Abstract:
A microwave oven and a method of controlling the same. The microwave oven is capable of using a plurality of input powers with different frequencies. The microwave oven includes input power sources, an interrupt generation unit and a control unit. The interrupt generation unit generates interrupt signals with different periods according to the frequencies of the input powers. The control unit cumulatively counts pulses generated on the basis of the interrupt signals outputted from the interrupt generation unit, compares the cumulatively counted value with a reference value, and discriminates the frequencies of the input powers depending on the number of instances where the cumulatively counted value is equal to or greater than the reference value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 2001-77568, filed Dec. 8, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a microwave oven and a method of controlling the same, and more particularly to a microwave oven which can discriminate the frequencies of input powers.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, microwave ovens are devices which heat/cook foods using microwaves. Each of the microwave ovens has various driving devices such as a high voltage transformer and a magnetron, and is supplied with power from the outside so as to operate the driving devices. However, frequencies of powers supplied from the outside can be different according to installation environments. In general, microwave ovens use an alternating current (AC) power of 50 or 60 Hz.  
           [0006]    A microcontroller which controls the overall operation of a microwave oven with respect to a cooking operation is installed on a circuit board within a body of the microwave oven. The microcontroller controls an operation of the driving devices according to a cooking menu set by a user and carries out the cooking operation. In addition, the microcontroller counts time based on an inputted power frequency and calculates a cooking time.  
           [0007]    Conventional microwave ovens are each produced to correspond to the frequency of a specific power. Therefore, a microcontroller installed within a body of a conventional microwave oven performs a control operation corresponding to only one of the 50 Hz and 60 Hz AC powers. As a result, the microcontroller must calculate a cooking time based on a preset power frequency.  
           [0008]    However, if the power whose frequency is different from that of the preset power is supplied to the conventional microwave oven, the microcontroller still calculates and measures the cooking time based on the preset power frequency which is different from the input power frequency. This, in part, results in a deterioration of the reliability of the microwave oven.  
           [0009]    Therefore, there is a need for a microwave oven and a method of enabling a microcontroller of a microwave oven to discriminate the frequency of a supplied power from the frequency of a preset power, where the frequency of the power supplied from the outside is different from that of the power preset in the microcontroller.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an object of the present invention to provide a microwave oven and method of controlling the same, which can determine the frequency of an input power.  
           [0011]    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.  
           [0012]    To achieve the above and other objects of the present invention, there is provided a microwave oven capable of using a plurality of input powers with different frequencies, comprising input power sources, an interrupt generation unit which generates interrupt signals with different periods according to the frequencies of the input powers, and a control unit which cumulatively counts pulses generated on a basis of the interrupt signals outputted from the interrupt generation unit, compares an cumulatively counted value with a reference value, and discriminates the frequencies of the input powers based on a number of times where the cumulatively counted value is equal to or greater than the reference value.  
           [0013]    To achieve the above and other objects of the present invention, there is also provided a method of controlling a microwave oven capable of using a plurality of input powers with different frequencies, the method comprising generating interrupt signals having different periods according to frequencies of the input powers, cumulatively counting pulses generated on a basis of the interrupt signals, comparing an cumulatively counted value with a reference value, cumulatively counting a number of times where the cumulatively counted value is equal to or greater than the reference value, and determining the frequencies of the input powers based on an accumulated number of times. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The above and other objects, features and advantages of the present invention will become more apparent and more readily appreciated by describing in detail preferred embodiments thereof with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a block diagram of a microwave oven according to an embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a waveform diagram showing interrupt signals of different periods and square pulses generated from the microwave oven shown in FIG. 1; and  
         [0017]    [0017]FIG. 3 is a flowchart of a method of controlling a microwave oven according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    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.  
         [0019]    [0019]FIG. 1 shows a microwave oven according to an embodiment of the present invention. The microwave oven comprises a low voltage transformer (LVT)  10 , an interrupt generation unit  20  and a control unit  40 . The LVT  10  drops AC 200V to a lower voltage of AC 17V and outputs the AC 17V. The interrupt generation unit  20  generates interrupt signals with different periods according to the frequencies of voltage-dropped powers of the low voltage transformer  10 . The control unit  40  internally generates square pulses in response to the interrupt signals from the interrupt generation unit  20 , and counts the square pulses to discriminate between the frequencies of powers.  
         [0020]    An input terminal (not shown) of the control unit  40  is connected to a key input unit  30  having various kinds of keys including a function key which sets the cooking menu and a function key which sets cooking start/end times. The key input unit  30  outputs a key signal based on a manipulation of a corresponding function key. An output terminal (not shown) of the control unit  40  is connected to both a load driving unit  50  and a display unit  60 . The load driving unit  50  drives a power relay  51  connected to various driving devices, for example, a high voltage transformer to cook foods contained in a cooking room according to a set cooking menu, and a cooling fan  52  installed in a machine room. The display unit  60  displays, for example, a cooking state of the foods.  
         [0021]    According to an aspect of the present invention, the present invention is applied to microwave ovens which use two power sources, that is, 50 Hz and 60 Hz powers.  
         [0022]    [0022]FIGS. 2A through 2C show that the interrupt generation unit  20  periodically outputs a first interrupt signal (FIG. 2A) in response to the frequency of the voltage-dropped power being 50 Hz, a second interrupt signal (FIG. 2B) in response to the frequency of the voltage-dropped power being 60 Hz. The period (T1) of the first interrupt signal is greater than that (T2) of the second interrupt signal, wherein T1 is 20 ms and T2 is 16.67 ms.  
         [0023]    As shown in FIGS. 2A through 2C, with reference to FIG. 1, the control unit  40  internally generates the square pulses (FIG. 2C) according to the first and second interrupt signals, wherein each square pulse has a period shorter than those of the first and second interrupt signals. The control unit  40  continuously generates the square pulses in response to the input interrupt signals, and simultaneously and cumulatively counts the square pulses using an internal counter.  
         [0024]    The first or second interrupt signal is periodically inputted to the control unit  40  according to the power which is voltage-dropped by the low voltage transformer  10  and applied to the interrupt generation unit  20 . The control unit  40  cumulatively counts the square pulses for each of these periods.  
         [0025]    At this point, it should be understood that the power supplied from the outside can be varied temporarily. Even though the power supplied from the outside may be slightly lower or higher than 50 Hz in its frequency, it is reasonable to consider the supplied power as 50 Hz power. Similarly, even though the power supplied from the outside may be slightly lower or higher than 60 Hz in its frequency, it is reasonable to consider the supplied power as 60 Hz power.  
         [0026]    The control unit  40  can, as many times as it is set to, determine whether the cumulatively counted value of the square pulses is equal to or greater than a reference value. Therefore, the reference value can be set to distinguish between the powers having a corresponding 50 Hz and 60 Hz. The reference value, as shown in FIG. 2, may correspond to a value obtained by cumulatively counting the square pulses during an average period, which is the arithmetic average of the period (T1) of the first interrupt signal and the period (T2) of the second interrupt signal. Therefore, if the cumulatively counted value does not reach the reference value, a determination is made that the second interrupt signal is generated and the power having 60 Hz is being supplied to the microwave oven. On the other hand, if the cumulatively counted value is equal to or greater than the reference value, a determination is made that the first interrupt signal is generated and the power having 50 Hz is being supplied to the microwave oven.  
         [0027]    The control unit  40  performs an operation to discriminate the frequency of the power after a predetermined period of time as, in general, stable power is not supplied initially after the manipulation of a power code. Furthermore, the control unit  40  counts, several times, the number of times where the cumulatively counted value is equal to or greater than the reference value even after the passage of the predetermined period of time, and determines the frequency of the power if the accumulated number of times is equal to or greater than a preset number. Therefore, the accuracy of discriminating the frequency of the power is increased.  
         [0028]    [0028]FIG. 3, with reference to FIG. 1, shows a method of controlling a microwave oven according to the present invention.  
         [0029]    In operation  100 , the control unit  40  performs an initializing operation in response to a supply of an input driving power from a power supply unit (not shown). The control unit  40  sets the initial value of variables, for example A, B and C, to “0,” to determine the frequency of the power.  
         [0030]    In operation  200 , the low voltage transformer  10  drops the voltage of the AC power and outputs a voltage-dropped AC power to the interrupt generation unit  20 . The interrupt generation unit  20  outputs a first or second interrupt signal corresponding to the frequency of the voltage-dropped AC power to the control unit  40 , and the control unit  40  determines whether the first or second interrupt signal has been inputted.  
         [0031]    In operation  300 , where the first or second interrupt signal has been inputted from the interrupt generation unit  20 , the control unit  40  stands by for a predetermined period of time (several seconds). At this time, the interrupt generation unit  20  periodically outputs a corresponding interrupt signal, while the control unit  40  internally and periodically generates the square pulses.  
         [0032]    In operation  400 , after the elapse of the predetermined period of time, the control unit  40  determines whether the first or second interrupt signal has been inputted. In this case, if it is determined that an interrupt signal is not inputted, the control unit  40  stands by until the interrupt signal is generated. On the other hand, if it is determined that an interrupt signal has been inputted, the control unit  40  cumulatively counts the square pulses generated internally using an internal counter and updates a cumulatively counted value (B) in operation  500 .  
         [0033]    In operation  600 , the control unit  40  then determines whether the cumulatively counted value (B) is equal to or greater than a reference value (that is, a value obtained by cumulatively counting the square pulses during an average period), which is the arithmetic average of the period (T1) of the first interrupt signal and the period (T2) of the second interrupt signal.  
         [0034]    In operation  700 , if the cumulatively counted value (B) is less than the reference value according to the determination result in operation  600 , the control unit  40  determines whether the internal counter is reset. This is due to the fact that the control unit  40  resets the internal counter and then recounts the square pulses before the counted value (B) reaches the reference value if the power supplied is 60 Hz, because the reference value is between the periods of first and second interrupt signals. If the internal counter is not reset according to the determination result in operation  700 , that is, if the first interrupt signal is inputted, or the second signal does not reach the period (T2) even though the second interrupt signal is inputted, the control unit  40  returns to operation  500  so as to continue to count the square pulses. If the internal counter is reset according to the determination result in operation  700 , that is, if the second interrupt signal reaches the period (T2), the control unit  40  proceeds to operation  900 .  
         [0035]    On the other hand, if the cumulatively counted value (B) is equal to or greater than the reference value according to the determination result in operation  600 , the control unit  40  increases a power frequency state variable (A) by 1 in operation  800 .  
         [0036]    In operation  900 , it is determined whether an accumulation state variable (C) is greater than a preset number (Ca). In this case, the preset number (Ca) is set to 20. If the accumulation state variable (C) is not greater than the preset number (Ca), according to the determination result in operation  900 , the control unit  40  clears the power frequency state variable (A), increases the cumulation state variable (C) by 1 in operation  950  and then returns to operation  400 . If the accumulation state variable (C) is greater than the preset number (Ca), according to the determination result in operation  900 , the control unit  40  determines whether the power frequency state variable (A) is greater than a preset value (Aa) in operation  1000 . In this case, the preset value (Aa) is set to 10.  
         [0037]    If the power frequency state variable (A) is greater than the preset value (Aa), according to the determination result in operation  1000 , the number of times where the cumulatively counted value (B) is equal to or greater than the reference value is high, resulting in the control unit  40  determining the input power as 50 Hz power in operation  1100  and returning to the initial operation. On the other hand, if the power frequency state variable (A) is not greater than the preset value (Aa), the number of times where the cumulatively counted value (B) is equal to or greater than the reference value is low, resulting in the control unit  40  determining the input power as 60 Hz power in operation  1200  and returning to the initial operation.  
         [0038]    As described above, the present invention provides a microwave oven and a method of controlling the same, which counts the number of times where a cumulatively counted value is equal to or greater than a reference value, and determines the frequency of power where the accumulated number of times is equal to or greater than a preset number. Accordingly, the frequency of the power supplied from the outside can be exactly discriminated, thus increasing the reliability of the microwave oven.  
         [0039]    While the present invention has been described with respect to a microwave oven which can utilize 50 Hz and 60 Hz power sources, it is understood that the present invention can be applied to a microwave oven which can utilize other frequency power sources and/or more than two power sources. That is, a microwave oven and a method of controlling the same according to the present invention can discriminate more than two corresponding frequencies of input powers.  
         [0040]    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.