JPH0368518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an induction cooking device that applies the principle of electromagnetic induction heating.

BACKGROUND ART Conventional induction heating cookers have been equipped with various output setting means so that the user can freely set the output for normal cooking. A typical means for this purpose is to control the heating output by changing the magnitude of the excitation current flowing through the heating coil depending on the oscillation frequency, as shown in Japanese Patent Application Laid-open No. 7441/1983. .

On the other hand, there is also a method (duty control method) in which the average output is controlled by alternately and periodically repeating heating and stopping. In this case, regardless of the output setting level, heating is always performed in the rated state, so the frequency is approximately constant, and there is no problem with the above-mentioned method of changing the frequency.

Problems to be Solved by the Invention However, although the method of changing the oscillation frequency has the characteristic that the output can be varied continuously, it is difficult to set the output to an extremely low level such as when cooking stews. had spread over a wide area, causing radio wave damage.

In addition, with the duty control method, in the case of induction heating, the metal pot itself is directly heated, so the response is quick, and the user can see the food boiling and stopping, which can give the user a strange feeling. . Also,
As boiling and stopping were repeated, the contents that sank when the boiling stopped would rise up from the bottom due to convection during the next boiling, pushing up the water and broth and causing it to boil over (hereinafter referred to as bumping). In addition, regardless of the output setting level, it is always in the rated state (generally
Since the power supply (over 1KW) was repeatedly turned on and off, it caused periodic fluctuations in the power supply voltage, which could cause the lights to flicker.

In view of the above problems, it is an object of the present invention to provide a variable range of output that is sufficient for cooking without causing discomfort to the user during actual cooking.

Means for Solving the Problems In order to achieve the above object, the induction heating cooker of the present invention starts the induction heating cooker gradually from a low output frequency every time the duty control device periodically repeats heating and stopping. A software circuit is provided that has at least one of a first output control circuit that performs a soft stop that gradually shifts to a low output frequency and stops, and this software circuit has at least one of a first output control circuit that performs a soft stop that gradually shifts to a low output frequency and stops. The time constant is changed according to the output setting level.

Effect The effect of this technical means is as follows.
That is, in the case where the first output control circuit is provided, the heating level can be gradually increased by lengthening the time constant, so there is no sudden transition to a boiling state, and no bumping or flickering occurs.
However, because the soft start time constant is long, the average output decreases, but the soft circuit shortens the soft start time constant when the output setting is high, so that an arbitrary output level can be obtained even at high output settings.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 2, a commercial power source 1 is inputted to a full-wave rectifier 3 via a switch 2. In FIG.
A smoothing capacitor 4 and a filter circuit consisting of a choke coil 5 and a filter capacitor 6 are connected in parallel to the output terminal of the full-wave rectifier 3, respectively. Also, a resonant circuit consisting of a heating coil 7 and a resonant capacitor 8, and a diode 1
A series circuit of an anti-parallel circuit of 0 and a transistor 9 is connected in parallel to a filter capacitor 6. The control device 11 has five connection terminals 101 to 105, which are connected to the full-wave rectifier 3, the transistor 9, and the output setting variable resistor 12, respectively. Although this embodiment shows the configuration of a series resonant inverter using transistors, a parallel resonant inverter using thyristors may also be used; There is no restriction as long as it excites 7.

The configuration of the control device 11 and its operation are shown in FIGS. 1 and 3.
This will be explained using figures. In Figure 1, connection terminal 1
Between 01 and 104, a resistor 82, a rectifier diode 81, a smoothing capacitor 83 and a constant voltage diode 8 are connected.
A DC constant voltage power supply circuit consisting of 4 is connected. A duty control device 20 and a software circuit 50 are connected to the output terminal of this DC constant voltage power supply circuit. The pulse output is supplied to transistor 9 from terminals 105 and 104.

The software circuit 50 includes a programmable UJT (hereinafter referred to as PUT) 62, resistors 58, 63, 64, 65,
A relaxation oscillation circuit consisting of a capacitor 59, a pulse amplification circuit consisting of a pulse transformer 70, a transistor 68, a transistor 53, a capacitor 56,
The first output control circuit 90 includes diodes 54 and 60.

The operation of the software circuit 50 starts when the output of the comparator 32 of the duty control device 20 rises from 0 to 1 as shown in FIG. 3A (when duty control starts to turn on). When the output of comparator 32 is low, diodes 60 and 5
7, the anode voltage (V _a ) and gate voltage (V _g ) of the PUT 62 are set to e ₁ and e ₂ shown in FIG. 3B. Then, when V _a becomes higher than V _g , the PUT 62 becomes conductive and discharges the capacitor 59 via the resistor 61, and during discharging, V _g becomes zero. Therefore, as shown in FIG. 3B, the capacitor 59 is repeatedly charged and discharged, and the charging time is controlled by the value of V _g .
While PUT62 is discharging capacitor 59,
Since V _g is zero, transistor 68 is
As shown in FIG. C, the capacitor 59 is conductive during the charging period and drives the pulse transformer 70. When transistor 9 becomes conductive, a collector current waveform of transistor 9 shown in FIG. 3D is generated.

At startup, V _g is determined by the comparator 32.
e ₁ , but after startup, the emitter follower transistor 53 connects the resistors 51, 52, and 7.
The capacitor 56 is charged at a predetermined time constant through the resistors 63, 64, and 65, and its voltage gradually increases until it reaches the divided voltage value e ₃ (the third
Figure B) becomes higher and diode 60 is reverse biased. Therefore, V _g is e ₁ immediately after startup, and then increases gradually as the capacitor 59 is charged, as shown by the broken line in FIG. 3B, and remains constant after V _g reaches e ₃ . In the circuit shown in Figure 1, the shorter the conduction period of transistor 9, the lower the output from heating coil 7, so it is clear that the output is low at startup, then gradually shifts to high output, and finally becomes constant. .

Here, the charging time of the capacitor 59 depends on the emitter potential of the transistor 53, and the base terminal of the transistor 53 is connected to a reference potential c determined by the output setting variable resistor 12. When a high output is set, the reference potential c becomes high, so the emitter potential of the transistor 53 also becomes high, and the soft start time constant becomes short.

The structure and operation of the duty control device 20 include a relaxation oscillation circuit using a comparator 29 and a comparator 3.
Only the main points of the pulse generating circuit according to No. 2 will be explained with reference to FIG. FIG. 4A shows the capacitor 26 (b) and reference voltage (a) of the comparator 29 and the reference voltage (c, c') of the comparator 32, and the reference voltage (c, c' ), the output waveform of the comparator 32 is shown in FIG.
Shown in C. As a result, the output of the duty control device 20 can be set by setting the variable resistor 12. (In the case of c, if the output is higher than c' and the voltage is set higher than the peak of b, continuous heating will occur.) In this example, a case where a comparator is applied is explained, but a combination of a heater and a temperature sensor is used. The effect is the same for both on and off switches.

As explained above, the software circuit 50 includes the first output control circuit 90 and the duty control device 20.
The output at start-up is gradually increased from a low output in synchronization with the start-up signal, and the time constant of the software circuit becomes shorter as the output setting becomes higher. As a result, when the output is set at a relatively low level, flickering due to bumping or frizz does not occur, and the low output necessary for stewing can be obtained. (Figure 4E shows the change in output when the induction heating cooker is set at a low setting.) On the other hand, when the output is set at a relatively high level, the food is almost boiling, so there is no need to worry about bumping, and unlike stewing food, there is no need to worry about boiling. Since it is not used for a long time, there is no problem with flickering and the necessary output settings can be obtained. (Figure 4D shows the instantaneous output of the induction heating cooker at the setting shown in Figure 4B.) Although the explanation has been made using an example of the software circuit equipped with the first output control circuit, the output gradually increases. The effect is exactly the same even if a second output control circuit is used that stops after tightening.

Effects of the Invention The present invention provides a soft start that starts gradually from a low output frequency, or a gradual transition to a low output frequency and then stops, every time the induction heating cooker repeats heating and stopping periodically by the duty control device. By having at least one of the soft stops and further including a soft circuit whose frequency changes in a time constant according to the level of the output setting, the heating level can be gradually increased.
There is no sudden transition to a boiling state, and bumping and frizz can be prevented.

Moreover, since the soft circuit shortens the soft start time constant as the output setting becomes higher, any desired output level can be obtained over a wide range from low output settings to high output settings.

Moreover, since the circuit configuration is simple, it has great effects such as high cost and reliability.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a control device for an induction heating cooker according to an embodiment of the present invention, and FIG. 2 is an overall circuit diagram of the same.
FIGS. 3 and 4 are waveform diagrams illustrating the operation of the same embodiment. 7...Heating coil, 9...Transistor, 20
... Duty control device, 50 ... Soft circuit,
90...First output control circuit.

Claims (1)

[Claims] 1. A duty control device that controls output by periodically turning on and off electricity to a heating coil to repeatedly heat and stop the heating coil, and a duty control device that gradually controls the instantaneous output at a predetermined time constant when the heating signal of this duty control device starts outputting. Software comprising at least either a first output control circuit that increases the output of the duty control device or a second output control circuit that gradually decreases the instantaneous output with a predetermined time constant when output of a stop signal of the duty control device is started. An induction heating cooker comprising a circuit, the soft circuit shortening the time constant of the soft circuit as the output controlled by the duty control device increases.