Microwave oven

This application claims the benefit of Korean Application No. 2001-84396, filed Dec. 24, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

1. Field of the Invention

The present invention relates to microwave ovens, and more particularly, to a microwave oven which eliminates noise to a satisfactory standard while enduring strong vibrations.

2. Description of the Related Art

Generally, a microwave oven carries out a cooking operation by receiving an alternating current (AC) voltage from a commercial AC power source, converting it into a high voltage, and driving a magnetron using the high voltage to generate microwaves to irradiate and cook foods.

Recently, a microwave oven has been developed to use a direct current (DC) power, such as a battery, as operating power, so as to install the microwave oven in mobile vehicles, such as cars or passenger ships.

The microwave oven using the DC power employs an inverter circuit to convert a DC voltage into an AC voltage required to drive a magnetron.

FIG. 1 shows a conventional microwave oven using DC power comprising a DC power source 1 , such as a portable battery, a switching unit 2 , an inverter unit 3 , a high voltage transformer 4 , a magnetron driving unit 5 and a magnetron filter box 6 . The magnetron filter box 6 includes choke coils 8 and a feed-through condenser 9 installed therein, which constitute a low pass filter, so as to prevent fundamental waves of 2450 MHz, harmonic waves and noise generated by the driving of the magnetron 7 , from radiating to the outside.

Ferrite cores (not shown) are inserted into the choke coils 8 , and ends of the coils 8 wound around the ferrite cores are fixed through a welding process. Typically, a large inductance of the choke coils 8 favors reduction of noise, so the choke coils 8 are designed to be as large as possible.

However, vibration standards established by a standards organization, with respect to microwave ovens using DC power, are strict compared with those of a microwave oven using AC power for a home use. For example, a vibration standard of a microwave oven using DC power and installed in a car is limited to 3.3 to 4G. Accordingly, if a magnetron filter box used in the conventional microwave oven for a home use is applied to the microwave oven for a car, welding portions of choke coils may be easily damaged as the installation structure of the choke coils in the magnetron filter box is too weak to endure significant vibrations.

Therefore, there is a need for a microwave oven usable with DC power which satisfies the vibration standards as well as noise standards with respect to a magnetron filter box used in the microwave oven.

Accordingly, it is an object of the present invention to provide a microwave oven having choke coils which are installed inside and outside of a magnetron filter box so as to endure strong vibrations and eliminate noise to desired noise standards.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.

To achieve the above and other objects of the present invention, there is provided a microwave oven comprising a magnetron filter box having a magnetron, at least one first choke coil, and a feed-through condenser installed therein, and at least one second choke coil arranged outside the magnetron filter box and connected in series to the first choke coil, wherein the second choke coil, together with the feed-through condenser, constitutes a low pass filter.

According to an aspect of the present invention, the first choke coil is set to have an inductance smaller than that of the second choke coil.

According to another aspect the present invention, the first and second choke coils comprise corresponding first and second ferrite cores inserted therein, wherein weights of the first and second ferrite cores are proportional to the inductances of the first and second choke coils.

According to still another aspect of the present invention, the second choke coil is mounted on a printed circuit board connected to the magnetron filter box through a lead wire.

The above and other objects, features and advantages of the present invention will become more apparent and more readily appreciated by describing in detail a preferred embodiment thereof with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a conventional microwave oven using DC power;

FIG. 2 is a block diagram of a microwave oven using DC power according to an embodiment of the present invention; and

FIG. 3 is a diagram illustrating the installation of second choke coils to first choke coils of the microwave oven shown in FIG. 2 .

Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

The present invention can be applied to microwave ovens using AC power for a home use as well as microwave ovens using DC power as a power source. Furthermore, the present invention can be applied to microwave ovens usable with a power source selected from DC and AC power sources. For convenience and to avoid unnecessary repetition, the present invention as applied to microwave ovens using DC power is described.

FIG. 2 shows a microwave oven using DC power according to an embodiment of the present invention. The microwave oven comprises a DC power source 1 , a switching unit 2 , an inverter unit 3 , a high voltage transformer 4 , a magnetron driving unit 5 and a magnetron filter box 6 and second choke coils 10 .

The DC power source 1 comprises, for example, a portable battery which supplies DC power of 6 to 48V. The switching unit 2 includes a door switch which detects the open/shut state of a door of a cooking room and blocks the DC power where the door is opened, and a low voltage transformer which supplies operating power to a controller (not shown).

The inverter unit 3 comprises a push-pull circuit having switching devices. The inverter 3 is driven by the controller (not shown) to convert the DC power into AC power, wherein its usable frequency is higher than 20 KHz. The high voltage transformer 4 comprises primary and secondary coils L 1 and L 2 which induce a high voltage, and a heater coil L 3 which heats a magnetron 7 .

The magnetron driving unit 5 comprises a half-wave voltage doubler circuit having a high voltage condenser (not shown) and a high voltage diode (not shown). The magnetron driving unit 5 supplies the high voltage of, for example, 4000V DC generated by the secondary coil L 2 and the half-wave voltage doubler circuit to the magnetron 7 .

The magnetron filter box 6 includes the magnetron 7 , first choke coils 8 a and feed-through condensers 9 . The first choke coils 8 a are connected in series to the second choke coils 10 arranged outside the magnetron filter box 6 , respectively.

In addition, rectifying diodes D may be arranged between the heater coil L 3 and the second choke coils 10 . Similar to the conventional microwave oven using the DC power (FIG. 1 ), where an operation frequency is high (higher than 20 KHz), it is difficult to drive the magnetron 7 using an AC voltage (3.3V AC) supplied from the heater coil L 3 . Therefore, in the present invention, DC power (7V DC) rectified by the rectifying diodes D may be supplied to the magnetron 7 .

The first choke coils 8 a are used to eliminate noise. However, their inductances are set to be considerably smaller than the choke coils of the conventional microwave oven. The weight of a ferrite core inserted into each of the first choke coils 8 a is also reduced in proportion to the reduced inductance. In order to compensate for the reduction of the inductance of each of the first choke coils 8 a , the inductance of each of the second choke coils 10 is set to be larger than that of each of the first choke coils 8 a . The inductance of each of the first choke coils 8 a is set to be as small as possible.

FIG. 3, with reference to FIG. 2, shows an example of an arrangement and the structure of the first and second choke coils 8 a and 10 . As shown in FIG. 3, ferrite cores 8 b and 10 b are inserted into the corresponding first and second choke coils 8 a and 10 . The ends A and B of the first choke coils 8 a wound around the ferrite cores 8 b are fixed through a welding process. The second choke coils 10 are mounted on a printed circuit board (PCB) so as to be connected to the first choke coils 8 a arranged in the magnetron filter box 6 through a socket 9 b connected to a connection plug 9 a of the feed-through condenser 9 and leading wires C.

The total inductance of the inductances of the first and second choke coils 8 a and 10 is set corresponding to frequencies of noise signals to be eliminated, and is set to an inductance value of choke coils used in, for example, a conventional microwave oven using AC power for a home use. The sizes of the first and second choke coils 8 a and 10 are determined according to their own inductances, wherein their sizes become smaller as their inductances become smaller. Therefore, the first choke coils 8 a are smaller compared to those of the conventional microwave oven for a home use, while the second choke coils 10 are relatively larger in their sizes.

Because the first choke coils 8 a are smaller, the ferrite cores 8 b inserted into the first choke coils 8 a can also be made to be smaller and lighter. Accordingly, the microwave oven of the present invention can satisfy vibration standards applied to microwave ovens using DC power, and prevent damage to the welded ends A and B of the first choke coils 8 a in the magnetron filter box 6 .

In addition, the first and second choke coils 8 a and 10 constitute separate low pass filters together with the feed-through condensers 9 , and serve to eliminate fundamental waves of 2450 MHz, harmonic waves and noise generated by the driving of the magnetron 7 . Therefore, the noise standards required in the microwave ovens using the DC power are also satisfied.

As described above, the present invention provides a microwave oven having first choke coils arranged in a magnetron filter box and second choke coils arranged outside the magnetron filter box. Each choke coil and a feed-through condenser constitute a low pass filter. The first choke coils are designed to be smaller than those in conventional microwave ovens, and the larger second choke coils are fixedly mounted on a PCB. Accordingly, the present microwave oven can endure strong vibrations and eliminate noise generated from a driving of the magnetron according to the noise standards.

Although an embodiment of the present invention has been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.