JPS627680B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an induction heating cooker that uses both frequency control and duty control to adjust the output during operation of the induction heating cooker.

(b) Prior art Induction heating cookers convert DC power into alternating current using a frequency conversion circuit, flow this alternating current through an induction heating coil in the frequency conversion circuit to generate an alternating magnetic field, and place the device close to this heating coil. This is for induction heating of cooking utensils made of iron-based metals.

In such an induction heating cooker, in order to adjust the heating output given to the cooking utensils, for example,
As shown in Japanese Patent No. 55-15955, it has been conventionally practiced to control the operating frequency and duty ratio during operation of a frequency conversion circuit.

By the way, in order to widen the adjustment range of output in such an induction heating cooker, a system is being considered in which the operating frequency control and operating duty ratio control of the frequency conversion circuit are performed simultaneously.

However, the operation amount S of the output operation knob and the period T of the operating frequency of the frequency conversion circuit are changed in a proportional relationship as shown in FIG. 2, and the operation amount S of the output operation knob and the duty D of the operation period of the frequency conversion circuit are When the heating output P is changed in a proportional relationship as shown in FIG. 3, the heating output P becomes approximately proportional to the square of the manipulated variable S as shown in FIG.

Therefore, when setting a high output, the output change △P with respect to the operation amount change △S of the operation knob becomes large,
There was an inconvenience that it became difficult to set the output.

(c) Purpose of the Invention The present invention has been made in view of the above points, and the purpose is to make the output change in response to the change in the operation amount of the output control knob substantially constant over the entire output adjustment range. do.

(d) Configuration of the Invention The present invention adopts a configuration in which the amount of change in the output due to frequency control within the oscillation duty period, which is changed in accordance with the change in the operation amount of the output operation means, becomes smaller as the output reaches a higher output region.

(E) Embodiment Figure 1 shows a circuit diagram showing an embodiment of the induction heating cooker of the present invention, in which 1 is connected to a DC power supply 2 which is a full-wave rectified alternating current. This is a frequency conversion circuit that generates a high-frequency current at a sonic frequency, and includes a heating coil 3, a resonant capacitor 4 connected in series to the heating coil 3, a switching transistor 5 connected in parallel to the resonant capacitor 4, and a switching transistor 5 connected in parallel to the resonant capacitor 4. It consists of a flyhole diode 6 connected in antiparallel to a switching transistor 5. 7 is a drive circuit that controls ON/OFF of the switching transistor 5 to drive the frequency conversion circuit 1; 8 is a drive circuit that detects the collector voltage of the switching transistor 5, and outputs a signal when this voltage falls below a predetermined level; The resonant voltage detection circuit 9 outputs a resonant voltage detection circuit 9, which is a reset circuit that receives a reset signal, and functions to stop the frequency conversion circuit 1 when receiving the reset signal. 10 indicates a frequency control circuit connected to this reset circuit 9 and the resonant voltage detection circuit 8,
A current transformer (not shown) that detects the current signal supplied to the heating coil 3; a first comparator 11 to which the current signal is input to the input terminal via a terminal S connected to the current transformer; an output operating means 12 for setting the set signal level to the input terminal of the first comparator 11, a holding capacitor 13 for holding the average voltage of the output of the first comparator 11, and a transistor for discharging the holding capacitor 13 by a signal from the reset circuit 9. 14. A second comparator 1 that inputs the terminal voltage of this holding capacitor 13 to its input terminal.
5. A time constant circuit 18 consisting of a resistor 16 and a capacitor 17 connected to the input terminal of the second comparator 15, and a transistor 19 that discharges the capacitor 17 in response to a signal from the resonant voltage detection circuit 8. .

Here, the output operating means 12 is a variable resistor having a characteristic that as the output is operated to the high output side, the resistance value that changes according to the change in the operating amount becomes smaller, and the change in the divided voltage signal level also becomes smaller, such as an audio device. Use the volume used to adjust the volume. Reference numeral 20 denotes a NOR gate that receives signals from the resonant voltage detection circuit 8, the reset circuit 9, and the second comparator 15 of the frequency control circuit 10, and its output is given to the drive circuit 7. Reference numeral 21 denotes a small object detection circuit that detects small objects and no load by detecting the input current input to the frequency conversion circuit 1, and sends a reset signal to the reset circuit 9 via the OR gate 22 when detecting small objects. send. Reference numeral 23 indicates a control power supply circuit that receives AC voltage from the power transformer 24, and includes a full-wave rectifier circuit 2.
5. Consists of a constant voltage circuit 26 and an output capacitor 27 connected to this full-wave rectifier circuit 25. 28 is a zero volt detection circuit connected to this power supply circuit, and detects zero volt of the full-wave rectified voltage of the AC voltage. Reference numeral 29 denotes a duty control circuit that controls the duty of the frequency conversion circuit 1 in the operating state and in the stopped state, and the duty control circuit 29 controls the duty of the frequency conversion circuit 1 in the operating state and in the stopped state. For example, an oscillation circuit 34 that performs charging and discharging at a one-second cycle and outputs the charging and discharging voltage of this capacitor 33, and the small object detection circuit 21.
a prohibition circuit 35 for stopping the operation of the oscillation circuit 34 in response to a detection signal from the oscillation circuit 34; The fourth comparator 36 detects the fourth voltage at the detection timing of the zero volt detection circuit 28.
a timing circuit 37 that passes the output of the comparator 36; a flip-flop circuit 38 that is set and reset by the signal from the timing circuit 37; and a flip-flop circuit 38 that delays the output of the flip-flop circuit 38 and transmits it to the reset circuit 9 via the OR gate 22 a delay circuit 39; discharging means 40 for discharging the charge of the resonant capacitor 4 of the frequency conversion circuit 1 during the delay period of the delay circuit 39;
Consists of. In addition, in the oscillation circuit 34 of the duty control circuit 29, the resistance value of the charging resistor 31 is set to be small, and the resistance value of the discharging resistor 32 is set to be large, so that the time constant for discharging is larger than the time constant for charging the oscillation capacitor 33. is large.

Next, the operation will be explained. By turning on the power switch (not shown) of the cooker, the DC power supply 2 performs full-wave rectification of the alternating current and supplies a pulsating voltage to the frequency conversion circuit 1. At the same time, the power supply circuit 23 supplies constant voltages +Vc and -Vs to the control circuit system such as the frequency control circuit 10 and the duty control circuit 29.
As a result, the oscillation circuit 3 of the duty control circuit 29
4 starts, and as shown in FIG. 5, a signal having a voltage-time characteristic that rises steeply from the oscillation capacitor 33 terminal, curves downward, and then falls gently is applied to the input terminal of the fourth comparator 36. Given. This comparator 36 compares the setting signal from the output operating means 12 transmitted to the input terminal with the output of the oscillation circuit 34, and becomes "H" when the setting signal level is higher than the output of the oscillation circuit 34, and "L" when the opposite is the case. Output. This “H”
The "L" signal is transmitted to the flip-flop circuit 38 via the timing circuit 37 in synchronization with the zero voltage of the AC full-wave rectified voltage. A signal generated by setting and resetting the flip-flop circuit 38 is transmitted to the reset circuit 9 via the delay circuit 39 and the OR gate 22. That is, this duty control circuit 29 resets the reset circuit 9 when the output of the oscillation circuit 34 rises above a set level, and releases the reset of the reset circuit 9 when the output of the oscillation circuit 34 falls below the set level. During the short delay time in the delay circuit 39 until the reset circuit 9 is released, the charge stored in the resonant capacitor 4 of the frequency conversion circuit 1 is discharged by the discharge means 40.

On the other hand, in the frequency control circuit 10, a first comparator 11 compares an input signal corresponding to an input current transmitted from a current transformer (not shown) through a terminal S with a setting signal from an output operating means 12, and sets the frequency. When the signal is at a higher level than the input signal, the output of this comparator 11 is "H", and when the setting signal is lower than the input signal, the output of this comparator 11 is "L". Therefore, the holding capacitor 13 is charged with an electric charge corresponding to the set signal level from the output operating means 12, and the terminal voltage of the holding capacitor 13 generated by this charging is supplied to the input terminal of the second comparator 15. Ru. Also, this second
The input terminal of the comparator 15 is supplied with the voltage at the terminal of the capacitor 17 of the time constant circuit 18 which repeats charging and discharging cyclically by turning the transistor 19 ON and OFF. Note that this transistor 19
ON is performed when the resonance voltage detection circuit 8 detects that the voltage of the switching transistor 5 has become lower than a predetermined voltage. After receiving such a signal, the second
The comparator 15 outputs an ON signal to turn on the switching transistor 5 when the input terminal voltage becomes lower than the input terminal voltage as shown in FIG. switching transistor 5
Outputs an OFF signal to turn OFF. The NOR gate 20 receives the ON/OFF signals of the switching transistor 5 from the frequency control circuit 10 and the frequency conversion circuit 1 from the reset circuit 9.
Receives a reset signal according to the OFF duty,
The above ON and OFF signals are transmitted to the drive circuit 7 only when there is no reset signal. In response, the drive circuit 7 switches the switching transistor 5
Turns on and off. That is, during the period according to the duty ratio determined by the duty control circuit 29,
The frequency conversion circuit 1 oscillates at an oscillation frequency determined by the frequency control circuit 10. Further, when a reset signal is issued from the reset circuit 9, the electric charge of the holding capacitor 13 is discharged by the transistor 14, and the ON signal is no longer output from the second comparator 15. When a small object is detected, this circuit 21 sends a detection signal to the reset circuit 9 via the OR gate 22, resets the reset circuit 9, and the oscillation operation of the frequency conversion circuit 1 is stopped in the same manner as described above. At the same time, the small object detection circuit 21
The detection signal from is transmitted to the prohibition circuit 35, which prohibits the operation of the oscillation circuit 34 and also stops the operation of the duty control circuit 29.

In such an induction heating cooker, when the output operating means 12 is operated to gradually increase the set signal level from the low output side, the amount of charge charged in the holding capacitor 13 increases as described above, and the second The voltage supplied to the input terminal of the comparator 15 increases, and the voltage is output from this comparator 15.
The ON signal period becomes longer as shown in FIG. The resonant current flowing within the frequency conversion circuit 1 also increases in proportion to the increase in the ON period length. On the other hand, the output operation means 1
The set signal level (broken line in FIG. 5) increased by the operation in step 2 is also applied to the input terminal of the fourth comparator 36 of the duty control circuit 29. As a result, the oscillation period duty of the frequency conversion circuit 1 increases. Conversely, when the set signal level at the output operating means 12 is lowered, the resonance current flowing in the frequency conversion circuit 1 decreases, and at the same time, the oscillation period duty also decreases. Therefore, frequency conversion circuit 1
The output changes with frequency control and duty control being superimposed.

By the way, as shown in FIG. 8, as the set output of the output operating means 12 becomes higher, the amount of change in the set signal level that changes in accordance with the change in the operating amount becomes smaller. Therefore, when setting a high output, the amount of change in the holding voltage between the terminals of the holding capacitor 13, which changes depending on the amount of operation of the output operating means 12, also becomes small.
As the set output increases, the rate of increase in the ON period of the switching element 5 also decreases. As a result, as the set output becomes higher, as shown in FIG. 9, the amount of change in the output by the frequency control means 10 becomes smaller when only the inverter oscillation duty period is considered relative to the amount of the output operation means 12.

Further, the setting signal having the characteristic that the signal level change corresponding to the manipulated variable becomes smaller as the output setting becomes higher is also transmitted from the output operating means 12 to the input terminal of the first comparator 11 in the duty control circuit 29. It will be done. Furthermore, as described above, the signal input to the input terminal of the fourth comparator 36 has a gradual fall and a downward convex shape as shown in FIG. 5, so that the signal level set at the output operating means 12 is high. In other words, when the output is set to high, the amount of change in duty with respect to a change in the set signal level becomes small. Therefore, as shown in FIG. 10, the change in the duty P with respect to the change in the operation amount S of the output heating means is reduced when the output is set to high.

Therefore, the output P adjusted by the control of both the frequency control circuit 10 and the duty control circuit 29 is the first
As shown in FIG. 1, it is corrected so that it changes approximately in proportion to the operation width of the output operation means 12.

The level of the setting signal issued from the output operating means 12 may be set to an appropriate level that is proportional to the manipulated variable S to a function that can be expressed as S raised to the x power (0<x<1). Specifically, when the values of the charging and discharging resistors 31 and 32 in the duty control circuit 29 are approximately equal and the time constants for charging and discharging the oscillation capacitor 33 are equal, approximately 1/2 of the operating amount S of the operating means 12
It is sufficient that the change is made proportional to the power of the power of is 0<x<1/
It must be set to an appropriate value within the range of 2.

(F) Effects of the Invention As described above, the induction heating cooker of the present invention uses a frequency control means that uses a frequency control means to change the set output according to a change in the operation amount of the output operation means as the set output increases. Since the amount of change in the output is made small, the synergistic effect of the above two types of control allows a wide range of set outputs to be obtained, as well as a change in the set output that changes in response to changes in the operating amount of the output operating means when setting high output. The amount can be suppressed, and the output setting at high output setting becomes easy.

Therefore, an induction heating cooker whose output can be easily set over a wide range is provided.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the induction heating cooker of the present invention;
4 to 4 are relationship diagrams showing the oscillation period, oscillation period duty, and output change of the frequency conversion circuit in a conventional cooking appliance with respect to the operation amount of the output operation means, respectively, and FIG. Waveform diagrams showing the relationship between the input voltage and the oscillation period duty of the frequency conversion circuit. Figures 6 and 7 show the relationship between the input voltage to the other main comparators of the present invention and the ON and OFF signals to the switching transistor. Waveform diagrams showing Fig. 8, Fig. 9, Fig. 10, Fig. 11
The figure is a relationship diagram showing changes in the set signal level, the output within the oscillation duty period, the oscillation duty of the frequency conversion circuit, and the output with respect to the operation amount of the output operation means in the present invention. 1... Frequency conversion circuit, 2... DC power supply, 7...
...Drive circuit, 8... Resonance voltage detection circuit, 9...
...Reset circuit, 10...Frequency control circuit, 12
... Output operation means, 23 ... Control power supply circuit, 2
8... Zero volt detection circuit, 29... Duty control circuit, 33... Oscillation capacitor, 34... Oscillation circuit.

Claims (1)

[Claims] 1 It has a frequency conversion circuit that generates an alternating current from a DC power source, and the alternating current is passed through a heating coil in this frequency conversion circuit to generate an alternating magnetic field, thereby induction heating cooking utensils placed close to this heating coil. The induction heating cooker includes a frequency control means for changing the oscillation frequency of the alternating current generated by the frequency conversion circuit, and a duty ratio for changing the conversion operating state and stop state of the frequency conversion circuit. a control means, and an output operation means that is interlocked with both the frequency control means and the duty control means and adjusts the output by simultaneously adjusting both the control means, and the frequency control means has a high set output. Accordingly, an induction heating cooker is characterized in that the amount of change in the output by the frequency control means within each oscillation duty period, which is changed in accordance with the change in the operation amount of the output operation means, is reduced.