Inductor devices – Core forms casing
Reexamination Certificate
2001-03-23
2003-07-01
Nguyen, Tuyen T. (Department: 2832)
Inductor devices
Core forms casing
C336S198000, C336S200000, C336S208000, C336S212000
Reexamination Certificate
active
06587023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic induction device such as, for example, a transformer utilizing an inverter and, more particularly, to the electromagnetic induction device of a type finding a principal application in, for example, driving a magnetron.
2. Description of the Prior Art
FIG. 27
illustrates an inverter-equipped high frequency heating apparatus such as, for example, an electronic oven, of a type disclosed in the Japanese Examined Patent Publication No. 7-40465. This known high frequency heating apparatus includes a rectifying circuit
62
for rectifying and smoothing an electric power from a commercial power source
61
, an inverter
63
for converting the rectified and smoothed electric power into a high frequency alternating current of a frequency equal to or higher than 20 kHz, and a transformer
64
including a gapped core and having a primary winding
64
p
to which the high frequency alternating current is supplied from the inverter
63
. The transformer
64
also has a secondary winding
64
s
, and a high frequency output voltage emerging from the secondary winding
64
s
of the transformer
64
is, after having been rectified and smoothed by a half-wave rectifying circuit
65
, supplied as a direct current high voltage to a magnetron
66
. The transformer
64
furthermore has a heater winding
64
h
for driving the magnetron
66
which, when receiving the direct current high voltage, generates microwaves.
The transformer
64
discussed above is shown in a sectional representation in FIG.
29
. The known transformer
64
comprises a bobbin
70
on which the primary winding
64
p
, the secondary winding
64
s
and the heater winding
64
h
are wound therearound in an axially spaced relation to each other. This known transformer
64
also comprises generally U-shaped magnetic core pieces
71
and
72
each having a pair of legs and a bridge arm
71
a
or
71
b
connecting the legs together, and one of the legs of each magnetic core piece
71
and
72
is received within a cylindrical hollow
70
s
of the bobbin
70
. The respective legs of the magnetic core pieces
71
and
72
received within the cylindrical hollow
70
s
are spaced from each other by a spacer
70
g
of a thickness G that is formed within the cylindrical hollow
70
s
to define a magnetic gap
73
between end faces of the pairs of the legs of the magnetic core pieces
71
and
72
. In a condition so assembled, the magnetic core pieces
71
and
72
form a core assembly
75
of a generally rectangular shape having a generally rectangular center void, wherein a coupling coefficient between the primary and secondary windings
64
p
and
64
s
is within the range of 0.6 to 0.8 so that the secondary winding can have a leakage inductance. This structure of the known transformer makes no use of a high frequency choke coil on the side of the secondary winding that has hitherto been required in the inverter circuit for use with the magnetron.
It has, however, been found that the known transformer
64
discussed above has a problem. Specifically, since a magnetic circuit C is formed only on one side of the primary and secondary windings
64
p
and
64
s
(i.e., on a left side as viewed in
FIG. 29
) and since the respective bridge arms
71
a
and
71
b
of the core pieces
71
and
72
forming the magnetic circuit C extend parallel to each other while spaced a substantial distance from each other, a magnetic loss is significant and no strong magnetic flux can be obtained. For this reason, in order to secure a required output voltage, the number of turns of the primary and secondary windings
64
p
and
64
s
cannot be reduced. Accordingly, with the known transformer
64
, if the width (as measured in a direction conforming to the longitudinal sense of the bobbin
70
) of each of the primary and secondary windings
64
p
and
64
s
is reduced so that the resultant transformer can have a substantially flat configuration, the coil outer diameter (as measured in a direction perpendicular to the longitudinal sense of the bobbin
70
) of each of the primary and secondary windings
64
p
and
64
s
tends to increase for the number of turns thereof necessitated to secure the required output voltage. The consequence is that the known transformer
64
is relatively bulky, having a relatively large transverse dimension as measured in a lateral direction conforming to the coil outer diameter. As such, the transformer
64
of the structure discussed above is incapable of being assembled compact and requires a relatively large space for mounting on a circuit substrate.
The above discussed transformer
64
has another problem. As discussed above, the transformer
64
has the spacer
70
g
for defining the gap
73
, that is positioned at a location surrounded by the primary winding
64
p
, and also makes use of the generally U-shaped core pieces
71
and
72
wherein the legs of the core piece
71
have a different from that of the core piece
72
and wherein one of the legs of the core piece
71
and one of the legs of the core piece
72
are inserted into the cylindrical hollow
70
s
of the bobbin
70
. Accordingly, the known transformer
64
requires two types of core pieces of different sizes and this leads to increase of the type of core pieces and, hence, that of the manufacturing cost. The high frequency heating apparatus constructed utilizing the transformer
64
of the structure shown in and described with particular reference to
FIG. 29
is generally mounted on a circuit substrate of a relatively large size on which electric component parts connected to the transformer
64
such as a primary circuit including the rectifying circuit
62
and the inverter
63
and a secondary circuit including the half-wave rectifying circuit
65
as shown in
FIG. 27
are formed. Considering that the transformer
64
has a relatively large transverse dimension as discussed hereinbefore, mounting of such transformer
64
requires a further increase of the size of the circuit substrate. Also, since the secondary circuit defines a high voltage generating circuit, the circuit substrate must have a correspondingly increased size so that the secondary circuit can be spaced a sufficient distance from the primary circuit and a ground to provide a sufficient electrical insulation therebetween. For these reasons, a circuit unit including the transformer
64
mounted on the circuit substrate requires a relatively large space for installation and, therefore, application thereof is limited, thereby constituting a cause of the high frequency heating apparatus incapable of being manufactured compact.
Accordingly, the present invention has been devised to substantially eliminate the above discussed problems and is intended to provide an electromagnetic induction device that can be assembled having a substantially flat configuration without incurring an increase of the transverse dimension.
SUMMARY OF THE INVENTION
In order to accomplish the foregoing object of the present invention, there is provided an electromagnetic induction device including a core assembly for defining a magnetic circuit and comprised of generally T-shaped or L-shaped first and second core pieces, a generally flat bobbin having an axial width and a radial size, the axial width being smaller than the radial size and also having a bore defined therein so as to extend in an axial direction of the bobbin, and a winding member mounted on the bobbin. The core legs of the first and second core pieces are inserted into the bore of the flat bobbin while the core arms of the first and second core pieces extend parallel to each other.
The term “T-shaped” referred to hereinbefore and hereinafter in connection with each of the core pieces is intended to mean the shape in a stereoscopic vision similar to the shape of a figure “T” and does not include the T-shape as viewed in a side representation of a disc having a leg secured at one end to a center of the disc so as to extend perpendicular to the disc. Simil
Kambara Seiji
Masuda Shin'ichi
Miyazaki Sinobu
Souma Hideaki
Takashige Yutaka
Nguyen Tuyen T.
Tabuchi Electric Co., Ltd.
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