JP2925839B2 - Electromagnetic cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic cooker having a configuration in which high frequency power is supplied to a heating coil by an inverter circuit, and more particularly to a device in which a switching element in the inverter circuit is protected from abnormally high temperatures.

[0002]

2. Description of the Related Art In an electromagnetic cooker, a heating coil is arranged on a lower surface side of a top plate, and high-frequency power is supplied to the heating coil to induction-heat a pot placed on the top plate and housed in the pot. The cooked food is cooked.

The supply of high-frequency power to the heating coil is as follows:
Generally, this is performed by an inverter circuit. This inverter circuit includes a switching element, and the frequency of the high-frequency power supplied to the heating coil is determined by the ON / OFF cycle of the switching element.

Since a large current flows through the switching element, the amount of heat generated is large. Therefore, conventionally, a cooling fin is attached to the switching element to cool the switching element, and in order to protect the switching element from abnormally high temperature, a bimetal switch is attached to the radiating fin, and the radiating fin exceeds a predetermined temperature. In this case, the switching element is turned off by turning off the bimetal switch.

[0005]

However, conventionally, a bimetal switch is used to protect the switching element from an abnormally high temperature. However, the mounting of the bimetal switch to the radiation fin is performed by screwing. Poor mounting workability. In addition, the bimetal switch has a configuration in which heat is transferred from the radiating fins to the bimetal by heat conduction, so that the bimetal is deformed and turned off. It wasn't.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the workability of mounting components for detecting the temperature of a switching element, and furthermore, the switching element has excellent followability to a temperature rise. It is an object of the present invention to provide an electromagnetic cooker that can ensure the protection of the food.

[0007]

The electromagnetic cooker according to the present invention comprises:
A heating coil is provided, an inverter circuit for supplying high-frequency power to the heating coil is provided, and a thermistor for temperature detection is attached to the printed circuit board together with the switching element by soldering so as to be in contact with a case of the switching element in the inverter circuit. And a control means for turning off the switching element when it is detected that the temperature of the case has become equal to or higher than a predetermined temperature based on a detection signal of the thermistor.

[0008]

The thermistor can be mounted by soldering simultaneously when the switching element and other electronic components are mounted on the printed wiring board on which the switching element is mounted, so that the thermistor is excellent in workability in mounting the thermistor.

Further, since the thermistor has good followability to temperature rise, it is possible to make every effort to protect the switching element.

In addition, since the thermistor detects the temperature of the case, which is the non-charged portion of the switching element, the thermistor can be brought into direct contact with the case, thus simplifying the configuration.

[0011]

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

First, in FIG. 3 showing the electric circuit configuration of the electromagnetic cooker, reference numeral 1 denotes an AC power supply. AC power supplied from the AC power supply 1 is rectified by a rectifier circuit 2, and is connected to a choke coil 3 and a smoothing capacitor. The signal is smoothed by a smoothing circuit 5 composed of four. A heating coil 6 and a resonance capacitor 7 are provided between both terminals of the smoothing capacitor 4 of the smoothing circuit 5.
And a resonance circuit 8 composed of a series circuit of A parallel circuit of the damper diode 9 and the switching element 10 is connected between both terminals of the resonance capacitor 7.

The switching element 10 includes a resonance circuit 8
Together with an inverter circuit 11, which is controlled at a high speed by a control circuit 12 mainly composed of a microcomputer (not shown). The inverter circuit 11 supplies high-frequency power to the heating coil 6 by turning on and off the switching element 10. The heating coil 6 is disposed on the lower surface side of the top plate (not shown), and induction heating of the pan A on the top plate is performed by supplying high-frequency power to heat the food in the pan A. .

The switching element 10 is shown in FIG.
2 is housed in a case 13 made of an insulating material shown in FIG. Here, the switching element 10
The heat radiating portion (not shown) is in contact with the heat radiating fin 14, and the heat generated by the switching element 10 is
4.

As shown in FIGS. 1 and 2, the switching element 10 mounted on the radiation fin 14 is mounted on a printed wiring board 16 together with electronic components (not shown) constituting the control circuit 12, and the like. I have. A thermistor 17 is mounted on the printed wiring board 16. The thermistor 17 is arranged so as to face the case 13 of the switching element 10, and its lead leg 17 a is soldered to the printed wiring board 16. Here, the length (height) of the lead leg 17a is set to a predetermined dimension so that the thermistor 17 contacts the lower surface of the case 13 of the switching element 10 in the drawing. Therefore, the thermistor 17 is directly connected to the case 1
3, the temperature of the switching element 10 can be detected indirectly.

The temperature detection signal of the thermistor 17 is
It is input to the control circuit 12 as a voltage signal. The control circuit 12 is configured to turn off the switching element 10 when detecting that the temperature of the case 13 has reached a predetermined temperature, for example, 90 ° C. or higher, based on a detection signal from the thermistor 17.

In the above configuration, a large current flows through the switching element 10 during cooking, so that the switching element 10 generates heat. This heat is transmitted to the radiation fins 14 and released from the radiation fins 14 into the air, whereby the switching element 10 is cooled. By the way, for some reason, the switching element 1
The temperature of 0 may rise abnormally. Then, the temperature of the case 13 of the switching element 10 also rises, and when the control circuit 12 detects that the temperature of the case 13 becomes 90 ° C. or higher based on the detection signal of the thermistor 17, the control element 12 turns off the switching element 10, The supply of the high-frequency power to the heating coil 6 is stopped. For this reason, the destruction of the switching element 10 due to the continuation of the on / off operation at an abnormally high temperature of the switching element 10 is prevented.

As described above, according to the present embodiment, the thermistor 17 is used as a temperature detecting element for preventing an abnormally high temperature of the switching element 10. Therefore, the thermistor 17 uses the switching element 10 and other electronic components for a printed circuit board. 16 and can be attached by soldering at the same time. For this reason, the workability of attaching the thermistor 17 is excellent, unlike the conventional case where the bimetal switch is attached to the radiation fins by screws or the like.

Since the thermistor 17 has a better response to a temperature change than a bimetal switch, even if the temperature rise rate of the case 13 (switching element 10) is high, the temperature of the case 13 can be detected by following the change rate well. As a result, the switching element 10 can be more reliably protected from destruction due to abnormally high temperatures.

In addition, since the thermistor 17 detects the temperature of the case 13 which is a non-charged portion, there is no need to provide an insulating distance or an insulator between the case 13 which is a detection target portion. For this reason, the thermistor 17 can be brought into direct contact with the case 13, which simplifies the configuration and allows the temperature of the case 13 to be detected more accurately and at the same time makes the response to the temperature rise of the case 13 better. Thus, the switching element 10 can be more reliably protected from destruction due to an abnormally high temperature.

[0021]

As described above, according to the present invention, a thermistor is used as a temperature detecting element for detecting the temperature of the switching element in order to protect the switching element from abnormal temperature rise. In this configuration, the thermistor can be attached to the printed circuit board together with the switching element by soldering. Therefore, the workability of mounting the thermistor is good, and the thermistor has excellent responsiveness to temperature rise. Can be more reliably protected from abnormally high temperatures.

In addition, since the case is a non-charged part, the temperature can be detected by directly contacting the thermistor without the interposition of an insulator or the like, so that the temperature can be detected. It has various effects such that it can be detected with good responsiveness and can be more reliably protected from abnormally high temperatures.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along line AA of FIG.
Enlarged vertical section along the line

FIG. 2 is a side view of a main part.

FIG. 3 is an electrical circuit configuration diagram

[Explanation of symbols]

2 is a rectifier circuit, 5 is a smoothing circuit, 6 is a heating coil, 7 is a resonance capacitor, 10 is a switching element, 11 is an inverter circuit, 12 is a control circuit (control means), 13 is a case, 14 is a radiation fin, 16 is Printed wiring board, 17
Is a thermistor.

Claims (1)

(57) [Claims] 1. A heating coil, an inverter circuit for supplying high-frequency power to the heating coil, and a temperature attached to a printed circuit board together with the switching element by soldering so as to be in contact with a case of the switching element in the inverter circuit. An electromagnetic cooker comprising: a thermistor for detection; and control means for turning off the switching element when detecting that the temperature of the case has reached a predetermined temperature or higher based on a detection signal of the thermistor.