High voltage discharge lamp apparatus for vehicles

• US 6,392,364 B1
• Filed: 06/19/2000
• Issued: 05/21/2002
• Est. Priority Date: 06/21/1999
• Status: Expired due to Term

• Current Assignee: DENSO Corporation, Koito Manufacturing Company Limited
• Original Assignee: DENSO Corporation
• Inventors: Ichikawa, Tomoyuki, Noyori, Yasushi, Okuchi, Hiroaki, Oda, Goichi, Hiranaka, Yukinobu, Yamamoto, Noboru, Hiramatsu, Hiromi, Horii, Yasutoshi, Kajita, Yuji, Yoneima, Kenji, Ishikawa, Masamichi
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Vo, Tuyet Thi
• Application Number:
  US09/597,733
• Time in Patent Office: 701 Days
• Field of Search: 315/291, 315/82, 315/209.R, 315/307, 315/282, 315/DIG.7, 315/57, 315/118, 315/117, 315/209.SC, 315/309
• US Class Current: 315/291
• CPC Class Codes: F21S 41/192 Details of lamp holders, terminals or connectors
• CPC Class Codes: H03K 17/08 Modifications for protecting switching circuit against overcurrent or overvoltage
• CPC Class Codes: H03K 17/16 Modifications for eliminating interference voltages or currents
• CPC Class Codes: H05B 41/02 Details
• CPC Class Codes: H05B 41/2886 comprising a controllable preconditioner, e.g. a booster
• CPC Class Codes: H05B 41/2888 the bridge being commutated at low frequency, e.g. 1kHz
• CPC Class Codes: H05B 41/2923 against abnormal power supply conditions
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A hybrid IC of electronic circuit for a discharge lamp is disposed on the bottom of a metal case. A transformer, an inductor, a transformer, and a capacitor are disposed in a resin case. The resin case is contained in a metal case. In this instance, the transformer, the inductor, the transformer, and the capacitor are located outside the outer periphery of the IC so that the IC does not overlap on the transformer and other components. The transformer for a starter circuit has a secondary winding the inductance of which is 2.5 mH or larger, and a capacitance of a smoothing capacitor of a DC—DC converter is 0.5 μF or smaller. The switching frequency f of a MOS transistor is selected so that L2×C1 is equal to or larger than 1×10⁻¹×f^−1.68.

Claims

1. A discharge lamp apparatus having a DC power source and a discharge lamp comprising:

a transformer for boosting a voltage of the power source;

a switching element connected to a primary side of the transformer; and

power control means for duty-controlling the switching element based on a signal indicating a lighting state of the discharge lamp to thereby control the power supplied to the discharge lamp,

wherein the power control means is provided with power reduction means for reducing the power supplied to the discharge lamp as a temperature increases;

the power reduction means has a plurality of diodes connected in series; and

the power control means controls the power supplied to the discharge lamp based on the temperature characteristic of the diodes.

2. A discharge lamp apparatus having a DC power source and a discharge lamp comprising:

a transformer for boosting a voltage of the power source;

a switching element connected to a primary side of the transformer; and

power control means for duty-controlling the switching element based on a signal indicating a lighting state of the discharge lamp to thereby control the power supplied to the discharge lamp;

wherein the power control means is provided with power reduction means for reducing the power supplied to the discharge lamp as an apparatus temperature increases in addition to a power control for stabilizing a lighting of the lamp during a start-up period.

3. A discharge lamp apparatus having a DC power source and a discharge lamp comprising:

a transformer for boosting a voltage of the power source;

a switching element connected to a primary side of the transformer; and

power control means for duty-controlling the switching element based on a signal indicating a lighting state of the discharge lamp to thereby control the power supplied to the discharge lamp,

wherein the power control means is provided with power reduction means for reducing the power supplied to the discharge lamp as an apparatus temperature increases.

4. The discharge lamp apparatus as in claim 3, wherein:

the power control means controls the power reduction means so as to control the power supplied to the discharge lamp corresponding to a difference in temperatures between the predetermined value and the apparatus temperature when the temperature exceeds a predetermined value so as to reduce the power supply as the temperature difference is large.

5. The discharge lamp apparatus as in claim 3, wherein:

the power control means controls the power reduction means so as to reduce the power supplied to the discharge lamp when the temperature exceeds a predetermined value.

6. The discharge lamp apparatus as in claim 5, wherein:

the predetermined value is set to at least about 100°

C.

7. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a DC—

DC converter including a transformer for boosting a voltage supplied from the power source;

a terminal connected electrically to the transformer;

a hybrid IC having a circuit connected electrically to the terminal;

a resin case to which the terminal is fixed and in which the transformer is contained; and

an outer container for containing the transformer, the terminal, the hybrid IC, and the resin case, for applying a voltage based on the voltage boosted by the first transformer to the discharge lamp,

wherein the hybrid IC is fixed on one face of the outer container in the outer container,

wherein the transformer and the terminal are contained and fixed in the outer container together with the resin case, and

wherein the transformer is disposed outside an outer periphery of the hybrid IC.

8. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a DC—

DC converter including a transformer for boosting a voltage supplied from the power source and a capacitor connected to the transformer in parallel;

a filter inductor connected between the DC—

DC converter and the power source for filtering noise generated from the DC—

DC converter;

a terminal connected electrically to the transformer, the capacitor, and the inductor;

a hybrid IC having a circuit connected electrically to the terminal;

a resin case to which the terminal is fixed and in which the transformer is contained; and

an outer container for containing the first transformer, the inductor, the terminal, the hybrid IC, and the resin case, for applying a high voltage based on a voltage boosted by the first transformer to the discharge lamp,

wherein the hybrid IC is fixed on one face of the outer container in the outer container,

wherein the transformer, the inductor, and the terminal are contained and fixed in the outer container together with the resin case,

wherein the first transformer, the capacitor, and the inductor are disposed outside an outer periphery of the hybrid IC, and

wherein the capacitor is located between the first transformer and the inductor.

9. A discharge lamp apparatus as in claim 8 further comprising:

another transformer connected electrically to the terminal for further boosting the voltage boosted by the DC—

DC converter and for applying the high voltage to the discharge lamp,

wherein the another transformer is located on an opposite side to the first-named transformer with interposition of the hybrid IC therebetween.

10. A discharge lamp apparatus as in claim 9 wherein:

a minimum distance between a core of the inductor and a core of the second transformer is larger than 10 mm.

11. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a DC—

DC converter including a first transformer for boosting a voltage supplied from the power source;

a second transformer for further boosting the voltage boosted by the DC—

DC converter and for applying a high voltage to the discharge lamp;

terminals connected electrically to the first transformer and the second transformer;

a hybrid IC having a circuit connected electrically to the terminals;

a resin case to which the terminals are fixed and in which the first transformer and the second transformer are contained; and

an outer container for containing the first transformer, the second transformer, the terminal, the hybrid IC, and the resin case;

wherein the hybrid IC is fixed on one face of the outer container in the outer container,

wherein the first and second transformers and the terminal are contained and fixed in the outer container together with the resin case, and

wherein the first transformer and the second transformer are disposed outside an outer periphery of the hybrid IC.

12. A discharge lamp apparatus as in claim 11, wherein:

a minimum distance between a core of the first transformer and a core of the second transformer is larger than 10 mm.

13. A discharge lamp apparatus as in claim 11, wherein:

a core of the transformer for boosting the voltage supplied from the power source is a ring-shaped toroidal type core.

14. A discharge lamp apparatus as in claim 11, wherein:

an outer periphery of a winding of the transformer for boosting the voltage of the power source is fixed to the resin base; and

the winding fixed to the resin base is assembled in the resin case.

15. The discharge lamp apparatus as in claim 11, wherein:

saturation magnetic flux density of a core of the transformer for boosting the voltage of the power source is above 6000 gauss at a core temperature of 1000°

C.

16. The discharge lamp apparatus as in claim 11, wherein:

an outside size of the outer container disposed perpendicular to one face of the outer container to which the hybrid IC is fixed is smaller than 25 mm in the case that a 35W bulb is used as the discharge lamp.

17. The discharge lamp apparatus as in claim 16, wherein:

internal volume and weight of the outer container are smaller than 300 cc and lighter than 500 g, respectively.

18. The discharge lamp apparatus as in claim 11, wherein:

an outer container is provided with a metal case having an opening on one side and a cover for covering the opening of the metal case; and

the metal case covered with the cover is assembled within a vehicle lamp fitting, with the opening of the metal case being disposed in a downward direction.

19. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a DC—

DC converter comprising a transformer for boosting a voltage supplied from the DC power source, a switching element connected to a primary winding of the transformer in series, and a capacitor connected in parallel with the transformer connected in series with the switching element, for generating the boosted voltage;

a starter circuit having a thyristor for turning on the thyristor when the high voltage discharge lamp is started to light and for applying a high voltage pulse to the high voltage discharge lamp based on the boosted voltage generated from the DC—

DC converter; and

a gate circuit for generating the gate signal to turn on the thyristor,

wherein the switching element and the gate circuit are both formed on a hybrid IC board,

wherein the negative electrode side terminal of the capacitor is connected to a first wiring member and then connected to the hybrid IC board by way of the first terminal,

wherein the cathode terminal of the thyristor is connected to a second wiring member and then connected to the hybrid IC board by way of the second terminal different from the first terminal, and

wherein the first terminal and the second terminal are electrically connected on the hybrid IC board.

20. The discharge lamp apparatus as in claim 19, wherein:

the gate circuit has a third terminal to be grounded; and

the hybrid IC board includes a first wiring pattern that extends from the third terminal to the ground, and a second wiring pattern that extends from the second terminal and connected to the first wiring pattern.

21. The discharge lamp apparatus as in claim 20, wherein:

the first terminal connected to the negative electrode side of the capacitor is electrically connected to the switching element by way of a third wiring pattern formed on the hybrid IC board;

the DC—

DC converter forms a current path in which a current flows in the order from the transformer, the switching element, the third wiring pattern, and to the capacitor when the switching element is turned on; and

the electrical wiring that extends from the cathode terminal to the ground including the second wiring pattern does not pass through the third wiring pattern.

22. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a DC—

DC converter comprising a transformer for boosting a voltage supplied from the DC power source, a switching element connected to a primary winding of the transformer in series, and a capacitor connected in parallel to the transformer connected in series and the switching element, for generating the boosted voltage;

a starter circuit having a thyristor for turning on the thyristor when a high voltage discharge lamp is started to light and for applying a high voltage pulse to the high voltage discharge lamp based on the boosted voltage generated from the DC—

DC converter; and

a gate circuit for generating a gate signal to turn on the thyristor,

where in the switching element and the gate circuit are both formed on a hybrid IC board,

wherein a n negative electrode terminal of the capacitor is connected to the hybrid IC board by way of a first terminal to thereby form electrical connection to the switching element, and

a cathode terminal of the thyristor is connected to the hybrid IC board by way of a second terminal different from the first terminal to thereby form electrical connection to a portion to be connected to a ground formed on the hybrid IC board.

23. A discharge lamp apparatus having a DC power source and a high voltage discharge lamp comprising:

a wiring member including a positive terminal to be connected to a positive terminal of the DC power source and a negative terminal to be connected to a negative electrode of the DC power source;

a circuit functional section connected to the DC power source by way of the wiring member in series for applying a high voltage pulse to the high voltage discharge lamp based on the voltage that is obtained by boosting a voltage supplied from the DC power source to thereby light the high voltage discharge lamp; and

a metal case for containing the wiring member and the circuit functional section,

wherein a filter circuit is provided and includes an inductor connected to the circuit functional section in series between a positive electrode of the DC power source and the circuit functional section and a first capacitor connected between both ends of the positive terminal and the negative terminal so as to be connected in parallel to the circuit functional section connected in series and the inductor,

wherein a portion of the negative terminal out of the wiring member is connected to the metal case, and

the first capacitor is connected directly to the portion of the negative terminal out of the wiring member.

24. The discharge lamp apparatus as in claim 23, wherein:

the circuit functional section includes a first circuit section formed on a hybrid IC board, and a second circuit section including various electrical parts connected directly to the wiring member; and

the first capacitor is connected directly to the portion of the negative terminal out of the wiring member not by way of the hybrid IC board.

25. The discharge lamp apparatus as in claim 24, wherein:

the circuit functional section comprises a transformer for boosting a voltage supplied from the DC power source, a first switching element connected in series with a primary winding of the transformer, and a second capacitor connected in parallel with the transformer connected in series and the first switching element;

the circuit functional section includes a DC—

DC converter connected in series to the DC power source to which the second capacitor is connected by way of wiring member and the second switching element connected in series with the second capacitor between the second capacitor and the portion of the negative terminal out of the wring member that serves for shutting down the electrical conduction when the polarity of the DC power source is reversed; and

the first capacitor is connected to the negative terminal side with respect to the second switching element.

26. The discharge lamp apparatus as in claim 25, wherein:

the first switching element and the second switching element are included in the first circuit section; and

the transformer and the second capacitor are included in the second circuit section.

27. A discharge lamp apparatus having a DC power source and a discharge lamp comprising:

a DC power source circuit for boosting a voltage of the DC power source by means of switching of a switching element and smoothing a boosted voltage by means of a smoothing capacitor;

an H-bridge circuit for AC-lighting the discharge lamp by means of an output voltage of the DC power source circuit; and

a starter circuit provided with a capacitor that is charged by means of an output voltage of the H-bridge circuit and a high voltage generation transformer having a primary winding connected to the capacitor and a secondary winding between the H-bridge circuit and the discharge lamp, the starter circuit being for boosting a charging voltage of the capacitor by means of the high voltage generation transformer when the discharge lamp is to be lighted and for applying the high voltage to the discharge lamp,

wherein the discharge lamp is an vehicle 35W bulb, and

wherein L2 (value at DC superimposition 1.5 A)≧

2.5×

10<sup>−

3</sup> (henry), capacitance C1≧

0.5×

10<sup>−

6</sup> (farad), and L2 (value at DC superimposition 0.4 A)×

C1≧

1×

10<sup>−

1</sup>×

f<sup>−

1.68</sup> are satisfied, with L2 denoting an inductance of the secondary winding of the high voltage generation transformer, C1 denoting a capacitance of the smoothing capacitor, and f denoting a switching frequency of the switching element.

28. The discharge lamp apparatus as in claim 27, wherein:

the high voltage generation transformer applies a high voltage of 17 kV or higher to the discharge lamp with a charging voltage of the capacitor of 350 V to 400 V.

29. A discharge lamp apparatus comprising:

an inverter circuit including a H-bridge circuit having four semiconductor switching elements having MOS structure disposed in a H-bridge configuration and bridge driving circuits having output terminals to be connected to the gate terminals of the semiconductor switching elements for driving the four semiconductor switching elements; and

high voltage pulse generation means for applying a high voltage pulse to a discharge lamp to start lighting the discharge lamp, the high voltage pulse generation means being contained together with the inverter circuit in the same case,

wherein the bridge driving circuits have four sets of two MOS transistors connected directly so as to correspond to the four semiconductor switching elements, respectively, and the four semiconductor switching elements are driven based on a potential of junction points of the two MOS transistors connected directly,

wherein the output terminals of the bridge driving circuits are connected to gate terminals of the semiconductor switching elements of the H-bridge circuit by way of first resistors, and

wherein, for at least any one set of the four sets of the MOS transistors connected directly of the bridge driving circuits, drains and sources of MOS transistors at a low side out of the elements connected directly are connected by way of first capacitors.

30. The discharge lamp apparatus as in claim 29, wherein:

a capacitance value of the first capacitors and a resistance value of the first resistors are set so that a time constant determined by the capacitance value of the first capacitors and the resistance value of the first resistors is at least 0.2 microsecond.

31. The discharge lamp apparatus as in claim 29, wherein:

a MOS capacitance value and a resistance value of the first resistors are set so that a time constant determined by the MOS capacitance of the semiconductor switching elements having the MOS structure and the resistance value of the first resistors is at least 0.2 microsecond.

32. The discharge lamp apparatus as in claim 29, wherein:

for two of the four driving circuits, the middle potential points of the H-bridge circuit are connected to the terminals provided as a negative electrode side reference potential, and, for other two of the four driving circuits, the ground potential point is connected to the terminals that are provided as the negative electrode side reference potential;

the four driving circuits drive the four semiconductor switching elements, respectively, based on a potential difference between the output terminals and the negative electrode side reference potential of the driving circuits; and

on at least any one of the two bridge driving circuits having the terminals provided as the negative electrode side reference potential are connected to the middle potential points of the H-bridge circuit, the middle potential points of the H-bridge circuit are connected to the terminals provided as the negative electrode side reference potential by way of second resistors, the middle points between the resistors and terminals provided as the negative electrode side reference potential are connected to the ground potential point by way of second capacitors.

33. A discharge lamp apparatus as in claim 32, wherein:

a resistance value of the second resistors and a capacitance value of the second capacitors are set so that a time constant determined by the resistance value of the second resistors and the capacitance value of the second capacitors is at least 0.01 microsecond.

34. A discharge lamp apparatus comprising:

an inverter circuit including a H-bridge circuit having four semiconductor switching elements having MOS structure disposed in a H-bridge configuration and bridge driving circuits for driving the four semiconductor switching elements; and

high voltage pulse generation means for applying a high voltage pulse to a discharge lamp to start the lighting of the discharge lamp, the high voltage pulse generation means being contained together with the inverter circuit in the same case,

wherein the bridge driving circuits have four driving circuits for driving the four semiconductor switching elements, respectively, output terminals of the four driving circuit are connected to gate terminals of the four semiconductor switching elements, respectively, and the four semiconductor switching elements are driven based on a potential difference between the output terminals and negative electrode side reference potential of the driving circuits, respectively,

wherein the output terminals of the bridge driving circuits are connected to the gate terminals of the semiconductor switching elements of the H-bridge circuit by way of first resistors, and

wherein, for at least any one of the four driving circuits, the output terminal is connected to a wiring provided as the negative electrode side reference potential by way of first capacitors.

35. A discharge lamp apparatus having a discharge lamp comprising:

an inverter circuit including a H-bridge circuit having four semiconductor switching elements having MOS structure disposed in a H-bridge configuration and bridge driving circuits having output terminals to be connected to gate terminals of the semiconductor switching elements for driving the four semiconductor switching elements; and

high voltage pulse generation means for applying a high voltage pulse to the discharge lamp to start lighting the discharge lamp, the high voltage pulse generation means being contained together with the inverter circuit in the same case,

wherein the output terminals of the bridge driving circuits are connected to gate terminals of the semiconductor switching elements of the H-bridge circuit by way of first resistors, and

a MOS capacitance value and a resistance value of the first resistors are set so that a time constant determined by the MOS capacitance value of the semiconductor switching elements having the MOS structure and the resistance value of the first resistors is at least 0.2 microsecond.

36. A discharge lamp apparatus comprising;

an inverter circuit including a H-bridge circuit having four semiconductor switching elements having a MOS structure disposed in a H-bridge configuration and bridge driving circuits for driving the four semiconductor switching elements; and

high voltage pulse generation means for applying a high voltage pulse to a discharge lamp to start lighting the discharge lamp, the high voltage pulse generation means being contained together with the inverter circuit in a same case,

wherein the bridge driving circuits have four driving circuits for driving the four semiconductor switching elements, respectively, output terminals of the four driving circuit are connected to gate terminals of the four semiconductor switching elements, respectively, for two of the four driving circuit middle potential points of the H-bridge circuit are connected to terminals provided as a negative electrode side reference potential, for other two of the four driving circuits a ground potential point is connected to terminals provided as a negative electrode side reference potential, the four driving circuits drive the four semiconductor switching elements, respectively, based on a potential difference between the output terminals and the negative electrode side reference potential of the driving circuits, and

on at least any one of the two bridge driving circuits having the terminals provided as the negative electrode side reference potential are connected to the middle potential points of the H-bridge circuit, the middle potential point of the H-bridge circuit is connected to the terminals provided as the negative electrode side reference potential by way of resistors, the middle points between the resistors and terminals provided as the negative electrode side reference potential are connected to the ground potential point by way of second capacitors.

37. A discharge lamp apparatus as in claim 36, wherein:

a resistance value of the resistors and a capacitance value of the capacitors are set so that a time constant determined by the resistance value of the resistors and the capacitance value of the capacitors is at least 0.01 microsecond.

38. A discharge lamp apparatus comprising:

an inverter circuit including a H-bridge circuit having four IGBTs disposed in a H-bridge configuration and bridge driving circuits for driving the four IGBTs,

wherein the bridge driving circuits have four driving circuits for driving the four IGBTS, respectively, output terminals of the four driving circuits are connected to gate terminals of the four IGBTS, respectively, and the four driving circuits drive the four IGBTs respectively based on a potential difference between the output terminals and negative electrode side reference potential of the driving circuits, and

wherein, for two of the four driving circuits, middle potential points of the H-bridge circuit are connected to terminals provided as the negative electrode side reference potential, for other two of the four driving circuits a ground potential point is connected to terminals provided as the negative electrode side reference potential, and

clamp means are connected to the terminal provided as the negative electrode side reference potential so that the terminal provided as the negative electrode side reference potential connected to the middle potential point of the H-bridge circuit in the bridge driving circuit is equalized to a predetermined voltage.

39. The discharge lamp apparatus as in claim 38, wherein:

the clamp means are diodes; and

the terminal provided as the negative electrode side reference potential is connected to the ground potential point.

40. The discharge lamp apparatus as in claim 38, wherein:

in the two bridge driving circuits in which the terminal provided as the negative electrode side reference voltage is connected to the middle potential point of the H-bridge circuit; and

the middle potential point of the H-bridge circuit is connected to the terminal provided as the negative electrode side reference potential by way of resistors.

41. A discharge lamp apparatus comprising:

an inverter circuit including a H-bridge circuit having four IGBTs disposed in a H-bridge configuration and bridge driving circuits for driving the four IGBTS,

wherein the bridge driving circuits have four driving circuits for driving the four IGBTs, respectively, output terminals of the four driving circuit are connected to gate terminals of the four IGBTs, respectively, and the four driving circuits drive the four IGBTs respectively based on a potential difference between the output terminals and the negative electrode side reference potential of the driving circuits,

wherein, for two of the four driving circuits middle potential points of the H-bridge circuit are connected to the terminals provided as a negative electrode side reference potential, for other two of the four driving circuits a ground potential point is connected to the terminals provided as a negative electrode side reference potential, and

wherein, in the two bridge driving circuits in which the terminal provided as the negative electrode side reference potential is connected to a middle potential point of the H-bridge circuit, the middle potential point of the H-bridge circuit is connected to the terminal provided as the negative electrode side reference potential by way of resistors, and a middle point between the resistors and the terminal provided as the e negative electrode side reference potential is connected to the ground potential point by way of diodes.

42. A discharge lamp apparatus having a DC power source and a discharge lamp comprising:

a DC—

DC converter for boosting a voltage of the DC power source by a transformer; and

an inverter circuit including a H-bridge circuit having four semiconductor switching elements disposed in a H-bridge configuration and bridge driving circuits for controlling on/off operation of the four semiconductor switching elements using the voltage boosted by the DC—

DC converter as a voltage supply source, the voltage boosted by the DC—

DC converter being converted to an AC voltage by the inverter circuit and the AC voltage being applied to the discharge lamp to AC-light the discharge lamp,

wherein the voltage of the DC power source is applied to the DC—

DC converter, on/off operation of the semiconductor switching elements is started after a predetermined time elapses from a time point when the DC—

DC converter starts the operation, and the semiconductor switching elements are kept in off state before the predetermined time elapses.

43. The discharge lamp apparatus as in claim 42, further comprising:

a capacitor charged by the voltage boosted by the DC—

DC converter as the voltage supply source,

wherein the boosted voltage of the DC—

DC converter is applied as an operating voltage of the bridge control circuits, and

wherein the charging voltage of the capacitor is applied instead when the boosted voltage of the DC—

DC converter drops.

44. The discharge lamp apparatus as in claim 42, further comprising:

an H-bridge control circuit for generating a control signal for controlling the bridge driving circuits,

wherein the bridge driving circuit controls the on/off operation of the four semiconductor switching elements based on the control signal, and

wherein the H-bridge control circuit supplies the control signal that functions to turn off all the four semiconductor switching element to the bridge driving circuits during the time before the predetermined time elapses.

45. The discharge lamp apparatus as in claim 42, further comprising:

a fail-safe circuit for detecting grounding based on the lamp voltage applied to the discharge lamp and a lamp current that flows through the discharge lamp; and

a H-bridge off circuit for supplying the control signal that functions to turn off all the four semiconductor switching elements to the bridge driving circuits when grounding is detected.