Light source device, dielectric barrier discharge lamp lighting circuit, and dielectric barrier discharge lamp lighting method

Abstract

To provide a light source device that can achieve power saving and reliability improvement without increase in size of the whole device, and to provide a lighting circuit and a lighting method for a dielectric barrier discharge lamp for achieving power saving and reliability improvement without increase in size of the whole device.SOLUTION: A light source device comprises: a lighting circuit that includes a DC power supply, a transformer, and a switching element, and generates an electromotive force at a secondary side coil of the transformer by switching of the switching element between an ON state and an OFF state; a dielectric barrier discharge lamp connected with the secondary side coil of the transformer; and a controller that performs ON / OFF control of the switching element. The controller executes a starting time mode in which the ON / OFF control of the switching element is repeatedly performed at a predetermined frequency at starting time, and a normal operation time mode in which first control of repeatedly performing the ON / OFF control of the switching element at the predetermined frequency and second control of maintaining the switching element to be in an OFF state are alternately performed after starting the dielectric barrier discharge lamp.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a light source device, and more particularly to a light source device including a dielectric barrier discharge lamp. The present invention also relates to a lighting circuit and a lighting method for a dielectric barrier discharge lamp. [Background technology]

[0002] Conventionally, a first control technique using a flyback type lighting circuit has been known for lighting dielectric barrier discharge lamps (see, for example, Patent Document 1). In addition to the flyback type, other lighting circuits such as push-pull type and full-bridge type are also known as lighting circuits for dielectric barrier discharge lamps. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-223384 [Patent Document 2] JP 2020-92968 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, technology that uses ultraviolet light to inactivate bacteria, viruses, and the like (hereinafter sometimes abbreviated as "bacteria, etc.") has been developed. The present applicant has also developed a technology for inactivating bacteria, etc., using an excimer lamp, which is a type of dielectric barrier discharge lamp (see, for example, the above-mentioned Patent Document 2).

[0005] Recently, due to the spread of coronavirus infections, etc., attention has been focused on inactivation treatment techniques using excimer lamps, which are capable of inactivating bacteria, etc. and which utilize ultraviolet light with a wavelength of 190 nm to 240 nm, as this inactivation treatment has an extremely low impact on humans and animals.

[0006] Known excimer lamps that emit light in this wavelength range include those in which rare gas and halogen gas are enclosed as luminous gas in the arc tube. Examples of such excimer lamps include excimer lamps in which krypton (Kr) and chlorine (Cl) are enclosed in the arc tube and have a main peak wavelength of about 222 nm, excimer lamps in which krypton (Kr) and bromine (Br) are enclosed in the arc tube and have a main peak wavelength of about 207 nm, and excimer lamps in which argon (Ar) and fluorine (F) are enclosed in the arc tube and have a main peak wavelength of about 193 nm.

[0007] In order to generate an initial discharge and start the lighting operation, a dielectric barrier discharge lamp may require the application of a voltage higher than that applied during steady operation at the time of start-up. For this reason, many light source devices incorporating a dielectric barrier discharge lamp may be provided with a control or mechanism for switching the voltage value applied to the dielectric barrier discharge lamp between the time of start-up and the time of steady operation.

[0008] In particular, as described above, in excimer lamps in which the light-emitting gas contains a halogen gas with high electron affinity, initial discharge is less likely to occur in the light-emitting tube than in excimer lamps in which the light-emitting gas does not contain a halogen gas. For this reason, light source devices equipped with excimer lamps in which the light-emitting gas contains a halogen gas are often configured to apply a higher voltage at start-up than during steady-state operation in order to more reliably generate initial discharge.

[0009] However, it is difficult to realize control for switching the value of the voltage applied to a dielectric barrier discharge lamp by simple ON / OFF control alone, and depending on the lighting circuit type, output voltage control by an analog circuit or a DC / DC converter for converting the voltage level may be required. For this reason, a light source device equipped with a voltage switching mechanism requires advanced circuit design technology to obtain the desired characteristics for the output voltage, transient characteristics, etc.

[0010] Furthermore, analog circuits are prone to reliability issues because the output voltage, etc., may fluctuate due to deterioration over time, etc., and in order to ensure high reliability, it becomes necessary to install a complex correction circuit, etc. In other words, installing a mechanism for switching the voltage applied to the dielectric barrier discharge lamp increases the size of the entire light source device, increases manufacturing costs, and further causes reliability issues.

[0011] As described above, light source devices equipped with excimer lamps that emit ultraviolet light with wavelengths of 190 nm to 240 nm have extremely low impact on people and animals, and are therefore expected to be used in a variety of situations, such as medical facilities, schools, government offices, and other facilities where people gather frequently, as well as vehicles such as automobiles, trains, buses, airplanes, ships, etc. For this reason, there is a strong demand for such light source devices to be more compact as a whole, highly reliable, and to be energy-efficient.

[0012] In view of the above problems, the present invention has an object to provide a light source device that realizes power saving and improved reliability without increasing the size of the entire device. It is also an object of the present invention to provide a lighting circuit and a lighting method for a dielectric barrier discharge lamp that realizes power saving and improved reliability without increasing the size of the entire device. [Means for solving the problem]

[0013] The light source device of the present invention comprises: a lighting circuit including a DC power source, a transformer having a primary winding and a secondary winding, and at least one switching element, the lighting circuit being configured to switch between an ON state and an OFF state of the switching element to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer, or to change the direction of the current flowing through the primary winding, thereby generating an electromotive force in the secondary winding of the transformer; a dielectric barrier discharge lamp connected to the secondary winding of the transformer; A control unit that performs ON / OFF control of the switching element, The control unit is a startup mode in which, at startup, a predetermined voltage is applied to the dielectric barrier discharge lamp by repeatedly controlling ON / OFF of the switching element at a predetermined frequency; After starting the dielectric barrier discharge lamp, a steady-state operation mode is executed in which a first control is executed in which the predetermined voltage is applied to the dielectric barrier discharge lamp by repeating ON / OFF control of the switching element at the predetermined frequency, and a second control is executed in which the switching element is maintained in an OFF state for a period longer than the cycle of the ON / OFF control of the switching element.

[0014] The startup mode executes ON / OFF control of the switching element to generate the electromotive force required for an initial discharge to occur in the dielectric barrier discharge lamp connected to the secondary winding of the transformer. Note that the magnitude of the electromotive force generated in the secondary winding of the transformer is preset by adjusting the output voltage of the DC power supply, the number of turns of each winding of the transformer, the time for which the switching element is kept ON, etc., according to the type and size of the dielectric barrier discharge lamp.

[0015] In the steady-state operation mode, in order to reduce power consumption per unit time and the load on the dielectric barrier discharge lamp and the lighting circuit, a first control that controls the switching element to be turned on / off, as in the startup mode, is alternately executed, and a second control that maintains the switching element in the OFF state.

[0016] In other words, the startup mode and the steady-state operation mode perform the same first control for controlling the ON / OFF of the switching element, but differ in that they include or do not include control (second control) for maintaining the switching element in the OFF state. The startup mode and the first control in the steady-state operation mode have substantially the same frequency for repeating the ON / OFF control of the switching element and the voltage applied to the dielectric barrier discharge lamp. Note that "substantially the same" here is used to mean that they are within the same range even if there are slight errors caused by noise generated in the control unit or variations in the elements that make up the device.

[0017] The light source device may be configured to temporarily execute a startup mode during execution of a steady-state operation mode after startup in order to prevent interruption, etc. The light source device may also be configured to continue the startup mode for a predetermined time even after it is confirmed that the dielectric barrier discharge lamp is lit, in order to more reliably stabilize the lighting state.

[0018] The light source device of the present invention, with the above configuration, reduces the amount of power per unit time supplied to the dielectric barrier discharge lamp during lighting operation compared to the case where the startup mode continues to be executed even after the dielectric barrier discharge lamp is lit, thereby suppressing power consumption. Also, although application of a high voltage required for generating an initial discharge in the light emitting tube of the dielectric barrier discharge lamp continues after startup, the frequency of voltage application is reduced compared to the startup mode by executing the second control, thereby reducing the load on the dielectric barrier discharge lamp and the lighting circuit.

[0019] The steady-state operation mode in which the first control and the second control are repeated is realized by switching the control signal input to the switching element, which can be realized by switching using digital signal processing, rather than switching an analog circuit configuration that changes the output voltage.

[0020] Furthermore, when the control unit is configured with a programmable device, MCU, etc., the light source device configured as described above can be realized by rewriting the program that defines the pattern of the control signal, without the need to change the circuit configuration, etc. Also, even when the light source device configured as described above is realized by a combination of a control signal that controls ON / OFF of a switching element at a predetermined cycle and a masking signal that is output from the control unit separately from the control signal for the switching element, it can be realized with at least one logic gate element (for example, an AND gate element for taking the logical product of the control signal and the masking signal).

[0021] In other words, the light source device of the above configuration does not require complex mechanisms or circuits, so it can be realized without increasing the size of the entire device compared to conventional devices, and depending on the configuration of the lighting circuit, the number of components can be reduced to make the entire device smaller. Also, since it can be realized only by digital signal processing, there is no need to worry about variations in output values ​​or characteristic fluctuations due to deterioration over time, and there are fewer concerns about reliability.

[0022] The light source device is The control unit may be configured to periodically execute the first control and the second control in the steady operation mode.

[0023] In the steady operation mode, when the first control and the second control are repeated in a specific cycle, the integrated irradiation amount on the area or the object irradiated with the light emitted from the dielectric barrier discharge lamp becomes almost constant for each cycle. Therefore, by configuring the light source device as described above, it becomes easier to manage the progress of the inactivation process on the area or the object irradiated with the ultraviolet light, compared to a case where the execution times of the first control and the second control are arbitrarily changed in the steady operation mode.

[0024] Furthermore, the above control can be simply configured to repeat the first control and the second control at a predetermined cycle, and therefore can be easily realized compared to configuring complex control that changes the cycle depending on the inactivation treatment status or the usage environment.

[0025] The light source device is The control unit may be configured to execute the steady operation mode such that the number of times that the ON / OFF control of the switching element is repeated in the first control differs before and after each of the second controls.

[0026] When a transformer is supplied with a periodic current, periodic magnetostriction occurs, causing minute vibrations corresponding to the frequency of the current. If the frequency of the vibrations is within the range of the human audible range (approximately 20 Hz to 20 kHz), an abnormal sound phenomenon called "sounding" may occur. In the present invention, the frequency of the operation for switching between the first control and the second control in the steady operation mode may be set to a frequency within the human audible range, which may be one of the factors that cause the sounding.

[0027] Therefore, by adopting the above configuration, the operation of switching between the first control and the second control in the steady operation mode is not an operation at a specific frequency, and the strength of the vibration generated in the transformer by magnetostriction is dispersed among a plurality of frequency components, thereby suppressing noise. Note that a method for preventing the operation of switching between the first control and the second control in the steady operation mode from being an operation at a specific frequency may be a method of making the execution time of the second control different before and after each of the first controls, or the like.

[0028] The light source device is It is preferable that the control unit is configured to execute the steady operation mode so that the sum of the execution time of the first control and the execution time of the second control immediately thereafter is four times or more of a period corresponding to the specified frequency, and the execution time of the second control is 100 ms or less.

[0029] If the execution time of the second control is too short, heat generation due to excessive power supply may become a problem depending on the shape and size of the dielectric barrier discharge lamp. Therefore, the execution time of the second control is preferably at least four times, and more preferably at least eight times, the cycle of ON / OFF control of the switching element in the first control so that heat generation in the dielectric barrier discharge lamp is sufficiently suppressed.

[0030] Moreover, if the execution time of the second control is too long, the plasma in the light emitting tube of the dielectric barrier discharge lamp may disappear or attenuate, and the dielectric barrier discharge lamp may be turned off. Note that, with respect to the light source device of the present invention, in the first control in the steady operation mode, the frequency at which the ON / OFF control of the switching element is repeated and the voltage applied to the dielectric barrier discharge lamp are the same as those in the start-up mode, so that a voltage required to generate an initial discharge in the dielectric barrier discharge lamp is applied. In other words, even if the dielectric barrier discharge lamp is turned off because the second control is too long, there is a possibility that it may be possible to light it again when the control unit starts the next first control.

[0031] Moreover, the first control in the steady operation mode may be a control in which a pulsed voltage is applied a necessary and sufficient number of times to maintain the lit state of the dielectric barrier discharge lamp from the viewpoint of reducing power consumption and load. However, in a dielectric barrier discharge lamp that has been turned off, although an initial discharge occurs in the first control in the steady operation mode, there is a possibility that the light emission state is unstable and the lit state cannot be maintained until the transition to the next second control is made. Therefore, in order to stably maintain the lit state of the dielectric barrier discharge lamp, the execution time of the second control in the steady operation mode is preferably 100 ms or less, more preferably 80 ms or less, and particularly preferably 10 ms or less.

[0032] The light source device is The lighting circuit may be a flyback type circuit.

[0033] Moreover, the light source device is The lighting circuit may be a push-pull type circuit.

[0034] Moreover, the light source device is The lighting circuit may be a full-bridge circuit.

[0035] The lighting circuit of each of the above types includes a DC power supply, a transformer having a primary winding and a secondary winding to which the dielectric barrier discharge lamp is connected, and at least one switching element.

[0036] A flyback type lighting circuit is a lighting circuit configured to switch between the ON and OFF states of a switching element to supply and stop current from a DC power source to a primary winding of a transformer, thereby generating an electromotive force in the secondary winding of the transformer.

[0037] A flyback type lighting circuit basically requires only one switching element such as an FET, and therefore has the economic advantage of being able to be constructed at low cost compared to lighting circuits of other types.

[0038] The push-pull and full-bridge lighting circuits are configured to change the direction of the current flowing through the primary winding of the transformer by switching the ON and OFF states of the switching element, thereby generating an electromotive force in the secondary winding of the transformer. Detailed circuit configurations and operations of each will be described later in the section "Mode for Carrying Out the Invention."

[0039] A push-pull lighting circuit has the advantage of being more power efficient than a flyback lighting circuit, because two switching elements are alternately switched to the ON state and the transformer is alternately driven in response to this switching operation.

[0040] A full-bridge lighting circuit has an advantage of being more power efficient than a flyback lighting circuit, since four switching elements are alternately switched to the ON state and the transformer is alternately driven in response to the switching operation. Also, although a full-bridge lighting circuit has a greater number of switching elements than a push-pull lighting circuit, it has an advantage of being even more power-conversion efficient than a push-pull lighting circuit, since the voltage of the DC power supply is alternately applied between the two terminals of the primary winding of the transformer.

[0041] In the above light source device, the lighting circuit is a flyback type circuit. The switching element may include a parasitic diode.

[0042] When the lighting circuit is a flyback type circuit, the simplest configuration is a configuration in which a DC power supply, a transformer primary winding, and one switching element are connected in series (see Figure 3). A circuit with this configuration generates an electromotive force in the secondary winding by switching on and off the supply of current (hereinafter sometimes referred to as "primary current") flowing into the transformer primary winding through the ON / OFF control of the switching element.

[0043] In a flyback lighting circuit, when the current flowing through the secondary winding of the transformer (hereinafter sometimes referred to as "secondary current") stops after the switching element is turned off, a voltage with polarity opposite to that of the DC power supply is induced in the primary winding of the transformer. If the circuit in which the DC power supply, the primary winding of the transformer, and the switching element are connected in series is open circuited because the switching element is turned off when this induced voltage occurs, a high voltage will be applied between the input and output terminals of the switching element, and in the worst case scenario, the switching element will be damaged.

[0044] Therefore, by using the above configuration, when the voltage induced in the primary winding of the transformer becomes larger than the voltage applied by the DC power supply, a path is formed through which current flows from the negative side to the positive side of the DC power supply. At this time, the voltage applied between the input / output terminals of the switching element becomes the same as the forward voltage of the parasitic diode, so damage to the switching element is suppressed. The current flowing through the primary winding of the transformer via the parasitic diode is sometimes called a "regenerative current."

[0045] The light source device in which the lighting circuit is a flyback type circuit, The control unit, in the first control, a first step of transitioning the switching element from an ON state to an OFF state; After the first step, a second step of transitioning the switching element from an OFF state to an ON state may be executed after a predetermined OFF hold time has elapsed from the point at which the regenerative current flowing through the primary winding reaches zero.

[0046] Although there is an applied voltage suitable for lighting a dielectric barrier discharge lamp, in reality, it is difficult to change the applied voltage for the purpose of adjusting the illuminance of a flyback-type lighting circuit. The reason for this is that when the frequency (switching frequency) at which a flyback-type lighting circuit switches between the ON and OFF states is changed, the voltage applied to the dielectric barrier discharge lamp also changes accordingly. In other words, in order to adjust the illuminance of a flyback-type lighting circuit, it is necessary to adjust the timing of switching between the ON and OFF states and appropriately adjust the ratio of the time the switching element is kept in the ON state to the time it is kept in the OFF state.

[0047] The amount of increase in the primary current of the transformer depends on the time it takes for the switching element to transition from the OFF state to the ON state again after the second step is executed. Therefore, with the above configuration, the execution timing of the second step, in which the switching element transitions from the OFF state to the ON state, is after the regenerative current reaches the zero value. Then, by adjusting the specified OFF holding time, the ratio of the time the switching element is maintained in the ON state to the time it is maintained in the OFF state is adjusted.

[0048] In this way, the ratio of the time for which the switching element is kept in the ON state to the time for which it is kept in the OFF state is adjusted, so that the lighting illuminance of the dielectric barrier discharge lamp is adjusted to a desired value.

[0049] This effect is particularly noticeable when the dielectric barrier discharge lamp is an excimer lamp that emits ultraviolet light.

[0050] For example, if the emission gas contains KrCl, the main peak will be emitted from the excimer lamp. The excimer lamp emits ultraviolet light with a wavelength of about 222 nm. For example, when the luminous gas contains KrBr, the excimer lamp emits ultraviolet light with a main peak wavelength of about 207 nm. Unlike ultraviolet light from a low-pressure mercury lamp that contains a component with a wavelength of 254 nm, ultraviolet light with a main peak wavelength in the range of 190 nm to 240 nm is absorbed by the stratum corneum of the skin even when irradiated to the human body, and does not progress further inward (toward the basal layer), so there is a low risk of the light being absorbed by cells and DNA being destroyed. For this reason, the excimer lamp can be used for inactivating bacteria and viruses in spaces where humans may be present.

[0051] However, although the effect on the human body is extremely low compared to the ultraviolet light emitted from a low-pressure mercury lamp, some users may wish to avoid situations in which the human body is continuously irradiated with ultraviolet light from the excimer lamp at high illuminance for a long period of time. Also, at the time of filing this application, it is recommended that the cumulative exposure dose of ultraviolet light irradiated to the human body be kept within the regulatory value set by the American Conference of Governmental Industrial Hygienists (ACGIH).

[0052] As a method for actually installing these excimer lamps that emit ultraviolet light, for example, a method of installing them on the ceiling is considered. In this case, when the excimer lamp is installed on a relatively high ceiling, the distance from the human body is sufficiently secured and the cumulative irradiation amount of ultraviolet light is small, but when the excimer lamp is installed on a relatively low ceiling, the distance from the human body is close and the cumulative irradiation amount is large. If an excimer lamp is to be operated in an environment where the illuminance is high and the distance from the human body is close, it will be necessary to repeat turning on and off at a corresponding ratio so as to achieve a predetermined cumulative irradiation amount (e.g., turning on for 10 seconds, turning off for 300 seconds). In such a method, sterilization and inactivation are not performed during the 300-second off period, and the risk of infection remains during that time.

[0053] Therefore, in such a case, it is preferable to operate the excimer lamp by reducing the illuminance of the emitted ultraviolet light. According to the above configuration, if the illuminance of the excimer lamp can be reduced, it is possible to further reduce the risk of infection by irradiating the human body for a longer period of time without adversely affecting the human body.

[0054] In this case, "inactivation" refers to the comprehensive concept of killing bacteria or viruses or rendering them non-infectious or toxic, and "microorganisms" refers to microorganisms such as bacteria and fungi.

[0055] Moreover, the above light source device in which the lighting circuit is a flyback type circuit, The control unit, in the first control, a first step of transitioning the switching element from an ON state to an OFF state; After the first step, a second step of transitioning the switching element from an OFF state to an ON state may be executed before the regenerative current flowing through the primary winding reaches a zero value or at the same time as the regenerative current reaches a zero value.

[0056] With the above configuration, the regenerative current is almost zero the moment the switching element transitions from the OFF state to the ON state. Therefore, when the switching element switches from the OFF state to the ON state, a large current does not suddenly flow into the switching element. In other words, the above switching control reduces the load applied to the switching element when it switches between the ON state and the OFF state, thereby contributing to extending the life of the switching element.

[0057] Incidentally, such a method of transitioning between the ON state and the OFF state at a timing when the voltage across the switching element is approximately zero is sometimes called "zero voltage switching (ZVS)."

[0058] The lighting circuit of the present invention comprises: A lighting circuit for lighting a dielectric barrier discharge lamp, comprising: A DC power source; a transformer having a primary winding and a secondary winding connected to the dielectric barrier discharge lamp; at least one switching element that is connected in series to the DC power source and the primary winding of the transformer and switches between an ON state and an OFF state to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer or to change a direction of a current flowing through the primary winding; A control unit that performs ON / OFF control of the switching element, The control unit is a startup mode in which, at startup, a predetermined voltage is applied to the dielectric barrier discharge lamp by repeatedly controlling ON / OFF of the switching element at a predetermined frequency; After starting the dielectric barrier discharge lamp, a steady-state operation mode is executed in which a first control is executed in which the predetermined voltage is applied to the dielectric barrier discharge lamp by repeating ON / OFF control of the switching element at the predetermined frequency, and a second control is executed in which the switching element is maintained in an OFF state for a period longer than the cycle of the ON / OFF control of the switching element.

[0059] The method for operating a dielectric barrier discharge lamp of the present invention comprises the steps of: A method for lighting a dielectric barrier discharge lamp using a lighting circuit, comprising: The lighting circuit includes: A DC power source; a transformer having a primary winding and a secondary winding connected to the dielectric barrier discharge lamp; At least one switching element; a switching element is configured to switch between an ON state and an OFF state to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer, or to change the direction of the current supplied to the primary winding, thereby generating an electromotive force in the secondary winding of the transformer, a first step of applying a predetermined voltage to the dielectric barrier discharge lamp by repeatedly switching the switching element on and off at a predetermined frequency at start-up; The method is characterized in that after the first step is performed, in order to maintain the lit state of the dielectric barrier discharge lamp, a second step is performed in which, as in the first step, the switching element is repeatedly switched ON / OFF at a predetermined frequency, and the switching element is maintained in the OFF state for a period longer than the ON / OFF switching cycle of the switching element in the first step. Effect of the Invention

[0060] According to the light source device of the present invention, power saving and improved reliability can be achieved without increasing the size of the entire device. Also, according to the lighting circuit and lighting method of the present invention, power saving and improved reliability can be achieved without increasing the size of the entire light source device. [Brief description of the drawings]

[0061] [Figure 1] FIG. 2 is a perspective view illustrating an example of the appearance of a light source device. [Diagram 2] FIG. 2 is a perspective view showing a schematic example of the appearance of a light source device, in which some elements are removed from FIG. [Diagram 3] FIG. 1 is a circuit diagram showing an example of the configuration of a flyback type lighting circuit for a dielectric barrier discharge lamp. [Figure 4] 4 is a timing chart showing a schematic diagram of the change over time of a control signal G(t) and a secondary side voltage V2 in a flyback lighting circuit. [Diagram 5] 4 is a timing chart showing schematic changes in a control signal G(t), a primary side current I1, a secondary side voltage V2, and a secondary side current I2 over time when a control unit is performing ON / OFF control of a switching element. [Figure 6] FIG. 1 is a circuit diagram showing an example of the configuration of a push-pull type lighting circuit for a dielectric barrier discharge lamp. [Figure 7]4 is a timing chart showing a schematic diagram of changes over time in a control signal G(t) and a secondary side voltage V2 in a push-pull lighting circuit. [Figure 8] FIG. 1 is a circuit diagram showing an example of the configuration of a full-bridge lighting circuit for a dielectric barrier discharge lamp. [Figure 9] 4 is a timing chart showing a schematic diagram of the change over time of a control signal G(t) and a secondary side voltage V2 in a flyback lighting circuit. [Figure 10] 1 is a timing chart showing schematic changes over time in a control signal G(t), a primary side current I1, a secondary side voltage V2, and a secondary side current I2 when a control unit is performing ON / OFF control of a switching element 22. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] The light source device, the driving circuit for a dielectric barrier discharge lamp, and the driving method for a dielectric barrier discharge lamp of the present invention will be described below with reference to the drawings. Note that the following drawings relating to the light source device are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily match the actual dimensional ratios and numbers.

[0063] [composition] (Light source device 1) 1 and 2 are perspective views that diagrammatically show the external appearance of the light source device 1. However, the structures shown in Fig. 1 and 2 are merely examples, and the structure of the light source device 1 according to the present invention is arbitrary.

[0064] 1 and 2 are perspective views each showing a schematic example of the appearance of a light source device 1, and in FIG. 2, some elements are removed from FIG. 1 for the sake of explanation. As shown in FIG. 1, the light source device 1 includes a lighting circuit 2, a cover part 5 having a light extraction surface 7 formed on one side, and a main body casing part 6. In the example shown in FIG. 2, the light source device 1 includes a dielectric barrier discharge lamp 10 including a plurality of arc tubes 13 and electrodes (11, 12) for applying a voltage to each of the arc tubes 13. The electrodes (11, 12) are connected to power lines (3, 4) via connection parts (11a, 12a), respectively. The power lines (3, 4) are connected to the lighting circuit 2.

[0065] The arc tube 13 is made of a dielectric material such as quartz glass, and a predetermined luminous gas is sealed inside. When a high-frequency voltage of, for example, about 1 kHz to 5 MHz is applied to the electrodes (11, 12), the voltage is applied to the luminous gas via the arc tube 13. At this time, a discharge plasma is generated in the discharge space in which the luminous gas is sealed, and the atoms of the luminous gas are excited to an excimer state, and excimer emission occurs when these atoms transition to the ground state. Light emitted from the dielectric barrier discharge lamp 10 by this excimer emission is emitted from the light extraction surface 7 to the outside of the light source device 1 as light Ry1.

[0066] The wavelength of the light Ry1 emitted from the light source device 1 is determined depending on the material of the luminous gas sealed in the light emitting tube 13. For example, when the luminous gas contains KrCl, the light Ry1 emitted from the light source device 1 shows a spectrum with a main peak wavelength of about 222 nm. When the luminous gas contains KrBr, the light Ry1 shows a spectrum with a main peak wavelength of about 207 nm. When the luminous gas contains ArF, the light Ry1 shows a spectrum with a main peak wavelength of about 193 nm.

[0067] However, in the present invention, the type of gas enclosed in the arc tube 13 of the dielectric barrier discharge lamp 10 is arbitrary and may be appropriately selected according to the wavelength of the light Ry1 to be obtained. Furthermore, the light source device 1 may be one in which a phosphor is applied to the tube wall or the light extraction surface 7 of the arc tube 13 for the purpose of converting the wavelength to the longer wavelength side.

[0068] Furthermore, the tube wall of the light emitting tube 13 and the light extraction surface 7 may be configured with a filter that transmits ultraviolet light in a wavelength band that has little effect on the human body and does not transmit ultraviolet light in a wavelength band that has a large effect on the human body. For example, the filter may be a dielectric multilayer filter or the like that transmits ultraviolet light with a wavelength of 190 nm to 240 nm and does not transmit ultraviolet light with a wavelength of 240 nm or more.

[0069] (Flyback type lighting circuit 2a) Fig. 3 is a circuit diagram showing an example of the configuration of a flyback type lighting circuit 2a for a dielectric barrier discharge lamp. As shown in Fig. 3, the flyback type lighting circuit 2a is an embodiment of the lighting circuit 2 for lighting the dielectric barrier discharge lamp 10, which includes a DC power source 21, one switching element 22, and a transformer 30.

[0070] The transformer 30 includes a primary winding L1 and a secondary winding L2. Among terminals included in the primary winding L1 of the transformer 30, a first terminal a1 is connected to a positive terminal of the DC power supply 21, and a second terminal a2 is connected to a negative terminal of the DC power supply 21 via the switching element 22.

[0071] The switching element 22 of this embodiment is composed of a field effect transistor (FET), and a parasitic diode 23 is formed, the anode of which is connected to the negative terminal of the DC power supply 21, and the cathode of which is connected to the primary winding L1 of the transformer 30. In this embodiment, this parasitic diode 23 functions as a regenerative circuit. Note that an element other than a field effect transistor (FET) may be used for the switching element 22. Also, an IGBT or a relay element not including the parasitic diode 23 may be used for the switching element 22, and a regenerative circuit may be configured by connecting a diode element alone in parallel with the switching element 22.

[0072] The DC power supply 21 may be, for example, an AC / DC converter that converts a commercial power supply (not shown) into an AC / DC converter. The smoothing capacitor 25 in the lighting circuit 2a is provided to smooth the voltage waveform. The DC power supply 21 may be a battery.

[0073] The lighting circuit 2a of this embodiment includes a control unit 24 for performing ON / OFF control of the switching element 22. The control unit 24 may be any device capable of outputting a control signal G(t) of a desired pattern, and may be, for example, a control unit such as a CPU or MPU. The control contents performed by the control unit 24 will be described below with reference to a timing chart.

[0074] Fig. 4 is a timing chart showing a schematic time change of the control signal G(t) and the secondary voltage V2 of the flyback lighting circuit 2a. The timing chart shown in Fig. 4 shows the fluctuation of the control signal G(t) and the secondary voltage V2 from the start of the dielectric barrier discharge lamp 10. In addition, in the graph of the control signal G(t) in Fig. 4, the high level (hereinafter referred to as "H level") corresponds to the ON control of the switching element 22, and the low level (hereinafter referred to as "L level") corresponds to the OFF control of the switching element 22. In addition, the graph of the secondary voltage V2 shown in Fig. 4 shows the potential difference with the first electrode terminal b1 connected to the electrode 11 when the potential of the second electrode terminal b2 connected to the electrode 12 of the dielectric barrier discharge lamp 10 shown in Fig. 3 is taken as a reference.

[0075] Graphs showing fluctuations in voltage and current shown in the drawings referred to in the following description, like the graph of the secondary side voltage V2 in Fig. 4, do not show offsets and the like that have little effect on the explanation of the main operation of the present invention, and show an example of an ideal waveform in a schematic manner. Moreover, whether the secondary side voltage V2 is configured to swing to the + side or - side with respect to a predetermined reference voltage (0V in this embodiment) may be arbitrarily set as appropriate according to the specifications of the dielectric barrier discharge lamp 10, the configuration of the lighting circuit 2, etc.

[0076] When the light source device 1 is powered on and starts operating, the control unit 24 switches to a start-up mode X1 for lighting the dielectric barrier discharge lamp 10.

[0077] 4, the startup mode X1 continuously executes control that repeats ON / OFF control of the switching element 22 at a predetermined frequency. The startup mode X1 generates a discharge plasma in the arc tube 13 of the dielectric barrier discharge lamp 10 and is executed until the light emission state of the dielectric barrier discharge lamp 10 becomes stable.

[0078] The control unit 24 executes the startup mode X1, and after the light emission state of the dielectric barrier discharge lamp 10 has stabilized, i.e., after the dielectric barrier discharge lamp 10 has started up, it switches to the steady-state operation mode X2 for maintaining the dielectric barrier discharge lamp 10 in a lit state.

[0079] 4, the steady operation mode X2 alternates between a first control C1 that repeats ON / OFF control of the switching element 22 at a predetermined frequency to apply a predetermined voltage, and a second control C2 that maintains the switching element 22 in an OFF state, to maintain the lighting state of the dielectric barrier discharge lamp 10. Note that the frequency at which the first control C1 repeats ON / OFF control of the switching element 22 and the predetermined voltage applied to the dielectric barrier discharge lamp 10 are substantially the same as the frequency at which the ON / OFF control of the switching element 22 is repeated and the predetermined voltage applied to the dielectric barrier discharge lamp 10 in the starting mode X1.

[0080] In the steady operation mode X2 in this embodiment, the switching element 22 is controlled by a control signal G(t) (in FIG. 4, the masked portion is shown by a broken line) that is masked so as to fix the output of the basic control signal S1 to the L level only during the period in which the second control C2 is executed, with respect to the basic control signal S1 that switches between H / L levels at a predetermined frequency. Therefore, as shown in FIG. 4, the first control C1 is executed for different periods of time in the start-up mode X1 and the steady operation mode X2, and the same pattern of secondary side voltage V2 is applied between the electrodes (11, 12) of the dielectric barrier discharge lamp 10 shown in FIG. 3 in both cases.

[0081] The masking process here refers to, for example, a process of periodically fixing the control signal G(t) to an L level for a predetermined period of time by program processing, or a process of inputting the basic control signal S1 and a masking signal that is at an H level in the section in which the first control C1 is executed and at an L level in the section in which the second control C2 is executed into an AND gate element to take the logical product.

[0082] In this embodiment, the period P1 of the fundamental control signal S1 for repeating the ON / OFF control of the switching element 22 is set to 17 μs, the execution time of the start-up mode X1 is set to 10 s, the execution time of the first control C1 in the steady operation mode X2 is set to 170 μs, and the execution time of the second control C2 in the steady operation mode X2 is set to 200 μs. In other words, the execution time of the second control C2 in the steady operation mode X2 is 12 times the period P1 of the fundamental control signal S1, and the period T1 for repeating the first control C1 and the second control C2 in the steady operation mode X2 is set to 22 times the period P1 of the fundamental signal frequency.

[0083] The period T1 for repeating the first control C1 and the second control C2 in the steady operation mode X2 is preferably four or more times, and more preferably eight or more times, the period P1 of the basic control signal S1 so as to suppress heat generation in the dielectric barrier discharge lamp 10. When the first control C1 and the second control C2 are repeated non-periodically in the steady operation mode X2, the total execution time of the first control C1 and the immediately preceding second control C2 is preferably four or more times, and more preferably eight or more times, the period P1 of the basic control signal S1.

[0084] Moreover, if the execution time of the second control C2 is too long, the plasma in the arc tube 13 of the dielectric barrier discharge lamp 10 may disappear or attenuate, and the dielectric barrier discharge lamp 10 may be turned off. As described above, the first control C1 in the steady operation mode X2 applies the same voltage to the dielectric barrier discharge lamp 10 in the same cycle as in the start-up mode X1, so that the turned-off dielectric barrier discharge lamp 10 may be turned on again. However, if the time for which the voltage application is continued is insufficient, the light emission state may not be stable before the next second control C2 is started, and the lighting state may not be maintained. Therefore, in order to stably maintain the lighting state of the dielectric barrier discharge lamp 10, the execution time of the second control C2 in the steady operation mode X2 is preferably 100 ms or less, and more preferably 80 ms or less. Furthermore, in order to further increase the stability of the lighting state, the execution time of the second control C2 in the steady operation mode X2 is preferably 10 ms or less, and more preferably 1 ms or less.

[0085] Here, a description will be given of the intensity of the light emitted from the dielectric barrier discharge lamp 10. The intensity of the light emitted from the dielectric barrier discharge lamp 10 is adjusted by the ratio of the execution time of the first control C1 to the execution time of the second control C2 per unit time. Specifically, in the cycle T1 in the steady operation mode X2, when the ratio of the execution time of the first control C1 increases, the intensity of the light emitted from the dielectric barrier discharge lamp 10 increases, and conversely, when the ratio of the execution time of the second control C2 increases, the intensity of the light emitted from the dielectric barrier discharge lamp 10 decreases.

[0086] The following is merely an example for reference, but when the light intensity near the arc tube 13 of the dielectric barrier discharge lamp 10 in the startup mode X1 is taken as 100%, the light intensity near the arc tube 13 of the dielectric barrier discharge lamp 10 in the steady operation mode X2 in which the execution time of the first control C1 is adjusted to 1 ms and the execution time of the second control C2 is adjusted to 100 μs is approximately 91%. Also, the light intensity near the arc tube 13 of the dielectric barrier discharge lamp 10 in the steady operation mode X2 in which the execution time of the first control C1 is adjusted to 1 ms and the execution time of the second control C2 is adjusted to 1 ms is approximately 50%.

[0087] Therefore, the light source device 1 can be configured to emit light of a desired intensity depending on the place of use and the purpose of use by adjusting the execution time of the first control C1 and the execution time of the second control C2 in the cycle T1 in the steady operation mode X2. Note that the execution time of the first control C1 and the execution time of the second control C2 in the steady operation mode X2 may be adjusted in advance and fixed, or may be configured to be variable depending on the purpose of use and the time period of operation, or may be configured to constantly change.

[0088] Moreover, a method of varying the execution time of the first control C1 in the steady operation mode X2 may be adopted as a method of adjusting the intensity of the light emitted from the dielectric barrier discharge lamp 10. As a specific example, the execution time of the second control C2 may be fixed to 1 ms, and the execution time of the first control C1 may be switched between 1 ms and 0.5 ms alternately every predetermined number of times or at a predetermined time.

[0089] Furthermore, the control unit 24 may be configured to temporarily switch to the starting mode X1 while the steady-state operation mode X2 is being executed, for example, for the purpose of preventing interruption, etc. Also, the control unit 24 may be configured to continue the starting mode X1 for a predetermined time even after it is confirmed that the dielectric barrier discharge lamp 10 is lit, so that the lighting state is more reliably stabilized.

[0090] In this embodiment, the ON time and OFF time of the basic control signal S1 are adjusted so that the peak voltage of the secondary voltage V2 is 5 to 6 kV. The peak voltage of the secondary voltage V2 is appropriately adjusted according to the shape and size of the dielectric barrier discharge lamp 10 and the luminous gas sealed in the arc tube 13.

[0091] Next, details of the operation of the first control C1 in the start-up mode X1 and the steady-state operation mode X2 will be described with reference to the configuration of the lighting circuit 2a and the timing chart in Fig. 3. Fig. 5 is a timing chart that shows schematic changes over time in the control signal G(t), the primary side current I1, the secondary side voltage V2, and the secondary side current I2 when the control unit 24 is executing the ON / OFF control of the switching element 22.

[0092] As shown in FIG. 5, when the control signal G(t) switches from L level to H level at time t1, the switching element 22 transitions from the OFF state to the ON state, and the primary side current I1 of the transformer 30 increases over time.

[0093] After that, when the control signal G(t) changes from H level to L level at time t2, the switching element 22 transitions from the ON state to the OFF state. At this time, a counter electromotive force is generated in the secondary winding L2 of the transformer 30, and a pulsed secondary voltage V2 is generated. When this secondary voltage V2 is applied to the inside of the light emitting tube 13 of the dielectric barrier discharge lamp 10 via the pair of electrodes (11, 12), light Ry1 is emitted from the dielectric barrier discharge lamp 10.

[0094] The magnitude of the secondary voltage V2 generated in the secondary winding L2 of the transformer 30 depends on the amount of change in the primary current I1 at time t2. The amount of change in the primary current I1 at time t2 varies with the time during which the control signal G(t) is maintained at the H level (time T H ) depends on the time T H is set to a time such that the secondary voltage V2 reaches a voltage value required to generate an initial discharge in the arc tube 13 of the dielectric barrier discharge lamp 10.

[0095] When the secondary voltage V2 is applied, a secondary current I2 flows through the secondary winding L2 of the transformer 30. This secondary current I2 flows while releasing the energy stored in the transformer 30, and therefore approaches zero over time (from time t2 to ta).

[0096] At this time, the dielectric barrier discharge lamp 10 has an arc tube 13 made of a dielectric material and a pair of electrodes (11, 12) sandwiching the arc tube 13, which can be regarded as an equivalent capacitor element that stores electric charge. In other words, as the energy stored in the transformer 30 is released, electric charge is gradually stored in the dielectric barrier discharge lamp 10.

[0097] When the release of the energy stored in the transformer 30 is completed by the secondary current I2, the charge stored in the dielectric barrier discharge lamp 10 is discharged. Due to this discharge, a current (secondary current I2) flows in the secondary winding L2 of the transformer 30 in the opposite direction to the previous current, and the secondary voltage V2 changes to approach zero (time ta to tb).

[0098] Even after the discharge of the dielectric barrier discharge lamp 10 is completed, the secondary winding L2 of the transformer 30 serves as a voltage source and continues to pass the secondary current I2 while charging the dielectric barrier discharge lamp 10. When the flow of the secondary current I2 eventually stops, a primary voltage V1 is induced in the primary winding L1 of the transformer 30.

[0099] This induced voltage is a voltage of reverse polarity to the DC power supply 21, but as described above, since the switching element 22 is provided with a parasitic diode 23, a primary current I1 flows in the reverse direction through the primary winding L1 via the parasitic diode 23. This primary current I1 is sometimes called a "regenerative current." The occurrence of such a regenerative current is a circumstance specific to the load constituted by the dielectric barrier discharge lamp 10.

[0100] The primary side current I1 gradually approaches zero, but when the switching element 22 is turned on again at time t3, the value of the primary side current I1 continues to increase, as in the period from time t1 to t2. After that, the same control is repeated.

[0101] In this embodiment, the switching element 22 is controlled to transition from the OFF state to the ON state at the same time that the primary side current I1 reaches a zero value (time t3). That is, zero voltage switching is performed. Note that, taking into consideration the transmission delay of the control signal G(t) and the time it takes for the switching element 22 to switch from the ON state to the OFF state, the control to transition the switching element 22 from the OFF state to the ON state may be performed before the primary side current I1 reaches a zero value.

[0102] The control for transitioning the switching element 22 from the ON state to the OFF state (e.g., the control at times t2, t4, and t6 shown in FIG. 5) corresponds to the “first step”, and the control for transitioning the switching element 22 from the OFF state to the ON state (e.g., the control at times t1, t3, t5, and t7 shown in FIG. 5) corresponds to the “second step”.

[0103] The light source device 1 configured as above does not require switching of an analog circuit configuration to change the output voltage, but can be realized by switching using digital signal processing. Therefore, since no complex mechanisms or circuits are required, the entire device does not become larger than conventional devices, and in some cases, the number of components can be reduced, making the entire device more compact.

[0104] Furthermore, since the light source device 1 having the above configuration can be realized using only digital signal processing, there is no need to worry about analog characteristics such as variations in output value and characteristic fluctuations due to deterioration over time, and reliability problems are unlikely to occur.

[0105] Hereinafter, configuration examples of the lighting circuit 2 other than the flyback type and the operation of the first control C1 in the starting mode X1 and the steady operation mode X2 by each lighting circuit 2 will be mainly described.

[0106] (Push-pull type lighting circuit 2b) Fig. 6 is a circuit diagram showing an example of the configuration of a push-pull lighting circuit 2b for a dielectric barrier discharge lamp. As shown in Fig. 6, the push-pull lighting circuit 2b is an embodiment of the lighting circuit 2 for lighting the dielectric barrier discharge lamp 10, which includes a DC power source 21, two switching elements (22a, 22b), and a transformer 30. On the primary side of the transformer 30, a circuit in which a winding L1a and a switching element 22a are connected in series, and a circuit in which a winding L1b and a switching element 22b are connected in series are connected in parallel to the DC power source 21.

[0107] In the transformer 30 of this embodiment, the primary winding L1 is constituted by the winding L1a and the winding L1b. For convenience of explanation, the transformer 30 in this configuration is constituted such that the primary winding L1 is divided into two windings (L1a, L1b), but it may be constituted by a single primary winding L1.

[0108] 7 is a timing chart showing a schematic time change of the control signal G1(t), the control signal G2(t), and the secondary side voltage V2 of the push-pull lighting circuit 2b. In the first control C1 of the start-up mode X1 and the steady operation mode X2 of the push-pull lighting circuit 2b, the control unit 24 outputs the control signal G1(t) to the switching element 22a and the control signal G2(t) to the switching element 22b to control the switching elements (22a, 22b) to be alternately switched to the ON state. Hereinafter, the operation of the first control C1 of the start-up mode X1 or the steady operation mode X2 in the push-pull lighting circuit 2b will be described with reference to FIGS. 6 and 7.

[0109] When the control unit 24 of the push-pull lighting circuit 2b starts the first control C1 in the start-up mode X1 or the steady-state operation mode X2, it switches the control signal G1(t) from L level to H level to switch the switching element 22a to the ON state (time t1). When the switching element 22a switches to the ON state, a current I1a starts to flow from the DC power source 21 to the winding L1a side. Then, when the current I1a starts to flow to the winding L1a, a secondary-side voltage V2 as shown in FIG. 7 is generated in the secondary-side winding L2 of the transformer 30.

[0110] Next, the control unit 24 switches the control signal G1(t) from H level to L level to switch the switching element 22a to the OFF state (time t2), and then switches the control signal G2(t) from L level to H level to switch the switching element 22b to the ON state (time t3). When the switching element 22b switches to the ON state, a current I1b starts to flow from the DC power supply 21 to the winding L1b side. Then, when the current I1b starts to flow through the winding L1b, a secondary-side voltage V2 as shown in FIG. 7 is generated in the secondary-side winding L2 of the transformer 30.

[0111] The current I1b generated in the primary winding L1 of the transformer 30 during the operation at time t3 flows in the opposite direction to the current I1a generated in the primary winding L1 during the operation at time t1. Therefore, the secondary voltage V2 generated in the secondary winding L2 of the transformer 30 during the operation at time t3 has a polarity opposite to that of the secondary voltage V2 generated during the operation at time t1, as shown in FIG.

[0112] Thereafter, the control unit 24 outputs a control signal G2(t) that switches the switching element 22b to the OFF state (time t4). After that, the same control is repeated until the mode is switched to the steady operation mode X2 or the second control C2.

[0113] It is preferable that the control for switching the switching element 22b to the ON state (time t3) is executed slightly later than the control for switching the switching element 22a to the OFF state (time t2), in order to prevent a period during which the two switching elements (22a, 22b) are simultaneously in the ON state from occurring, causing a short circuit between the positive terminal and the negative terminal of the DC power supply 21.

[0114] (Full-bridge lighting circuit 2c) FIG. 8 is a circuit diagram showing an example of a full-bridge type lighting circuit 2c for a dielectric barrier discharge lamp. As shown in FIG. 8, the full-bridge type lighting circuit 2c is an embodiment of a lighting circuit 2 for lighting a dielectric barrier discharge lamp 10, which includes a DC power source 21, four switching elements (22a, 22b, 22c, 22d), and a transformer 30. The primary side of the transformer 30 has a circuit configuration in which a circuit in which two switching elements (22a, 22b) are connected in series and a circuit in which two switching elements (22c, 22d) are connected in series are connected in parallel to the DC power source 21. The primary winding L1 of the transformer 30 is connected to a first node n1 between the switching elements (22a, 22b) and a second node n2 between the switching elements (22c, 22d). In FIG. 8, the control unit 24 is divided into four for convenience of illustration, but there may be only one control unit 24 as in the lighting circuits (2a, 2b) of other types.

[0115] The full-bridge lighting circuit 2c has a different circuit configuration from the push-pull lighting circuit 2b, and the magnitude of the secondary voltage V2 generated in the secondary winding L2 of the transformer 30 is also different. However, the full-bridge lighting circuit 2c is the same in that the pair of switching elements (22a, 22b, 22c, 22d) are ON / OFF controlled by two control signals (G1(t), G2(t)), thereby changing the direction of the current (I1a, I1b) flowing through the primary winding L1, and electromotive forces of opposite polarities are alternately generated in the secondary voltage V2. For this reason, the timing chart of the control signals (G1(t), G2(t)) and the secondary voltage V2 shown in FIG. 8 is almost the same as the timing chart of the push-pull lighting circuit 2b shown in FIG. 7, ignoring the difference in the scale of the secondary voltage V2. Hereinafter, the operation of the first control C1 in the start-up mode X1 or the steady-state operation mode X2 in the full-bridge lighting circuit 2c will be described with reference to FIG. 7 and FIG. 8.

[0116] When the control unit 24 of the full-bridge lighting circuit 2c starts the first control C1 in the startup mode X1 or the steady operation mode X2, it switches the control signal G1(t) from L level to H level to switch the switching elements (22a, 22c) to the ON state (time t1). When the switching elements (22a, 22c) are switched to the ON state, a current I1a starts to flow from the DC power supply 21 through the path of the switching element 22a, the primary winding L1, and the switching element 22c. Then, when the current I1a starts to flow through the primary winding L1, a secondary voltage V2 is generated.

[0117] Next, the control unit 24 switches the control signal G1(t) from H level to L level to switch the switching elements (22a, 22c) to the OFF state (time t2), and then switches the control signal G2(t) from L level to H level to switch the switching elements (22b, 22d) to the ON state (time t3). As the switching elements (22b, 22d) switch to the ON state, a current I1b starts to flow from the DC power supply 21 through the path of the switching element 22d, the primary winding L1, and the switching element 22b. Then, as the current I1b starts to flow through the primary winding L1, a secondary voltage V2 is generated.

[0118] The current I1b generated in the primary winding L1 of the transformer 30 during the operation at time t3 flows in the opposite direction to the current I1a generated in the primary winding L1 during the operation at time t1. Therefore, the secondary voltage V2 generated in the secondary winding L2 of the transformer 30 during the operation at time t3 has a polarity opposite to that of the secondary voltage V2 generated during the operation at time t1, as shown in FIG.

[0119] Thereafter, the control unit 24 switches the control signal G2(t) from H level to L level (time t4) in order to switch the switching elements (22b, 22d) to the OFF state. After that, the same control is repeated until the mode is switched to the steady operation mode X2 or the second control C2.

[0120] Note that the control for switching the switching elements (22b, 22d) to the ON state (time t3) is preferably executed slightly later than the control for switching the switching elements (22a, 22c) to the OFF state (time t2). The reason for this is to prevent a period in which the switching elements (22a, 22b, 22c, 22d) are simultaneously in the ON state, which would cause a short circuit between the positive terminal and the negative terminal of the DC power supply 21, similar to the push-pull lighting circuit 2b.

[0121] Although three types of lighting circuits (2a, 2b, 2c) have been described above, the lighting circuit 2 may adopt a type other than the above-described lighting circuits (2a, 2b, 2c), such as a half-bridge type.

[0122] [Another embodiment] Hereinafter, another embodiment of the light source device 1 or the lighting circuit 2 according to the present invention will be described.

[0123] <1> FIG. 9 is a timing chart showing a schematic time change of the control signal G(t) and the secondary side voltage V2 in the flyback lighting circuit 2a (see FIG. 3), which is different from FIG. 4. In the first control C1 in the steady operation mode X2, the control unit 24 of this embodiment controls the number of times the ON / OFF control of the switching element 22 is repeated to be different before and after the second control C2 is executed. For example, as shown in FIG. 9, in the first control C1 after switching to the steady operation mode X2, the ON / OFF control of the switching element 22 is repeated three times, and in the next first control C1, the ON / OFF control of the switching element 22 is repeated two times. In this embodiment, the number of times the ON / OFF control of the switching element 22 is repeated in the first control C1 is three times → two times → three times → two times → .... Note that the number of times the ON / OFF control of the switching element 22 is repeated in the first control C1 may be configured to change randomly, rather than periodically repeating several patterns.

[0124] As described above, when a transformer is supplied with a periodic current, periodic magnetostriction occurs, which generates minute vibrations corresponding to the frequency of the current. If the frequency of the vibrations is within the range of the human audible range (approximately 20 Hz to 20 kHz), noise may occur.

[0125] Therefore, as described above, by changing the number of times that the first control C1 repeats the ON / OFF control of the switching element 22 before and after each second control C2 in the steady operation mode X2, the operation of switching between the first control C1 and the second control C2 is no longer an operation at a specific frequency. Therefore, the intensity of the vibration generated in the transformer due to magnetostriction resulting from the switching operation between the first control C1 and the second control C2 is dispersed into multiple frequency components, thereby suppressing noise.

[0126] <2> Fig. 10 is a timing chart different from Fig. 5, which shows a schematic diagram of time changes of the control signal G(t), the primary side current I1, the secondary side voltage V2, and the secondary side current I2 when the control unit 24 is executing the ON / OFF control of the switching element 22. As shown in Fig. 10, the flyback type lighting circuit 2a (see Fig. 3) of this embodiment delays the timing of transition of the switching element 22 from the OFF state to the ON state by intentionally setting an OFF hold time Ts.

[0127] More specifically, as shown in FIG. 10, at time t3, which is after time t2a when the primary side current I1 (regenerative current) during regenerative operation reaches zero, the control unit 24 changes the control signal G(t) from an L level to an H level, thereby transitioning the switching element 22 from an OFF state to an ON state.

[0128] This reduces the frequency with which a high voltage (secondary voltage V2) is applied to the dielectric barrier discharge lamp 10 within a unit time, and therefore reduces the illuminance of the light Ry1. By appropriately adjusting this OFF hold time Ts, it becomes possible to adjust the illuminance of the light Ry1. In other words, by varying the OFF hold time Ts in a short lighting cycle in microsecond units (1000 μsec or less), it becomes possible to adjust the illuminance of the light Ry1.

[0129] This also means that the amount of light Ry1 emitted from the dielectric barrier discharge lamp 10 can be adjusted without relying on ON / OFF control in units of seconds. Furthermore, according to this method, the ON / OFF switching frequency of the switching element 22 is reduced, so the problem of power loss in the switching element 22 is also alleviated.

[0130] <3> In the above embodiment, the case where the switching element 22 is connected between the negative terminal of the DC power supply 21 and the primary winding L1 of the transformer 30 has been described, but the polarity may be reversed. That is, the switching element 22 may be connected between the positive terminal of the DC power supply 21 and the primary winding L1 of the transformer 30. Here, when the switching element 22 is configured as a MOSFET, whether it is an n-channel type or a p-channel type is appropriately selected depending on the polarity of the DC power supply 21 to be connected. [Explanation of symbols]

[0131] 1 : Light source device 2, 2a, 2b, 2c: Lighting circuit 3,4 :Power line 5: Lid 6: Main casing 7: Light extraction surface 10: Dielectric barrier discharge lamp 11,12 : Electrode 11a, 12a: Connection 13: Arc tube 21: DC power supply 22, 22a, 22b, 22c, 22d: switching elements 23: Parasitic diode 24: Control section 25: Smoothing capacitor 30: Trance C1: First control C2: Second control G, G1, G2: Control signal I1,I1a,I1b: Primary current I2: Secondary current L1: Primary winding L1a, L1b: Windings L2: Secondary winding Ry1: Light S1: Basic control signal Ts: OFF holding time V1: Primary voltage V2: Secondary voltage X1: Start-up mode X2: Normal operation mode a1 : First terminal a2 : Second terminal b1: First electrode terminal b2: Second electrode terminal n1: First node n2: Second node

Claims

1. a lighting circuit including a DC power source, a transformer having a primary winding and a secondary winding, and at least one switching element, the lighting circuit being configured to switch between an ON state and an OFF state of the switching element to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer, or to change the direction of the current flowing through the primary winding, thereby generating an electromotive force in the secondary winding of the transformer; a dielectric barrier discharge lamp connected to the secondary winding of the transformer; a control unit that controls ON / OFF of the switching element, The control unit is a startup mode in which, at startup, a predetermined voltage is applied to the dielectric barrier discharge lamp by repeatedly controlling ON / OFF of the switching element at a predetermined frequency; a first control for applying the predetermined voltage to the dielectric barrier discharge lamp by repeating ON / OFF control of the switching element at the predetermined frequency after the dielectric barrier discharge lamp is started, and a second control for maintaining the switching element in an OFF state for a period longer than the cycle of the ON / OFF control of the switching element, thereby executing a steady-state operation mode in which an operating pattern is set in advance, thereby maintaining the dielectric barrier discharge lamp in a lit state.

2. The light source device according to claim 1 , wherein the control unit periodically executes the first control and the second control in the steady operation mode.

3. The light source device according to claim 1, characterized in that the control unit executes the steady-state operation mode so that the number of times that the ON / OFF control of the switching element is repeated in the first control is different before and after each of the second controls.

4. The light source device according to any one of claims 1 to 3, characterized in that the control unit executes the steady operation mode so that the sum of the execution time of the first control and the execution time of the second control immediately thereafter is four times or more of a period corresponding to the specified frequency, and the execution time of the second control is 100 ms or less.

5. 4. The light source device according to claim 1, wherein the lighting circuit is a flyback type circuit.

6. 4. The light source device according to claim 1, wherein the lighting circuit is a push-pull type circuit.

7. 4. The light source device according to claim 1, wherein the lighting circuit is a full-bridge circuit.

8. 6. The light source device according to claim 5, wherein the switching element includes a parasitic diode.

9. The control unit, in the first control, A first step of transitioning the switching element from an ON state to an OFF state; 9. The light source device according to claim 8, further comprising: a second step of transitioning the switching element from an OFF state to an ON state after a predetermined OFF hold time has elapsed from the point at which the regenerative current flowing through the primary winding reaches zero after the first step;

10. The control unit, in the first control, A first step of transitioning the switching element from an ON state to an OFF state; The light source device according to claim 8, characterized in that after the first step, a second step of transitioning the switching element from an OFF state to an ON state is executed before the regenerative current flowing through the primary winding reaches a zero value or at the same time as the regenerative current reaches a zero value.

11. A lighting circuit for lighting a dielectric barrier discharge lamp, comprising: A DC power source; a transformer having a primary winding and a secondary winding connected to the dielectric barrier discharge lamp; at least one switching element that is connected in series to the DC power source and the primary winding of the transformer and switches between an ON state and an OFF state to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer or to change a direction of a current flowing through the primary winding; a control unit that controls ON / OFF of the switching element, The control unit is a startup mode in which, at startup, a predetermined voltage is applied to the dielectric barrier discharge lamp by repeatedly controlling ON / OFF of the switching element at a predetermined frequency; a first control for applying the predetermined voltage to the dielectric barrier discharge lamp by repeating ON / OFF control of the switching element at the predetermined frequency after starting the dielectric barrier discharge lamp, and a second control for maintaining the switching element in an OFF state for a period longer than the cycle of the ON / OFF control of the switching element, thereby executing a steady operation mode in which an operating pattern is set in advance, thereby maintaining the dielectric barrier discharge lamp in a lit state.

12. A method for lighting a dielectric barrier discharge lamp using a lighting circuit, comprising: The lighting circuit includes: A DC power source; a transformer having a primary winding and a secondary winding connected to the dielectric barrier discharge lamp; At least one switching element; a switching element is configured to switch between an ON state and an OFF state to switch between supplying and stopping a current from the DC power source to the primary winding of the transformer, or to change the direction of the current supplied to the primary winding, thereby generating an electromotive force in the secondary winding of the transformer, a first step of applying a predetermined voltage to the dielectric barrier discharge lamp by repeatedly switching the switching element on and off at a predetermined frequency at start-up; A method for operating a dielectric barrier discharge lamp, comprising: a second step, the operation pattern of which is determined in advance, in which, after execution of the first step, in order to maintain the lit state of the dielectric barrier discharge lamp, the switching element is repeatedly switched on / off at a predetermined frequency, as in the first step, and the switching element is maintained in the OFF state for a period longer than the cycle of the ON / OFF switching of the switching element in the first step, thereby maintaining the lit state of the dielectric barrier discharge lamp.

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