Electric heating – Microwave heating – With control system
Reexamination Certificate
1999-09-01
2001-04-17
Walberg, Teresa (Department: 3742)
Electric heating
Microwave heating
With control system
C219S505000, C307S135000
Reexamination Certificate
active
06218652
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for APPARATUS FOR ELIMINATING INRUSH CURRENT OF A MICROWAVE OVEN earlier filed in the Korean Industrial Property Office on the 29th of May 1999 and there duly assigned Ser. Nos. 19599/1999 and 19600/1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to an apparatus for eliminating inrush current in an application of initial voltage in a microwave oven.
2. Description of the Prior Art
As well known, a microwave oven is a device for radiating microwave generated from a magnetron to a foodstuff safely placed in a cooking chamber and cooking the foodstuff by fictional heat generated by an inner molecular movement. This microwave oven is generally classified into two types; an electronic type using a microcomputer and a mechanical type using a timer.
FIG. 1
is a disassembled perspective view of a conventional electronic type microwave oven. Referring to
FIG. 1
, in the aspect of its structure, the conventional microwave oven
10
is roughly composed of a controlling part
20
, a high voltage driving part
30
and a heating part
40
.
The controlling part
20
has a plurality of buttons
21
for determining the cooking time and the cooking power in the microwave oven, and the plurality of buttons
21
are connected to a printed circuit board (PCB)
6
on the rear side of which a microcomputer
9
and various components are built-in. The microcomputer
9
of the PCB
6
performs the cooking mode by turning on/off the driving status of the microwave oven according to the time and power determined by the respective buttons
21
. Further, the controlling part
20
includes a display window
24
for displaying various kinds of cooking times and cooking statuses, and a door lever
25
, which will be described later, for opening and closing a door
43
.
The high voltage driving part
30
consists of a magnetron MGT for generating microwave, a waveguide (not shown) for guiding the microwave generated from the magnetron MGT to a cooking chamber
41
, a high voltage transformer HVT for generating high voltage and pre-heating voltage needed for the driving of the magnetron MGT, a cooling fan
3
for cooling the high voltage transformer HVT, a high voltage capacitor HVC, a high voltage diode HVD, and the magnetron MGT, and a lamp
2
for lighting the cooking chamber
41
, etc.
The heating part
40
consists of the cooking chamber
41
as a closed space, a rotary tray
42
on which foodstuffs may be securely placed in the cooking chamber
41
, and a door
43
for opening and closing the cooking chamber
41
.
FIG. 2
shows the circuit diagram of FIG.
1
. As shown in
FIG. 2
, first and second power lines L
1
, L
2
for receiving general alternating current, AC 220V, are connected with both ends of a primary coil
7
a
of the high voltage transformer HVT via a noise filter
1
. This noise filter
1
is composed of a main fuse FUSE
1
, capacitors C
1
to C
3
, an inductor L, a resistor R
1
, etc. A detailed description about operations of the noise filter is herein omitted since it is the same as a general noise filter for cutting off high frequency (HF) transferred to the outside through the power lines L
1
and L
2
.
The first power line L
1
is connected in series with a magnetron temperature sensor TCO
1
which is turned on/off according to the temperature of the magnetron MGT to prevent overheating of the magnetron, a first door switch SW
1
which is turned on/off according to the opening or closing status of the door
43
, and a monitor switch SW
MT
for monitoring the opening or the closing state of the door
43
.
The second power line L
2
is connected in series with a cooking chamber temperature sensor TCO
2
which is turned on/off according to the temperature of the cooking chamber
41
to prevent the overheating of the cooking chamber
41
, and a power relay RY
3
for turning on/off main power. The power relay RY
3
is also connected in parallel with an inrush relay RY
2
for eliminating inrush current. The inrush switch SW
IR
is connected to a resistor R
2
for restricting the current, wherein the resistor R
2
for current restriction is generally a cement resistor having a high resistance capability.
The power relay RY
3
and the inrush relay RY
2
constitute respective relay elements, together with individual coils, respectively. The power relay RY
3
and the inrush relay RY
2
are turned on/off by the respective relay coil which is disposed on the PCB
6
and controlled by the microcomputer
9
.
At this time, the inrush relay RY
2
is firstly turned on by a control of the microcomputer
9
, and after a given time period, e.g., 20-40 ms, the power relay RY
3
is operated. Therefore, after an application of initial power, the inrush current of high reverse-electromotive force generated by the high voltage transformer HVT is consumed by the current restriction resistor R
2
and the inrush relay RY
2
, and then, the power relay RY
3
is turned on, to thereby prevent an overload of each driving circuit and damage to the microwave oven.
For the operation of the microwave, the microcomputer
9
turns on the main relay RY
4
, the inrush relay RY
2
and the power relay RY
3
through the respective coils arranged on the PCB
6
. Accordingly, the main relay RY
4
is turned on, and the lamp
2
, the fan motor
3
and the driving motor
4
of the microwave oven are operated. Further, as the inrush relay RY
2
and the power relay RY
3
are sequentially turned on, voltage is generated by the high voltage driving part
30
, and the magnetron MGT of the high voltage driving part
30
generates the microwave for cooking foodstuff placed in the cooking chamber
41
.
Meanwhile, the heater is operated by the same operation of the above components, except that the microcomputer
9
turns off the inrush relay RY
2
and the power relay RY
3
, while turning on the heater relay RY
1
, to operate the heater
8
instead of the magnetron MGT so that the grill cooking is performed.
FIG. 3
is a disassembled perspective view of a conventional mechanical type microwave oven. In
FIG. 3
, in its structural aspect, a conventional microwave oven
10
may be roughly divided into a controlling part
20
′, a high voltage driving part
30
, and a heating part
40
, which is the same as in the above-mentioned electronic type. The difference of the mechanical type microwave oven from the electronics type is that the controlling part
20
′ is composed of respective time control knob
21
and power control knob
22
for determining each of the cooking time and cooking power of the microwave oven. Each of knobs
21
and
22
is connected to a timer
23
placed on its rear side. Due to the timer
23
which turns on or off the driving status of the microwave oven according to the time and the power determined by each of the knobs
21
and
22
, the microwave oven performs a cooking operation properly. Further, the controlling part
20
′ also includes a display window
24
for displaying various cooking times and statuses, and a door lever
25
for opening or closing the door
43
, which will be described later.
FIG. 4
is the circuit diagram of FIG.
3
. As shown in
FIG. 4
, the first and second power lines L
1
and L
2
for receiving the general alternating current, AC 220V, are connected with both ends of the primary coil
7
a
of the high voltage transformer HVT via the noise filter
1
. The noise filter
1
is composed of the main fuse FUSE
1
, the capacitors C
1
to C
3
, the inductor L, the resistor R
1
, etc. The detailed description about operations of the noise filter will be omitted since it is the same as a general noise filter used for cutting off the high frequency (HF) transferred to the outside through the power lines L
1
and L
2
.
The first power line L
1
is connected in series with the magnetron temperature sensor TCO
1
which is turned on/off acc
Choi Won-woo
Kim Cheol-jin
Bushnell , Esq. Robert E.
Pwu Jeffrey
Samsung Electronics Co,. Ltd.
Walberg Teresa
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