JPH01144593A - Composite cooking utensil - Google Patents

Abstract

PURPOSE:To secure the safety of high-voltage circuit components by suppressing the level of the output set signal to the preset value or below until the input current to an inverter circuit exceeds a fixed value when high-frequency induction heating is started. CONSTITUTION:The input current to an inverter circuit 30 is detected by a current transformer 80, the DC voltage with the level corresponding to it is fed to a microcomputer MC 62 from a bridge rectifier 81. The MC 62 calculates the average value of r.m.s. value of the input current to the circuit 30 from the output of the rectifier 81 and increases the level of the output set signal when it is smaller than the preset value to increase the on period of a power transistor Tr35. The MC 62 decreases the level of the set signal when it is larger than the preset value to decrease the on period of the power transistor Tr35. When the on period of the Tr35 is increased, the high-frequency current flowing through a heating coil 50 or the primary coil 40a of the driving transformer of a magnetron 44 is increased, and the output is increased. When the on period is decreased, the output is decreased. No overload is thereby applied to elements of the circuit, the life of the elements is improved, and the safety of high-voltage circuit components can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a composite cooking device that enables high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker.

(Prior Art) Recently, a composite cooker equipped with an inverter circuit and capable of high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker has been developed and is being put into practical use.

This has the advantage of combining two heating functions, and due to the high frequency, the high voltage transformer is much lighter than that of a general microwave oven. It has the advantage of being small.

(Problem to be Solved by the Invention) By the way, in such a composite cooker, when starting heating, the output of the inverter circuit is increased to the set output, but when starting high-frequency dielectric heating, the magnetron heater is not fully activated. Because the magnetron is not heated properly, the magnetron's anode voltage increases, causing stress (overvoltage) on the surrounding high-voltage diodes and high-voltage capacitors.

That is, as shown in FIG. 5, at the start of high-frequency dielectric heating, the level of the output setting signal is raised to raise the output of the inverter circuit to the set output, but at this time the anode voltage of the magnetron becomes extremely high. Note that the input current refers to the current input to the inverter circuit.

Therefore, it is necessary to use expensive high-voltage circuit components such as high-voltage diodes and high-voltage capacitors that can withstand overvoltage, which is a major factor in increasing costs.

This invention was made in view of the above circumstances,
The purpose is to provide an excellent composite cooker that does not apply overvoltage to high-voltage circuit components, thereby ensuring sufficient safety of high-voltage circuit components, and that also enables cost reduction. It's about doing.

[Structure of the Invention] (Means for solving the problem) A means for controlling the output of an inverter circuit according to an output setting signal, a means for detecting an input current to the inverter circuit, and an output according to the detected current. A means for controlling the level of the setting signal and a means for suppressing the level of the output setting signal to a predetermined value or less until the detection current exceeds a certain value at the start of high-frequency dielectric heating are provided.

(Function) At the start of high-frequency dielectric heating, the level of the output setting signal is kept below a predetermined level until the input current to the inverter circuit exceeds a certain value.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a main body of the composite cooking device, which has a door 2 pivotably supported on the front surface so as to be freely openable and closable, and a top plate 3 on the upper surface.

A heating chamber (not shown) is provided in the main body 1 corresponding to the door 2, and a magnetron 44 (described later) is installed in the heating chamber.
High frequency radio waves are supplied from Furthermore, a turntable (not shown) for placing food is provided in the heating chamber.

Inside the main body 1 corresponding to the top plate 3, a heating coil 50, which will be described later, is arranged spaced apart and facing the lower surface of the top plate 3.
is provided.

A corner portion where the front surface and the top surface of the main body 1 are connected serves as an operating section 4. This operation section 4 is sloped for easy viewing and operation, and includes a tack plate key 5 for setting electromagnetic induction heating, a range key 6 for setting high frequency dielectric heating, and a tuck plate key 5 for setting high frequency dielectric heating. key 7, down key 8 for output setting, start key 9, cancel key 10,
A time setting knob 11 and a display 12 are provided.

The control circuit is shown in FIG.

20 is a commercial AC power supply, and a fuse 21 is connected to the power supply 20.
A door monitor switch (short switch) 22C is connected via the door switch 22a1, door switch 22b, and magnetron thermal 23. , power supply 20, fuse 21, door switch -22a1
A heating indoor lighting lamp (interior lamp) 24 is connected via the relay contact 72a, the main relay contact 71a, the door switch 22b1, and the magnetron thermal 23. A turntable drive motor 25 is connected in parallel to the heating interior illumination lamp 24.

A blower motor 26 for cooling the magnetron and heating coil is connected to the power source 20 via a fuse 21, a main relay contact 71a of the door switch 22a1, a door switch 22b1, and a magnetron thermal 23.

Furthermore, electric rA20, fuse 21, door switch 2
2a1 main relay contact 71a, door switch 22b1
Inverter circuit 30 via magnetron thermal 23
is connected.

The inverter circuit 30 includes a diode bridge 31, a choke coil 32 . It has a rectifier circuit consisting of a smoothing capacitor 33, and one end of each of the primary coil 40a and heating coil 50 of an eight-voltage transformer 40 is connected to the output end of the rectifier circuit. Then, the other end of the secondary coil 40 is connected to one end of the resonant capacitor 34 via the normally closed side of the relay contact (bidirectional contact) 73a, and the other end of the resonant capacitor 34 is connected to the other end of the rectifier circuit. are doing. Further, the other end of the heating coil 50 is connected to one end of the resonant capacitor 34 via the normally open side of the relay contact 73a.

In other words, when the relay contact 73a is not activated, the negative coil 4
A series resonant circuit is formed by Oa and the resonant capacitor 34. When relay contact 73a is activated, heating coil 50 and resonant capacitor 34 form a series resonant circuit.

The resonant capacitor 34 includes a switching element such as NP.
The collector and emitter of the N-type power transistor 35 are connected in parallel, and a damper diode (flywheel) 36 is connected in parallel. Note that the power transistor 35 and damper diode 36 are packaged into one.

The power transistor 35 excites the resonant circuit by turning on and off, thereby causing the primary coil 40a to
Alternatively, a high frequency current is caused to flow through the heating coil 50.

The secondary coil 40b of the high voltage transformer 4o is connected between the seven nodes and the cathode of the magnetron 44 via a voltage doubler rectifier circuit consisting of a high voltage capacitor 41 and ^ voltage diodes 42 and 43. The 7 nodes of the magnetron 44 are grounded, and the heater (cathode) is connected to the high voltage transformer 40.
is connected to the secondary coil 40C.

On the other hand, a primary coil of a step-down transformer 27 is connected to the power source 20 via a fuse 21 and a magnetron thermal 23, and a control unit 60 is connected to the secondary coil.

The control unit 60 controls the entire cooking device, and includes a power supply circuit 61, a microcomputer 62, a relay drive circuit 63, a D/A (digital/analog) converter 64, a timing circuit 65, an oscillation circuit 66, and a pulse width modulation circuit. A comparator 67 which is a circuit (PWM circuit),
It has a base drive circuit 68.

Relay drive circuit 63 drives main relay 71 and relays 72 and 73.

The D/A converter 64 issues an output setting signal of a voltage level corresponding to an output setting command from the microcomputer 62.

The timing circuit 65 is designed to minimize loss due to switching of the inverter circuit 30.
The voltage of the smoothing capacitor 33 and the collector voltage of the power transistor 35 are taken in, and the oscillation timing of the oscillation circuit 66 is determined accordingly.

Oscillator circuit 66 generates a sawtooth signal.

The comparator 67 pulse-width modulates the sawtooth wave signal generated from the oscillation circuit 66 using the output setting signal from the D/A converter 64.

The base drive circuit 68 turns on and off the transistor 35 of the inverter circuit 30 based on the output of the comparator 67.

Thus, the operating section 4 is connected to the microcomputer 62.

Roughly speaking, a current transformer 80 is provided on the input line to the inverter circuit 30. This current transformer 80
constitutes input current detection means together with a bridge rectifier 81 that rectifies its output, and the output of the bridge rectifier 81 is supplied to the microcomputer 62.

Next, the operation of the above configuration will be explained with reference to FIG.

The pot 51 is placed on the top plate 3, and the tack plate key 5 of the operating section 4 is pressed. Further, a desired cooking time is set using the time setting knob 11, and a desired output is set using the up key 7 or the down key 8.

At this time, the characters "tack plate" are displayed on the display 4, and the set cooking time is displayed numerically. Further, on the display 4, a number of light emitting elements corresponding to the set output light up.

When the start key 9 is pressed, the microcomputer 6
2 operates relays 71.73. When the relay 71 operates, the contact 71a is turned on, and an energizing path to the inverter circuit 30 and the propeller motor 26 is formed. relay 7
3 operates, the normally open side of the contact 73a closes and the heating coil 50 is selected.

Furthermore, the microcomputer 62 issues an output setting command based on the above setting output. This output setting command is D/
The A converter 64 converts the output setting signal into an analog value output setting signal, and supplies the signal to the comparator 67.

Further, an oscillation circuit 66 generates a sawtooth wave signal, which is pulse width modulated by a comparator 67.

That is, when the voltage of the output setting signal is higher than the voltage of the sawtooth wave signal, the output voltage of the comparator 67 is at a high level.

When the voltage of the output setting signal is lower than the voltage of the sawtooth signal, the output voltage of the comparator 67 is at a low level.

The output of the comparator 67 is amplified by a base drive circuit 68 and applied between the base and emitter of the power transistor 35.

When the power transistor 35 is turned on, current flows into the heating coil 50 through the collector and emitter of the power transistor 35. When the power transistor 35 is turned off, the current flowing through the heating coil 50 begins to charge the resonant capacitor 34. Then, current flows from the resonant capacitor 34 to the heating coil 50.

In this way, a high frequency current flows through the heating coil 50 by turning on and off the power transistor 35, and a high frequency magnetic field is emitted from the heating coil 50.

The high frequency magnetic field is applied to the pot 51 through the top plate 3, causing eddy currents to be generated in the pot 51. When eddy currents occur,
Vortex 2! 151 generates self-heating due to the leakage, and the food inside is heated. In other words, cooking begins.

The timing circuit 65 generates a trigger pulse at the intersection of the voltage of the smoothing capacitor 33 (rectified voltage) and the collector voltage of the power transistor 35, and triggers the oscillation circuit 66. As a result, the power transistor 35 is turned on with its own collector voltage being low, and the switching loss of the power transistor 35 can be reduced.

When the set cooking time has elapsed, the microcomputer 62
stops the operation of relays 71 and 73.

When the operation of the relay 71 stops, the contact 71a turns off,
The energizing path to the inverter circuit 30 is cut off. In other words,
This is the end of cooking.

Meanwhile, place the food on the turntable inside the heating chamber and open the door 2.
At the same time, the range key 6 of the operation unit 4 is pressed. Further, a desired cooking time is set using the time setting knob 11, and a desired output is set using the up key 7 or the down key 8.

At this time, the characters "range" are displayed on the display 4, and the set cooking time is displayed numerically.

Further, on the display 4, a number of light emitting elements corresponding to the set output light up.

When the start key 9 is pressed, the microcomputer 6
2 operates relays 71.72.

When relays 71 and 72 operate, contact 71a.

72a is turned on, and the inverter circuit 30. Heating interior lighting lamp 24. An energizing path is formed between the turntable drive motor 25 and the propeller motor 26.

Thus, the inverter circuit 30 operates in the same way as electromagnetic induction heating, and a high frequency current flows through the secondary coil 40a. Then, the voltage generated in the secondary coil 40b is voltage doubled and rectified and applied to the magnetron 44, so that the magnetron 44 performs an oscillating operation. When the magnetron 44 oscillates, high-frequency radio waves are supplied into the heating chamber, and high-frequency dielectric heating starts.

When the set cooking time has elapsed, the microcomputer 62
stops the operation of relays 71 and 72.

When the operation of the relay 71 stops, the contact 71a turns off,
The energizing path to the inverter circuit 30 is cut off. In other words,
This is the end of cooking.

By the way, when the inverter circuit 30 is in operation, the input current to the inverter circuit 30 is detected by the current transformer 80, and a DC voltage at a level corresponding to the detected current is supplied from the bridge rectifier 81 to the microcomputer 62.

The microcomputer 62 calculates the average value or actual value of the input current to the inverter circuit 30 from the output of the bridge rectifier 81, and changes the level of the output setting signal when the calculated value becomes smaller than the set value (corresponding to the set output). This increases the on-period of the power transistor 35. Conversely, when the calculated value becomes larger than the set value, the level of the output setting signal is lowered and the on period of the power transistor 35 is shortened.

When the on period of the power transistor 35 becomes longer, the high frequency current flowing through the heating coil 50 or the primary coil 40a becomes larger, and the output increases.

When the ON period becomes shorter, the high frequency current flowing through the heating coil 5o or the primary coil 40a becomes smaller, and the output decreases.

Therefore, during electromagnetic induction heating, even if the pot 51 is different from standard steel, the output can be maintained at the set output regardless of the difference. That is, the elements of the inverter circuit 30 are not overloaded, and the life of the elements is improved. Furthermore, proper heating is possible, and reliability can be significantly improved.

Furthermore, during high-frequency dielectric heating, the output can be maintained at the set output regardless of temperature changes in the magnetron 44.
Appropriate heating can be performed.

However, at the start of high-frequency dielectric heating, as shown in FIG. 4, the microcomputer 62 suppresses the level of the output setting signal below a predetermined value until the calculated value exceeds a certain value.

By controlling the level in this manner, it is possible to prevent the anode voltage of the magnetron 44 from becoming extremely high in a state where the heater of the magnetron 44 is not sufficiently heated.

Therefore, the high voltage capacitor 41 and the high voltage diode 42
．． No overvoltage is applied to 43, and the life of the high-voltage circuit components can be improved. In other words, there is no need to use expensive high-voltage circuit components that can withstand overvoltage.
This results in cost reduction.

In this case, when the heater of the magnetron 44 is sufficiently heated, the 7-node N flow begins to flow. When the anode current flows, the applied voltage stabilizes at a constant value due to the characteristics of the magnetron. During this period, the calculated value exceeds a constant value) S,
In response, the level suppression for the output setting signal is canceled.

Regarding this level suppression, since the input N flow is used as a reference, there is no variation in the characteristics of the heater of the magnetron 44.
Appropriate control is possible without being affected by Moreover, since the current transformer 80 for output control and the bridge rectifier are also used as the input current detection means, there is no cost problem.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without changing the summer days.

[Effects of the Invention] As described above, according to the present invention, there are provided a means for controlling the output of an inverter circuit according to an output setting signal, a means for detecting an input current to the inverter circuit, and a means for controlling the output of an inverter circuit according to an output setting signal. By providing means for controlling the level of the output setting signal and means for suppressing the level of the output setting signal below a predetermined level until the detected current exceeds a certain value at the start of high-frequency dielectric heating, overvoltage is not applied to high-voltage circuit components. Therefore, it is possible to provide an excellent composite cooker that can ensure sufficient safety of high-voltage circuit components and reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a control circuit in an embodiment of the present invention, FIG. 2 is an external perspective view of the same embodiment, and FIG.
FIG. 4 is a diagram showing the voltage waveforms of various parts in the figure, FIG. 4 is a diagram for explaining the operation of the same embodiment, and FIG. 5 is a diagram for explaining the conventional problem. DESCRIPTION OF SYMBOLS 1...Main body, 2...Door, 3...Top plate, 4...Operation unit, 30...Inverter circuit, 40...
... High voltage transformer, 44... Magnetron, 50...
- Heating coil, 60...control unit, 80...current transformer. Applicant's agent Patent attorney Takehiko Suzue Figure 2 B-v Cabinet - Ichika Figure 3

Claims (2)

[Claims] (1) In a composite cooker equipped with an inverter circuit and capable of high-frequency dielectric heating and electromagnetic induction heating, means for controlling the output of the inverter circuit according to an output setting signal and detecting the input current to the inverter circuit. and means for suppressing the level of the output setting signal below a predetermined value until the detected current exceeds a certain value at the start of high-frequency dielectric heating. (2) The output setting signal is set after the detected current exceeds a certain value.
2. The composite cooking device according to claim 1, wherein the level is controlled to a predetermined output depending on the detected current.