Electric heating – Microwave heating – With control system
Reexamination Certificate
2002-03-11
2004-01-13
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With control system
C219S705000, C219S757000, C219S716000
Reexamination Certificate
active
06677562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency heating apparatus including an inverter power supply as the power source for performing dielectric heating by using magnetron such as a microwave oven. The invention also relates to a cooling construction of a magnetron-driving power supply of the high-frequency heating apparatus. The present invention further relates to a power control method for the safe operation of a high-frequency power supply apparatus and for the overheat protection of the detection performance of a cooking detection sensor.
2. Description of the Related Art
A magnetron-driving power supply, in which a high-voltage circuit, a low-voltage circuit, and a leakage transformer are integrated on a printed circuit board and which is a so-called inverter circuit, has been widely used as a microwave oven power supply.
FIG. 6
is a front and side view of a prior-art magnetron-driving power supply.
As such, respective components are integrally mounted on one board and provided as one unit board.
1
denotes a leakage transformer, and
2
denotes a radiating fin for cooling a power switching element.
FIG. 7
is a block diagram showing an inverter circuit.
Voltage from a commercial power supply is converted to a unidirectional voltage by a unidirectional power supply portion
3
composed of diode bridges. The unidirectional voltage undergoes current smoothing and voltage smoothing by a rectifying filter
6
composed of a choke coil
4
and a smoothing capacitor
5
. Output from the rectifying filter
6
is converted to high-frequency power of 30-50KHz by an inverter portion
7
. As a method for this inverter portion, various styles including a voltage resonant type, a current resonant type, a partial resonant type, and a half-bridge method are applicable. The electric power is converted to high-frequency high-voltage by the leakage transformer
1
. This high-frequency voltage is converted to a direct current high voltage by means of a high-voltage rectifying means
8
composed of a capacitor and a diode.
The leakage transformer
1
includes tertiary winding, supplies electric power to a filament of a magnetron
9
through a high-voltage lead wire
10
, and makes electrons radiate from a cathode. On the other hand, the voltage which has been converted to a direct current high voltage by the high-voltage rectifying means
8
is applied, similarly through the high-voltage lead wire
10
, to an anode-cathode section of the magnetron
9
and radiates a microwave output into a microwave oven, thereby heating food by dielectric heating. Moreover, the inverter portion
7
is controlled by an inverter control portion
11
, and a power switching element inside the inverter portion
7
is ON/OFF controlled. A magnetron-driving power supply
12
is constructed by the above construction. In addition,
13
is connected to a chassis to be a ground potential.
Next,
FIG. 6
is a front and side view of a magnetron-driving power supply
12
, which have been already described, and
14
denotes a power switching element, which is screwed on the radiating fin
2
to be closely fitted. Loss of this power switching element
14
is conducted as heat to the radiating fin
2
and cooled by forcedly cooling air together with the radiating fin
2
.
15
denotes a high-pressure capacitor and
16
denotes a high-pressure diode, thereby constructing a high-pressure rectifying means
8
. All of these components are mounted on a paper phenol board
17
, thus constructing the integrated magnetron-driving power supply
12
, which has been described for FIG.
7
. As this inverter method, a dual transistor method is assumed, therefore, two power switching elements
14
are provided.
The radiating fin is constructed by a group of fins laterally protruding from a core portion which is in the parallel direction with respect to the transistor, and is cooled by air passing therethrough. The power switching element
14
is connected to the radiating fin
2
with heat-conductive silicone grease or the like sandwiched therebetween and transmits heat to the radiating fin
2
. When the fin group of the radiating fin
2
is sufficiently exposed to the air, it is unnecessary to use a very expensive low-loss power switching element as a power switching element
14
. Also, the magnetron-driving power supply
12
is completed in this condition, therefore, it is unnecessary to prepare an assortment of various models according to the setting type and extremely unified and efficient manufacturing can be realized.
In a magnetron-driving power supply using this inverter circuit, it is very common that cooling of the respective components is performed by forced cooling by the cooling fan.
FIG. 8
is a cooling constructional view of a prior-art magnetron-driving power supply.
18
denotes a cooling fan, which is activated by a motor
19
. In addition,
20
denotes an orifice of the cooling fan. In addition,
21
denotes an air guide for guiding air from the cooling fan to a magnetron-driving power supply
12
. The air from the cooling fan is centralized by this air guide
21
so as to contact the magnetron-driving power supply
12
.
FIG. 9
is a cooling constructional view in a case of transmission through the air guide
21
. The most significant theme is cooling the radiating fin
2
connected to the leakage transformer
1
and a power switching element
14
whose temperature is most intensive.
FIG. 10
is a view showing airflow with a prior-art cooling construction. When a propeller fan is used as a cooling fan, outflow of the air from the cooling fan becomes radial in the direction A. Accordingly, the air A from the cooling fan, first, contacts a part of the air guide
21
-P then flows in the direction A′ of the drawing. Accordingly, the air velocity of A′ considerably decreases compared to the initial air A flowed out from the cooling fan. Moreover, air B which is directly parallel with the axial direction of the cooling fan directly contacts the magnetron-driving power supply, however, the air force is weak compared to that of the air A flowing out radially. Accordingly, although the air of the cooling fan cannot be effectively utilized perfectly, an advantage such as a simple cooling construction exists, therefore, such a cooling construction has been conventionally used.
However, in recent years, with strong demand for a higher microwave oven output, power consumption of a magnetron-driving power supply, in particular, power consumption of a switching element and a leakage transformer has become remarkably high. Accordingly, it has become necessary to design a more efficient cooling construction for a magnetron-driving power supply. In addition, in order to deal with downsizing and novel designs of microwave ovens, restrictions on a machine room space for a cooling system, a magnetron-driving power supply, etc., have became stricter and an efficient cooling construction within a limited space has become necessary.
Such a high-frequency heating apparatus using an inverter power supply as the power source is disclosed, for example, in Japanese Unexamined Patent Publication No. Hei-6-50550. FIG.
14
and
FIG. 15
show the high-frequency heating apparatus according to the prior art disclosed in the above-mentioned publication.
FIG. 14
is a cross sectional view showing a power supply section in the high-frequency heating apparatus. Numeral
31
indicates a heating chamber. Numeral
32
indicates a magnetron for generating high-frequency power. Numeral
33
indicates an inverter power supply for supplying power to the magnetron. Numeral
34
indicates a cooling fan for cooling the power supply section.
FIG. 15
is a perspective view showing the appearance of the inverter power supply
33
. Numeral
35
indicates a semiconductor rectifier element for rectifying the commercially available electric power. Numeral
36
indicates a semiconductor switching element for converting the rectified power into high-frequency power. Numeral
37
indicates a high-vo
Abe Yukio
Oshima Kosho
Sumi Hiroshi
Yamauchi Masato
Leung Philip H.
Pearne & Gordon LLP
LandOfFree
High-frequency heating apparatus and cooling system for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High-frequency heating apparatus and cooling system for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-frequency heating apparatus and cooling system for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3195942