JPH04118888A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To eliminate the striking and abrupt fluctuation in temperature of a heated container, and thereby enhance cooking performance by allowing the output of a charge/discharge circuit to act as the input of the other side, and thereby providing a device with a comparator which changes the output of a control section in such a way that the energizing condition of a switching element is continuously changed. CONSTITUTION:A device is provided with a temperature detecting circuit 12c detecting the temperature of a switching element 10 which controls the quantity of energized electricity to a coil 6 heating a heated container P, and the output of both a charge/discharge circuit 166c which charges/discharges electricity in response to the on/off action of a switching element, and a temperature detecting circuit 12c is made to act as the input of one side. And furthermore, the device is provided with a comparator 168 which makes the output of the charge/discharge circuit 166c to act as the input of the other side, and changes the output of a control section 15 in such a way that energizing condition of the switching element is continuously changed as the switching element is increased in temperature. By this constitution, when the switching element 10 comes close to a critical temperature, the comparator 168 which inputs both of the output of the charge/discharge circuit 166c in a state of charging/ discharging, and the output of the temperature detecting circuit 12c in response to the temperature of the switching element, produces an output in response to both of the output. Heating at which the temperature of the switching element is stabilized, is thereby continuously carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an induction heating cooker that is capable of heating a non-magnetic heated container such as a non-magnetic stainless steel pot.

[Prior Art] FIG. 5 is a configuration diagram of a control circuit of a conventional induction heating cooker disclosed in, for example, Japanese Patent Laid-Open No. 150579/1983.

In Figure 5, (1) is a commercial power supply, and this power supply (1)
includes a diode bridge (2) and a choke coil (3).
, and a rectifier circuit (5) consisting of a smoothing capacitor (4)
A series resonant circuit (8) consisting of a heating coil (6) and a capacitor (7) is connected via. A diode (9) is connected in parallel to the capacitor (7), and the collector and emitter of a switching element 1, such as an NPN transistor (10), are connected in parallel. That is, rectifier circuit (5), diode (9)
A sixth inverter circuit (12) is configured to drive the series resonant circuit (8) by a switching element (10) and the like. As shown in the figure, it is attached to the heat sink (13) of the switching element (10). (I4) is a control circuit for controlling the switching element (10) by the output of the temperature detection element (12). The internal circuit configuration is shown in Figure 7 below.
) is a control unit that turns on and off the switching element (10) by the output of this control circuit (14), and (P) is a non-magnetic stainless steel heated by the heating coil (6), such as 18-8 stainless steel, a pot, etc. A non-magnetic heated container into which the food to be cooked is placed.

In Figure 7, (141) (142) (143)
(144) (145) are resistors, (146) are comparators,
(147) is an NPN type transistor. Then, a DC voltage Vcc is applied to the series circuit of the resistor (141) and the temperature detection element (12) and the series circuit of the resistor (142) and the resistor (143).

In addition, the voltage obtained at the interconnection point between the temperature detection element (12) and the resistor (141) is supplied to the non-inverting input terminal (+) of the comparator (146), and
The voltage obtained at the interconnection point with the comparator (146)
is supplied to the inverting input terminal (-) of The output of the comparator (146) is connected to the transistor (147) via the resistor (144).
is supplied between the base and emitter of this transistor (
The collector voltage of 147) is supplied to the control unit (15) as an output setting command via a resistor (145). The control section (15) turns on/off the switching element (10) at a timing according to an output setting command from the control circuit (14).
The output of the heating coil (6) is set by performing off control.

Next, the operations shown in FIGS. 5 to 7 will be explained.

When the non-magnetic heated container (P) containing the food to be cooked is placed in the heating coil (6) and the power source (1) is turned on, the switching element (10) is turned on and off under the control of the control section (15). Then, the resonant circuit (8) oscillates and the heating coil (
A high frequency current flows through 6). That is, the heating coil (6
), a high-frequency magnetic field is emitted from the heated container (P).
is applied to the container to be heated (P) to self-heat. In this case, the output of the heating coil (6) is set to the usual 1200W or so.

When cooking starts in this way, the container to be heated (P) becomes 18
When the switching element (10) is made of -8 stainless steel, that is, a non-magnetic material, the temperature of the switching element (10) gradually increases. When the temperature of the switching element (10) exceeds a certain value (for example, 85°C or higher), the resistance value of the temperature detection element (thermistor with negative temperature characteristics) (12) decreases, so that the temperature detection element (12) and the resistance The voltage obtained at the interconnection point with (141) is the resistance (142) (143
), the comparator (146) outputs a logic 1 signal and the transistor (14
7) is conductive, and the control circuit (14) is connected to the control section (15).
An output reduction command is supplied to the Upon receiving this output reduction command, the control unit (15) determines the on/off timing of the switching element (10) to reduce the output of the heating coil (6), and sets the output of the heating coil (6) to, for example, 900W. Set. When the output of the heating coil (6) is reduced in this way, the switching element (10)
temperature also decreases. This prevents damage to the equipment. Then, when the temperature of the switching element (lO) becomes below a certain value, the output of the comparator (146) becomes logic O.
signal, the transistor (147) becomes non-conductive, the output reduction command is released from the control unit (15), the switching element (10) performs normal on/off control, and the output of the heating coil (6) is the normal state, i.e. 1
It will be reinstated in 2001.

In this way, when the temperature of the switching element (10) is below a certain value, the output of the heating coil (6) is reduced to the normal 120%.
011, and the output of the heating coil (6) is controlled to be reduced to, for example, 900 W when the temperature of the switching element (10) exceeds a certain value that is in a dangerous state.

In addition, normally, when the input to the switching element (10) is a non-magnetic heated container (P), the current flowing through the switching element (10) increases and exceeds the allowable value, causing the switching element (10) to break. Therefore, this destruction is prevented by limiting the input and using the current and voltage within the permissible values. It is detected by a transformer, and if the load is an 18-8 stainless steel pot, an excessive current will flow through the switching element, so the ON period of the switching element is shortened and the current is controlled to be within the appropriate range of the switching element. There is.

In addition, the method disclosed in Japanese Utility Model Application Publication No. 58-60891 is that when a non-magnetic material pot such as 18-8 stainless steel is used, the current flowing through the switching element increases and the element is damaged. The relationship between the anode voltage detection signal vb and the control voltage Ve is V b > Ve
Therefore, it is possible to detect that the current has increased, and upon this detection, an input limiting operation is performed to protect the switching element.

[Problems to be Solved by the Invention] Since the conventional induction heating cooker is configured as described above, the voltage and current of the switching elements such as transistors that control the supply of electricity to the heating coil (6) are within the permissible values. Even if the temperature is within the range of 1 to 2, the temperature of the switching element increases due to the loss of the switching element.

If the temperature of the switching element exceeds the allowable value due to this temperature rise, the switching element will be destroyed, so cooling fins or cooling fans are generally provided to keep the temperature of the switching element within the allowable value, and to prevent the thermistor near the switching element. When the temperature exceeds a certain value, the output of the switching element is limited so that, for example, the output of the heating coil (6) is reduced from 12001 to 900V, but if the output reduction due to temperature is only one value and the switching element is A value small enough to protect, for example a heating coil output of 90011. Since the switching element is fixed at In this case, not only the capability of the device cannot be fully utilized, but also the thermistor is sufficiently cooled and the recovery time is shortened. That is, the output of the heating coil, i.e. the temperature of the container to be heated, frequently and significantly increases.
In addition, there was a problem in that the temperature fluctuated rapidly, making it extremely difficult for the cook to use.

This invention was made to solve the above-mentioned problems, and when a non-magnetic heated container is used, it does not simply protect the switching element, but also prevents the temperature of the heated container from frequently increasing significantly. To provide an induction heating cooker that enables good heating that does not cause sudden cooking and makes it easy to cook, and that makes full use of the capabilities of the device.

[Means for Solving the Problems] The induction heating cooker according to the present invention includes: a temperature detection circuit that detects the temperature of a switching element that controls the amount of current applied to a heating coil that heats a container to be heated; a charging/discharging circuit that performs charging/discharging in response to on/off of the switching element, and an output of the temperature detection circuit as one input, and an output of the charging/discharging circuit as the other input, and as the temperature of the switching element rises. The device includes a comparator that changes the output of the control section so that the conduction state of the switching element changes continuously.

[Function] In the induction heating cooker according to the present invention, when the temperature of the switching element approaches a dangerous temperature, the output of the charging/discharging circuit that is in a charging or discharging state corresponding to the on/off of the switching element at that time and the output of the switching element A comparator that inputs the output of the temperature detection circuit corresponding to the temperature outputs an output corresponding to the magnitude of both outputs, and the control section continuously changes the conduction state of the switching element based on the output of this comparator. Continuously reduce the output of the heating coil.

Continuous heating is performed with an output that stabilizes the temperature of the switching element, and frequent and drastic fluctuations in the output of the heating coil are suppressed.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In Figures 5 and 2, (1) to (12), (15), and (P) are the same or equivalent parts as the conventional ones shown in Figures 5 to 7, so detailed explanations thereof will be omitted. . (16
) is a control circuit that supplies an output reduction command to the control section (15), and its internal circuit configuration is shown in FIG.

In Figure 2, (160) (161) (162) (1
63)(164)(165) are resistances, (166)(1
67) is a capacitor, (168) is a comparator, (169)
is a diode, and (12c) is a temperature detection circuit, which is composed of a temperature detection element (12) and a resistor (160).
(166c) is a charging/discharging circuit, which is composed of a capacitor (166), resistors (161), (162), (163), and a diode (169). Comparator (168) (
A voltage obtained at the interconnection point between the temperature detection element (12) that detects the temperature of the switching element (10) and the resistor (160), that is, a temperature signal, is applied to the +) terminal.

Further, Vcc is applied to the series circuit of the resistors (161) and (162), and the capacitor (
166) is connected, and the voltage obtained at the interconnection point of these capacitor (166) and resistors (161) and (162) is supplied to the (-) terminal of the comparator (168). Furthermore, the (-) terminal of this comparator (168) is connected to the output of the control section (15) via a resistor (163) and a diode (169).
That is, it is connected to the base of the switching element (lO). Resistor (164) (165) and capacitor (
167) is for smoothing the output of the comparator (16g) to obtain an averaged DC voltage, and this DC voltage is supplied to the control unit (15) as an output reduction command.

Next, the operation will be explained.

Figure 3 shows the output (150UT) of the control section (15), the input (168IN+) (168TN-) of the comparator (168)
, the output (168OUT) of the comparator (168), and the output (160UT) of the control circuit (16).

The control unit (15) outputs a pulse waveform (15 in Fig. 3 (a)) for turning on and off the switching element (10).
OUT). The capacitor (166) is the resistor (161)
), but the output (150
0 cho) Gari.

When it becomes, the resistor (163) and diode (169)
The input voltage (16gIN-) at the (-) terminal of the comparator (168) becomes a triangular wave (16gIN-) due to the charging and discharging described above.
168IN-) in FIG. 3(b). If the temperature of the switching element (10) is low enough, the comparator (16)
The input voltage (168IN+) of the (+) terminal of 8) is (-)
Higher than the terminal voltage (168IN-) (1 in Figure 3 (b)
68IN, comparator (168) output (168OUT)
is Hi (168OUT in Figure 3 (c)), the capacitor (167) remains charged, and the control unit M
The output (160LIT) of (16) becomes Hi (16OUT in FIG. 3(c)), and the output of heating coil (6) is in the normal state 1, for example, 120011.

Here, as the temperature of the switching element (10) rises and approaches the dangerous temperature, the (+) terminal voltage (168IN+) of the comparator (168) becomes low as shown by the broken line in FIG. 3 (b). It crosses the triangular wave voltage (168IN-) of the (=) terminal, and the output of the comparator (168) (168O
UT) becomes a pulse signal as shown in Figure 3 (d),
The output (160UT) of the control circuit (16) is connected to the resistor (164
) (165) and the capacitor (167), the voltage is smoothed and averaged to be lower than normal (Figure 3 (
D) 1000 guns), the controller (15) is instructed to reduce the output. Therefore, the control unit (15) controls the switching element (10) so that the output of the heating coil (6) (hereinafter referred to as heating output) is reduced. The amount of reduction in heating output depends on how low the output voltage (160UT) of the control circuit (16) is. ( of the comparator (168) in the control circuit (16)
-) Since the terminal voltage (168IN-) is a triangular wave, the higher the temperature of the switching element (10), the longer the L0 period of the output (1680UT) of the comparator (168).
The output (160UT) of the control circuit (16) is reduced, the heating output is reduced, and this operation is controlled by the switching element (10).
This is done continuously and steplessly as the temperature changes. In other words, when the cooling conditions of the switching element (10) are constant, the temperature of the switching element (lO) is higher when the heated container (P) is non-magnetic because the current of the switching element (10) is larger. If the temperature exceeds the allowable temperature under these conditions, the heating output is reduced to the minimum necessary level to protect the switching element (10). In addition, protection against the maximum current and maximum voltage of the switching element (lO) can be achieved by detecting the collector current of the switching element (10) with a current transformer (not shown), and reducing the collector voltage by resistor division, as in the past. These values are compared with the reference voltage provided for each using a voltage comparator (not shown), and if the collector current or collector voltage exceeds the allowable value of the switching element (10), the control circuit By shortening the conduction period of the switching element (10) in (16), the collector current and voltage are kept within permissible values. In addition, since the input voltage of the (-) terminal of the comparator (168) is charged and discharged by the pulse signal of the control section (15) and becomes a triangular wave, when the heating output is reduced, the input voltage of the (-) terminal of the control section (15) is ) will change, and the waveform of the (-) terminal voltage of the comparator (168) will also change, but ultimately it will change depending on the balance between the temperature rise of the switching element (10) and the heating output. , becomes stable as shown in FIG.

In the above embodiment, the time constant was set for discharging the capacitor (166) at the (-) terminal of the comparator (168) via the resistor (163) and the diode (169). (-) of comparator (168)
The waveform of the terminal may be changed to intermittent wave control, and the same effect as in the above-mentioned embodiment can be obtained.

[Effects of the Invention] As described above, the present invention includes a heating coil for a container to be heated, a switching element that controls the amount of current to the heating coil by being turned on and off, and a switching element that controls on and off the switching element. A temperature detection circuit for detecting the temperature of the switching element in an induction heating cooker including a control section.

A charging and discharging circuit that performs charging and discharging in response to turning on and off of the switching element, and an output of the temperature detection circuit are used as one input, and the output of the charging and discharging circuit is used as the other human power, and the output is used to control the control section. Since a comparator is provided that changes the output so that the conduction state of the switching element changes continuously, when the temperature of the switching element rises and approaches the dangerous temperature, the conduction state of the switching element changes continuously, causing the heating coil to change. The output changes in the direction of decreasing continuously, and it no longer changes frequently, drastically, and suddenly as in the past, and even when the heated container is a non-magnetic material, the temperature of the heated container changes frequently. There is an effect that an induction heating cooker that is easy to cook can be obtained since there is no possibility of a drastic change.

[Brief explanation of the drawing]

FIG. 1 is an overall circuit configuration diagram showing an embodiment of an induction heating cooker according to the present invention, FIG. 2 is an internal circuit configuration diagram of the control circuit in FIG. 1, and FIGS. This is a diagram showing the relationship between input and output signals of each part in Figure 2, and Figure 3 (
A) and FIG. 4(A) show the output (150) of the control section (15).
UT) waveform diagrams, Figures 3 (b) and 4 (b) show the non-inverting input (16gIN) to the (+) terminal of the comparator (168).
and the inverted input (1) to the (-) terminal of the comparator (168).
68IN-) waveform diagram, Figure 3 (C), Figure 3 (D),
and Fig. 4(c) shows the output (168O) of the comparator (168).
UT) and the output (160UT) of the control circuit (16). Figures 5 to 7 are diagrams showing a conventional induction heating cooker, with Figure 5 showing the overall circuit configuration and Figure 6 showing the state in which the switching element (10) and temperature detection element are attached to the heat sink. The perspective view, FIG. 7, is an internal circuit configuration diagram of the control circuit in FIG. 5. In the figure, (P) is a heated container, (6) is a heating coil, (10) is a switching element, (15) is a control unit,
(12c) is a temperature detection circuit, (166c) is a charge/discharge circuit, and (168) is a comparator. Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1 Figure b Figure 1 I 1

Claims (1)

[Claims] In an induction heating cooker comprising a heating coil that heats a container to be heated, a switching element that controls the amount of current to the heating coil by being turned on and off, and a control section that controls the switching element on and off. , a temperature detection circuit that detects the temperature of the switching element, a charging/discharging circuit that performs charging/discharging in response to on/off of the switching element, and one input of which is the output of the temperature detection circuit, and the charging/discharging circuit. induction heating, characterized in that it is provided with a comparator whose output is the other input and whose output changes the output of the control section so that the conduction state of the switching element changes continuously as the temperature of the switching element increases. Cooking device.