This application claims the benefit of Korean Patent Application No.  2002-37793 filed on Jul. 2, 2002, 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 having a high voltage control circuit which prevents an overheating of a high voltage transformer. 
2.  Description of the Related Art
Generally, microwave ovens are cooking devices which oscillate molecular arrangements of food by generating microwaves and irradiating the microwaves to the food.  That is, the food is cooked using a heat generated during the oscillation of the molecular arrangements of the food. 
FIG.  1 shows a circuit diagram of a high voltage control circuit of a conventional microwave oven. 
As shown in FIG.  1, the high voltage control circuit of the conventional microwave oven comprises a main fuse FUSE which is connected to one AC terminal of an input alternating current (AC) power source, a high voltage transformer HVT which boosts an input voltage, a high voltage condenser HVC and a high voltage diode HVD which convert the voltage boosted by the high voltage transformer HVT into a high direct current (DC) voltage, and a magnetron MGT which is driven by a rectified high voltage to generate microwaves. 
In such a conventional microwave oven, a maximum current resistible by the main fuse FUSE is set to be a current that can excessively increase the temperature of the high voltage transformer HVT.  Therefore, where the maximum current is exceeded, the main fuse FUSE is blown. 
However, the conventional microwave oven is problematic in that, where the main fuse FUSE is blown, the supply of a voltage to a primary coil of the high voltage transformer HVT is shut off, thus stopping the magnetron MGT and preventing the microwave oven from operating until the FUSE is changed. 
Accordingly, it is an aspect of the present invention to provide a microwave oven having a high voltage control circuit which decreases a voltage supplied to a magnetron and prevents overheating of a high voltage transformer by increasing a number of turns of a primary coil of the high voltage transformer so as to decrease the output of the magnetron where a temperature of the high voltage transformer reaches a predetermined temperature. 
Additional aspects 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 aspects of the present invention there is provided a microwave oven comprising a magnetron to cook food contained in the oven, a voltage converting unit which supplies a predetermined voltage to the magnetron by boosting an input voltage, and an output variable unit which varies an output of the magnetron by varying a voltage supplied to the magnetron according to a temperature of the voltage converting unit. 
To achieve the above and other aspects of the present invention, there is further provided a high voltage control circuit of a microwave oven, comprising a high voltage transformer having a primary coil connected to a power stage of the oven and a secondary coil connected to a load stage of the oven, wherein the high voltage transformer boosts a voltage input from the power stage, a magnetron which is connected to the secondary coil of the high voltage transformer and generates microwaves, a tap formed at the primary coil of the high voltage transformer so as to allow the primary coil to have different numbers of coils, and a switching unit disposed between a first fixed terminal of the tap formed at the primary coil and a second fixed terminal connected to the power stage, and is switched to one of on and off according to a temperature of the high voltage transformer.