JPS603889A - induction heating cooker - 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 Field of Industrial Application The present invention relates to an induction heating cooker, and particularly to electromagnetic fields leaking to the outside from an internal high-frequency power converter, particularly leaking electromagnetic fields in the AM radio frequency band. This relates to a structure that reduces the

Conventional structure and problems Conventionally, induction heating cookers have been equipped with a heating coil that generates a high-frequency high magnetic flux and a magnetic field of m degrees, and a high-frequency power converter that supplies high-frequency large current to the heating coil. In particular, high-frequency circuit components such as resonant capacitors of high-frequency power converters, semiconductor switching elements, and filter capacitors for high-frequency power supplies have a dog turtle flow θIL with a steep rise and fall. Therefore, the leakage magnetic field generated from the high frequency power converter particularly harms the reception of AM radio. In order to reduce this leakage magnetic field, conventionally, as shown in FIG. Measures have been taken to cover the entire upper part of the internal chassis 4 with a shield cover 6 made of a conductive material such as aluminum. Due to the interlinking of high-density high-frequency magnetic fields, an induced current flows through the shield cover 6, where heat loss occurs, reducing the heating efficiency of the cooker, and the demagnetizing field generated by the induced current reduces the equivalent inductance of the heating coil. , it becomes necessary to compensate by increasing the number of turns of the heating coil accordingly in the design of the high-frequency power converter. Further, since the shield plate 6 is a conductor, there are problems such as requiring a large space in order to ensure electrical insulation from other electrical parts. All of these problems can be solved by lowering the height of the cooker (making it thinner).
This is a serious limitation item. If a conductive plate is installed inside the cooker that covers the entire high-frequency power converter like the Ushida shield cover 5, the conductive plate will become hot due to the radiant heat received from the heating coil 2 and the bottom of the load pot, raising the temperature inside the device. This may adversely affect the cooling of semiconductor components and other electrical components, and may impair their reliability.

Furthermore, in FIG. 1, the internal chassis 4 and the external casing 6 are
When the high frequency power converter 3 is made of resin, the magnetic field generated from the high frequency power converter 3 cannot be sufficiently reduced only by the shield plate 6 covering the upper surface thereof.

That is, since the magnetic field leaks to the outside from the resin portion, at least the internal chassis 4 must be a conductor, or the external casing 6 must be a conductor and have a magnetic shielding effect. Making the housing of resin is very advantageous for reducing the weight of the device and the product price. With the shielding structure, it is difficult to completely use resin for the casing, and it has not been possible to fully bring out the advantages of using resin for the casing. Therefore, recently, high-frequency power converters are made of resin without taking any measures to reduce the radiated noise emitted from the equipment, so the radiated noise in the radio frequency band may have a considerable effect on external radio broadcast reception. Ta.

Object of the Invention The object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to reduce the electromagnetic field in the radio frequency V frequency band leaking to the outside from the high frequency power converter of an induction heating cooker with a simple configuration. In addition, it makes the casing of the induction heating cooker more greasy.

The aim is to promote thinning and miniaturization.

Structure of the Invention In order to achieve the above object, the induction heating cooker of the present invention includes a plurality of semiconductor switching elements and a damper diode connected in antiparallel to the semiconductor switching elements, and controls the conduction between #vJ of the semiconductor switching elements. In a high-frequency power conversion device that controls output power by controlling the output power, a high-frequency current including a steep falling waveform that occurs when the semiconductor switching element is cut off and a sudden rising of the charging current of the resonant capacitor due to the steep falling waveform that occurs when the semiconductor switching element is cut off, including a nine-waveform etc. It is configured to selectively minimize the opening of the closed loop formed by the components,
In particular, in the present invention, by defining the configuration of a plurality of semiconductor switching elements constituting the closed loop of the high-frequency current component and the distribution line connected thereto, it is possible to reduce the harmful electromagnetic field in the radio broadcast wave band. ing. In conventional induction heating cookers, when the current capacity is insufficient and it is necessary to use the same semiconductor switching elements in parallel, each semiconductor switching element is placed on a separate metal base 8 as shown in Figure 2. The metal base is used as one electrode and it is connected and fixed to the cooling fin 9, and the other electrode is connected to the conductive metal rod 11 using the terminal 10 taken out from each packaging.
Normally, they were connected to each other with leads i12 and 13, and to components such as the resonant capacitor 14,
In the present invention, a plurality of sets of the same semiconductor junctions are arranged on the same metal base, one electrode of the semiconductor junction through which the main current flows is connected to the metal base, and the other electrodes are connected to each other near the semiconductor connection. It is configured to be connected to other parts as a single electrode, and by doing this,
When using multiple semiconductor switching elements connected in parallel, the opening area of the high-frequency current closed loop when the semiconductor switching elements are cut off can be made extremely small, and the magnetic field generated therefrom can be reduced. have This effect is further enhanced by twisting or bundling the lead wires connected to the semiconductor switching elements.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 3 is an example of a high frequency power conversion device for an induction heating cooker, and is a basic circuit diagram of a transistor inverter. In FIG. 3, a commercial low-frequency power supply 16 is full-wave rectified by a full-wave rectifier 17 and connected to a high-frequency power supply capacitor 19 via a filter coil 18. A heating coil 21 is connected to the positive terminal of the high frequency power supply capacitor 19, and a diode is connected in antiparallel between the collector emitter terminals between the other terminal of the heating coil 21 and the negative terminal of the high frequency power supply capacitor 19. The two parallel circuits of the rJ P N reverse conduction transistors 22 and the parallel circuit of the resonant capacitor 23 are connected.

Further, a drive signal is supplied to the base of the reverse conduction switching transistor 22 from the control circuit block 20, and the control circuit block 2o is supplied with control power from the power transformer 16. The operation of this inverter circuit will be explained in detail with reference to FIG. FIG. 4d shows the drive current of the reverse conduction switching transistor 22, and at time t1, the forward current begins to flow, and after the diode current ID flows through the reverse conduction switching transistor 22 as shown in FIG.
The switching transistor becomes conductive and the heating coil becomes 2
Collector current IC increases with a slope determined by the combined impedance of 1 and the load pan. After a predetermined time TON (time t
2), the supply of 1 is stopped from the drive current of the reverse conduction transistor 22, the reverse conduction transistor 22 starts to be cut off, the collector current decreases rapidly, and it is completely cut off after the falling time T (time t3). , the collector current IC becomes zero.

On the other hand, the reverse conduction transistor 22 begins to shut off, and at the same time the collector current IC (approximately the same current flows through the heating coil 21 during the ToN period) begins to decrease, a back electromotive force is generated in the heating coil 21, charging the resonant capacitor 23. Flow an electric current. The rising time corresponds to the falling time Tf of the reverse conduction transistor 22 and is very steep, and then the resonant current of the heating coil 21 and the resonant capacitor 23 flows through the resonant capacitor 23 as shown in FIG. 4d. As shown in FIG. 4C, the resonant voltage of the heating coil 21 and the resonant capacitor 23 is applied between the collector and emitter of the reverse conduction transistor 22 at the same time as the collector current begins to decrease. At the point where the trailing edge of the collector voltage crosses the zero point (time t4), the drive current "B1" is again applied to the pace of the reverse conduction transistor 22. After this, the above-described operation is repeated.

Note that the diode of the reverse conducting transistor 22 is a damper diode. Furthermore, as shown in FIG. 4e, the current flowing through the heating coil 21 is the sum of the current flowing through the reverse conduction transistor 22 (FIG. 4b) and the current flowing through the resonant capacitor 23 (FIG. 4d), and has a steep rise. There is no falling waveform.

An embodiment of the present invention will be described by taking the inverter circuit described above as an example. 6 and 6 show one embodiment of the present invention, and in the inverter circuit diagram of FIG. 3, a block A surrounded by a dashed line consisting of a reverse conduction transistor 22, a resonant capacitor 23, and their wiring is shown. A configuration diagram is shown in FIG. 6, and a cross-sectional configuration diagram of two reverse conducting transistors 22 connected in parallel is shown in FIG. In Figure 6, reverse conduction i(P
Two identical silicon chips 22 constituting an N transistor are arranged on one metal base 26, and the metal base 25 is connected to the collector so as to have the same potential.

On the other hand, the two emitter electrodes are tangential to each other with conductive leads near the silicon chip and connected to the emitter terminal 27, which tells my colleague, ? The base electrodes are also connected to each other near the silicon chip and to the base terminal 28, and these are integrally molded with the resin case 26 and the injected resin 29 to form a single component. On the other hand, in Figure 6,
A reverse conducting transistor (11 P N ) having the structure shown in FIG. 6 is mounted on the cooling fin 24 with screws, and the lead wires 31 and 30 connected to the emitter terminal 27 and the metal base 26 (collector terminal) are twisted together. The other terminal is connected to a connection terminal 33 of the resonant capacitor 32. The resonant capacitor 32 and its lead wires near the connection terminals 33 are surrounded by a conductor 34 such as an aluminum plate. As mentioned above, a substantially continuous current as shown in FIG. 4e flows through the heating coil 21, and there is no sudden change in current. On the other hand, the current shown in FIG. 4S flows through the reverse conduction transistor 22, and the current shown in FIG.
A sudden change in current occurs over the course of the period. In order to analyze this waveform, a closed circuit consisting of a reverse conduction transistor 22 and a resonant capacitor 23 is taken out and shown in FIG.

FIG. 8 shows the waveform of the current flowing through each element.

The direction of the current is defined as the direction indicated by the arrow in FIG. 7 as positive.

The steep current change from time t2 to time t3 described above can be considered to be equivalent to the high-frequency pulse current shown in FIG. 8C flowing in the direction shown by the arrow in the closed circuit of FIG. 7. Time t2
The time + iJJ interval between times t2 and t3 corresponds to the fall time of the collector current of the switching transistor, and when the output power of the inverter is about 1.2KW, the peak current of the collector current is about 608, which is the difference between times t2 and t3. The interval is approximately 1μ. Therefore, the frequency spectrum of the high frequency current component when this transistor is cut off is 600 KHz)
2 MHz is dominant. On the other hand, the tiger: y
)xi Interruption''R (IJ), % 8 #Denyu 1sei 7116
8206 The intensity increases or decreases in proportion to the area (hatched area) surrounded by the closed loop of the high-frequency current component at the time of interruption as shown in FIG. In order to minimize the area created by a closed circuit through which a high-frequency current component flows when the transistor is cut off, the wires 30 and 31 connecting the collector and emitter of the reverse conduction transistor 22 to the terminal 33 of the resonant capacitor 32 are twisted together, and then the resonant capacitor 32 is connected. A conductive metal rod 1 that surrounds the opening of the high frequency current closed loop generated by the element and the wiring near the connection terminals 30 and 31 with a shield plate 34 made of a conductive material, and further connects the emitters of the reverse conducting transistors.
1, a reverse conduction transistor, and a heat dissipating fin 24 are made extremely small by arranging semiconductor chips on the same metal base, as shown in FIGS. It shows the difference in the opening area of the closed circuit formed by the high frequency current component when the transistor is cut off in the example and the present example. FIG. 9a shows a conventional example, and FIG. 9a shows an example of the configuration of this embodiment. The high frequency reduction effect of this example is, for example, when measured at a location approximately 3 meters away from the induction heating cooker, the frequency is 500 KHz to 2 MHz.
The radiation noise can be reduced by about 10 to 16 dB at z.

As described above, this embodiment has the effect that the radiation noise in the radio frequency band generated from the induction heating cooker can be reduced with a simple configuration and with almost no effect on the arrangement of other parts or the cooling configuration. . That is, this embodiment uses a means for shielding the radiated noise in the radio frequency band generated from the vicinity of a transistor having a plurality of switching elements by surrounding the switching element with a shielding plate or the like. It can be reduced without any damage, does not adversely affect the cooling of transistors where large currents flow, high voltages are applied, and high losses occur, and electrical insulation between the radiation fins and shielding plates to which high voltages are applied, and between the shielding plates and other There is no need to consider electrical insulation between high-voltage charging parts, and this greatly contributes to making the induction heating cooker thinner and smaller.

Other configuration examples of a plurality of semiconductor switching elements are shown in FIGS. 10a and 10b. In Figure 1o, two semiconductor junctions having the same junction are arranged in close proximity on the same metal base, while in Figure 10a, a plurality of transistor junctions having the same junction are configured on the same semiconductor chip, The damper diode 37 is made of a separate chip and placed close to each other on the same metal base, and FIG. 10 shows an example in which a plurality of switching transistors 36 and diode junctions are formed on the same semiconductor chip 36. The reason why the damper diode is placed near the switching diode junction in the above embodiment is because the damper diode may also undergo a large and steep current change at time t1 in FIG. 8 due to the load. This is because it comes out. This is because the diode current increases especially when near no load.

Effects of the Invention As described above, according to the present invention, in a high frequency power converter device having a plurality of semiconductor switching junctions and having a steep cutoff current waveform, the semiconductor switching element can be blocked by a shielding plate made of a conductive material, etc. Alternatively, the noise-to-noise in the radio frequency band can be reduced by devising the wiring without covering the entire high-frequency power converter, resulting in the following effects.

1. The cooling conditions inside the induction heating cooker, including the cooling conditions for the switching elements, are hardly deteriorated. 0. 2. At least a shielding plate made of a conductive material is unnecessary around the switching element or damper diode to which high voltage is applied. There is no need to consider the insulation distance between the parts and other parts, making it easier to arrange other parts, making the parts arrangement of the entire induction heating cooker extremely compact, and making the device more compact.

Can be made thinner.

3. Radiation in the present invention can be reduced by selectively electromagnetically shielding components and wiring other than the switching transistor, such as a resonant capacitor, among the components and wiring that constitute the closed circuit through which the high-frequency current component flows when the switching transistor is cut off. The noise reduction effect becomes even higher, and almost the same noise reduction effect 1 can be obtained whether the housing is made of resin or metal. Therefore, the casing can be easily made of resin, which has the effect of increasing the weight of the induction heating cooker and promoting improvement of I#i requirements.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a conventional electromagnetic induction cooking device, Fig. 2 is a perspective view of essential parts showing the relationship between a resonant capacitor, a reverse conduction transistor, and its distribution line in a conventional high-frequency power converter, and Fig. 3 4 is a circuit diagram of a high-frequency power converter for an electromagnetic induction cooking device showing an embodiment of the present invention, FIG. 4 is a signal waveform diagram of the same main part, and FIG. FIG. 6 is a front view of only the semiconductor switching element of the high-frequency power converter, and FIG. 7 is a perspective view of the main parts showing the relationship between the semiconductor switching element and its distribution line. An electric circuit diagram of a closed loop, FIG. 8 is a signal waveform diagram of the main parts in the same electric circuit, FIG. 9a is a front view of the main parts showing the closed loop in the conventional example, and FIG. The main part front view, FIG. 10a and FIG. 10s shown in FIG. 19...High frequency power supply capacitor, 21...
... Heating coil, 22 ... Reverse conducting transistor, 23 ... Resonance capacitor, 26 ...
Metal base, 30.31...Lead wire, 32.
...Resonance capacitor, 34... Conductor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 5
Figure 6 Figure 7 Figure 2 Figure 8 "#, t', "1.t 't4

Claims (4)

[Claims] (1) A heating coil, a resonant capacitor, a filter capacitor for high-frequency power supply, and a semiconductor switching element are connected in antiparallel with a Dunno diode, and the output power is controlled by controlling the conduction time of the semiconductor switching element. The semiconductor switching element has a plurality of sets of the same semiconductor junction, which are arranged on the same metal base, and the main current of the semiconductor junction is One electrode is connected to the MfJδ metal base, and the other electrodes are connected to each other near the semiconductor junction as a single electrode, which was connected to the IS product in the past in induction heating cookers. (2) The induction heating cooker according to claim 1, wherein the semiconductor junction of the damper diode is arranged on a metal base and connected to the semiconductor junction of the semiconductor switching element in the vicinity thereof. (3) The induction heating cooker according to claim 1, wherein the distribution lines connected to the semiconductor switching elements and through which the main current flows are burnt together or bundled and placed close to each other. (4) The induction heating cooker according to claim 1, wherein the resonance capacitor or the power supply capacitor is surrounded by a conductive metal plate together with a part of the power distribution line to which it is connected.