at time t1) is applied with a voltage higher than the glow discharge voltage Vg, usually called a no-load open-circuit voltage Vf, applied to the discharge lamp. (Also referred to as a starter) to cause dielectric breakdown in the discharge space to start glow discharge. At this time, the glow discharge voltage Vg is high,
It becomes about 250V. Since the duration of the glow discharge (period t1-t2) varies depending on various conditions, the duration may be several microseconds, several tens of milliseconds, or more. When the glow discharge ends, as shown at time t2, the initial arc discharge (period t2-t)
Go to 3). The initial arc discharge voltage Va is low, usually about 10 to 50V. The initial arc discharge is often a special arc discharge that is not a so-called thermal arc, which is caused by mercury or halogen adhering or adsorbing to the electrode. This kind of arc discharge may also occur when the discharge lamp being turned on is turned off and then turned on again when the temperature is not sufficiently cooled.

As a known technique of a discharge lamp power supply device, Japanese Unexamined Patent Application Publication No. 5-234885 discloses a boost voltage circuit and a discharge lamp lighting device such as a metal halide lamp for the purpose of improving the startability of the discharge lamp. Using the charge stored in the boost capacitor, the boost current flows at the time of startup without excessively increasing the peak current value by the action of the current limiting resistor.After the startup, the boost voltage circuit is disconnected by a switch. A technique is disclosed in which a current limiting resistor is short-circuited by a switch so that a boost capacitor functions as a smoothing capacitor for reducing ripple. In this known technique, the boost voltage circuit disconnecting switch is also used as a short-circuiting switch for the current limiting resistor of the boosting capacitor, thereby preventing the peak current value from becoming excessive at the time of startup and reducing the ripple during steady lighting. I'm trying.

Further, in Japanese Patent Application Laid-Open No. 2000-123939, since the smoothing capacitor needs to be charged, the operation of the step-down chopper circuit cannot fully respond to the fast operation from breakdown to arc discharge, and the arc discharge fails. For the purpose of preventing the phenomenon, a switch is provided on the smoothing capacitor so that the capacitance can be changed, and the capacitance is small until the transition from igniter breakdown to glow discharge to arc discharge, and to the arc discharge Immediately after or after the transition to, a technique for reducing the ripple by changing to a large capacitance has been disclosed.

[0007]

By the way, in the power supply device for a discharge lamp as shown in FIG. 6, since the initial arc discharge is mainly a special arc discharge as described above, as shown at time t3 in FIG. When the adsorbed substances adsorbed on the electrode are depleted, the arc discharge stops, and the discharge must be continued again by glow discharge (t3 and thereafter). In order to shift from an arc discharge having a low discharge voltage to a glow discharge having a high discharge voltage, the power supply device for a discharge lamp needs to have an ability to instantaneously increase the output voltage.

However, in such a power supply device for a discharge lamp, the steep voltage increase cannot be realized, so that the glow discharge cannot be sustained and the discharge lamp goes out as shown by a broken line in FIG. Often occurs. In that case, it is necessary to perform restart by the starter. In other words, every time the discharge lamp is lit once, the cycle of dielectric breakdown by the starter, glow discharge, arc discharge, and extinguishing must be repeated several times, which has shortened the life of the discharge lamp.

In the above-mentioned Japanese Patent Application Laid-Open No. H5-223485, the startability of a discharge lamp is improved.
Similar to the above-described power supply device for a discharge lamp, the power supply device does not have a function of preventing the discharge from extinction at the transition from arc discharge to glow discharge.

In addition, the above-mentioned Japanese Patent Application Laid-Open No. 2000-123939
Also, until the transition to arc discharge, the smoothing capacitor has a small capacitance, so that the step-down chopper circuit can quickly reach the arc discharge of the discharge lamp without unnecessary charging and discharging of the smoothing capacitor. Although it can respond to the operation, it cannot be applied to prevent the extinction of the discharge when returning from the arc discharge to the glow discharge.

[0011] In the documents described in these documents, special arc discharge which is remarkably generated when a large amount of mercury is filled is not considered.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems by causing a discharge lamp such as a high-pressure mercury vapor discharge lamp or a metal halide lamp to extinguish when returning from an arc discharge to a glow discharge. An object of the present invention is to provide a discharge lamp power supply device capable of reducing the probability.

[0013]

The present invention employs the following means in order to solve the above-mentioned problems. The first means includes a variable DC power supply for controlling the power of the discharge lamp, a smoothing capacitor connected in parallel with the discharge lamp to an output terminal of the variable DC power supply, and a high voltage at the start of lighting the discharge lamp. In a power supply device for a discharge lamp including a starter for applying a voltage, immediately after the lighting state of the discharge lamp shifts from a glow discharge to an arc discharge,
The capacitance of the smoothing capacitor is set to a small value, and the capacitance of the smoothing capacitor is changed to a large value in a state where the arc discharge is stably maintained.

According to a second feature, in the first feature, the capacitance of the smoothing capacitor is set to a large value after the transition from the arc discharge to the glow discharge again.

The third means is characterized in that in the first means or the second means, the capacitance of the smoothing capacitor is set to a large value when the starter is started.

According to a fourth aspect, in the first aspect, the discharge lamp includes a pair of electrodes disposed in a discharge space surrounded by a lamp envelope. In the space, noble gas and 1mm ³ 0.15 mg or more of mercury is enclosed per unit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration of a power supply device for a discharge lamp according to the present embodiment. In FIG. 1, reference numeral 1 denotes a discharge lamp such as a high-pressure mercury vapor discharge lamp or a metal halide lamp. A relatively large amount of mercury is sealed in a discharge space 5 of a lamp envelope 2, and a cathode 3 and an anode 4 face each other. Placed. The discharge space 5 is filled with, for example, a rare gas and 0.15 mg or more of mercury per 1 mm ³ . Reference numeral 6 denotes a DC power supply, and the voltage of the DC power supply 6 is supplied to a lamp power supply circuit 7 having a step-down chopper function. Although not shown, the DC power supply 6 is configured by converting a commercial power supply into a direct current using a rectifier diode or a diode bridge and a smoothing capacitor, a power supply module having a harmonic current suppressing function, a battery, and the like. . The lamp power supply circuit 7 includes a switch element 8, a gate drive circuit 9, a diode 10, an inductor 11, and a first smoothing capacitor 1.
2. Second smoothing capacitor 13, switch element 14, voltage detection circuit 15, current detection circuit 16, lamp power supply circuit 7.
And a lamp control circuit 17 for outputting a control signal to each of the elements. Here, mainly, the switch element 8, the gate drive circuit 9, the diode 10, the inductor 1
Reference numeral 1 denotes a step-down chopper 18 as a variable DC power supply.

The voltage detection circuit 15 is configured by using a voltage dividing resistor or the like, detects an applied voltage applied to the discharge lamp 1, and the current detection circuit 16 is configured by a shunt resistor, CT, or the like. The current flowing through the mercury vapor lamp 1 is detected.

Reference numeral 19 denotes a starter (starter) which is inserted between the lamp power supply circuit 7 and the discharge lamp 1 and between the cathode 4 and the anode 5 to cause discharge breakdown of the sealed gas when the discharge lamp 1 is started to light. is there. The starter 19 is provided with charging circuits R1 and C2 charged by the voltage supplied from the lamp power supply circuit 7, and is switched by the switch element S1 when the charged voltage becomes equal to or higher than a predetermined voltage. A transformer T1 for charging the capacitor C3, a transformer T2 for rapidly discharging through the gap G1 when the voltage charged in the capacitor C3 exceeds a predetermined voltage, and generating a high voltage pulse of several kilovolts to several tens kilovolts on the secondary side, etc. Consists of

Reference numeral 17 denotes a lamp control circuit, which inputs a lamp voltage signal detected by the voltage detection circuit 15 and a lamp current signal detected by the current detection circuit 16, and performs gate drive based on these signals. Circuit 9
And has a function of controlling the opening and closing of the switch element 8 by supplying a gate drive signal to the switch.

Further, a second smoothing capacitor 13 is arranged in parallel with the first smoothing capacitor 12 via a switch element 14, and in response to a command from a lamp control circuit 17,
When the switch element 14 is turned on, the second smoothing capacitor 13 is connected in parallel with the first smoothing capacitor 12, so that the combined capacitance can be increased. When the switch element 14 is turned off to disconnect the second smoothing capacitor 13, the capacitance of only the first smoothing capacitor 12 can be set to a small value.

Next, control of the smoothing capacitor at the start of lighting of the power supply device for a discharge lamp of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG. In the conventional power supply device for a discharge lamp, when the discharge state of the discharge lamp returns to the glow discharge from the arc discharge, the glow discharge cannot be maintained and the lamp goes out. This is because the ability to instantaneously increase the output voltage up to the discharge voltage Vg was insufficient. That is, even if the lamp power supply circuit attempts to increase the output voltage, energy is distributed to the charging of the smoothing capacitor, and cannot cope with the rate of increase of the lamp voltage.

Therefore, in the power supply device for a discharge lamp of the present invention, at the start of lighting, the lamp control circuit 17 detects immediately after the transition from the glow discharge to the arc discharge based on the signal detected from the voltage detection circuit 15. , The switching element 14 is turned off to disconnect the second smoothing capacitor 13,
When the capacitance of only the first smoothing capacitor 12 is set to a small value, and when it is detected that the arc discharge has reached a stable state, the switch element 14 is turned on and the second smoothing capacitor 13 is turned on. Insert the first smoothing capacitor 1
The value is set so that the combined capacitance with the value 2 is large.

As described above, according to the power supply device for a discharge lamp of the present invention, at the time when the return to the glow discharge occurs, the lamp power supply circuit 7 increases the voltage from the arc discharge voltage Va to the glow discharge voltage Vg. In trying,
By setting the capacitance of the smoothing capacitor to a small value, the part of the energy supplied from the step-down chopper 18 that is distributed to the charging of the smoothing capacitor is suppressed,
The response speed can be increased. That is,
Since the rising speed of the lamp voltage from the arc discharge to the glow discharge can be increased, the arc discharge (period t2-
It is possible to reliably prevent the discharge lamp from extinguishing when returning to the glow discharge (from time t3) after t3).

Further, after the transition to the arc discharge (period t2-t3), the timing at which the return to the glow discharge (period t3 or later) occurs cannot be predicted. If the capacitance of the entire smoothing capacitor is set to a large value, the switch element 14 is turned off as soon as possible to disconnect the second smoothing capacitor 13 and reduce the capacitance of the entire smoothing capacitor. Change to a small value.

Here, in order to set the capacitance of the smoothing capacitor to a small value, it is necessary to grasp the timing when the discharge lamp 1 shifts to arc discharge. This can be easily achieved by monitoring the voltage. Since the arc discharge voltage Va immediately after the transition to the arc discharge is low, as shown in FIG. 3, an appropriate threshold voltage Vth1 is set, and the discharge lamp 1 detects the state where the lamp voltage is lower than the threshold voltage Vth1. The timing may shift to the discharge.

Further, after the stable arc discharge, if the capacitance of the smoothing capacitor remains at a small value, the ripple component of the lamp current is large and the discharge lamp 1 flickers due to the acoustic resonance phenomenon induced by the ripple current. At the time when the arc discharge is stably maintained, the second smoothing capacitor 13 is added to change the capacitance of the smoothing capacitor to a large value when the arc discharge is stably maintained. This is to reduce the ripple component of the current.

Here, the timing at which the capacitance of the smoothing capacitor is changed to a large value is determined by monitoring the arc discharge voltage by the voltage detection circuit 15 in the same manner as described above while maintaining stable arc discharge. Can be easily realized. That is, as shown in FIG. 2, since the lamp voltage after the transition to the arc discharge gradually increases, an appropriate threshold voltage Vth2 is determined, and the arc discharge becomes stable when a state where the lamp voltage is higher than this is detected. It may be a timing when the state shifts to a state where the state is maintained.

It should be noted that the threshold voltage Vt of the lamp voltage for obtaining the timing of shifting to the arc discharge described above.
h1 and the threshold voltage Vth2 of the lamp voltage for obtaining the timing at which the arc discharge is stably maintained are set to the same value and are detected using a common circuit, thereby simplifying the structure of the device. It is also possible to convert.

Further, as shown in FIGS. 2 and 3, during lamp operation, the lamp current is small when the lamp voltage is high, and the lamp current is large when the lamp voltage is low.
Each timing can also be obtained by monitoring the lamp current by the current detection circuit 16 instead of monitoring the lamp voltage.

Further, in the invention of this embodiment, as shown in FIGS. 2 and 3, the case where the glow discharge occurs again after the initial arc discharge has been described, but the discharge lamp is in the state of the discharge lamp, for example, The discharge mode is not uniform depending on the lighting process up to and so on, and an initial arc discharge, so-called special arc discharge or re-glow discharge does not always occur. However, in the present invention, even if the initial arc discharge or the re-glow discharge does not occur or occurs,
Immediately after the transition from glow discharge to arc discharge, by setting the capacitance of the smoothing capacitor to be large, it is possible to effectively cope with any case where the discharge lamp exhibits a discharge phenomenon. be able to.

Next, control of the smoothing capacitor when the re-glow discharge occurs in the power supply device for a discharge lamp of the present invention will be described with reference to FIGS. In the power supply device for a discharge lamp of the present invention, when a return from an arc discharge to a glow discharge occurs, the second smoothing capacitor 13 is added to the first smoothing capacitor 12 to set a large combined capacitance of the smoothing capacitors. Thus, heating of the electrodes 3 and 4 of the discharge lamp 1 is promoted.

When the discharge lamp 1 returns from the arc discharge to the glow discharge, that is, a so-called re-glow discharge (period t3 or later) occurs, in order to shift from the re-glow discharge to the arc discharge, the electrodes 3 and 3 are re-glowed. It is desirable to perform the heating of No. 4 to complete the re-glow discharge in a short time. In addition, when the re-glow discharge (period t3 or later) ends and the arc discharge starts, the arc discharge voltage is much lower than the glow discharge voltage Vg2. Energy corresponding to the voltage difference between the discharge voltages is released, the electrode heating is promoted, and the transition to arc discharge can be ensured. Therefore, it is understood that the larger the capacitance of the smoothing capacitor is, the more advantageous immediately before the transition to the arc discharge.

Next, control of the smoothing capacitor when the starter of the power supply device for a discharge lamp of the present invention is operated will be described with reference to FIGS. In the power supply device for a discharge lamp according to the present invention, the second smoothing capacitor is added to the first smoothing capacitor 12 from the start of the starter 19 to the time immediately after the transition to the arc discharge after the glow discharge, to synthesize the smoothing capacitor. The capacitance is set to be large to promote heating of the electrodes 3 and 4 of the discharge lamp 1. Further, immediately after the transition to the arc discharge, the second smoothing capacitor 13 is disconnected and the capacitance is changed to a small value, and the response speed of the lamp power supply circuit 7 is increased in preparation for the occurrence of the re-glow discharge. When the re-glow discharge actually occurs,
The purpose is to increase the lamp voltage rapidly to prevent the discharge lamp from going out.

As described above, the electrodes 3 and 4 must be heated by the glow discharge in order for the discharge lamp 1 to promptly shift from the glow discharge to the arc discharge. Since the state is high, if this continues for a long time, the metal such as tungsten constituting the electrodes 3 and 4 jumps out due to the sputtering phenomenon and adheres to the lamp envelope 2, causing blackening of the lamp envelope and increasing the lamp life. The result is shrinking. Therefore, it is better to end the glow discharge in as short a time as possible.

When the discharge lamp 1 is started, the starter 19 is operated while the no-load opening voltage Vf higher than the glow discharge voltage Vg is applied to the discharge lamp 1 as shown at time t1 in FIG. Although a dielectric breakdown occurs in the discharge space and a glow discharge (period t1-t2) is started, the smoothing capacitor is charged with a voltage higher than the glow discharge voltage Vg when the no-load open voltage Vf is applied. Therefore, at the start of glow discharge,
Energy corresponding to the difference voltage between the no-load open voltage Vf and the glow discharge voltage Vg is released to promote electrode heating,
This has the effect of shortening the glow discharge time. Therefore, at the time of operation of the starter 19, it is understood that the larger the capacitance of the smoothing capacitor is, the more advantageous it is.

Also, when the glow discharge (period t1-t2) ends and the arc discharge (after time t2) is reached,
Since the initial arc discharge voltage Va is much lower than the glow discharge voltage Vg, energy corresponding to the difference voltage between the glow discharge voltage Vg and the arc discharge voltage Va is released from the smoothing capacitor, and electrode heating is promoted. This has the effect of ensuring the transition to arc discharge. Therefore, it is understood that the larger the capacitance of the smoothing capacitor is, the more advantageous immediately before the transition to the arc discharge.

Next, control of turning on / off the smoothing capacitor at the start of lighting of the discharge lamp 1 will be described with reference to FIG. FIG. 4 is a diagram showing an example of a smoothing capacitor control circuit for controlling the on / off of the second smoothing capacitor in FIG. In the figure, reference numeral 20 denotes a smoothing capacitor control circuit for controlling on / off of a second smoothing capacitor provided in the lamp control circuit 17 shown in FIG. 1 correspond to the configuration of the same reference numerals in FIG.

The switch element 14 is constituted by an FET (Qsw), and a signal detected by a ramp voltage detection circuit 15 composed of voltage dividing resistors (Rm1, Rm2) is supplied to a comparator (C
mp), and the non-comparison voltage (Vr) is input to the other terminal of the comparator (Cmp) to determine whether the lamp voltage is higher or lower than a set threshold voltage. The comparator (Cmp) has a positive feedback resistor (R
fb) and a positive feedback capacitor (Cfb) to stabilize the transient operation by the hysteresis characteristic.

In a state where the lamp voltage is higher than the threshold voltage (Vth1), such as when the starter is started or during glow discharge, the comparator (Cmp) outputs a low-level signal. Qt) is turned off, so that the capacitor (Ct) is charged with the charging resistance (R
c) and charged to a high-level voltage via the charge / discharge resistor (Rd), and a high-level signal is input to a driver circuit (Bf) composed of two complementary transistors via a Schmitt circuit (A). , Switch element 14
Is turned on, the second smoothing capacitor 13 is connected in parallel with the first smoothing capacitor 12, and the overall capacitance of the smoothing capacitor as a combined capacitance is increased. Set.

Further, when the arc discharge is started and the lamp voltage becomes lower than the threshold voltage (Vth1), the transistor (Qt) is turned on by the logic opposite to the above, and the capacitor (Ct) is turned on. Charge / discharge resistance (R
d), the voltage becomes a low level voltage, the FET switch (Qsw) of the switch element 14 is turned off, the second smoothing capacitor 13 is separated, and the electrostatic capacitance of the entire smoothing capacitor as a combined capacitance is reduced. Set the capacity to a small value to prepare for a return to glow discharge.

When the return to the glow discharge occurs, the lamp voltage returns to a state higher than the threshold voltage (Vth1). Therefore, as described above, the capacitor (Ct) includes the charge resistance (Rc) and the charge / discharge resistance (Rd). ), The capacitor is charged with a high-level voltage, the capacitance of the entire smoothing capacitor is set to a large value, and preparations are made for transition to arc discharge.

Here, the time from the transition to the arc discharge to the time when the capacitance of the entire smoothing capacitor is set to a small value, that is, waiting for the smoothing capacitor to discharge to the discharge lamp having the arc discharge voltage. The time is determined by the charge / discharge resistance (R
This is set by setting the resistance value of d) and the capacitance value of the capacitor (Ct) to appropriate values. The time from the return to the glow discharge to the time when the capacitance of the entire smoothing capacitor is set to a large value, that is, the waiting time for waiting for the smoothing capacitor to be charged to the glow discharge voltage, is the charge resistance (Rc ) And the charge / discharge resistance (Rd) and the capacitance of the capacitor (Ct) are set to appropriate values. Note that the Schmitt circuit (A) is inserted to stably binarize a signal having a relatively slow change such as charging or discharging of the capacitor (Ct).

As described above, the smoothing capacitor control circuit 2
By the control of 0, when the glow discharge state occurs, the capacitance of the entire smoothing capacitor is set to a large value, and when the operation shifts to arc discharge, the capacitance of the entire smoothing capacitor is set to a small value. No matter how many cycles of transition to and return to glow discharge occur, excellent control characteristics can be obtained in that the operation can be performed in a well-matched manner.

As described above, since the lamp voltage gradually rises after the transition to the thermal arc discharge, the arc discharge is stabilized by the smoothing capacitor control circuit 20 by appropriately setting the threshold voltage (Vth2). After that, the capacitance of the smoothing capacitor can be changed to a large value, and a transition can be made to a state in which the ripple component of the lamp current is suppressed to a small value.

In this smoothing capacitor control circuit 20, a transistor (Qx) is added, and a signal (Sx) is added.
As a result, if the transistor (Qx) can be turned on, the non-comparison voltage (Vr) can be substantially short-circuited to zero, so that the smoothing capacitor does not depend on the detection signal from the lamp voltage. Can be set to a large value. For example, a certain period of time from the start of the discharge lamp 1 until the arc discharge is stably maintained is predicted in advance, and the elapse of the certain period of time from the start of the discharge lamp is actually detected, and a signal ( By providing a timer circuit that generates Sx), the capacitance of the capacitor is changed to a large value, and the transition to a state in which the ripple component of the lamp current is reduced is controlled based on time without depending on the lamp voltage. It is also possible.

Furthermore, at the time of operation of the starter 19 or immediately before the transition to the arc discharge, it is described that the larger the capacitance of the smoothing capacitor is, the more advantageous it is. If the capacitance of the smoothing capacitor is unduly large, the electrodes may be consumed and the lamp envelope may be blackened. Therefore, the large value of the capacitance of the smoothing capacitor should be within an appropriate range suitable for the application. Must be selected in

The upper limit of the above range is mainly determined by the size of the discharge lamp, and the larger the discharge lamp, the higher the upper limit. The lower limit of the above range is determined by the switching frequency of the lamp power supply circuit 7 such as the step-down chopper 18 and the allowable amount of ripple. The lower the lower the switching frequency or the larger the allowable amount of ripple, the smaller the lower limit.

Further, the value of the capacitance of the smoothing capacitor is set to a value that can sharply increase the lamp voltage so as to prevent the discharge lamp from going out when the return from the arc discharge to the glow discharge occurs. It is necessary to set, but the upper limit of this value becomes smaller as the control response speed of the lamp power supply circuit is lower. However, since this upper limit value depends on the tendency of the discharge lamp to extinguish, it varies depending on the type of the sealing element of the discharge lamp and the gas pressure. In addition, the lower limit of this value is defined in consideration of the occurrence of a phenomenon that when the value of the capacitance is too small, the ripple becomes excessive and the operation of the lamp power supply circuit becomes unstable. Further, the lower limit value can be reduced as the switching frequency of the lamp power supply circuit increases.

As described above, how large the capacitance of the smoothing capacitor is set and how small the capacitance is set are determined by the type and size of the discharge lamp,
Since it depends on the switching frequency, response speed, and allowable ripple of the lamp power supply circuit, it needs to be determined experimentally.
In a power supply device for a high-pressure mercury lamp with a rating of 200 W, the switching frequency of the lamp power supply circuit is 50 kHz to 100 k.
Hz, the capacitance value when the capacitance of the smoothing capacitor is small is 10 nF to 100 nF, preferably 30 nF to 60 nF, and the capacitance value when the capacitance of the smoothing capacitor is large is appropriate. The value is 5 times to 50 times the capacitance value when the capacitance of the smoothing capacitor is small.
A value of 2 times, preferably 10 times to 20 times is appropriate. It should be noted that appropriate values of these capacitance values may be considered to be approximately proportional to the rated power of the discharge lamp.

In the present embodiment, one switch element 14 is turned on or off so that the capacitance of the smoothing capacitor can take two values. Or you may comprise so that a value more than that may be taken. In the case of such a configuration, when selecting a large one and a small one from the combined capacitance, the discharge state of the discharge lamp, the environmental temperature, the use time of the discharge lamp, the state of the electric circuit of the DC power supply, and the like. , It is possible to select the most suitable one.

For example, regarding a large capacitance value, a large capacitance value before the transition to the arc discharge and a state where the arc discharge is stably maintained, that is,
It is possible to set a value different from the large capacitance value in the thermal arc discharge state. Here, the latter capacitance value can be an arbitrary value according to the target level of the ripple amount.

Further, in this embodiment, the capacitor 13
The switching element 14 is connected in series with the other capacitor 12, and the one connected in parallel with the other capacitor 12 is configured as a smoothing capacitor, and its capacitance is switched between a large value and a small value. The means for changing the capacitance is not limited to such a circuit configuration. For example, two capacitors may be connected in series, and one of the capacitors may be configured to be short-circuitable by a switch element to switch the state of the capacitance.

Further, when the smoothing capacitor is composed of a plurality of components, its impedance is not limited to a purely capacitance component, but also has a resistance component or a band having a very high frequency, for example, a chopper frequency. In the band of 10 times or more, a band having an induction component may be used.

As shown in FIG. 1, the power supply device for a discharge lamp according to the present embodiment, as shown in FIG. 1, serves as a starter 19 so as to be superimposed on the output voltage supplied from the lamp power supply circuit 7 between the cathode 3 and the anode 4 of the discharge lamp 1. In the present invention, a high voltage pulse is applied to the discharge space from outside of the lamp envelope 2 to apply a high voltage pulse to the discharge space. It can also function satisfactorily by using what is called an external trigger method or a parallel trigger method (which is frequently used in triggering a flash lamp) which starts by generating a dielectric breakdown by discharge.

FIG. 5 is a diagram showing the configuration of the discharge lamp power supply device of the present invention when the external trigger system or the parallel trigger system is used as the starter 19. As shown in the figure, the high voltage pulse generated by the starter 19 is applied from an external electrode to the discharge lamp 1 via the lamp envelope 2. Although not shown, as the starter of the power supply device for a discharge lamp of the present invention, the absolute value gradually increases instead of applying the high voltage pulse instead of the internal trigger method or the external trigger method described above. It goes without saying that a good function can be achieved even by using a so-called DC starter system that applies a DC voltage.

Further, in the present invention, the discharge lamp and the smoothing capacitor are connected in parallel. However, this is not limited to the case where these two elements are simply connected in parallel. When a starter is connected in series, or a filter in which a noise filter element or the like is connected in series, and a smoothing capacitor are connected in parallel, or further, a device including a discharge lamp and a smoothing capacitor or a smoothing capacitor And other elements connected in series and those connected in parallel. That is, this includes the case where at least one including a discharge lamp and at least one including a smoothing capacitor are connected in parallel.

[0058]

According to the first aspect of the present invention, the capacitance of the smoothing capacitor is set to a small value immediately after the lighting state of the discharge lamp shifts from the glow discharge to the arc discharge. If a situation such as returning from discharge to glow discharge occurs, of the energy supplied from the variable DC power supply, the amount distributed to the charging of the smoothing capacitor is suppressed, and the rising speed from arc discharge to glow discharge is reduced. Therefore, the discharge lamp can be reliably prevented from going out when returning from the arc discharge to the glow discharge.

Further, since the capacitance of the smoothing capacitor is changed to a large value while the arc discharge is stably maintained, the flicker of the discharge lamp due to the acoustic resonance phenomenon induced by the ripple component of the lamp current. Also, it is possible to prevent the occurrence of the disappearance.

According to the second aspect of the invention, the capacitance of the smoothing capacitor is set to a large value after the transition from the arc discharge to the glow discharge again, so that the arc discharge returns to the glow discharge. If that happens,
The electrode is heated at the time of the glow discharge, the glow discharge can be completed in a short time, and the transition to the arc discharge can be quickly performed. Also, when the glow discharge ends and the arc discharge starts, the arc discharge voltage is lower than the glow discharge voltage, so that energy corresponding to the difference voltage between the glow discharge voltage and the arc discharge voltage is released from the smoothing capacitor. And
Electrode heating is promoted, and the transition to arc discharge can be ensured.

According to the third aspect of the present invention, the capacitance of the smoothing capacitor is set to a large value immediately after the start-up of the starter. Since the battery is charged at a voltage higher than the glow discharge voltage, at the start of the glow discharge, energy corresponding to the difference voltage between the no-load release voltage and the glow discharge voltage is released from the smoothing capacitor, and electrode heating is promoted. The glow discharge time can be shortened. Also, when the glow discharge ends and the operation shifts to the arc discharge, the arc discharge voltage is lower than the glow discharge voltage, so that the energy corresponding to the difference voltage between the glow discharge voltage and the arc discharge voltage is supplied from the smoothing capacitor. It is released and the electrode heating is promoted, so that the transition to arc discharge can be ensured.

According to the fourth aspect of the present invention, a rare gas and 1 mm ³ are filled in the discharge space surrounded by the lamp envelope. 4. When using a discharge lamp in which 0.15 mg or more of mercury is sealed per unit, the above-mentioned claim 1 to claim 3 are used.
The effects of the invention can be made to function extremely effectively as described.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a power supply device for a discharge lamp according to an embodiment of the present invention.

FIG. 2 is a diagram showing lamp voltage characteristics and lamp current characteristics from the start of a discharge lamp to a steady lighting state.

FIG. 3 is an enlarged view showing a lamp voltage characteristic and a lamp current characteristic when the discharge lamp shown in FIG. 2 is started.

FIG. 4 is a diagram showing an example of a smoothing capacitor control circuit for controlling turning on and off of a second smoothing capacitor shown in FIG. 1;

FIG. 5 is a diagram showing a configuration of a discharge lamp power supply device of the present invention when an external trigger method or a parallel trigger method is used as a starter 19;

FIG. 6 is a diagram showing an example of a power supply device for a discharge lamp for lighting a discharge lamp according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Lamp envelope 3 Cathode 4 Anode 5 Discharge space 6 DC power supply 7 Lamp power supply circuit 8 Switch element 9 Gate drive circuit 10 Diode 11 Inductor 12 First smoothing capacitor 13 Second smoothing capacitor 14 Switch element 15 Voltage detection Circuit 16 Current detection circuit 17 Lamp control circuit 18 Step-down chopper 19 Starter 20 Smoothing capacitor control circuit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Minoru Fukuda 1194 Sado, Bessho-cho, Himeji-shi, Hyogo USHIO Electric Co., Ltd. F-term (reference) 3K083 AA04 AA46 AA66 BC33 BC42 BC47 BD03 BD04 BD16 BD22 CA33

Claims (4)

[Claims] 1. A variable DC power supply for controlling power of a discharge lamp, a smoothing capacitor connected in parallel with the discharge lamp to an output terminal of the variable DC power supply, and a high voltage when starting lighting of the discharge lamp. And a starter for applying a voltage to the discharge lamp, wherein immediately after the lighting state of the discharge lamp shifts from glow discharge to arc discharge, the capacitance of the smoothing capacitor is set to a small value, and arc discharge is performed. Wherein the capacitance of the smoothing capacitor is changed to a large value in a state where is stable. 2. The power supply device for a discharge lamp according to claim 1, wherein the capacitance of the smoothing capacitor is set to a large value after the transition from the arc discharge to the glow discharge again. 3. The power supply device for a discharge lamp according to claim 1, wherein the capacitance of the smoothing capacitor is set to a large value when the starter is started. 4. The discharge lamp has a pair of electrodes disposed in a discharge space surrounded by a lamp envelope, and a rare gas and 1 mm ^{3 in the} discharge space. The power supply device for a discharge lamp according to any one of claims 1 to 3, wherein 0.15 mg or more of mercury is enclosed per unit.