JPS6343879B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an induction heating cooker.

Induction heating cookers rectify commercial AC power and convert it into DC voltage, use this DC voltage to oscillate an inverter at a high frequency of about 20 to 40KHz, and the high frequency alternating current generated by this is sent to an induction heating coil. In addition to a cooking pot made of iron, stainless steel, etc. placed nearby, this is heated by induction.
Many of these cookers have a temperature setting function and an output setting function so that the heating temperature and heating output can be obtained according to the cooking process, and in recent years, microcomputers have been used to control these functions. .

The present invention is an improvement aimed at efficiently controlling temperature and output, and embodiments thereof will be described below with reference to the drawings. In Fig. 1, 1 is an AC power supply, 2 is a power switch, 3 is a rectifier circuit, 4 is a choke coil, 5 is a smoothing capacitor, 6 is an inverter circuit, and includes an induction heating coil 7, a resonant capacitor 8, a diode 9, and a switching element. Consists of 10 GCSs (Gate Controlled Switches: Product Name) that work as Reference numeral 11 denotes a cooking pot made of a ferrous material such as iron or stainless steel, and is placed on a top plate 12 made of a ceramic plate or the like. 13 is a step-down transformer; 14 is a power supply for the control circuit; 15 is a thermistor attached to the back surface of the top plate 12 to detect the temperature of the pot 14;
6 is a drive circuit that turns on and off the GCS10;
Reference numeral 17 denotes an oscillation control circuit that provides an oscillation drive signal to the drive circuit 16. This oscillation control circuit 17
is the voltage across the induction heating coil 7 and the GCS1
0 through the current transformer 18 is inputted, and the inverter circuit is caused to self-oscillate. 19 is a control circuit that provides a start signal and an output control signal to the oscillation control circuit 17, and turns on and off the oscillation control circuit 17 within a certain period of time.
It generates a so-called duty control signal that operates and controls the output by changing the off-ratio. This control circuit 19 is manufactured by NEC Corporation.
One-chip microcomputer LSI such as LSI μPD546C and μPD553C can be used. 20
determines when there is no load or when there is an unsuitable small load such as a knife or fork,
A load detection circuit sends a signal to the control circuit 19 to stop oscillation, 21 is a buzzer that operates when an abnormal load is detected or when cooking is completed, 22 is a buzzer drive circuit, and 23 displays temperature. A light emitting diode is used in the display. 24 is a display driving circuit, and 25 is a time base circuit that receives a commercial frequency (50/60 Hz) signal and obtains a reference time signal for duty control. 26 is a reference level signal generation circuit that generates a plurality of reference level signals in response to a signal from the control circuit 19; 27 is a reference level signal generation circuit that compares the reference level signal V _L with the voltage signal set by the variable resistor 28; 29 is a heating output setting circuit that outputs a signal when both signals match; 29 is a temperature detection circuit that compares the reference level signal V _L and the temperature detection signal S _P from the thermistor 15 and outputs a signal when both signals match; 3
0 is a temperature setting circuit that compares the reference level signal V _L and the voltage signal set by the variable resistor 31 and outputs a signal when both signals match.

FIG. 2 shows specific circuits of the reference level signal generation circuit 26, output setting circuit 27, temperature detection circuit 29, and temperature setting circuit 30. The reference level signal generation circuit 26 is connected in series to a constant voltage V. 4
resistors 32 to 35 and resistors 36 to 39 connected in parallel to the connection points of these resistors, and the other ends of the resistors 32 to 35 are supplied with "0" or "1" from the control circuit 19. binary signal of
D ₀ D ₁ D ₂ D ₃ is added. 40 is an adjustment resistor. Reference level signal generation circuit 26 having such a configuration
is generally called a ladder circuit, and its output V _L is
It is expressed by the following formula. Here resistors 32 to 35 and 3
6 resistance value is 2R resistance 37-39 is R, resistance 40
Let be X.

V _L = -XV/2 (X + R) (D ₃ +D ₂・2 ^-1 +D ₁・2 ^-2 +
In other words, when ( _{D 0 D 1} D _{2 D 3} ⁾ = (0000), the output is minimum, and when (D ₀ D ₁ D ₂ D ₃ ) = (1111), the output is maximum, and during that time 16 voltage levels are available. The signal (D ₀ D ₁ D ₂ D ₃ ) is output from the control circuit 19 so as to increase by 1 at regular time intervals,
Therefore, the signal V _L becomes a stepped voltage signal. 41
is a first comparison circuit which inputs the signal V _L to the (+) input terminal and inputs the output signal from the output setting variable resistor 28 to the (-) input terminal, and constitutes the output setting circuit 27. 42 is the signal V _L (+)
a second comparator circuit that inputs the output signal S _P of the thermistor 15 to the input terminal and to the (-) input terminal, respectively;
43 and 44 are dividing resistors, which constitute the temperature detection circuit 29. 45 is the signal V _L (+)
The temperature setting circuit 30 is constituted by a third comparison circuit which inputs the output signal from the temperature setting variable resistor 31 to the input terminal and the (-) input terminal, respectively.

First, second and third comparison circuits 41, 42, 45
The outputs (hereinafter referred to as A, B, and C) are input to the control circuit 19, and operate the functions of output setting, temperature detection, and temperature setting, respectively.

FIGS. 3 and 4 show each of the above comparison circuits 41 and 4.
A program chart that is processed within the control circuit 19 upon receiving each of the outputs 2 and 45 is shown, and the temperature setting operation will be explained based on FIG. First, a value 0 is written in the level register, which is outputted as signals D ₀ to D ₃ from four output terminals through an accumulator. Note that the level register stores 16 levels, and its contents correspond to the voltage level signal of the reference level signal generation circuit 26. After a certain period of time has elapsed after the D signal is output, the signal C is read and the "H" or "L" level of the signal C is detected. If the signal C is "L", the contents of the temperature register are incremented by 1, then 1 is added to the level register, this contents is sent to the accumulator, and the above-described process is repeated. On the other hand, if the signal C is determined to be "H", the contents of the temperature register are transferred to the temperature control section and the temperature is actually set. Thereafter, the contents of the temperature register are cleared and temperature setting is completed.

FIG. 4 shows a level detection flowchart executed following the temperature setting operation, which will be explained in order below. First, 0 is written into the level register, and its contents are output as signals D ₀ to D ₃ from four output terminals via an accumulator, and after a certain period of time, signals A and B are read.
Following this, first the signal B becomes “H” or “L”.
A level determination is performed, and if it is determined to be "L", the contents of the heating output (power) register are incremented by 1. Next, it is determined whether the signal A is at the "H" level, and if it is at the "L" level, +1 processing is performed on the temperature register, and then +1 processing is performed on the level register.
1 processing is performed. Furthermore, if the signal B is determined to be at the "H" level in the B signal determination step, the heating output is actually controlled based on the contents of the heating output register, and the on/off ratio is set according to this content.
The oscillation control circuit 17 is driven at a predetermined duty. After such heating output control, it is determined whether the signal A is at the "H" level, and if it is at the "L" level, the process proceeds to the temperature register +1 step, and if it is at the "H" level, the process proceeds to the 1 second elapse step. Note that if the signal A is determined to be at the "H" level in the signal A determination step, the process skips the temperature register +1 step and moves to the level register +1 step. The above process 1
Repeat for 1 second, and after 1 second has passed, transfer the contents of the temperature register to the temperature display section. This is to prevent the displayed temperature from changing drastically and to make the display easier to read by displaying the temperature once per second. After the temperature is displayed, the temperature register and heating output register are cleared and the system returns to its original state.

As described above, according to the induction heating cooker of the present invention,
A control signal extracted as an analog signal such as a temperature detection signal or an output setting signal is compared with a reference level signal output from a common reference level signal generation circuit to obtain a matching signal, and the control signal is determined by the timing of this matching signal. Since it converts the signal into a digital signal and digitally controls temperature adjustment, output adjustment, etc., one type of reference level signal is sufficient, and conventionally, ladder circuits were provided for each control such as temperature adjustment and output adjustment. Compared to conventional cookers, the number of output ports of the microcomputer that functions as the control circuit can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a main part of the embodiment, and FIGS. 3 and 4 are flowcharts for explaining the operation of the embodiment. DESCRIPTION OF SYMBOLS 1... AC power supply, 6... Inverter circuit, 7... Induction heating coil, 11... Cooking pot, 14... Control circuit power supply, 16... Drive circuit, 17... Oscillation control circuit, 19
...Control circuit, 20...Load detection circuit, 23...Display unit, 26...Reference level signal generation circuit, 27...Heating output setting circuit, 29...Temperature detection circuit, 30...Temperature setting circuit.

Claims (1)

[Claims] 1. Generation of a plurality of control signals that extract signals from a heat-sensitive element that detects the temperature of the cooking pot or the temperature of electrical components in the cooking pot, or signals from an output setting means that sets the heating output applied to the cooking pot, as analog quantities. a single reference level signal generating means for generating different voltage level signals in response to a predetermined bit signal; and a single reference level signal generating means for generating different voltage level signals in response to a predetermined bit signal; a comparison means for outputting a signal when the two signals match, and a comparison means for outputting the bit signal and inputting output signals from each of the comparison means to determine the content of the bit signal at the time of inputting each signal. 1. An induction heating cooker comprising: control means for digitally controlling temperature adjustment, heating output adjustment, etc. by digitizing each of the above control signals based on the above information.