JP5246099B2 - rice cooker - Google Patents

Description

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

  Conventionally, this type of rice cooker has a heating coil that induction-heats the pan, an energization control element (semiconductor switching element) that turns the heating coil on and off, a drive circuit (drive circuit) that drives the energization control element, and a power supply to the drive circuit A first power supply circuit that supplies current; and a second power supply circuit that steps down the first power supply circuit and supplies power supply current to the control means (control unit) and the operation unit. The output voltage of one power supply circuit is switched, and the power supply voltage changing means sets the output voltage set value of the first power supply circuit lower than the first voltage set value in the standby state when the heating sequence is not executed. Some have been configured to switch to the second voltage set value (see, for example, Patent Document 1).

  With such a configuration, the power supply voltage of the first power supply circuit can be set to a second voltage set value lower than the first voltage set value in the standby state where the heating sequence is not executed. It is described that the power consumption of the drive circuit to which the power supply current is supplied from the first power supply circuit can be reduced and the standby power can be suppressed.

  Although not specifically described, as a general technique, in order to suppress the loss of the semiconductor switching element at the time of starting or turning on the semiconductor switching element, a resistance value for limiting the input current to the gate terminal of the semiconductor switching element is set. There is a way to make it bigger.

JP 2006-156147 A

  However, in the conventional configuration, when the heating sequence is executed, the power supply voltage of the first power supply circuit is the higher first voltage set value, and the drive circuit and the second power supply when the heating sequence is executed However, the power consumption of the power supply circuit cannot be reduced.

  The present invention solves the above-mentioned conventional problem, and when the on-time of the semiconductor switching element is short, the output voltage of the first DC power supply circuit is lowered to a voltage that guarantees that the gate terminal of the semiconductor switching element can be turned on. An object of the present invention is to provide a rice cooker that can cook rice with low power consumption by reducing the power consumption of the drive circuit and the second DC power supply circuit even during the heating sequence.

In order to solve the conventional problems, the rice cooker of the present invention includes a heating coil that induction-heats a pan, an inverter circuit that is connected to the heating coil, and has a semiconductor switching element that conducts and blocks the heating coil, A rectifier circuit that rectifies an AC power source and supplies power to the inverter circuit; a drive circuit that turns on and off a gate terminal of the semiconductor switching element; and a control unit that controls on / off of the semiconductor switching element via the drive circuit;
A first DC power supply circuit that converts the AC power supply into a DC power supply; and a second DC that is supplied with a power supply voltage from the first DC power supply circuit and has a voltage lower than the output voltage of the first DC power supply circuit. A power circuit,
The control unit is supplied with a power supply voltage from the second DC power supply circuit,
The first DC power supply circuit has a plurality of output voltages, the drive circuit is supplied with a predetermined output voltage from the first DC power supply circuit according to a control signal of the control unit, and the control unit When the ON time of the semiconductor switching element is a predetermined time or more, the output voltage of the first DC power supply circuit is set to a first voltage setting value lower than the maximum rated voltage of the gate terminal of the semiconductor switching element of the semiconductor switching element When the ON time of the semiconductor switching element is shorter than a predetermined time, the output voltage of the first DC power supply circuit is set to a second voltage set value lower than the first voltage set value.

  Accordingly, when the on-time of the semiconductor switching element is short, the second voltage setting value is set. For example, the saturation voltage between the collector and the emitter of the IGBT which is an example of the semiconductor switching element is the first voltage setting value. However, since the collector current itself is low because of the short on-time, the steady loss of the IGBT is slightly increased. Rather, it is possible to reduce the collector current at turn-on at the start-up, reduce the turn-on loss, and allow the collector current to flow within the maximum current rating of the semiconductor switching element such as IGBT. The power supply voltage to the drive circuit is also reduced, and power consumption can be reduced. In addition, the power consumption of the second DC power supply circuit can be reduced.

  Further, when the on-time of the semiconductor switching element (IGBT) is long, the current flowing through the heating coil also increases and the collector current of the semiconductor switching element also increases. However, since the output voltage of the first DC power supply circuit is the first voltage set value, the gate voltage input to the gate terminal of the IGBT via the drive circuit becomes high, so that the collector-emitter between the IGBT The saturation voltage becomes lower than that at the second voltage set value, and the steady loss of the IGBT can be reduced. When the on-time of the IGBT is long, the turn-on voltage is almost zero, and the turn-on loss hardly occurs.

  In other words, the loss of the semiconductor switching element is largely classified into a turn-on loss, a steady loss, and a turn-off loss, but the ratio of these three losses changes according to the length of the on-time of the semiconductor switching element. Therefore, the pan is induction-heated by setting the voltage setting value of the output voltage of the first DC power supply circuit that supplies power to the drive circuit and the second DC power supply circuit according to the length of the ON time of the semiconductor switching element. In this case, the power consumption of the drive circuit and the second DC power supply circuit can be reduced.

  The rice cooker of the present invention switches the output voltage of the first DC power supply circuit according to the length of the on-time of the semiconductor switching element, and operates the drive circuit and the control unit for driving the semiconductor switching element. Since the power consumption of the second DC power supply circuit can be reduced, the power consumption can be reduced even when the pot is induction-heated.

Main part block diagram of rice cooker in Embodiment 1 of this invention Cross-sectional configuration diagram of main parts of the rice cooker in Embodiment 1 of the present invention Main part block diagram of first DC power supply circuit in Embodiment 1 of the present invention The graph which showed the relationship between the ON time of the semiconductor switching element of the rice cooker in Embodiment 1 of this invention, and the collector current which flows into a semiconductor switching element The graph which showed the relationship between the collector-emitter voltage and collector current of IGBT which comprise the semiconductor switching element of the rice cooker in Embodiment 1 of this invention. (A) in Embodiment 1 of the present invention is a voltage waveform diagram of both ends of an AC power source (b) is an output pulse waveform diagram of a zero voltage synchronization signal output circuit (c) is an on-time waveform diagram set by an on-time setting unit ( (d) is an analog voltage waveform diagram output from the voltage detection circuit at both ends (e) is an envelope waveform diagram of the collector voltage (CE) terminal of the IGBT (f) is an output voltage waveform diagram (g) of the first DC power supply circuit Output control signal waveform diagram of the first DC power supply voltage setting unit (A) in Embodiment 1 of the present invention is a time chart of the bottom temperature detected by the temperature detector (b) is a time chart of the ON time of the switching means Main part block diagram of rice cooker in Embodiment 2 of this invention

A first invention is a heating coil for induction heating a pan, an inverter circuit having a semiconductor switching element connected to the heating coil and conducting and blocking the heating coil, and an AC power source rectified to supply power to the inverter circuit A rectifier circuit, a drive circuit that turns on and off the gate terminal of the semiconductor switching element, and a control unit that controls on and off of the semiconductor switching element via the drive circuit;
A first DC power supply circuit that converts the AC power supply into a DC power supply; and a second DC that is supplied with a power supply voltage from the first DC power supply circuit and has a voltage lower than the output voltage of the first DC power supply circuit. A power circuit,
The control unit is supplied with a power supply voltage from the second DC power supply circuit,
The first DC power supply circuit has a plurality of output voltages, the drive circuit is supplied with a predetermined output voltage from the first DC power supply circuit according to a control signal of the control unit, and the control unit When the ON time of the semiconductor switching element is a predetermined time or more, the output voltage of the first DC power supply circuit is set to a first voltage setting value lower than the maximum rated voltage of the gate terminal of the semiconductor switching element of the semiconductor switching element When the ON time of the semiconductor switching element is shorter than a predetermined time, by setting the output voltage of the first DC power supply circuit to a second voltage setting value lower than the first voltage setting value,
When the on-time of the semiconductor switching element is short, the steady loss of the IGBT is only slightly increased, so that the turn-on loss can be reduced and the power consumption of the drive circuit and the second DC power supply circuit can be reduced. The steady loss of the IGBT can be reduced, and almost no turn-on loss occurs. Therefore, the ratio of the three losses of the turn-on loss, steady loss, and turn-off loss changes according to the length of on-time of the semiconductor switching element, and the drive The consumption of the drive circuit and the second DC power supply circuit even when the pan is induction heated by setting the voltage setting value of the output voltage of the first DC power supply circuit that supplies power to the circuit and the second DC power supply circuit Electric power can be reduced.

  2nd invention stops especially the heating sequence for induction heating of the operation part according to the rice cooker of 1st invention according to the rice cooking sequence or heat retention sequence set by the said operation part, and the said heating sequence The control unit discriminates the standby state, and when the control unit discriminates the standby state, the output voltage of the first DC power supply circuit is set to the second voltage set value to drive in the standby state. The power consumption of the circuit and the second DC power supply circuit can be reduced.

  The first aspect of the third invention is to determine whether the detection voltage of the voltage detection circuit that detects the output voltage of the first DC power supply voltage is higher than the first predetermined value, particularly in the rice cooker of the second aspect of the invention. And a second determination value for determining a second predetermined value lower than the first determination value, and the control unit is configured to detect the voltage detection circuit when the ON time of the semiconductor switching element is shorter than the predetermined time. When the output voltage is lower than the second determination value, the semiconductor switching element is turned off. When the on-time of the semiconductor switching element is a predetermined time or more, the detection voltage of the voltage detection circuit is lower than the first determination value. By turning off the semiconductor switching element, the power supply voltage to the drive circuit can be optimized depending on the on-time of the semiconductor switching element, and the loss of the semiconductor switching element is prevented from becoming excessive. Since it is possible to provide a safe induction heating cooker.

In the fourth invention, in particular, when the control unit of the first invention makes the on-time of the semiconductor switching element larger than a predetermined time, the output voltage of the first DC power supply circuit is changed from the second voltage setting value to the second voltage setting value. The amount of change in the power supply voltage of the first DC power supply circuit can be taken into account by changing the voltage to one voltage setting value and making the on-time of the semiconductor switching element longer than a predetermined time after a certain time or more has elapsed. Since the power supply voltage of the drive circuit can be surely set to the first voltage setting value when the ON time of the switching element is set to a predetermined time or longer, the input voltage to the gate terminal of the semiconductor switching element is increased, and the semiconductor switching element (for example, The saturation voltage between the collector and emitter of (IGBT) can be reduced. That is, it is possible to prevent a voltage from being applied to the gate terminal of the semiconductor switching element at a second voltage setting value lower than the first voltage setting value, and the saturation voltage is high when a large current flows through the semiconductor switching element. It is possible to prevent the steady loss from increasing.

  In particular, the fifth invention has a cooling fan for cooling the semiconductor switching element according to any one of the first to fourth inventions, and power to the cooling fan is supplied from the first DC power supply circuit. When the on / off control of the cooling fan is performed by the control unit, when the on-time of the semiconductor switching element is short, the output voltage of the first DC power supply circuit is lowered to the second voltage set value. Therefore, the rotation speed or the air volume of the cooling fan decreases. However, the loss of the semiconductor switching element is short because the on-time is short and the current value of the semiconductor switching element is also low, so the loss of the semiconductor switching element is small. Can be cooled. Therefore, when the ON time of the semiconductor switching element is shorter than the predetermined time, the output voltage of the first DC power supply circuit can be lowered to the second voltage set value, so that the power consumption of the drive circuit and the second DC power supply circuit Power consumption and power consumption of the cooling fan can be reduced.

  Further, when the ON time of the semiconductor switching element is longer than the predetermined time, the output voltage of the first DC power supply circuit can be increased to the first voltage set value, so that a large current flows through the semiconductor switching element and the loss increases. However, since the number of rotations of the cooling fan is increased and the air volume is increased, the semiconductor switching element can be sufficiently cooled.

  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: shows the principal part block diagram of the rice cooker in the 1st Embodiment of this invention.

  In FIG. 1, the pan 1 is not particularly shown, but is composed of a laminate using a plurality of magnetic metals and nonmagnetic metals.

  Although not shown in particular, the heating coil 2 includes a first heating coil that faces the center of the bottom surface of the pan 1 and a second heating coil that faces the corner portion of the bottom surface of the pan 1. The first heating coil and the second heating coil are electrically connected in series. The first heating coil has a spiral shape and is arranged at a constant distance in the center of the bottom surface of the pan 1. The second heating coil is disposed on the concentric outer side of the first heating coil, and is disposed at a certain distance from the corner portion of the bottom surface of the pan 1. The heating coil 2 is constituted by a wire obtained by twisting more than 20 litz wires, each of which is a bundle of a plurality of copper wires, and makes the current distribution uniform when a high-frequency current flows.

  The inverter circuit 3 includes a capacitor 4, a semiconductor switching element 5, and a diode 6. The inverter circuit 3 turns on and off the semiconductor switching element 5 to supply high-frequency power to the heating coil 2 of the resonance circuit composed of the heating coil 2 and the capacitor 3 described later, thereby inductively heating the pot 1.

  The capacitor 4 is connected in parallel to the heating coil 2 as shown in FIG. In this embodiment, a polypropylene capacitor is used which has little loss even when a high frequency current flows.

  The semiconductor switching element 5 is composed of a semiconductor element such as a MOSFET or an IGBT. MOSFETs and IGBTs have high withstand voltage, can be switched at 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. is there. In this embodiment, an IGBT is used for this semiconductor element.

  The diodes 6 are connected in parallel so that a current flows in a direction opposite to the current direction of the semiconductor switching element 5.

  Generally, such a configuration of the inverter circuit is called a one-stone voltage resonance type inverter because the heating coil 2 and the capacitor 3 form a parallel resonance circuit.

  The AC power supply 7 supplies power to the rice cooker, and the power supply frequency is 50 Hz in the eastern Japan region and 60 Hz in the western Japan region.

  The rectifier circuit 8 includes a diode bridge 9, a coil 10, and a capacitor 11. Here, the capacity of the capacitor 11 is as small as several μF, and ripple occurs when a current is passed through the heating coil 2. In this embodiment, this ripple voltage waveform is the same as the voltage waveform when the AC power supply 7 is full-wave rectified.

  The control unit 12 includes a microcomputer 13, a synchronization signal generation circuit 14, and a both-end voltage detection circuit 15, and performs on / off control of the semiconductor switching element 5 via the drive circuit 11.

  The drive circuit 11 is composed of a push-pull circuit composed of an NPN transistor and a PNP transistor (not shown), and applies a voltage to the gate terminal of the IGBT constituting the semiconductor switching element 5 while the output from the microcomputer 13 is high. When the voltage is applied, the IGBT is turned on, and the voltage at the gate terminal of the IGBT is set to 0 V while the output is low, the IGBT is turned off. Note that this is an example, and the components constituting the push-pull circuit may be constituted by MOSFETs or the like. The operation of the drive circuit 11 will be described in detail later.

  The both-end voltage detection circuit 15 is a circuit that detects the voltage across the semiconductor switching element 5, a resistance voltage dividing circuit that divides the (CE) terminal by a plurality of resistors at a predetermined voltage dividing ratio, and an output of the resistance voltage dividing circuit It comprises an emitter follower circuit for peak-holding the voltage, and outputs an analog voltage to the AD conversion port of the microcomputer 13.

  The synchronization signal generation circuit 14 is composed of a comparator, a resistance voltage dividing circuit, and the like, and compares the voltage obtained by dividing the (C2) terminal by a predetermined ratio and the voltage obtained by dividing the (CE) terminal by a predetermined ratio. The high signal is output to the microcomputer 13 when the divided voltage at the terminal (C2) is higher, and the low signal is output to the microcomputer 13 when the divided voltage at the terminal (C2) is lower. To do.

  The microcomputer 13 configures an on-time setting unit 17, a pulse generation unit 18, a both-end voltage setting value 19, a first DC power supply voltage setting unit 20, etc. using a number of counter functions, timer functions, and memory functions. ing.

When the pulse generation unit 18 detects the synchronization signal of the synchronization signal generation circuit 14, the pulse generation unit 18 outputs a high pulse of the set on-time to the drive circuit 11. In the present embodiment, the microcomputer 13 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 18 composed of the microcomputer 13 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 17 changes the output data (8 bits) by 1 digit, the high pulse width of the pulse generation unit 18 is changed by 0.125 μs. In addition, the microcomputer 13 constitutes a rice cooking process control function for controlling the rice cooking process.

  As the both-end voltage setting value 19, a plurality of values are stored for each heating sequence to be described later using the memory of the microcomputer 13, and the both-end voltage setting value 19 of the semiconductor switching element 5 is previously stored in the ROM. .

  The on-time setting unit 17 sets the on-time by comparing the output value of the both-end voltage detection circuit 15 and the both-end voltage setting value 19. The on-time setting unit 17 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 inverter circuit 3 is activated, it starts from Ton1 and gradually increases the on time.

  The first DC power supply voltage setting unit 20 stores a first voltage setting value 22 and a second voltage setting value 23 in order to set a voltage output from the first DC power supply circuit 21, and the ON time Based on the ON time set by the setting unit 17, the set value of the output voltage of the first DC power supply circuit 21 is determined and controlled. In the present embodiment, the first voltage set value 22 is set when the on time is equal to or longer than the on time Tons, and the second voltage set value 23 lower than the first voltage set value is set when the on time is less than the tons Tons. I am trying to set it.

  Although not shown in particular, the first DC power supply circuit 21 is configured by a switching power supply, and a voltage obtained by half-wave rectifying the AC power supply 7 is set by the first DC power supply voltage setting unit 20 configured by the microcomputer 13. The output voltage is converted to DC power. Since the semiconductor switching element 5 is not driven immediately after the AC power supply 7 is input, the first DC power supply voltage setting unit 20 outputs the second voltage set value 23 as the set value to the first DC power supply circuit 21, The DC power supply circuit 21 controls the output voltage to be 10V.

  In the present embodiment, the guaranteed variation value of the cutoff voltage of the gate terminal of the IGBT constituting the semiconductor switching element 5 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 set to 10 V is that the collector-emitter voltage of the IGBT is sufficiently turned on even if the cut-off voltage varies. That is, it is important that the second voltage setting value 23 is set so that the output voltage of the first DC power supply circuit 21 is higher than the cutoff voltage of the gate terminal.

  The first DC power supply circuit 21 also supplies power for driving the cooling fan 24. Although not particularly shown in the present embodiment, the cooling fan 24 can be driven or stopped by turning on and off the transistors and MOSFETs as the fan drive circuit by the microcomputer 13.

Here, the operation of the drive circuit 11 briefly described above will be described in a little more detail. The drive circuit 11 uses the power supply voltage of the first DC power supply circuit 21 while the output of the pulse generator 18 formed by the microcomputer 13 is high, and applies a voltage to the gate terminal of the IGBT that constitutes the semiconductor switching element 5. Is applied, the IGBT collector-emitter is turned on, and while the pulse generator 20 is outputting low, the voltage at the gate terminal of the IGBT is set to 0 V, and the collector-emitter of the IGBT is turned off. Note that this is an example, and the components constituting the push-pull circuit may be constituted by MOSFETs or the like. The output voltage of the first DC power supply circuit 21 used by the drive circuit 11 is based on the output voltage value of the first DC power supply circuit 21 based on the ON time set by the ON time setting unit 17 as described above. The voltage is set by the first DC power supply voltage setting unit 20.

  The second DC power supply circuit 25 is composed of an emitter follower circuit composed of an NPN transistor 26, a constant voltage diode 27, a resistor 28, and a capacitor 29, and steps down the first DC power supply circuit 21 to about 5V. The second DC power supply circuit 25 is a power supply for the microcomputer 13 and the zero voltage synchronization signal output circuit 30.

  Although not specifically shown, the zero voltage synchronization signal output circuit 30 has the (u) pole of the AC power supply 7 connected to the base terminal of the transistor through a resistor. The collector terminal of this transistor is connected to the second DC power supply circuit 25 through a resistor. (U) Low when the potential of the pole is higher than the other pole, and high when the potential is low. Output to. The microcomputer 13 inputs the voltage of the both-end voltage detection circuit 15 in synchronization with the output signal, and sets the on-time in the on-time setting unit 17 as compared with the both-end voltage setting value 19. The first DC power supply voltage setting unit 20 sets the output voltage of the first DC power supply circuit 21 to the first voltage set value 22 or the second voltage set value 23 based on the set ON time. Further, the microcomputer 13 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 30.

  The operation unit 31 includes a plurality of momentary switches. When each switch is pressed by the user, the microcomputer 13 detects that the switch has been pressed, and performs a predetermined rice cooking operation or heat insulation operation in accordance with each switch.

  The display unit 32 includes an LCD and a plurality of LEDs such as red, green, and orange. The microcomputer 13 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.

  FIG. 2 is a cross-sectional configuration diagram of a main part of the rice cooker according to the first embodiment of the present invention. In order to simplify the drawing, lead wires for electrical connection and screws for fixing components are omitted.

  In FIG. 2, the body (main body) 41 of the rice cooker is provided with a lid 42 covering its upper surface so as to be freely opened and closed. The housing portion 43 of the body 41 has the heating coil 2 disposed on the bottom and side portions thereof, and the ferrite cores 44 are disposed radially on the outer peripheral side of the heating coil 2. The heating coil 2 is a winding having a center substantially directly below the center of the bottom of the pan 1.

  The pan 1 is formed of a magnetic material such as stainless steel, iron, or copper. The pan 1 has a flange 45 protruding outward from the upper end opening, and the flange 45 is placed in a state of being lifted from the upper end of the storage unit 43 so as to be detachably stored in the storage unit 43. Therefore, the pan 1 has a gap between the storage portion 43 during storage.

  The temperature detection unit 51 that detects the temperature of the pan 1 is composed of a thermistor and is arranged at the approximate center of the bottom of the pan 1. Since the resistance value of the thermistor changes with temperature, a voltage dividing circuit is configured with this thermistor and a resistor having a predetermined resistance value, and the resistance value of the thermistor is analogized by supplying a predetermined voltage to both ends of the voltage dividing circuit. Can be converted to voltage. The microcomputer 13 shown in FIG. 1 estimates the temperature from this analog voltage using a built-in AD converter.

  The lid 42 includes a lid heating plate 46, a lid heater 47, and a first circuit board 48. The lid heating plate 46 is made of a metal such as stainless steel and is detachably set on the lid 42.

  The lid heater 47 is built in the lid 42 and heats the lid heating plate 46. The lid heater 47 is not particularly shown in FIG.

  The first circuit board 48 includes a switch, an LCD, a microcomputer 13 and the like.

  The body (main body) 41 of the rice cooker is also provided with a second circuit board 49, a take-up power cord storage unit 50, and a cooling fan 24.

  The second circuit board 49 is mounted with an IGBT, a capacitor 4, a diode bridge 9, a choke coil 10, a capacitor 11 and the like constituting the semiconductor switching element 5, although not particularly shown.

  The wind-up type power cord storage unit 50 can wind up the power cord using a stopper and a spring. The power cord is connected to the AC power source 7 and supplies power to the rice cooker. The power cord storage part 50 is electrically connected to the second circuit board 49 via a lead wire.

  The cooling fan 24 exhausts and air-cools the heat generated from the second circuit board 49, particularly the semiconductor switching element 5, and is constituted by a fan motor in which a fan is attached to the rotor of a DC brushless motor. As shown in FIG. 1, the cooling fan 24 is supplied with power from the first DC power supply circuit 21 and is controlled to be turned on / off by the microcomputer 13.

  The first circuit board 48 and the second circuit board 49 are not particularly shown, but are electrically connected by lead wires, and are turned on by the on-time setting unit 17 and the pulse generation unit 18 configured inside the microcomputer 13. The semiconductor switching element 5 is controlled to be turned on / off, and a high frequency current is supplied to the heating coil 2. The heating coil 2 generates an alternating magnetic field when a high-frequency current flows, and an eddy current flows in the pan 1 due to the alternating magnetic field, and the pan 1 generates heat.

  As mentioned above, the rice cooker of a present Example induction-heats the pan 1, and heats the cooking in the pan 1. Here, the cooked product is rice before cooking rice and water or cooked rice.

  FIG. 3 is a block diagram showing the main part of the first DC power supply circuit according to the first embodiment of the present invention.

  In FIG. 3, the first DC power supply circuit 21 includes a half-wave rectifying and smoothing circuit 61 and a switching power supply 64. The switching power supply 64 further includes a power semiconductor built-in control circuit 65, a coil 66, a smoothing capacitor 67, and an output. And a voltage detection circuit 68.

  The half-wave rectifying / smoothing circuit 61 uses the diode 62 and the capacitor 63 to half-wave rectify and smooth the AC power supply 7 and convert it to a DC voltage of about 141V. However, for example, the AC power supply 7 may be full-wave rectified and smoothed using a diode bridge.

  The switching power supply 64 receives power supply from the half-end rectifying / smoothing circuit 61 and outputs a DC voltage in the range of about 7V to about 20V. The switching power supply 64 includes a power semiconductor element control circuit 65 including a power semiconductor element (not shown) such as a MOSFET, and a control circuit that controls on / off of the power semiconductor element within a range of a predetermined current value, a coil 66, A smoothing capacitor 67 and an output voltage detection circuit 68 for feedback control of the power semiconductor built-in control circuit 65 so that the voltage of the capacitor 67 becomes a predetermined set value.

  The power semiconductor built-in control circuit 65 charges the capacitor 67 via the coil 66 by controlling on / off of the built-in MOSFET within a predetermined current value range.

  The output voltage detection circuit 68 includes a photocoupler (not shown), a zener diode of about 20 V, and a zener diode of about 10 V, and the output voltage for feedback control is switched by switching the two zener diodes. For example, when setting an output voltage of about 20 V, a photocoupler and a Zener diode are connected in series. When the voltage of the capacitor 67 exceeds 20V, the Zener diode for 20V is energized and the photocoupler is turned on to transmit to the power semiconductor built-in control circuit 65 that the output voltage has exceeded 20V. When the power semiconductor built-in control circuit 65 receives this signal, the switching operation of the built-in MOSFET is turned off, the power supply to the capacitor 67 is stopped, the voltage drops, and when it becomes lower than 20 V, the Zener diode for 20 V is energized. The photocoupler is turned off and the power semiconductor built-in control circuit 65 transmits that the output voltage is lower than 20V. When the power semiconductor built-in control circuit 9 receives this signal, it starts the switching operation of the built-in MOSFET and charges the capacitor 67 via the coil 66. When the output voltage is set to 10V, the same operation can be performed by connecting a photocoupler and a 10V Zener diode in series. The output voltage detection circuit 68 of the present embodiment is different from the voltage detection circuit shown in claim 3. This voltage detection circuit will be described later.

  In other words, in the present embodiment, the switching power supply 64 steps down the output voltage of about 141 V of the half-wave rectifying / smoothing circuit 61 to a DC voltage of about 10 V or about 20 V.

  The control unit 12 includes a microcomputer 13 and a transistor 69 for switching the detection voltage of the output voltage detection circuit 68.

  The transistor 69 switches the output voltage of the first DC power supply voltage circuit 21 by turning on and off according to the voltage setting value set by the DC power supply voltage setting unit 20 configured by the microcomputer 13.

  The second DC power supply circuit 25 is the same as that shown in FIG. 1, and a description thereof is omitted here.

  The microcomputer 13 of the induction heating rice cooker according to the present embodiment outputs high or low to the transistor 69 and switches the set value of the detection voltage of the output voltage detection circuit 68 constituting the first DC power supply circuit 21. . In the present embodiment, the microcomputer 13 outputs a low signal to the transistor 69 when the output voltage of the first DC power supply circuit 21 is set to about 20V, and the output voltage of the first DC power supply circuit 21 is set to about 10V. When setting, a high signal is output to the transistor 68.

  FIG. 4 is a graph showing the relationship between the ON time of the semiconductor switching element 5 and the collector current flowing in the semiconductor switching element 5 of the rice cooker according to the first embodiment of the present invention.

  As shown in FIG. 4, the collector current increases as the ON time increases. That is, when the on-time is short like Ton1, even if the voltage at the gate terminal of the IGBT constituting the semiconductor switching element 5 is lowered to increase the collector-emitter voltage, the switching loss does not increase so much. The on-time Tons for switching the output voltage of the first DC power supply circuit is set between Ton1 and Ton2.

FIG. 5 is a graph showing the relationship between the collector-emitter voltage and the collector current of the IGBT constituting the semiconductor switching element 5 of the rice cooker according to the first embodiment of the present invention.
The gate terminal voltage of the IGBT is 10V, (b) is a graph when the gate terminal voltage of the IGBT is 15V, and (c) is a graph when the gate terminal voltage of the IGBT is 20V.

  As shown in FIG. 5, the collector-emitter voltage and the collector current vary depending on the gate terminal voltage. Considering that the collector current increases as the on-time becomes longer as shown in FIG. 4, the collector current itself is lower when the on-time is short as in Ton 1, so that the gate terminal of the IGBT constituting the semiconductor switching element 5 is low. Even if the voltage is lowered to increase the collector-emitter voltage, it can be determined that the switching loss does not increase so much.

  FIG. 6: has shown the operation | movement waveform of the principal part of the rice cooker of the induction heating type rice cooker of the 1st Embodiment of this invention.

  In FIG. 6, (a) shows the voltage waveform across the AC power supply 7. (B) shows a pulse waveform output from the zero voltage synchronization signal output circuit 30 to the microcomputer 13. (C) shows the on-time set by the on-time setting unit 17. (D) shows an analog voltage waveform output from the both-end voltage detection circuit 15 to the microcomputer 13. (E) has shown the envelope waveform of the collector voltage (CE) terminal of IGBT which comprises the semiconductor switching element 5. FIG. (F) shows the output voltage waveform of the first DC power supply circuit 21. FIG. 3G shows a control signal output from the first DC power supply voltage setting unit 20 of FIG. 3 to the output voltage detection circuit 68 via the transistor 69. In FIG. 6G, a control signal is output so as to output the second voltage set value 23 when Hi, and a control signal is output so that the first voltage set value 22 is output when Lo. To do. That is, when the on-time of the on-time setting unit 17 is equal to or longer than Tons, Lo is output to set the first voltage set value 22, and when the on-time setter 17 is smaller than the on-time Tons, the second voltage lower than the first voltage set value is output. In order to set the voltage set value 23, a Hi output is set.

  6 will be described with reference to FIGS. 1 and 3. FIG.

  After a predetermined time from the low signal to high signal edge of the output signal of the zero voltage synchronization signal output circuit 30, the on time setting unit 17 compares the both-end voltage detection circuit 15 with the both-end voltage setting value 19, and updates the on-time. To go. More specifically, after a predetermined time (t = T3, T5, T7,...) After an edge (t = T2, T4, T6,...) From the low signal to the high signal of the output signal of the zero voltage synchronization signal output circuit 30. Then, the output voltage of the both-end voltage detection circuit 15 is read, and the on-time setting unit 17 compares the output voltage of the both-end voltage detection circuit 15 with the both-end voltage setting value 19 to change the on-time setting value. When the output signal of the zero voltage synchronizing signal output circuit 30 switches from low to high at the next timing (t = T4, T6,...), The on-time is updated to the changed value.

  For example, when the microcomputer 13 detects an edge at which the output signal of the zero voltage synchronization signal output circuit 30 in FIG. 6B switches from low to high at time T2 in FIG. 6, the edge is used as a trigger in the microcomputer 13. The counter measures the time using the period of the oscillator connected to the microcomputer 13. The output voltage of the both-end voltage detection circuit 15 in FIG. 6D is read by using the AD converter of the microcomputer 13 at the timing T3 when the measured time has passed for a predetermined time.

  The on-time setting unit 17 compares the detection voltage of the both-end voltage detection circuit 15 with the both-end voltage setting value 19, and if this detection voltage is lower than the both-end voltage setting value 19, the on-time setting unit 17 changes the on-time longer. However, this changed value is not used until the timing of the next edge T4 at which the output signal of the zero voltage synchronizing signal output circuit 30 switches from low to high.

In the induction heating type rice cooker of the present embodiment, the on-time of the semiconductor switching element 5 is set to Ton.
While the ON time is gradually increased from 1, the target ON time (Ton2 and Ton3) is controlled.

  First, at time T0, the on-time setting unit 17 sets the on-time of the semiconductor switching element 5 to be Ton1. Since the ON time Ton1 of the semiconductor switching element 5 is shorter than the predetermined value Tons, the first DC power supply voltage setting unit 20 sends a high signal to the output voltage detection circuit 68 via the transistor 69 as shown in FIG. Output. The output voltage detection circuit 68 is controlled so that the detection voltage is 10V based on this signal and the output voltage of the first DC power supply circuit 21 is 10V.

  Next, at time T1, the on-time setting unit 17 compares the both-end voltage setting value 19 with the output voltage of the both-end voltage detection circuit 15, and the on-time of the semiconductor switching element 5 is set to Tons. The first DC power supply voltage setting unit 20 determines that the set on-time is Tons, and changes the second voltage setting value 23 to the first voltage setting value 22. However, this change is not used until the timing of the edge T2 at which the output signal of the zero voltage synchronization signal output circuit 30 switches from low to high is reached in the same manner as the change timing of the on-time.

  At time T2, when the output signal of the zero voltage synchronization signal output circuit 30 in FIG. 6B switches from low to high, the on-time changed by the on-time setting unit 17 in FIG. The signal is updated to Tons, and a high signal is output from the pulse generator 18. Next, the microcomputer 13 outputs a low signal to the output voltage detection circuit 68 through the transistor 69 so that the output voltage of the first DC power supply circuit 21 is 20V, and the detection voltage is set to 20V. To do. Further, the microcomputer 13 starts measuring the timing for reading the output voltage of the both-end voltage detection circuit 15.

  At the timing T3 when the predetermined time has elapsed, the output voltage of the both-end voltage detection circuit 15 is read using the AD converter of the microcomputer 13 as in the case of T1, and the on-time setting unit 17 reads the both-end voltage detection circuit 15. The output voltage is compared with the both-end voltage setting value 19 and the output voltage is lower than the both-end voltage setting value 19 as shown in FIG. In FIG. 6, the ON time reaches between Tons and Ton2. The first DC power supply voltage setting unit 20 determines that the ON time set by the ON time setting unit 17 is greater than Tons, and holds the setting of the first voltage setting value 22. However, the changed on-time is not updated until the next timing T4 is reached.

  In the present embodiment, the output voltage of the first DC power supply circuit 21 gradually increases and reaches 20 V at time T3 as shown in FIG.

  At time T4, as in time T2, when the output signal of the zero voltage synchronization signal output circuit 30 in FIG. 6B switches from low to high, the on-time setting in FIG. 6C is substantially synchronized. The on-time changed by the unit 17 is updated, and the microcomputer 13 starts measuring the timing for reading the output voltage of the both-end voltage detection circuit 15.

  At time T5, the on-time of the semiconductor switching element 5 is updated. Similarly to the time T1, the output voltage of the both-end voltage detection circuit 15 is read using the AD converter of the microcomputer 13, and the on-time setting unit 17 outputs the output voltage of the both-end voltage detection circuit 15 and the both-end voltage setting value. 19 is compared, and the output voltage is lower than the both-end voltage setting value 19 as shown in FIG. In FIG. 6, the on-time reaches Ton2 at this time. The first DC power supply voltage setting unit 20 determines that the ON time set by the ON time setting unit 17 is greater than Tons, and holds the setting of the first voltage setting value 22. However, the changed on-time is not updated until the next timing T6 is reached.

  In the present embodiment, the power supply voltage of the AC power supply 7 in FIG. 6 (a) fluctuates during the period from T6 to T7, the voltage across the semiconductor switching element 5 rises, and at timing T7, FIG. 6 (d) Since the output voltage of the both-end voltage detection circuit 15 exceeds the both-end voltage setting value 19 as shown in FIG. However, this change value is not updated until the next timing T8. The first DC power supply voltage setting unit 20 determines that the changed ON time is longer than Tons, and holds the first voltage setting value 22.

  When the time T8 is reached, the ON time of the semiconductor switching element 5 is updated to a time shorter than Ton2, and the voltage across the semiconductor switching element 5 becomes a value lower than the voltage setting value 19 as shown in FIG.

  In addition, in the rice cooker of this Embodiment, if the 8-bit output of the on time setting part 17 changes, the high pulse period of the pulse generation part 18 will change.

  FIG. 7 shows a time chart of the temperature detection unit of the rice cooker and the on-time of the semiconductor switching element 5 according to the first embodiment of the present invention. (A) has shown the time chart of the pan bottom temperature which the temperature detection part detected. (B) shows a time chart of the ON time of the semiconductor switching element 5.

  In the time chart of the ON time of the semiconductor switching element 5 in FIG. 7B, the vertical time indicates the ON time of the semiconductor switching element 5, and the horizontal axis indicates that the semiconductor switching element 5 is turned ON / OFF by this ON time and the heating coil has a high frequency. The period during which current flows is shown.

  Operation | movement of the rice cooker of this Embodiment is demonstrated using FIGS.

  In S0 of FIG. 7, among the plurality of momentary switches (operation unit 31) mounted on the first circuit board 48 arranged in the lid of the rice cooker shown in FIG. When pressed, the microcomputer 13 shown in FIG. 1 detects a signal from the input operation unit 31 and starts a rice cooking sequence. The state before S0 is a state where the rice cooker is on standby, and the output voltage of the first DC power supply circuit 21 is set to the second voltage setting value 23 (about 10 V).

  The rice cooking sequence is composed of a plurality of subsequences. In this Embodiment, it is comprised by the pre-cooking process, the rice cooking amount determination process, the boiling maintenance process, and the additional cooking process.

  The period from S0 to S2 corresponds to the pre-cooking process. In the pre-cooking process, the high-frequency current is supplied to the heating coil 2 by setting the on-time of the semiconductor switching element 5 to Ton2 to a temperature at which water is easily absorbed by rice during the period from S0 to S1. At this time, the on-time of the semiconductor switching element 5 starts with Ton1 as an initial value, gradually increases the on-time, and finally reaches Ton2. Although the heating coil 2 is not particularly shown, it operates at about 40 kHz in the case of Ton2. The conduction ratio at which the heating coil 2 operates at 40 kHz is 10 seconds / 16 seconds.

  When the temperature detection unit 51 shown in FIG. 2 detects 60 degrees in S1, the microcomputer 13 sets the on-time of the semiconductor switching element 5 to Ton2 according to the preprogrammed contents, and the conduction ratio at which the heating coil operates at 40 kHz. And a temperature of about 60 ° C. is controlled to be maintained for a period until S2.

The period from S2 to S3 corresponds to the rice cooking amount determination process. In the rice cooking amount determination step, the on-time of the semiconductor switching element 5 is set to Ton3, and a high-frequency current is supplied to the heating coil 2.
Since the on-time is long, the current supplied to the heating coil also increases and the amount of induction heating increases. That is, the temperature of the pan 1 also rises rapidly. In the present embodiment, the elapsed time from the start of driving of the heating coil 2 by setting the on-time of the semiconductor switching element 5 to Ton3 until the temperature detection unit 51 detects 100 degrees (time from S2 to S3). Therefore, the microcomputer 13 determines the amount of rice cooking, and sets the conduction ratio of the heating coil 2 in the subsequent boiling maintenance process and the conduction ratio of the heating coil 2 drive in the additional cooking process.

  The period from S3 to S4 corresponds to the boiling maintenance process. In the boiling maintenance process, the microcomputer 13 sets the on-time of the semiconductor switching element 5 to Ton2, and drives the heating coil 2 with a conduction ratio of 10 seconds / 16 seconds. When the heating coil 2 is driven to continue induction heating of the pan 1, the water remaining in the pan 1 also evaporates, and the temperature of the pan 1 exceeds 100 degrees and reaches 130 degrees in S4. When the temperature detection unit 51 detects 130 degrees, the microcomputer 13 turns off the semiconductor switching element 5, stops driving the heating coil 2, ends the boiling maintenance process, and shifts to the cooking process.

  The period from S4 to S5 corresponds to the additional cooking process. In the reheating process, the microcomputer 13 sets the on-time of the semiconductor switching element 5 to Ton2, and performs high-frequency switching of the heating coil 2 at a conduction ratio of 2 seconds / 16 seconds. The microcomputer 13 counts the elapsed time from S4, and when S5 is reached, the rice cooking sequence is terminated, the buzzer is notified of the end of rice cooking, and the LED indicating the meaning of the rice cooking that constitutes the display unit 32 is extinguished. Shows that it has finished.

  At the same time, in S5, the microcomputer 13 starts a heat retention sequence, turns off the semiconductor switching element 5 until the temperature of the temperature detection unit 51 becomes lower than a predetermined temperature, and when the temperature becomes lower than the predetermined temperature, the semiconductor switching element 5 is turned on again. It is turned on and off, and the pan 1 is heated by induction so as to maintain this temperature.

  As described above, in FIG. 7, a plurality of ON times of the semiconductor switching element 5 are set as Ton2 and Ton3.

  Further, as shown in FIG. 7, when the semiconductor switching element 5 is controlled to be turned on / off and a high-frequency current is caused to flow through the heating coil 2, the on-time at the start-up of the semiconductor switching element 5 is set to Ton1, as shown in FIG. Then, the on time is gradually lengthened and the on time is set to Ton2 and Ton3.

  As described above, in the induction heating rice cooker according to the present embodiment, the first DC power supply circuit that supplies power to the drive circuit 11 that drives the semiconductor switching element 5 according to the length of the on-time of the semiconductor switching element 5. Since the power supply voltage of 21 is switched, when the ON time of the semiconductor switching element 5 is short and the energization current is small, the output voltage of the first DC power supply circuit 21 is lowered to reduce the power consumption of the drive circuit 21 and the second DC. The power consumption of the power supply circuit 25 can be reduced. Since the power supply voltage of the cooling fan 24 is also supplied from the first DC power supply circuit 21, the rotational speed and the air volume of the cooling fan 24 are reduced, but the energization current is small and the loss of the semiconductor switching element 5 is sufficiently small. Cooling can be achieved and the driving current of the cooling fan can be reduced. Therefore, the power consumption of the rice cooker can be reduced during the sequence.

Moreover, in the induction heating type rice cooker of this Embodiment, the period until the set value of the output voltage of the 1st DC power supply circuit 21 rises from the 2nd voltage set value to the 1st voltage set value is set from T2. Although the period up to T3 (about 12 ms) is set, the rise time varies depending on the constants of the power semiconductor built-in circuit 65, the coil 66, and the capacitor 67 constituting the first DC power supply circuit of FIG. Taking that into account, the fixed time from Tons to the on-time is increased to 100 ms.
It doesn't matter if it's about.

(Embodiment 2)
FIG. 8 is a main part block diagram of the rice cooker in the second embodiment of the present invention.

  In FIG. 8, the voltage detection circuit 81 is formed of a resistance voltage dividing circuit and outputs an analog voltage. At this time, the voltage dividing ratio of the resistance voltage dividing circuit is set so as not to exceed 4 V when the output voltage of the first DC power supply circuit 21 is 20 V.

  The control unit 82 includes a microcomputer 83, a synchronization signal generation circuit 14, a both-end voltage detection circuit 15, and the like.

  The microcomputer 83 includes an on-time setting unit 17, a pulse generation unit 18, a both-end voltage setting value 19, a first DC power supply voltage setting unit 20, and a first DC power supply voltage determination unit 84 configured by a counter or a memory. Yes.

  The first DC power supply voltage determination unit 84 stores a first determination value 85 and a second determination value 86 using the memory of the microcomputer 83.

  Other configurations are the same as those of the first embodiment, and a description thereof is omitted here.

  The operation of the induction heating rice cooker of FIG. 8 will be described.

  Similarly to the first embodiment of the present invention, when the first DC power supply voltage setting unit 20 sets the second voltage set value 23 according to the ON time set by the ON time setting unit 17, the first DC power supply The voltage determination unit 84 sets the second determination value 86 as the determination value. In the induction heating rice cooker of the present embodiment, the second determination value is set such that the output voltage of the first DC power supply voltage 21 is equivalent to 8V. When the microcomputer 83 inputs the output voltage of the voltage detection circuit 81 to the AD conversion port and detects a value lower than the second determination value 86, the microcomputer 83 stops the output pulse of the pulse generator 18 and turns off the semiconductor switching element 5. .

  When the ON time set by the ON time setting unit 17 becomes longer and exceeds Tons, the first DC power supply voltage setting unit 20 sets the first voltage setting value 22. The first DC power supply voltage determination unit 84 detects the information and sets the first determination value 85 as the determination value. In the induction heating type rice cooker of the present embodiment, the first determination value 85 is set such that the output voltage of the first DC power supply voltage 21 is equivalent to 15V. When the microcomputer 83 inputs the output voltage of the voltage detection circuit 81 to the AD conversion port and detects a value lower than the first determination value 85, the microcomputer 83 stops the output pulse of the pulse generator 18 and turns off the semiconductor switching element 5. .

  As described above, by determining the lower limit value of the output voltage of the first DC power supply circuit according to the ON time of the semiconductor switching element, the power supply voltage to the drive circuit is optimized by the ON time of the semiconductor switching element. Since it can suppress that the loss of a semiconductor switching element becomes excessive, a safe induction heating type rice cooker can be provided.

  As described above, the rice cooker according to the present invention is not only in the standby state in which the semiconductor switching element is turned off, but also during the rice cooking sequence or the heat retention sequence, the power consumption and control of the drive circuit without increasing the loss of the semiconductor switching element. Since the power consumption of the second DC power supply circuit serving as the power supply for the section can be reduced, it can also be applied to other cooking appliances.

DESCRIPTION OF SYMBOLS 1 Pan 2 Heating coil 3 Inverter circuit 5 Semiconductor switching element 7 AC power supply 8 Rectifier circuit 11 Drive circuit 12 Control part 21 1st DC power supply circuit 22 1st voltage setting value 23 2nd voltage setting value 24 Cooling fan 25 1st Second DC power supply circuit 81 Voltage detection circuit 82 Control unit 85 First determination value 86 Second determination value

Claims (5)

A heating coil for inductively heating the pan, an inverter circuit having a semiconductor switching element connected to the heating coil and conducting and blocking the heating coil, a rectifier circuit for rectifying an AC power source and supplying power to the inverter circuit, A drive circuit for turning on and off the gate terminal of the semiconductor switching element; and a control unit for controlling on and off of the semiconductor switching element through the drive circuit;
A first DC power supply circuit that converts the AC power supply into a DC power supply; and a second DC that is supplied with a power supply voltage from the first DC power supply circuit and has a voltage lower than the output voltage of the first DC power supply circuit. A power circuit,
The control unit is supplied with a power supply voltage from the second DC power supply circuit,
The first DC power supply circuit has a plurality of output voltages, the drive circuit is supplied with a predetermined output voltage from the first DC power supply circuit according to a control signal of the control unit, and the control unit When the ON time of the semiconductor switching element is a predetermined time or more, the output voltage of the first DC power supply circuit is set to a first voltage setting value lower than the maximum rated voltage of the gate terminal of the semiconductor switching element of the semiconductor switching element And a rice cooker that sets the output voltage of the first DC power supply circuit to a second voltage set value lower than the first voltage set value when the ON time of the semiconductor switching element is shorter than a predetermined time. The control unit discriminates the operation unit, the heating sequence for induction heating of the pan according to the rice cooking sequence or the heat retention sequence set in the operation unit, and the standby state in which the heating sequence is stopped, and the control unit The rice cooker according to claim 1, wherein when the standby state is determined, the output voltage of the first DC power supply circuit is set to the second voltage set value. A first determination value for determining whether or not a detection voltage of a voltage detection circuit for detecting an output voltage of the first DC power supply voltage is higher than a first predetermined value, and a second predetermined lower than the first determination value A second determination value for determining the value, and the control unit turns off the semiconductor switching element when the output voltage of the voltage detection circuit is lower than the second determination value when the ON time of the semiconductor switching element is shorter than a predetermined time. And the rice cooker of Claim 2 which turns off the said semiconductor switching element when the detection voltage of the said voltage detection circuit is lower than said 1st determination value when the ON time of the said semiconductor switching element is more than predetermined time. The control unit changes the output voltage of the first DC power supply circuit from the second voltage setting value to the first voltage setting value when the ON time of the semiconductor switching element is longer than a predetermined time, and a certain time or more elapses. The rice cooker according to claim 1, wherein the on-time of the semiconductor switching element is set longer than a predetermined time later. The cooling fan for cooling a semiconductor switching element is provided, the electric power to the said cooling fan is supplied from a 1st DC power supply circuit, and on / off control of the said cooling fan is performed by the control part. Or the rice cooker according to item 1.

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