Information
-
Patent Grant
-
6700328
-
Patent Number
6,700,328
-
Date Filed
Thursday, September 5, 200222 years ago
-
Date Issued
Tuesday, March 2, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 315 85
- 315 209 R
- 315 246
- 315 291
- 315 363
- 315 224
- 313 313
- 313 402
- 313 440
-
International Classifications
-
Abstract
A discharge lamp driver circuit is provided which features a field canceller. The driver circuit includes a power supply circuit which turns on and off a switching element to step up a dc voltage and provide it 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 electric line through which the interrupted current having passed through the electrical path flows in an opposite direction, thereby producing a field canceling a field caused by flow of the interrupted current through the electrical path.
Description
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 arising from the interrupted current flowing through the electrical path.
The electrical line of the field canceller may be so geometrically shaped as to have an area surrounded by the electrical line which is substantially identical with an area surrounded by the electrical path of the power supply circuit. The field provided by the field canceller will, thus, be identical in strength with that produced around the electric path, thereby resulting in complete cancellation of noises arising from the field produced around the electrical path.
The electrical line of the field canceller may be laid over the electrical path of the power supply circuit so that a magnetic flux produced by the electric line of the field canceller overlaps a magnetic flux produced by the electrical path of the power supply circuit, thereby promoting cancellation of noises arising from the field produced around the electric path.
The field canceller includes an insert molded body within which the electrical line is disposed.
The field canceller may be implemented by a flexible substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
FIG. 1
is a circuit diagram which shows a discharge lamp driver circuit according to the first embodiment of the invention;
FIG. 2
is a partially cutaway view which shows the discharge lamp driver circuit of
FIG. 1
installed in a casing;
FIG. 3
is a partially cutaway view which shows a discharge lamp driver circuit according to the second embodiment of the invention is installed in a casing;
FIG. 4
is an illustration which shows a positional relation between a magnetic flux arising from an on-off operation of a switching element and a magnetic flux working to cancel the former;
FIG. 5
is a circuit diagram which shows a discharge lamp driver circuit in a first modification of the invention;
FIG. 6
is a circuit diagram which shows a discharge lamp driver circuit in a second modification of the invention;
FIG. 7
is a circuit diagram which shows a typical discharge lamp driver circuit; and
FIG. 8
is a partially cutaway view which shows the discharge lamp driver circuit of
FIG. 7
installed in a casing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to
FIG. 1
, there is shown a discharge lamp driver circuit
100
according to the first embodiment of the invention which may be employed in turning on headlamps of an automotive vehicle. The same reference numbers as employed in
FIG. 7
will refer to the same parts, and explanation thereof in detail will be omitted here.
The discharge lamp driver circuit
100
of this embodiment is different from the one shown in
FIG. 7
in structure of the DC/DC converter
120
. Specifically, the DC/DC converter
120
includes, as shown in
FIG. 2
, a field canceller
127
which works to cancel a magnetic field produced by the interrupted current i
1
which arises, as already described in the introductory part of this application, from on and off operations of the MOS transistor
122
and flows through the first electrical path Lp
1
.
The field canceller
127
is, as clearly shown in
FIG. 1
, made of a circuit line
127
a
which is connected in series with the first electrical path Lp
1
and has the interrupted current i
1
bypass the first electrical path Lp
1
. In the conventional structure as illustrated in
FIG. 7
, the first electrical path Lp
1
, as discussed above, extends from the capacitor
113
to the primary winding
121
a
of the transformer
121
to the drain and source of the MOS transistor
122
and back to the capacitor
113
, however, the first electrical path Lp
1
of this embodiment extends from the capacitor
113
to the primary winding
121
a
of the transformer
121
to the drain and source of the MOS transistor
122
and to a junction
210
. The circuit line
127
a
extends from the junction
210
to the capacitor
113
along the first electrical path Lp
1
and is so laid that a magnetic flux produced by the circuit line
127
a
may overlap with that produced by the first electrical path Lp
1
vertically.
The circuit line
127
a
works to carry a current which is identical in scale with the interrupted current i
1
and oriented, as indicated by a dashed line in
FIG. 1
, in a direction opposite the flow of the interrupted current i
1
to produce a field which is identical in strength and 180° out of phase with the field arising from the interrupted current i
1
, thereby canceling noises radiated by the on and off operations of the MOS transistor
122
controlled by the gate control circuit
150
a.
The circuit line
127
a
of the field canceller
127
may be provided flush with the first electrical path Lp
1
or on a plane which is in the proximity of the first electrical path Lp
1
and different in level from a plane containing the flow of the interrupted current i
1
through the first electrical path Lp
1
.
FIG. 2
is a partially cutaway view which shows an internal structure of the DC/DC converter
120
. Similarly,
FIG. 8
is a partially cutaway view which shows the DC/DC converter
120
in the typical discharge lamp driver circuit
100
of FIG.
7
. In
FIG. 8
, a hatched portion is the first electrical path Lp
1
.
The circuit line
127
a
of the field canceller
127
is, as shown in
FIG. 2
, implemented by a terminal made of, for example, copper wire which is installed in a resinous insulator in the insert molding and joined in series with the first electrical path Lp
1
. The circuit line
127
a
extends over the first electrical path Lp
1
on a plane defined at a level different from the first electrical path Lp
1
. The use of the resinous insulator results in fixing of a geometric pattern of the circuit line
127
a,
thus keeping the strength of the field produced by the interrupted current flowing through the circuit line
127
a
constant.
It is advisable that the circuit line
127
a
be arranged along at least a portion of the first electrical path Lp
1
in order to produce the field which is exactly identical and 180° out of phase with the field arising from the interrupted current i
1
flowing through the first electrical path Lp
1
.
The discharge lamp driver circuit
100
may be, as shown in
FIG. 2
, disposed in a metal casing
170
. In the illustrated case, the control circuit
150
, the MOS transistor
122
, etc. are fabricated in a hybrid IC. The circuit line
127
a
is connected in series with the first electrical path Lp
1
through a terminal
171
a
installed in a resinous inner casing
171
.
FIG. 3
shows a discharge lamp driver circuit
100
according to the second embodiment of the invention.
The circuit line
127
a
of the field canceller
127
of this embodiment is, unlike the first embodiment, shifted horizontally from the first electrical path Lp
1
. An area S
127
, as shown in
FIG. 4
, surrounded by the circuit line
127
a
is set substantially equal to an area SLp surrounded by the first electrical path Lp
1
so that the field φ
127
produced from the circuit line
127
a
may be identical in strength with the field φLp produced from the first electrical path Lp
1
. Therefore, to the extent that the interval Ld between the circuit line
127
a
and the first electrical path Lp
1
is much smaller than both distance L
1
between the first electrical path Lp
1
and a field-applied point B (e.g., an antennal installed on the rear of a vehicle traveling ahead of a vehicle equipped with the discharge lamp driver circuit
100
) and distance L
2
between the circuit line
127
a
and the field-applied point B, the field φ
127
cancels the field φLp sufficiently at the field-applied point B, thus eliminating an electric disturbance arising from the field φLp.
The circuit line
127
a
of the field canceller
127
may be made of a flexible substrate, thereby facilitating setting of the area S
127
surrounded by the circuit line
127
a.
The use of such a flexible substrate also allows the discharge lamp driver circuit
100
, especially circuit elements around the DC/DC converter
120
to be reduced in size.
The field canceller
127
may also be installed, as shown in
FIG. 5
, in the discharge lamp driver circuit
100
in order to cancel the field arising from the interrupted current i
2
flowing through the second electrical path Lp
2
extending from the junction
310
to the secondary winding
121
b
to the rectifier diode
123
and to the smoothing capacitor
124
. The field canceller
127
is implemented by the circuit line
127
a
extending from an end of the second electrical path Lp
2
extending downward, as viewed in the drawing, from the smoothing capacitor
124
to the junction
410
along the second electrical path Lp
2
.
Further, the field canceller
127
may be installed, as shown in
FIG. 6
, in the discharge lamp driver circuit
100
in order to cancel the field arising from the interrupted current i
3
flowing through the third electrical path Lp
3
extending from the junction
510
to the MOS transistor
122
to the gate control circuit
150
a.
The field canceller
127
is implemented by the circuit line
127
a
extending from an end of the third electrical path Lp
3
(i.e., the collector of the transistor of the gate control circuit
150
a
) to the junction
410
along the third electrical path Lp
3
.
While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims.
The invention is not limited to use with the DC/DC converter
122
. For instance, the field canceller
127
may be installed in a power supply unit including a semiconductor switching element such as a MOS transistor.
Claims
- 1. A discharge lamp driver circuit comprising:a power supply circuit connected to a dc power supply, including a switching element, said power supply circuit performing 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, said power supply circuit including an electrical path through which an interrupted current arising from the on-off operation of the switching element flows; and a field canceller including an electrical line through which the same interrupted current as that flowing through the electrical path of said power supply circuit flows to thereby produce a field canceling a field caused by flow of the interrupted current through the electrical path.
- 2. The discharge lamp driver circuit as set forth in claim 1, wherein said power supply circuit includes a DC/DC converter which has a transformer consisting of a primary winding connected to the dc power supply and a secondary winding connected to the discharge lamp and the switching element and which works to turning on and off the switching element to provide the stepped up dc voltage to the discharge lamp through the transformer.
- 3. The discharge lamp driver circuit as set forth in claim 1, wherein the electrical line of said field canceller is connected in series with the electrical path of said 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.
- 4. The discharge lamp driver circuit as set forth in claim 1, wherein the electrical line of said field canceller is so geometrically shaped as to have an area surrounded by the electrical line which is substantially identical with an area surrounded by the electrical path of said power supply circuit.
- 5. The discharge lamp driver circuit as set forth in claim 1, wherein the electrical line of said field canceller is laid over the electrical path of said power supply circuit so that a magnetic flux produced by the electric line of said field canceller overlaps a magnetic flux produced by the electrical path of said power supply circuit.
- 6. The discharge lamp driver circuit as set forth in claim 1, wherein said field canceller includes an insert molded body within which the electrical line is disposed.
- 7. The discharge lamp driver circuit as set forth in claim 1, wherein said field canceller is implemented by a flexible substrate.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2001-272675 |
Sep 2001 |
JP |
|
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
4998006 |
Perlman |
Mar 1991 |
A |
5675220 |
Dault et al. |
Oct 1997 |
A |
6201350 |
Okuchi et al. |
Mar 2001 |
B1 |
Foreign Referenced Citations (2)
Number |
Date |
Country |
2000-156294 |
Jun 2000 |
JP |
2001-43984 |
Feb 2001 |
JP |