JP2000200690A - Light source device for dielectric barrier discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient light source device for a dielectric barrier discharge lamp by efficiently producing excimer molecules. SOLUTION: This device includes a lamp 1 having a discharge plasma space filled with a discharge gas to produce excimer molecules with dielectric barrier discharge and constructed with dielectrics 5, 6 laid between at least one of both electrodes 3, 4 for inducing a discharge phenomenon in the discharge gas and the discharge gas and a feeder 7 using a flyback inverter and a step-up transformer to apply high voltage to the electrodes 3, 4 for the lamp 1. Even when a switching element for the flyback inverter is turned on, effective discharge is generated in the discharge lamp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a kind of discharge lamp in which excimer molecules are formed by dielectric barrier discharge.
The present invention relates to a light source device including a so-called dielectric barrier discharge lamp using light emitted from the excimer molecule.

[0002]

2. Description of the Related Art As a technique related to the present invention, a dielectric barrier discharge lamp is disclosed in, for example, Japanese Patent Laid-Open Publication No. Hei 2-7353, which discloses a discharge gas for forming excimer molecules in a discharge vessel. And excimer molecules are formed by a dielectric barrier discharge (also known as an ozonizer discharge or a silent discharge; see the revised Electric Discharge Handbook, published by the Institute of Electrical Engineers of Japan, reprinted 7th edition, page 263, June 1991). An emitter for extracting emitted light is described.

As shown in FIG. 1, a dielectric barrier discharge lamp (1) has one or two dielectrics between electrodes (3, 4) sandwiching a discharge plasma space (2). . FIG. 1 shows a lamp in which two dielectrics (5, 6) are present. Incidentally, in FIG. 1, the lamp envelope (9) is
Also serves as a dielectric (5, 6).

When the dielectric barrier discharge lamp (1) is turned on, for example, 10 k
Hz to 200 kHz, and a high-frequency AC voltage of 2 kV to 10 kV is applied. However, because of the dielectric (5, 6) interposed between the discharge plasma space (2) and the electrodes (3, 4), a current may flow directly from the electrodes (3, 4) to the discharge plasma space (2). Instead, current flows due to the dielectric (5, 6) acting as a capacitor. That is, electric charges having the same sign opposite to that of the surface on the side of each electrode (3, 4) are induced on the surface of each dielectric (5, 6) on the side of the discharge plasma space (2) by polarization of the dielectric, and the discharge is performed. Plasma space (2)
Is discharged between the surfaces of the dielectrics (5, 6) opposed to each other.

Since a small amount of current flows along the surface of the dielectric (5, 6) on the side of the discharge plasma space (2), the discharge plasma space (5, 6) of the dielectric (5, 6) 2) The charge induced on the side surface is neutralized by the charge transferred by the discharge, and the electric field in the discharge plasma space (2) is reduced, so that the voltage application to the electrodes (3, 4) is continued. Also, the discharge current eventually stops. However, when the voltage applied to the electrodes (3, 4) further increases, the discharge current continues. After one discharge occurs, the portion where the discharge has stopped does not re-discharge until the polarity of the voltage applied to the electrodes (3, 4) is reversed.

For example, in the case of a lamp filled with xenon gas, the xenon gas is separated into ions and electrons by electric discharge, and becomes xenon plasma. In this plasma, xenon excited to a specific energy level is combined to form excimer molecules. Xenon excimer is dissociated after a certain lifetime, and the energy released at this time is emitted as a photon having a vacuum ultraviolet wavelength. In order for the lamp to operate efficiently as a vacuum ultraviolet light source, it is necessary to efficiently form this excimer molecule.

A major factor that hinders efficient excimer molecule formation during discharge is that the discharge plasma is excited to an energy level that does not contribute to excimer molecule formation. The electron motion of the discharge plasma immediately after the start of discharge is collective, and the energy is high but the temperature is low. In this state, there is a high probability that the discharge plasma will transition to a resonance state necessary for forming excimer molecules.

However, when the discharge energy is excessive or the discharge time is long, the electron motion of the plasma gradually becomes thermal, ie, a thermal equilibrium state called Maxwell-Boltzmann distribution, and the plasma temperature rises, causing excimer molecules to move. The probability of transition to a higher excited state that cannot be formed increases.

Further, even when excimer molecules are formed, the excimer molecules may be destroyed by a subsequent discharge before the intended photons are emitted and naturally dissociated after the elapse of the lifetime. . In fact, in the case of xenon excimer, it takes 1 μs from the start of discharge to the emission of photons of vacuum ultraviolet wavelength.
It takes a certain period, and the subsequent discharge or re-discharge during this period lowers the efficiency of excimer light emission.

[0010] That is, it is very important that once the discharge starts, the required power is applied to the plasma in a short time and the discharge is terminated as soon as possible, so that the energy of the subsequent discharge is made as small as possible. It can be seen that it is. In this respect, the conventional dielectric barrier discharge lamp light source device has not been satisfactory.

[0011]

Here, Japanese Patent Application Laid-Open No. 9-199285 is an invention which has been made to efficiently form excimer molecules. The present invention specifies a pulse width of a voltage applied to a lamp as a necessary condition for efficiently realizing excimer molecule formation.

Further, as an invention made to make excimer molecule formation efficient, Japanese Patent Application Laid-Open No. 10-223384 is disclosed.
There is a number. The present invention specifies a rise time of a voltage applied to a lamp as a necessary condition for efficiently realizing excimer molecule formation. In these inventions, description has been mainly given of embodiments using a flyback inverter as an inverter for generating a high-frequency AC voltage.

FIG. 3 shows a general example of a high-frequency AC voltage generating circuit using a flyback inverter. Also,
FIG. 4 shows a conventional lamp applied voltage waveform using this. The flyback inverter basically requires only one switching element such as a transistor or an FET, and therefore has an economic advantage of low cost.

However, on the other hand, since the generation of the high voltage is manifested when the switching element is turned off, there is a disadvantage that the operation is easily affected by the load impedance. Further, in order to satisfy the conditions specified in the above-mentioned Japanese Patent Application Laid-Open No. 10-223384, it has to be achieved by adjusting the inductance and the like of the step-up transformer, and the degree of freedom in design is low.

In the dielectric barrier discharge lamp, discharge is generated by reversing the polarity of the voltage in the discharge plasma space. Therefore, a plurality of discharges are usually generated in one cycle of the voltage waveform applied to the lamp. In the configurations of the inventions of JP-A-9-199285 and JP-A-10-223384, in the two peak discharges which occur in the first half and the second half of the main peak part (Wm) of the voltage applied to the lamp, Since the rise time and the fall time are short, it almost meets the above-mentioned condition that once the discharge is started, the required power is supplied to the plasma in a short time and the discharge is terminated as soon as possible. However, with respect to the other portion of the vibration waveform (Ws), there is not much difference from the conventional sinusoidal driving, and therefore it contributes to an increase in the amount of lamp light emission, but the efficiency of excimer light emission is not good. Met.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a dielectric barrier discharge lamp light source device according to the present invention comprises a discharge plasma filled with a discharge gas for generating excimer molecules by dielectric barrier discharge. There is a space (2), and a dielectric (5, 6) is interposed between at least one of the bipolar electrodes (3, 4) for inducing a discharge phenomenon in the discharge gas and the discharge gas. And a power supply device (7) using a flyback inverter and a step-up transformer for applying a high voltage to the electrodes (3, 4) of the lamp. An effective discharge is generated in the discharge lamp even when the switch element (10) of the flyback inverter is turned on.

[0017]

In FIG. 3, a gate signal (G (t)) from a gate drive circuit (13) is supplied to a gate terminal of a switch element (10) such as an FET. Here, it is assumed that the switch element (10) turns on when the gate signal (G (t)) is at a high level and turns off when the gate signal (G (t)) is at a low level.

When the switch element (10) is turned on, the power supply (14) is applied to the primary winding (11) of the step-up transformer (8).
And the primary side current (Ip (t)) starts to flow. The primary current (Ip (t)) is equal to the switching element (10).
Increases in proportion to the length of the period during which the switch is on, and accumulates magnetic energy in the core of the step-up transformer (8).

When the switch element (10) turns off, 1
Since the secondary current (Ip (t)) is rapidly cut, a voltage of the opposite polarity is generated in the primary winding (11). A voltage multiplied by the number of turns of the wire is generated as a secondary voltage, that is, a lamp applied voltage (E (t)). Lamp applied voltage (E
(t)) increases rapidly based on the resonance frequency determined by the secondary side inductance and the lamp capacitance, and the voltage of the discharge plasma space (2) of the lamp (1) reaches the discharge starting voltage. Then, the discharge (F1) is started. After the discharge starts, when the lamp applied voltage (E (t)) reaches a peak, the discharge stops. This situation is as shown in FIG. However, the discharge current (Id (t)) conceptually represents the flow of charges in the discharge plasma space (2), and is not the same as the secondary current (Is (t)) but directly It is impossible to measure.

Thereafter, when the voltage applied to the lamp (E (t)) approaches 0 volts in accordance with the resonance phenomenon, the discharge discharge space (2) is moved by the previous discharge, and the dielectric (5, 5) is moved.
Due to the electric field formed by the charges attached to 6), a discharge (F2) in the opposite direction to the previous discharge is generated. The two peak discharges (Wm) so far account for most of the lamp power input, but usually the lamp applied voltage (E (t)) oscillates according to the resonance phenomenon. As long as the condition that the voltage of the discharge plasma space (2) reaches the discharge start voltage can be satisfied, the start and stop of the discharge are repeated.

In the above-mentioned period (τon) when the switch element (10) is on, the voltage multiplied by the number of turns of the secondary winding with respect to the primary winding is equal to the lamp applied voltage (E). (t)), but in the conventional dielectric barrier discharge lamp light source device, an effective discharge was not generated by the voltage generated at this time.

However, when the switching element (10) turns on (ton), the transition of the primary voltage (Vp (t)) is caused by the switching of the primary winding (11) by the switching element (10). Since it is caused by being directly connected to 14), it is driven with a very low impedance. Therefore, at this time, the step-up transformer (8) viewed from the lamp (1)
The impedance of the side winding (12) is also very low. Since the lamp (1) is strongly driven by a circuit having a low output impedance, the voltage applied to the lamp changes sharply. Further, since the lamp (1) has a step-like waveform that maintains a constant voltage, it is discharged at this time. Then, once the discharge has started to make the excimer molecule formation efficient,
It meets very well the requirements of supplying the required power to the plasma in a short time and ending the discharge as soon as possible. In the dielectric barrier discharge lamp, the current flows when the dielectric (5, 6) acts as a capacitor, so that the current flows only when the voltage of the step function waveform changes sharply. In the subsequent flat period, no current flows, so that the discharge occurs in a short time and ends immediately.

In addition, as described above, the output impedance of the power supply device is low when the switch element (10) is turned on (ton) and during the period when the switch element (10) is turned on (τon) thereafter. Since the state is maintained, there is also an advantage that the operation is less affected by the load impedance. For example, even if there is a change in the temperature of the lamp, a change in the length of the wiring on the primary side or the secondary side of the step-up transformer (8), or a change in the wiring, the load impedance as seen from the flyback inverter fluctuates. 10)
Is on (τon) is hardly affected by the fluctuation.

When, for example, a power MOSFET is used as the switch element (10), the switch element (10) usually contains a built-in diode (15). As a result, the primary current (Ip (t)) flows almost freely in the reverse direction, so that a flat portion (Wf) appears in the lamp applied voltage waveform (E (t)) after the main peak portion (Wm). Occurs. if,
When the diode (16) is inserted in series with the switch element (10), the function of the built-in diode (15) is blocked, so that the lamp applied voltage waveform (E (t)) as shown in FIG. No flat portion (Wf) occurs. In the present invention, the presence or absence of the series diode (16) is not of essential importance and functions independently.

[0025]

FIG. 6 shows a lamp applied voltage waveform (E (t)) as an embodiment of the present invention. In the figure, the switch element (1) is passed before the main peak portion (Wm) has passed and the subsequent vibration waveform portion (Ws) has not been completed.
(0) turns on (ton), causing a discharge due to the voltage transition. In order to realize this, the voltage of the power supply (E) is set so that the voltage of the step-up transformer (8) during the ON period (τon) of the switch element (10), that is, the lamp applied voltage (E (t)) reaches the discharge start voltage. 14) voltage and 1
The winding ratio of the secondary winding to the secondary winding is determined, and the period and duty cycle ratio of the gate drive circuit (13) are determined so that the switch element (10) is turned on at a predetermined timing. I just need.

The electric power supplied when the switch element (10) is turned on (ton) may be smaller than that of the main peak portion (Wm). However, as described above, the luminous efficiency is extremely low. , Excimer molecule formation can be made efficient as a whole. Further, as described above, even if the load impedance seen from the flyback inverter fluctuates, the operation during the ON period (τon) of the switch element (10) is hardly affected by the fluctuation, so that the light quantity can be stabilized. High in nature.

When the switch element (10) is turned on (ton), the portion of the vibration waveform (W
s), the period (τo) when the switch element (10) is on
It is advantageous to be near the timing (t1) of the maximum point of the absolute value of the opposite polarity to the lamp applied voltage (E (t)) of n). Since the lamp (1) is effectively driven by a circuit having a low output impedance by causing an effective discharge to occur even when the switch element (10) of the flyback inverter is turned on (ton), The voltage applied to the lamp changes abruptly, and once the discharge starts, it meets the condition that the required power is applied to the plasma in a short time and the discharge is completed as soon as possible, and excimer molecule formation is achieved. Can be efficient,
As a result, a highly efficient dielectric barrier discharge lamp light source device can be realized.

FIG. 7 shows the above-mentioned ramp applied voltage waveform (E
(t)) and the measured data of the secondary current waveform (Is (t)). FIG. 8 is an enlarged measurement of a section (Z) generally shown in FIG. FIG. 9 illustrates a discharge current waveform (Id (t)) calculated by analyzing the waveform of FIG. 8 by a computer, and a lamp applied voltage waveform (E (t)) and a secondary current waveform (Is (t)). )
It is shown together with.

Here, a method of calculating the discharge current waveform (Id (t)) from the ramp applied voltage waveform (E (t)) and the secondary current waveform (Is (t)) as shown in FIG. 9 will be described. I do.
When the dielectric barrier discharge lamp (1) of FIG. 1 is represented by the equivalent circuit shown in FIG. 2, the capacitance C1 of the discharge plasma space (2), the capacitance C2 of the dielectric (5, 6), and the lamp The following two coefficients, Cu = 1 + C1 / C2 (Equation 1), which are determined by the stray capacitance C3 existing in parallel with the following equation, are used. Can be obtained by the following equation. Id (t) = Cu · Is (t) −Cv · dE (t) / dt (Equation 3) However, when there are two dielectrics, if the capacitance obtained by combining the respective capacitances in series is C2 Good. This method uses numerical differentiation, so the accuracy is not very good in the region where the current value is small in the waveform of the obtained result, but since it shows a fast rise at the start of discharge, it is used for finding out this No problem.

The analysis conditions and the experimental conditions in the case of FIGS. 7, 8 and 9 are as follows. C1: 35 pF C2: 220 pF C3: 15 pF Frequency: 36 kHz Transformer primary inductance: 33 μH Transformer secondary inductance: 6.1 mH Transformer coupling coefficient: 0.9930 Dielectric: quartz glass—thickness 1 mm Discharge gas: xenon—pressure 33 kPa discharge gap: 4.3 mm

In FIG. 9, the discharge current waveform (Id
(t)) rises sharply at two points, time Td1 and time Td2, and accordingly, the switching element (10)
It can be seen that a major discharge occurs when is turned on (ton) and when the switch element (10) is turned off. When the discharge current waveform (Id (t)) is further carefully observed, the time Td3 and the time Td4 also show that
It can be determined that discharge has occurred. Here, the timing of turning on (ton) of the switch element (10) is compared with the conceptual diagram shown in FIG.
From the sharp falling point of (t)), the ON point (ton) can be understood as shown in the figure. Similarly, the timing at which the switching element (10) is turned off (toff) is related to the fact that the lamp applied voltage sharply increases when the switching element is turned off in the conceptual diagram of FIG.
The timing of t (off) can be read. Further, since a slight time delay occurs in an actual circuit, the time Td1 is set after the switch element (10) is turned on.
It can be seen that a discharge is generated at the time Td2 with a slight time delay after the switch element (10) is turned off.

In the above-described embodiment, the switch is applied before the main peak portion (Wm) of the ramp applied voltage waveform (E (t)) has passed and the subsequent vibration waveform portion (Ws) has not ended. The case where the element (10) is turned on has been introduced. When the switch is turned on after the main peak portion (Wm) and the subsequent vibration waveform portion (Ws) are completed, or when the main peak (Wm) falls. The switch can be turned on before, simultaneously with, or immediately after the spontaneous discharge. To realize this, as described above, the voltage of the step-up transformer (8) during the period when the switch element (10) is on (τon), that is, the lamp applied voltage (E (t)) reaches the discharge starting voltage. Thus, the voltage of the power supply (14) and the ratio of the number of turns of the secondary winding to the primary winding are determined, and the gate is turned on so that the switch element (10) is turned on at a desired timing. The period and the duty cycle ratio of the drive circuit (13) may be determined.

Here, in the latter case, that is, when the switch is turned on before, simultaneously with, or immediately after the spontaneous discharge at the fall of the main peak (Wm), the switch element (10) is turned on (τon ), The lamp applied voltage (E (t)) is lower than the lamp applied voltage (E (t)) when the switch is turned on in the middle of the vibration waveform portion (Ws) following the main peak portion (Wm) and at the end thereof. )) May be smaller. This is because, after the completion of the discharge in the first half (rising) of the main peak portion (Wm), a large amount of charges adhere to the dielectrics (5, 6) by moving in the discharge plasma space (2) by the previous discharge.
This is because a strong electric field is formed at (ton) by turning on the switch element (10).

The circuit configuration and the like mentioned here are simplified conceptual diagrams for explaining the features of the present invention, and additional circuits and protection circuits are added as necessary at the time of actual design. Should be. In addition, the polarity of the power supply (14), the switching element (10) of the flyback inverter, and the logic of the gate drive of the switching element (10) are not related to the features of the present invention. It may be changed for convenience. In addition, the lamp applied voltage waveform (E
Even if the polarity of (t)) is reversed, the excellent features of the present invention are well maintained.

The circuit operations, waveforms, and the like described here are merely examples, and may vary slightly depending on the circuit configuration, the structure and size of the lamp, the components of the sealed gas, and the like. As is clear from comparison, ringing, noise, and the like are superimposed on the actual waveform in the conceptual waveform diagram of FIG. 6, but the excellent advantages of the present invention are these subtle changes and superimposed components. Even if there is, it is effective.

The present invention also works well with a lamp in which a fluorescent substance is applied to the inner surface or the outer surface of the sealing (9) glass.

[0037]

[Effect] Flyback inverter switch element (10)
When the lamp is turned on (ton), the effective discharge of the lamp is generated, so that the lamp (1) is strongly driven by a circuit having a low output impedance, so that the lamp applied voltage changes sharply, and Since it has a step function waveform that maintains a constant voltage thereafter, once the discharge has started, it is extremely necessary to apply the necessary power to the plasma in a short time and finish the discharge as soon as possible. The excimer molecules can be formed efficiently, and the efficiency of the excimer molecule formation can be improved. As a result, a highly efficient dielectric barrier discharge lamp light source device can be realized.

Further, for example, there is a change in the temperature of the lamp, a change in the length of the wiring on the primary side or the secondary side of the step-up transformer (8) or a change in the wiring, and the load impedance seen from the flyback inverter fluctuates. Also switch element (1
The operation during the period (τon) when (0) is on (τon) is hardly affected by the fluctuation, and an excellent dielectric barrier discharge lamp light source device can be realized.

[Brief description of the drawings]

FIG. 1 shows a dielectric barrier discharge lamp.

FIG. 2 shows an equivalent circuit of a dielectric barrier discharge lamp.

FIG. 3 shows a circuit for generating a high-frequency AC voltage.

FIG. 4 shows a conventional lamp applied voltage waveform.

FIG. 5 shows a lamp applied voltage waveform.

FIG. 6 shows a lamp applied voltage waveform.

FIG. 7 shows actually measured values of a lamp applied voltage waveform and a current waveform.

FIG. 8 shows a partially enlarged view of FIG. 7;

FIG. 9 shows a diagram obtained by analyzing the waveform of FIG. 8 by a computer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Discharge plasma space 3 Electrode 4 Electrode 5 Dielectric 6 Dielectric 7 Power supply device 8 Step-up transformer 10 Switch element

Claims (1)

[Claims] 1. A discharge plasma space (2) filled with a discharge gas for generating excimer molecules by a dielectric barrier discharge, and bipolar electrodes (3, 3) for inducing a discharge phenomenon in the discharge gas. 4) A discharge lamp (1) having a structure in which a dielectric (5, 6) is interposed between at least one of the discharge gas and the discharge gas, and a high voltage is applied to the electrodes (3, 4) of the discharge lamp. Power supply device using flyback inverter and step-up transformer for applying voltage (7)
Wherein the discharge lamp generates an effective discharge even when the switch element (10) of the flyback inverter is turned on. Discharge lamp light source device.