Cut-off vehicular discharge lamp circuit having wait and monitor modes

• US 5,422,548 A
• Filed: 09/14/1993
• Issued: 06/06/1995
• Est. Priority Date: 09/16/1992
• Status: Expired due to Fees

• Current Assignee: Koito Manufacturing Company Limited
• Original Assignee: Koito Manufacturing Company Limited
• Inventors: Toda, Atsushi, Yamashita, Masayasu
• Primary Examiner(s): Lee, Benny
• Assistant Examiner(s): Philogene, Haissa
• Application Number:
  US08/120,467
• Time in Patent Office: 630 Days
• Field of Search: 315/127, 315/209 R, 315/77, 315/82, 315/291, 315/307, 315/308, 315/224, 315/DIG. 7
• US Class Current: 315/308
• CPC Class Codes: B60Q 11/00 Arrangement of monitoring devices for devices provided for in groups B60Q1/00 - B60Q9/00
• CPC Class Codes: H05B 41/2925 against abnormal lamp operating conditions
• CPC Class Codes: H05B 47/20 Responsive to malfunctions or to light source life; for protection
• 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

Disclosed is a lighting circuit for a vehicular lamp which cuts off power supply to the discharge lamp when the discharge lamp flickers due to the expiration of its service life or the like, thus ensuring safety for an approaching vehicle. In the lighting circuit for a metal halide lamp, when a lighting switch is set on, the battery voltage is boosted by a DC booster circuit and is then converted into an AC voltage by a DC/AC converter. This AC voltage is applied to the metal halide lamp. An abnormality detector is provided to detect that the lamp gets into a flickering state. When the output voltage of the DC booster circuit becomes greater than a threshold value after a predetermined wait time elapses from the point at which the output voltage has exceeded the threshold value, the abnormality detector determines this situation as abnormal lighting and sends a signal to a power cutoff relay circuit to stop supplying the battery voltage to the DC booster circuit.

Claims

1. A lighting circuit for a vehicular discharge lamp for cutting off power supply to said discharge lamp when detecting an abnormal state of said discharge lamp, comprising:

means for detecting a level of a tube voltage of said discharge lamp or a signal equivalent to said tube voltage;

abnormality detecting means having a wait period mode and a monitor period mode of operation and operable to detect abnormal operation of said discharge lamp in response to said detected level, said abnormality detecting means commences said wait period mode of operation when said detected level is equal to or above a predetermined value and, after a predetermined time elapses, enters said monitor period mode of operation, said detecting means outputting a signal when said level is above said predetermined value during said monitor period mode; and

power cutoff means for cuttign off power supply to said discharge lamp in response to said output signal received from said abnormality detecting means.

2. The lighting circuit according to claim 1, further comprising a DC/AC current converting means for converting a DC voltage into an AC voltage and supplying said AC voltage to said discharge lamp.

3. The lighting circuit according to claim 2, further comprising:

a DC booster circuit, connected to said DC/AC converting means, for boosting an input DC voltage;

an igniter circuit; and

an control circuit for controlling an output voltage of said DC booster circuit, whereby said DC/AC converting means converts an output DC voltage from said DC booster circuit into an AC voltage and supplies said AC voltage of said igniter circuit.

4. The lighting circuit according to claim 1, wherein said power cutoff means includes a power cutoff relay circuit having a relay contact for cutting off power supply to said discharge lamp when abnormality is detected.

5. The lighting circuit according to claim 1, wherein said abnormality detecting means includes:

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor.

a hold circuit connected via a diode to an output terminal of said operational amplifier; and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier.

6. The lighting circuit according to claim 2, wherein said power cutoff means includes a power cutoff relay circuit having a relay contact for cutting off power supply to said discharge lamp when abnormality is detected.

7. The lighting circuit according to claim 2, wherein said abnormality detecting means includes:

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor;

a hold circuit connected via a diode to an output terminal of said operational amplifier; and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier.

8. The lighting circuit according to claim 3, wherein said power cutoff means includes a power cutoff relay having a relay contact for cutting off power supply to said discharge lamp when abnormality is detected.

9. The lighting circuit according in claim 3, wherein said abnormality detecting means includes:

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor;

a hold circuit connected via a diode to an output terminal of said operational amplifier; and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier.

10. The lighting circuit according to any one of claims 2 to 9, wherein said AC voltage from said DC/AC converting means has a rectangular waveform.

11. The lighting circuit according to any one of claims 2 to 8, wherein said AC voltage from said DC/AC converting means has a sine waveform.

12. A lighting circuit for a vehicular discharge lamp for cutting off power supply of said discharge lamp when detecting an adnormal state of said discharge lamp from a detected level of a tube voltage of said discharge lamp or a signal equivalent to said tube voltage, said circuit comprising:

abnormality detecting means for detecting flickering of said discharge lamp, said abnormality detecting means entering a wait period mode of operation upon detecting that said level of said tube voltage of said discharge lamp or said equivalent signal is equal to or above a predetermined voltage, and switching to a monitor mode of operation a predetermined time thereafter, said abnormality detecting means generating an abnormality signal upon detecting that said level of said tube voltage of said discharge lamp or said equivalent signal is equal to or above a predetermined value during said monitor period of mode operation; and

power cutoff means for cutting off power supply to said discharge lamp when receiving said abnormality signal indicating an abnormal state of said lighting circuit from said abnormality detecting means.

13. The lighting circuit according to claim 12, further comprising:

a DC/AC current converting means for converting a DC voltage into an AC voltage and supplying said AC voltage to said discharge lamp;

a DC booster circuit, connected to said DC/AC converting means, for boosting an input DC voltage;

an igniter circuit; and

a control circuit for controlling an output voltage of said DC booster circuit, whereby said DC/AC conversing means converts an output DC voltage from said DC booster circuit into an AC voltage and supplies said AC voltage to said igniter circuit.

14. The lighting circuit according to claim 12, wherein said power cutoff means includes a power cutoff relay circuit having a relay contact for cutting off power supply to said discharge lamp when adnormality is detected.

15. The lighting circuit according to claim 12, wherein said abnormality detecting means includes:

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor;

a hold circuit connected via a diode to an output terminal of said operational amplifier; and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier.

16. The lighting circuit according to claim 13, wherein said power cutoff means includes a power cutoff relay circuit having a relay contact for cutting off power supply to said discharge lamp when abnormality is detected.

17. The lighting circuit according to claim 13, wherein said abnormality detecting means includes:

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor;

a hold circuit connected via a diode to an output terminal of said operational amplifier; and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier.

18. The lighting circuit according to any one of claims 12 to 17, wherein said AC voltage from said DC/AC converting means has a rectangular waveform.

19. The lighting circuit according to any one of claims 12 to 17, wherein said AC voltage from said DC/AC converting means has a sine waveform.

20. A lighting circuit for a vehicular discharge lamp for cutting off power supply to said discharge lamp when detecting an abnormal state of said discharge lamp from a detected level of a tube voltage of said discharge lamp or a signal equivalent to said tube voltage, said circuit comprising:

abnormality defecting means for detecting flickering of said dicharge lamp in such a way that when detecting that said level of said tube voltage of said discharge lamp or said equivalent signal still becomes equal to or above a predetermined voltage during a monitor time after a predetermined wait time elapses from the point at which said level of said tube voltage or said equivalent signal has become equal to or above said predetermined voltage, said abnormality detecting means judges the situation as an abnormal state of said discharge lamp and sends a signal to said power cutoff means to stop supplying power to said discharge lamp, said abnormality detection means including,

a first operational amplifier having a non-inverting input terminal connected to an output terminal of said DC booster circuit via a resistor and a capacitor, an inverting input terminal supplied with a reference voltage, and an output terminal connected to a cathode of a diode and connected to a power terminal via a first pull-up resistor,

a hold circuit connected via a diode to an output terminal of said operational amplifier, and

a second operational amplifier having an inverting input terminal supplied with a second reference voltage, and an output terminal connected to said power terminal via a second pull-up resistor, with a resistor inserted between said output terminal and a non-inverting input terminal of said second operational amplifier;

power cutoff means including a power cutoff relay circuit relay having a relay contact for cutting off power supply to said discharge lamp when receiving a signal indicating an abnormal state of said lighting circuit;

a DC/AC current converting means for converting a DC voltage into an AC voltage and supplying said AC voltage to said discharge lamp;

a DC booster circuit, connected to said DC/AC converting means, for boosting an input DC voltage;

an igniter circuit; and

a control circuit for controlling an output voltage of said DC booster circuit, whereby said DC/AC converting means converts an output DC voltage from said DC booster circuit into an AC voltage and supplies said AC voltages to said igniter circuit.

21. The lighting circuit according to claim 20, wherein said AC voltage from said DC/AC converting means has a rectangular waveform.

22. The lighting circuit according to claim 20, wherein said AC voltage from said DC/AC converting means has a sine waveform.