JP2014002969A - Lighting device of electric discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device of an electric discharge lamp capable of keeping a stable lighted-state of the electric discharge lamp by configuring appropriately an interruption period where detecting of fade-away is interrupted when a polarity of an electric-discharge lamp is switched.SOLUTION: There are provided a lightning circuit 4 which makes an electric discharge lamp 5 turned on by repeating periodically polarity changeover where electric conduction direction is switched; fade-away detection means 14 which detects whether a fade-away arises in the electric discharge lamp 5 on the basis of a magnitude of a current which is energized to the electric discharge lamp 5; re-lightning means 15 which re-lights the electric discharge lamp 5 when an occurrence of the fade-away is detected; changeover period calculation means 12 which calculates a changeover period TM from starting to ending of the polarity changeover on the basis of at least one of the magnitude of a voltage applied to the electric discharge lamp 5 and the magnitude of a current energized to the electric discharge lamp 5; and detection interruption means 13 which makes the detection of the fade-away interrupted during the changeover period TM when the polarity changeover is executed.

Description

  The present invention relates to a discharge lamp lighting device for lighting a discharge lamp by converting a current from a power source into an alternating current and supplying the current.

  As a conventional discharge lamp lighting device, for example, one disclosed in Patent Document 1 is known. The discharge lamp lighting device (hereinafter simply referred to as “lighting device”) includes a DC-AC converter that converts a DC current from a DC power source into an AC, a discharge lamp that is lit when supplied with the AC output, and the like. It has. The voltage applied to the discharge lamp is detected as a lamp voltage by the lamp voltage detection circuit, and the current supplied to the discharge lamp is detected as the lamp current by the lamp current detection circuit.

  In addition, in order to keep the power supplied to the discharge lamp constant during the stable period from the completion of the polarity switching of the discharge lamp to the start of the next polarity switching, a re-ignition that occurs at the time of polarity switching of the discharge lamp is performed. A mask signal is generated so as not to detect the voltage. The mask signal is generated by the signal generation circuit according to the detected lamp voltage or lamp current, or the voltage at the output stage of the DC-AC converter, and the lamp voltage is applied during the mask period, which is the generation period of the re-ignition voltage. Is interrupted based on the mask signal. Thus, the lighting control of the discharge lamp is appropriately executed according to the lamp voltage by avoiding the effect of the re-ignition voltage on the detection of the lamp voltage.

  In addition, since the discharge lamp may be turned off when the voltage of the power source is lowered, for example, the lighting device usually monitors the lighting state of the discharge lamp according to the lamp voltage or lamp current, and the discharge lamp is discharged. When the discharge lamp is turned off (hereinafter referred to as “disappearance”) while the electric lamp is controlled to be turned on, the discharge lamp is controlled to be turned on again. In addition, when the polarity switching is executed, the detection of the extinction is interrupted so that the extinction is not erroneously detected due to a change in voltage or current during the execution of the polarity switching of the discharge lamp.

JP 2006-79983 A

  In general, the time required for switching the polarity of the discharge lamp varies depending on the lamp voltage and the lamp current at the start of polarity switching. For this reason, in the lighting device according to the above-mentioned patent document, when the extinction is detected, if the mask period is set shorter than the time required for polarity switching, the lamp voltage and the lamp current during the polarity switching are detected. As a result, there is a risk of erroneously detecting that the disappearance has occurred. In that case, re-lighting control is performed even though the lamp has not disappeared, so that a large amount of power is supplied to the discharge lamp, the brightness of the discharge lamp fluctuates and flickers, which adversely affects visibility. End up.

  On the other hand, in order to prevent false detection of extinction, if the mask period is set to be longer than the maximum time required for polarity switching regardless of the re-ignition voltage generation period, the actual extinction will occur at the time of polarity switching. However, since the extinction is not detected until the mask period ends, the detection of the extinction is delayed. As a result, as the discharge lamp turn-off time increases, the temperature of the discharge lamp electrode decreases, so the time and power required for relighting increase, which also adversely affects visibility.

  The present invention has been made to solve the above-described problems. When switching the polarity of the discharge lamp, the discharge lamp can be stably turned on by appropriately setting an interruption period for interrupting the detection of extinction. It aims at providing the lighting device of the discharge lamp which can maintain a state.

  In order to achieve the above object, a lighting device for a discharge lamp according to the present invention lights a discharge lamp 5 with power supplied from a power source (DC power source 2 in the embodiment (hereinafter, the same in this section)). The discharge lamp lighting device 1 according to the first aspect of the present invention includes a polarity switching for switching between energization from one electrode side of the discharge lamp 5 to the other electrode side and energization from the other electrode side to the one electrode side. The lighting circuit (DC-AC conversion unit 4, polarity switching control circuit 11) for lighting the discharge lamp 5 and the voltage (lamp voltage VL) applied from the power source to the discharge lamp 5 are repeated. A voltage detection circuit 6 to detect, a current detection circuit 7 to detect the magnitude of the current (lamp current IL) energized to the discharge lamp 5, and the discharge lamp 5 based on the magnitude of the detected current Has the disappearance occurred? A extinction detecting means (extinguishing determination circuit 14) for detecting the extinction, a relighting means (power control circuit 15) for relighting the discharge lamp 5 when the occurrence of extinction is detected by the extinction detecting means, A switching period calculation for calculating a switching period (mask period TM) from the start to the end of the polarity switching based on at least one of the voltage detected by the voltage detection circuit 6 and the magnitude of the current detected by the current detection circuit 7 Detection for interrupting detection of the extinction by the extinction detection means during the switching period calculated by the switching period calculation means when the polarity switching is performed by the means (mask signal generation circuit 12) and the lighting circuit Interrupting means (signal mask circuit 13).

  According to this lighting device, the energization from one electrode side of the discharge lamp to the other electrode side and the energization from the other electrode side to the one electrode side are periodically switched by the lighting circuit. The discharge lamp is turned on by periodically repeating the polarity switching. Also, when polarity switching is performed, the current due to the inductance of the inductor connected in series with the discharge lamp flows from the start of polarity switching, so the magnitude of the current passed through the discharge lamp gradually decreases. The direction of current flow can be switched smoothly.

  Further, the magnitude of the current supplied to the discharge lamp is detected by the current detection circuit, and based on the detected magnitude of the current, whether or not the discharge lamp has disappeared is detected by the extinction detecting means. The When the extinction is detected, the discharge lamp is relighted by the relighting means.

  The switching period from the start to the end of polarity switching is based on at least one of the magnitude of the current detected by the current detection circuit and the voltage applied to the discharge lamp detected by the voltage detection circuit. Calculated by calculating means. When the discharge lamp polarity switching is executed, the detection interruption means is interrupted by the detection interruption means during the calculated switching period.

  As described above, the switching period is calculated based on the magnitude and voltage of the current that affects the period required to switch the polarity of the discharge lamp, and during the switching period in which the magnitude of the current supplied to the discharge lamp varies, The detection of extinction based on the magnitude of the current is interrupted. Accordingly, erroneous detection of extinction during execution of polarity switching can be prevented and re-lighting operation associated with erroneous detection can be prevented, so that the discharge lamp can be maintained in a stable lighting state. Also, even if the extinction occurs during the switching period, the detection of the extinction is resumed when the polarity switching is completed, so the period from the occurrence of the extinction until the relighting operation is executed is detected as an erroneous detection of extinction. Can be minimized while preventing. Further, since the re-lighting operation of the discharge lamp is started immediately with the end of the polarity switching in this way, the temperature drop of the discharge lamp electrode due to the extinction is suppressed, and as a result, the power required for re-lighting and A reduction in visibility can be suppressed.

It is a block diagram which shows the lighting device of the discharge lamp which concerns on embodiment. It is a schematic circuit diagram which shows the lighting circuit of the lighting device of FIG. It is a timing chart which shows an example of operation | movement of the lighting device in a normal lighting state. It is a timing chart which shows an example of operation | movement of the lighting device in a warm-up state. It is a timing chart which shows an example of operation | movement of the lighting device in the state which the secular change generate | occur | produced in the discharge lamp. It is a timing chart which shows an example of operation of a lighting device concerning a comparative example.

  Hereinafter, a lighting device for a discharge lamp according to an embodiment of the present invention will be described with reference to the drawings. The lighting device 1 is mounted on, for example, a vehicle (not shown), and as shown in FIG. 1, a DC power source 2, a DC booster 3, a DC-AC converter (hereinafter referred to as an “inverter circuit”) 4, a discharge lamp, and the like. An electric lamp 5 and a control circuit 10 are provided.

  The DC power supply 2 is a battery that outputs a DC current, and the current output from the DC power supply 2 is input to the DC boosting unit 3. The DC booster 3 has a DC-DC converter (not shown) and the like, and is controlled by the control circuit 10 to boost the voltage of the DC power supply 2 to a required voltage and output it. The inverter circuit 4 is also controlled by the control circuit 10, converts the direct current input from the direct current booster 3 into an alternating current, and outputs the alternating current to the discharge lamp 5.

  The discharge lamp 5 is a high-intensity discharge lamp such as a metal halide lamp, and emits light by arc discharge generated between two electrodes (not shown) in a high-pressure vapor of enclosed metal atoms. The discharge lamp 5 is provided as a vehicle headlamp, for example, and is connected to the inverter circuit 4 as described later.

  As shown in FIG. 2, the inverter circuit 4 is configured as an H-bridge circuit having first to fourth switch elements Q1 to Q4. The first switch element Q1 is composed of, for example, a p-channel type MOSFET and is disposed on the DC power supply 2 side, and the second switch element Q2 is composed of, for example, an n-channel type MOSFET and is output from the DC power supply 2 The switch elements Q1 and Q2 are connected in series with each other. Specifically, the drains of the first and second switch elements Q1 are connected to each other.

  The third and fourth switch elements Q3 and Q4 are provided in parallel with the first and second switch elements Q1 and Q2, and are connected in series with each other in the same manner as the first and second switch elements Q1 and Q2. The p-channel MOSFET and the n-channel MOSFET are respectively configured. The third switch element Q3 is disposed on the DC power supply 2 side, while the fourth switch element Q4 is disposed on the ground 8 side, and the drains of the third and fourth switch elements Q3 and Q4 are connected to each other. The sources of the first and third switch elements Q1 and Q3 are connected to the DC booster 3, and the sources of the second and fourth switch elements Q3 and Q4 are grounded to the ground 8 via the shunt resistor RS. ing. Instead of the MOSFET, each switch element may be composed of, for example, a transistor or an IGBT.

  The discharge lamp 5 described above is provided between the first intermediate terminal 4a between the first and second switch elements Q1 and Q2 and the second intermediate terminal 4b between the third and fourth switch elements Q3 and Q4. Of the two electrodes of the discharge lamp 5, one electrode side is connected to the first intermediate terminal 4a and the other electrode side is connected to the second intermediate terminal 4b. The inverter circuit 4 is provided with a coil L (inductor) connected in series to the discharge lamp 5 on the first intermediate terminal 4a side. The coil L has a predetermined inductance H.

  A voltage VL output from the DC booster 3 and applied to the discharge lamp 5 via the inverter circuit 4 (hereinafter referred to as “lamp voltage”) VL is detected by a voltage detection circuit 6, and the voltage detection circuit 6 A voltage signal representing the lamp voltage VL is output to the control circuit 10. The shunt resistor RS described above is an element for detecting a current (hereinafter referred to as “lamp current”) IL passed through the discharge lamp 5, and the terminal on the inverter circuit 4 side of the shunt resistor RS is a current detection circuit. 7 is connected. The current detection circuit 7 detects the lamp current IL based on the voltage VS of the shunt resistor RS, and outputs a current signal representing the magnitude of the lamp current IL to the control circuit 10.

  When the lighting switch (not shown) is turned on by a driver of the vehicle or the like, the control circuit 10 turns on the discharge lamp 5 and keeps the lighting at a constant brightness. Part 3, inverter circuit 4, etc., polarity switching control circuit 11, mask signal generation circuit 12 (switching period calculation means), signal mask circuit 13 (detection interruption means), extinction determination circuit 14 (extinction detection means) ) And a power control circuit 15 (relighting means).

  The polarity switching control circuit 11 constitutes a lighting circuit for lighting the discharge lamp 5 together with the inverter circuit 4 described above, and is connected to the gates of the first to fourth switch elements Q1 to Q4 described above. A control signal for turning on / off each of the first switch elements Q1 to Q4 is periodically output to each gate. When the first and fourth switch elements Q1 and Q4 are turned on by the polarity switching control circuit 11, while the second and third switch elements Q2 and Q3 are turned off, current is supplied from the DC booster 3 to the first switch element. The ground 8 is energized through Q1, the first intermediate terminal 4a, the coil L, the discharge lamp 5, the second intermediate terminal 4b, the fourth switch element Q4, and the shunt resistor RS in this order (hereinafter, this energization path is referred to as “ First energization path ”). On the other hand, when the second and third switch elements Q2 and Q3 are turned on while the first and fourth switch elements Q1 and Q4 are turned off, the current is supplied from the DC booster 3 to the second switch element Q2 and the second intermediate element. The grant 8 is energized through the terminal 4b, the discharge lamp 5, the coil L, the first intermediate terminal 4a, the second switch element Q2, and the shunt resistor RS in this order (hereinafter, this energization path is referred to as “second energization path”). "). The polarity switching control circuit 11 periodically switches the current energization path between the first energization path and the second energization path, thereby energizing the discharge lamp 5 and turning on the discharge lamp 5.

  The mask signal generation circuit 12 is supplied with the voltage signal from the voltage detection circuit 6 and the current signal from the current detection circuit 7, and from the polarity switching control circuit 11, the first to fourth switch elements Q1 to Q4. A control signal representing ON / OFF of each is input. Based on the input voltage signal and current signal, the mask signal generation circuit 12 calculates a switching period required for polarity switching of the discharge lamp 5 as a mask period TM as will be described later, and turns on / off each switch element. The switching timing for starting the polarity switching is calculated from the control signal representing. Then, the mask signal generation circuit 12 generates and outputs a mask signal SM representing the mask period TM and switching timing.

  The mask signal SM output from the mask signal generation circuit 12 and the current signal output from the lamp current detection circuit 7 are input to the signal mask circuit 13. The signal mask circuit 13 suspends the output of the current signal until the mask period TM elapses from the switching timing represented by the mask signal, and passes the current signal when it is outside the mask period TM.

  The extinction determination circuit 14 determines whether or not the discharge lamp has extinguished in accordance with the signal output from the signal mask circuit 13. In the extinction determination circuit 14, for example, the extinction occurs in the discharge lamp 5 when the current value represented by the current signal that has passed through the signal mask circuit 13 has remained below a predetermined threshold value for a predetermined period. It is determined that Further, the detection of extinction by such determination is executed when a current signal is input, while it is not executed when the output of the current signal is interrupted by the signal mask circuit 13 during the mask period TM. A determination signal representing the determination result is output from the extinction determination circuit 14 to the power control circuit 15.

  The power control circuit 15 controls the DC booster 3 according to the voltage signal and current signal output from the voltage detection circuit 6 and the current detection circuit 7 respectively, and the determination signal output from the extinction determination circuit 14. Specifically, when the extinction is not detected and the determination signal indicates that the discharge lamp 5 is normally lit, the voltage signal is set so that the brightness of the discharge lamp 5 is maintained constant. Based on the current signal, the DC booster 3 is controlled so as to output a required constant voltage. Further, when the determination signal indicates that the discharge lamp 5 has disappeared, the DC boosting unit is configured so that a higher voltage is output in order to supply a larger amount of power to the discharge lamp 5 to re-light it. 3 is controlled.

  FIG. 3 is a timing chart showing an example of the operation of the lighting device 1. The figure shows a normal lighting state in which the discharge lamp 5 is stably lit at a constant brightness. The energization path of the lamp current IL is switched to the first energization path by the polarity switching control circuit 11. When the constant first voltage VL1 is applied to the discharge lamp 5 as the lamp voltage VL, the lamp current IL having the constant first current value IL1 is changed from one electrode side of the discharge lamp 5 to the other electrode. Energized to the side. Further, in such a stable state, the mask signal SM indicates that it is not the mask period TM (shown as OFF in FIG. 3 (the same applies in FIGS. 4 and 5)), and the discharge lamp is changed according to the detected lamp current IL. 5 is always determined by the extinction determination circuit 14.

  When starting the polarity switching from the above stable state, the polarity switching control circuit 11 switches the on / off combination of the first to fourth switch elements Q1 to Q4, for example, at the timing t1, thereby energizing the lamp current IL. The route is switched to the second energization route. At this time, a current due to the inductance H of the coil L is energized through the first energization path, and this current gradually attenuates at a speed corresponding to the first voltage VL1 and the inductance H at the start of polarity switching. At timing t2, the current energization path is switched to the second energization path, and energization of the lamp current IL from the other electrode side to the one electrode side is started. The magnitude of the lamp current IL energized in the second energization path gradually increases, reaches the second current value IL2 having the same magnitude as the first current value IL1 at the timing t3, and stabilizes.

  Further, when the energization path is switched at the timing t1, a re-ignition voltage is generated as a current due to the inductance H of the coil L is generated. The ramp voltage VL rises from the timing t1 by the re-ignition voltage, reaches the second voltage VL2, attenuates, and returns to the first voltage VL1 and stabilizes at the timing t4 immediately after the timing t3.

  The mask signal SM indicates that the mask period TM is from the time when the polarity switching is started at the timing t1 (shown as ON in FIG. 3 (the same in FIGS. 4 and 5)). Meanwhile, the judgment of extinction is interrupted by the interruption of the output of the current signal by the signal mask circuit 13. The mask period TM is calculated by the mask signal generation circuit 12 based on the following equation (1) in the stable period before the timing t1 when the polarity switching is started.

TM≈ ((IL × 2) × H) / (VL × 2) (1)
TM: Mask period
IL: magnitude of lamp current
H: Inductance of coil L
VL: Lamp voltage According to this equation (1), the mask period TM is calculated as substantially the same period as the period actually required for polarity switching. The mask period TM is calculated as a longer period as the lamp current IL is larger, and is calculated as a shorter period as the lamp voltage VL is larger. Further, the lamp voltage VL and the lamp current IL used in the equation (1) are detected in a stable period from the timing when the previous polarity switching is completed and the lamp voltage VL and the lamp current IL are both stable to the timing t1. It has been done. Note that the mask period TM calculated by the above equation (1) is an approximate value of the period actually required for polarity switching, and in order to make the mask period TM closer to the switching period, the discharge lamp 5, the inverter circuit 4 and the like. A constant reflecting the characteristics may be multiplied or added to the calculated mask period TM. The above formula (1) calculates the mask period TM based on both the detected lamp voltage VL and the lamp current IL. For example, one of the average value of the lamp voltage VL and the lamp current IL or The mask period TM may be calculated using a maximum value obtained in advance and the other of the detected lamp voltage VL and lamp current IL.

  As described above, in the stable period immediately before the timing t1, the first mask period TM1 is calculated as the mask period TM according to the first voltage VL1 and the first current value IL1, and the polarity is switched at the timing t1. When started, the mask signal SM is switched on and detection of extinction is interrupted. Then, when the first mask period TM1 has elapsed from the timing t1, the mask signal SM is switched off, and the detection of the disappearance is resumed.

  When the polarity switching as described above ends at timing t3 and the re-ignition voltage disappears at timing t4, a constant first lamp voltage VL1 is applied to the discharge lamp 5 until a predetermined stable period T1 elapses. In addition, a constant second lamp current IL2 is energized. During this stable period T1, a mask period TM for executing the next polarity switching is calculated according to the first voltage VL1 and the second current value IL2. Then, at the timing t5 when the predetermined first polarity switching period TF1 has elapsed from the timing t1 at which the previous polarity switching was started, the polarity switching is started so as to switch from the second to the first energization path. At the same time, the detection of extinction is interrupted until the first mask period TM1 calculated during the stable period T1 elapses. After this, the polarity switching is periodically repeated for each first polarity switching period TF1, whereby the energizing direction of the lamp current IL is switched for each first polarity switching period TF1, and the discharge lamp 5 When the alternating current is applied to the discharge lamp 5, the discharge lamp 5 is maintained in a lighted state with a certain brightness.

  On the other hand, in the warm-up period immediately after the lighting switch of the discharge lamp 5 is turned on, the control circuit 10 supplies a larger electric power to the discharge lamp 5 than in the normal lighting state in order to light the discharge lamp 5. In this manner, the DC booster 3 and the like are controlled. In such a warm-up state of the discharge lamp 5, the lamp voltage VL fluctuates without being stable, while a larger lamp current IL is supplied to the discharge lamp 5. FIG. 4 is a timing chart showing the operation of the lighting device 1 when the third lamp voltage VL3 lower than the first lamp voltage VL1 is applied to the discharge lamp 5 during the warm-up period.

  As shown in the figure, the lighting device 1 basically operates in the same manner as the normal lighting control described above even during the warm-up period. For example, the timing t11 from the state where the third lamp voltage VL3 is applied and the lamp current IL having the third current value IL3 larger than the first current value IL1 is stably supplied to the first energization path. When the polarity switching is started at, the lamp current IL is gradually attenuated, the energization path is switched at timing t12, and energization through the second energization path is started. The lamp current IL is stabilized at the fourth current value IL4 having the same magnitude as the third current value IL3 at the timing t13.

  Further, since the larger third current value IL3 is energized, a larger re-ignition voltage is generated, and the ramp voltage VL reaches the fourth voltage VL4 that is larger than the second voltage VL2. It attenuates and stabilizes at the third voltage VL3 at timing t14 after timing t13.

  Further, in the stable period immediately before the timing t11, the second mask period longer than the first mask period TM based on the above-described equation (1) according to the third current value IL3 and the third voltage VL3. TM2 is calculated, and the mask signal SM is switched on until the second timer period TM2 elapses from the timing t11, so that the detection of extinction is interrupted during this time. In a stable period T2 from timing t14 to t15, a constant third lamp voltage VL3 is applied to the discharge lamp 5 and a lamp current IL having a constant fourth current value IL4 is energized.

  Then, at timing t15 when a predetermined second polarity switching period TF2 has elapsed from timing 11, polarity switching is started again, and at the timing t16, the energization path of the lamp current IL is switched from the second to the first energization path. At time t17, the lamp current IL is stabilized at the third current value IL3. Similarly to the timings t11 to t14, a re-ignition voltage is generated from the timings t17 to t18, and after the ramp voltage VL4 temporarily rises to the fourth voltage VL4, it returns to the third voltage VL3 and becomes stable. . In addition, from the timing t15, the mask signal is turned on and the detection of extinction is interrupted only during the second mask period TM2 calculated in the stable period T2.

  After that, the polarity switching is repeated every second polarity switching period TF2, whereby the energization direction of the lamp current IL is switched every second polarity switching period TF2, and the discharge lamp 5 is supplied with an alternating current. Is energized. Then, the control circuit 10 gradually decreases the power supplied to the discharge lamp 5 when the discharge lamp 5 shifts from the warm-up state to the normal control state, so that the first voltage VL1 is stably output. Controls the DC booster 3 and the like.

  On the other hand, as the cumulative lighting period of the discharge lamp 5 increases, secular change occurs in the discharge lamp 5, whereby the relationship between the lamp current IL and the lamp voltage VL gradually changes. Specifically, when the two electrodes deteriorate, the distance between the electrodes gradually increases, and as a result, the discharge resistance increases. On the other hand, since the control circuit 10 controls the DC boosting unit 3 and the like so as to supply constant power, the lamp voltage VL increases while the lamp current IL decreases as the discharge resistance increases. FIG. 5 is a timing chart showing the operation of the lighting device 1 when the discharge lamp 5 having undergone secular change is controlled to be in a lighting state.

  As shown in the figure, even when the discharge lamp 5 has changed over time, the lighting device 1 operates in the same manner as the normal lighting control described above. In this case, the fifth voltage VL5 larger than the first voltage VL1 is applied to the discharge lamp 5, and the lamp current IL having the fifth current value IL5 smaller than the first current value IL1 is supplied to the first energization path. When the polarity switching is started at the timing t21 from the energized state, the lamp current IL gradually decreases, and energization is started in the second energization path at the timing t22. The lamp current IL is stabilized at the sixth current value IL6 having the same magnitude as the fifth current value IL5 at the timing t23.

  Further, since the lamp current IL having the smaller fifth current value IL5 is energized, a smaller re-ignition voltage is generated, and the lamp voltage VL is attenuated after reaching the sixth lamp voltage VL6. Then, at the timing t24 after the timing t23, the fifth ramp voltage VL5 is stabilized.

  Further, according to the fifth voltage VL5 and the fifth current value IL5 detected in the stable period immediately before the timing t21, the third timer shorter than the first timer period TM1 based on the above-described equation (1). The period TM3 is calculated, and the detection of extinction is interrupted until the third timer period TM3 elapses from the timing t21. Then, in a stable period T3 from timing t24 to t25, a constant fifth voltage VL5 is applied to the discharge lamp 5, and a constant sixth current IL6 lamp having the same magnitude as the fifth current value IL5 is applied. The current IL is energized.

  Then, at timing t25 when a predetermined third polarity switching period TF3 has elapsed from timing t21, polarity switching is started again, and at timing t26, the energization path of the lamp current IL is switched from the second to the first energization path. At timing t27, the lamp current IL is stabilized at the fifth current value IL5. Similarly to the timings t21 to t24, a re-ignition voltage is generated from the timings t27 to t28, and after the ramp voltage VL temporarily rises to the sixth voltage VL6, it returns to the fifth voltage VL5 and is stabilized. . Further, only during the third mask period TM3 calculated in the stable period T3, the mask signal is turned on from the timing t25, and the detection of extinction is interrupted.

  After this, the polarity switching is repeated every third polarity switching period TF3, whereby the energizing direction of the lamp current IL is switched every third polarity switching period TF3, and the lighting state of the discharge lamp 5 is changed. Is maintained.

  FIG. 6 is a timing chart showing a comparative example of the lighting device 1 according to the above-described embodiment. In the lighting device according to this comparative example, in order to prevent erroneous detection of extinction at the time of polarity switching, the warm-up state and aging of the discharge lamp 5 are changed so that the period required for polarity switching does not exceed the mask period TM. Considering this, the predetermined period TMa is set as the mask period TM. That is, the predetermined period TMa is set to be at least longer than the mask period TM in the warm-up state, which is longer than the period required for polarity switching compared to the normal lighting state or the like.

  In this comparative example, the voltage VLa is applied to the discharge lamp 5 and the lamp current IL having the current value ILa is applied to the first energization path, and then the lamp current is applied to the second energization path at the timing ta. Polarity switching is started so that IL is energized, and detection of extinction is interrupted. At the timing ta, the polarity switching is started. For example, when the extinction occurs when the lamp current IL becomes 0 at the timing tb, it is not yet detected that the extinction has occurred since the predetermined period TMa has elapsed. .

  Then, at the timing tc when the predetermined period TMa has elapsed, the detection of the disappearance is resumed, and at this time, the occurrence of the disappearance is detected. That is, there is a delay in the detection of the extinction during the detection delay period TDa between timings tb and tc. Further, the ramp voltage VL rises to the voltage VLb from the timing ta due to the occurrence of the re-ignition voltage. When the re-lighting operation of the discharge lamp 5 is started at the timing tc when the extinction is detected, the DC boosting unit 3 and the like are controlled so that a larger voltage is supplied to the discharge lamp 5, thereby the lamp voltage VL. Further rises from the voltage VLb.

  As described above, as a result of the delay in the detection of the extinction, the temperature of the electrode decreases during the detection delay period TDa, so that the discharge lamp 5 does not immediately light up again. When the lamp voltage VL reaches the relighting voltage VLc at the time td when the relighting period Ta has elapsed from the timing tc, the insulation between the electrodes is broken, and a short circuit current having a relatively large current value ILc is instantaneously generated between the electrodes. The discharge lamp 5 is turned on again. Thus, during the extinguishing period Tb from timing tb to td, the lamp lamp IL is not energized, and the discharge lamp 5 continues to be extinguished.

  When the discharge lamp 5 is turned on again at the timing td, the control of the DC boosting unit 3 and the like is returned from the relighting operation to the control of the normal lighting state, and the lamp voltage VL is controlled to be lowered to the voltage VLa and stabilized. Is done. Further, the lamp current IL increases to a current value ILb having the same magnitude as the current value ILa at the start of polarity switching and is stabilized.

  On the other hand, when the present invention is applied to this comparative example, a mask period TMb shorter than the predetermined period TMa is calculated based on the above-described equation (1) according to the voltage VLa and the current value ILa. As a result, since extinction is detected at timing tx before timing tc, the detection delay period TDb from the occurrence of extinction to detection is shorter than the detection delay period TDa of the above-described comparative example.

  Thus, as a result of detecting the extinction earlier, the temperature drop of the electrode of the discharge lamp 5 when the relighting operation is started becomes smaller, and the voltage necessary for relighting is also the relighting voltage VLc described above. Smaller than. Thereby, the re-lighting period Ta and the light-off period tb are also shortened, and the discharge lamp 5 is re-lighted earlier, and the power consumed for re-lighting is suppressed.

  As described above, according to the lighting device 1 according to the embodiment, the switching period required to switch the polarity of the discharge lamp 5 is calculated as the mask period TM, and from when the polarity switching is started until the mask period TM elapses. The detection of extinction based on the magnitude of the lamp current IL is interrupted. As a result, false detection of extinction during execution of polarity switching can be prevented, and re-lighting operation associated with erroneous detection can be prevented, so that the discharge lamp 5 is stably lit at a constant brightness. Can be maintained.

  Further, the mask period TM having the optimum length is calculated according to the detected mask voltage VL and the magnitude of the lamp current IL, that is, according to the lighting state of the discharge lamp 5 such as the normal lighting state and the warm-up state. Is done. Thereby, even if the extinction occurs during the switching period, the detection of the extinction is immediately resumed when the polarity switching is completed, so the period from the occurrence of the extinction until the relighting operation of the discharge lamp 5 is executed. Can be minimized while preventing false detection of disappearance. Further, since the relighting operation of the discharge lamp 5 is immediately started with the end of the polarity switching in this way, the temperature drop of the electrode of the discharge lamp 5 due to the extinction is suppressed. As a result, since the discharge lamp 5 can be relighted earlier, it is possible to suppress a reduction in power and visibility required for relighting.

  The period required for polarity switching varies according to the lamp voltage VL and the lamp current IL at the start of polarity switching, so that a constant lamp voltage VL is applied during a stable period immediately before the polarity switching is started. When the constant lamp current IL is energized, the magnitudes of the lamp voltage VL and the lamp current IL are detected, and the mask period TM is calculated based on these. As a result, the mask period TM can be accurately calculated as being closer to the period actually required for polarity switching.

  The mask period TM is shorter as the lamp voltage VL detected in the stable period is higher, and longer as the lamp current IL detected in the stable period is larger. Calculated based on 1). Thus, the mask period TM can be calculated with higher accuracy while reflecting the respective relationships between the lamp voltage VL and the lamp current IL and the actual polarity switching period.

  Further, since the coil L is connected in series with the discharge lamp 5 between the first and second intermediate terminals 4a and 4b of the inverter circuit 4, a current due to the inductance H is energized when switching the polarity. The polarity of the discharge lamp 5 can be switched smoothly.

  In the above-described embodiment, the lighting device 1 has been described as a lighting device for a headlamp mounted on a vehicle. However, the lighting device 1 is not limited to this, and is used for various other purposes such as indoor lighting and industrial use. It can also be applied to a discharge lamp lighting device used. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 lighting device 2 DC power supply
4 Inverter circuit (lighting circuit)
5 Discharge lamp 6 Voltage detection circuit 7 Current detection circuit 11 Polarity switching control circuit (lighting circuit)
12 Mask signal generation circuit (switching period calculation means)
13 Signal mask circuit (detection interruption means)
14 Disappearance determination circuit (disappearance detection means)
15 Power control circuit (relighting means)
L coil (inductor)

Claims (6)

A discharge lamp lighting device (1) for lighting a discharge lamp (5) with electric power supplied from a power source (2),
An inductor (L) connected in series with the discharge lamp; energization from one electrode side of the discharge lamp to the other electrode side; and energization from the other electrode side to the one electrode side; A lighting circuit (4) for lighting the discharge lamp by periodically repeating polarity switching for switching between
A voltage detection circuit (6) for detecting a voltage (VL) applied from the power source to the discharge lamp;
A current detection circuit (7) for detecting the magnitude of the current (IL) energized in the discharge lamp;
A extinction detection means (14) for detecting whether or not the discharge lamp has extinguished based on the magnitude of the detected current;
Re-lighting means (15) for re-lighting the discharge lamp when occurrence of the turn-off is detected by the turn-off detecting means;
A switching period calculation means for calculating a switching period (mask period TM) from the start to the end of the polarity switching based on at least one of the voltage detected by the voltage detection circuit and the magnitude of the current detected by the current detection circuit. (Mask signal generation circuit 12);
Detection interruption means (13) for interrupting detection of the extinction by the extinction detection means during the switching period calculated by the switching period calculation means when the polarity switching is performed by the lighting circuit;
A discharge lamp lighting device comprising: The lighting circuit applies a constant voltage to the discharge lamp and applies a constant current in a stable period until the next polarity switching is performed after the polarity switching is performed,
The switching period calculation means is configured to execute the next polarity switching based on at least one of the voltage detected by the voltage detection circuit and the magnitude of the current detected by the current detection circuit in the stable period. The discharge lamp lighting device according to claim 1, wherein the switching period is calculated.   The switching period calculation means calculates the switching period based on both the voltage detected by the voltage detection circuit and the magnitude of the current detected by the current detection circuit. The discharge lamp lighting device described.   The switching period calculation means calculates the switching period so that the switching period becomes longer as the magnitude of the current detected by the current detection circuit is larger in the stable period. 4. A discharge lamp lighting device according to 3.   5. The switching period calculation means calculates the switching period so that the switching period becomes shorter as the voltage detected by the voltage detection circuit is larger in the stable period. 6. The discharge lamp lighting device described in 1. The lighting circuit is
The first and third switch elements disposed on the power supply side, and the second and third switch elements disposed on the ground (8) side having a lower voltage than the power supply and connected in series to the first and third switch elements, respectively. A bridge circuit having a fourth switch element;
Polarity switching that is connected to the first to fourth switch elements and performs the polarity switching by switching the energization direction between the electrodes of the discharge lamp by a combination of on / off of the first to fourth switch elements. A control circuit (11);
Have
The discharge lamp and the inductor are connected between a first intermediate terminal between the first and second switch elements and a second intermediate terminal between the third and fourth switch elements. The discharge lamp lighting device according to any one of claims 1 to 5, characterized in that:

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