JPS634400Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electromagnetic cooker that heats a cooking container by induction heating, and in particular, the heating output is controlled according to the size, material, etc. of the cooking container. This invention relates to an electromagnetic cooker with functions.

[Background technology and its problems]

Generally, with an electromagnetic cooker that uses the principle of induction heating, even if you try to heat a cooking container made of non-magnetic metal such as a copper product, the inductive load is too light, so internal loss increases and the heating cannot be done effectively. can't do it. Therefore, conventionally, a magnetic metal detector is used to distinguish between non-magnetic metal cooking containers unsuitable for induction heating and magnetic metal cooking containers suitable for induction heating. A high frequency current is caused to flow through the heating coil only when the cooking container is placed on the heating coil.

In addition, a high-frequency current is passed through the heating coil only when a cooking container of a predetermined size or more is placed on the heating coil, so that a magnetic metal spoon or the like is accidentally placed on the heating coil. Induction heating was not performed even if the Conventionally, when a small-shaped magnetic metal such as a spoon is placed on a heating coil, the above-mentioned protection measures have been taken by utilizing the characteristic that the high frequency current flowing through the heating coil becomes smaller.

By the way, even if the cooking utensil is made of non-magnetic metal, the stainless steel cooking container that is commonly used in households can effectively perform induction heating due to the skin effect, as long as the wall thickness is relatively thin. be able to.

However, as mentioned above, with conventional induction cookers that use a magnetic metal detector to identify the material of the cooking container and control the heating output, stainless steel cooking containers are unsuitable for induction heating. It will be judged as such.

[Purpose of invention]

Therefore, in view of the above-mentioned conventional problems, the present invention aims to provide efficient heating with an inappropriate load on induction heating, where only the internal loss of the electromagnetic cooker itself increases and effective heating cannot be performed. Provided is an electromagnetic cooker with a new configuration that controls heating output by accurately determining the load suitable for induction heating based on the operating state of a drive circuit that flows high-frequency current through a heating coil. It is something to do.

[Summary of the idea]

In order to achieve the above-mentioned object, the electromagnetic cooker according to the present invention operates an output switch to which a heating coil is connected using the oscillation output of an oscillation circuit, thereby causing a high-frequency current to flow through the heating coil for cooking. In an electromagnetic cooker that performs induction heating of a dish, a damper diode is connected in parallel to the output switch, an inverting amplification type level comparator that detects the damper section in which the damper diode is made conductive by the switching operation of the output switch, and a level comparator that detects the level An integrating circuit that integrates the damper section detection pulse obtained by the comparator and a judgment circuit that judges whether the signal level of the integrated output obtained by this integrating circuit has reached the judgment reference level are provided. The load condition caused by the cooking container placed on the coil is determined by the determination circuit based on the damper section detection pulse obtained when the oscillation circuit is oscillated at a predetermined frequency, and the determination output is used. Accordingly, the operation of the oscillation circuit is controlled.

〔Example〕

Hereinafter, one embodiment of the electromagnetic cooker according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the electromagnetic cooker of this embodiment, a DC output obtained by rectifying a commercial power supply in a rectifier circuit 1 is supplied to a heating coil 2 via an output switch 3, and the output switch 3 is connected to the oscillation output of an oscillation circuit 4. Thus, by switching, a high frequency current is caused to flow through the heating coil 2.

That is, in this embodiment, the rectifier circuit 1
A commercial power supply is supplied to the inverter through a relay switch 6 which is operated by closing a power switch 5, and a smoothing capacitor 7 and a current detection resistor 8 are connected in series between the output terminals of the inverter. A choke coil 9 and a capacitor 10 are connected in series between both ends of the smoothing capacitor 7.

And the capacitor 1 of the above-mentioned chiyoke coil 9
One end of the heating coil 2 is connected to the connection point with 0. The other end of this heating coil 2 is connected via an output switch 3 to a connection point between the smoothing capacitor 7 and the current detection resistor 8. Further, a capacitor 11 is connected in parallel to the heating coil 2. Furthermore, a damper diode 12 is connected in parallel to the output switch 3.

Moreover, at the control input terminal of the output switch 3,
Oscillation output from the oscillation circuit 4 is supplied via the drive circuit 13. The oscillation circuit 4 is triggered by a trigger circuit 14 which detects the voltage across the heating coil 2 and operates. The oscillation circuit 4 is also supplied with detection outputs from a power supply detection circuit 15 and a load detection circuit 16, as well as a control signal from an output control section 17.

The power supply detection circuit 15 operates the oscillation circuit 4 when the power supply voltage of the commercial power supply is normal;
When the power supply voltage is abnormally high or low, the oscillation of the oscillation circuit is stopped and heating by the electromagnetic cooker is prohibited.

Further, the output control section 17 causes the oscillation circuit 4 to output an oscillation output based on the adjusted value of the heating output temperature adjustment resistor 18 . A detection output from an input current detection circuit 19 that detects a voltage drop occurring in the current detection resistor 8 connected to the rectifier circuit 1, that is, a drive current flowing through the heating coil 2, is fed back to the output control section 17.

Furthermore, the load detection circuit 16 identifies the size and material of the cooking container 20 placed on the heating coil 2 based on the damper current flowing through the damper diode 12, and identifies the size and material of the cooking container 20 placed on the heating coil 2.
is inappropriate as an inductive load for this electromagnetic cooker, it works to stop the oscillation operation of the oscillation circuit 4.

The load detection circuit 16 is configured as shown in FIG. That is, the signal input terminal 21 of the load detection circuit 16 connects two resistors 2 connected in series.
It is grounded via 2 and 23. A midpoint between the resistors 22 and 23 is connected to an inverting input terminal of a high gain operational amplifier 24. The non-inverting input terminal of the operational amplifier 24 is connected to two resistors 2 connected in series between the power supply input terminal 25 and the ground.
It is connected to the connection midpoint of 6 and 27. Further, the inverting input terminal is connected to the power input terminal 25 via a clamp diode 28. Furthermore, the signal output terminal of the operational amplifier 24 is connected to the power input terminal 25 via a load resistor 29 and to a determination circuit 31 via an integrating circuit 30. The determination circuit 31 is supplied with a determination reference level signal from the output control section 17 described above.

Here, the signal input terminal 21 is connected to the cathode of the damper diode 12 described above.

In the load detection circuit 16 configured as described above,
An anode voltage waveform as shown in FIG. 3 is applied to the signal input terminal 21 by the output switch 3 performing a switching operation in response to the oscillation output of the oscillation circuit 4 described above. Then, the signal obtained by resistance-dividing the anode voltage waveform by two resistors 22 and 23 and converting it to a low voltage is sent to the operational amplifier 24.
is supplied to the inverting input terminal of

The operational amplifier 24 functions as a high-gain inverting amplification type level comparator, and detects the damper section T _D in which the damper diode 12 is conductive and the anode voltage waveform is at _a negative potential. A digital damper section detection pulse that becomes logic "H" is output.

The clamp diode 28 clamps the potential of the inverting input terminal to the potential +B of the power supply input terminal 25 so that the input of the operational amplifier 24 does not exceed the common-mode input voltage range. Further, two resistors 26 and 27 connected in series between the power input terminal 25 and the ground are connected to the operational amplifier 2.
A bias is applied to the non-inverting input terminal so as to avoid the offset of 4 and always operate in the active region.

The damper section detection pulse obtained as the inverted amplified waveform output from the operational amplifier 24 is integrated by the integrating circuit 30 and converted into a DC level signal. The determination circuit 31 obtains a load detection output by comparing the levels of the DC level signal and the determination reference level signal.

Here, the damper diode 12 connected in parallel to the output switch 3 operates according to the load state caused by the cooking container 20 placed on the heating coil 2.
As the frequency of the drive current changes, the damper section T _D also changes.

In an example of the configuration described above, an experiment was conducted by setting the circuit constants so that a high frequency current of about 33KHz was passed through the heating coil 2 during no load. For a cooking container or a stainless steel cooking container with a wall thickness of 0.6 mm or less (hereinafter referred to as sample A), a logic "L" load detection output was obtained as a result of the judgment by the judgment circuit 31 described above. Also, the diameter is 8
For enamel or aluminum cooking containers with a wall thickness of 0.9 mm or more (hereinafter referred to as sample B),
A load detection output of logic "H" was obtained.

Further, the DC level signal obtained by the integrating circuit 30 of the load detection circuit 16 has the characteristics shown in FIG. 4 when the oscillation frequency at no load is changed, and the DC level signal obtained by the integration circuit 30 of the load detection circuit 16 has the characteristics shown in FIG. By operating the output switch 3, a signal level characteristic that allows the samples A and B to be reliably distinguished is provided.

In the above-described embodiment, since the size and material of the load are identified based on the presence or absence of a damper section at a predetermined frequency, there is no need to detect the pulse width of the damper pulse as an absolute value, and the load detection circuit 16 has a simple configuration. The load status can be reliably identified by

[Effect of idea]

As is clear from the description of the embodiments described above, in the electromagnetic cooker according to the present invention, the load caused by the cooking container is reduced based on the damper section in which the damper diode connected in parallel to the output switch that sends high-frequency current to the heating coil conducts. By identifying the condition,
It is possible to reliably identify a cooking container that is inappropriate as an inductive load and control the heating output, thereby fully achieving the intended purpose.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit configuration diagram showing a specific configuration of the load detection circuit in this embodiment. FIG. 3 is a waveform diagram showing the operation of the load detection circuit.
FIG. 4 is a characteristic diagram showing actual measurement results of the DC level signal obtained by the integrating circuit of the load detection circuit. DESCRIPTION OF SYMBOLS 1... Rectifier circuit, 2... Heating coil, 3... Output switch, 4... Oscillation circuit, 12... Damper diode, 16... Load detection circuit, 24... Operational amplifier, 30... Integrating circuit, 31 ...Judgment circuit.

Claims (1)

[Scope of utility model registration request] In an electromagnetic cooker that performs induction heating of a cooking utensil by passing a high-frequency current through the heating coil by switching the output switch to which the heating coil is connected using the oscillation output of an oscillation circuit, the output switch is connected in parallel to the output switch. an inverting amplification type level comparator for detecting the damper section in which the damper diode is turned on by the switching operation of the output switch; an integrating circuit for integrating the damper section detection pulse obtained by the level comparator; A determination circuit is provided to determine whether the signal level of the integral output obtained by the integration circuit has reached the determination reference level, and the oscillation circuit determines the load state due to the cooking container placed on the heating coil. The electromagnetic device is characterized in that the judgment circuit makes a judgment based on a damper section detection pulse obtained when the damper section is oscillated at a predetermined frequency, and the operation of the oscillation circuit is controlled based on the judgment output. Cooking device.