Discharge-lamp illumination circuit

Details Discharge-lamp illumination circuit Discharge-lamp illumination circuit

2001-01-18

2002-12-03

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Periodic switch in the supply circuit

Periodic switch in the primary circuit of the supply...

C315S215000, C315S217000, C315S312000

Reexamination Certificate

active

06489730

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a technique for generating secondary outputs from a transformer comprising a DC power supply circuit in an illumination circuit, which controls illumination of a plurality of discharge lamps and controls the secondary outputs individually.
A known illumination circuit of a discharge lamp, for example, a metal halide lamp, comprises a DC power supply circuit, a DC-AC converter circuit, and a starter circuit.
The DC power supply circuit has a DC-DC converter, and the DC-AC conversion circuit has a driver circuit and a full-bridge circuit having four semiconductor switching elements, which in pairs controls switching operation. A voltage from a DC-DC converter is supplied to the discharge lamp after being converted into a rectangular-waveform voltage by the full-bridge circuit.
If discharge lamps are used as vehicle headlamps, a circuit to control the lighting of these lamps would be required. A main beam (high beam) lamp and a dipped beam (low beam) lamp are provided in a single headlamp body, which is provided on each side of the front of a vehicle.
If a circuit is provided for each discharge lamp, many individual components, such as DC-DC converters and full-bridge circuits, will be duplicated. This results in increased costs.
To address this problem, a circuit comprising a DC power circuit and a DC-AC conversion circuit may be employed. Along with the DC power supply circuit, two DC-DC converters are provided, each delivering an output of positive and negative polarity. The DC-AC conversion circuit commonly provided to the discharge lamps switches between the outputs of the two DC-DC converters.
For example, if a plurality of secondary coils are provided in a transformer constituting the DC-DC converter, the DC-DC converter can be controlled to make the output voltage of each secondary coil constant. However, variations may exist in lamp voltages of the discharge lamps because of differences in the lamps. Discharge lamp power must be controlled individually according to startup conditions (i.e., cold start or hot start) of each discharge lamp. Neither condition can be addressed by a simple use of a transformer equipped with a plurality of secondary coils.
The present invention provides a low-cost discharge-lamp illumination circuit that controls illumination of a plurality of discharge lamps. The invention is also amenable to miniaturization.
SUMMARY OF THE INVENTION
The present invention provides a discharge-lamp illumination circuit including a DC power supply circuit for providing a DC voltage, a DC-AC conversion circuit for supplying a voltage from the DC conversion circuit to discharge lamps after having converted the voltage into an AC voltage, and a control circuit for controlling the voltage from the DC power supply circuit. Power supplied to the plurality of discharge lamps, respectively, is controlled individually.
Preferably, the DC power supply circuit has a transformer and a first switching element connected to a primary coil of the transformer, and activation/deactivation of the first switching element is controlled by means of a control signal from a control circuit.
Preferably, a secondary coil for each discharge lamp is provided in the transformer of the DC power supply circuit, and a second switching element whose activation or deactivation is controlled by a signal from the control circuit is separately provided on each secondary coil for the secondary coils to output different voltages.
According to the present invention, a plurality of secondary coils comprising a DC power supply circuit are provided. Voltages from the secondary coils can be controlled individually by the second switching elements. The DC power supply circuit is shared among a plurality of discharge lamps, thereby compacting the discharge-lamp illumination circuit and diminishing the costs. Further, the primary energy of the transformer is transferred to the secondary coils by means of activation/deactivation of the second switching elements. Accordingly, distribution of power to the respective discharge lamps can be controlled, thereby individually controling the illumination of the discharge lamps.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an exemplary block diagram of a discharge-lamp illumination circuit according to the present invention.
FIG. 2
is an exemplary circuit diagram of a DC power supply circuit.
FIG. 3
is an exemplary circuit diagram of the DC power supply circuit using thyristors as second switching elements.
FIG. 4
is an exemplary circuit diagram of a DC power supply circuit using FETs as first and second switching elements.
FIG. 5
is an exemplary circuit diagram of a DC power supply circuit producing a secondary output of positive polarity and negative polarity.
FIG. 6
is an exemplary circuit diagram of a DC power supply circuit using FETs as first and second switching elements.
FIG. 7
is an exemplary circuit diagram of a section of a control circuit.
FIG. 8
is an exemplary timing chart for describing the operation of a DC power supply circuit.
FIG. 9
illustrates an example of control signals to be sent to first and second switching elements.
FIG. 10
is an exemplary circuit diagram showing a section of the circuit configuration shown in FIG.
9
.
FIG. 11
illustrates another example of control signals to be sent to first and second switching elements.
FIG. 12
is an exemplary circuit diagram showing a section of the circuit configuration shown in FIG.
11
.
FIG. 13
is an exemplary timing chart for describing the circuit operation of the circuit configuration shown in FIG.
12
.
FIG. 14
illustrates yet another example of control signals to be sent to first and second switching elements.
FIG. 15
is an exemplary circuit diagram showing a sawtooth waveform generation section.
FIG. 16
is an exemplary timing chart for describing the operation of the circuit configuration shown in FIG.
15
.
FIG. 17
illustrates still another example of control signals to be sent to first and second switching elements.
FIG. 18
is an exemplary circuit diagram for carrying out the control operation shown in FIG.
17
.
FIG. 19
is an exemplary circuit diagram showing a section of a circuit configuration for controlling activation/deactivation of a first switching element by making a deactivated period of the switching element constant and changing an activated period of the same.
FIG. 20
is an exemplary timing chart for describing the circuit operation of the circuit configuration shown in FIG.
19
.
FIG. 21
is an exemplary circuit diagram showing a section of a circuit configuration for controlling activation/deactivation of a first switching element by changing a deactivated period and an activated period of the switching element.
FIG. 22
is an exemplary circuit diagram showing a section of a circuit configuration for controlling activation/deactivation of a first switching element by changing either a deactivated period or an activated period of the switching element.


REFERENCES:
patent: 4757238 (1988-07-01), Rhee
patent: 5142203 (1992-08-01), Oda et al.
patent: 5212428 (1993-05-01), Sasaki et al.
patent: 5914566 (1999-06-01), Matsumoto et al.
patent: 6023131 (2000-02-01), Okita

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