Inverter transformer

Details Inverter transformer Inverter transformer

1999-09-30

2001-03-13

Donovan, Lincoln (Department: 2832)

Inductor devices

With supporting and/or spacing means between coil and core

Preformed insulation between coil and core

C336S200000

Reexamination Certificate

active

06201463

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverter transformer for use with DC/AC inverter adapted to turn on cathode ray tube or the like for illuminating the back of a liquid crystal display.
2. Description of the Prior Art
In order to give a better understanding of the present invention, description will first be made with reference to
FIG. 6
of the accompanying drawings, which illustrates a conventional inverter transformer wherein a primary winding
3
is wound on a cylindrical spool
2
a
of insulator bobbin
2
having terminals
1
mounted thereto; and a secondary winding
4
is provided under the bobbin
2
. Further, a pair of magnetic cores
5
and
6
are disposed in abutting relationship with each other through an insulator sheet
7
and holding the bobbin
2
therebetween from above and below, thus establishing a closed magnetic circuit.
FIG. 7
illustrates distribution of electric field which occurs between two plate-like electrodes
8
a
and
8
b
disposed in opposing relationship to each other with a distance d kept therebetween. Let it be assumed that a voltage of V
G
volts is applied to the electrode
8
b
while the electrode
8
a
is maintained at 0 volt. For the case where the space between the electrodes
8
a
and
8
b
is filled with air alone, the electric field occurring therebetween is given by V
G
/d as shown by a dotted line. In contrast thereto, for the case where a dielectric body
9
is inserted between the electrodes
8
a
and
8
b
, the electric field turns out to be as shown by solid line arrows electric field E
2
(=V
2
/d
2
) occurring in the dielectric body
9
has a gentle slope depending on the dielectric constant of the dielectric body
9
, while electric fields E
1
(=V
1
/d
1
) and E
3
(=V
3
/d
3
) occurring in the air-filled portions each represent a steep slope which is increased by an amount corresponding to the decrease in the slope caused in the dielectric body
9
.
In the conventional inverter transformer such as shown in
FIG. 6
, resin such as varnish or the like (not shown) is filled between the primary winding
3
and the bobbin
2
and between the secondary winding
4
and the bobbin
2
in order to increase the withstand voltage. However, it may happen that the resin fails to be completely filled between the primary winding
3
or secondary winding
4
and the bobbin
2
so that bubbles or the like are generated which tend to result in formation of numerous voids. With the electrodes
8
a
and
8
b
of
FIG. 7
being replaced with the primary winding
3
and secondary winding
4
respectively, the intensity of electric fields occurring in the gap portions between the primary winding
3
and the bobbin
2
and between the secondary winding
4
and the bobbin
2
is increased due to the fact that the primary and secondary windings are close to each other and the dielectric body of the bobbin
2
is interposed therebetween. As a result, corona discharge is liable to occur especially between the secondary winding
4
and the neighboring components such as cores
5
,
6
, primary winding
3
and etc. which assume a high voltage, thus leading to dielectric breakdown.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an inverter transformer arranged such that a portion where a high electric field occurs is provided to be remote from the secondary winding so that the intensity of electric filed occurring in the vicinity of the secondary winding turns out to be reduced, thereby increasing the withstand voltage of the inverter transformer.
It is another object of the present invention to provide an inverter transformer comprising: an insulating bobbin including a base portion having terminals attached thereto, and a spool upwardly extending from center of said base portion, said insulating bobbin being formed with a hole extending through said spool; a primary winding wound on said spool; a secondary winding disposed under said base portion and electromagnetically coupled to said primary winding; a pair of cores formed of a magnetic material, said pair of cores being disposed in abutting relationship with each other holding said bobbin therebetween from above and below; and a center leg provided on at lease one of said cores and adapted to be inserted in an aperture of said spool; wherein a plurality of grooves are defined by a plurality of flanges provided at side surface of said spool; said primary winding is provided in one of said grooves; said groove having no winding provided therein is interposed between said primary winding and said secondary winding; and an air gap is defined between said center leg and said secondary winding.
Other objects, features and advantages of the present invention will become apparent from the ensuing description taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 4060783 (1977-11-01), Harnden, Jr.
patent: 4587506 (1986-05-01), Hoeksma
patent: 4931761 (1990-06-01), Kijima
patent: 6124842 (1994-05-01), None
patent: 6-163287 (1994-06-01), None
patent: 10-233325 (1998-09-01), None

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