Kitchen appliances

Abstract

This prevents failures of switching elements and other components caused by water entering from the outside or condensation inside the device. [Solution] The heating cooker comprises a switching module 50 housing IGBTs 41 and 42 that constitute an induction heating circuit, a controller for turning the IGBTs 41 and 42 on and off, and a first guard electrode 58 and a second guard electrode 59. The first control terminal 54 and the second control terminal 55 of the switching module 50 are connected to the controller to turn the IGBTs 41 and 42 on and off. The first guard electrode 58 is connected to the intermediate terminal 53 and the intermediate auxiliary terminal 57 of the switching module 50, which are at the same potential, and is positioned to physically separate the high-potential terminal 51 and the first control terminal 54. The second guard electrode 59 is connected to the low-potential terminal 52 and the low-potential auxiliary terminal 56 of the switching module 50, which are at the same potential, and is positioned to physically separate the intermediate terminal 53 and the high-potential terminal 51 from the second control terminal 55.

Description

Technical Field

[0001] The present invention relates to a kitchen appliance in which a semiconductor switching circuit for power is housed in a predetermined space.

Background Art

[0002] In kitchen appliances, an inverter circuit is used for heating control such as an IH cooker or a steam convection oven, and rotation control of a compressor of a refrigerator or a freezer. The electromagnetic induction heating device disclosed in Patent Document 1 below is an example thereof. Generally, in this type of inverter circuit, a switching circuit composed of semiconductor switching elements for power control applications such as IGBTs and power MOSFETs (hereinafter referred to as "switching elements"), that is, a semiconductor switching circuit for power is used. In the electromagnetic induction heating device of Patent Document 1, the first switching circuit 16 and the second switching circuit 18 correspond to this.

[0003] When a large current flows between the input and output (collector-emitter) of a switching element for power constituting such a semiconductor switching circuit or the switching frequency becomes high, the switching loss increases and the amount of heat generation becomes large. Therefore, the switching element for power is often attached to a large heat sink and provided at a position away from the control circuit that controls the inverter circuit. The same applies to a power module in which two switching elements or the like are connected and packaged so as to constitute the upper and lower arms of the inverter circuit.

[0004] For example, a switching element for power or a power module is arranged in a space such as a machine room in a kitchen appliance, physically separated from a printed board on which electronic components of the control circuit are mounted. Therefore, the electrical connection between the switching element or the like and the control circuit is made via a lead wire. The connection of the lead wire to the switching element or the like is performed by fixing it with a bolt to a terminal block provided on the package of the switching element or the like or fitting a socket to a tab terminal in consideration of work efficiency such as installation during manufacturing and replacement during maintenance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-158366 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, kitchen equipment, due to its nature as a cooking facility that serves food and beverages, often involves the use of water both inside and outside the equipment. Therefore, although machine rooms containing inverter circuits and control circuits, including switching elements, are waterproofed with sealing materials such as rubber gaskets, there is still a non-zero possibility of water entering from the outside or condensation forming inside, compared to other equipment used indoors.

[0007] For example, in the case of induction cooktops, it is considered necessary to take precautions against liquids such as soup or water spilling from a pot entering the machine room through unexpected gaps and coming into contact with the packages of switching elements, etc. (hereinafter referred to as "water exposure"). It is also considered necessary to take precautions against dust and dirt adhering to the packages of switching elements, etc., absorbing moisture condensed due to the temperature difference between the outside and inside of the equipment, causing water droplets to form. Since such water exposure and condensed water can cause malfunctions or failures in electronic circuits, waterproofing measures such as resin coating of electronic components mounted on the printed circuit board of the control circuit are effective countermeasures.

[0008] However, as mentioned above, since power switching elements and the like are located physically away from the printed circuit boards of the control circuits, it is necessary to consider work efficiency during installation and replacement. For this reason, resin coatings are unsuitable, and there is a problem in that it is difficult to prevent failures caused by water exposure or condensation. Furthermore, even in configurations where power switching elements and the like are provided on the printed circuit board of the control circuit, similar problems exist if these cannot be coated with resin.

[0009] In particular, switching elements and power modules used for power applications are subjected to high voltages and large currents during operation. Therefore, if conductive paths (current paths) are formed on the surface of these packages due to water exposure or condensation, depending on the configuration of these paths, there is a possibility that the switching elements themselves and the electronic components of their surrounding circuits may suffer significant damage, as will be described later. The present invention aims to prevent failures of switching elements and control circuits caused by water entering from the outside or condensation inside. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a kitchen appliance in which a semiconductor switching circuit for power is housed in a predetermined space, comprising: a switching element constituting a semiconductor switching circuit having a high-potential side terminal, a low-potential side terminal, and a control terminal; a control circuit connected to the control terminal to control the on / off state of the switching element; and a guard line arranged to physically partition the high-potential side terminal and the control terminal and connected to the low-potential side terminal. The concept of "water" also includes water mixed with seasonings, cooking oil, detergent components, etc. (the same applies hereinafter in this specification).

[0011] In the kitchen equipment configured as described above, a guard line is positioned to physically separate the high-potential terminal and the control terminal of the switching element constituting the power semiconductor switching circuit, and the guard line is connected to the low-potential terminal of the switching element. In other words, a guard line at the same potential as the low-potential terminal exists between the high-potential terminal and the control terminal. For example, even if water enters the predetermined space in which the semiconductor switching circuit is housed from the outside and the switching element is exposed to water, or if dust and dirt adhering to the switching element inside the predetermined space absorb condensed moisture and form water droplets, and these water droplets could flow from the high-potential terminal to the control terminal of the switching element and form a conductive path (current path), the presence of the above-mentioned guard line ensures that another conductive path (another current path) connecting the high-potential terminal and the low-potential terminal is formed before or during the formation of such a conductive path from the high-potential terminal to the control terminal by the water. Therefore, even if a high voltage is applied or a large current flows through the high-potential terminal of the semiconductor switching circuit, these can be discharged through this alternative conductive path to the low-potential terminal, which has a lower potential and input impedance (input resistance) than the control terminal. Consequently, since high voltage is not applied or large current flows through the control terminal, the switching element itself and the electronic components of its surrounding circuitry are not significantly damaged, thus preventing failures of the switching element and control circuit caused by water.

[0012] In kitchen equipment configured as described above, the switching elements constituting the power semiconductor switching circuit may be mounted (assembled) on the printed circuit board of the control circuit that controls their on / off state. However, the switching elements may also be physically separated from the printed circuit board on which the control circuit is located, and connected to the control circuit via lead wires. In other words, in configurations where the switching elements are located in a different place from the printed circuit board of the control circuit, the switching elements and the control circuit are typically connected via lead wires. Therefore, considering work efficiency during installation or replacement, waterproofing such as resin coating of the switching elements is unsuitable, and it was difficult to prevent failures caused by water exposure or condensation. However, with the existence of the above-mentioned guard line, it is now possible to prevent failures of the switching elements and control circuits caused by water without resin coating or other methods.

[0013] Furthermore, in kitchen equipment configured as described above, the switching elements constituting the semiconductor switching circuit for power also include cases where they are connected in series with a DC voltage source to control whether or not DC power can be supplied. In other words, the semiconductor switching circuit for power may be a power switch circuit, but it may also be part of an inverter circuit that supplies AC power, consisting of an upper arm and a lower arm. When it is part of an inverter circuit, the switching elements consist of a first switching element that has a first high-potential terminal, a first low-potential terminal and a first control terminal and constitutes the upper arm, and a second switching element that has a second high-potential terminal connected to the first low-potential terminal, a second low-potential terminal and a second control terminal and constitutes the lower arm. The guard line consists of a first guard line that separates the first high-potential terminal and the first control terminal and is connected to the first low-potential terminal, and a second guard line that separates the second high-potential terminal and the first high-potential terminal and the second control terminal and is connected to the second low-potential terminal. Furthermore, the control circuit is connected to the first and second control terminals to exclusively control the on / off states of the first and second switching elements. The concept of "upper arm and lower arm" includes cases where the inverter circuit is a full-bridge circuit or a half-bridge circuit. In addition, the first and second switching elements, which are connected to form the upper and lower arms of the inverter circuit in this way, may also be packaged together to form a single power module.

[0014] In such first and second switching elements, as well as in power modules that package them, the presence of the first and second guard lines allows for the formation of an alternative conductive path connecting the first high-potential terminal and the first low-potential terminal before or during the formation of a conductive path from the first high-potential terminal to the first control terminal, due to water ingress from the outside or water droplets (water) formed from dust and dirt adhering to the switching element. Similarly, an alternative conductive path connecting the second high-potential terminal and the second low-potential terminal is formed before or during the formation of a conductive path from the second high-potential terminal to the second control terminal. Furthermore, an alternative conductive path connecting the first high-potential terminal and the second low-potential terminal is formed before or during the formation of a conductive path from the first high-potential terminal to the second control terminal. Therefore, even if a high voltage is applied or a large current flows through the first high-potential terminal of the semiconductor switching circuit, these can be diverted to the first low-potential terminal and the second low-potential terminal, which have lower potential and input impedance (input resistance) than the first control terminal, via these alternative conductive paths. Furthermore, even if a high voltage is applied or a large current flows through the second high-potential terminal or the first high-potential terminal of the semiconductor switching circuit, it is possible to dissipate this through this alternative conductive path to the second low-potential terminal, which has a lower potential and input impedance (input resistance) than the second control terminal. Therefore, since high voltages are not applied or large currents flow through the first and second control terminals, the switching element itself and the electronic components of its surrounding circuitry are not significantly damaged, thus preventing failures of the switching element and control circuit caused by water. [Brief explanation of the drawing]

[0015] [Figure 1] This is a front view of a heating appliance, which is one embodiment of the kitchen equipment of the present invention. [Figure 2] This is a cross-sectional view of line AA in Figure 1. [Figure 3] These are side view (a) and top view (b) of the steam generator. [Figure 4] This is a block diagram of the electrical control system. [Figure 5] This is a block diagram of the steam generator. [Figure 6] Examples of the configuration of the induction heating circuit, including a full-bridge inverter circuit (a) and a half-bridge inverter circuit (b). [Figure 7] Examples of the configuration of the switching module and the guard electrode, including a perspective view (a), a plan view (b), and a connection diagram (c). [Figure 8] Other examples of the configuration of the switching module and the guard electrode, including a perspective view (a), a plan view (b), and a connection diagram (c). [Figure 9] A diagram showing the operation of the guard electrode when water adheres to the switching module, including a switching circuit diagram (a), a plan view in the case of the configuration example shown in FIG. 7 (b), and a plan view in the case of the other configuration example shown in FIG. 8 (c).

Best Mode for Carrying Out the Invention

[0016] Hereinafter, an embodiment in which the kitchen appliance of the present invention is applied to a cooking appliance will be described with reference to the accompanying drawings. The cooking appliance in this embodiment is called a steam convection oven, and generates steam by a steam generation device using electromagnetic induction heating and convects hot air containing the steam to heat and cook food ingredients.

[0017] As shown in FIGS. 1 and 2, the cooking appliance 10 includes a cooking chamber 14 for heating and cooking food ingredients in a portion of the housing 11 excluding the left side portion, a door 12 that can open and close the front of the cooking chamber 14, a machine room 15 in the space on the left side of the housing 11, and an operation panel 13 that covers the front of the machine room 15.

[0018] As shown in Fig. 2, a heater 16 for heating the inside of the cooking chamber 14 is provided with the left side portion inside the cooking chamber 14 as a heating space 14a, and a blower fan 17 for circulating (convecting) the air inside the cooking chamber 14 is provided. A portion excluding the heating space 14a is used as a storage space 14b for storing food ingredients. The blower fan 17 is a centrifugal fan such as a sirocco fan, which sucks air from the central portion and blows the air outward in the centrifugal direction. When the blower fan 17 is driven, air is sucked from the storage space 14b as shown by the arrow in Fig. 2, and the air sent outward in the centrifugal direction is heated by the heater 16 to become hot air, and is sent back to the storage space 14b along the peripheral wall (front wall, rear wall, upper wall and lower wall) of the cooking chamber 14.

[0019] Rack frames 18 for supporting trays (not shown) for receiving food ingredients called hotel pans in a multi-stage manner in the vertical direction are provided on both the left and right sides of the storage space 14b of the cooking chamber 14. A steam generator 20 for supplying steam into the cooking chamber 14 is provided at the rear of the machine room 15. Also, a control device 60 for controlling the heater 16, the blower fan 17, the steam generator 20, etc. is provided on the back side of the operation panel 13 at the front of the machine room 15. The control device 60 is configured by mounting electronic components such as a microcomputer on a printed circuit board 61, as will be described later. Note that reference numeral 70 indicates a cooling fan for cooling the heat sink to which the IGBT of the induction heating circuit described later is attached.

[0020] As shown in Figs. 3 to 5, the steam generator 20 includes a steam generation container 21 storing water at a predetermined water level, a steam outlet cylinder 22 connected to the upper part of the steam generation container 21 and sending out steam into the cooking chamber 14, a water level detection tank 23 connected to the lower part of the steam generation container 21 for detecting the water level inside the steam generation container 21, a water level sensor 24 provided inside the water level detection tank 23 for detecting the water level inside to detect the water level inside the steam generation container 21, and a heating unit 30 for heating the water inside the steam generation container 21, and is controlled by the control device 60.

[0021] The steam generating container 21 has a cylindrical shape with openings at the top and bottom. The top opening serves as a steam outlet, and the bottom opening serves as a drain. A drain pipe is connected to the bottom of the steam generating container 21, and water inside the steam generating container 21 is drained by opening a drain valve provided in the drain pipe. A temperature sensor 39 capable of detecting the overheating state of the heating element 31 (described later) is provided on the upper part of the circumferential surface of the steam generating container 21.

[0022] A water level detection tank 23 is erected adjacent to the steam generation vessel 21, and the lower part of the water level detection tank 23 is connected in communication with the lower part of the steam generation vessel 21. A water level sensor 24 is attached to the water level detection tank 23. The water level sensor 24 detects the water level in the steam generation vessel 21 by detecting the water level in the water level detection tank 23. A water supply pipe 25, which leads from a water supply source such as a water tap, is connected to the upper part of the water level detection tank 23. By opening a water supply valve 27 interposed in the water supply pipe 25, water is supplied into the water level detection tank 23. Excess water in the water level detection tank 23 is discharged to a drain tank (not shown) that receives wastewater from the cooking area 14 via a drain pipe 26 connected to the lower part.

[0023] The heating unit 30 includes a heating element 31 inside a steam generating container 21, an induction heating coil 34 wound around the outer circumference of the steam generating container 21 from the middle to the bottom in the vertical direction, an induction heating circuit 40 including the induction heating coil 34, a rectifier circuit 36 ​​that supplies DC power to the induction heating circuit 40, a controller 37 that controls the induction heating circuit 40, a voltage sensor 38a for detecting the input voltage of an external AC power supply 90, and a current sensor 38b for detecting the input current of the AC power supply 90.

[0024] Of these, the voltage sensor 38a, current sensor 38b, and controller 37 are located on a printed circuit board 61 on the back of the operation panel 13, similar to the control device 60, away from the heating element 31 and induction heating coil 34. The rectifier circuit 36 ​​and the IGBTs 41-44 of the induction heating circuit 40 (see Figure 6) are mounted on a heat sink (not shown) located physically away from the printed circuit board 61, and can be cooled by a cooling fan 70. The voltage and current values ​​of the AC power supply 90 detected by the voltage sensor 38a and current sensor 38b are output to the controller 37.

[0025] The heating element 31 comprises a substantially annular holder 32 supported at the top of the steam generating container 21, and a plurality of heating rods 33 arranged in an annular shape with their upper ends fixed to the holder 32. In this embodiment, the heating rods 33 have a circular radial cross-sectional shape. For example, the holder 32 is made of austenitic stainless steel (non-magnetic material), while the heating rods 33 are made of ferritic stainless steel (magnetic material).

[0026] An induction heating coil 34 is wound around the outer circumference of the steam generating container 21 that houses the heating element 31 configured in this way, approximately coaxially with a ring-shaped arrangement of multiple heating rods 33. For example, the induction heating coil 34 can be made of Litz wire (stranded wire) made by twisting together multiple enameled copper wires, or a single enameled copper wire. As a result, as will be described later, magnetic field lines repeatedly generated as a high-frequency current flows through the induction heating coil 34 pass through the multiple heating rods 33, causing eddy currents to flow within the heating rods 33. This generates Joule heat due to the electrical resistance of the heating rods 33, causing the heating rods 33 themselves to heat up.

[0027] The rectifier circuit 36 ​​is a bridge circuit consisting of silicon diodes that rectify an AC voltage into a DC voltage. In this embodiment, it is configured to rectify the voltage according to each phase of the AC power supply 90 that supplies a three-phase AC 200V, and then output a DC 280V (for example, a maximum of 200A) to the induction heating circuit 40. In this embodiment, the positive side of the DC voltage output from the rectifier circuit 36 ​​is called the high-potential power line 35H, and the negative side of the same DC voltage is called the low-potential power line 35L. The rectifier circuit 36 ​​generates heat during operation, and is therefore attached to a heat sink as described above.

[0028] The controller 37 includes a one-chip microcontroller (not shown) that controls the induction heating circuit 40 based on control information input from the control device 60. The one-chip microcontroller is a microcomputer having a CPU, RAM, ROM, timer, and input / output interface, etc. (all not shown), connected via a bus. The ROM stores programs for switching control of the IGBTs 41 to 44 that constitute the induction heating circuit 40, as will be described below.

[0029] As shown in Figure 6(a), the induction heating circuit 40 includes IGBTs 41 and 43, whose collectors are connected to the high-potential power line 35H; IGBT 42, whose collector is connected to the emitter of IGBT 41 and whose emitter is connected to the low-potential power line 35L of the same circuit 40; IGBT 44, whose collector is connected to the emitter of IGBT 43 and whose emitter is connected to the low-potential power line 35L of the same circuit 40; and an induction heating coil 34 and a capacitor 45 connected in series between the connection points of IGBTs 41 and 42 and the connection points of IGBTs 43 and 44. It is composed of the above, and four guard lines 46 to 49 are provided corresponding to each gate of the IGBTs 41 to 44. In addition, a current sensor (not shown) is provided to detect the current flowing through the induction heating coil 34 and the capacitor 45, and the current value is configured to be output to the controller 37.

[0030] Although not shown in the diagram, freewheeling diodes are connected in antiparallel between the collector and emitter of each IGBT 41-44. Furthermore, the symbols Vdrv1, Vdrv2 and Vdrv3, ​​Vdrv4, indicated within the dashed box representing the controller 37, represent the gate drive voltages that the controller 37 can output to each gate of IGBT 41-44. IGBTs 41-44 are configured to allow, for example, a current of 150A to flow between the input and output (collector-emitter).

[0031] In other words, the induction heating circuit 40 shown in Figure 6(a) is an inverter circuit capable of supplying high-frequency current (AC power) to the induction heating coil 34 and capacitor 45 connected in series, and is called a full-bridge inverter circuit or full-bridge circuit. IGBTs 41 and 43 constitute the upper arm, and IGBTs 42 and 44 constitute the lower arm. The correspondence with the claims (in quotation marks) is as follows: The collectors of IGBTs 41 and 43 may correspond to the "high-potential side terminal" and the "first high-potential side terminal". The emitters of IGBTs 41 and 43 may correspond to the "low-potential side terminal" and the "first low-potential side terminal". The gates of IGBTs 41 and 43 may correspond to the "control terminal" and the "first control terminal". The collectors of IGBTs 42 and 44 may correspond to the "high-potential side terminal" and the "second high-potential side terminal". The emitters of IGBT42 and 44 may correspond to the "low-potential terminal" and the "second low-potential terminal." The gates of IGBT42 and 44 may correspond to the "control terminal" and the "second control terminal."

[0032] In the induction heating circuit 40 configured in this way, AC current flows through the induction heating coil 34 by the controller 37 alternately switching the IGBT 41,44 pair and the IGBT 42,43 pair on and off. Specifically, at the moment when both IGBT 41 and 44 are controlled to be on and both IGBT 42 and 43 are controlled to be off, current flows through the path IGBT 41 → capacitor 45 → induction heating coil 34 → IGBT 44. At the moment when both IGBT 42 and 43 are controlled to be on and both IGBT 41 and 44 are controlled to be off, current flows through the path IGBT 43 → induction heating coil 34 → capacitor 45 → IGBT 42. By performing this switching of IGBTs 41 to 44 on the order of microseconds, for example, it becomes possible to supply high-frequency current (AC power) to the induction heating coil 34.

[0033] The induction heating circuit 40 may also be configured as a half-bridge inverter circuit or a half-bridge circuit, as shown in Figure 6(b). In this case, it is composed of an IGBT 41 whose collector is connected to the high-potential power line 35H, an IGBT 42 whose collector is connected to the emitter of IGBT 41 and whose emitter is connected to the low-potential power line 35L of the circuit 40, two capacitors 45a and 45b of the same capacitance connected in series between these power lines 35H and 35L, and an induction heating coil 34 whose ends are connected between the connection point of IGBTs 41 and 42 and the connection point of capacitors 45a and 45b, with two guard lines 46 and 47 provided corresponding to the gates of IGBTs 41 and 42. Although not shown, freewheeling diodes are connected in antiparallel between the collectors and emitters of IGBTs 41 and 42. Furthermore, the symbols Vdrv1 and Vdrv2, which represent DC voltage sources indicated within the dashed box showing controller 37, represent the gate drive voltages that controller 37 can output to the gates of IGBTs 41 and 42.

[0034] As shown in Figure 6(b), when the induction heating circuit 40 is configured as a half-bridge inverter circuit, the controller 37 alternately switches IGBT 41 and IGBT 42 on and off, causing alternating current to flow through the induction heating coil 34. That is, at the moment IGBT 41 is switched on and IGBT 42 is switched off, current flows through the path IGBT 41 → induction heating coil 34 → capacitor 45b. At the moment IGBT 42 is switched on and IGBT 41 is switched off, current flows through the path capacitor 45a → induction heating coil 34 → IGBT 42. By performing this switching of IGBT 41 and 42 on the order of microseconds, for example, it becomes possible to supply high-frequency current (alternating current power) to the induction heating coil 34.

[0035] As described above, the induction heating circuit 40 can be configured as a full-bridge inverter circuit or a half-bridge inverter circuit. In this embodiment, in the case of a full-bridge inverter circuit, guard lines 46 to 49 are provided corresponding to each gate of IGBTs 41 to 44, and in the case of a half-bridge inverter circuit, guard lines 46 and 47 are provided corresponding to each gate of IGBTs 41 and 42. This point differs from typical full-bridge inverter circuits and half-bridge inverter circuits.

[0036] As shown in Figures 2 and 4, the control device 60 is located on the back of the operation panel 13 and is connected to the liquid crystal touch panel 13a, start button 13b, heater 16, blower fan 17, controller 37 of the heating unit 30 of the steam generator 20, water level sensor 24, water supply valve 27, and temperature sensor 39. The control device 60 has a microcomputer (not shown), which includes a CPU, RAM, ROM, timer, and input / output interface (all not shown) connected via a bus. The ROM stores cooking programs for heating and cooking food in the cooking chamber 14.

[0037] The heating appliance 10 operates, for example, the heater 16 and blower fan 17 to circulate hot air inside the cooking chamber 14, and the steam generator 20 to supply steam inside the cooking chamber 14, according to the cooking program of the cooking mode selected by the user via the liquid crystal touch panel 13a. As a result, steam and hot air circulate inside the cooking chamber 14, and the food inside the cooking chamber 14 is heated and cooked by this steam-infused hot air.

[0038] By the way, as mentioned in the section on [Problems the invention aims to solve], the heating appliance 10 is used in cooking facilities that serve food and beverages, and therefore water is often used inside and outside the appliance. For this reason, although the machine room 15, which houses the induction heating circuit 40, is waterproofed by a sealing member (not shown), there is still a possibility that water may enter the machine room 15 from the outside or condensation may form inside.

[0039] For example, if steam contained in the hot air circulating in the cooking chamber 14 enters the machine room 15 through an unexpected gap, and condensation forms on the surface of the resin molds (packages) of IGBTs 41-44 or the switching module (package) 50 as described later, or if liquids such as soup or water spilled in the cooking chamber 14 enter the machine room 15 through an unexpected gap and the resin molds of IGBTs 41 or the switching module 50 are exposed to water, such exposure to water or condensation can cause malfunctions or failures of IGBTs 41, the controller 37 that controls IGBTs 41, and the rectifier circuit 36 ​​that supplies DC power to the induction heating circuit 40.

[0040] In particular, when the resin molds of IGBTs 41-44 and the switching module 50 are mounted on a heatsink that is physically separated from the printed circuit board 61 of the control device 60, the connections between the IGBTs 41 and the switching module 50 and the control device 60 must be made with insulated wires such as lead wires or power cables. Therefore, considering the work efficiency when installing or replacing the IGBTs 41 and the switching module 50, it is inappropriate to apply a resin coating or similar to the electrodes and terminals of the IGBTs 41 and the switching module 50 as a waterproofing measure against water exposure or condensation.

[0041] Therefore, if water exposure or condensation forms conductive paths (current paths) on the surface of resin molds such as IGBT41 or the switching module 50, depending on the configuration of these paths, significant damage may occur to IGBT41-44, the controller 37, and the rectifier circuit 36. For example, in the induction heating circuit 40, which is composed of a full-bridge inverter circuit as shown in Figure 6(a), if water exposure or condensation forms conductive paths between the collectors and emitters of IGBT41 and IGBT43, which constitute the upper arm, the area between the collector and emitter, which should be open, will be partially closed due to these conductive paths.

[0042] However, the collectors of both IGBTs 41 and 43 are connected to power line 35H, and a DC voltage of 280V is applied to power lines 35H and 35L from the rectifier circuit 36. Therefore, even if such a conductive path is formed, the electrical resistance of the water forming the conductive path will limit the current flow to, for example, a few amperes, and the water will evaporate in a short time due to the heat (resistive heat) generated by that electrical resistance, meaning the conductive path will disappear in a few seconds. The rectifier circuit 36 ​​is selected to have a sufficient absolute maximum rating for forward current (e.g., 200A) assuming that currents of the order of 100A will flow during the switching operation of IGBTs 41 and 43, so even if a current of a few amperes flows, the rectifier circuit 36 ​​will not be damaged.

[0043] In contrast, if water splashes or condensed water forms a conductive path (A) between the collector and gate of IGBT41 or IGBT43, significant damage may occur to IGBT41,43, controller 37, and rectifier circuit 36. A DC voltage of, for example, -6V to +15V is applied to the gates of IGBT41 and IGBT43 as gate drive voltages Vdrv1 and Vdrv3 output from controller 37. Furthermore, many power IGBTs have an absolute maximum rated voltage between the gate and emitter set to around ±20V. Therefore, if such a conductive path is formed, a DC voltage of 280V, which significantly exceeds the absolute maximum rated voltage, may be applied between the gate and emitter of IGBT41 and IGBT43. As a result, even slight contact between these gates by water splashes or condensed water may cause IGBT41 and IGBT43 to transition from the off state to the on state.

[0044] In this case, when the IGBTs 42 and 44 of the lower arm are switched to the ON state by the ON / OFF control of the controller 37, the upper and lower arms will be switched ON at the same time. That is, since both IGBT 41 and IGBT 42, and IGBT 43 and IGBT 44 are turned ON at the same time, these IGBTs 41-44 will be short-circuited between power lines 35H and 35L, and a current that may exceed the absolute maximum rated current of the rectifier circuit 36 ​​will flow from the rectifier circuit 36 ​​to the input / output (collector-emitter) of IGBTs 41-44. As a result, IGBTs 41-44 are highly likely to fail in short-circuit mode. In addition, the rectifier circuit 36 ​​is also highly likely to fail if a current exceeding the absolute maximum rated current flows through it.

[0045] As mentioned above, the gates of both IGBT41 and IGBT43 are connected to the controller 37 via insulated wires such as lead wires or power cables. Therefore, if a conductive path is formed between the collector and gate due to water exposure or condensation, and a DC voltage of 280V is applied to the gates of IGBT41 and IGBT43, 280V will be input (applied) to the controller 37 via the insulated wires, regardless of whether IGBT41 and IGBT43 switch to the ON state or not. Therefore, in this case, it is highly likely that a failure will occur in the gate drive circuit of the controller 37.

[0046] Furthermore, if water exposure or condensation forms a conductive path (a) between the collector and gate of IGBT42 and IGBT44, which constitute the lower arm, a DC voltage of 280V will be applied to the collectors of IGBT42 and IGBT44 from the power line 35H at the moment when IGBT41 and IGBT43 of the upper arm are switched to the ON state by the control of the controller 37. Therefore, there is a high possibility that IGBT41-44 will fail in short-circuit mode due to the same failure mechanism as IGBT41 and IGBT43 of the upper arm described above. In addition, if a current exceeding the absolute maximum rated current flows through the rectifier circuit 36, there is a high possibility that the rectifier circuit 36 ​​will also fail. Furthermore, it is expected that the controller 37 will also fail in the gate drive circuit due to the same failure mechanism described above.

[0047] Furthermore, if water or condensed water forms a conductive path (c) between the collectors of IGBT41 and IGBT43, which constitute the upper arm, and the gates of IGBT42 and IGBT44, which constitute the lower arm, then when water or condensed water slightly contacts the gates of IGBT42 and IGBT44 in the lower arm, IGBT42 and IGBT44 will transition from the off state to the on state. When the controller 37 controls IGBT41 and IGBT43 in the upper arm to the on state, at that moment, these IGBTs 41 to 44 will be short-circuited between power lines 35H and 35L. As a result, a current that may exceed the absolute maximum rated current of the rectifier circuit 36 ​​will flow from the rectifier circuit 36 ​​to the input / output (collector-emitter) of IGBTs 41 to 44. This makes it highly likely that IGBTs 41 to 44 will fail in short-circuit mode. Also, the rectifier circuit 36 ​​is highly likely to fail if a current exceeding its absolute maximum rated current flows through it. Furthermore, due to the same failure mechanism as described above, it is highly likely that the controller 37 will also experience a failure in its gate drive circuit.

[0048] Therefore, the inventors of this application focused on the possibility that three conductive paths (a) to (c) that could cause failure in IGBT 41, etc., may be formed in the resin molds of IGBTs 41 to 44 and the switching module 50 due to water exposure or condensation, and decided to provide guard lines 46 to 49 in the resin molds of IGBTs 41 to 44 and the switching module 50 that can prevent the formation of these conductive paths (a) to (c). In the induction heating circuit 40, which is configured as a half-bridge inverter circuit as shown in Figure 6(b), three conductive paths (a) to (c) that could cause failure in IGBTs 41, 42 may also be formed, similar to the case where it is configured as a full-bridge inverter circuit.

[0049] As shown in Figures 6(a) and (b), guard lines 46 to 49 are all linear or strip-shaped conductors. Guard line 46 is connected to the emitter of IGBT 41 and positioned to physically separate the collector of IGBT 41 from its gate. Guard line 47 is connected to the emitter of IGBT 42 and positioned to physically separate the collectors of IGBT 41 and IGBT 42 from their gates. Guard line 48 is connected to the emitter of IGBT 43 and positioned to physically separate the collector of IGBT 43 from its gate. Guard line 49 is connected to the emitter of IGBT 44 and positioned to physically separate the collectors of IGBT 43 and IGBT 44 from its gate. More specifically, guard lines 46 to 49 are conductive tapes or conductive plates with a thin plate structure provided on the surface of each resin mold, which is the package of IGBTs 41 to 44, and are made of a metallic material such as copper or aluminum.

[0050] In this embodiment, IGBTs 41 to 44 are not individually packaged in resin molds or the like. Instead, as shown in Figure 7, for example, IGBTs 41 and 42 are pre-connected with freewheeling diodes (not shown) to form the upper and lower arms of an inverter circuit and housed in a single package as a switching module 50. Similarly, IGBTs 43 and 44 are also housed in a single package as a switching module 50. Now, the configuration of the switching module 50 will be described with reference to Figure 7.

[0051] As shown in Figure 7(a), the switching module 50 consists of a main body 50a made of heat-resistant resin with a rectangular parallelepiped shape that houses two IGBTs and two freewheeling diodes, etc., and a metal heat dissipation section 50b with a plate shape that is provided at the bottom of the main body 50a and capable of dissipating the heat generated by these IGBTs to the outside. In this embodiment, the two IGBTs are IGBTs 41, 42 or IGBTs 43, 44. Here, the case of IGBTs 41, 42 will be used as an example for explanation, but the case of IGBTs 43, 44 is configured similarly (it can be explained similarly by replacing IGBT 41 with IGBT 43 and IGBT 42 with IGBT 44).

[0052] Three roughly cubic protrusions 50c are formed on the upper part of the main body 50a, aligned along the longitudinal direction of the main body 50a. A high-potential terminal 51, a low-potential terminal 52, and an intermediate terminal 53 are provided at the top of these protrusions, extending from one end to the other in the longitudinal direction (from the right to the left side of the page in Figure 7). Female screw holes 51a, 52a, and 53a are formed in these terminals 51, 52, and 53, respectively, which are used when screwing in the aforementioned lead wires or the like.

[0053] As shown in Figure 7(b), recesses 50d are formed in the middle of the short side of the main body 50a and at both ends in the long side, exposing mounting holes 50e formed in the heat dissipation section 50b. These mounting holes 50e are through holes used when the heat dissipation section 50b side of the switching module 50 is attached to the heat sink by screw fastening or the like. On the upper part of one end of the main body 50a in the long side, the first control terminal 54, the second control terminal 55, the low-potential auxiliary terminal 56, and the intermediate auxiliary terminal 57 are positioned in a row so as to straddle the recess 50d in the short side.

[0054] In this embodiment, the mounting hole 50e formed on one end of the main body 50a in the longitudinal direction is sandwiched between the first control terminal 54, the intermediate auxiliary terminal 57, and then, sandwiching the recess 50d, the low-potential auxiliary terminal 56 and the second control terminal 55, which are arranged in that order from one end in the longitudinal direction to the other end (from the bottom to the top of the paper in Figure 7), and are provided to protrude from the top of the main body 50a. These terminals 51 to 57, including the high-potential terminal 51 mentioned above, are connected to the terminals of IGBTs 41 and 42, which are connected to constitute the upper and lower arms of the inverter circuit within the switching module 50.

[0055] Specifically, as shown in Figure 7(c), the high-potential terminal 51 is connected to the collector of IGBT41, which constitutes the upper arm, and the low-potential terminal 52 and the low-potential auxiliary terminal 56 are connected to the emitter of IGBT42, which constitutes the lower arm. The intermediate terminal 53 and the intermediate auxiliary terminal 57 are connected to the emitter of IGBT41 and the collector of IGBT42, that is, to the connection point of the upper and lower arms. In addition, the first control terminal 54 is connected to the gate of IGBT41, and the second control terminal 55 is connected to the gate of IGBT42.

[0056] In this embodiment, for the switching module 50 configured in this way, the first guard electrode 58 and the second guard electrode 59 are provided on the upper part of the protrusion 50c and the main body 50a as guard lines 46 to 49 that constitute the induction heating circuit 40 of the full-bridge inverter circuit shown in Figure 6(a).

[0057] As shown in Figures 7(a) and (b), the first guard electrode 58 is connected to the intermediate terminal 53 by having one end 58a attached to it. The first guard electrode 58 is attached to the protrusion 50c on which the intermediate terminal 53 is located, extending down along the side surface of the protrusion 50c (the side on the short side of the main body 50a (the bottom side of the paper in Figure 7)) to the upper surface of the main body 50a. After extending along the upper surface to the short side of the main body 50a, it is attached to the upper surface of the main body 50a so as to extend toward the long side. The other end 58b is attached to the intermediate auxiliary terminal 57 and connected to it. As a result, the first guard electrode 58, which is at the same potential as the intermediate terminal 53 and the intermediate auxiliary terminal 57, is physically positioned between the first control terminal 54 connected to the gate of the IGBT 41 and the high-potential side terminal 51 connected to the collector of the IGBT 41.

[0058] Thus, the first guard electrode 58 electrically connects the intermediate terminal 53 and the intermediate auxiliary terminal 57, but as shown in Figure 7(c), the intermediate terminal 53 and the intermediate auxiliary terminal 57 are wired and electrically connected within the switching module 50. Therefore, it is possible to physically separate the first control terminal 54 and the high-potential side terminal 51 without affecting the circuit configuration of the upper and lower arms of the inverter circuit.

[0059] Furthermore, the second guard electrode 59 is connected to the low-potential terminal 52 by having one end 59a attached to it. The second guard electrode 59 is attached to the protrusion 50c on which the low-potential terminal 52 is located, extending down along the side surface of the protrusion 50c (the other end in the short direction of the main body 50a (the upper side of the paper in Figure 7)) to the upper surface of the main body 50a. After extending along the upper surface to the other end in the short direction of the main body 50a, it is attached to the upper surface of the main body 50a so as to extend toward the one end in the longitudinal direction. The other end 59b is then attached to the low-potential auxiliary terminal 56 and connected to it. As a result, the second guard electrode 59, which is at the same potential as the low-potential terminal 52 and the low-potential auxiliary terminal 56, is physically positioned between the second control terminal 55 connected to the gate of the IGBT 42 and the high-potential terminal 51 connected to the collector of the IGBT 41.

[0060] Thus, the second guard electrode 59 electrically connects the low-potential terminal 52 and the low-potential auxiliary terminal 56. As shown in Figure 7(c), the low-potential terminal 52 and the low-potential auxiliary terminal 56 are wired and electrically connected within the switching module 50. Therefore, it is possible to physically separate the second control terminal 55 from the intermediate terminal 53 and the high-potential terminal 51 without affecting the circuit configuration of the upper and lower arms of the inverter circuit.

[0061] Furthermore, as shown in Figure 8, a first guard electrode 58' and a second guard electrode 59' may be configured. That is, as shown in Figures 8(a) and (b), the first guard electrode 58' provided on the switching module 50' is attached to the upper surface of the main body 50a on one end in the longitudinal direction and one end in the short direction (lower right side of the page in Figure 7), connected to the intermediate auxiliary terminal 57, and is formed in a rectangular frame shape that surrounds the first control terminal 54 connected to the gate of the IGBT 41 with a predetermined gap around it. The intermediate auxiliary terminal 57 is at the same potential as the intermediate terminal 53 connected to the emitter of the IGBT 41 and the collector (connection part of the upper and lower arms) of the IGBT 42.

[0062] Furthermore, the second guard electrode 59' is attached to the upper surface of the main body 50a at one end in the longitudinal direction and the other end in the short direction (upper right side of the page in Figure 7), connected to the low-potential auxiliary terminal 56, and formed in a rectangular frame shape that surrounds the second control terminal 55 connected to the gate of the IGBT 42, while ensuring a predetermined gap around it. The low-potential auxiliary terminal 56 is at the same potential as the low-potential terminal 52 connected to the emitter of the IGBT 42.

[0063] Thus, the first guard electrode 58' and the second guard electrode 59' are both attached to the upper surface of the switching module 50, surrounding the first control terminal 54 and the second control terminal 55, so as to prevent the three conductive paths (a) to (c) from being formed by water exposure or condensation. They are also connected to the intermediate auxiliary terminal 57 connected to the emitter of IGBT 41 and the low-potential auxiliary terminal 56 connected to the emitter of IGBT 42 at the same upper surface within the switching module 50'. Therefore, the first guard electrode 58' can physically separate the first control terminal 54 from the high-potential terminal 51 without affecting the circuit configuration of the upper and lower arms of the inverter circuit. The second guard electrode 59' can physically separate the second control terminal 55 from the intermediate terminal 53 and the high-potential terminal 51.

[0064] The heating cooker 10 configured as described above has an induction heating circuit 40 housed in the machine room 15, and comprises a switching module 50 housing IGBTs 41 and 42 and another switching module 50 housing IGBTs 43 and 44, a controller 37 that controls the on / off switching of IGBTs 41 to 44, and a first guard electrode 58 (guard lines 46, 48) and a second guard electrode 59 (guard lines 47, 49).

[0065] As shown in Figures 9(a) and (b), a switching module 50 housing IGBTs 41 and 42 can be used as an example. The switching module 50 has a high-potential terminal 51 (collector of IGBT 41), a low-potential terminal 52 (emitter of IGBT 42), an intermediate terminal 53 (emitter of IGBT 41 and collector of IGBT 42), a first control terminal 54 (gate of IGBT 41), a second control terminal 55 (gate of IGBT 42), a low-potential auxiliary terminal 56, and an intermediate auxiliary terminal 57. Of these, the first control terminal 54 and the second control terminal 55 are connected to the controller 37 and controlled on / off.

[0066] The first guard electrode 58 (guard line 46) is connected to the intermediate terminal 53 (emitter of IGBT 41) of the switching module 50 and the intermediate auxiliary terminal 57, which is at the same potential, and is positioned to physically separate the high-potential side terminal 51 (collector of IGBT 41) and the first control terminal 54 (gate of IGBT 41). The second guard electrode 59 (guard line 47) is connected to the low-potential side terminal 52 (emitter of IGBT 42) of the switching module 50 and the low-potential side auxiliary terminal 56, which is at the same potential, and is positioned to physically separate the intermediate terminal 53 (collector of IGBT 42) and the high-potential side terminal 51 (collector of IGBT 41) from the second control terminal 55 (gate of IGBT 42).

[0067] As a result, a first guard electrode 58 (guard line 46) exists between the high-potential terminal 51 (collector of IGBT41) and the first control terminal 54 (gate of IGBT41) at the same potential as the intermediate terminal 53 (emitter of IGBT41), and a second guard electrode 59 (guard line 47) exists between the intermediate terminal 53 (collector of IGBT42) and the second control terminal 55 (gate of IGBT42), and between the high-potential terminal 51 (collector of IGBT41) and the second control terminal 55 (gate of IGBT42) at the same potential as the low-potential terminal 52 (emitter of IGBT42).

[0068] For example, even if water enters the machine room 15 where the induction heating circuit 40 is housed from the outside and the switching module 50 is exposed to water, or if dust and dirt adhering to the switching module 50 in the machine room 15 absorbs condensed moisture and water droplets form, and these water droplets Wa and Wb flow from the high-potential side terminal 51 of the switching module 50 toward the first control terminal 54 (water Wa) and the second control terminal 55 (water Wb), the switching module 50 has a first guard electrode 58 and a second guard electrode 59. Furthermore, the gates of IGBTs and power MOSFETs used as switching elements generally have higher input impedance (input resistance) than the collector, emitter, drain, and source.

[0069] Therefore, before or during the formation of the conductive path (a) (thin solid arrow shown in Figure 9(b)) from the high-potential terminal 51 to the first control terminal 54 by the water Wa,Wb, another conductive path CPa connecting the high-potential terminal 51 and the intermediate terminal 53 is formed. As a result, even if a high voltage is applied to the high-potential terminal 51 of the induction heating circuit 40 or a large current flows, these can be discharged to the intermediate terminal 53, which has a lower potential and input impedance (input resistance) than the first control terminal 54, via the other conductive path CPa.

[0070] Furthermore, because the water forms another conductive path CPb connecting the intermediate terminal 53 and the low-potential terminal 52 before or during the formation of the conductive path (a) (the dashed arrow shown in Figure 9(b)) from the intermediate terminal 53 to the second control terminal 55, even if a high voltage is applied or a large current flows through the intermediate terminal 53 of the induction heating circuit 40, these can be discharged to the low-potential terminal 52, which has a lower potential and input impedance (input resistance) than the second control terminal 55, via the other conductive path CPb.

[0071] Furthermore, because the water forms another conductive path CPc connecting the high-potential terminal 51 and the low-potential terminal 52 before or during the formation of the conductive path (c) (dashed arrow shown in Figure 9(b)) from the high-potential terminal 51 to the second control terminal 55, even if a high voltage is applied or a large current flows through the high-potential terminal 51 of the induction heating circuit 40, these can be discharged to the low-potential terminal 52, which has a lower potential and input impedance (input resistance) than the second control terminal 55, via the other conductive path CPc.

[0072] Furthermore, since a DC voltage of 280V is applied to power lines 35H and 35L from the rectifier circuit 36, even if water molecules Wa and Wb form separate conductive paths CPa to CPc, the current flowing through them will be limited to, for example, a few amperes due to the electrical resistance of the water molecules Wa and Wb. Also, since the water molecules Wa and Wb will evaporate within a few seconds due to the resistive heat generated by their electrical resistance and will not remain, the separate conductive paths CPa to CPc will disappear immediately. Moreover, the rectifier circuit 36 ​​is selected to have a sufficient absolute maximum rating for forward current (e.g., 200A) assuming that currents of the order of 100A will flow during the switching operation of IGBTs 41 and 43, so even if a current of a few amperes flows, the rectifier circuit 36 ​​will not be damaged.

[0073] Therefore, since high voltage is not applied to the first control terminal 54 and the second control terminal 55 and large currents do not flow through them, the induction heating circuit 40 itself, the controller 37 and rectifier circuit 36 ​​that control it, and other electronic components are not significantly damaged, and water-related failures of the IGBTs 41 and 42 of the switching module 50, the controller 37 and the rectifier circuit 36, etc. can be prevented. In the switching module 50 that houses IGBTs 43 and 44, the same explanation can be given by replacing IGBT 41 with IGBT 43 and IGBT 42 with IGBT 44. Also, the switching module 50' shown in Figure 9(c) can be explained in the same way as the switching module 50 by replacing the first guard electrode 58 with the first guard electrode 58' and the second guard electrode 59 with the second guard electrode 59'.

[0074] In the above-described heating appliance 10, the induction heating circuit 40 was constructed using IGBTs 41-44 as the switching elements of the semiconductor switching circuit for power. However, for example, power MOSFETs may be used instead of IGBTs. In this case, the collectors of IGBTs 41-44 are replaced by the drains of the power MOSFETs, the emitters of IGBTs 41-44 are replaced by the sources of the power MOSFETs, and the gates of IGBTs 41-44 are replaced by the gates of the power MOSFETs. Alternatively, GTO thyristors or the like may be used.

[0075] Furthermore, in the above-described heating cooker 10, the IGBTs 41 to 44 are housed in two switching modules 50 as switching elements for the power semiconductor switching circuit, and these two switching modules 50 are configured to be attached to a heat sink (not shown) located at a position physically separate from the printed circuit board 61 on which the control device 60 is mounted. However, this is not the only option; for example, the IGBTs 41 to 44 may be assembled (mounted) on the printed circuit board 61 on which the control device 60 is mounted. In this case, for example, for IGBTs 41, etc., which are assembled on the printed circuit board 61 and whose collector terminal, emitter terminal, and gate terminal are exposed into the machine room 15 from the resin mold, a guard electrode (guard line) connected to the emitter terminal is positioned to physically separate the collector terminal and the gate terminal. This prevents water-related failures of IGBTs 41, etc., the controller 37, the rectifier circuit 36, etc., as described above.

[0076] Furthermore, in the above-described heating appliance 10, the induction heating circuit 40 was configured using four IGBTs 41-44 as a semiconductor switching circuit for power. However, for example, a single IGBT may be connected in series between a DC power supply and a load to configure a power switch circuit that controls whether or not DC power can be supplied to the load. In this case, the guard electrode (guard line) that is positioned to physically separate the collector and emitter is connected to the emitter or a line or node with a lower potential or input impedance (input resistance) than the emitter.

[0077] Furthermore, in the above-described heating cooker 10, the induction heating circuit 40 of the steam generator 20 utilizing electromagnetic induction heating was configured as the semiconductor switching circuit for power, but this is not limited to this. For example, an induction heating circuit (inverter circuit) such as an IH cooktop or IH plate may be configured as a heating device utilizing electromagnetic induction heating. Alternatively, an inverter circuit that controls the rotation of a multiphase AC motor that drives a compressor in a refrigerator or freezer, or other rotating mechanism, may be configured. [Explanation of symbols]

[0078] 10... Cooking appliance (kitchen equipment), 11... Housing, 12... Door, 13... Control panel, 14... Cooking cabinet, 15... Machine room (designated space), 20... Steam generator, 21... Steam generating container, 30... Heating unit, 31... Heating element, 33... Heating rod, 34... Induction heating coil, 35H... Power line (high potential side), 35L... Power line (low potential side), 36... Rectifier circuit, Controller 37 (control circuit), 40... Induction heating circuit (switching circuit, inverter circuit), 41, 43... IGBT (switching element, upper arm), 42, 44... IGBT (switching element, lower arm), 46, 48... Guard line (first guard line), 47, 49... Guard line (second guard line) Line), 50, 50'... Switching module, 51... High-potential side terminal (1st high-potential side terminal), 52... Low-potential side terminal (2nd low-potential side terminal), 53... Intermediate terminal (1st low-potential side terminal, 2nd high-potential side terminal), 54... 1st control terminal (control terminal), 55... 2nd control terminal (control terminal), 56... Low-potential side auxiliary terminal (low-potential side terminal, 2nd low-potential side terminal), 57... Intermediate auxiliary terminal (low-potential side terminal, 1st low-potential side terminal, 2nd high-potential side terminal), 58, 58'... 1st guard electrode (guard line, 1st guard line), 59, 59'... 2nd guard electrode (guard line, 2nd guard line), CPa, CPb, CPc... Conductive path (another conductive path), Wa, Wb... Water.

Claims

1. Kitchen equipment in which a semiconductor switching circuit for power is housed within a predetermined space, A switching element having a high-potential side terminal and a low-potential side terminal and a control terminal, which constitutes the semiconductor switching circuit, A control circuit connected to the control terminal for controlling the on / off state of the switching element, A guard line is positioned to physically separate the high-potential terminal and the control terminal and is connected to the low-potential terminal, Kitchen equipment characterized by having the following features.

2. The kitchen equipment according to claim 1, characterized in that the switching element is physically separated from the printed circuit board on which the control circuit is provided and located within the predetermined space, and is connected to the control circuit via lead wires.

3. In the kitchen equipment according to claim 1 or 2, the semiconductor switching circuit is part of an inverter circuit that supplies AC power and is composed of an upper arm and a lower arm. The aforementioned switching element is A first switching element having a first high-potential terminal, a first low-potential terminal, and a first control terminal, and constituting the upper arm; and a second switching element having a second high-potential terminal, a second low-potential terminal, and a second control terminal connected to the first low-potential terminal, and constituting the lower arm. The aforementioned guard line is A first guard line separates the first high-potential terminal and the first control terminal and is connected to the first low-potential terminal, and a second guard line separates the second high-potential terminal and the first high-potential terminal and the second control terminal and is connected to the second low-potential terminal, The aforementioned control circuit is A kitchen appliance characterized by being connected to the first control terminal and the second control terminal to exclusively control the on / off state of the first switching element and the second switching element.

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