JPS60167294A - Induction heating cooking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an induction heating cooker equipped with a temperature control function.

[Technical background of the invention and its problems]

Generally, in an induction heating cooker, if a pot is not set, or even if it is set, if the pot is made of an inappropriate material or size, an excessive current will flow through the heating coil, causing the heating to occur. This will cause damage to various carriers including the coil. Therefore, conventionally, it is detected whether the pot is appropriate or not, and if the pot is not present, the operation of the heating coil is prohibited and the detection result is notified. However, there is a method to detect whether the pot is suitable or not, for example, by using a magnet.
This method can only detect magnetic bodies, and 18
Detection was not possible for pots that are non-magnetic but can be heated, such as the -8 stainless steel pot. To deal with this, we temporarily operate the heating coil at the start of heating,
Many methods are used to detect the voltage and current of the heating coil at that time, or to detect the voltage and current of the heating coil during heating, and to detect whether the pot is suitable or not according to the detection results. ing. In other words, not only magnetic steel but also 1
This method also makes it possible to detect 8-8 stainless steel.

By the way, in recent years, easy-to-use induction heating cookers equipped with a temperature control function have come on the market.

This device has a temperature detection section that detects the temperature of the pot and a temperature setting section that sets the temperature of the pot.When the temperature of the pot is lower than the set temperature, heating is performed, and when the temperature of the pot is higher than the set temperature. The heating is interrupted, thereby maintaining the temperature of the pot at the set temperature. However, if such an induction heating cooker employs a load detection function based on voltage and current detection as described above, the following problems will occur. In other words, when the heating is interrupted, the load detection function does not work, so even if the pot is removed or replaced with an inappropriate pot in that state, it will not be reported and the user will feel distrusted. It makes me embrace.

[Object of the invention] This invention was made in view of the above circumstances,
The purpose of this is to be able to constantly detect the load without being affected by the temperature control function in induction heating cookers that control heating by comparing the humidity of the load with the set temperature. It is an object of the present invention to provide an induction heating cooker with excellent reliability that can accurately notify whether or not it is appropriate.

[Summary of the invention]

This invention operates the inverter circuit continuously when the load temperature is lower than the set temperature, and operates the inverter circuit intermittently for the time required for load detection when the load temperature is higher than the set temperature. It is.

[Practical example of invention]

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

In Fig. 1, 1 is a commercial AC power supply, and this power supply 1 is equipped with a fuse 2 and a power switch 3.

A TNR 4, a noise prevention capacitor 5, a heating coil cooling fan motor 6, and a rectifier circuit 7 are connected through the TNR 4, a noise prevention capacitor 5, a heating coil cooling fan motor 6, and a rectifier circuit 7, respectively. The rectifier circuit 7 includes a diode bridge 8. Choke coil9. It consists of a smoothing capacitor 10. A resonant circuit consisting of a heating coil 11 and a capacitor 12 is connected to the output end of the rectifier circuit 7, and a damper diode 13 and a collector-emitter of an NPN transistor 14, which is a switching element, are connected in parallel to the capacitor 12. Ru. That is, the rectifier circuit 7, the damper diode 13, the transistor 14, and the like constitute an inverter circuit that drives the resonant circuit. Therefore, a current transformer 15 is connected to the input power line of the rectifier circuit 7.
is provided, and the output voltage of the current transformer 15 is supplied to the main control section 2o. Further, the voltage applied to the heating coil 11 is taken out, and the voltage is supplied to the main control section 20.

The main control unit 20 includes a temperature detector such as a thermistor 16 that detects the temperature of the load, that is, the temperature of the pot, an output/temperature setting volume 17, and a so-called cooking lamp (light emitting diode) 18 that reports whether the load is appropriate or not. are connected to each other.

Here, the main control section 20 will be explained. First, a DC voltage ycc is applied to the thermistor 16 via the resistor 21. In addition, a DC voltage Vc is connected to the output/temperature setting volume 17 through a resistor 22.23 in series.
c is applied. 24 is a comparator circuit that compares the voltage obtained at the interconnection point of the thermistor 16 and the resistor 21 with the voltage obtained at the sliding terminal of the volume 17, so that the temperature of the pot is lower than the set temperature. When it is high, the output is a logic "0" signal. 25 is an astable multi-by-break circuit (NM
The V circuit generates a rectangular wave signal of a constant frequency, and the rectangular wave signal is outputted as appropriate in accordance with the output of the comparator circuit 24. 26 is a constant heating/temperature adjustment heating changeover switch, which has a constant heating terminal 26a and a temperature adjustment heating terminal 26b;
When set to the a side, the constant voltage obtained at the interconnection point of the resistors 27 and 28 is extracted, and when set to the temperature regulator heating terminal 26b side, the sliding terminal voltage of the volume 17 is extracted. be. On the other hand, 30 is a voltage detection circuit that outputs a signal at a level corresponding to the voltage applied to the heating coil 11. Note that 31 is a voltage adjustment resistor for adjusting the input voltage to the voltage detection circuit 30. 3
2 is a current detection circuit that outputs a signal at a level corresponding to the output voltage of the current transformer 15; 33 is a comparison circuit that compares the output voltage of the voltage detection circuit 30 with the current detection circuit 3.
This is used to compare the output voltage of step 2, and outputs a logic "1" signal when the load is appropriate, that is, when a pot of material and size that allows induction heating is set. .

That is, a load detection section is configured by the voltage detection circuit 30, the current detection circuit 32, the comparison circuit 33, and the like. 34 is a delay circuit which delays the output of the comparator circuit 33 by a slight time and supplies it to the cooking lamp 18.

35 is an output level setting circuit that sets the heating output based on the difference between the output of the current detection circuit 32 and the extracted voltage of the changeover switch 26. 36 is pulse width modulation (PWM)
) A level setting circuit that generates a reference signal for pulse width modulation in the pulse width modulation circuit 42, which will be described later.
The reference signal is the above-mentioned astable multivibrator circuit 25.
, the output of the comparison circuit 33 , and the output of the output level setting circuit 35 .

A feedback circuit 40 generates a pulse signal synchronized with changes in the voltage applied to the heating coil 11. Reference numeral 41 denotes a triangular wave generating circuit which generates a triangular wave signal using a pulse signal generated from the feedback circuit 4o as a trigger. 42
is a pulse width modulation (PWM) circuit, and the triangular wave generation circuit 41
The triangular wave signal emitted from the pulse width modulation level setting circuit 36 is pulse width modulated by the reference signal supplied from the pulse width modulation level setting circuit 36. Reference numeral 43 denotes an inverter drive circuit that turns on and off the transistor 14 in accordance with a pulse width modulation signal obtained by the pulse width modulation circuit 42.

FIG. 2 specifically shows the main parts of FIG. 1. As shown in FIG. 2, the output terminal of the pulse width modulation level setting circuit 36 is connected to the output terminal of the comparison circuit 33 and the output terminal of the output level setting circuit 35, and is further connected between the collector and emitter of the NPN transistor 52. grounded through.

A resistor 53 is connected between the base and emitter of the transistor 52.
A rectangular wave signal of the astable multivibrator circuit 25 is supplied via 54. However, the output end of the astable multivibrator circuit 25 is grounded via the movable terminal of the changeover switch 55 and the steady heating terminal 55a, and the output end of the astable multivibrator circuit 25 is
b and the collector of the NPN transistor 56.
The emitters are connected in series to ground. Here, the changeover switch 55 is linked to the changeover switch 26.

A resistor 57 is connected between the base and emitter of the transistor 56.
The output of the comparator circuit 24 is supplied via 58.

Next, the operation of the above configuration will be explained with reference to FIG.

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Set it to the Prisoner's Section 96b side, and set the volume to 1.
Set the temperature at step 7. Then, set the pot on the top plate and turn on the power switch 3.3. Then, first, the inverter circuit is temporarily driven and the heating coil 11
A resonant circuit consisting of a capacitor 12 and a capacitor 12 operates in oscillation, and a high frequency current flows through the heating coil.

At this time, the current input to the rectifier circuit 7 and the voltage applied to the heating coil 11 are detected by the current detection circuit 32 and the voltage detection circuit 30, respectively, and if the pot is suitable, a logic "1" signal is sent from the comparison circuit 33. When the comparison circuit 33 outputs a logic "1" signal, the cooking lamp 1 is output with a slight time delay based on the delay circuit 34.
8 lights up.

On the other hand, since the output/temperature changeover switch 26 is set to the temperature adjustment heating terminal 26b side, the output level is set to a voltage corresponding to the difference between the sliding terminal voltage of the volume 17 and the output voltage of the current detection circuit 32. It is output from the circuit 35. Further, the sliding terminal voltage of the volume 17, that is, the set temperature, and the voltage based on the resistance change of the thermistor 16, that is, the temperature of the pot, are compared in the comparator circuit 24. At this time, the temperature of the pot is still lower than the set temperature, so the comparison is made. A logic 11111 signal is output from circuit 24. If the output of comparison circuit 24 is a logic 11111 signal, transistor 56 is turned on and the output of astable multivibrator circuit 25 is removed from ground, thereby maintaining transistor 52 in the off state. In this way, if the output of the comparison circuit 33 is logic "1" and the transistor 52 is in the off state, the reference signal of the pulse width modulation level setting circuit 36 is supplied to the pulse width modulation circuit 42. The voltage level of the reference signal supplied to the modulation circuit 42 is determined by the output voltage of the output setting circuit 35.The pulse width modulation circuit 42 receives the voltage level of the reference signal supplied from the triangular wave generation circuit 41 based on the voltage level of the supplied reference signal. The triangular wave signal is pulse width modulated.

Then, the inverter drive circuit 43 drives the inverter circuit in accordance with this pulse width modulation signal, whereby the oscillation operation of the resonant circuit continues and a high frequency current flows continuously through the heating coil 11. That is, heating is started.

Thus, when heating occurs, the temperature of the steel increases.

When the temperature of the pan rises above the set temperature, the output of comparator circuit 24 becomes logic 110 II and transistor 56 turns off. When the transistor 56 turns off, the transistor 52 turns on and off in response to a rectangular wave signal generated from the astable multivibrator circuit 25. Therefore, the reference signal output from the pulse width modulation level setting circuit 36 is removed from ground when the transistor 52 is turned off, and the reference signal is intermittently supplied to the pulse width modulation circuit 42. In this way, the inverter circuit is driven only when the reference signal is supplied to the pulse width modulation circuit 42,
In other words, the inverter circuit operates intermittently, and the resonant circuit operates in intermittent oscillation accordingly. In this case, the circuit constants of the astable multivibrator circuit 25 are determined so that each operation time of the intermittent operation of the inverter circuit is sufficient time for the load detection section to detect the load.

Furthermore, in this case, heating is actually being performed because the resonant circuit operates in oscillation, but this is essentially the same as heating being interrupted. The intermittent operation of this inverter circuit (at A, if the load is appropriate, the load detection section, that is, the comparator circuit 33
I-I! Since a delay circuit 34 is interposed between the signal power (output power ζ) and the comparison circuit 33 and the cooking lamp 18, the cooking lamp 18 does not blink, and the cooking lamp 18 does not turn on ( During this intermittent operation, if the pot is removed from the top plate or replaced with an incorrect one, the load detection section will detect this. , the output of the comparison circuit 33 becomes IJ\logic (OII). When the output of the comparison circuit 33 becomes the logic 2, the car user is notified that high power is not being applied or that the pot is not suitable.Furthermore, when the output power of the comparator circuit 33 reaches 1'0°, the standard of the pulse width modulation level setting circuit ig 36 is The signal is grounded and the inverter circuit is driven (forcibly inhibited, causing the resonant circuit to operate in oscillation (while heating is interrupted (actually, intermittent oscillation of the resonant circuit)), the temperature of the pot returns to the set temperature. , the output of the comparator circuit 24 becomes logic 111 IT, transistor 56 turns on and transistor 52 remains off, which causes the inverter circuit to operate continuously again, i.e. heating takes place. It will be done.

In this way, in temperature-controlled cooking, if the temperature of the pot is lower than the set temperature, the inverter circuit is operated continuously,
When the humidity of the pot becomes higher than the set temperature, the inverter circuit is activated to detect the load at the load detection section.The inverter circuit operates intermittently for a sufficient period of time, so the load can be detected at all times, and the load is detected properly. It becomes possible to accurately notify whether or not the situation is true.

Incidentally, in the above embodiment, the case where a discrete circuit is used has been described, but it is also possible to perform the same implementation by program control using a microcomputer. In addition, although the cooking lamp is used to notify whether the load is appropriate, a buzzer or other indicator may also be used. It goes without saying that the present invention is not limited, and that various modifications can be made without changing the gist.

〔Effect of the invention〕

As described above, according to the present invention, in an induction heating cooker that performs heating control by comparing the humidity of the load with a set temperature, it is possible to constantly detect the load without being affected by the temperature control function. Thereby, it is possible to provide a highly reliable induction heating cooker that can always accurately notify whether or not the load is appropriate.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is a configuration diagram of a control circuit, FIG. 2 is a detailed configuration diagram of the main part of FIG. 1, and FIG. 3 is a diagram for explaining the operation. It is a diagram. 11... Heating coil, 12... Capacitor, 15.
...Current transformer, 16...Thermistor (temperature detector), 17...Output/temperature setting volume, 18...
Cooking lamp (notification means), 20...main control section. Figure 1 Figure 3

Claims (1)

[Claims] A heating coil, a capacitor that forms a resonant circuit together with the heating coil, an inverter circuit that drives this resonant circuit, a load detection section that detects a load based on the voltage and current of the heating coil, and a detection result of this load detection section. a temperature detection section for detecting the temperature of the load; a temperature setting section for setting the temperature of the load; In addition to operating the inverter circuit continuously,
An induction heating cooker comprising: control means for intermittently operating an inverter circuit when the temperature detected by the temperature detection section is higher than the set temperature of the temperature setting section.