Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2003-01-10
2004-11-16
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S303000, C361S329000, C361S306100
Reexamination Certificate
active
06819541
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a capacitor for a magnetron of a microwave oven, and more particularly to a capacitor for a magnetron of a microwave oven capable of effectively shielding noise generated from the magnetron of the microwave oven.
PRIOR ARTS
Generally, various apparatuses such as home microwave oven, commercial thawing machine, industrial dryer and the like using microwave include a magnetron for generating the microwave and a capacitor for shielding noises.
The magnetron for generating the microwave is provided in an electric field space of the microwave oven. Such microwave is generated when a high voltage conducted by first and second conductive coils of a high voltage transformer attached on a substrate in the electromagnetic field space is stably supplied to the magnetron. The high voltage is generated by a conducting action of the conduction coils. Such microwave is emitted through an irradiating tube in a cooking chamber.
After passing through the irradiating tube, the microwave is emitted in the cooking chamber to heat and to cook foods placed in the cooking chamber.
The electric power line of the magnetron is mainly comprised of filament, cathode and anode. When the high voltage is applied to the magnetron to generate the microwave, the microwave having a basic frequency suitable for heating the foods as well as an unnecessarily emitted microwave, i.e. noise are generated. Then, the noise flows backward through the filament and the cathode to conduct the wave interruption to adjacent appliances.
Especially, as a television broadcasting using a satellite is widely used, the unnecessary microwave of the magnetron interacts with the broadcasting frequency so as to make an obstruction to the television receiver.
A chock coil and a capacitor connected thereto are provided to the cathode in order to reduce the reverse effect on the adjacent appliance by the noises of the magnetron. The cathode supplies electricity to the filament. The choke coil having a conductive resistance and the capacitor connected thereto absorb the unnecessary microwave, thereby preventing a leakage of the unnecessary microwave.
The choke coil is enclosed within the insulation case which is provided under the magnetron, while the capacitor is mounted outside of the insulation case. One end of the choke coil is connected to the power supply line of the filament, of which the other end is connected to a lead line of the capacitor.
A through type capacitor is widely used, which is disclosed in U.S. Pat. No. 4,811,161 (issued to Sasaki, et al on Mar. 7, 1989). In a magnetron using the through type capacitor, the choke coil is in series connected between the cathode of the magnetron and a through conduction of the through type capacitor, and the through type capacitor is inserted in a sidewall of an insulating case.
FIG. 1
is an exploded perspective view of a noise insulation apparatus including a through type capacitor according to the conventional art, and
FIG. 2
is a sectional view of the through type capacitor shown in FIG.
1
.
As shown in
FIGS. 1 and 2
, the conventional through type capacitor
10
includes an ellipse ceramic dielectric
20
. The ceramic dielectric
20
has a pair of parallel thru-holes
22
a
and
22
b
. A spaced pair of electrodes
24
a
and
24
b
is provided on an upper surface of the ceramic dielectric
20
while a common electrode
26
is provided on a lower surface of the dielectric
20
. The spaced electrodes
24
a
and
24
b
, and the common electrodes
26
respectively comprise thru-hole corresponding to the thru-holes
22
a
and
22
b
of the ceramic dielectric
20
. The capacitor
10
further includes a grounding fitment
30
of metal material of which an ellipse opening
32
is formed at the center portion. An upstanding is formed at a desired height along a periphery of the opening on the grounding figment
30
. The ceramic dielectric
30
is fixed via the common electrode
26
on the upstanding of the grounding fitment
30
in a suitable manner of soldering and the like.
Furthermore, the capacitor
10
includes a pair of conductor coated with insulation tubes
36
a
and
36
b
. The insulation tubes
36
a
and
36
b
are made of a proper material such as silicon and the like. The insulation tubes
36
a
and
36
b
are respectively inserted into the respective thru-holes
22
a
and
22
b
. The opening
32
and the through conductor
38
a
and
38
b
are respectively fitted to the respective electrode connectors
40
a
and
40
b
by press. The respective electrode connector
40
a
and
40
b
are fixed to the spaced electrodes
24
a
and
24
b
in a proper manner of soldering and the like. The through conductors
38
a
and
38
b
may be fixed to the electrode connectors
40
a
and
40
b
by the soldering and the like.
The grounding fitment
30
is formed by pressing a metal plate so that the upstanding
34
is projected to enclose the opening
32
and so that a surface of the grounding fitment
30
has a recess
42
to form an inner surface of the upstanding
34
. Four thru-holes
31
are formed at four corners of the grounding fitment
30
, through which the grounding fitment
30
can be attached to the shielding case
50
.
The capacitor
10
further includes an insulation case
52
enclosing the ceramic dielectric
20
and an insulation cylinder
54
enclosing the thru-conductor
38
a
and
38
b
. A lower portion of the insulation case
52
is fixed to the upstanding
34
of the grounding fitment
30
while an upper portion of the insulation cylinder
54
is fixed into the recess
42
of the grounding fitment
30
. The insulation case
52
and the insulation cylinder
54
are filled with insulation materials
60
and
62
such as epoxy resin and the like so that the ceramic dielectric
20
is covered with the resin or in which the resin is filled in order to be waterproof and to secure insulation property of the ceramic dielectric
20
. The reference numeral
64
denotes a surface of the insulation resin in FIG.
2
. The insulation case
52
and the insulation cylinder
54
are made of thermoplastic resin such as polybutylene terepthalate (PBT).
The respective through conductors
38
a
and
38
b
have respective fixing tabs
39
a
and
39
b
integrally formed at an end thereof, which are received in the insulation case
52
to apply high voltage. Since one end of the fixing tabs
39
a
and
39
b
is projected through one end of the insulation case
52
, the fixing tabs
39
a
and
39
b
are easily connected to an outer terminal.
When the grounding fitment
30
is fixedly pressed to the shielding case
50
, a large opening
56
corresponding to the capacitor
10
and four bearing holes
58
corresponding to four thru-holes
31
of the grounding fitment
30
are formed in the shielding case
50
. Then, the bearing holes
58
face the thru-holes
31
so that the grounding fitment
30
is assembled by means of bolts with the shielding case
50
.
The thru type capacitor
10
connecting the choke coil of the shielding case
50
to the outer terminal prevents the noises from being conducted through the lead line, which shields the radiated noises.
As described above, however, since the apparatus for shielding the noises from the magnetron according to the conventional art includes a plurality of assembling parts, the structure of the apparatus is complicated so that the cost of material increases as well as the assembling process becomes very difficult to reduce productivity. Furthermore, after assembling, some microwaves leak through the inserting hole of the shielding case, the thru-holes of the grounding fitment and the bearing holes of the shielding case, failing to prevent the noises to the utmost.
SUMMARY OF THE INVENTION
Therefore, the present invention has been developed to solve the above-mentioned problems.
It is an object of the present invention to provide a capacitor of a magnetron for a microwave oven capable of shielding noise such as unnecessary microwave generated from the magnetron, which has a simple structure to re
Daewoo Electronics Corp.
Dinkins Anthony
Jones Day
LandOfFree
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