Electric heating – Microwave heating – With control system
Reexamination Certificate
2000-02-10
2001-04-24
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With control system
C219S702000, C363S021030, C363S131000, C361S002000, C361S118000
Reexamination Certificate
active
06222169
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 Magnetron driving Circuit for an AC/DC Microwave Oven earlier filed in the Korean Industrial Property Office on Sep. 21, 1999 and there duly assigned Serial No. 1999-40702.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetron driving circuit, and more particularly to a magnetron driving circuit capable of preventing the production of a reverse surge voltage during a supply of direct current power.
2. Description of the Related Art
Generally, a microwave oven is a device for cooking food by using microwaves, and has a high voltage transformer (hereinafter called HVT), and a magnetron MGT. The HVT steps up the normal voltage into the higher voltage, and the magnetron MGT is driven by the higher voltage to generate the microwaves of a certain frequency.
Meanwhile, such a microwave oven is designed to be driven by alternating current (hereinafter called AC), and can not be used in the places such as the outdoors, vehicles such as ship, airplane, etc., where the AC is not available. In order to solve such a shortcoming of the microwave oven, an inverter is used to convert the direct current (hereinafter called DC) into the AC for using the microwave oven in the place where the AC is not available.
The AC generated by the inverter is stepped up by the HVT to drive the magnetron MGT. Here, when the DC voltage is converted into the AC power and is outputted by the inverter, there occurs a reverse surge voltage induced at a primary part of the HVT from a secondary part of the HVT, which generates a spark at the inverter. For example, before the high voltage capacitor (hereinafter called HVC) at the secondary part of the HVT is charged, the secondary side circuit forms the short circuit and the reverse surge voltage occurs at the primary coil, resulting in a spark at the inverter. Further, after the HVC is charged, the energy of the secondary coil is reversely induced to the primary coil every half-period, again resulting in the spark at the inverter due to the energy reversely induced.
Hereinafter, the construction, operation, and problems of the inverter driven by the DC power and a magnetron driving part connected with the inverter will be briefly described as a related art.
There are various types of invertors such as the inverter using a relay, and the inverter using semiconductor devices, etc. The same applicant has disclosed a non-directional frequency generator (hereinafter called NDFG), which is an improved version of the inverter, in the Korean Patent Application, and here, the construction, operation, and the shortcomings of the NDFG and the magnetron driving section connected thereto will be described.
The NDFG converts the DC power into the AC power source by using rotatable AC converting means, and is disclosed in the Korean Patent Applications Nos. 98-18589 (filed May 22, 1998), and 98-21117 (filed Jun. 8, 1998) which have not been opened to the public yet.
FIG. 1
is a circuit diagram for showing the NDFG driven by the DC power and the magnetron driving part connected thereto according to the related art of the present invention. Referring to
FIG. 1
, the NDFG
100
includes a motor
110
driven by the DC for generating rotational force, a commutator
130
rotated by the motor
110
, and a plurality of brushes such as first, second, third, and fourth brushes
121
-
124
as shown in
FIG. 1
, which are in contact with the outer circumference of the commutator
130
. The commutator
130
includes a conductive part which is divided into at least two parts
132
a
and
132
b
as shown in
FIG. 1
, but into an even number of parts. The conductive parts
132
a
and
132
b
have an insulating part
133
of a certain width formed therebetween. The conductive parts
132
a
and
132
b
are in simultaneous contact with at least two neighboring brushes
121
-
124
. The DC is applied to the input sides of the first to fourth brushes
121
-
124
, while the output sides of the first to fourth brushes
121
-
124
are connected with a high voltage transformer (hereinafter called HVT). The first and second relays RY
1
and RY
2
switch on/off the operation of the NDFG
100
.
The operation of the NDFG
100
is as follows: The first and second relays RY
1
and RY
2
are in on-state, and the commutator
130
is rotated by the DC. Accordingly, the brushes
121
-
124
in contact with the commutator
130
come in contact with the conductive part
132
a
, the insulating part
133
, the conductive part
132
b
, and the insulating part
133
which are formed on the outer circumference of the commutator
130
, sequentially.
More specifically, as the first brush
121
on the upper side of the commutator
130
comes in contact with the conductive part
132
a
, the electric current from the positive (+) terminal of the DC power source is inputted into the first brush
121
, and flows through the conductive part
132
a
of the commutator
130
and the fourth brush
124
, and to the upper portion of the primary coil
202
of the HVT downwardly to the lower portion of the primary coil
202
of the HVT. Then, the electric current is inputted into the second brush
122
, and circulates through the conductive part
132
b
, the third brush
123
, and to the negative (−) terminal of the DC power source.
Next, as the commutator
130
is further rotated and as the first brush
121
accordingly comes in contact with the insulating part
133
, the electric current does not flow through the commutator
130
.
Then as the commutator
130
is further rotated to 90°, the electric current from the positive (+) terminal of the DC power source is inputted into the first brush
121
, flows through the conductive part
132
b
of the commutator
130
and the second brush
122
, reverses its direction, and flows from the lower portion of the primary coil
202
of the HVT to the upper portion of the primary coil
202
of the HVT. Then, the electric current is inputted into the fourth brush
124
, flows through the conductive part
132
a
, and the third brush
123
, and then circulates to the negative (−) terminal of the DC power source.
By the constant rotation of the commutator
130
of the NDFG, the AC is generated at the primary coil
202
of the HVT in a manner as described above, then the AC is transmitted to a secondary coil of the HVT through the primary coil
202
thereof. Then, the HVT converts the normal voltage into a higher voltage, and the magnetron MGT is driven by the higher voltage converted by the HVT.
When the magnetron is driven, there occurs a problem that the secondary circuit forms a short circuit until the high voltage capacitor HVC of the secondary part of the HVT is charged. That is, when the AC induced from the NDFG
100
is applied to the HVT, the high voltage capacitor HVC connected to the secondary coil of the HVT is shorted instantaneously, and thus a reverse surge voltage occurs in the primary coil. Nearly infinite inrush current due to the reverse surge voltage generates a spark between the brushes and the commutator of the NDFG
100
.
Furthermore, even after the high voltage capacitor HVC is normally charged, there occurs another problem that the electric energy of the secondary coil is induced reversely to the primary coil every half period. The reversely induced electric energy generates a spark between the brushes and the commutator of the NDFG
100
.
Meanwhile, the problems do not only occur between the magnetron driving part and the NDFG driven by the DC, rather they occur between the magnetron driving part and the inverter in a broad sense for inverting the DC to the AC, including the NDFG.
SUMMARY OF THE INVENTION
The present invention has been developed to overcome the above ploblems of the related art, and accordingly it is an object of the present invention to provide a magnetron driving circuit capable of preventing a reverse surge voltage when driven b
Han Yong-Woon
Jang Seong-deog
Kang Kwang-Seok
Sung Han-Jun
Bushnell , Esq. Robert E.
Leung Philip H.
Samsung Electronics Co,. Ltd.
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