JPH09167680A - Control method of microwave heating and microwave generating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control a quantity of a microwave, and perform proper cooking by actuating a timer by detecting a start of oscillation of a magnetron, and impressing the microwave for a fixed time by this timer. SOLUTION: An actuating part 12 of a timer to control a start of a count of a timer 11 to turn off a timer switch 10, is provided. The actuating part 12 starts a count by actuating the timer 11 by generating, for example, a trigger pulse by information from an oscillation detector 4 to detect a start of oscillation of a magnetron. Therefore, time counted by the timer 11 is time after the magnetron starts oscillation, and microwave impressing time is accurately set. In an electromagnetic switch 15b, since a cooking switch 17 is normally a temporary contact type switch, a closed circuit of an exciting coil 15a is formed so that an electromagnetic switch 15 can maintain an on-condition even if the switch 17 separates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave heating control method and a microwave generation circuit used for the microwave heating control method, in which a substantial heating time such as food heating by a microwave oven is controlled to be constant. More specifically, the present invention relates to a microwave heating control method in which a timer is actuated after the magnetron actually oscillates to keep the heating time substantially constant, and a microwave generation circuit used therefor.

[0002]

2. Description of the Related Art For example, a microwave oven is set in a microwave oven by inverting a dipole in a dielectric body at a high frequency by an alternating electromagnetic field of microwaves emitted from a magnetron and utilizing the dielectric loss due to this inversion. It heats an object to be heated. Since it can heat an electrical insulator from inside the substance, it is conveniently used for heating food.

FIG. 3 shows an example of a conventional microwave generation circuit for a microwave oven. In FIG. 3, 1 is a power supply transformer, 1a is a heater power supply transformer for a low voltage section, and 1b is a high voltage transformer for a high voltage section. One end of the secondary coil 1c of the high-voltage transformer 1b is connected to ground, and the other end is connected to ground via a high-voltage capacitor 3 and a high-voltage diode 2 connected in series. The cathode 6a of the magnetron 6 is connected between the high voltage capacitor 3 and the high voltage diode 2, and the anode 6b of the magnetron 6 is connected to the ground. A control unit 5 is provided on the primary side of the power transformer 1, and is a control unit for turning on / off the power supply or changing the input voltage by a door switch, a timer switch, or the like, and an AC power supply.

The high voltage diode 2 and the high voltage capacitor 3
A half-wave voltage doubler rectifier circuit is configured by the dipole action of the magnetron 6. That is, when the direction of the current of the AC power supply 7 is the same as the forward direction of the high voltage diode 2, the current flows through the high voltage diode 2 and the high voltage capacitor 3 is charged. When the direction of the current of the AC power supply 7 is opposite to the forward direction of the high voltage diode 2, the current flows through the magnetron 6. At this time, the electric charge charged in the high-voltage capacitor 3 also discharges and flows.
Therefore, a double voltage is applied to the magnetron 6 with a half wave for each half cycle to form a half wave voltage doubler circuit.

When the magnetron 6 is oscillated with this configuration, microwaves are radiated from the magnetron 6, and the food is efficiently heated by the above-mentioned action of the microwaves. The type of food that is heated differs depending on the type of food, and the microwave is applied until the temperature reaches the specified temperature while setting the time depending on the type of food and measuring the temperature of the object to be heated. Is cooked by doing. This microwave control of heating has recently been computer-controlled, and when the user of the microwave oven selects a cooking mode (output level, heating time, etc.), the information is transmitted to the control unit 5 and automatically. This is performed by adjusting the power level from the AC power supply 7 on the primary side of the power transformer 1 and controlling the power application time by a timer.

The setting of the heating time by the conventional timer is
The timer is operated at the same time when the power switch is turned on by the control unit 5, and the time corresponding to the object to be heated is set from that time. That is, the cooking time is counted from the time when the voltage is applied to the magnetron 6 by the door switch or the timer switch.

[0007]

However, in the power supply transformer 1, as described above, the heater power supply transformer 1a for the low voltage portion and the high voltage transformer 1b for the high voltage portion are shared,
In recent microwave ovens, the primary side controller controls duty of controlling high voltage on / off, so that the heater voltage of the magnetron 6 and the high voltage of the anode are applied simultaneously. Therefore, even if a voltage is applied, the anode current of the magnetron does not flow until the cathode is heated, and the magnetron does not oscillate. That is, there is an unstable oscillation time of 2 to 4 seconds after the timer is activated and before the magnetron normally starts oscillation.

On the other hand, when the microwave oven is used for a long time, the degree of vacuum inside the magnetron may be lowered or the state of the heater may be changed, and the unstable oscillation time until the magnetron normally starts oscillating. Fluctuates, and
Variations of several seconds to 10 seconds occur. For example, when the automatic cooking time is 30 seconds, the oscillation start time needs to be 4 seconds at the beginning of the magnetron, and if it is delayed by 5 seconds due to long-term use, the effective heating time at the initial time is 26 seconds and delayed by 5 seconds. When the effective heating time is 21 seconds, the effective heating time is further reduced by 19% from the initial time. Further, the set value is reduced by 13% at the initial stage and by 30% after long-term use. Therefore, when cooking in a microwave oven with a pre-programmed automatic cooking function that is commercially available in recent years, even if you cook according to the automatic cooking program, the ideal finished state and the actual finished state will be obtained. A difference occurs depending on the state.

The present invention solves such a problem, and a microwave heating control method and a microwave generation circuit used therefor in which the state of completion of automatic cooking of microwave heating of a microwave oven or the like is made uniform and optimum cooking is possible. The purpose is to provide.

[0010]

A method for controlling microwave heating according to the present invention is a method for controlling microwave heating in which microwaves are applied to an object to be heated for a certain period of time to heat the object to be heated. Then, the timer is activated by detecting the start of oscillation of the magnetron, and the microwave is applied for a certain period of time by the timer.

The microwave generation circuit of the present invention generates a high voltage to be applied to the magnetron, a high-voltage transformer in which one end of the secondary coil is connected to the ground, and a primary side of the high-voltage transformer. A control unit for turning on / off a power source, a high-voltage capacitor and a high-voltage diode connected in series between the other end of the secondary coil of the high-voltage transformer and the ground, and a cathode connected between the high-voltage capacitor and the high-voltage diode. And a magnetron having an anode connected to the ground, and an oscillation detector for detecting the start of oscillation of the magnetron, and an operating portion for operating the timer in response to a signal from the oscillation detector is provided in the control portion. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a microwave heating control method of the present invention and a microwave generation circuit used therein will be described with reference to the drawings.

FIG. 1 is an explanatory diagram of an embodiment of a microwave generation circuit of the present invention, and FIG. 2 is an equivalent circuit diagram of an example of its control section. In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. An oscillation detector 4 detects the start of oscillation of the magnetron 6. The operation of the magnetron shows the same voltage-current characteristics as the Zener diode,
When a high voltage above a certain value is applied, the anode current suddenly flows and oscillation starts. This anode current value is set at the time of design by the capacitance value of the high voltage capacitor or the like. However, as described above, if the cathode 6a is not preheated sufficiently, the anode current does not flow and the oscillation does not occur. When the cathode 6a is sufficiently heated, the anode current suddenly flows and oscillation is started. Therefore, it is possible to easily know the oscillation of the magnetron by detecting that the anode current of the magnetron above a certain value starts to flow. However, the oscillation detector 4 may be another means such as directly detecting the generated microwave.

As described above, the magnetron operating circuit is a half-wave voltage doubler rectifying circuit, and when the direction of the current of the power supply 7 is the same as the forward direction of the high voltage diode 2, the high voltage diode 2 is used. Charge current 8 in the secondary coil 1c
Flows in the direction shown in the figure, and the high voltage capacitor 3 is charged. Further, in the half cycle in which the direction of the current of the power supply 7 is reversed, the current is in the reverse direction to the forward direction of the high voltage diode 2 and therefore does not flow to the high voltage diode 2 side, but via the magnetron 6 the anode current 9 of the magnetron. Is the secondary coil 1
Flow in the direction shown in the figure via c. At this time, the electric charge charged in the high voltage capacitor 3 is also discharged and contributes as the anode current (discharge current) 9 of the magnetron, and operates as a voltage doubler. Therefore, as shown in FIG. 1, the detection of the anode current for knowing the start of the magnetron oscillation is 2
The charging current 8 may be detected by interposing a small resistance constituting the oscillation detector 4 between the high voltage diode 2 on the side of the secondary coil 1c and the ground, or between the anode 6b of the magnetron and the ground (see FIG. It is also possible to directly detect the anode current (discharge current) 9 of the magnetron by interposing a low resistance in (see B of 1).

As described above, the oscillation of the magnetron can be known by detecting the anode current 9 of the magnetron or the charging current 8 to the high voltage capacitor 3, and the information detected by the oscillation detector 4 is fed back to the control unit 5. . For example, as shown in FIG. 2, the control unit 5 includes an electromagnetic switch 15 between the power source 7 and the primary side of the high voltage transformer 1b.
Is connected to the exciting coil 15 for opening and closing the electromagnetic switch 15.
a is connected to the power supply 7 via the timer switch 10, the door switch 16, the cooking switch 17, and the like.

According to the present invention, a timer operating unit 12 for controlling the counting start of the timer 11 for turning off the timer switch 10 is provided, and the timer operating unit 12 receives information from the oscillation detector 4 for detecting the oscillation start of the magnetron. By, for example, a trigger pulse is generated and the timer 1
It is characterized by activating 1 and starting counting. Therefore, the time counted by the timer 11 is the time after the magnetron starts oscillating, and the time to which the microwave is applied is set accurately. In FIG. 2,
In 15b, since the cooking switch 17 is usually a temporary contact type switch, even if the cooking switch 17 is released, the electromagnetic switch 1
5 is an electromagnetic switch that forms a closed circuit of the exciting coil 15a so that 5 can be maintained in the ON state. Timer 11
Is usually composed of a frequency synchronous motor, a frequency pulse counting type time counter and the like, and operates by the voltage from the power source 7, but its wiring is omitted in FIG.

In the operating portion 12 of the timer, the oscillation detector 4
Judge whether the peak value or average value of the voltage or current sent from has reached a preset reference level,
When the level is above the reference level, the magnetron starts oscillating normally, and the cooking time timer 11 is activated. That is, the magnetron starts to oscillate when the cathode is heated and a high voltage is applied and a constant anodic current begins to flow, but as long as the anodic current is small, normal oscillation is possible even if the anodic voltage is applied. No regular microwave is generated. On the other hand, when a normal anode current starts to flow, a normal microwave is generated and starts contributing to heating. Therefore, it is possible to know that normal microwaves are being generated by detecting that the anode current of a certain value or more has begun to flow. As a result, the charging current 8 flows in the first half cycle of the alternating current even if the temperature of the cathode has not risen sufficiently, but the anode current 9 of the magnetron does not flow until the temperature of the cathode rises.
Since the charging current 8 also does not flow thereafter, it becomes a small value on average and the timer 11 is not activated. By setting this reference level, the timer 11 can be set accurately after the oscillation of the magnetron is started.

In the above-mentioned example, in order to detect the anode current of the magnetron, a low resistance is inserted between the high voltage diode 2 on the side of the secondary coil 1c and the ground or between the anode 6b of the magnetron and the ground, and both ends of the low resistance are inserted. Although it was detected by voltage or shunt current, the anode current of the magnetron is also 300 if the resistance is about 0.1 to 1Ω near the ground.
It is as small as about 400 mA, can be taken out at a low voltage, and information on the high voltage side can be used as it is as a low voltage. However, if a line with an insulation coating such as a ferrite clamp is arranged around the line through which the charging current 8 or the anode current 9 flows and the magnetic field such as the anode current is detected and output as voltage or current, the circuit on the high voltage side Information on the oscillation of the magnetron can be easily obtained as a low-voltage signal without shutting off the signal. According to this method, even if it is not a low potential portion on the ground side, it can be taken out regardless of the high voltage. Therefore, for example, even if a ferrite clamp or the like is provided in the high voltage portion as shown by point A in FIG. It can be easily taken out as a low voltage signal.

Further, although the above-mentioned example is the case of the microwave oven, the present invention can be similarly applied to the heating using the microwave for food heating or industrial heating other than the microwave oven.

[0020]

As described above, according to the present invention, even in the case of automatic cooking under program control of a microwave oven or the like, the timer is activated after detecting that the magnetron actually starts oscillating. It is possible to accurately control the amount of microwave applied to an object to be heated such as food. As a result, appropriate cooking can be performed according to the type of object to be heated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a microwave generation circuit of the present invention.

FIG. 2 is an equivalent circuit diagram showing an example of a control unit in FIG.

FIG. 3 is a diagram illustrating a conventional microwave generation circuit.

[Explanation of symbols]

 1 Power Transformer 1b High Voltage Transformer 1c Secondary Coil 2 High Voltage Diode 3 High Voltage Capacitor 4 Oscillation Detector 5 Control Section 6 Magnetron 6a Cathode 6b Anode 11 Timer 12 Timer Operation Section

Claims (2)

[Claims] 1. A microwave heating control method for heating a material to be heated according to the material to be heated by applying microwaves for a predetermined time, wherein a timer is activated by detecting the start of oscillation of a magnetron. A method for controlling microwave heating in which microwaves are applied for a certain period of time by the timer. 2. A high voltage transformer for generating a high voltage to be applied to a magnetron, one end of a secondary coil of which is connected to ground, and a control unit which is provided on the primary side of the high voltage transformer and turns on / off a power supply by a timer. A high-voltage capacitor and a high-voltage diode connected in series between the other end of the secondary coil of the high-voltage transformer and the ground, and a cathode connected between the high-voltage capacitor and the high-voltage diode,
The magnetron has an anode connected to the ground, and an oscillation detector that detects the start of oscillation of the magnetron. An operating unit that operates the count of the timer in response to a signal from the oscillation detector is provided in the control unit. Microwave generation circuit.