Electric lamp and discharge devices: systems – With electromagnetic wave radiation preventing or shielding...
Reexamination Certificate
2002-09-05
2004-03-02
Vo, Tuyet T. (Department: 2821)
Electric lamp and discharge devices: systems
With electromagnetic wave radiation preventing or shielding...
C315S2090SC, C315S224000, C315S246000, C315S291000, C313S313000
Reexamination Certificate
active
06700328
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a discharge lamp driver circuit working to turn on a discharge lamp, and more particularly to a noise canceller structure of such a discharge lamp driver circuit which is designed to minimize radiation of noises arising from a switching operation of the driver circuit.
2. Background Art
FIG. 7
shows a typical discharge lamp driver circuit
100
for automotive vehicles which includes a filter circuit
110
, a DC/DC converter
120
, an inverter
130
, and a control circuit
150
. The discharge lamp driver circuit
100
works to step up a dc voltage supplied from a storage battery
10
through the DC/DC converter
120
when a lighting switch
20
is turned on and converts it into an ac voltage through the inverter
130
to initiate a discharge in a lamp
30
.
The lamp
30
is a discharge lamp such as a metal halide lamp typically used as a headlamp of the vehicle. Starting the lamp
30
is achieved by inducing a dielectric breakdown through a transformer (not shown) of a starter circuit to develop a high voltage between electrodes of the lamp
30
. After the dielectric breakdown, the status of the lamp
30
is shifted from a glow discharge to an arc discharge to keep the lamp
30
lightened stably.
The filter circuit
110
consists of a coil
111
, a capacitor
112
, and a capacitor
113
and works as a noise filter.
The DC/DC converter
120
consists of a transformer
121
made up of a primary winding
121
a
connected to the battery
10
and a secondary winding
121
b
connected to the lamp
30
, a MOS transistor (field-effect transistor)
122
connected to the primary winding
121
a,
rectifier diode
123
, and a smoothing capacitor
124
and works to step up and output the voltage from the battery
10
. Specifically, when the MOS transistor
122
is turned on, it will cause a primary current to flow through the primary winding
121
a
so that energy is accumulated in the primary winding
121
a.
When the MOS transistor
122
is turned off, it will cause the energy in the primary winding
121
a
to be supplied to the secondary winding
121
b.
Such turning on and off the MOS transistor
122
is repeated, thereby causing a high voltage to be outputted from a junction of the diode
123
and the smoothing capacitor
124
. The transformer
121
may alternatively be so constructed that the primary and secondary windings
121
a
and
121
b
are electrically connected to each other.
The inverter
130
includes MOS transistors (not shown) arrayed in the form of an H-bridge which work to provide the ac current for turning on the lamp
30
.
The control circuit
150
is responsive to a signal (lamp power signal) provided by a power detector (not shown) as functions of a lamp current and a lamp voltage to control the MOS transistor
122
in a PWM mode so as to bring the lamp power into agreement with a maximum (e.g., 65 W) when turning on the lamp
30
and with a constant power (e.g., 35 W) subsequently.
The control circuit
150
consists of a gate control circuit
150
a
controlling the on-off operation of the MOS transistor
122
in the PWM mode, the power detector detecting the lamp voltage, and a lamp power control circuit (not shown) controlling the lamp power to bring it into agreement with a target one based on the detected lamp current and voltage.
In operation, when the lighting switch
20
has been turned on, and the control circuit
150
has started to control the MOS transistor
122
in the PWM mode, the DC/DC converter
120
outputs the voltage produced by stepping up the voltage of the battery
10
through the transformer
121
. The high-voltage produced by the DC/DC converter
120
(300V to 500V in the course of preparation for turning on the lamp
30
, and about 100V after turning on the lamp
30
) is further stepped up to, for example, 25 kV through the inverter
130
so that the dielectric breakdown may occur in the transformer of the starter circuit and applied to the lamp
30
. This causes the lamp
30
to be turned on. After turning on the lamp
30
, the polarity of the voltage to be outputted by the inverter
130
is reversed cyclically to provide the ac voltage to the lamp
30
.
The above structure of the discharge lamp driver circuit
100
has a drawback in that interrupted currents arising from the on and off operations of the MOS transistor
122
of the DC/DC converter
120
to step up the voltage of the battery
10
result in radiation of noises.
The interrupted currents flow through three electrical loops: a first electrical path Lp
1
extending from the capacitor
113
through a power source positive line to the primary winding
121
a
of the transformer
121
to a drain and a source of the MOS transistor
122
and back to the capacitor
113
through a ground line, a second electrical path Lp
2
extending from the rectifier diode
123
to the smoothing capacitor
124
to the ground line to the secondary winding
121
b
and back to the rectifier diode
123
, and a third electrical path Lp
3
extending from the gate control circuit
150
a
to the gate of the MOS transistor
122
to the ground line and back to the gate control circuit
150
a.
The first, second, and third electrical paths Lp
1
, Lp
2
, and Lp
3
carry currents i
1
, i
2
, and i
2
arising from the on and off operations of the MOS transistor
122
by the gate control circuit
150
a.
Particularly, in a case where the above structure of the discharge lamp driver circuit
100
is installed in an automotive vehicle for lighting headlamps, when a traffic light has changed to red, and the vehicle has stopped close to an antenna installed in the rear of a preceding vehicle, it may cause electric noises to be radiated forwardly, which raise a radio disturbance in the preceding vehicle.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a discharge lamp driver circuit designed to minimize adverse effects caused by interrupted currents produced in the driver circuit.
According to one aspect of the invention, there is provided a discharge lamp driver circuit which may be employed in turning on a discharge lamp as used as a headlamp of automotive vehicles. The discharge lamp driver circuit comprises: (a) a power supply circuit connected to a de power supply; and (b) a field canceller. The power supply circuit includes a switching element and performs an on-off operation on the switching element to step up a dc voltage from the dc power supply and provide the stepped up dc voltage for turning on a discharge lamp. The power supply circuit includes an electrical path through which an interrupted current arising from the on-off operation of the switching element flows. The field canceller includes an electrical line through which the same interrupted current as that flowing through the electrical path of the power supply circuit flows, thereby producing a field canceling a field caused by flow of the interrupted current through the electrical path. This causes electrical noises radiated outside from the electrical path of the power supply circuit to be eliminated.
In the preferred mode of the invention, the power supply circuit includes a DC/DC converter. The DC/DC converter consists of a transformer made up of a primary winding connected to the dc power supply and a secondary winding connected to the discharge lamp and the switching element and works to turning on and off the switching element to provide the stepped up dc voltage to the discharge lamp through the transformer.
The electrical line of the field canceller is connected in series with the electrical path of the power supply circuit and extends so as to have the interrupted current bypass the electrical path in an orientation opposite flow of the interrupted current through the electrical path. This causes the field to be produced by the field canceller which is identical in strength and 180° out of phase with the field arisin
Denso Corporation
Posz & Bethards, PLC
Vo Tuyet T.
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