High-voltage discharge lamp device

Details High-voltage discharge lamp device High-voltage discharge lamp device

2001-10-26

2004-06-08

Clinger, James (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

C315S308000, C315S291000

Reexamination Certificate

active

06747422

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application No. 09-127677 filed on May 16, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to controlling a high voltage discharge lamp which is preferably used particularly in a vehicle.
2. Description of Related Art
A device for turning on a high voltage discharge lamp (lamp) applied to a headlight for a vehicle is proposed in JP-A 9-180888 (U.S. Ser. No. 08/756,556 and now U.S. Pat. No. 5,751,121) or JP-A 9-306684.
In the proposed device, as shown in
FIG. 26
, the voltage of a vehicular battery
300
is transformed into high voltage by a primary transformer winding
302
a
and a secondary transformer winding
302
b
that is changed by the transformed high voltage. Further, when the charge voltage of capacitor
303
reaches a set voltage or higher, discharge is carried out at discharge gap
304
, the charge voltage of capacitor
303
is further increased by the discharge through transformer windings
305
a
,
305
b
and high voltage is applied to lamp
306
. Thereby, lamp
306
is turned on.
Further, lamp
306
is maintained turned on by supplying predetermined power from vehicular battery
300
on the primary side to a secondary side transformer winding
302
c
installed for use in a direct current power source circuit
307
separately from starting circuit
301
. At this occasion, in order to turn on lamp
306
by alternating current, the direction of discharge current is alternately inverted by inverter circuit
310
having an H-bridge circuit
309
comprising four MOS transistors
309
a
-
309
d.
Further, primary current I flowing in the primary side transformer
302
a
is controlled by MOS transistor
311
for the primary which is a semiconductor switching element. On/off switching of MOS transistor
311
is controlled by a PWM control circuit
312
. The PWM control circuit
312
carries out a duty-cycle control based on lamp voltage VL applied to lamp
306
and lamp current IL flowing in lamp
306
and controls power supply to the secondary side in accordance with a condition (for example, electrode temperature) of lamp
306
.
However, there occurs a problem of limited life of gap
304
since gap
304
is used as a switching element for turning on lamp
306
.
For example, when the gap interval is shortened by foreign matter adhering to gap
304
, there occurs a problem of lessening turn-on performance of lamp
306
since the discharge is carried out at gap
304
before a predetermined discharge voltage is achieved since the discharge voltage is lowered. Meanwhile, when the gap interval is lengthened by wear of gap
304
, there occurs a problem where the gap discharge cannot be carried out since the discharge voltage is made too high.
Further, there occurs a problem where seal gas inside of gap
306
is deteriorated with the number of times of use of the lamp
306
.
Meanwhile, there also occurs a problem where cost is increased since the two transformer windings
302
b
and
302
c
are used for starting circuit
301
and direct current power source circuit
307
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide lamp discharge device which provides a stable operation at low cost.
According to one aspect of the present invention, a capacitor in a starting circuit is charged based on the voltage of a direct current power source which has been transformed into high voltage by a transformer. The voltage of the direct current power source which has been transformed into high voltage by the transformer is sufficiently high that it is sufficient for charging the capacitor of the starting circuit. In this way, by charging the capacitor by the transformed high voltage, a single transformer can commonly be used for both of the starting circuit and the direct current power source circuit.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description.


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