JPH09320746A - Electromagnetic cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply, surely repeat cooking with strong heating power by installing an output lowering means which lowers output and retain it for the specified time, when a load is removed in an inverter which carries a high frequency current through heating coil of an induction heating cooker. SOLUTION: AC current from a commercial power source 1 is rectified by a rectifier bridge 3 having a smoothing capacitor 4 in parallel, and DC current obtained is supplied to an inverter 10. High-frequency current obtained is supplied to a parallel resonance circuit, comprising a heating coil 5 and a resonance capacitor 6 to generate electromagnetic force, and pot load 21 is heated with the electromagnetic force through a top plate 19. In an induction heating cooker, an output lowering means comprising a weak output timer 13 arranged in an output control circuit 12, having a variable volume 18 of a driving circuit 9 of the inverter 10. The removal of pot load is detected with a load-detecting circuit 14, output is lowered and retained for the specified time, and when load is applied again, strong output is quickly recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic cooker used in homes and the like.

[0002]

2. Description of the Related Art Conventionally, in an electromagnetic cooker, the inverter is momentarily stopped when there is no load such as a pan on the top plate, for example, when something that should not be heated such as a kitchen knife is carelessly placed. The structure is such that the inverter is driven next 5 to 6 seconds later. By the way, it is known that when a cooked food such as a Chinese food is returned to and mixed with a pan, the whole is well mixed, and the stir-fried food is very successful. However, in the case of the conventional electromagnetic cooker, when the pan is moved as described above, the inverter stops, and when the pan is moved to mix the food, the inverter hardly operates and cannot be used.

FIG. 5 shows a circuit configuration of such a conventional electromagnetic cooker. Rectification bridge 3 in which commercial power supply 1 is configured of diodes 3a to 3d via power switch 2
It is connected to the. A smoothing capacitor 4 of about several μF is connected between the positive electrode and the negative electrode of the rectifying bridge 3.
Further, a parallel resonance circuit of the heating coil 5 and the resonance capacitor 6 is connected to the positive side of the rectification bridge 3, and the other end of the parallel resonance circuit is connected to the collector of the transistor 7. The emitter of the transistor 7 is connected to the negative side of the rectifying bridge 3. A damper diode 8 is connected in parallel with the transistor 7. The heating coil 5, the resonance capacitor 6, the transistor 7, and the damper diode 8 constitute an inverter 10. The pan load 21 is placed on the top plate 19 arranged on the heating coil 5. The base of the transistor 7 is connected to the output control circuit 11 via the drive circuit 9. The output control circuit 11 includes an externally operable variable volume 1 for controlling the magnitude of the output to the heating coil 5.
8. Safety circuit 15 including a pan temperature detection circuit for detecting the temperature of the heating coil 5 to stop the inverter 10 or detecting the temperature of the pan load 21 on the heating coil 5 and the pan on the top plate 19. A load detection circuit 14 as a load detection unit for detecting the presence or absence of the load 21 is connected. One input terminal of the load detection circuit 14 is connected to the collector of the transistor 7, and the other input terminal is connected to the output terminal of the output control circuit 11. Reference numeral 16 is an oscillator, which oscillates at a predetermined frequency lower than the frequency for driving the transistor 7. A feedback circuit 17 is provided for the oscillator 16 in order to synchronize with an appropriate frequency of the inverter 10 including the transistor 7. One input terminal of the feedback circuit 17 is connected to the positive electrode side of the rectifying bridge 3, the other input terminal is connected to the collector of the transistor 7, and the output terminal is connected to the oscillator 16.

The operation of the above electromagnetic cooker will be described from the operation of the inverter 10 with reference to the operation waveform diagram of FIG. The oscillator 16 oscillates at a frequency lower than the resonance frequency of the inverter 10, that is, at a long cycle t ₀ . FIG. 6A shows the output waveform Vosc of the oscillator 16, which has a sawtooth shape. The output control circuit 11 shapes a pulse for driving the transistor 7 to the drive circuit 9. This is a variable volume 18 for the output waveform Vosc of the oscillator 16.
Is generated in comparison with the voltage level Vr. That is, when the output waveform Vosc is lower than the voltage level Vr, the output voltage Vd of the output control circuit 11 shown in FIG. 6B becomes the H level, and when the output waveform Vosc is higher than the voltage level Vr, the output voltage Vd is It becomes the L level. The output voltage Vd of the output control circuit 11 is amplified by the drive circuit 9, and a drive voltage having the same waveform as the output voltage Vd is applied to the base of the transistor 7. When the output voltage Vd is at the H level, the transistor 7 is turned on, and a high frequency current Ic having a sawtooth waveform as shown in FIG. 6C flows through the collector (heating coil 5) of the transistor 7. Output voltage Vd
When the transistor 7 is turned off at L level, the parallel resonance circuit of the heating coil 5 and the resonance capacitor 6 resonates, and a sinusoidal resonance voltage Vc as shown in FIG. 6D is applied to the collector of the transistor 7. The feedback circuit 17 detects the rear crossing end of the voltage Va with respect to the waveform of the resonance voltage Vc, and applies a synchronizing signal to the oscillator 16. As a result, the cycle t ₀ of the oscillator 16 is shortened to t ₁ to synchronize with the resonance frequency of the heating coil 5 and the resonance capacitor 6, so that the inverter 10 operates normally. The output of the inverter 10 of this type can be changed by changing the ON period T of the transistor 7.

FIG. 8 is a diagram for explaining the operation of the load detection circuit 14. As described above, the output of the inverter 10 changes by controlling the on period T of the transistor 7. Therefore, when the pan load 21 is placed on the top plate 19, the output voltage Vd and the resonance voltage Vc of the output control circuit 11 are smoothed and the divided voltage characteristic is Vca that can be input to the load detection circuit 14. Show as. On the other hand, when the pan load 21 is removed from the top plate 19, the oscillation frequency of the inverter 10 hardly changes but the peak value of the resonance voltage Vc decreases, so that the voltage characteristic decreases like V'ca. Therefore, it is possible to detect the presence or absence of the pan load 21 by comparing the magnitude relationship between the voltages Vca and V'ca with respect to the threshold voltage Vda that is appropriately determined.

FIG. 7 is a flow chart for explaining the operation of the electromagnetic cooker as a whole. When the power switch 2 is turned on (step 101), the load detection circuit 14 operates,
When the pan load 21 is placed on the top plate 19, the output control circuit 11 detects that the pan load 21 is present.
To the inverter 1 (Yes in step 102)
0 is driven (step 103). When the pan load 21 is removed during cooking, the load detection circuit 14 detects that the pan load 21 is not present, this is transmitted to the output control circuit 11, and the time for operating the load detection circuit 14 is measured. The no-load timer is set (step 104),
At the same time, the operation of the inverter 10 is stopped (step 105). When the time measured by the no-load timer reaches zero (step 106), the load detection circuit 14 is restarted.
To work. This state continues until the power switch 2 is turned off (Yes in step 107) and the inverter 10 is set to the off state (step 108).

[0007]

The conventional electromagnetic cooker has the following problems.
When the pan load is not placed on the top plate or when the pan load is removed, the operation of the inverter stops momentarily. For this reason, particularly in the case of Chinese food and the like, when the cooked food is returned using the pan, the operation of the inverter is stopped, and there is a problem that cooking cannot be performed.

The present invention has been made in view of the above,
An electromagnetic cooker that can be used for cooking Chinese dishes and the like that require strong firepower and the return of cooked foods, increases the range of cooking, is extremely easy to use, and has a simple structure and high reliability. The purpose is to provide.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a heating coil, and an inverter for supplying a high-frequency current to the heating coil, and an inverter arranged on the heating coil. And a load detection means for detecting the presence or absence of a load including a pan on the top plate, the load on the top plate during heating the load on the top plate with a predetermined output from the inverter. Is removed, the output reducing means reduces the output of the inverter below the predetermined output for a predetermined time. With this configuration,
When the load including the pan is placed on the top plate and heated at a predetermined output, and when the load including the pan is removed from the top plate to return the food, for example, the output of the inverter is output for a predetermined time. It keeps being held in a weak output state.

According to a second aspect of the present invention, in the electromagnetic cooker according to the first aspect, the output of the inverter is output when the load returns to the top plate within a predetermined time during which the output reducing means is operating. Is restored to the predetermined output, and when the load does not return to the top plate within the predetermined time, the inverter is stopped. With this configuration, the load including the pan is removed from the top plate during heating at the predetermined output, and the load including the pan is removed during the predetermined time during which the output of the inverter is held in the weak output state. When returning to the top plate, the output of the inverter returns to a predetermined output and heating is continued. On the other hand, if the no-load state continues after the predetermined time, the inverter stops.

According to a third aspect of the present invention, in the electromagnetic cooker according to the second aspect, the inverter includes a resonance capacitor connected to the heating coil to cause voltage resonance, and the heating coil. The gist of the present invention is to have a transistor connected in series. With this configuration,
The circuit configuration of the electromagnetic cooker can be simplified.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 are views showing a first embodiment of the present invention. In addition, in FIG. 1 and FIG. 3 showing a second embodiment to be described later, the same or equivalent parts as the devices and elements in FIG. To do.

First, the configuration of the electromagnetic cooker will be described with reference to FIG. 1. In the present embodiment, for example, while heating the pan load 21 placed on the top plate 19 with a predetermined output from the inverter 10, Load that pan to return the cooked food 2
The output control circuit 12 includes a weak output timer 13 that counts a predetermined time of, for example, about 1 second when the load detection circuit 14 detects that 1 has been removed from the top plate 19. The output control circuit 12 uses the weak output timer 1
The output of the inverter 10 is controlled so as to be a weak output lower than the predetermined output for a predetermined time period measured in 3. Thus, the output control circuit 12 including the weak output timer 13 constitutes output lowering means for making the output of the inverter 10 a weak output for a predetermined time.

Next, the operation of the electromagnetic cooker configured as described above will be described with reference to the flowchart of FIG. When the power switch 2 is turned on (step 201), the load detection circuit 14 operates, and when the pan load 21 is placed on the top plate 19, it is detected that the pan load 21 is present in the output control circuit 12. Transmitted (Yes in step 202)
s), the inverter 10 starts operating at the set predetermined output (step 203). When the pan load 21 is removed from the top plate 19 during heating with a predetermined output from the inverter 10 in order to return the food, for example, the load detection circuit 14 detects this and the pan load 21 is removed. Is transmitted to the output control circuit 12 (step 20).
No. 4). At this time, the output control circuit 12 sets the weak output timer 13 to start measuring a predetermined time of, for example, about 1 second (step 205), and at the same time, the inverter 1
The output of 0 is made a weak output to protect the transistor 7 (step 206). Then, the weak output timer 13 operates and while the pan load 21 is not on the top plate 19, the inverter 10 continues to hold the weak output (N in step 207).
No, step 208). When the pan load 21 returns to the top plate 19 while the weak output timer 13 is operating, the load detection circuit 14 detects this and the inverter 1
0 returns to the initial predetermined output (step 209).
When the pan load 21 does not return to the top plate 19 during the predetermined time when the output is weak, the inverter 10
Is turned off (step 210). On the other hand, immediately after the power switch 2 is turned on, when the load detection circuit 14 does not detect the pan load 21 (No in step 202), the no-load timer is set (step 21) as in the conventional case.
1), the inverter 10 is turned off (step 21)
2). Then, the inverter 10 is kept off until the time measured by the no-load timer becomes zero, and when the time measured becomes zero (Yes in step 213), the load detection circuit 14 is operated again. This state continues until the power switch 2 is turned off (Yes in step 214) and the inverter 10 is set to the off state (step 2).
15).

As described above, in this embodiment, when the power switch 2 is turned on without placing the pan load 21 on the top plate 19, the output control circuit 12 detects the no load by the load detection circuit 14. The inverter 10 is momentarily turned off. This operation is repeated at intervals of 5 to 6 seconds as in the conventional example, but since the inverter 10 is always stopped instantaneously, the user feels that the electromagnetic cooker is always stopped, as in the conventional example. . On the other hand, the pan load 21 is placed on the top plate 19 and the pan load 2 is heated during heating at a predetermined output.
When 1 is removed from the top plate 19, the output of the inverter 10 drops to a weak output for a predetermined time. If the no-load state continues even after a predetermined time, the inverter 10
However, when the pan load 21 returns to the top plate 19 for a predetermined time and the load is detected by the load detection circuit 14, the output of the inverter 10 returns to the initial state and continues at the predetermined output. Then heating is continued. For this reason, even if the cooked food is returned using a pan for Chinese food or the like, sufficient cooking is performed.

FIGS. 3 and 4 show a second embodiment of the present invention. In the present embodiment, two transistors 7a and 7b connected in series are used as the transistors forming the inverter 20, and the two transistors 7a and 7b are used.
The heating coil 5 is connected to the midpoint of connection between a and 7b, and the resonance capacitor 6 is connected in series to the other end of the heating coil 5. This circuit is called a SEPP circuit. In the case of this circuit, a resonance type SEPP circuit using the heating coil 5 and the resonance capacitor 6 in a resonance state, and a non-resonance type SEPP circuit.
There is a circuit, but in the case of the circuit of FIG.
It is a circuit and does not have a circuit for detecting resonance between the heating coil 5 and the resonance capacitor 6. The base of the transistor 7a is connected to the output control circuit 12 via the drive circuit 9a, and the base of the other transistor 7b is connected to the other drive circuit 9a.
It is connected to the output control circuit 12 via b. Further, the output control circuit 12 is connected to a current transformer 22 that detects a current flowing through the commercial power supply 1. Output control circuit 12
Controls the output value determined by the variable volume 18 and the current value flowing through the commercial power supply 1 so that a predetermined current flows through the heating coil 5. A current transformer 23 that detects the current flowing through the transistor 7b is connected to the load detection circuit 14.

FIG. 4 is a diagram for explaining the operation of the load detection circuit 14. The output voltage of the output control circuit 12 and the voltage corresponding to the detected current value of the current transformer 23 in a state where the pan load is placed on the top plate are smoothed and divided so that the voltage can be input to the load detection circuit 14. The voltage characteristic is V
Shown as cr. On the other hand, when the pan load is removed from the top plate, the current flowing through the transistor 7b becomes large, so that the voltage characteristic rises like V'cr. Therefore, each voltage Vcr with respect to an appropriately determined threshold voltage Vdr,
By comparing the large and small relations of V'cr, it becomes possible to detect the presence or absence of the pan load on the top plate.

As for the operation of the electromagnetic cooker, as in the case of the first embodiment, when the pan load is removed from the top plate during heating with the predetermined output from the inverter 20, the load detection circuit. 14 detects this, and the fact that the pan load has been removed is transmitted to the output control circuit 12. At this time, the output control circuit 12 sets the weak output timer to start measuring a predetermined time, and
Is weakened to protect the transistors 7a and 7b. When the pan load returns to the top plate while the weak output timer is operating, this is detected by the load detection circuit 14,
The inverter 20 returns to a predetermined output. If the pan load does not return to the top plate during the predetermined time held at the weak output, the inverter 20 is turned off.

[0020]

As described above, according to the first aspect of the present invention, a heating coil is included, an inverter for supplying a high frequency current to the heating coil, and a top plate arranged on the heating coil. A load detecting means for detecting the presence / absence of a load including a pot on the top plate, and the load on the top plate is removed while heating the load on the top plate with a predetermined output by the inverter. When the load including the pan is removed from the top plate to return the food, for example, the inverter is provided with output lowering means for lowering the output of the inverter below the predetermined output for a predetermined time. Since the output of is maintained at a weak output for a predetermined time, it becomes possible to cook even Chinese dishes that require strong firepower,
The range of dishes that can be cooked is increased, and an electromagnetic cooker that is extremely easy to use can be provided.

According to the second aspect of the present invention, when the load returns to the top plate within a predetermined time during which the output reducing means is operating, the output of the inverter is returned to the predetermined output, Since the inverter is stopped when the load does not return to the top plate within the predetermined time, the pan is included during the predetermined time in which the output of the inverter is held in the weak output state. When the load returns to the top plate, the output of the inverter automatically returns to the specified output, so it is possible to provide an electromagnetic cooker that is more suitable for cooking Chinese food and other foods that require strong heating power and the return of food. can do. Further, if the no-load state continues after the predetermined time, the inverter stops, so that safety can be improved.

According to a third aspect of the present invention, the inverter includes a resonance capacitor connected to the heating coil so as to perform voltage resonance, and a transistor connected in series to the heating coil. With this configuration, it is possible to provide an electromagnetic cooker with a simple circuit configuration and high reliability.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an electromagnetic cooker according to the present invention.

FIG. 2 is a flowchart for explaining the operation of the first embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the load detection circuit according to the second embodiment.

FIG. 5 is a circuit diagram of a conventional electromagnetic cooker.

FIG. 6 is a diagram showing operation waveforms of the inverter in the conventional example.

FIG. 7 is a flowchart for explaining the operation of the above conventional example.

FIG. 8 is a diagram for explaining the operation of the load detection circuit in the conventional example.

[Explanation of symbols]

5 Heating Coil 6 Resonance Capacitor 10, 20 Inverter 12 Output Control Circuit 13 that constitutes Output Reduction Means Including Weak Output Timer 13 Weak Output Timer 14 Load Detection Circuit (Load Detection Means) 19 Top Plate 21 Pan Load

Claims (3)

[Claims] 1. A presence / absence of a load including a heating coil, a high-frequency current flowing through the heating coil, a top plate disposed on the heating coil, and a pan on the top plate is detected. When the load is removed from the top plate during heating of the load on the top plate by the load detection means and the predetermined output by the inverter, the output of the inverter is output from the predetermined output for a predetermined time. An electromagnetic cooker characterized by having an output lowering means for lowering the output. 2. The output of the inverter is returned to the predetermined output when the load returns to the top plate within a predetermined time during which the output reducing means is operating, and the load is reduced within the predetermined time. The electromagnetic cooker according to claim 1, wherein the inverter is configured to be stopped when it does not return to the top plate. 3. The inverter includes a resonance capacitor connected to the heating coil so as to perform voltage resonance, and a transistor connected in series to the heating coil. Induction cooker described.