JP5858794B2 - Induction heating cooker - Google Patents

Description

  The present invention relates to an induction heating cooker that induction-heats a pan placed on a top plate by a heating coil.

  As a conventional induction heating cooker, when the switching element generates heat for some reason, the thermistor operates with the temperature gradient of the thickness of the radiating fin, the operation signal is transmitted to the control circuit board, and the energization to the switching element is stopped. (For example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 61-77730 (2nd page, FIG. 3)

  In the conventional induction heating cooker described above, when measuring the junction temperature of the switching element, the surface of the radiating fin is measured with a thermistor, and the thermal power is limited or stopped when the switching element reaches the rated temperature. However, in the above-mentioned technology, the difference between the temperature at the measurement point and the junction temperature varies depending on the amount of heat generated by the switching element, so there is a possibility that the thermal power cannot be limited or stopped at the junction temperature from the surface temperature of the radiating fin. It was.

  The present invention has been made to solve the above-described problems, and an induction heating cooker that can reliably protect a switching element without being affected by the heat generation amount even if the heat generation amount of the switching element changes. The purpose is to provide.

An induction heating cooker according to the present invention includes a DC power supply circuit that rectifies AC power of an AC power supply and converts it into DC power, and converts DC power of the DC power supply circuit into high-frequency power by a switching element, and outputs it to a heating coil. An inverter circuit, an input current detecting means for detecting an input current input from the AC power source to the DC power source circuit, a switching element of the inverter circuit, and a radiation fin for cooling the switching element, and a temperature of the radiation fin or the switching element The temperature sensor limit temperature is set lower each time the input current detected by the input current detection means becomes larger than the temperature sensor to be detected and the rated temperature of the switching element, and the temperature sensor detection temperature exceeds the limit temperature. Control means for limiting the driving of the switching element.

  In the present invention, according to the input current detected by the input current detection means, a temperature sensor limit temperature corresponding to the rated temperature of the switching element is set, and when the temperature sensor detection temperature exceeds the limit temperature, The driving of the switching element is limited. Thereby, a switching element can be protected reliably.

It is a perspective view which shows the external appearance of the induction heating cooking appliance in Embodiment 1. FIG. It is a figure which shows the circuit structure of the induction heating cooking appliance in Embodiment 1. FIG. It is a side view which shows the state which attached the switching element and the thermistor of FIG. 2 to the radiation fin. It is a figure which shows the relationship of the temperature difference of the emitted-heat amount of a switching element, junction temperature, and the detection temperature of a thermistor. FIG. 3 is a diagram illustrating a relationship between an input current and a temperature limit of the thermistor in the first embodiment. It is a figure which shows the relationship between the coil current in Embodiment 2, and the limiting temperature of a thermistor. It is a figure which shows the relationship between the setting electric power in Embodiment 3, and the limiting temperature of a thermistor.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing an appearance of the induction heating cooker in the first embodiment.
In FIG. 1, a top plate 2 attached to the main body case 1 via a frame 3 is provided on the upper portion of the main body case 1 of the induction heating cooker 100. The top plate 2 is made of heat-resistant tempered glass, and is printed on the back surface so that the inside cannot be seen. On the surface of the top plate 2, for example, three circular heating ports HL, HR, and HC indicating the mounting position of the pan 14 are displayed by a method such as printing. In the main body case 1, three heating coils are arranged corresponding to the heating ports HL, HR, and HC.

  On the front side of the top plate 2, the heating power display units 4 and 5 for displaying the heating power of the heating ports HL and HR and the liquid crystal display units 7 and 8 for displaying the operation states of the heating ports HL, HR and HC are provided. , 9 are provided. Furthermore, a thermal power display unit 6 that displays the thermal power of the heating port HC is provided in the center of the rear portion of the top plate 2.

  An upper surface operation unit 10 is provided on the front side of the frame 3. The upper surface operation unit 10 includes, for example, a heating power setting operation unit provided corresponding to each of the heating ports HL, HR, and HC, and a grill operation unit that operates heating of the grill. An intake / exhaust cover 11 that covers the intake and exhaust ports provided in the main body case 1 is detachably provided on the frame 3 on the rear side of the top plate 2. A grill door 12 and a front operation unit 13 that are movable back and forth are provided on the front surface of the main body case 1. The front operation unit 13 is an operation unit for adjusting the heating power of the heating ports HL, HR, and HC.

FIG. 2 is a diagram showing a circuit configuration of the induction heating cooker in the first embodiment.
In FIG. 2, for example, power supplied from a commercial AC power supply 21 is converted into DC power by a DC power supply circuit 22. The DC power supply circuit 22 includes a rectifier diode bridge 22a that rectifies AC power, a reactor 22b, and a smoothing capacitor 22c. The input current input to the DC power supply circuit 22 is detected by the input current detection circuit 23. The DC power converted by the DC power supply circuit 22 is supplied to the inverter circuit 24.

  The inverter circuit 24 includes an upper switch 25a and a lower switch 25b connected in series between the positive and negative buses of the DC power supply circuit 22, and diodes 25c and 25d connected in antiparallel to the switches 25a and 25b, respectively. A configured switching element 25 is provided. In the inverter circuit 24, the upper switch 25 a and the lower switch 25 b are alternately turned on and off by a drive signal from the control circuit 28, and supplies a high-frequency current to the resonance circuit 26 configured by the heating coil 26 a and the resonance capacitor 26 b. The high-frequency current flowing through the heating coil 26 a is detected by the coil current detection circuit 27.

  The control circuit 28 is constituted by, for example, a microcomputer, and the heating power in which the input power obtained from the input current detected by the input current detection circuit 23 and the voltage of the commercial AC power supply 21 is set by the upper surface operation unit 10 or the front operation unit 13. The frequency and on / off time of the drive signal are controlled so as to be (electric power). Further, the control circuit 28 periodically monitors whether or not the detected temperature of the temperature sensor 29 exceeds the limit temperature during power feedback control, and when the detected temperature exceeds the limit temperature, It is determined that the rated temperature of the switching element 25 has been exceeded, and the driving of the switching element 25 is limited.

  As a method of restricting the driving of the switching element 25, for example, there is a method of controlling the frequency and on / off time of the drive signal or stopping the output of the drive signal so that the output power of the inverter circuit 24 is lowered. . The limit temperature will be described later. The above-described temperature sensor 29 is composed of, for example, a thermistor, and detects the temperature of the switching element 25 of the inverter circuit 24 and inputs it to the control circuit 28. Hereinafter, the temperature sensor 29 will be described as a thermistor.

Next, the radiation fin for cooling the switching element 25 will be described with reference to FIG.
FIG. 3 is a side view showing a state in which the switching element and the thermistor of FIG. 2 are attached to the radiation fin.
A switching element 25 and a thermistor 29 are attached to the heat radiating fin 30 by a fixing tool 31 such as a screw. The thermistor 29 is connected to the control circuit 28 via a lead wire 29a. The heat radiating fin 30 radiates heat generated during driving of the switching element 25 by the fin.

Next, a method for detecting the temperature of the switching element 25 by the thermistor 29 will be described with reference to FIG.
The junction 40 is a semiconductor junction surface constituting the switching element 25, and the junction temperature is referred to as a junction temperature Tj. In the component manufacturer, the value of the junction temperature Tj is set so as not to exceed the rated temperature of the switching element 25. Further, the case 41 is a portion where the switching element 25 and the radiation fin 30 are in contact with each other, and the surface temperature of the case 41 is referred to as a case temperature Tc. The thermistor 29 detects the case temperature Tc.

  When the switching element 25 is driven, the junction temperature Tj increases. When the junction temperature Tj increases, heat is transferred to the thermistor 29 through the case 41 by heat conduction and heat transfer from the junction temperature Tj. At this time, the junction temperature Tj and the detected temperature of the thermistor 29 are not proportional to each other, and the junction temperature Tj and the detected temperature of the thermistor 29 are not necessarily equal depending on the amount of heat generated by the switching element 25. However, there is a temperature difference.

The reason why the temperature difference between the junction temperature Tj and the detected temperature of the thermistor 29 is not necessarily equal due to the amount of heat generated by the switching element 25 is as follows.
As shown in FIG. 3, a thermal resistance Rth exists between the junction temperature Tj and the case temperature Tc. The thermal resistance Rth is a fixed value determined by the type of the switching element 25 and the rated capacity. The relationship among the thermal resistance Rth, the junction temperature Tj, the case temperature Tc, and the heat generation amount W can be expressed by the following equation.
Tj = Tc + W · Rth (1)

  From the above equation (1), it can be seen that the junction temperature Tj increases as the heating value W increases even if the case temperature Tc is the same value. Therefore, even if the detected temperature value of the thermistor 29 is the same, if the calorific value W changes, a temperature difference is generated between the junction temperature Tj and the detected temperature of the thermistor 29. This temperature difference increases as the calorific value W increases.

Here, as an example, a change in temperature difference will be described with reference to FIG.
FIG. 4 is a diagram showing the relationship between the amount of heat generated by the switching element and the temperature difference between the junction temperature and the detected temperature of the thermistor.
As shown in FIG. 4, for example, the temperature difference is small when the heat generation amount W is as low as 10 W, while the temperature difference is large when the heat generation amount W is as large as 40 W. Therefore, the control circuit 28 in the present embodiment sets the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 according to the input current detected by the input current detection circuit 23. This limit temperature is set lower each time the input current detected by the input current detection circuit 23 increases. That is, when the detected temperature of the thermistor 29 exceeds the limit temperature, the control circuit 28 determines that the rated temperature (predetermined temperature) of the switching element 25 has been exceeded, and limits the driving of the switching element 25.

Next, the protection operation of the switching element will be described with reference to FIG.
FIG. 5 is a graph showing the relationship between the input current and the limit temperature of the thermistor in the first embodiment.
After the pan 14 is placed on the top plate 2 by the user, the power is turned on. For example, when the heating power (electric power) is set by the upper surface operation unit 10, the control circuit means 28 converts the drive signal into an inverter. The output is output to the circuit 24 to drive the switching element 25, and a high frequency current is supplied to the resonance circuit 26. At this time, the control circuit 28 calculates input power based on, for example, the input current detected by the input current detection circuit 23, and performs feedback control so that the input current becomes the power set by the upper surface operation unit 10. Do.

  The control circuit 28 sets the limit temperature of the thermistor 29 according to the input current detected by the input current detection circuit 23 when performing feedback control of power, and the detected temperature of the thermistor 29 sets the limit temperature. When it exceeds, it determines with the temperature of the switching element 25 having exceeded the rated temperature, for example, the drive of the switching element 25 is stopped.

  For example, as shown in FIG. 5, when the input current detected by the input current detection circuit 23 is 2.5 A, the heat generation amount of the switching element 25 is low, and the temperature difference between the junction temperature Tj and the thermistor 29 is small. The limit temperature of the thermistor 29 is set as high as 111 ° C. Further, when the input current detected by the input current detection circuit 23 is 15 A, the heat generation amount of the switching element 25 becomes high, and the temperature difference between the junction temperature Tj and the thermistor 29 becomes large, so the limit temperature of the thermistor 29 is set to 84 ° C. And set it low.

As described above, in the first embodiment, the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 is set according to the input current detected by the input current detection circuit 23, and the detected temperature of the thermistor 29 is When the limit temperature is exceeded, the driving of the switching element 25 is limited. That is, when the input current is large, the amount of heat generated by the switching element 25 increases. Therefore, the temperature limit of the thermistor 29 is set low. When the input current is small, the amount of heat generated by the switching element 25 decreases. The temperature is set high. Thereby, compared with the prior art which compares the case temperature Tc of the switching element 25 and the rated temperature of the switching element 25, the switching element 25 can be protected reliably and the lifetime of the switching element 25 can be extended.
Further, by changing the limit temperature of the thermistor 29 according to the amount of heat generated by the switching element 25, the driving of the switching element 25 is limited when the junction temperature Tj of the switching element 25 is low even when the detection temperature of the thermistor 29 is high. Therefore, it is possible to provide an induction heating cooker 100 that is free from problems due to erroneous determination and is easy to use.

Embodiment 2. FIG.
In the first embodiment, the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 is set in accordance with the input current detected by the input current detection circuit 23. The limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 is set according to the coil current detected by the current detection circuit 27. In the present embodiment, the components of induction heating cooker 100 are the same as those in the first embodiment.

  As described above, the control circuit 28 in the present embodiment sets the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25, and when the detected temperature of the thermistor 29 exceeds the limit temperature, the switching element It is determined that the temperature of 25 has exceeded the rated temperature, and the drive of the switching element 25 is limited.

  As described above, as a method for restricting the driving of the switching element 25, as described above, the frequency and on / off time of the drive signal are controlled so that the output power of the inverter circuit 24 is lowered, or the output of the drive signal is changed. There is a way to stop.

Next, the protection operation of the switching element will be described with reference to FIG.
FIG. 6 is a diagram showing the relationship between the coil current and the limit temperature of the thermistor in the second embodiment.
After the pan 14 is placed on the top plate 2 by the user, the power is turned on. For example, when the heating power (electric power) is set by the upper surface operation unit 10, the control circuit means 28 converts the drive signal into an inverter. The output is output to the circuit 24 to drive the switching element 25, and a high frequency current is supplied to the resonance circuit 26. At this time, the control circuit 28 calculates input power based on, for example, the input current detected by the input current detection circuit 23, and performs feedback control so that the input current becomes the power set by the upper surface operation unit 10. Do.

  The control circuit 28 sets the limit temperature of the thermistor 29 according to the coil current detected by the coil current detection circuit 27 when performing feedback control of power, and the detected temperature of the thermistor 29 sets the limit temperature. When it exceeds, it determines with the temperature of the switching element 25 having exceeded the rated temperature, for example, the drive of the switching element 25 is stopped.

  For example, as shown in FIG. 6, when the coil current detected by the coil current detection circuit 27 is 10 A, the amount of heat generated by the switching element 25 is low, and the temperature difference between the junction temperature Tj and the thermistor 29 is small. Is set to a high temperature of 105 ° C. Further, when the coil current detected by the coil current detection circuit 27 is 40 A, the heat generation amount of the switching element 25 becomes high, and the temperature difference between the junction temperature Tj and the thermistor 29 becomes large, so the limit temperature of the thermistor 29 is set to 90 ° C. And set it low.

As described above, in the second embodiment, the limit temperature of the thermistor 29 is set according to the coil current detected by the coil current detection circuit 27. That is, when the coil current is large, the amount of heat generated by the switching element 25 increases. Therefore, the limit temperature of the thermistor 29 is set low, and when the coil current is small, the amount of heat generated by the switching element 25 decreases. The temperature is set high. Thereby, compared with the prior art which compares the case temperature Tc of the switching element 25 and the rated temperature of the switching element 25, the switching element 25 can be protected reliably and the lifetime of the switching element 25 can be extended.
Further, by changing the limit temperature of the thermistor 29 according to the amount of heat generated by the switching element 25, the driving of the switching element 25 is limited when the junction temperature Tj of the switching element 25 is low even when the detection temperature of the thermistor 29 is high. Therefore, it is possible to provide an induction heating cooker 100 that is free from problems due to erroneous determination and is easy to use.

Embodiment 3 FIG.
In the third embodiment, the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 is set according to the set thermal power (electric power) of the upper surface operation unit 10 or the front operation unit 13, and the detected temperature of the thermistor 29 is limited. When the temperature is exceeded, the driving of the switching element 25 is limited. In the present embodiment, the components of induction heating cooker 100 are the same as those in the first embodiment.

  As described above, the control circuit 28 according to the present embodiment sets the limit temperature of the thermistor 29 corresponding to the rated temperature of the switching element 25 according to, for example, the upper surface operation unit 10, and the detected temperature of the thermistor 29 is the limit. When the temperature is exceeded, it is determined that the temperature of the switching element 25 has exceeded the rated temperature, and the driving of the switching element 25 is limited. The method for limiting the driving of the switching element 25 is the same as in the first embodiment.

Next, the protection operation of the switching element will be described with reference to FIG.
FIG. 7 is a diagram showing the relationship between the set power and the limit temperature of the thermistor in the third embodiment.
After the pan 14 is placed on the top plate 2 by the user, the power is turned on. For example, when the heating power (electric power) is set by the upper surface operation unit 10, the control circuit means 28 converts the drive signal into an inverter. The output is output to the circuit 24 to drive the switching element 25, and a high frequency current is supplied to the resonance circuit 26. At this time, the control circuit 28 calculates input power based on, for example, the input current detected by the input current detection circuit 23, and performs feedback control so that the input current becomes the power set by the upper surface operation unit 10. Do.

  The control circuit 28 sets the limit temperature of the thermistor 29 according to the power (thermal power) set by the upper surface operation unit 10 when performing feedback control of power, and the detected temperature of the thermistor 29 is the limit temperature. Is exceeded, it is determined that the temperature of the switching element 25 has exceeded the rated temperature, and for example, the driving of the switching element 25 is stopped.

  For example, as shown in FIG. 7, when the heating power set by the upper surface operation unit 10 is “2”, that is, when the power is 300 W, the amount of heat generated by the switching element 25 is low, and the temperature difference between the junction temperature Tj and the thermistor 29 Therefore, the limit temperature of the thermistor 29 is set as high as 100 ° C. Further, when the heating power set by the upper surface operation unit 10 is “9”, that is, when the power is 3 kW, the heat generation amount of the switching element 25 becomes high, and the temperature difference between the junction temperature Tj and the thermistor 29 becomes large. The limit temperature of 29 is set as low as 80 ° C.

As described above, in the third embodiment, the limit temperature of the thermistor 29 is set according to the electric power (thermal power) set by the upper surface operation unit 10. That is, when the set power is large, the amount of heat generated by the switching element 25 increases. Therefore, the temperature limit of the thermistor 29 is set low. When the set power is small, the amount of heat generated by the switching element 25 decreases. The temperature is set high. Thereby, compared with the prior art which compares the case temperature Tc of the switching element 25 and the rated temperature of the switching element 25, the switching element 25 can be protected reliably and the lifetime of the switching element 25 can be extended.
Further, by changing the limit temperature of the thermistor 29 according to the amount of heat generated by the switching element 25, the driving of the switching element 25 is limited when the junction temperature Tj of the switching element 25 is low even when the detection temperature of the thermistor 29 is high. Therefore, it is possible to provide an induction heating cooker 100 that is free from problems due to erroneous determination and is easy to use.

  In the first to third embodiments, a half-bridge type inverter circuit is used, but an effect can be obtained even with a full-bridge type inverter circuit. 3 has been described with the thermistor 29 attached to the radiation fin 30, the same effect can be obtained even if the thermistor 29 is attached to the surface of the switching element 25.

  DESCRIPTION OF SYMBOLS 1 Main body case, 2 Top plate, 3 Frame, 4, 5, 6 Thermal display part, 7, 8, 9 Liquid crystal display part, 10 Upper surface operation part, 11 Intake / exhaust cover, 12 Grill door, 13 Front surface operation part, 14 Pan, HL, HR, HC heating port, 21 commercial AC power supply, 22 DC power supply circuit, 22a rectifier diode bridge, 22b reactor, 22c smoothing capacitor, 23 input current detection circuit, 24 inverter circuit, 25 switching element, 25a upper switch, 25b Lower switch, 25c, 25d Diode, 26 Resonance circuit, 26a Heating coil, 26b Resonance capacitor, 27 Coil current detection circuit, 28 Control circuit, 29 Temperature sensor (thermistor), 29a Lead wire, 30 Radiation fin, 31 Fixing tool, 40 junctions, 41 cases, 100 invitations Heating cooker.

Claims (3)

A DC power supply circuit that rectifies AC power of the AC power supply and converts it into DC power;
An inverter circuit that converts the DC power of the DC power supply circuit into high-frequency power by a switching element and outputs it to a heating coil;
An input current detecting means for detecting an input current input from the AC power source to the DC power source circuit;
A switching element of the inverter circuit is attached, and a heat dissipating fin for cooling the switching element,
A temperature sensor for detecting the temperature of the radiating fin or the switching element;
Each time the input current detected by the input current detection means becomes larger than the rated temperature of the switching element, the temperature sensor limit temperature is set low, and the temperature sensor detection temperature exceeds the limit temperature. And an induction heating cooker characterized by comprising control means for restricting driving of the switching element. A DC power supply circuit that rectifies AC power of the AC power supply and converts it into DC power;
An inverter circuit that converts the DC power of the DC power supply circuit into high-frequency power by a switching element and outputs it to a heating coil;
Coil current detection means for detecting a coil current flowing in the heating coil;
A switching element of the inverter circuit is attached, and a heat dissipating fin for cooling the switching element,
A temperature sensor for detecting the temperature of the radiating fin or the switching element;
Each time the coil current detected by the coil current detection means becomes larger than the rated temperature of the switching element, the temperature sensor limit temperature is set low, and the temperature sensor detection temperature exceeds the limit temperature. And an induction heating cooker characterized by comprising control means for restricting driving of the switching element. A DC power supply circuit that rectifies AC power of the AC power supply and converts it into DC power;
An inverter circuit that converts the DC power of the DC power supply circuit into high-frequency power by a switching element and outputs it to a heating coil;
A switching element of the inverter circuit is attached, and a heat dissipating fin for cooling the switching element,
A temperature sensor for detecting the temperature of the radiating fin or the switching element;
An operation unit for setting the heating power of the output of the heating coil;
Each time the set thermal power of the operation unit increases with respect to the rated temperature of the switching element, the temperature sensor is set to a lower limit temperature, and when the detected temperature of the temperature sensor exceeds the limit temperature, the switching is performed. An induction heating cooker comprising control means for restricting driving of the element.

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