JP2792962B2 - High frequency heating equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-frequency heating device such as a microwave oven which heats an object to be heated by intermittently oscillating a magnetron.

<Prior Art> Conventionally, a so-called microwave oven that performs cooking mainly by heating using microwaves generated from a magnetron has been used. Recently, however, fine heating control has been performed by program control. What has realized the raw thawing function and the rice cooking function for uniformly thawing the frozen material has come to be used.

A heating device used in a microwave oven applies a voltage from a commercial AC power supply to the primary side of a step-up transformer, and connects a high-voltage generating circuit that generates a high voltage to be applied to a magnetron to a secondary side of the step-up transformer. The electric power to be supplied to the heater of the magnetron is extracted from the heater winding, which is another winding provided on the secondary side of the step-up transformer. The high-voltage generating circuit includes a high-voltage capacitor and a rectifier circuit, and charges the high-voltage capacitor with a current through the rectifier circuit during a period in which the voltage from the boost transformer becomes a reverse voltage to the magnetron. Is applied to the magnetron during a period in which the voltage of the rectifier circuit becomes a forward voltage with respect to the magnetron (a voltage obtained by superimposing the voltage from the step-up transformer and the voltage across the high-voltage capacitor). It is like that.

When performing the heating operation with the maximum output, the magnetron may be continuously oscillated.For example, when thawing frozen foods, continuous microwave irradiation may cause dielectric loss between ice and water. Due to the difference, the partially thawed portion of the water is locally heated, causing uneven heating.
In order to prevent such uneven heating, conventionally, during the thawing operation, the magnetron is repeatedly oscillated / stopped,
The temperature of the object to be heated is made uniform by the heat transmission during the oscillation stop period.

For example, when oscillating / stopping is repeated in a device with a maximum output of 500 W, the magnetron is controlled to oscillate / stop so that the total oscillation time of the magnetron is, for example, 1/5 of the total operation time (as a result, the microwave The output is 100 W.), and if one cycle of the oscillation / stop is 25 seconds, the oscillation time of the magnetron is 5 seconds, and the pause is 20 seconds.

When such control is performed on the primary side of the step-up transformer, the energization of the heater and the application of the high voltage to the magnetron are performed at the same time. Therefore, the temperature of the heater after the application of the high voltage to the magnetron is increased. The magnetron cannot be oscillated for a few seconds until the height of the magnetron increases. Considering this so-called rise time, usually, the above-mentioned 5
In the case of performing the oscillation control in which the second oscillation is suspended for 20 seconds, it is necessary to set the ion time of the power supply voltage supplied to the primary side of the step-up transformer to 7 to 8 seconds and the off time to 17 to 18 seconds.

In such a configuration, for example, when the power supply voltage decreases from 100 V to 95 V, the output decreases by about 6% due to the decrease in the anode current of the magnetron. Further, the voltage applied to the heater of the magnetron is reduced due to this voltage drop, and the temperature rise is delayed. This causes the emission of electrons from the heater surface to be reduced, so that the oscillation rise time of the magnetron becomes longer, The oscillation time of the magnetron when performing the oscillation / stop control as described above is shorter than the expected time. Due to such an influence, when the oscillation / stop control is performed such that an output of, for example, 100 W is obtained when the power supply voltage is in a normal state, only an output of about 85 W can be obtained. Due to the remarkable drop in output due to the drop in power supply voltage, a problem occurs in detailed heating control by program control, and the above-described raw thawing function and rice cooking function cannot be exhibited properly.

If a transformer for supplying power to the magnetron heater is provided separately from the step-up transformer and the heater is always energized, a decrease in output is suppressed, but in this case, a transformer for the heater is required. Since special preparation is required, the number of parts increases and the cost increases.

Also, a switch inserted on the primary side of the step-up transformer for opening and closing the power supply voltage for controlling the oscillation of the magnetron has a large inrush current in which the excitation inrush current of the transformer and the load inrush current overlap. A large current capacity that can perform the switching operation stably is required. Further, there is a problem that a voltage drop occurs at a wiring portion having a small power supply capacity due to the large rush current, which adversely affects other devices.

Prior art which solved such a problem is Japanese Patent Publication No. 52-1293.
No. 1 and Japanese Patent Publication No. 52-12932. That is, in these prior arts, a high withstand voltage switch is provided on the secondary side of the step-up transformer, and the high withstand voltage switch controls opening and closing of a high voltage from a high voltage generating circuit to oscillate / stop the magnetron. I have. In such a configuration, the high breakdown voltage switch only requires a current capacity corresponding to the load inrush current. Also, since the voltage from the commercial AC power supply can always be supplied to the primary side of the step-up transformer, if the heater winding for extracting the voltage for the magnetron heater is provided on the secondary side, the heater is always energized. can do. Thereby, the oscillation / stop of the magnetron can be favorably performed. That is, there is no need to consider the time for the heater to rise, and the output does not fluctuate significantly even if the power supply voltage fluctuates.

<Problems to be Solved by the Invention> However, in this prior art, since the high-voltage switch directly opens and closes a high voltage applied to a magnetron, it is necessary to apply a highly reliable switch such as a vacuum switch. However, since such a high voltage switch is extremely expensive, there is a problem in practical use. Furthermore, since the power supply voltage is always applied to the primary side of the step-up transformer,
There is also a problem that unnecessary power loss due to iron loss of the step-up transformer and resistance loss in the heater and the heater winding is large.

Although a technique has been considered in which the power supply voltage to the primary side of the step-up transformer is controlled by a bidirectional thyristor so as to protect the high-voltage switch, such a technique has been proposed. The problem of degradation will occur.

Accordingly, the present invention solves the above-mentioned technical problem, and has a small output fluctuation due to a power supply voltage fluctuation, and is advantageous for cost reduction, and can contribute to reduction of power consumption. It is intended to provide a device.

<Means for Solving the Problems> In order to achieve the above object, a high-frequency heating apparatus according to the present invention provides a first secondary battery which extracts a high voltage obtained by boosting a voltage from an AC power supply and supplies the high voltage to a magnetron. A step-up transformer having a side winding and a second secondary winding for supplying power to a heater of the magnetron; a step-up transformer provided on a primary side of the step-up transformer and controlling opening and closing of a voltage from the AC power supply. 1 switching means, 2nd switching means provided on the secondary side of the step-up transformer for controlling opening and closing of a high voltage to be supplied to the magnetron, and control means for controlling the first and second switching means. The control means closes the first switching means to energize the heater during an oscillation stop period preceding the oscillation period of the magnetron, A first switching means to open, the closed and the second switching means immediately after, in which so as to close said first switching means this immediately.

<Operation> According to such a configuration, the first switching means is closed during the oscillation stop period preceding the oscillation period of the magnetron, and the power supply voltage from the AC power supply is supplied to the step-up transformer. Power is supplied from the second secondary winding of the transformer to the heater of the magnetron, whereby the temperature of the heater rises and the magnetron can be oscillated. When the temperature of the heater rises, the first switching means is opened once, and immediately after the opening of the first switching means, the second switching means is closed. As soon as the second switching means is closed, the first switching means is closed again. The period from the closing of the first switching means to the energization of the heater to the closing of the first switching means immediately after the closing of the second switching means is sufficiently short, and therefore the first switching means is closed. When the switching means is closed again and a high voltage is supplied to the magnetron from the first secondary winding of the step-up transformer, the temperature of the heater is already sufficiently high, so that the magnetron starts oscillating immediately. I do.

<Example> Hereinafter, an example will be described in detail with reference to the accompanying drawings.

FIG. 1 is an electric circuit diagram showing an electric configuration of a microwave oven which is an embodiment of the high-frequency heating device of the present invention. The AC voltage from the commercial AC power supply 1 is applied to the primary winding 3a of the step-up transformer 3 via the fuse 2 and the contact 11a of the first relay 11 as the first switching means. On the secondary side of the step-up transformer 3, a first secondary side winding 3b for supplying power to a high voltage generating circuit 5 for generating a high voltage to be applied to the magnetron 4 and a heater 4h for the magnetron 4 A heater winding 3c, which is a second secondary winding for power supply, is provided. The high-voltage generating circuit 5 includes a high-voltage capacitor 6 connected to the secondary winding 3b, a rectifier 7, and a contact 12a of a second relay 12, which is a second switching means. Then, a voltage appearing at both ends of a series circuit including the rectifier 7 and the contact 12a is applied between the anode and the cassort of the magnetron 4.

The operations of the first and second relays 11 and 12 are controlled by the control unit 8. The control unit 8 controls the operation of the entire electric range, and includes a microcomputer and its peripheral circuits. The control unit 8 is connected to an operation unit 9 provided on the entire surface of the microwave oven for selecting various functions including a raw thawing function and a rice cooking function. It is supplied from an AC power supply 1 via a step-down transformer 10.

Both the first and second relays 11 and 12 are energized to make contact 11
The operation when a and 12a are closed, that is, the operation during heating by normal continuous oscillation is as follows. During a period in which the voltage appearing on the secondary winding 3b of the step-up transformer 3 is a reverse voltage to the magnetron 4, a current flows through the rectifier 7, and at this time, the high-voltage capacitor 6 is charged. During a period in which the voltage appearing in the secondary winding 3b is a forward voltage with respect to the magnetron 4 (a reverse voltage with respect to the rectifier 7), this voltage and the voltage across the high-voltage capacitor 6 are superimposed. The voltage is applied between the cathode and the anode of the magnetron 4. By applying the half-wave rectified high voltage to the magnetron 4 in this manner, the magnetron 4
Oscillate to generate microwaves.

Next, an operation when the magnetron 4 is intermittently oscillated by opening and closing control of the first and second relays 11 and 12 will be described. When, for example, a raw thawing function or a rice cooking function is selected by operating the operation unit 9, the magnetron 4
The microwave output is controlled such that the oscillation operation is intermittently performed. FIG. 2 is a timing chart for explaining the operation when the magnetron 4 is intermittently oscillated. FIG. 2A shows the operation of the first relay 11,
FIG. 2 (b) shows the operation of the second relay 12, and FIG. 2 (c) shows the temperature change of the heater 4h of the magnetron 4.

At time t1, the first relay 1 is energized and the contact 11a
Is closed, power supply to the heater 4h of the magnetron 4 is started, and the temperature of the heater 4h rises as indicated by reference numeral A1 in FIG. 2 (c), whereby the magnetron 4 is ready to oscillate. Becomes At time t2 after a predetermined time (for example, 3 to 5 seconds) elapses from time t1 and the heater temperature becomes sufficiently high, the first relay 11 is deenergized and the contact 11
a is opened, whereby the temperature of the heater 4h is slightly lowered.
Time t3 (for example, time t2 to t
The period of 3 is set to about 0.1 to 0.2 seconds. ), The second relay 12 is energized and its contact 12a is closed. further,
Time t4 immediately after the contact 12a is closed (for example, time t4
The period from 3 to t4 is about 0.1 to 0.2 seconds. ), The first relay 11 is re-energized and the contact 11a is closed. As a result, during the period from time t4, the temperature of the heater
, And the high voltage from the high voltage generating circuit 5 is applied to the anode of the magnetron 4 by closing the contacts 11a and 12a.
When applied between the cathodes, the magnetron 4 starts oscillating.

At time t5, the first relay 11 is deenergized and its contact 11a
Is opened, and at a time t6 delayed from the time t6, the second relay 12 is deenergized to open its contact 12a.
During the period from time t5, power is not supplied to the step-up transformer 3, so that the heater 4h is not energized, so that its temperature decreases as indicated by reference numeral A3.

In the period from time t7, the same control as in the period from time t1 is performed. In this manner, the same operation as the operation in the period T1 from the time t1 to t7 is repeated in the subsequent periods T2 and T3.

Both the first and second relays 11 and 12 are energized and the magnetron 4 oscillates during the period T _ON between times t4 and t5.
And one of the relays is deactivated T
_{When OFF} , the magnetron 4 does not oscillate. In this way, the maximum output Heating at twice the power will be performed.

As described above, in this embodiment, first, during the oscillation stop period preceding the oscillation operation period of the magnetron 4, the first relay 11
Is supplied to the heater 4h to raise its temperature to such an extent that the magnetron 4 oscillates immediately, and then the second relay 12 is activated to supply the high voltage from the high voltage generating circuit 5 to the magnetron 4. 4, so that the period T _ON
In this case, the magnetron 4 can be reliably oscillated.
Therefore, even when the power supply voltage from the commercial AC power supply 1 decreases, the microwave output only slightly decreases due to the decrease in the anode current of the magnetron 4 and does not undesirably decrease. . That is, the same effect as the conventional configuration in which the step-up transformer is always energized can be obtained. By suppressing the fluctuation of the microwave output in this way, the raw thawing function, the rice cooking function, and the like, which require detailed heating control, can be operated well.

In addition, prior to the oscillation period of the magnetron, the temperature of the heater is increased so that the magnetron can be oscillated reliably, so that the rise time caused by individual differences among a plurality of magnetrons does not vary.
The length of the oscillation period during the intermittent oscillation operation can be made constant. That is, the microwave output can be made constant regardless of the individual difference of the magnetron.

Further, since the power supply voltage is supplied only during a necessary period by controlling the first relay 11 instead of energizing the step-up transformer 3 all the time, iron loss, windings and heaters in the step-up transformer 3 are controlled. Unnecessary power loss due to resistance loss and the like in 4h can be prevented to contribute to a reduction in power consumption.

Further, when the contact 12a of the second relay 12 is closed / opened (for example, at times t3 and t6 in FIG. 2), the first relay 11 is closed.
Is open, the contact 12a of the second relay 12 is opened and closed in a state where no voltage is applied, and therefore, a second relay 12 having an extremely high withstand voltage is used. No need to use. This can contribute to cost reduction. In addition, there is no occurrence of a reverse voltage surge to the step-up transformer 3 when the second relay 12 is opened and closed.

Also, despite the soft start, magnetron 4
The transformer for energizing the heater 4h is a boost transformer 3
It is not necessary to prepare separately, and this can also contribute to cost reduction.

In the above-described embodiment, a relay is used as each of the first and second switching means. However, other switching means such as a bidirectional thyristor may be applied. Various other design changes can be made without changing the gist of the present invention. Furthermore, the present invention can be widely applied to a high-frequency heating device other than a microwave oven.

<Effects of the Invention> As described above, according to the high-frequency heating device of the present invention, during the oscillation stop period preceding the oscillation period of the magnetron, the heater of the magnetron is energized to increase its temperature and the magnetron can oscillate immediately. Therefore, even if the power supply voltage is reduced, a problem such as a reduction in the length of the oscillation period does not occur, and thus fluctuations in the high-frequency output are suppressed.

In addition, since the supply of power from the commercial AC power supply to the boosting transformer is performed only for a necessary period by opening and closing control of the first switching means, power loss in the boosting transformer is minimized, and power consumption is reduced. Can be reduced.

Further, the opening and closing of the second switching means provided on the secondary side of the step-up transformer and controlling the supply of the high voltage of the magnetron is performed in a state where the first switching means is open. It is not required that the switching means operate at a high withstand voltage and have high reliability. This can contribute to cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram showing an electric configuration of a microwave oven which is an embodiment of a high-frequency heating device according to the present invention, and FIG. 2 is a timing chart for explaining its operation. It is a chart. 1 ... commercial AC power supply, 3 ... step-up transformer, 3 b ... 1st
, A heater winding (second secondary winding), 4 ... a magnetron, 5 ... a high voltage generating circuit, 8
... Control unit, 11... First relay (first switching means), 12... Second relay (second switching means)

Continued on the front page (72) Inventor Yukihiro Kitada 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Takahiro Hayashi 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. In-company (72) Inventor Naomi Sugihara 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-64-81191 (JP, A) JP-A-53-138560 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05B 6/68

Claims (1)

(57) [Claims] A high-frequency heating device in which a magnetron is intermittently oscillated to heat an object to be heated, wherein a high voltage obtained by boosting a voltage from an AC power source is taken out and a first voltage is applied to the magnetron. A step-up transformer having a secondary winding and a second secondary winding for supplying power to the heater of the magnetron; provided on the primary side of the step-up transformer, for opening and closing a voltage from the AC power supply. A first switching means for controlling; a second switching means provided on a secondary side of the step-up transformer for controlling opening and closing of a high voltage to be supplied to the magnetron; and controlling the first and second switching means. Control means for closing the first switching means during an oscillation stop period prior to the oscillation period of the magnetron. Energizing the first switching means, then opening the first switching means, closing the second switching means immediately thereafter, and closing the first switching means immediately thereafter. apparatus.