Patent Publication Number: US-5026955-A

Title: Drive control method for an electromagnetic induction heating apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electromagnetic induction heating apparatus which heats a magnetic vessel with a magnetic force that is generated by switching on the current flow in a working coil in order to cook food contained in the magnetic vessel More particularly, the present invention relates to a method for controlling the drive of an electromagnetic induction heating apparatus, that is, an electromagnetic heating cooker, which is designed to control the drive of a power transistor by commonly utilizing a time control method and a linear control method according to the power level selected by a user. 
     In order to control the apparatus drive, a conventional electromagnetic induction heating apparatus, a time control method varies the number of times that a power transistor is switched ON/OFF according to the power setting level, while the power control level is maintained constant on one hand. On the other hand, a linear control method varies the ON/OFF switching time of a power transistor by changing the power control level according to the power setting level. 
     However, in case where the former method is adopted because the power control level is constant, the ON/OFF switching time of the power transistor is constant. Thereby, a so-called &#34;flicker effect&#34; may be generated when the power control level is high. 
     On the other hand, in the case where the latter method is adopted, the above stated &#34;flicker effect&#34; does not occur. However, an extreme amount of noise is generated when the power control level is low since the switching frequency varies upon the change of the ON/OFF switching time of the power transistor. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a method for controlling the drive of an electromagnetic heating apparatus in order to present the flicker effect and noise irrespective of high and low values power control level of a power transistor. 
     The above object of the present invention is accomplished by controlling the ON/OFF switching of a power transistor with the time control method in the case where the power level established by a user is below a predetermined level, such as, below 600 watts for example, and controlling the ON/OFF switching of the power transistor with a linear control method in the case where the power level established by a user is above a predetermined level, such as, over 700 watts for example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in con]unction with the accompanying drawings, in which : 
     FIG. 1 is a circuit diagram illustrating the drive control method for a embodiment of the present invention; 
     FIGS. 2(A) to 2(J) are waveforms of the data signals stored in the micro-processor of FIG. 1; and 
     FIG. 3 is a flow-chart of the micro-processor illustrating the drive control method for an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a circuit diagram of an electromagnetic induction heating apparatus is illustrated for the drive control method for an embodiment of the present invention. The circuit is constructed in a manner such that an ON/OFF switch SW0 and power level setting switches SW1-SW10 are connected in common with resistors R1-R11 that are connected to Vcc power terminals and input terminals IN0-IN10 of a micro-processor 10, respectively. Output terminals OT0-OT10 of the micro-processor 10 are connected in common with resistors R12-R22 and light emitting diodes LED0-LED10, respectively and the resistors R12-R22 are connected to Vcc power terminals. Predetermined data signals are stored in a memory 1 of the micro-processor 10 according to the respective setting level so that the data signals are output from an output terminal OT1 of the micro-processor 10 in response to closing the power level setting switches SW1-SW10. Then, the signals are applied to a digital/analog converter of a driving part of the power transistor. 
     Referring to FIGS. 2(A) to (J), the waveforms of the data signals stored in the memory 1 of FIG. 1 according to each of the power setting levels are illustrated. In an address &#34;0&#34; of the memory 1, a low potential signal is stored. In addresses &#34;1-6&#34; pulse signals having a predetermined width T0 and reset pulse signals, as illustrated in FIGS. 2(A)-(F), are stored at the predetermined time differences t1-t6 from the point of time that the output of the pulse signals is finished. 
     Thereby, the data signals stored in the addresses &#34;0-6&#34; of the memory 1 are repeatedly output at a constant period Tt when low potential signals are input to the input terminals IN0-IN6. 
     In the addresses &#34;7-10&#34; of the memory 1, pulse signals having, the predetermined widths T7-T10 are different from each other, as illustrated in FIGS. 2(G)-(J), are stored. Thereby the pulse signals stored in the addresses &#34;7-10&#34; of the memory 1 are output, respectively, when low potential signals are input to the input terminals IN7-IN10 of the micro-processor 10. 
     The operation and effect of the present invention will now be described in detail with reference to FIG. 3. 
     When power is applied to the Vcc power terminal, the microprocessor 10 outputs low potential signals through the output terminals OT0-OT11 as illustrated in FIG. 3. Under such a state, when a user closes an ON/OFF switch SW0 and a low potential signal is applied to an input terminal IN0 of the micro-processor 10, the micro-processor 10 outputs through a high potential signal through the output terminal OT0 and turn on a light emitting diode LED0. At the same time, a low potential signal stored in the address &#34;0&#34; of the memory 1 is through the output terminal OT11. 
     Under this state, when a low potential signal is applied to the input terminal IN1 of the micro-processor 10 by closing a power level setting switch SW1 by a user, the micro-processor 10 outputs a high potential signal through the output terminal OT1 to light a light emitting diode LED1. At the same time, the data signal stored in the address &#34;1&#34; of the memory is output through the output terminal OT11 and then is applied to a digital/analog converter of the driving part of the power transistor. 
     That is to say, after outputting a high potential signal during a predetermined time T0 as shown in FIG. 2(A), the micro-processor 10 repeats the process and outputs reset pulse signals at a constant period Tt after a predetermined time t1. Accordingly, ON and OFF operations of the power transistor are repeated during the times T0 and t1 at a constant power level. 
     Similarly, when a user closes one of the power level setting switch is SW2, SW3, SW4, SW5 or SW6 so that a low potential signal is input to an input terminal IN2, IN3, IN4, IN5 or IN6 of the micro-processor 10, the micro-processor 10 outputs high potential signals through the output terminals OT1, OT2; OT1-OT3; OT1-OT4; OT1-OT5 or OT1-OT6 to light the light emitting diodes LED1, LED2; LED1-LED3; LED1-LED4; LED1-LED5 or LED1-LED6. At the same time, the data signals stored in the address &#34;2&#34;, &#34;3&#34;, &#34;4&#34;, &#34;5&#34; or &#34;6&#34; of the memory are applied from the output terminal OT11 to the digital/analog converter of the driving part of the power transistor. That is to say, at this moment the micro-processor 10 outputs the waveform signals as shown in FIG. 2(B), (C), (D), (E) or (F) from the output terminal OT11 at a constant period Tt repeatedly. Thereby, the ON and OFF operations of the power transistor are repeated at a constant power level during the predetermined times T0+t2; T0+t3; T0+t3; T0+t5 or T0+t6. 
     Under the above described state where the ON/OFF switch SW0 is closed, when the power level setting switch SW1, SW2, SW3, SW4, SW5 or SW6 is closed, the waveform signal as illustrated in FIG. 2(A), (B), (C), (D), (E) or (F) is applied to the digital/analog converter of the driving part of the power transistor from the memory 1 of the micro-processor 10. Thereby the power transistor repeats the ON and OFF operations at a constant power level during the predetermined times T0+t1; T0+t2; T0+t3; T0+t4; T0+t5 or T0+t6. 
     That is, at this time the ON and OFF operation of the power transistor are controlled by the time control method. 
     On the other hand, a low potential signal may be applied to an input terminal IN7 of the micro-processor 10 by closing a power level setting switch SW7. The micro-processor 10 outputs high potential signals from the output terminals OT1-0T7 to light the light emitting diodes LED1-LED7, and at, the same time, outputs the data signal stored in the address &#34;7&#34; of the memory is output from the output terminal OT11. That is to say, a high potential signal is output during a predetermined time T7, as illustrated in FIG. 2(G), and the signal is applied to the digital/analog converter of the driving part of the power transistor. Thereby the power transistor is turned on and off at the power level in proportion to the time T7. 
     Similarly, when a low potential signal is applied to the input terminal IN8, IN9 or IN10 of the micro-processor 10 by closing the power level setting switch SW8 or SW9 by a user, the micro-processor 10 outputs high potential signals from the output terminals OT1-OT8; OT1-OT9 or OT1-OT10 to light the light emitting diodes LED1-LED8; LED1-LED9 or LED1-LED10, at the same time, the waveform signal stored in the address &#34;8&#34;, &#34;9&#34; or &#34;10&#34; of the memory 1, as is applied as illustrated in FIG. 2(H), (I) or (J) to the digital/analog converter through the output terminal T11. Thereby, the ON and OFF operations of the power transistor are controlled at the power level in proportion to the predetermined time T8, T9 or T10. 
     That is to say, in the case of closing the power level setting switch SW7, SW8, SW9 or SW10. When the ON/OFF switch SW0 being is closed, the light emitting diodes LED1-LED7; LED1-LED8; LED1-LED9 or LED1-LED10 are turned on. At the same time the ON and OFF operations of the power transistor are controlled by the linear control method at the power level in proportion to the predetermined times of T7, T8, T9 or T10 that are different from each other. 
     As described above in detail, the present invention has an advantage of controlling the power transistor by a time control method when the power level established by a user is below a predetermined level and is controlled by a linear control method when the power level is over a predetermined level. Thereby, the flicker effect and noise are prevented from being generated.