JP2013000203A - Induction heating rice cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely stop power supply from an AC power source to a heater and to an induction heating coil when a temperature fuse is broken in a configuration not to distribute a heater current to the temperature fuse within a lid.SOLUTION: The induction heating rice cooker includes: a relay 61 for connecting or disconnecting a current pathway to the AC power source, an inverter circuit 32 and the heater 66; the temperature fuse 60 for detecting a value corresponding to the temperature of the heater and disconnected when the detected value exceeds a prescribed value; a first DC power source circuit to which the power is supplied from the AC power source via the temperature fuse to convert the power to DC power source; and a second DC power source circuit 64 to which the power source voltage is supplied from the first DC power source circuit to change the voltage to a voltage value lower than the output voltage of the first DC power source circuit 59. The first DC power source circuit is configured to output the voltage of at least about two times of the threshold voltage of a gate terminal of a semiconductor switching element. A control part is supplied with the power source voltage from the second DC power source circuit, and a drive circuit, the relay and a triac drive circuit are supplied with the electric power from the first DC power source circuit.

Description

  The present invention relates to a rice cooker using induction heating and heater heating used in general households.

  2. Description of the Related Art Conventionally, a cooker using induction heating and heater heating of this type includes a pan for storing cooked food and water, an induction coil for induction heating the pan, and an inverter circuit for applying an alternating current to the induction coil. And a heater for heating the pan, and a control means for driving the inverter circuit when cooking the cooked food or water in the pan, and for energizing the heater when keeping warm after cooking. (For example, refer patent document 1).

  According to the above configuration, when cooking rice or the like, the pot is induction-heated by the induction coil, so that it is not limited to 1000 W like an electric heater, and the wattage can be increased. This makes it possible to cook delicious rice because it can be cooked with strong heat. Furthermore, since the heater is energized during the heat retention to perform the heat retaining operation, it is possible to eliminate the generation of noise due to induction heating. As described above, according to the conventional configuration, cooking can be performed with a simple configuration and with a strong heating power, and since it is kept warm with a heater, there is no noise, and an easy-to-use cooker is provided. Is something that can be done.

  Although not shown in particular in this conventional example, particularly when the pan is heated with an electric heater, the electric heater control element becomes uncontrollable and is continuously energized. When the electric heater is overheated, the electric heater is disconnected at the time of overtemperature. Therefore, the temperature fuse is operated to prevent the electric heater from being energized and stop.

  However, in such a configuration, the induction coil and the inverter circuit operate even if the temperature fuse is disconnected and the energization of the electric heater is stopped. As a result, the customer cannot determine that the rice cooker has failed, only feel that the heat insulation performance has deteriorated, and delay in requesting repairs.

  In this conventional example, the heat retaining heater is an electric heater and is used in combination with induction heating. For example, the pan bottom may be heated with an induction coil, and the pan side surface and the lid inner surface may be heated with an electric heater. (For example, refer to Patent Document 2).

  Even in this case, if the electric heater on the side of the pan or inside the lid overheats and the thermal fuse breaks, the inner surface of the lid will not be heated, and it will feel that the inner surface of the lid has increased, but it is not clear what caused the problem. The repair of the rice cooker will be delayed.

  As described above, in a rice cooker that uses both an induction coil and an electric heater, even if the electric heater is shut off due to overheating of the electric heater, only the induction coil operates, and the user's rice cooking performance and heat retention performance are reduced. There was a problem that the cause could not be determined as a rice cooker failure.

  There is also a method of inserting a thermal fuse that shuts off when the electric heater is overheated into the AC power supply path. In this case, since a large current exceeding 10 A flows during induction heating, the current rating of the thermal fuse is increased, and the thermal fuse itself Since it becomes large, it cannot be put in the narrow gap of the lid. When a large current is passed through the temperature fuse, the temperature fuse self-heats during induction heating, and there is a possibility of disconnection even though the electric heater is not overheated.

In the first place, since a path for passing a large current of 10 A or more is routed inside the lid, it is necessary to increase the safety of the lid. As a result, the subject of the enlargement of a lid | cover and the enlargement of the rice cooker main body generate | occur | produced.

JP-A-1-265479 JP-A-7-327815

  However, in the conventional configuration, even if the current path to the electric heater is interrupted by the thermal fuse when the electric heater is overheated, the induction heating coil operates, so the rice cooker operates, and the electric heater is disconnected. It had the subject that a user cannot judge the cause of a rice cooking performance or the heat retention performance fall.

  In addition, since a path for flowing a large current of 10 A or more is routed inside the lid, it is necessary to increase the safety of the lid. As a result, it had the subject of the enlargement of a lid | cover and the enlargement of the rice cooker main body.

  The present invention solves the above-mentioned conventional problem, and when the thermal fuse is disconnected when the heater is overheated, the relay cuts off the power supply from the AC power source to the heater and the induction heating coil, thereby ensuring safety. In addition, the rice cooking or the heat retaining operation is stopped, and the induction heating type rice cooker that allows the user to determine the failure of the rice cooker is provided.

  It is another object of the present invention to provide an induction heating rice cooker that reduces the current flowing through the thermal fuse and prevents the lid from becoming large by providing the thermal fuse in the current path of the power source for driving the relay.

  In order to solve the conventional problem, an induction heating rice cooker of the present invention is connected to a heating coil for induction heating a pan, a capacitor connected in parallel or in series to the heating coil, and the heating coil, An inverter circuit having a semiconductor switching element that conducts and shuts off a heating coil; a rectifier circuit that rectifies an AC power supply and supplies power to the inverter circuit; a drive circuit that turns on and off an input terminal of the semiconductor switching element; and the drive circuit A control unit for controlling on / off of the semiconductor switching element, a water container for containing water, a water vapor generation unit for heating the water container to generate water vapor, a heater for heating water vapor generated from the water vapor generation unit, A triac that turns on and off the heater, and a triac drive circuit that sends an on / off signal to the triac; From the AC power supply, a relay that conducts and cuts off a current path to the AC power supply, the inverter circuit, and the heater, a temperature fuse that detects a value corresponding to the temperature of the electric heater and cuts off when a predetermined value is exceeded, and A first DC power supply circuit that is supplied with power through the thermal fuse and converts to a DC power supply, and a power supply voltage is supplied from the first DC power supply circuit, and is lower than an output voltage of the first DC power supply circuit A second DC power supply circuit for generating a voltage, wherein the first DC power supply circuit is configured to output a voltage that is about twice or more the threshold voltage of the gate terminal of the semiconductor switching element, The power supply voltage is supplied from the second DC power supply circuit, and the drive circuit, the relay, and the triac drive circuit are supplied with power from the first DC power supply circuit. A.

As a result, when the thermal fuse is disconnected, the current path from the AC power supply to the first DC power supply circuit is interrupted, the first DC power supply circuit is stopped, the power supply to the relay is lost, and the relay becomes AC power supply. Since the power supply to the heater and the induction heating coil is stopped by cutting off the current path from, the heater will not stop and the rice cooking performance and heat insulation performance will not be messed up, and the user will have a malfunction of the rice cooker. It can be judged immediately and repairs can be reliably requested.

  Especially for the heater that heats water vapor, if the heater function stops, the inside of the heater will dew, water will accumulate inside the heater, water may fall from the superheated steam ejection hole, and rice may become sticky. Since the power supply from the AC power supply is stopped and rice cannot be cooked, it can be repaired before it becomes sticky.

  In addition, when the first DC power supply circuit stops, the power supply to the second DC power supply circuit is lost and the control unit stops, so the user can immediately know that the rice cooker will not operate and repair it. Can be requested.

  In addition, since a large current does not flow through the thermal fuse, the lead wire of the thermal fuse can be made thin, and an increase in the size of the lid can be prevented.

  The rice cooker of the present invention is an inverter having a heating coil for induction heating of a pan, a capacitor connected in parallel or in series to the heating coil, and a semiconductor switching element connected to the heating coil and conducting and blocking the heating coil. A circuit, a rectifier circuit that rectifies an AC power supply and supplies power to the inverter circuit, a drive circuit that turns on and off an input terminal of the semiconductor switching element, and a control unit that controls on / off of the semiconductor switching element via the drive circuit; A water container for containing water; a water vapor generating part for heating the water container to generate water vapor; a heater for heating the water vapor generated from the water vapor generating part; a triac for turning on and off the heater; and an on / off signal for the triac. A TRIAC drive circuit to be sent, the AC power source, the inverter circuit, and the heater A relay that conducts and cuts off the current path to the inverter, a temperature fuse that detects a value corresponding to the temperature of the electric heater and shuts off when a predetermined value is exceeded, and power is supplied from the AC power supply via the temperature fuse A first DC power supply circuit for converting to a DC power supply, and a second DC power supply circuit that is supplied with a power supply voltage from the first DC power supply circuit and lowers the output voltage of the first DC power supply circuit. And the first DC power supply circuit is configured to output a voltage that is about twice or more the threshold voltage of the gate terminal of the semiconductor switching element, and the control unit supplies power from the second DC power supply circuit. The voltage is supplied, and the drive circuit, the relay, and the triac drive circuit are supplied with power from the first DC power supply circuit, so that the temperature fuse is set when the heater is overheated. When the wire is connected, the thermal fuse cuts off the current path from the AC power supply to the first DC power supply circuit, so the power supply from the first DC power supply circuit to the relay disappears and the relay is cut off, so the heater and induction heating coil The current path is cut off by a relay to ensure safety and the operation of the rice cooker is stopped, so that the user can immediately determine the failure of the rice cooker and request repair.

Sectional drawing of the induction heating type rice cooker in Embodiment 1 of this invention. The top view which shows typically the state which notched some lids of the induction heating type rice cooker of FIG. 1 in Embodiment 1 of this invention. The main block diagram of the drive circuit of the induction heating type rice cooker in Embodiment 1 of this invention

The first invention is an inverter circuit having a heating coil for inductively heating a pan, a capacitor connected in parallel or in series to the heating coil, and a semiconductor switching element connected to the heating coil and conducting and blocking the heating coil. A rectifier circuit that rectifies AC power and supplies power to the inverter circuit, a drive circuit that turns on and off the input terminal of the semiconductor switching element, and a control unit that controls on / off of the semiconductor switching element via the drive circuit; A water container for containing water, a water vapor generating part for heating the water container to generate water vapor, a heater for heating the water vapor generated from the water vapor generating part, a triac for turning on and off the heater, and an on / off signal to the triac Triac drive circuit, AC power supply, inverter circuit, and heater A relay that conducts and cuts off the current path, a value corresponding to the temperature of the electric heater is detected, a temperature fuse that is cut off when a predetermined value is exceeded, and power is supplied from the AC power source via the temperature fuse, A first DC power supply circuit for converting to a DC power supply; and a second DC power supply circuit supplied with a power supply voltage from the first DC power supply circuit and having a voltage lower than an output voltage of the first DC power supply circuit. And the first DC power supply circuit is configured to output a voltage that is about twice or more the threshold voltage of the gate terminal of the semiconductor switching element, and the control unit supplies a power supply voltage from the second DC power supply circuit. The drive circuit, the relay, and the triac drive circuit are supplied with power from the first DC power supply circuit.

  As a result, if the temperature fuse is disconnected when the heater is overheated, the temperature fuse cuts off the current path from the AC power supply to the first DC power supply circuit, so there is no power supply from the first DC power supply circuit to the relay. Since the relay is cut off, the current path of the heater and induction heating coil is cut off by the relay to ensure safety, and the operation of the rice cooker stops, so the user immediately determines the failure of the rice cooker, You can request repairs.

  Especially for the heater that overheats water vapor, if the heater function stops, the inside of the heater will dew, water will accumulate inside the heater, water may fall from the overheated steam ejection hole, and rice may become sticky, Since the power supply from the AC power supply is stopped and rice cannot be cooked, it can be repaired before it becomes sticky.

  In addition, when the first DC power supply circuit stops, the power supply to the second DC power supply circuit is lost and the control unit stops, so the user can immediately know that the rice cooker will not operate and repair it. Can be requested.

  In addition, since a large current does not flow through the thermal fuse, the lead wire of the thermal fuse can be made thin, and an increase in the size of the lid can be prevented.

  In particular, the triac drive circuit according to the first invention includes an optical semiconductor element in which an input side and an output side are electrically insulated, so that a drive power supply and a triac for a semiconductor switching element constituting an inverter circuit are provided. The power supply of the drive circuit can be shared, and the power supply circuit can be downsized.

  Therefore, the board to be mounted can be downsized as the power supply circuit is downsized, and the rice cooker can be downsized.

  The third invention has a current detection circuit for detecting a value corresponding to the current supplied from the AC power source to the inverter circuit through the rectifier circuit, particularly in the induction heating rice cooker of the first or second invention. By arranging the current detection circuit downstream of the series circuit composed of the triac and the heater, the current flowing through the heater does not flow through the current detection circuit, so that only the current flowing through the inverter circuit can be detected.

In a fourth aspect of the invention, in particular, the induction heating rice cooker according to any one of the first to third aspects of the invention has a microcomputer storing a rice cooking sequence and a heat retention sequence, and the microcomputer is a rice cooking sequence. And a predetermined current setting value according to the heat retention sequence, the current setting value is compared with the output value of the current detection circuit, and the ON time is set so that the output value of the current detection circuit becomes the current setting value. In addition, when the current set value is larger than a predetermined value, by prohibiting the driving of the heater, the allowable current of the breaker in a general household is not exceeded, and the breaker falls exceeding the allowable current of the breaker. The rice cooker will not stop. Therefore, a rice cooking sequence and a heat retention sequence can be reliably executed.

  In the fifth aspect of the invention, in particular, the control unit of any one of the first to third aspects cuts off the relay and supplies power to the first DC power supply circuit in a standby state where the rice cooking sequence or the heat retention sequence is not operated. By supplying, power supply to the inverter circuit is stopped, so that power consumption in the standby state can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of an induction heating rice cooker according to an embodiment of the present invention. FIG. 2 is a top view schematically showing a state in which a part of the lid of the induction heating rice cooker in FIG. 1 according to Embodiment 1 of the present invention is cut away.

  The whole structure of the rice cooker provided with the superheated steam generator concerning embodiment of this invention is demonstrated using FIG. 1 or FIG. FIG. 1 is a schematic cross-sectional view of a rice cooker including an overheated steam generator according to Embodiment 1 of the present invention. FIG. 2 is a top view schematically showing a state in which a part of the lid of the rice cooker of FIG. 1 is cut away.

  As shown in FIG. 1, the rice cooker concerning this embodiment is accommodated in the substantially bottomed cylindrical rice cooker main body 1 in which the pot accommodating part 1a was formed, and the pot accommodating part 1a, and rice and water are contained. It has a pan 2 that can be put in. A lid 3 having a hollow structure capable of opening and closing the upper opening of the rice cooker body 1 is attached to the top of the rice cooker body 1.

  A substantially disc-shaped inner lid (also referred to as a heating plate) 4 capable of sealing the upper opening of the pan 2 is detachably attached to the inside of the lid 3 (the side covering the opening of the pan 2).

  The pot storage part 1a of the rice cooker body 1 is composed of an upper frame 1b and a coil base 1c. The upper frame 1b has a cylindrical portion 1ba that is arranged so that a predetermined gap is provided with respect to the side wall of the stored pan 2, and an upper opening of the rice cooker body 1 that protrudes outward from the upper portion of the cylindrical portion 1ba. And a flange portion 1bb fitted to the inner peripheral portion.

  Further, a water container storage portion 1bc for storing the water container 5 is formed in the flange portion 1bb. The water container 5 is a bottomed cylindrical container for containing water for generating steam. A water container heating coil 6 that is a water container heating section for heating (induction heating) the water container 5 is attached to the outer peripheral surface of the water container storage section 1bc. In addition, it may replace with the water container heating coil 6, and may be comprised so that the water container 5 may be heated with a heater.

  When the water container heating coil 6 heats the water container 5, the water in the water container 5 boils and steam of about 100 ° C. is generated. Moreover, the opening is provided in the side part of the water container accommodating part 1bc. In the opening portion, a water container temperature sensor 7 for measuring the temperature of the water container 5 is disposed so as to be able to contact a side portion of the water container 5 stored in the water container storage portion 1bc.

The coil base 1c is formed in a bottomed cylindrical shape corresponding to the shape of the lower portion of the pan 2, and the upper portion is attached to the lower end portion of the cylindrical portion 1ba of the upper frame 1b. A pan bottom heating unit 8 which is an example of a pan heating device for heating (induction heating) the pan 2 is attached to the outer peripheral surface of the coil base 1c.

  The pan bottom heating unit 8 includes an in-bottom heating coil 8a and an out-bottom heating coil 8b, and corresponds to a heating coil for induction heating the pan of the present invention. The in-bottom heating coil 8a is disposed so as to face the periphery of the center of the bottom of the pan 2 via the coil base 1c. Outer bottom heating coil 8b is arranged so as to face the corner portion of the bottom of pan 2 via coil base 1c.

  An opening is provided in the central portion of the bottom of the coil base 1c. In the opening portion, a pan temperature sensor 9 which is an example of a pan temperature detecting unit for measuring the temperature of the pan 2 is disposed so as to be able to contact the bottom of the pan 2 stored in the pan storage unit 1a. . Since the temperature of the pan 2 is substantially the same as the temperature of the cooked rice in the pan 2, the pan temperature sensor 9 can detect the temperature of the cooked rice in the pan 2 by detecting the temperature of the pan 2. .

  The lid 3 includes an upper outer member 3 a and a lower outer member 3 b that constitute the outer shell of the lid 3. The lid 3 includes a hinge shaft 3A. The hinge shaft 3A is an opening / closing shaft for the lid 3, and both ends of the hinge shaft 3A are rotatably fixed to the upper frame 1b of the rice cooker body 1.

  The lid 3 is provided with a through hole 3c so as to penetrate the vicinity of the center portion in the thickness direction of the lid 3, and the steam cylinder 10 is detachably attached to the through hole 3c. Steam escape holes 10a and 10b are provided on the upper and bottom walls of the steam cylinder 10 so that excess steam in the pot 2 can be discharged to the outside of the rice cooker.

  An annular packing 11 is attached around the through hole 3 c on the inner lid 4 side of the lid 3. The packing 11 is provided so as to be in close contact with the periphery of the steam escape hole 4 a provided in the inner lid 4 when the inner lid 4 is attached to the lid 3.

  An inner lid temperature sensor 12, which is an example of an inner lid temperature detector that detects the temperature of the inner lid 4, is attached to the lid 3. An inner lid heating coil 13, which is an example of an inner lid heating device for inductively heating the inner lid 4, is attached to the inner surface (inner side of the lid) of the lower outer member 3 b serving as the bottom wall of the lid 3.

  The inner lid 4 is made of a magnetic metal such as stainless steel capable of induction heating. An annular packing 14 is attached to the surface of the outer peripheral portion of the inner lid 4 on the pan 2 side. The packing 14 is provided in close contact with the flange portion of the pan 2 when the lid 3 is in the closed state.

  Inside the lid 3, a superheated steam generator 15 for introducing superheated steam exceeding 100 ° C. into the pan 2 is provided. A heater that generates heat when energized is built in the superheated steam generator 15.

  The superheated steam generator 15 is configured to be able to generate superheated steam by heating steam at about 100 ° C. generated in the water container 5. A steam supply pipe 16 and a superheated steam input pipe 17 are connected to the superheated steam generator 15. In addition, the superheated steam generator 15 is in contact with a superheated steam temperature sensor 18 that is an example of a superheated steam temperature detection unit that detects the temperature of the superheated steam generated by the superheated steam generator 15.

  The steam supply pipe 16 communicates with the inside of the water container 5 when the lid 3 is in a closed state, and is provided so as to guide the steam generated in the water container 5 to the superheated steam generator 15. An annular packing 19 is attached to the end of the steam supply pipe 16 on the water container 5 side. The packing 19 is provided in close contact with the flange portion of the water container 5 when the lid 3 is in the closed state.

  The superheated steam input pipe 17 communicates with the inside of the pan 2 through the superheated steam input hole 4b provided in the inner lid 4 when the lid 3 is in the closed state, and the superheated steam generated by the superheated steam generator 15 is stored in the pan 2. It is provided to be put in.

  An annular packing 20 is attached to the end of the superheated steam input pipe 17 on the pan 2 side. The packing 20 is provided in close contact with the periphery of the superheated steam supply hole 4b of the inner lid 4 when the lid 3 is in the closed state.

  As shown in FIG. 2, the lid 3 has a display unit 21 such as a liquid crystal display that displays various information such as a rice cooking course and a rice cooking time, and a plurality of rice cooking such as a white rice course, a brown rice course, and a white rice (softer) course. The operation part 22 which is an example of the rice cooking course selection part which can select a specific rice cooking course from the course is provided. The operation unit 22 includes a plurality of buttons such as a rice cooking start button so that instructions for starting, canceling, or making a reservation for cooking can be given in addition to selecting a rice cooking course. The user can select a specific rice cooking course with the operation unit 22 while referring to the display content of the display unit 21 and instruct the start of rice cooking.

  A first circuit board on which the display unit 21 and the operation unit 22 are mounted is mounted inside the lid 3, and a microcomputer constituting a control unit of the rice cooker is mounted on the substrate. The microcomputer will be described with reference to FIG. 3, but includes a storage unit that stores a plurality of rice cooking sequences for cooking rice, a heat retaining sequence for keeping rice warm, and the like.

  Here, the “rice cooking sequence” is mainly composed of four steps of preheating, temperature rising, boiling maintenance, and steaming. In performing each step in turn, the energizing time, heating temperature, heating time, heating output, etc. This is a predetermined cooking procedure. Each rice cooking sequence corresponds to one of a plurality of rice cooking courses. The microcomputer controls the drive of each unit and each device based on the rice cooking course selected by the operation unit 22 and the detected temperature of each temperature sensor 7, 9, and 12, and executes the rice cooking sequence. Further, the microcomputer causes the superheated steam generator 15 to generate superheated steam based on the rice cooking course selected by the operation unit 22 and the detected temperature of the superheated steam temperature sensor 18.

  The second circuit board 23, which will be described with reference to FIG. 3, includes an inverter circuit for supplying power to the bottom heating coil 8a and the bottom heating coil 8b, and a second circuit for supplying power to the water container heating coil 6. An inverter circuit and a triac for turning on and off a heater built in the superheated steam generator 15 are mounted.

  Although not shown, the first circuit board and the second circuit board 23 are electrically connected by lead wires, and the inverter circuit, the second inverter circuit, and the heater are controlled by a control signal from the microcomputer. And a rice cooking sequence and a heat retention sequence are performed.

FIG. 3 is a main part block diagram of the rice cooker in the first embodiment of the present invention.
In FIG. 3, the pan 2 is composed of a laminated body using a plurality of magnetic metals and nonmagnetic metals, although not particularly shown.

The heating coil 31 includes the bottom heating coil 8a and the bottom heating coil 8b shown in FIG.
The bottom heating coil 8a and the bottom heating coil 8b are electrically connected in series.

The inverter circuit 32 includes a capacitor 33, a first semiconductor switching element 34 that is a semiconductor switching element that conducts and blocks the heating coil, and a diode 35.

The capacitor 33 is connected in parallel to the heating coil 31 as shown in FIG. In this embodiment, a polypropylene capacitor is used which has little loss even when a high frequency current flows.
In the present embodiment, the first semiconductor switching element 34 is constituted by a semiconductor element such as an IGBT. An IGBT has a high withstand voltage, can switch at a high frequency, and can flow a large current by applying a voltage to the gate terminal. Therefore, there is an advantage that a large current can be flowed with less power than a power transistor.

  The diode 35 is connected in parallel so that a current flows in a direction opposite to the current direction of the first semiconductor switching element 34. The second inverter circuit 36 includes a capacitor 37, a second semiconductor switching element 38, and a diode 39, and supplies a high frequency current to the water container heating coil 6.

  In general, such an inverter circuit configuration is called a one-stone voltage resonance type inverter because a parallel resonance circuit is constituted by a heating coil and a capacitor.

  The power supply frequency of the AC power supply 40 that supplies power to the rice cooker is 50 Hz in the East Japan region and 60 Hz in the West Japan region.

  The rectifier circuit 41 includes a diode bridge 42, a coil 43, and a capacitor 44. Here, the capacity | capacitance of the capacitor | condenser 44 is as small as several micro F, and if an electric current is sent through the heating coil 31, it will become the same as the voltage waveform when the alternating current power supply 40 is full-wave rectified.

  The first drive circuit 45, which is a drive circuit that turns on and off the input terminal of the semiconductor switching element, limits the current charged to the parasitic capacitance of the gate terminal of the IGBT that constitutes the NPN transistor, the PNP transistor, and the first semiconductor switching element 34. And a push-pull circuit having a current limiting resistor and a discharge resistor for quickly pulling out the parasitic capacitance of the gate terminal.

  The second drive circuit 55 includes a current limiting resistor for limiting the current charged to the parasitic capacitance of the gate terminal of the IGBT that constitutes the NPN transistor, the PNP transistor, and the second semiconductor switching element 38 and the parasitic capacitance of the gate terminal. It is composed of a push-pull circuit having a discharge resistor for quickly pulling out.

  The current detection circuit 46 is connected to a current path from the AC power supply 40 to the rectifier circuit 41. Although not particularly shown, the current transformer and a rectifying / smoothing circuit for rectifying and smoothing an alternating current output from the current transformer are configured to convert an input current value into an analog voltage value. An analog voltage corresponding to this input current value is output to the AD conversion port of the microcomputer 48 constituting the control unit 47.

  The control unit 47 includes a microcomputer 48, a first synchronization signal generation circuit 49, a second synchronization signal generation circuit 50, and the like.

  The microcomputer 48 includes an on-time setting unit 51, a pulse generation unit 52, a current setting unit 53, a sequence setting unit 54, and the like using a number of counter functions, timer functions, and memory functions.

The on-time setting unit 51 sets the on-time within the range of the minimum on-time Ton1 and the maximum on-time Ton4. In the present embodiment, when the first inverter circuit 32 is started and when the second inverter circuit 36 is started, the initial value of the on-time of the semiconductor switching element is started from Ton1, and the on-time is gradually increased. .

  When the pulse generation unit 52 detects the synchronization signal of the first synchronization signal generation circuit 49, the pulse generation unit 52 outputs a high pulse of the set on time to the first drive circuit 45. When the synchronization signal of the second synchronization signal generation circuit 50 is detected, the set high pulse is output to the second drive circuit 55.

  The microcomputer 48 operates with an 8 MHz oscillator and a 32.728 kHz oscillator. Therefore, the minimum setting unit of the high pulse width of the pulse generator 52 constituted by the microcomputer 48 is controlled in units of 0.125 μs which is the minimum period set by the 8 MHz oscillator. That is, when the on-time setting unit 51 changes the output data (8 bits) by 1 digit, the high pulse width of the pulse generating unit 52 is changed by 0.125 μs.

  The current setting unit 53 stores a plurality of current setting values for each rice cooking sequence set by the sequence setting unit 54 using the memory of the microcomputer 48.

  In the rice cooker of the present embodiment, the first current set value 56 (Iin1 in the present embodiment), the second current set value 57 (the present embodiment) having a value lower than the first current set value 56. , Iin2), and a third current set value 58 (Iin3 in the present embodiment) that is lower than the second current set value 57 is stored.

  The sequence setting unit 54 sets a rice cooking sequence or a heat retention sequence in accordance with an operation set by the user using the operation unit 22. Moreover, a standby state is set when neither the rice cooking sequence nor the heat retention sequence is operating.

  The first synchronization signal generation circuit 49 is composed of a comparator, a resistance voltage dividing circuit, and the like, and (C2) terminal voltage is divided by a predetermined ratio and (CE) terminal voltage is divided by a predetermined ratio. The voltages are compared by a comparator, and a high signal is output to the microcomputer 48 when the divided voltage at the (C2) terminal is higher, and a low signal is output to the microcomputer when the divided voltage at the (C2) terminal is lower. Output to 48.

  The second synchronization signal generation circuit 50 is composed of a comparator, a resistance voltage dividing circuit, and the like, and (C2) terminal is resistance-divided at a predetermined ratio and (CE2) terminal is resistance-divided at a predetermined ratio. The voltages are compared by a comparator, and a high signal is output to the microcomputer 48 when the divided voltage at the (C2) terminal is higher, and a low signal is output to the microcomputer when the divided voltage at the (C2) terminal is lower. Output to 48.

  As described above, the pulse generation unit 52 of the microcomputer 48 corresponds to the signals of the first synchronization signal generation circuit 49 and the second synchronization signal generation circuit 50 from the first synchronization signal generation circuit 49. When a synchronization signal is received, a high pulse is output to the first drive circuit, and when a synchronization signal is received from the second synchronization signal generation circuit 50, a high pulse is output to the second drive circuit.

  Although not particularly shown, the first DC power supply circuit 59 is configured by a switching power supply, and a half-wave rectified voltage from one pole (u) of the AC power supply 40 via the temperature fuse 60 is about 20V. It is converted to a DC power supply to output a DC voltage.

  In the present embodiment, the guaranteed variation value of the cutoff voltage (threshold voltage) of the gate terminals of the IGBTs constituting the first semiconductor switching element 34 and the second semiconductor switching element 38 is 6V.

  That is, when a voltage of 6 V or higher is turned on at the gate terminal, the emitter-collector of the IGBT is turned on. The reason why the voltage is about 20 V is that a voltage exceeding the cut-off voltage can be supplied via the first drive circuit 45 and the second drive circuit 55 even if the cut-off voltage varies.

  That is, when driving the IGBT, the output voltage of the first DC power supply circuit 59 that is the power source of the first drive circuit 45 and the second drive circuit 55 that supplies voltage to the IGBT is larger than the cutoff voltage of the gate terminal. It is important to.

  Here, the operations of the first drive circuit 45 and the second drive circuit 55 described briefly above will be described in a little more detail using the first drive circuit 45. The first drive circuit 45 configures the first semiconductor switching element 34 using the power supply voltage of the first DC power supply circuit 59 while the output of the pulse generator 52 formed by the microcomputer 48 is high. A voltage is applied to the IGBT gate terminal, the IGBT collector-emitter is turned on, and while the pulse generator 52 is outputting low, the IGBT gate terminal voltage is set to 0 V, and the IGBT collector-emitter is turned off. To. Note that this is an example, and the components constituting the push-pull circuit may be constituted by MOSFETs or the like.

  The first DC power supply circuit 59 supplies power to the coil of the relay 61. The relay 61 is configured to generate an electromagnetic force and to turn on and off the contact when a current flows through the coil. The relay 61 is arranged in a current path from the AC power source 40, and the heater 66 and the inverter circuit 32 are connected from the AC power source 40. The current path to and from is interrupted. The relay 61 is electrically connected to the side closer to the AC power supply 40 than the current detection circuit 46.

  The relay drive circuit 62 is configured by a transistor with a built-in resistor, and is turned on / off in response to a signal from the microcomputer 48. When the transistor is turned on, the coil of the relay 61 is energized and the contact of the relay 61 is turned on. In this embodiment, the driving power for the relay 61 is supplied from the first DC power supply circuit 59, so that the number of power supply circuits is reduced and the circuit board is made compact.

The cooling fan 63 is configured by a fan motor in which a fan is attached to a rotor of a DC brushless motor. The cooling fan 63 is supplied with power from the first DC power supply circuit 59. Although not specifically shown in the present embodiment, the cooling fan 63 can be driven or stopped by turning on and off the transistor as a fan drive circuit by the microcomputer 48. Second DC power supply circuit 64 Although not specifically shown, a constant voltage circuit is configured by an emitter follower circuit composed of an NPN transistor, a constant voltage diode, a resistor, and a capacitor, and the output voltage of the first DC power supply circuit 59 is reduced to about 5V. Yes. The second DC power supply circuit 64 is a power supply for the microcomputer 48, the zero voltage synchronization signal output circuit 65, and the like.

  The configuration of the second DC power supply circuit 64 is merely an example, and for example, a dedicated power supply IC may be used to realize a constant voltage circuit that suppresses variations in output voltage.

  The heater 66 has a rod-like shape, and is not particularly shown, but is disposed in a metal tube having blades. The blades are for facilitating heat conduction from the heater 66 to water vapor. The tip of the metal tube is closed, and the metal tube and the heater are electrically insulated by an insulating material. The thermal fuse 60 is disposed in the vicinity of the metal tube, and is disconnected when the heater 66 is overheated and the metal tube is abnormally overheated.

The triac 67 is connected in series to the heater 66 and is turned on / off according to the output signal of the triac drive circuit 68. Since it is a triac, it is not turned on when there is no on signal from the triac drive circuit 68 when the voltage of the AC power supply 40 is near zero.

  The triac drive circuit 68 uses a switch using an optical coupling element called a solid state relay in which the light emitting portion is a light emitting diode and the light receiving portion is a triac. By using the optical coupling element, the series circuit composed of the heater 66 and the triac 67 and the microcomputer 48 can be electrically insulated. Therefore, when the heater 66 or the triac 67 breaks down, the current or voltage is applied to the microcomputer. The computer 48 is not destroyed.

  The zero voltage synchronization signal output circuit 65 is not particularly shown, but the (u) pole of the AC power supply 40 is connected to the base terminal of the transistor via a resistor. The collector terminal of this transistor is connected to a second DC power supply circuit 64 generated from the AC power supply 40 via a switching power supply via a resistor, and (u) the potential of the pole is higher than the other pole. Are output to the microcomputer 48. In synchronization with this output signal, the microcomputer 48 inputs the output voltage of the current detection circuit 46 after a predetermined time, and compares the current set value set by the current setting unit 53 with the on-time setting unit 51. Set up.

  The set on-time is updated at the next synchronization signal. In addition, the microcomputer 48 starts displaying the current time, processing related to rice cooking control, and the like in synchronization with the output signal of the zero voltage synchronization signal output circuit 65.

  The operation unit 22 includes a plurality of momentary switches. When each switch is pressed by the user, the microcomputer 48 detects that the switch has been pressed, and performs a predetermined rice cooking operation or heat retaining operation in accordance with each switch.

  The display unit 21 includes an LCD and a plurality of LEDs such as red, green, and orange. The microcomputer 48 sets the display content of the LCD and the LED to be lit according to the state of the rice cooker such as during rice cooking or heat insulation. The display contents of the LCD include a display of the current time, a display of the time until the end of cooking, and a display of the elapsed time of heat insulation.

  The water container 5 is induction-heated by a water container heating coil 6 constituting a water container heating section, whereby an eddy current flows in the metal part of the water container 5 to heat the water container 5, to heat and boil the water in the water container 5. Is generated.

  In the present embodiment, the water container heating unit is configured by the water container heating coil 6 and the water container 5 is induction heated. However, instead of the water container heating coil 6, the water container 5 is replaced with a heater. It may be heated.

  As mentioned above, the induction heating type rice cooker of this Embodiment induction-heats the water container 5 with the water container heating coil 6, heats the water which entered the water container 5, and generates a vapor | steam. The steam is heated by the heater 66 to generate superheated steam.

  For example, if the heater 66 is continuously heated despite the absence of steam, the temperature of the heater 66 gradually increases. When the rising temperature exceeds a certain temperature, the thermal fuse 60 is blown, the supply current path from the AC power supply 40 to the first DC power supply circuit 59 is cut off, and the power supply to the first DC power supply circuit 59 is stopped. To do. When the first DC power supply circuit 59 stops, the first drive circuit 45 that drives the first semiconductor switching element 34, the relay drive circuit 62 that drives the relay 61, and the triac 67 that turns on and off the heater 66 are driven. All power supply to the triac drive circuit 68 and the second DC power supply circuit 64 that is the power supply of the microcomputer 48 is stopped.

  In particular, since the power supply of the relay drive circuit 62 is stopped, the relay 61 is cut off, and the power supply from the AC power supply 40 to the heater 66, the heating coil 31, and the water container heating coil 6 can be stopped. The phenomenon that only 31 and the water container heating coil 6 operate | moves does not generate | occur | produce.

  Therefore, even when the temperature of the heater 66 becomes a predetermined temperature or higher, the rice cooker is safely stopped. Since the power supply to the microcomputer 48 is also stopped, the display content on the display unit 21 disappears or changes, and the operation unit 22 is not accepted. Therefore, the user can easily determine the failure of the rice cooker and request repair of the rice cooker.

  Further, in the induction heating rice cooker of the present embodiment, the first semiconductor switching element 34 and the second semiconductor switching element 38 are not turned on simultaneously. That is, current is not supplied to the heating coil 31 and the water container heating coil 6 at the same time. As described above, the power supplied to the heating coil 31 and the power supplied to the water container heating coil 6 can be detected by the current detection circuit 46.

  For example, when supplying power to the heating coil 31 and the water container heating coil 6 at the same time, it is necessary to provide a current detection circuit in each heating coil in order to grasp the power supplied to each heating coil. If there is a difference between the operating frequencies of the heating coil 31 and the water container heating coil 6, an interference sound may be generated.

  That is, by not supplying power to the heating coil 31 and the water container heating coil 6 at the same time, the heating control to the pan 2 and the water container 5 is made accurate, and interference noise between the heating coils is not generated.

  Further, the configuration of the triac drive circuit 68 is a switch using an optical coupling element called a solid state relay in which the light emitting portion is a light emitting diode and the light receiving portion is a triac. By using the optical coupling element, the series circuit composed of the heater 66 and the triac 67 and the microcomputer 48 can be electrically insulated. Therefore, when the heater 66 or the triac 67 breaks down, the current or voltage is applied to the microcomputer. The computer 48 is not destroyed. Since the destruction of the microcomputer 48 can be prevented, the abnormality can be notified through the display unit 21.

  The current detection circuit may be configured such that a current detection resistor is connected between the semiconductor switching element and the rectifier circuit, and the output voltage of the current detection resistor is read into a microcomputer. Also in this case, it is possible to detect the current supplied to the heating coil without mixing the current flowing through the heater.

  Moreover, in the rice cooker of this Embodiment, the relay 61 is interrupted | blocked at the time of the standby state waiting for a user's operation that the microcomputer 48 is not operating neither a rice cooking sequence nor a heat retention sequence.

  By shutting off the relay 61, a safe rice cooker can be provided in which the triac 67 does not make a false call and does not heat the heater 66 even if there is an external noise coming through the AC power supply 40.

As described above, the rice cooker according to the present invention is provided with a relay in the current path that leads from the AC power source to the load such as the heater and the inverter circuit, and is provided with a temperature fuse in the supply path of the relay drive power source, so that the heater temperature rises. When the temperature fuse is disconnected, it can be safely stopped by stopping the power supply to the relay drive power supply and shutting off the relay, so it is effective for cooking equipment using household rice cookers and heaters. is there.

2 Pan 5 Water container 6 Water container heating coil 31 Heating coil 32 Inverter circuit 33, 37, 44 Capacitor 34 First semiconductor switching element 36 Second inverter circuit 40 AC power supply 41 Rectifier circuit 45 First drive circuit 46 Current detection Circuit 47 Control unit 59 First DC power supply circuit 60 Thermal fuse 61 Relay 64 Second DC power supply circuit 66 Heater 67 Triac 68 Triac drive circuit

Claims (5)

A heating coil for induction heating of the pan, a capacitor connected in parallel or in series with the heating coil, an inverter circuit having a semiconductor switching element connected to the heating coil and conducting and blocking the heating coil, and rectifying the AC power supply A rectifier circuit that supplies power to the inverter circuit, a drive circuit that turns on and off the input terminal of the semiconductor switching element, a control unit that controls on and off of the semiconductor switching element via the drive circuit, and a water container that contains water A water container heating unit for heating the water container; a heater for heating water vapor generated from the heated water container; a triac for turning on and off the heater; a triac drive circuit for sending an on / off signal to the triac; and the AC power source And a relay that conducts and cuts off the current path to the inverter circuit and the heater. -A temperature fuse that detects a value corresponding to the temperature of the heater and shuts off when a predetermined value is exceeded, and a first DC that is supplied with power from the AC power source via the temperature fuse and converts to a DC power source A power supply circuit; and a second DC power supply circuit that is supplied with a power supply voltage from the first DC power supply circuit and has a voltage lower than an output voltage of the first DC power supply circuit. The circuit is configured to output a voltage more than about twice the threshold voltage of the gate terminal of the semiconductor switching element, and the control unit is supplied with a power supply voltage from the second DC power supply circuit, The relay and the triac drive circuit are induction heating rice cookers in which power is supplied from the first DC power supply circuit. The induction heating rice cooker according to claim 1, wherein the triac drive circuit includes an optical semiconductor element in which an input side and an output side are electrically insulated. 2. A current detection circuit for detecting a value corresponding to a current supplied from an AC power source to an inverter circuit via a rectifier circuit, wherein the current detection circuit is arranged at a stage subsequent to a series circuit including a triac and a heater. 2. Induction heating rice cooker according to 2. The control unit has a microcomputer storing a rice cooking sequence and a heat retention sequence, and the microcomputer has a predetermined current set value according to the rice cooking sequence and the heat retention sequence, and the current set value and the output value of the current detection circuit are set. In comparison, the on-time is set so that the output value of the current detection circuit becomes a current set value, and when the current set value is larger than a predetermined value, the heater is prohibited from driving. The induction heating type rice cooker of any one of Claims. The induction heating rice cooker according to any one of claims 1 to 4, wherein the control unit shuts off the relay and supplies power to the first DC power supply circuit in a standby state where the rice cooking sequence or the heat retention sequence is not operated. .