JP2009252410A - Discharge lamp device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp device of which the power loss is suppressed without delay in the spread of light emission in a tube axis direction, and which reduces audible noise generated when burst light control is performed. <P>SOLUTION: The discharge lamp device includes: an AC conversion circuit 2 in which switching elements Q1, Q2 are alternately operated to convert a DC voltage into an AC voltage: a transformer 5 which steps up the AC voltage from the AC conversion circuit 2; and a discharge lamp 6 which is connected to a secondary side of the transformer 5, and performs burst light control of the discharge lamp 6. In the discharge lamp device which includes a short-circuiting circuit 4 for short-circuiting a coil L3 of the transformer 5 during an off period of burst light control or in the discharge lamp device concerned, the switching element switched on first in an on period of burst light control is a switching element Q2 (Q1) corresponding to a switching element Q1 (Q2) switched on last at the end of the preceding on-period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a discharge lamp device, and more particularly to a rare gas fluorescent lamp device used for a backlight of a liquid crystal display panel, general illumination, and the like.

  Conventionally, cold cathode fluorescent lamps and hot cathode fluorescent lamps are often used as backlight sources and illumination light sources of liquid crystal display panels. These lamps contain a very small amount of mercury inside, and emit phosphors by ultraviolet rays generated from mercury excited by discharge, so that high-luminance and efficient light emission can be obtained. Are better.

  However, a new light source that does not contain mercury is desired from the viewpoint of preventing environmental pollution. As a fluorescent lamp that does not contain mercury, a plurality of strip-shaped electrodes are arranged on the outer surface of a glass tube, and a high-frequency high voltage boosted by a transformer, for example, is applied to these electrodes to turn on the rare gas fluorescence. A lamp has been proposed.

  In general, the screen brightness of the liquid crystal display panel is required to be adjustable to an appropriate level according to ambient brightness, user preference, image information, and the like. The screen brightness is adjusted by dimming the backlight, and burst dimming is generally used for the dimming of the backlight. Also in lighting applications, a wide light control range is required in order to adjust the brightness according to the usage environment in indirect lighting or the like. As the dimming means, burst dimming is generally used like the backlight. Burst dimming is also referred to as duty dimming, and the lighting period and the extinguishing period are periodically repeated at about 60 to 1 kHz, and the dimming is performed by controlling the time ratio between the lighting period and the extinguishing period. The dimming period is appropriately selected from about 60 to 300 Hz for a liquid crystal backlight and about 1 kHz for lighting applications.

  Patent Document 1 discloses a technique for suppressing flicker and surge voltage that occurs when burst dimming of a rare gas fluorescent lamp. Patent Document 2 discloses that a backlight device using an external electrode type fluorescent lamp soft-starts the rise of the on period in order to suppress an audible sound that is annoying to humans when performing burst dimming. Has been. Further, in Patent Document 3, in a backlight device using a cold cathode fluorescent lamp, the discharge lamp does not light even during an off period in order to suppress generation of an audible audible sound when performing burst dimming. It is disclosed that a current of a certain level flows.

FIG. 17 is a diagram showing a circuit configuration of a discharge lamp device according to the prior art having the techniques described in Patent Document 2 and Patent Document 3.
In the figure, the DC voltage output from the DC power supply 101 is input to the DC-DC converter circuit 102, and the output voltage from the DC-DC converter circuit 102 is input to the AC conversion circuit 103. The AC conversion circuit 103 includes switching elements Q1 and Q2 and diodes D1 and D2, and constitutes a push-pull circuit. One end of each of the switching elements Q1 and Q2 is connected to the low potential side of the DC power supply 101. The diodes D1 and D2 are parasitic diodes of the switching elements Q1 and Q2, or are added separately, and are individually connected in parallel to the switching elements. The direction is a forward direction from a low potential to a high potential. Signals S1 and S2 output from the control circuit 104 are input to the switching elements Q1 and Q2, respectively. The switching elements Q1 and Q2 are turned on when the signals are at a high level and are turned off when the signals are at a low level. The signals S1 and S2 are periodic pulse signals and are output with a phase shift of 180 °. In the transformer 105, coils L1 and L2 are magnetically coupled. Both ends of the coil L1 are connected to the switching elements Q1 and Q2 of the AC conversion circuit 103, and the middle point of the coil L1 is a DC-DC converter. Connected to the positive output side of the circuit 102. Both ends of the coil L2 are connected to the electrodes of the discharge lamp 106. The brightness control signal is a PWM signal having a duty ratio associated with the brightness instruction value, and this signal is input to the DC-DC converter circuit 102. The DC-DC converter circuit 102 changes the output voltage in accordance with the brightness control signal.

FIG. 18 is a diagram showing electric waveforms of respective parts of the discharge lamp device shown in FIG.
In the figure, a brightness control signal is a PWM signal having a brightness instruction value as a duty ratio, and is an on period when the level is high and an off period when the level is low. The output voltage of the DC-DC converter 102 is the voltage V1 during the off period, and gradually rises through the initial soft start period and reaches the voltage V2 during the on period. The voltage V1 during the off period is a low voltage that does not cause the discharge lamp 6 to be lit, and the voltage V2 during the on period is a voltage at which the discharge lamp 6 is normally lit. By operating in this manner, a large change in the energization current of the transformer 105 does not occur, and audible sound from the transformer 105 can be reduced.
JP 2007-294399 A JP 2006-202682 A JP 2001-196196 A

  However, in the discharge lamp device according to the related art as shown in FIG. 17, when the start of the on-period is soft-started, the discharge lamp 106 is a rare gas fluorescent lamp. There is a problem that the spread of light emission in the tube axis direction is delayed. In addition, if energization is performed even during the off period, power loss of the transformer 105 occurs, the efficiency is reduced, and a DC-DC converter circuit 102 for changing the magnitude of the voltage is necessary, which increases the size of the apparatus. Problem of increasing the number of components.

  In view of the above-described problems, an object of the present invention is to provide a discharge lamp device capable of reducing audible sound generated during burst dimming without delaying the spread of light emission in the tube axis direction and suppressing power loss. Is to provide.

The present invention employs the following means in order to solve the above problems.
The first means includes an AC conversion circuit that alternately switches two or two sets of switching elements to convert a DC voltage into an AC voltage, a transformer that boosts the AC voltage from the AC conversion circuit, the transformer A discharge lamp connected to the secondary side of the discharge lamp, and in a discharge lamp device that performs burst dimming of the discharge lamp, a short circuit that short-circuits at least one of the coils of the transformer during an off period of the burst dimming A discharge lamp device comprising:
According to a second means, in the first means, in the burst dimming, a switching element or a set of switching elements that is turned on at the beginning of the on period is one of the switching elements that is turned on last at the end of the immediately preceding on period. Or it is the other switching element corresponding to the group of one switching element, or the group of the other switching element, It is a discharge lamp apparatus characterized by the above-mentioned.

According to the first aspect of the present invention, it is possible to reduce the generation of audible sound that has occurred in the voltage non-application period during burst dimming.
According to the second aspect of the present invention, it is possible to reduce the generation of audible sound that has occurred during the voltage non-application period and the voltage application period during burst dimming.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing a circuit configuration of a discharge lamp device according to the invention of this embodiment.
In the figure, the DC voltage output from the DC power source 1 is input to the AC conversion circuit 2. The AC conversion circuit 2 includes switching elements Q1 and Q2 and diodes D1 and D2, and constitutes a push-pull circuit. One end of each of the switching elements Q1 and Q2 is connected to the low potential side of the DC power supply 1. The diodes D1 and D2 are parasitic diodes of the switching elements Q1 and Q2, or are added separately, and are individually connected in parallel to the switching elements Q1 and Q2. The direction is a forward direction from a low potential to a high potential. The switching elements Q1 and Q2 are respectively input with signals S1 and S2 output from the control circuit 3, and operate so as to be turned on when the signals are at a high level and turned off when the signals are at a low level.

  The coil short circuit 4 includes switching elements Q3 and Q4 and diodes D3 and D4, and one ends of the switching elements Q3 and Q4 are connected to each other. The diodes D3 and D4 are parasitic diodes of the switching elements Q3 and Q4, or are added separately, and are individually connected in parallel to the switching elements. The direction is the anode where the ends of the switching elements Q3 and Q4 are connected to each other. The switching elements Q3 and Q4 operate so that the coil short-circuit control signal from the control circuit 3 is input and is turned on when the signal is at a high level and turned off when the signal is at a low level.

  The transformer 5 is obtained by magnetically coupling coils L1, L2, and L3. Both ends of the coil L1 are connected to the switching elements Q1 and Q2 of the AC conversion circuit 2, and the middle point of the coil L1 is connected to the high potential side of the DC power supply 1. Both ends of the coil L2 are connected to electrodes of a discharge lamp 6 formed of a rare gas fluorescent lamp or an excimer lamp. Both ends of the coil L3 are connected to the switching elements Q3 and Q4 of the coil short circuit 4. The brightness control signal output from an external device or the like is a PWM signal in which the magnitude of the duty ratio is associated with the brightness instruction value, and this signal is input to the control circuit 3. From the control circuit 3, signals S1 and S2 controlled based on the brightness control signal and a coil short-circuit control signal are output.

FIG. 2 is a diagram showing an electrical waveform showing the operation of each part of the discharge lamp device shown in FIG.
In the figure, the voltage application period and the no-voltage application period are periods determined in synchronization with the internal signal of the control circuit 3 based on the on period and the off period of the brightness control signal. The beginning of the voltage application period is synchronized with the rising time of the pulse waveform of the signal S1 or the signal S2, and the beginning of the voltage non-application period is synchronized with the time when the time τ has elapsed from the rising of the pulse waveform of the signal S1 or the signal S2. To do. The signals S1 and S2 are signals in which a pulse waveform with a pulse width t1 is repeatedly output with a period T of, for example, 10 μs to 50 μs during the voltage application period, and the relationship in which the phases of the pulse waveforms are shifted from each other by 180 °. It is in. The switching elements Q1 and Q2 of the AC conversion circuit 2 operate according to the signals S1 and S2, and generate AC voltage in the coils L1, L2, and L3 of the transformer 5.
If the pulse waveform of the signal S1 (S2) is output at the end of the voltage application period, the first pulse waveform of the next voltage application period is controlled to be output from the signal S2 (S1). That is, the polarity of the AC voltage at the beginning of the next voltage application period is controlled to be opposite to the polarity of the AC voltage at the end of the voltage application period. The coil short-circuit control signal is at a low level during a voltage application period and is at a high level during a voltage non-application period. That is, during the voltage non-application period, the coil short circuit 4 is in a short circuit state, the voltage of the coil L3 becomes 0V, and at the same time, the residual charge of the discharge lamp 6 is released, and the lamp voltage becomes 0V.

FIG. 3 is a diagram showing an internal configuration of the control circuit 3 shown in FIG.
As shown in the figure, the control circuit 3 includes an oscillation circuit 31, a synchronization circuit 32, a voltage polarity storage circuit 33, and the like. The oscillation circuit 31 outputs a signal A that is a periodic pulse signal. The synchronization circuit 32 receives the signal A and the brightness control signal, and outputs a voltage application period control signal. The voltage application period control signal is a signal in which the rising edge of the brightness control signal is synchronized with the rising edge of the signal A, and the falling edge of the brightness control signal is synchronized with the time point τ has elapsed from the rising edge of the signal A. The negative circuit NOT2 receives the voltage application period control signal and outputs a coil short-circuit control signal. The AND circuit AND1 receives the signal A and the voltage application period control signal and outputs a signal B. The voltage polarity memory circuit 33 receives the signal B and outputs a signal C and a signal D. The signals C and D are in a negative relationship with each other, and the logic is inverted in synchronization with the rising of the signal B. The AND circuit AND2 receives the signal B and the signal C and outputs the signal S1, and the AND circuit AND3 receives the signal B and the signal D and outputs the signal S2. The synchronization circuit 32 includes a D-FF (delay flip-flop circuit), an OR circuit OR1, a NOT circuit NOT1, a resistor R1, and a capacitor C1. A brightness control signal is input to the D terminal of the D-FF, and a signal A is input to the CK terminal. The signal from the Q terminal is input to the OR circuit OR1, and the signal from the inverted output terminal of Q is input to the OR circuit OR1 via the integrating circuit including the resistor R1 and the capacitor C1, and the NOT circuit NOT1. The magnitude of time τ is adjusted by the time constant of the integration circuit. The OR circuit OR1 outputs a voltage application period control signal. In the voltage polarity memory circuit 33, the signal B is input to the T terminal of the T-FF composed of the T-FF (toggle flip-flop circuit), the signal C is output from the Q terminal, and the inverted output terminal of Q Outputs a signal D.

FIG. 4 is a timing chart showing the operation of each part in the control circuit 3 shown in FIG.
The brightness control signal is a PWM signal in which the magnitude of the duty ratio is associated with the brightness instruction value, and a high level period is an on period and a low level period is an off period. The signal A is an output signal from the oscillation circuit 31, and is a pulse signal having a cycle T / 2 and a pulse width t1. The voltage application period control signal is a signal in which the rising edge of the brightness control signal is synchronized with the rising edge of the signal A and the falling edge of the brightness control signal is synchronized with the time point when τ has elapsed from the rising edge of the signal A. A high level period is a voltage application period, and a low level period is a no-voltage application period. The signal B is a signal that is the same as the signal A during the voltage application period and is at a low level during the voltage non-application period. The signal C and the signal D are in a negative relationship with each other and are inverted in synchronization with the rise of the signal B. Signals S1 and S2 are output signals of the AND circuits AND2 and AND3, the signal S1 is a logical product of the signals B and C, and the signal S2 is a logical product of the signals B and D. The coil short circuit control signal is an output signal of NOT2, and is a negative of the voltage application period control signal.

  In the discharge lamp device according to the present embodiment, the AC conversion circuit 2 need not be limited to the push-pull method, and may be a half-bridge method or a full-bridge method. Further, the configuration of the control circuit 3 is not limited to this as long as it has the same function, and may be configured using another circuit configuration, a microcomputer, a PLD, or the like. The brightness control signal may be in the form of an analog voltage signal other than the PWM signal or a digital signal, and the signal may be converted into a PWM signal inside the control circuit.

A second embodiment of the present invention will be described with reference to FIGS.
FIG. 5 is a diagram showing a circuit configuration of the discharge lamp device according to the invention of the present embodiment.
In the figure, the DC voltage output from the DC power source 1 is input to the AC conversion circuit 2A. The AC conversion circuit 2A includes switching elements Q1, Q2, Q3, and Q4 and diodes D1, D2, D3, and D4, and constitutes a full bridge circuit. Switching elements Q1 and Q2 and switching elements Q3 and Q4 are connected in series, and DC power supply 1 is connected to both ends thereof. The switching elements Q1, Q3 are arranged on the high side, and the switching elements Q2, Q4 are arranged on the low side. The diodes D1 to D4 are parasitic diodes of the switching elements Q1 to Q4 or added separately, and are individually connected in parallel to the switching elements Q1, Q2, Q3, and Q4. The direction is a forward direction from a low potential to a high potential. Signals S1, S2, S3, and S4 output from the control circuit 3A are input to the switching elements Q1, Q2, Q3, and Q4, respectively. The signals are turned on when the signal is high, and turned off when the signal is low. It works to be. The transformer 5A is obtained by magnetically coupling the coils L1 and L2. Both ends of the coil L1 are connected to a connection point between the switching elements Q1 and Q2 of the AC conversion circuit 2A and a connection point between the switching elements Q3 and Q4, and both ends of the coil L2 are a discharge lamp 6 made of a rare gas fluorescent lamp or an excimer lamp. Connected to the electrode. The brightness control signal output from an external device or the like is a PWM signal in which the magnitude of the duty ratio is associated with the brightness instruction value, and this signal is input to the control circuit 3A. The control circuit 3A outputs signals S1, S2, S3, and S4 that are controlled based on the brightness control signal.

FIG. 6 is a diagram showing an electrical waveform showing the operation of each part of the discharge lamp device shown in FIG.
In the figure, the voltage application period and the no-voltage application period are periods determined in synchronization with the internal signal of the control circuit 3A based on the brightness control signal of the PWM signal. The beginning of the voltage application period is synchronized with the rising edge of the pulse waveforms of the signals S1 and S4 or the signals S2 and S3, and the beginning of the voltage non-application period is the signal S1 and the signal S4 or the signals S2 and S3. Synchronized with the time when the time τ has elapsed from the rise of the pulse waveform. The signals S1, S2, S3, and S4 are signals in which a pulse waveform having a pulse width t1 is repeatedly output with a period T during the voltage application period. The signals S1 and S4 and the signals S2 and S3 are pulse waveforms with respect to each other. The phases are shifted by 180 °. Switching elements Q1, Q2, Q3, and Q4 of AC conversion circuit 2A operate according to signals S1, S2, S3, and S4, respectively, and generate an AC voltage in coil L2. If the pulse waveforms of the signals S1 (S2) and S4 (S3) are output at the end of the voltage application period, the first pulse waveform of the next voltage application period is from the signals S2 (S1) and S3 (S4). Controlled to output. That is, the polarity of the AC voltage at the beginning of the next voltage application period is controlled to be opposite to the polarity of the AC voltage at the end of the voltage application period. During the voltage non-application period, the signals S2 and S4 are fixed at a high level, and the signals S1 and S3 are fixed at a low level. That is, when the low-side switching elements are simultaneously turned on during the voltage non-application period, the coil L1 is short-circuited, the voltage of the coil L1 becomes 0V, and the residual charge of the discharge lamp 6 is simultaneously released, and the lamp voltage is also 0V. become.

FIG. 7 is a diagram showing an internal configuration of the control circuit 3A shown in FIG.
In the figure, the control circuit 3A includes an oscillation circuit 31, a synchronization circuit 32, a voltage polarity storage circuit 33, and the like. The oscillation circuit 31 outputs a signal A that is a periodic pulse signal. The synchronization circuit 32 receives the signal A and the brightness control signal and outputs a voltage application period control signal. The voltage application period control signal is a signal in which the rising edge of the brightness control signal is synchronized with the rising edge of the signal A, and the falling edge of the brightness control signal is synchronized with the time point τ has elapsed from the rising edge of the signal A. The negative circuit NOT2 receives the voltage application period control signal and outputs a coil short-circuit control signal. The AND circuit AND1 receives the signal A and the voltage application period control signal, and outputs a signal B. The voltage polarity memory circuit 33 receives the signal B and outputs a signal C and a signal D. The signals C and D are in a negative relationship with each other, and the logic is inverted in synchronization with the rising of the signal B.

  A signal B and a signal C are input to the AND circuit AND2, and a signal S1 is output. The logical sum circuit OR2 receives the signal S3 and the coil short circuit control signal and outputs the signal S2. A signal B and a signal D are input to the AND circuit AND3, and a signal S3 is output. A signal S2 and a coil short-circuit control signal are input to the OR circuit OR3, and a signal S4 is output. The synchronization circuit 32 includes a D-FF (delay flip-flop circuit), an OR circuit OR1, a NOT circuit NOT1, a resistor R1, and a capacitor C1. A brightness control signal is input to the D terminal of the D-FF, and a signal A is input to the CK terminal. A signal from the Q terminal is input to the OR circuit OR1, and a signal from the inverted output terminal of Q is input to the OR circuit OR1 via an integrating circuit including a resistor R1 and a capacitor C1, and a negation circuit NOT1. The magnitude of time τ is adjusted by the time constant of the integration circuit. The OR circuit OR1 outputs a voltage application period control signal. The voltage polarity memory circuit 33 is composed of a T-FF (toggle flip-flop circuit). A signal B is input to the T terminal of the T-FF, a signal C is output from the Q terminal, and a signal D is output from the inverted output terminal of Q.

FIG. 8 is a timing chart showing the operation of each part in the control circuit 3 shown in FIG.
The brightness control signal is a PWM signal in which the magnitude of the duty ratio is associated with the brightness instruction value, and a high level period is an on period and a low level period is an off period. The signal A is an output signal from the oscillation circuit 31, and is a pulse signal having a cycle T / 2 and a pulse width t1. The voltage application period control signal is a signal in which the rising edge of the brightness control signal is synchronized with the rising edge of the signal A and the falling edge of the brightness control signal is synchronized with the time point when τ has elapsed from the rising edge of the signal A. A high level period is a voltage application period, and a low level period is a no-voltage application period. The signal B is a signal that is the same as the signal A during the voltage application period and is at a low level during the voltage non-application period. The signal C and the signal D are in a negative relationship with each other and are inverted in synchronization with the rise of the signal B. The signal S1 and the signal S3 are output signals of the AND circuit AND2 and the AND circuit AND3, the signal S1 is a logical product of the signal B and the signal C, and the signal S3 is a logical product of the signal B and the signal D. Signals S2 and S4 are output signals of the OR circuit OR1 and OR circuit OR2. The signal S2 is the logical sum of the signal S3 and the coil short circuit control signal. The signal S4 is the logical sum of the signal S1 and the coil short circuit control signal. It becomes. The coil short circuit control signal is an output signal of NOT2, and is a negative of the voltage application period control signal.

  In the invention of this embodiment, the low-side switching elements are simultaneously turned on to short-circuit the coil L1, but the high-side switching elements may be simultaneously turned on. Further, the configuration of the control circuit 3A is not limited to this as long as it has the same function, and another circuit configuration, a configuration using a microcomputer, a PLD, or the like may be used. The brightness control signal may be in the form of an analog voltage signal other than the PWM signal or a digital signal, and the signal may be converted into a PWM signal inside the control circuit.

Next, the reason why the audible sound is reduced in the discharge lamp device of the present invention will be described.
First, a rare gas fluorescent lamp as an example of the discharge lamp 6 applied to the discharge lamp device of the present invention will be described.
FIG. 9A is a cross-sectional view of the rare gas fluorescent lamp 6 viewed from a cross-section orthogonal to the tube axis direction, and FIG. 9B is a perspective view of the rare gas fluorescent lamp 6.
As shown in these figures, the rare gas fluorescent lamp 6 is, for example, a straight tube envelope that is hermetically sealed with a glass tube 61, and has a rare earth phosphor and a halophosphate fluorescence on its inner surface. A fluorescent material 62 made of a fluorescent material such as a body is formed. The sealing structure of the glass tube 61 is configured by sealing a disc-shaped sealing glass plate at the end of the glass tube 61. For example, the glass tube 61 is simply heated while the glass tube 61 is heated and melted. It can also be constituted by a top seal. The external electrodes 63 and 64 are configured, for example, by bonding an aluminum tape cut to a width of 1 mm to a position facing the center axis of the rare gas fluorescent lamp 6 on the outer surface of the glass tube 61. The external electrodes 63 and 64 may be formed by screen printing and baking a conductive paste, for example. The sealed space of the glass tube 61 is filled with a predetermined amount of a rare gas whose main component is at least one of He, Ar, Xe, and Kr that does not contain metal vapor such as mercury. The easily startable portion 65 is made of a conductive material or an easily electron emitting material, and is disposed at least one place inside the glass tube 61 in order to facilitate the start of discharge. Discharge occurs from the easily startable portion 65 and spreads throughout the rare gas fluorescent lamp 6 from there. Usually, it is provided at the end of the glass tube 61 and the like so as not to affect the light extraction efficiency during lighting.

FIG. 10 is a diagram showing an equivalent circuit of the discharge lamp 6 composed of a rare gas fluorescent lamp or an excimer lamp.
The discharge lamp 6 is represented in such a manner that the capacitance Cg of the glass tube 61 and the discharge impedance p are connected in series, and the capacitance Cd of the discharge space is connected in parallel with the discharge impedance p. As described above, the discharge lamp 6 composed of a rare gas fluorescent lamp or an excimer lamp is a capacitive load that discharges through the capacitance of the glass tube 61. When the electric discharge occurs, the electric charge generated by the electric discharge in the glass tube 61 is accumulated on the inner wall of the glass tube 61 so as to be attracted to the electric field from the outside, and is maintained until an electric field in the reverse direction is applied. Therefore, even if the supply of electric power from the discharge lamp device is stopped, the lamp voltage does not immediately become zero due to the electric charge accumulated in the discharge lamp 6, and it has a property like a large charged capacitor element.

FIG. 11 shows the waveform of the primary voltage V of the transformer 105 and the waveform of the magnetic flux density B of the transformer 105 in the discharge lamp apparatus according to the prior art shown in FIG. 17, without the DC-DC converter 102. FIG. 11A is a diagram showing the whole from the latter half of the voltage application period to the no-voltage application period and the first half of the voltage application period, and FIG. 11B shows the voltage from the voltage application period to the voltage. FIG. 11C is an enlarged view at the time of switching from the voltage non-application period to the voltage application period. Here, assuming that the effective cross-sectional area of the core of the transformer 105 is Ae and the number of turns of the coil is n, the magnetic flux density B and the voltage V have a relationship of B = {1 / (Ae × n)} × ∫Vdt.
As shown in these figures, the operation of the AC conversion circuit 103 is stopped during the period in which no voltage is applied. However, the capacitance component of the discharge lamp 106, the stray capacitance, and the secondary side coil of the transformer 105 are mainly used. In a resonance state due to inductance, a resonance voltage is generated in the initial stage of no voltage application as shown in the enlarged view of FIG. Therefore, even after the voltage application period ends, the magnetic flux density B continues to increase as shown by the portion A of the resonance voltage, and the center of vibration of the magnetic flux density B is biased to the plus side. In this way, when the vibration of the magnetic flux density B is biased and a peak as shown in part B of FIG. 11A occurs, an audible sound is generated, which is an audible sound in the initial period of no voltage application. Possible cause. Next, in the initial period of the voltage application period, since the bias excitation is performed in the voltage polarity direction to be applied first, a peak of the magnetic flux density B as shown in a portion C of FIG. This is considered to be the cause of the audible sound in the initial period of voltage application.

FIG. 12 shows the waveform of the primary voltage V of the transformer 5 (5A) and the waveform of the magnetic flux density B of the transformer 5 (5A) in the discharge lamp device according to the invention of the first (and second) embodiment. FIG. 12A is a diagram showing the whole from the latter half of the voltage application period to the no-voltage application period and the first half of the voltage application period, and FIG. 12B shows the voltage from the voltage application period to the voltage. FIG. 12C is an enlarged view at the time of switching from the voltage non-application period to the voltage application period. Here, when the effective cross-sectional area of the core of the transformer 5 (5A) is Ae and the number of turns of the coil is n, the magnetic flux density B and the voltage V have a relationship of B = {1 / (Ae × n)} × ∫Vdt. is there.
As shown in these figures, during the voltage non-application period, the coil L3 (L1) of the transformer 5 (5A) is short-circuited, so that no resonance voltage is generated. At this time, the exciting current continues to flow through the short-circuited coil L3 (L1), and it can be considered that the magnetic flux density B maintains the same magnitude in the short term. Therefore, at the beginning of the voltage non-application period, a peak with a high magnetic flux density B as shown in part B of FIG. 11A does not occur, so that audible sound is suppressed. In addition, since the polarity of the primary voltage at the beginning of the voltage application period is controlled to be opposite to the polarity at the end of the previous voltage application period, the magnetized direction is the direction that cancels the magnetic flux density during the voltage non-application period. It becomes. Therefore, at the beginning of the voltage application period, a peak with a high magnetic flux density B as shown in part C of FIG. 11A does not occur, so that an audible sound is suppressed.

Next, a method for setting the magnitude of the period τ in the primary voltage in FIG.
Since the polarity of the primary voltage (or lamp voltage) of the transformer 5 (5A) is reversed at the end of the voltage application period, the coil L3 (L1) of the transformer 5 (5A) is short-circuited, and the primary voltage of the transformer 5 (5A) is It is desirable to set the magnitude of the period τ until it reaches 0V with a magnitude smaller than 0.5T. T corresponds to the cycle of the lamp voltage immediately before the end of the voltage application period.
FIG. 13 is a table showing the result of evaluation of the audible sound from the transformer 5 (5A) when the magnitude of the period τ is changed from 0.10 T to 0.50 T by the sensory test of five people. is there. Here, the period T of the signals S1, S2 (S1, S2, S3, S4) to the switching elements Q1, Q2 (Q1, Q2, Q3, Q4) is set to 20 μs.
As shown in the figure, by setting the period τ from 0.20T to 0.40T, the audible sound becomes almost unnoticeable, especially at 0.25T to 0.30T. It was. Therefore, by setting the period τ in the range of 0.20T to 0.40T, the audible sound from the transformer 5 (5A) can be set to a level that does not matter. This is considered to be due to the correlation between the voltage waveform at the end and the start of the voltage application period, and the residual magnetic flux density during the voltage non-application period. The reason why the voltage waveform at the end of the voltage application period is different from the voltage waveform at the start is thought to be because the discharge at the start is undeveloped and the capacity component of the discharge lamp is small.

  Furthermore, the magnitude of the period τ must be τ> t1. t1 is the on-time of the switching elements Q1, Q2 (Q1, Q2, Q3, Q4) shown in FIG. 2 (FIG. 4) and the like. In the circuit shown in FIG. 1, when τ ≦ t1, the coil short circuit 4 and the switching element Q1 or the switching element Q2 are temporarily turned on at the same time. When the coil short circuit 4 is turned on, the coil L1 is in a low impedance state. Therefore, when the switching element Q1 or the switching element Q2 is turned on, there is a risk that a large current flows and the circuit breaks down. In the circuit shown in FIG. 4, when τ ≦ t1, the low-side switching element and the switching element Q1 or Q3 are temporarily turned on at the same time, so-called arm short circuit state, and a large current flows. Risk of circuit failure.

FIG. 14 is a diagram showing waveforms of signals S1, S2, lamp current, and lamp voltage in the circuit shown in FIG.
As shown in the figure, the discharge of the lamp is generated immediately after the polarity of the lamp voltage is reversed and the lamp voltage is rapidly changed, and accordingly, a high peak discharge current flows. Subsequently, a small peak resonance current without discharge flows in the opposite direction. This resonance current is mainly due to the leakage inductance of the transformer 5 and the capacitance of the discharge lamp 6. Assuming that the time during which this discharge current flows is td and the time during which the resonance current flows is tr, the pulse width t1 of the signals S1, S2 is preferably adjusted to td ≦ t1 ≦ td + tr. When t1 <td, there is a problem that the magnitude of the discharge current changes and the output becomes unstable. Further, if t1> td + tr, a resonance current not related to discharge continues to flow, and there is a problem that loss increases and efficiency decreases.

Next, a comparison between the discharge lamp device according to the present invention and the discharge lamp device according to the prior art having no function of reducing audible sound will be described.
FIG. 15 shows an audible sound in a discharge lamp device without a so-called audible sound reduction function which does not have a DC short-circuit function and a voltage polarity control function of the present invention and a DC-DC converter as disclosed in Patent Documents 2 and 3. FIG. 16 is a diagram showing the level of audible sound in the discharge lamp device according to the invention of the first and second embodiments. The vertical axis represents the output voltage from the sound level meter, and the horizontal axis represents time. In addition, the measuring instrument used for the measurement uses NA-41 manufactured by Rion Co., Ltd., and measures the sound from the transformer in the discharge lamp device.
As shown in FIG. 15, in the discharge lamp device according to the related art that does not have an audible sound reduction function, it can be seen that a large audible sound is generated at the initial stage of the voltage application period and at the initial stage of the voltage non-application period. On the other hand, as shown in FIG. 16, in the discharge lamp device according to the present invention, it can be seen that the generation of audible sounds occurring at the beginning of the voltage application period and the initial period of no voltage application is reduced and improved. The audible sound that was generated at the beginning of the voltage non-application period was improved mainly by short-circuiting the transformer coil during the voltage non-application period. This is mainly improved by making the polarity of the AC voltage at the beginning of the next voltage application period opposite to the polarity of the AC voltage at the end of the voltage application period.

It is a figure which shows the circuit structure of the discharge lamp apparatus which concerns on invention of 1st Embodiment. It is a figure which shows the electrical waveform which shows the operation | movement of each part of the discharge lamp apparatus shown in FIG. It is a figure which shows the internal structure of the control circuit 3 shown in FIG. 4 is a timing chart showing the operation of each unit in the control circuit 3 shown in FIG. 3. It is a figure which shows the circuit structure of the discharge lamp apparatus which concerns on invention of 2nd Embodiment. It is a figure which shows the electrical waveform which shows the operation | movement of each part of the discharge lamp apparatus shown in FIG. FIG. 6 is a diagram showing an internal configuration of a control circuit 3A shown in FIG. It is a timing chart which shows operation | movement of each part in the control circuit 3 shown in FIG. FIG. 4 is a cross-sectional view of the rare gas fluorescent lamp 6 as viewed from a cross section orthogonal to the tube axis direction and a perspective view of the rare gas fluorescent lamp. It is a figure which shows the equivalent circuit of the discharge lamp 6 which consists of a noble gas fluorescent lamp and an excimer lamp. FIG. 18 is a diagram illustrating a waveform of a primary voltage V of a transformer 105 and a waveform of a magnetic flux density B of the transformer 105 in a discharge lamp device having no DC-DC converter in the discharge lamp device according to the related art illustrated in FIG. 17. It is the figure which showed the waveform of the primary voltage V of the transformer 5 (5A) and the waveform of the magnetic flux density B of the transformer 5 (5A) in the discharge lamp device according to the invention of the first and second embodiments. It is a table | surface which shows the result of having evaluated the magnitude of the audible sound from the transformer 5 (5A) at the time of changing the magnitude | size of period (tau) from 0.10T to 0.50T by the sensory test of five people. FIG. 2 is a diagram illustrating waveforms of signals S1 and S2, a lamp voltage, and a lamp current in the circuit illustrated in FIG. The level of the audible sound in the discharge lamp device without the function of reducing the audible sound without the DC short-circuit function and the voltage polarity control function of the present invention and the DC-DC converter as shown in Patent Documents 2 and 3 is shown. FIG. It is the figure which showed the level of the audible sound in the discharge lamp apparatus which concerns on invention of 1st and 2nd embodiment. It is a figure which shows the circuit structure of the discharge lamp apparatus which concerns on the prior art which has the technique of patent document 2 and patent document 3 together. It is a figure which shows the electrical waveform of each part of the discharge lamp apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2, 2A AC conversion circuit 3, 3A Control circuit 31 Oscillation circuit 32 Synchronization circuit 33 Voltage polarity memory circuit 4 Coil short circuit 5, 5A Transformer 6 Discharge lamp 61 Glass tube 62 Fluorescent material 63, 64 External electrode 65 Easy start Parts Q1 to Q4 Switching elements D1 to D4 Diodes L1 to L3 Coils AND1 to AND3 AND circuits OR1 to OR3 OR circuits NOT1, NOT2 Negative circuits R1-C1 Integration circuit D-FF Delay flip-flop circuit T-FF Toggle flip-flop circuit

Claims (2)

An AC conversion circuit that alternately switches two or two sets of switching elements to convert a DC voltage into an AC voltage, a transformer that boosts the AC voltage from the AC conversion circuit, and a secondary side of the transformer A discharge lamp device for performing burst dimming of the discharge lamp,
A discharge lamp device comprising a short circuit that short-circuits at least one of the coils of the transformer during an off period of the burst dimming.   In the burst dimming, the switching element or the set of switching elements that is turned on at the beginning of the on period is the other one corresponding to the one switching element or the set of the switching elements that is turned on last at the end of the immediately preceding on period. 2. The discharge lamp device according to claim 1, wherein the discharge lamp device is a switching element or a set of the other switching element.

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