Discharge lamp lighting device and headlight using same

The present invention relates to a discharge lamp lighting device and a headlight using the discharge lamp lighting device.

Conventionally, high-pressure discharge lamp lighting devices used for lighting high-pressure discharge lamps have been proposed (for example, see JP 2010-135195 A (hereinafter, referred to as “Literature 1”)). In the high-pressure discharge lamp lighting device disclosed in Literature 1, a full bridge circuit converts a DC output of a step-down chopper circuit into an AC current having a rectangular wave and supplies the AC current to a lamp (high-pressure discharge lamp).

In this high-pressure discharge lamp lighting device, by applying a high-voltage pulse to a lamp using an igniter circuit at a startup time, insulation breakdown of the lamp is caused, and glow discharge occurs. Thereafter, the lamp transits to arc discharge from the glow discharge, so that light fluxes rise.

The full-bridge circuit is configured by connecting first and second arms each formed by a series circuit of two transistors in parallel with each other, a set of transistors that are diagonally located are caused to be simultaneously in the On state, and On/Off of each set is alternately switched. Here, out of the transistors configuring each arm, a high potential-side transistor is caused to be in the On state when a low potential-side transistor is in the Off state. Thus, in order to cause the high potential-side transistor to be in the On state, a bootstrap capacitor supplying electric charge to a gate electrode of the transistor is arranged.

Here, in an unloaded condition before the startup of the discharge lamp, it may be considered to perform a startup operation in a speedy manner by shortening a time required for raising the output voltage of the step-down chopper circuit up to a predetermined voltage by operating the step-down chopper circuit during the process of charging the bootstrap capacitor. However, in a case where the full bridge circuit is operated in a state in which the output voltage of the step-down chopper circuit is raised by operating the step-down chopper circuit during the process of charging the bootstrap capacitor, when the load forms a short circuit, there is a problem in that an overcurrent flows in the circuit.

In addition, in the high-pressure discharge lamp lighting device disclosed in Literature 1, in a case where the step-down chopper circuit is a non-insulation type, when the load forms a short circuit at the start-up time, energy input from the power supply side is delivered to the output side even in a case where the step-down chopper circuit is stopped, and there is a problem in that an overcurrent flows in the circuit.

The present invention has been made in view of such a problem, and an object thereof is to provide a discharge lamp lighting device and a headlight using the discharge lamp lighting device, configured to make it difficult for an overcurrent to flow in the circuit when an abnormality such as formation of a short circuit occurs.

A discharge lamp lighting device according to the present invention includes a DC/DC converter, a DC/AC inverter, a drive unit, a measurement unit, and a control unit. The DC/DC converter is configured to convert an input voltage input from a DC power supply into a voltage value that is necessary for lighting a discharge lamp by performing switching. The DC/AC inverter is configured by a bridge circuit in which at least one series circuit of a first switching element disposed on a high potential side and a second switching element disposed on a low potential side is connected between output terminals of the DC/DC converter, and is configured to convert a DC output of the DC/DC converter into an AC output and supply the AC output to a load including the discharge lamp. The drive unit converts the DC output of the DC/DC converter into an AC output acquired by alternating polarity of the DC output at a predetermined period by alternately turning on the first switching element and the second switching element at the predetermined period at least at a time of stable lighting. The measurement unit measures at least one of an output voltage and an output current for the load. When a measured value acquired by the measurement unit is in an abnormal range, the control unit is configured to decrease power to be supplied to the discharge lamp to be lower than power to be supplied to the discharge lamp at a normal time. The drive unit includes a capacitor that supplies, to a control electrode of the first switching element disposed on the high potential side, electric charge necessary for turning on the first switching element when the second switching element disposed on the low potential side is turned off. The capacitor is charged when the second switching element is turned on. When the discharge lamp is started up, the capacitor is started to be charged before the DC/DC converter starts to be operated, and the DC/DC converter and the DC/AC inverter are operated after completion of the charging of the capacitor. The control unit has a determination period for determining presence/absence of an abnormality based on the measured value acquired by the measurement unit in this state.

In this discharge lamp lighting device, it is preferable that, when the measured value acquired by the measurement unit is in the abnormal range during the determination period, the control unit is configured to stop a switching operation of the DC/DC converter.

In addition, in this discharge lamp lighting device, it is preferable that the control unit is configured to detect formation of a short circuit in the load as the abnormality based on the measured value acquired by the measurement unit during the determination period.

In addition, in this discharge lamp lighting device, it is preferable that the drive unit is configured to charge the capacitor again in a case where the control unit determines that no abnormality is present during the determination period.

In addition, in this discharge lamp lighting device, it is preferable that the measurement unit is configured to measure an output current of the DC/DC converter during the determination period, and the control unit is configured to determine that formation of a short circuit has occurred in the load when a current value measured by the measurement unit is a predetermined threshold current or more.

In addition, in this discharge lamp lighting device, it is preferable that the measurement unit is configured to measure an output voltage of the DC/DC converter during the determination period, and the control unit is configured to determine that formation of a short circuit has occurred in the load when a voltage value measured by the measurement unit is a predetermined threshold voltage or less.

In addition, in this discharge lamp lighting device, it is preferable that the measurement unit is configured to measure both an output current and an output voltage of the DC/DC converter during the determination period, and the control unit is configured to determine that formation of a short circuit has occurred in the load when the current value measured by the measurement unit is a predetermined threshold current or more, and the voltage value measured by the measurement unit is a predetermined threshold voltage or less.

In addition, in this discharge lamp lighting device, it is preferable that, when determining that the abnormality has occurred during the determination period, the control unit is configured to turn off the first switching element disposed on the high potential side within a predetermined time.

In addition, in this discharge lamp lighting device, it is preferable that the DC/DC converter is of a non-insulating type.

A headlight according to the present invention includes one of the discharge lamp lighting devices described above.

According to the present invention, a discharge lamp lighting device suppressing the flow of an overcurrent in the circuit at the time of the occurrence of an abnormality such as formation of a short circuit can be realized.

In addition, a headlight suppressing the flow of an overcurrent in the circuit of a discharge lamp lighting device at the time of the occurrence of an abnormality such as formation of a short circuit can be realized.

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to Embodiment 1.

FIG. 2 is a circuit diagram that illustrates a main portion of the discharge lamp lighting device according to Embodiment 1.

FIG. 3 is a waveform chart that illustrates an operation of the discharge lamp lighting device according to Embodiment 1 from start-up to stable lighting.

FIG. 4 is a waveform chart that illustrates an operation of a DC/AC inverter of the discharge lamp lighting device according to Embodiment 1.

FIGS. 5A to 5G are waveform charts of units that illustrate the operation of the discharge lamp lighting device according to Embodiment 1.

FIGS. 6A to 6H are waveform charts of units that illustrate the operation of a discharge lamp lighting device according to Embodiment 2.

FIGS. 7A to 7H are waveform charts of units that illustrate a different operation of the discharge lamp lighting device according to Embodiment 2.

FIGS. 8A to 8I are waveform charts of units that illustrate another different operation of the discharge lamp lighting device according to Embodiment 2.

FIGS. 9A to 9G are waveform charts of units that illustrate still another different operation of the discharge lamp lighting device according to Embodiment 2.

FIGS. 10A to 10H are waveform charts of units that illustrate yet another different operation of the discharge lamp lighting device according to Embodiment 2.

FIG. 11 is a circuit diagram of a discharge lamp lighting device according to Embodiment 3.

FIGS. 12A to 12I are waveform charts of units that illustrate an operation of the discharge lamp lighting device according to Embodiment 3.

FIGS. 13A to 13I are waveform charts of units that illustrate an operation of the discharge lamp lighting device according to Embodiment 3.

FIG. 14 is a diagram that schematically illustrates a vehicle in which a headlight according to Embodiment 4 is mounted.

Hereinafter, embodiments in which a discharge lamp lighting device according to the present invention is applied to a lighting device for a high-pressure discharge lamp will be described with reference to the drawings. As examples of the high-pressure discharge lamp, there are a metal halide lamp, a high-pressure sodium lamp, and the like. Compared to an incandescent lamp, such high-pressure discharge lamps have a high luminance level and a long life and are also used as headlights of vehicles.

(Embodiment 1)

FIG. 1 illustrates a circuit diagram of a discharge lamp lighting device A according to this embodiment. This discharge lamp lighting device A includes a DC/DC converter 1 , a DC/AC inverter 2 , a measurement unit 3 , a control unit 4 , a startup auxiliary circuit unit 5 , a startup voltage generating circuit unit 6 , an igniter unit 7 , a power supply voltage measuring unit 8 , a temperature measuring unit 9 , and a drive unit 10 .

The DC/DC converter 1 is configured by a fly-back type converter circuit that boosts a power supply voltage of a DC power supply E 1 to a desired voltage value. The DC/DC converter 1 includes: a transformer T 1 , a switching element Q 1 configured by a field effect transistor, a diode D 1 , and capacitors C 1 and C 2 . The capacitor C 1 is connected across the DC power supply El through a power supply switch SW 1 . Across the capacitor C 1 , a series circuit of a primary winding P 1 of the transformer T 1 and the switching element Q 1 is connected. One end side of a secondary winding S 1 of the transformer T 1 is connected to the negative electrode side of the DC power supply E 1 , and the capacitor C 2 is connected across the secondary winding S 1 through the diode D 1 . Here, the winding directions of the primary winding P 1 and the secondary winding S 1 of the transformer T 1 are opposite to each other.

The DC/AC inverter 2 includes switching elements Q 2 to Q 5 each configured by a field effect transistor (FET) and a drive circuit (drive unit) 2 a . The DC/AC inverter 2 is configured to convert a DC voltage output from the DC/DC converter 1 into a low-frequency rectangular wave AC voltage and supplies the AC voltage to a load 11 (see FIG. 2 ) including a high-pressure discharge lamp LP 1 . A first arm that is configured by a series circuit of the switching elements Q 2 and Q 4 and a second arm that is configured by a series circuit of the switching elements Q 3 and Q 5 are connected between output terminals of the DC/DC converter 1 . Between a connection point X 1 of the switching elements Q 2 and Q 4 configuring the first arm and a connection point X 2 of the switching elements Q 3 and Q 5 configuring the second arm, the high-pressure discharge lamp LP 1 that is a load is connected through the igniter unit 7 . Here, the switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 are not limited to FETs but, for example, may be switching elements such as bipolar transistors or IGBTs.

The measurement unit 3 is configured to measure an output voltage V 3 and an output current I 1 for the high-pressure discharge lamp LP 1 that is the load. In this embodiment, the measurement unit 3 , in order to measure the output voltage V 3 , includes a series circuit of resistors R 1 , R 2 , and R 3 connected to the high-potential side output terminal of the DC/DC converter 1 and measures a voltage V 5 that is proportional to the output voltage V 3 . In addition, the measurement unit 3 , in order to measure the output current I 1 , includes a resistor R 4 used for current detection, which is connected between the DC/DC converter 1 and the DC/AC inverter 2 , and measures a voltage V 4 generated across the resistor R 4 according to the flow of the output current I 1 in the resistor R 4 .

The startup auxiliary circuit unit 5 includes a series circuit of resistors R 5 and R 6 and a capacitor C 3 connected between the output terminals of the DC/DC converter 1 , and a diode D 2 connected to the resistor R 6 in parallel therewith. The anode of the diode D 2 is connected to the capacitor C 3 , and the cathode of the diode D 2 is connected to the resistor R 5 . At the unloaded time before the startup of the high-pressure discharge lamp LP 1 , the capacitor C 3 is charged according to the output voltage of the DC/DC converter 1 . Then, immediately after the high-pressure discharge lamp LP 1 is lighted, during a period in which the DC/DC converter 1 cannot be operated, in order not to cause the high-pressure discharge lamp LP 1 to fade away, electric charge charged in the capacitor C 3 is supplied to the high-pressure discharge lamp LP 1 through the diode D 2 and the resistor R 5 .

The startup voltage generating circuit unit 6 is a circuit that generates a high voltage causing a discharge gap SG 1 of the igniter unit 7 , which will be described later, to be broken down and, for example, is a multi-stage voltage boosting circuit configured by a capacitor and a diode, a voltage boosting circuit that boosts a voltage according to a winding ratio of a transformer, or the like.

The igniter unit 7 includes a voltage boosting transformer T 2 , a discharge gap SG 1 , and capacitors C 4 and C 5 . The capacitor C 4 is connected between the connection point X 1 and the connection point X 2 , and the capacitor C 5 is connected between the output terminal of the startup voltage generating circuit unit 6 and the connection point X 2 . In addition, a series circuit of the secondary winding S 2 of the voltage boosting transformer T 2 and the high-pressure discharge lamp LP 1 is connected between the connection point X 1 and the connection point X 2 , and a series circuit of the primary winding P 2 of the voltage boosting transformer T 2 and the discharge gap SG 1 is connected between the output terminal of the startup voltage generating circuit unit 6 and the connection point X 2 . At the time of a startup/lighting operation, a high voltage is applied from the startup voltage generating circuit unit 6 to the discharge gap SG 1 , and, when the discharge gap SG 1 is broken down, a high-pressure pulse of about several tens of kV boosted according to the winding ratio is applied to the high-pressure discharge lamp LP 1 through the secondary winding S 2 .

The control unit 4 includes a power target storing unit 4 a , a stable power limiting unit (stable power control unit) 4 b , a current target calculating unit 4 c , an error amplifier 4 d , a drive control unit 4 e , and an abnormality determining unit 4 f , and is configured to control On/Off of the switching elements Q 1 to Q 5 .

In the power target storing unit 4 a , a target value of power output from the DC/DC converter 1 is stored in advance. The stable power limiting unit 4 b corrects the target value of the power that is stored in the power target storing unit 4 a based on a temperature measured by the temperature measuring unit 9 or a power supply voltage of the DC power supply E 1 that is measured by the power supply voltage measuring unit 8 and outputs a target value after the correction to the current target calculating unit 4 c . The current target calculating unit 4 c acquires a target value of the output current I 1 by dividing the target value of the power that is input from the stable power limiting unit 4 b by an output voltage acquired based on the voltage V 5 measured by the measurement unit 3 . The error amplifier 4 d compares the target value of the output current I 1 that is acquired by the current target calculating unit 4 c with the output current I 1 acquired based on the voltage V 4 measured by the measurement unit 3 , and outputs a signal acquired by amplifying an error therebetween to the drive unit 10 . The drive unit 10 , according to the signal input from the error amplifier 4 d , controls the duty ratio of a signal LF 3 to be applied to the gate electrode of the switching element Q 1 such that the measured value of the output current I 1 coincides with the target value.

By controlling the operation of the drive circuit 2 a , the drive control unit 4 e performs switching of the four switching elements Q 2 to Q 5 included in the DC/AC inverter 2 between On/Off. Here, the On/Off operations of the switching elements Q 2 to Q 5 will be described in more detail with reference to a circuit diagram of FIG. 2 . FIG. 2 illustrates details of a circuit portion that drives the switching elements Q 2 and Q 4 configuring the first arm, and the other circuit configurations are not illustrated therein.

Between the connection point X 1 of the switching elements Q 2 and Q 4 and the connection point X 2 of the switching elements Q 3 and Q 5 , the load 11 including the high-pressure discharge lamp LP 1 is connected.

The drive circuit 2 a includes a drive circuit 22 that is connected between the gate and the source of the high-potential side switching element (first switching element) Q 2 , and a drive circuit 24 that is connected between the gate and the source of the low-potential side switching element (second switching element) Q 4 . The drive circuit 24 driving the second switching element Q 4 disposed on the low potential side receives an operation voltage Vcc from a drive power supply (not illustrated in the figure) that receives the supply of power from the DC power supply E 1 and generates operation power of the control unit 4 and the like. On the other hand, the drive circuit 22 driving the first switching element Q 2 disposed on the high potential side, in order to cause the first switching element Q 2 to become On in the Off state of the second switching element Q 4 disposed on the low potential side, causes the first switching element Q 2 to become On using the electric charge charged in the bootstrap capacitor C 6 (a current path RT 1 illustrated in FIG. 2 ). One end of the bootstrap capacitor C 6 is connected to the drive power supply through the diode D 3 , and the other end of the bootstrap capacitor C 6 is connected to the connection point X 1 .

By causing the first switching elements Q 2 and Q 3 and the second switching elements Q 4 and Q 5 to alternately become On at a predetermined period at least at the time of stable lighting, the drive circuit 2 a is configured to convert an DC output of the DC/DC converter 1 into an AC output by alternating the polarity of the DC output at a predetermined period.

When the high-pressure discharge lamp LP 1 is started up, the abnormality determining unit 4 f is configured determine presence/absence of an abnormality based on at least one of the output voltage and the output current measured by the measurement unit 3 .

Next, the operation of the discharge lamp lighting device

A will be described. This discharge lamp lighting device A, as illustrated in FIG. 3 , transits to a stable lighting mode MD 5 through four operation modes MD 1 to MD 4 .

The mode MD 1 illustrated in FIG. 3 is an operation mode at the unloaded time before the startup of the high-pressure discharge lamp LP 1 , and the high-pressure discharge lamp LP 1 is in an open state. When the power supply switch SW 1 is turned on at the time of starting the mode MD 1 , the control unit 4 starts to operate and starts the voltage boosting operation of the DC/DC converter 1 . When the drive unit 10 turns on the switching element Q 1 in response to a control signal transmitted from the control unit 4 , current flows from the DC power supply E 1 to the primary wiring P 1 of the transformer T 1 and the switching element Q 1 . At this time, current does not flow in the secondary winding S 1 due to a rectification action of the diode D 1 , and the energy is stored in the transformer T 1 . Thereafter, when the drive unit 10 turns off the switching element Q 1 in response to a control signal transmitted from the control unit 4 , current flows through a path of the secondary winding S 1 →the diode D 1 →the capacitor C 2 →the secondary winding S 1 . Accordingly, the energy stored in the transformer T 1 when the switching element Q 1 is turned on is transferred to the capacitor C 2 . The on-duty of the switching element Q 1 is controlled by the control unit 4 , so that the output voltage V 2 of the DC/DC converter 1 is controlled to be a target value. The DC/DC converter 1 performs the voltage boosting operation as described above, so that the output voltage V 2 is increased.

Thereafter, when a transition to the startup mode MD 2 is made, the control unit 4 turns on the switching elements Q 2 and Q 5 and turns off the switching elements Q 3 and Q 4 . When the output voltage V 2 is gradually increased according to the voltage boosting operation of the DC/DC converter 1 , the voltage of the capacitor C 4 of the igniter unit 7 is also increased. Meanwhile, when the voltage applied across the capacitor C 5 exceeds a predetermined threshold level according to an increase in the output voltage of the startup voltage generating circuit unit 6 , the discharge gap SG 1 is broken down, and a high voltage is applied to the primary winding P 2 of the voltage boosting transformer T 2 . At this time, a high-voltage pulse (about several tens of kV) acquired by boosting a high voltage applied to the primary side according to the winding ratio is generated in the secondary winding S 2 . When this high-voltage pulse is applied to the high-pressure discharge lamp LP 1 , insulation breakdown occurs in the high-pressure discharge lamp LP 1 , and glow discharge is started. Immediately after the start of the glow discharge, since the electrode temperature of the high-pressure discharge lamp LP 1 is low, the fading-away may easily occur. Thus, in this embodiment, in order to suppress the occurrence of the fading-away, a DC phase mode MD 3 is arranged in which currents having the same direction are caused to continuously flow to both electrodes for a time longer than that of the time of stable lighting. In addition, during a first period t 2 that is a first half of the DC phase mode MD 3 , the switching elements Q 2 and Q 5 are turned on, the switching elements Q 3 and Q 4 are turned off, and current having the same direction as that of the startup mode MD 2 is caused to flow in a path of the connection point X 1 →the high-pressure discharge lamp LP 1 →the connection point X 2 . Furthermore, during a second period t 3 that is a second half of the DC phase mode MD 3 , the switching elements Q 2 and Q 5 are turned off, the switching elements Q 3 and Q 4 are turned on, and current having a direction opposite to that during the first period t 2 is caused to flow in a path of the connection point X 2 →the high-pressure discharge lamp LP 1 →the connection point X 1 .

When it is determined that the temperatures of both electrodes are sufficiently high, the control unit 4 ends the

DC phase mode MD 3 . Then, by alternately turning on the set of the switching elements Q 2 and Q 5 and the set of the switching elements Q 3 and Q 4 at a predetermined period by controlling the drive circuit 2 a , the control unit 4 converts the DC output into an AC output of a rectangular wave and supplies the AC output to the high-pressure discharge lamp LP 1 . In addition, the control unit 4 compares the target value of the output current that is acquired based on the target value of the output power or the like with a measured value by using the error amplifier 4 d , and controls the output power W 1 of the DC/DC converter 1 by adjusting the on-duty of the switching element Q 1 according to the error amount (modes MD 4 and MD 5 ). Here, the mode MD 4 is an operation mode of a transient state, and the mode MD 5 is an operation mode at the time of stable lighting.

As described above, the discharge lamp lighting device A according to this embodiment performs stable lighting of the high-pressure discharge lamp LP 1 through the modes MD 1 to MD 4 described above (stable lighting mode MD 5 ).

Here, the DC/AC inverter 2 according to this embodiment is of a static electric potential type, and the switching elements Q 2 and Q 5 need to be continuously turned on for a time t 1 from the unloaded operation mode MD 1 before the startup of the high-pressure discharge lamp LP 1 to the first period t 2 of the DC phase mode MD 3 . In order to continuously turn on the switching elements Q 2 and Q 5 for a predetermined time, it is necessary to store electric charge, which is required for operating the first switching element Q 2 to be in the On state for the predetermined time, in the bootstrap capacitor C 6 that supplies the electric charge to the gate electrode of the first switching element Q 2 disposed on the high potential side. In addition, in this embodiment, in order to improve the starting characteristics of the high-pressure discharge lamp LP 1 , the operation of the DC/DC converter 1 is started during the charging process of the bootstrap capacitor C 6 , and a time for the output voltage V 2 of the DC/DC converter 1 to be boosted to a predetermined voltage is shortened.

Here, the On/Off operations of the switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 and the charging operation of the bootstrap capacitor C 6 arranged on the side of the first switching element Q 2 disposed on the high potential side will be described with reference to FIG. 2 . The On/Off operations of the switching elements Q 2 to Q 5 are determined based on control signals LF 1 and LF 2 input to the drive circuit 2 a from the drive control unit 4 e of the control unit 4 .

The control signals input to the drive circuit 2 a from the drive control unit 4 e are boosted by the drive circuits 22 and 24 to voltages required for driving the gate electrodes. Here, since the second switching element Q 4 disposed on the low potential side is turned off when the first switching element Q 2 disposed on the high potential side is turned on, the drive circuit 22 supplies an On voltage to the gate electrode of the first switching element Q 2 using the electric charge charged in the bootstrap capacitor C 6 . While the first switching element Q 2 is turned on, the bootstrap capacitor C 6 is in a discharged state but is not charged, and then, when the first switching element Q 2 is turned off, and the second switching element Q 4 is switched to be turned on, the bootstrap capacitor C 6 is charged again. At this time, as denoted by a dotted line RT 2 in FIG. 2 , current flows through a path of the diode D 3 from the drive power supply→the bootstrap capacitor C 6 →the second switching element Q 4 , so that the bootstrap capacitor C 6 is charged. Accordingly, in a case where the bootstrap capacitor C 6 is to be charged, it is necessary for the control unit 4 to output a signal LF 1 turning off the first switching element Q 2 disposed on the high potential side and a signal LF 2 turning on the second switching element Q 4 disposed on the low potential side. Such a charging system is called a bootstrap system. In addition, also for the first switching element Q 3 and the second switching element Q 5 configuring the second arm, a bootstrap capacitor (not illustrated in the figure) used for driving the first switching element Q 3 disposed on the high potential side is charged using a similar method, and thus, description thereof will not be presented.

In addition, in the transient operation mode MD 4 and the stable lighting mode MD 5 , the control unit 4 alternately controls the switching elements Q 2 to Q 5 , so that the DC output of the DC/DC converter 1 is converted into an AC and is supplied to the high-pressure discharge lamp LP 1 . As illustrated in FIG. 4 , in a case where signal level of the signal LF 1 is a high level H, and the signal level of the signal LF 2 is a low level L, the gate voltages of the switching elements Q 2 and Q 5 become the high level H, and the switching elements Q 2 and Q 5 are turned on, and the switching elements Q 3 and Q 4 are turned off. On the other hand, in a case where signal level of the signal LF 1 is the low level L, and the signal level of the signal LF 2 is the high level H, the gate voltages of the switching elements Q 3 and Q 4 become the high level H, and the switching elements Q 3 and Q 4 are turned on, and the switching elements Q 2 and Q 5 are turned off. Then, by alternately repeating the period of the high level H of the signal LF 1 and the period of the high level H of the signal LF 2 , the set of the switching elements Q 2 and Q 5 and the set of the switching elements Q 3 and Q 4 are alternately switched between On/Off, so that the output of the DC/DC converter 1 is converted into an AC. In addition, between the period of the high level H of the signal LF 1 and the period of the high level H of the signal LF 2 , in order not to simultaneously turn on all the switching elements Q 2 to Q 5 , a dead time td is provided at which the signal levels of both the signals LF 1 and LF 2 are at the low level L. In addition, when both the signals LF 1 and LF 2 are at the high level H, the first switching elements Q 2 and Q 3 disposed on the high potential side are turned off, and the second switching elements Q 4 and Q 5 disposed on the lower potential side are turned on, and an operation of charging the bootstrap capacitor driving the first switching elements Q 2 and Q 3 is performed.

Here, also in this embodiment, when the load (for example, the high-pressure discharge lamp LP 1 ) 11 forms a short circuit at the time of starting up the high-pressure discharge lamp LP 1 , there is a possibility that an overcurrent flows in the circuit according to the electric charge stored in the capacitors C 2 and C 4 after the start of the operation of the DC/AC inverter 2 .

Thus, in this embodiment, as illustrated in FIGS. 5A to 5G , when the DC power supply E 1 is started to be supplied, before time t 11 when the DC/DC converter 1 starts to operate and before the arrival of the output voltage V 2 thereof at a predetermined voltage V 0 , the control unit 4 starts an operation of charging the bootstrap capacitor (a period t 10 illustrated in FIGS. 5A to 5G ). Here, the predetermined voltage V 0 , for example, is a threshold voltage (about 15 V) of the output voltage for which the load is determined to form a short circuit by the control unit 4 . FIGS. 5A to 5G are waveform diagrams of the units at the startup time. FIG. 5A illustrates the input voltage V 1 of the DC/DC converter 1 , FIG. 5B illustrates the signal LF 1 transmitted from the control unit 4 , and FIG. 5C illustrates the signal LF 2 transmitted from the control unit 4 . In addition, FIG. 5D illustrates the output voltage V 2 of the DC/DC converter 1 , and FIG. 5E illustrates the voltage V 3 applied to the high-pressure discharge lamp LP 1 . Furthermore, FIG. 5F illustrates the signal LF 3 transmitted from the control unit 4 , and FIG. 5G illustrates the output current I 1 flowing through the high-pressure discharge lamp LP 1 .

Then, at the time t 11 after the completion of the charging of the bootstrap capacitor, the control unit 4 applies the output voltage V 2 of the DC/DC converter 1 to the load (the high-pressure discharge lamp LP 1 ) by turning on the switching elements Q 2 and Q 5 of the DC/AC inverter 2 . Until a predetermined time t 12 elapses after the time t 11 , the abnormality determining unit 4 f of the control unit 4 determines presence/absence of an abnormality of the load based on at least one of the output voltage V 3 (actually the voltage V 5 ) and the output current I 1 (actually, the voltage V 4 ) measured by the measurement unit 3 . This time t 12 is a determination period for determining presence/absence of an abnormality (for example, formation of a short circuit or a ground fault of the load) of the load.

In a case where the load forms a short circuit, the load impedance is markedly decreased to be lower than that of a normal time, and accordingly, an electric potential difference generated between the output terminals of the DC/DC converter 1 is markedly decreased to be lower than that of the normal time, so that an overcurrent flows between the output terminals of the DC/AC inverter 2 .

In a case where the presence/absence of an abnormality is determined based on the output voltage for the load, the abnormality determining unit 4 f compares a voltage V 5 that is proportional to the output voltage V 3 with a voltage value corresponding to a predetermined threshold voltage. Then, in a case where the output voltage V 3 is the threshold voltage or lower, in other words, in a case where the voltage V 5 is a voltage corresponding to the threshold voltage or lower, the abnormality determining unit 4 f determines that an abnormality has occurred. On the other hand, in a case where the voltage V 5 is higher than the voltage corresponding to the threshold voltage, the abnormality determining unit 4 f determines that no abnormality is present.

On the other hand, in a case where the presence/absence of an abnormality is determined based on the output current for the load, the abnormality determining unit 4 f compares a voltage V 4 that is proportional to the output current I 1 with a voltage value corresponding to a predetermined threshold current. Then, in a case where the output current I 1 is the threshold current or higher, in other words, in a case where the voltage V 4 is a voltage corresponding to the threshold current or higher, the abnormality determining unit 4 f determines that an abnormality has occurred. On the other hand, in a case where the voltage V 4 is lower than the voltage corresponding to the threshold current, the abnormality determining unit 4 f determines that no abnormality is present.

In a case where absence of an abnormality is determined by the abnormality determining unit 4 f in the determination period t 12 , the control unit 4 continues the startup operation (the unloaded operation mode MD 1 ) and performs stable lighting of the high-pressure discharge lamp LP 1 through the modes MD 2 to MD 4 described above. On the other hand, in a case where presence of an abnormality is determined by the abnormality determining unit 4 f in the determination period t 12 , the control unit 4 does not continue the startup operation but stops the operations of the DC/DC converter 1 and the DC/AC inverter 2 (time t 13 illustrated in FIGS. 5A to 5G ).

The discharge lamp lighting device according to this embodiment described above includes the DC/DC converter 1 , the DC/AC inverter 2 , the drive unit (the drive circuit 2 a ), the measurement unit 3 , and the control unit 4 . The DC/DC converter 1 is configured to convert an input voltage V 1 input from the DC power supply E 1 into a voltage value that is necessary for lighting the discharge lamp LP 1 by switching the input voltage V 1 . The DC/AC inverter 2 is configured by the bridge circuit in which at least one series circuit of the first switching elements Q 2 and Q 3 disposed on the high potential side and the second switching elements Q 4 and Q 5 disposed on the low potential side is connected between the output terminals of the DC/DC converter 1 , and is configured to convert the DC output of the DC/DC converter 1 into an AC output, and supply the AC output to the load including the discharge lamp LP 1 . The drive unit is configured to convert the DC output of the DC/DC converter 1 into an AC output acquired by alternating the polarity of the DC output at a predetermined period by alternately turning on the first switching elements Q 2 and Q 3 and the second switching elements Q 4 and Q 5 at a predetermined period at least at the time of stable lighting. The measurement unit 3 is configured to measure at least one of the output voltage V 3 and the output current I 1 for the load. When a measured value acquired by the measurement unit 3 is in an abnormal range, the control unit 4 is configured to decrease the power to be supplied to the discharge lamp LP 1 to be lower than that of the normal time. The drive unit includes the capacitor (the bootstrap capacitor C 6 ) that supplies, to the control electrodes of the first switching elements Q 2 and Q 3 disposed on the high potential side, electric charge that is necessary for turning on the first switching elements Q 2 and Q 3 when the second switching elements Q 4 and Q 5 disposed on the low potential side are turned off. The capacitor is charged when the second switching elements Q 4 and Q 5 are turned on. When the discharge lamp LP 1 is started to operate, the charging of the capacitor is started before the DC/DC converter 1 is started to operate, and, the control unit 4 has the determination period t 12 for determining whether or not an abnormality is present based on a measured value acquired by the measurement unit 3 in a state in which the DC/DC converter 1 and the DC/AC inverter 2 are operated after the completion of the charging of the capacitor.

As above, when the discharge lamp is started up (the unloaded operation mode MD 1 illustrated in FIG. 3 ), the control unit 4 starts to charge the bootstrap capacitor before the DC/DC converter 1 is started to operate. Then, the determination period t 12 is provided in which the control unit 4 determines whether or not an abnormality is present based on a measured value acquired by the measurement unit 3 in a state in which the DC/DC converter 1 and the DC/AC inverter 2 are operated after the completion of the charging of the bootstrap capacitor. Then, when the measured value acquired by the measurement unit 3 is in an abnormal range, the control unit 4 decreases the power to be supplied to the load to be lower than that of the normal time (at the time of stable lighting).

Accordingly, after the capacitor operating the first switching elements disposed on the high potential side is charged, in a state in which the DC/AC inverter 2 is started to operate, the presence/absence of an abnormality can be determined based on the measured value acquired by the measurement unit 3 . Then, in a case where the presence of an abnormality is determined during the determination period t 12 , the control unit 4 decreases the power to be supplied to the high-pressure discharge lamp LP 1 to be lower than that of the normal time, and accordingly, an overcurrent flowing through the circuit is decreased, so that heat stress to be applied to the circuit components is suppressed.

In addition, in a case where the presence of an abnormality is determined by the abnormality determining unit 4 f during the determination period t 12 , the control unit 4 may be configured to turn off all of the four switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 by setting the signal levels of both the signals LF 1 and LF 2 to the low level L. In such a case, the flow of an overcurrent in the DC/AC inverter 2 is suppressed, and the circuit can be protected. In addition, in a case where the presence of an abnormality is determined by the abnormality determining unit 4 f during the determination period t 12 , the control unit 4 may be configured to turn off at least the two first switching elements Q 2 and Q 3 disposed on the high potential side. Also in such a case, the flow of an overcurrent in the DC/AC inverter 2 is suppressed, and the circuit can be protected.

As in this discharge lamp lighting device, when an abnormality is determined to have occurred during the determination period t 12 , it is preferable that the control unit 4 is configured to turn off at least all the first switching elements Q 2 and Q 3 disposed on the high potential side within a predetermined time.

In addition, the determination period t 12 is preferably set to a short time as possibly as can so as not to have bad influence on the starting ability of the high-pressure discharge lamp LP 1 . Furthermore, the output voltage V 2 of the DC/DC converter 1 is preferably set according to a rated voltage of the discharge lamp (the high-pressure discharge lamp LP 1 ) of the load, and, in the case of a high-pressure discharge lamp that is generally used, it is preferable that the output voltage is set in the range of 350 V to 450 V. In addition, a time during which the bootstrap capacitor is charged is preferably set to a level of a time in which the charging of the bootstrap capacitor is completed and may be appropriately set according to the capacitance of the bootstrap capacitor. In addition, a frequency at which the DC/AC inverter 2 alternates the polarity of the output voltage of the DC/DC converter 1 is preferably set between 200 to 600 Hz.

(Embodiment 2)

A discharge lamp lighting device A according to Embodiment 2 will be described with reference to FIGS. 6A to 10H .

In the discharge lamp lighting device A according to this embodiment, an abnormality determining operation at the startup time is different from that of the discharge lamp lighting device A according to Embodiment 1, and the circuit configuration and the other operations are similar to those of the discharge lamp lighting device A according to Embodiment 1. Thus, the same reference numeral is assigned to a constituent element that is common to the discharge lamp lighting device A according to Embodiment 1, and description thereof will not be presented.

FIGS. 6A to 6H are waveform diagrams of units at the startup time (the unloaded operation mode MD 1 described in Embodiment 1). FIG. 6A illustrates the input voltage V 1 of a DC/DC converter 1 , FIG. 6B illustrates a signal LF 1 transmitted from a control unit 4 , and FIG. 6C illustrates a signal LF 2 transmitted from the control unit 4 . In addition, FIG. 6D illustrates the output voltage V 2 of the DC/DC converter 1 , and FIG. 6E illustrates a voltage V 3 applied to a high-pressure discharge lamp LP 1 . Furthermore, FIG. 6F illustrates a signal LF 3 transmitted from the control unit 4 , FIG. 6G illustrates an output current I 1 flowing through the high-pressure discharge lamp LP 1 , and FIG. 6H illustrates a voltage V 4 that is generated in a resistor R 4 used for detecting an output current.

In this embodiment, when a DC power supply E 1 is started to be supplied, before the operation of the DC/DC converter 1 is started, the control unit 4 starts the operation of charging a bootstrap capacitor. At time t 11 after the completion of the charging of the bootstrap capacitor, the control unit 4 applies a voltage to the load by turning on switching elements Q 2 and Q 5 of a DC/AC inverter 2 and then starts the voltage boosting operation of the DC/DC converter 1 . Then, until a predetermined time t 12 elapses after the time t 11 , an abnormality determining unit 4 f of the control unit 4 determines the presence/absence of an abnormality of the load based on the output current I 1 measured by a measurement unit 3 , actually, a voltage V 4 generated in a resistor R 4 used for detecting an output current. In other words, the abnormality determining unit 4 f compares the voltage V 4 measured by the measurement unit 3 with a voltage Vth 1 corresponding to a predetermined threshold current. Then, in a case where the voltage V 4 is the voltage Vth 1 or higher (in other words, in a case where the output current I 1 is a threshold current or higher), the abnormality determining unit 4 f determines that an abnormality has occurred. On the other hand, in a case where the voltage V 4 is lower than the voltage Vth 1 , the abnormality determining unit 4 f determines that no abnormality is present. This time t 12 is a determination period in which the presence/absence of an abnormality (for example, formation of a short circuit or a ground fault) of the load is determined. Here, the threshold current is set to a current value that is larger than the range of the output current I 1 flowing though the high-pressure discharge lamp LP 1 of a case where the load including the high-pressure discharge lamp LP 1 is normal and is smaller than current generated at the time of an abnormality such as formation of a short circuit or a ground fault.

In a case where the load forms a short circuit, the load impedance is markedly decreased to be lower than that of a normal time, and accordingly, an electric potential difference generated between the output terminals of the DC/DC converter 1 is markedly decreased to be lower than that of the normal time, so that the output current I 1 that is the threshold current or higher flows between the output terminals of the DC/AC inverter 2 . In this case, the voltage V 4 measured by the measurement unit 3 is the voltage Vth 1 corresponding to the threshold current or higher. Accordingly, since the voltage V 4 is the voltage Vth 1 or higher at time t 15 during the determination period t 12 , the control unit 4 determines that the load forms a short circuit and does not continue the startup operation but stops the operations of the DC/DC converter 1 and the DC/AC inverter 2 (time t 13 ). In addition, after the voltage V 4 is the voltage Vth 1 or higher at the time t 15 , until the operations of the DC/DC converter 1 and the DC/AC inverter 2 are stopped by the control unit 4 , a delay of a time t 16 occurs. This time delay is due to a delay in the circuit feeding back the current value or a delay of the process performed by the control unit 4 .

On the other hand, in a case where the load is normal, during the determination period t 12 described above, the voltage V 4 measured by the measurement unit 3 is lower than the voltage Vth 1 . Thus, since the voltage V 4 is lower than the voltage Vth 1 , the abnormality determining unit 4 f determines absence of an abnormality, and the control unit 4 continues the startup operation and starts and lights the high-pressure discharge lamp LP 1 .

As described above, also in the discharge lamp lighting device A according to this embodiment, when the discharge lamp is started up, the control unit 4 starts charging the bootstrap capacitor before the DC/DC converter 1 is started to operate. Then, after the completion of the charging of the bootstrap capacitor, the voltage boosting operation of the DC/DC converter 1 is started, and the DC/AC inverter 2 is operated (in other words, the switching elements Q 2 and Q 5 are turned on), and the output of the DC/DC converter 1 is applied to the high-pressure discharge lamp LP 1 . A determination period t 12 is provided in which the control unit 4 determines whether or not an abnormality is present based on a measured value acquired by the measurement unit 3 in such a state. Then, when the measured value acquired by the measurement unit 3 is in an abnormal range, the control unit 4 decreases the power to be supplied to the load to be lower than that of the normal time (at the time of stable lighting).

Accordingly, after the capacitor operating the first switching elements disposed on the high potential side is charged, in a state in which the DC/AC inverter 2 is started to operate, and the DC/DC converter 1 is started to operate, the presence/absence of an abnormality can be determined based on the measured value acquired by the measurement unit 3 . Then, in a case where the presence of an abnormality is determined during the determination period t 12 , the control unit 4 decreases the power to be supplied to the high-pressure discharge lamp LP 1 to be lower than that of the normal time, and accordingly, an overcurrent flowing through the circuit is decreased, so that heat stress to be applied to the circuit components is suppressed.

In addition, in a case where the presence of an abnormality is determined by the control unit 4 during the determination period t 12 , the control unit 4 maybe configured to turn off all of the four switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 by setting the signal levels of both the signals LF 1 and LF 2 to the low level L. In such a case, the flow of an overcurrent in the DC/AC inverter 2 is suppressed, and the circuit can be protected. In addition, in a case where the presence of an abnormality is determined by the control unit 4 during the determination period t 12 , the control unit 4 may be configured to turn off at least all the first switching elements Q 2 and Q 3 disposed on the high potential side. Also in such a case, the flow of an overcurrent from the DC/DC converter 1 to the DC/AC inverter 2 is suppressed, and the circuit can be protected.

As in the discharge lamp lighting device according to this embodiment, in a case where the measured value acquired by the measurement unit 3 is in the abnormal range during the determination period t 12 , it is preferable that the control unit 4 is configured to stop the switching operation of the DC/DC converter 1 .

As in the discharge lamp lighting device according to this embodiment, it is preferable that the control unit 4 , during the determination period t 12 , is configured to detect the presence/absence of formation of a short circuit in the load as an abnormality based on the measured value acquired by the measurement unit 3 .

As in the discharge lamp lighting device according to this embodiment, in a case where the control unit 4 determines absence of an abnormality during the determination period t 12 , it is preferable that the drive unit is configured to charge the capacitor (bootstrap capacitor) again.

As in the discharge lamp lighting device according to this embodiment, it is preferable that the measurement unit 3 is configured to measure the output current of the DC/DC converter 1 during the determination period t 12 . In such a case, in a case where a current value measured by the measurement unit 3 is a predetermined threshold current or more, the control unit 4 determines that the formation of a short circuit has occurred in the load.

In this embodiment, during the determination period t 12 , the measurement unit 3 measures the output current I 1 (actually, a voltage V 4 that is proportional to the output current I 1 ) for the load. Then, in a case where the output current I 1 is a predetermined threshold current or higher (in other words, in a case where the voltage V 4 is a voltage Vth 1 corresponding to the threshold current or higher), the control unit 4 determines that formation of a short circuit has occurred in the load.

As above, when the formation of a short circuit occurs in the load, an overcurrent flows from the DC/DC converter 1 to the load side. Accordingly, by detecting the overcurrent, the control unit 4 can reliably detect formation of a short circuit by employing a simple circuit configuration. In addition, also in the discharge lamp lighting device A described in Embodiment 1, it is apparent that the control unit 4 may determine the presence/absence of an abnormality based on the output current measured by the measurement unit 3 .

In the description presented above, during the determination period t 12 , while the control unit 4 determines the presence/absence of an abnormality based on the output current I 1 for the load, the presence/absence of an abnormality may be determined based on the output voltage V 3 for the load.

In other words, during the determination period t 12 , the measurement unit 3 may measure the output voltage of the DC/DC converter 1 . In such a case, in a case where the voltage value measured by the measurement unit 3 is a predetermined threshold voltage or less, the control unit 4 may determine that formation of a short circuit has occurred in the load.

Here, an operation for measuring the output voltage V 3 for the load, actually, the voltage V 5 that is proportional to the output voltage V 3 using the measurement unit 3 and determining the presence/absence of an abnormality based on a measured value using the abnormality determining unit 4 f will be described with reference to FIGS. 7A to 7H . FIGS. 7A to 7H are waveform diagrams of units at the startup time (the unloaded operation mode MD 1 described in Embodiment 1). FIG. 7A illustrates the input voltage V 1 of the DC/DC converter 1 , FIG. 7B illustrates a signal LF 1 transmitted from the control unit 4 , and FIG. 7C illustrates a signal LF 2 transmitted from the control unit 4 . In addition, FIG. 7D illustrates the output voltage V 2 of the DC/DC converter 1 , and FIG. 7E illustrates a voltage V 3 applied to the high-pressure discharge lamp LP 1 . Furthermore, FIG. 7F illustrates a signal LF 3 transmitted from the control unit 4 , FIG. 7G illustrates the output current I 1 flowing through the high-pressure discharge lamp LP 1 , and FIG. 7H illustrates the voltage V 5 measured by the measurement unit 3 .

As illustrated in FIGS. 7A to 7H , at time t 11 after the completion of the charging of the bootstrap capacitor, the control unit 4 applies a voltage to the load by turning on switching elements Q 2 and Q 5 of the DC/AC inverter 2 and then starts the voltage boosting operation of the DC/DC converter 1 . Then, until a predetermined time t 12 elapses after the time t 11 (the determination period described above), an abnormality determining unit 4 f of the control unit 4 compares the voltage V 5 measured by the measurement unit 3 with a voltage Vth 2 corresponding to a predetermined threshold voltage. In a case where the load forms a short circuit, the load impedance is markedly decreased to be lower than that of the normal time, and accordingly, an electric potential difference generated between the output terminals of the DC/DC converter 1 is markedly decreased to be lower than that of the normal time, so that an overcurrent flows between the output terminals of the DC/AC inverter 2 . Thus, during the determination period t 12 , in a case where the output voltage V 3 is the threshold voltage or lower, in other words, in a case where the voltage V 5 is the voltage Vth 2 or lower, the abnormality determining unit 4 f determines that formation of a short circuit has occurred in the load. On the other hand, in a case where the voltage V 5 is above the voltage Vth 2 , the abnormality determining unit 4 f determines that no abnormality is present. In addition, in consideration of a rise time of the voltage V 5 , the abnormality determining unit 4 f determines the presence/absence of formation of a short circuit based on the voltage value V 5 at time t 17 when a predetermined time elapses after the transition to the determination period t 12 . Here, while a delay of a time t 18 from when the formation of a short circuit is determined to have occurred at time t 17 to when the operations of the DC/DC converter 1 and the DC/AC inverter 2 are stopped occurs, this time delay is due to a delay of the process performed by the control unit 4 or the like.

As above, during the determination period t 12 , in a case where the output voltage V 3 is a predetermined threshold voltage or lower, in other words, in a case where the voltage V 5 measured by the measurement unit 3 is the voltage Vth 2 corresponding to the threshold voltage or lower, the abnormality determining unit 4 f of the control unit 4 determines that the load has formed a short circuit. When the formation of a short circuit occurs in the load, the output voltage generated in the load is decreased due to a marked decrease in the load impedance, and accordingly, by measuring the decrease in the output voltage, the control unit 4 can reliably detect the formation of a short circuit in the load by employing a simple circuit configuration. In addition, the threshold voltage is set to a voltage value that is lower than the voltage range of a voltage supplied to the load in a case where the load including the high-pressure discharge lamp LP 1 is normal and is higher than a voltage generated in the load at the time of the occurrence of an abnormality such as formation of a short circuit or a ground fault. In addition, also in the discharge lamp lighting device A described in Embodiment 1, it is apparent that the control unit 4 may determine the presence/absence of an abnormality based on the output voltage measured by the measurement unit 3 .

In addition, during the determination period t 12 , the abnormality determining unit 4 f of the control unit 4 may determine the presence/absence of the formation of a short circuit based on both the output current and the output voltage for the load. In other words, during the determination period t 12 , the measurement unit 3 may measure both the output current and the output voltage of the DC/DC converter 1 . In such a case, the control unit 4 may determine that the formation of a short circuit has occurred in the load in a case where a current value measured by the measurement unit 3 is a predetermined threshold current or more, and a voltage value measured by the measurement unit 3 is a predetermined threshold voltage or less.

The operation of determining the presence/absence of an abnormality based on the output current and the output voltage measured by the measurement unit 3 using the abnormality determining unit 4 f of the control unit 4 will be described with reference to FIGS. 8A to 8I . FIGS. 8A to 8I are waveform diagrams of units at the startup time (the unloaded operation mode MD 1 described in Embodiment 1). FIG. 8A illustrates the input voltage V 1 of the DC/DC converter 1 , FIG. 8B illustrates a signal LF 1 transmitted from the control unit 4 , and FIG. 8C illustrates a signal LF 2 transmitted from the control unit 4 . In addition, FIG. 8D illustrates the output voltage V 2 of the DC/DC converter 1 , and FIG. 8E illustrates a voltage V 3 applied to the high-pressure discharge lamp LP 1 . Furthermore, FIG. 8F illustrates a signal LF 3 transmitted from the control unit 4 , FIG. 8G illustrates the output current I 1 flowing through the high-pressure discharge lamp LP 1 , FIG. 8H illustrates the voltage V 5 measured by the measurement unit 3 , and FIG. 8I illustrates the voltage V 4 measured by the measurement unit 3 .

As illustrated in FIGS. 8A to 8I , at time t 11 after the completion of the charging of the bootstrap capacitor, the control unit 4 applies a voltage to the load by turning on switching elements Q 2 and Q 5 of the DC/AC inverter 2 and then starts the voltage boosting operation of the DC/DC converter 1 . Then, until a predetermined time t 12 elapses after the time t 11 (the determination period t 12 described above), an abnormality determining unit 4 f of the control unit 4 compares the voltage V 5 measured by the measurement unit 3 with the voltage Vth 2 and compares the voltage V 4 measured by the measurement unit 3 with the voltage Vth 1 . In a case where the load forms a short circuit, the load impedance is markedly decreased to be lower than that of the normal time, and accordingly, an electric potential difference generated between the output terminals of the DC/DC converter 1 is markedly decreased to be lower than that of the normal time, so that an overcurrent flows between the output terminals of the DC/AC inverter 2 .

Thus, during the determination period t 12 , in a case where the output current I 1 is the threshold current or higher, and the output voltage V 3 is the threshold voltage or lower, in other words, the voltage V 4 is the voltage Vth 1 or higher, and the voltage V 5 is the voltage Vth 2 or lower, the abnormality determining unit 4 f determines that formation of a short circuit has occurred in the load. On the other hand, in a case where the voltage V 4 is below the voltage Vth 1 , or in a case where the voltage V 5 is above the voltage Vth 2 , the control unit 4 determines that no abnormality is present. Here, the threshold current is set to a current value that is higher than the range of the output current I 1 flowing through the load in a case where the load including the high-pressure discharge lamp LP 1 is normal and is lower than the current generated at the time of the occurrence of an abnormality such as formation of a short circuit or a ground fault. In addition, the threshold voltage is set to a voltage value that is lower than the range of the voltage (the output voltage V 3 ) generated in the load in a case where the load including the high-pressure discharge lamp LP 1 is normal and is higher than the voltage generated in the load at the time of the occurrence of an abnormality such as formation of a short circuit or a ground fault.

As above, during the determination period t 12 , in a case where the output current I 1 is in the current range of the short-circuit state, and the output voltage V 3 is in the range of the voltage of the short-circuit state, the control unit 4 determines that the formation of a short circuit has occurred in the load. Accordingly, during the startup operation, by detecting an abnormal decrease in the output voltage that occurs according to a load abnormality or an overcurrent flowing through the load, the formation of a short circuit can be reliably detected by using a simple circuit. In addition, also in the discharge lamp lighting device A described in Embodiment 1, it is apparent that the control unit 4 may determine the presence/absence of an abnormality based on both the output current and the output voltage measured by the measurement unit 3 .

In addition, in a case where the control unit 4 determines that no abnormality is present during the determination period t 12 , as illustrated in FIGS. 9A to 9G , the control unit 4 causes the DC/DC converter 1 to continue the operation also after the time t 13 when the determination period t 12 ends. Here, at the time t 13 when the determination period t 12 ends, the control unit 4 may recharge the bootstrap capacitor by setting the signal levels of both the signals LF 1 and LF 2 to the high level H. In such a case, the bootstrap capacitor is charged again after the end of the determination period t 12 , the On-time of the first switching element Q 2 that is turned on during the first period t 1 of the startup mode MD 2 or the DC phase mode MD 3 after that can be maintained to be long.

As illustrated in FIGS. 10A to 10H , when the control unit 4 turns on the switching elements Q 2 and Q 5 of the DC/AC inverter 2 during the determination period t 12 , the bootstrap capacitor C 6 is discharged, and the voltage VC 6 between both ends thereof decreases. For this reason, a time during which the first switching element Q 2 can be turned on using the electric charge that is charged in the bootstrap capacitor C 6 is shortened. Thus, during a period t 21 from the time t 13 to the start of the startup mode MD, the control unit 4 performs an operation of charging the bootstrap capacitor C 6 by turning on the second switching elements Q 4 and Q 5 . As above, by recharging the bootstrap capacitor C 6 , electric charge that is necessary for turning on the first switching element Q 2 during the first period t 1 of the startup mode MD 2 or the DC phase mode MD 3 after that can be charged.

Thus, even when the bootstrap capacitor C 6 not having a large electrostatic capacity is used, the first switching element Q 2 disposed on the high potential side can be turned on for a longer time, and a decrease in the size of the circuit can be realized, so that the mounting area can be decreased.

In addition, also in the discharge lamp lighting device A described in Embodiment 1, in a case where the abnormality determining unit 4 f of the control unit 4 determines that no abnormality is present during the determination period, the control unit 4 may restart the operation of charging the bootstrap capacitor. Accordingly, even in a case where the On time is set to be long so as to prevent fading-away when the operation of the DC/AC inverter 2 is started, by recharging the bootstrap capacitor, the On state of the switching element disposed on the high potential side can be maintained to be long.

(Embodiment 3)

A discharge lamp lighting device A according to Embodiment 3 will be described with reference to FIGS. 11 to 13I .

The discharge lamp lighting device A according to this embodiment includes a non-insulating type DC/DC converter 1 , which is different from Embodiments 1 and 2, and the other configurations and operations are similar to those of Embodiments 1 and 2. Thus, the same reference sign is assigned to a constituent element common to Embodiments 1 and 2, and description thereof will not be presented.

The DC/DC converter 1 includes a transformer T 3 including windings P 3 and S 3 that are magnetically coupled, a switching element Q 1 , a diode D 1 , and capacitors C 1 and C 2 . The capacitor C 1 is connected across a DC power supply E 1 through a power supply switch SW 1 . Across the capacitor C 1 , the winding P 3 of the transformer T 3 and the switching element Q 1 are connected in series. One end of the winding S 3 is connected to a connection point of the winding P 3 and the switching element Q 1 , and, between the other end of the winding S 3 and a negative electrode of the DC power supply E 1 , the capacitor C 2 is connected through the diode D 1 . The DC/DC converter 1 illustrated in the figure is configured by a boost chopper circuit, and the operation thereof is conventionally known, and thus detailed description thereof will not be presented. The On/Off of the switching element Q 1 is controlled by the control unit 4 , and a constant voltage acquired by boosting the input voltage is generated between both ends of the capacitor C 2 . Here, as an example, while the boost chopper circuit has been illustrated as the

DC/DC converter 1 that is of the non-insulating type, a step-down chopper circuit or a boost/step-down chopper circuit may be used.

In a case where the DC/DC converter 1 is of the non-insulating type, even in a state in which the DC/DC converter 1 is not operated, when the load forms a short circuit, and switching elements Q 2 and Q 5 of the DC/AC inverter 2 are turned on, an overcurrent flows in a path denoted by a dotted line RT 3 in FIG. 11 .

Thus, also in this embodiment, an abnormality of the load is determined at the startup time. In a case where the load is determined to be abnormal, the operations of the DC/DC converter 1 and the DC/AC inverter 2 are stopped. Here, an operation of determining an abnormality of the load at the startup time will be described with reference to FIGS. 12A to 12I . FIGS. 12A to 12I are waveform diagrams of units at the startup time (the unloaded operation mode MD 1 described in Embodiment 1). FIG. 12A illustrates the input voltage V 1 of the DC/DC converter 1 , FIG. 12B illustrates a signal LF 1 transmitted from the control unit 4 , and FIG. 12C illustrates a signal LF 2 transmitted from the control unit 4 . In addition, FIG. 12D illustrates the output voltage V 2 of the DC/DC converter 1 , and FIG. 12E illustrates a voltage V 3 applied to the high-pressure discharge lamp LP 1 . Furthermore, FIG. 12F illustrates a signal LF 3 transmitted from the control unit 4 , FIG. 12G illustrates the output current I 1 flowing through the high-pressure discharge lamp LP 1 , FIG. 12H illustrates a voltage V 5 measured by the measurement unit 3 , and FIG. 12I illustrates a voltage V 4 measured by the measurement unit 3 .

Also in this embodiment, when the DC power supply E 1 is started to be supplied, the control unit 4 starts the operation of charging the bootstrap capacitor before the DC/DC converter 1 is started to operate. At time t 11 after the completion of the charging of the bootstrap capacitor, the control unit 4 applies a voltage to the load by turning on the switching elements Q 2 and Q 5 of the DC/AC inverter 2 and then starts the voltage boosting operation of the DC/DC converter 1 . Then, until a predetermined time t 12 elapses after the time t 11 , the abnormality determining unit 4 f of the control unit 4 determines presence/absence of an abnormality in the load based on the voltage V 4 (corresponding to the output current I 1 ) and the voltage V 5 (corresponding to the output voltage V 3 ) measured by the measurement unit 3 .

In other words, the abnormality determining unit 4 f compares the voltage V 4 measured by the measurement unit 3 with the voltage Vth 1 corresponding to a predetermined threshold current and compares the voltage V 5 measured by the measurement unit 3 with the voltage Vth 2 corresponding to a predetermined threshold voltage. Then, in a case where the output current I 1 is the threshold current or higher, and the output voltage V 3 is the threshold voltage or lower, in other words, in a case where the voltage V 4 is the voltage Vth 1 or higher, and the voltage V 5 is the voltage Vth 2 or lower, the abnormality determining unit 4 f determines that an abnormality of the load has occurred. On the other hand, in a case where the voltage V 4 is lower than the voltage Vth 1 , or the voltage V 5 exceeds the voltage Vth 2 , the abnormality determining unit 4 f determines that no abnormality is present.

In a case where the load forms a short circuit, the load impedance is markedly decreased to be lower than that of a normal time, and accordingly, an electric potential difference generated between the output terminals of the DC/DC converter 1 is markedly decreased to be lower than that of the normal time, so that the output current I 1 that is the threshold current or higher flows between the output terminals of the DC/AC inverter 2 . In this case, the voltage V 4 measured by the measurement unit 3 is the voltage Vth 1 or higher, and the voltage V 5 measured by the measurement unit 3 is the voltage Vth 2 or lower. Accordingly, since the voltage V 4 is the voltage Vth 1 or higher and the voltage V 5 is the voltage Vth 2 or lower at time t 13 during the determination period t 12 , the control unit 4 determines that the load forms a short circuit and does not continue the startup operation but stops the voltage boosting operation of the DC/DC converter 1 (time t 13 ). Here, since the DC/DC converter 1 is configured by a converter circuit that is of the non-insulating type, also after the operation of the DC/DC converter 1 is stopped at the time t 13 , current continuously flows through the high-pressure discharge lamp LP 1 . Thus, at time t 20 when a predetermined time t 19 elapses after the stop of the operation of the DC/DC converter 1 , all of the four switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 are turned off by the control unit 4 by setting the signal levels of both the signals LF 1 and LF 2 to the low level L. Accordingly, also in a case where the DC/DC converter 1 is of the non-insulating type, the current does not continuously flow through the high-pressure discharge lamp LP 1 that is the load, and, in a case where the load forms a short circuit, a short current can be stopped from continuously flowing through the circuit.

In addition, as illustrated in FIGS. 13A to 13I , in a case where the load is determined to forma short circuit, the control unit 4 , first, may turn off all of the four switching elements Q 2 to Q 5 configuring the DC/AC inverter 2 at time t 13 and then stop the operation of the DC/DC converter 1 at time t 20 . Also in such a case, since the short current can be stopped from continuously flowing through the circuit, a time during which the short current flows in the circuit can be shortened to be less than that of the protection operation illustrated in FIGS. 12A to 12I , and accordingly, stress to be applied to the circuit can be further decreased.

On the other hand, in a case where the load is normal, during the determination period t 12 described above, the voltage V 4 measured by the measurement unit 3 is lower than the voltage Vth 1 , and the voltage V 5 is higher than the voltage Vth 2 .

Thus, since the voltage V 4 is lower than the voltage Vth 1 , or the voltage V 5 is higher than the voltage Vth 2 , the control unit 4 determines absence of an abnormality, continues the startup operation, and starts and lights the high-pressure discharge lamp LP 1 .

As above, also in a case where the DC/DC converter 1 is of the non-insulating type, the load abnormality determination described in Embodiments 1 and 2 is performed, and, in a case where the load is determined to be abnormal, the operations of the DC/DC converter 1 and the DC/AC inverter 2 are stopped, so that an overcurrent flowing through the circuit can be suppressed.

In addition, the control unit 4 may determine the presence/absence of an abnormality in the load based on one of the output voltage and the output current measured by the measurement unit 3 , and an abnormality of the load can be detected by employing a relatively simple circuit configuration for comparing the output voltage or the output current with the threshold.

As in the discharge lamp lighting device according to this embodiment described above, it is preferable that the DC/DC converter 1 is of the non-insulating type.

(Embodiment 4)

An embodiment in which the discharge lamp lighting device

A described in one of Embodiments 1 to 3 is applied to a headlight of a vehicle will be described with reference to FIG. 14 . In other words, the headlight according to this embodiment includes the discharge lamp lighting device A.

The vehicle C includes the high-pressure discharge lamps LP 1 as left and right headlights. In addition, the vehicle C includes the discharge lamp lighting devices A that light the high-pressure discharge lamps LP 1 by using the DC power supply E 1 as a power source. Here, the headlight is configured by the high-pressure discharge lamp LP 1 and the discharge lamp lighting device A.

The discharge lamp lighting device A is one of the discharge lamp lighting devices described in Embodiments 1 to 3, and, in a case where an abnormality of the load including the high-pressure discharge lamp LP 1 is detected, the discharge lamp lighting device stops the operations of the DC/DC converter 1 and the DC/AC inverter 2 , so that an overcurrent is suppressed from flowing through the circuit.

In recent years, in vehicles, the weight and the size are decreased for the improvement of fuel efficiency, and the residential space inside the vehicles is requested to be increased for improving the comfort. As a result, the engine room tends to be small.

Thus, the temperature of the inside of the engine room becomes high, and a distance between the engine having a high temperature and the discharge lamp lighting device A lighting the headlights becomes narrow, and accordingly, the discharge lamp lighting device A is used in the environment of a higher temperature.

In a case where an abnormality of the load is detected at the time of starting up the high-pressure discharge lamp LP 1 , the discharge lamp lighting device A included in the headlight according to this embodiment stops the operations of the DC/DC converter 1 and the DC/AC inverter 2 . Accordingly, an overcurrent can be suppressed from flowing through the circuit, and heat stress to be applied to the circuit components can be decreased. Thus, a headlight including the discharge lamp lighting device A having high robustness also in the case of being used under a high-temperature environment can be realized.