JPH03167778A - Microwave oven - Google Patents

Abstract

PURPOSE:To shorten the cooking time by limiting power supplied from a power supply circuit so that the high frequency output of a magnetron decided depending upon the temp. sensed by a temp sensor may become the output upper limit value, and thereby providing the variable high frequency output. CONSTITUTION:A temp. sensor 20 and an upper limit value output setting means 17 are installed, wherein the temp. sensor 20 is to sense the temp. of a heat emission part in a magnetron 3 or a power supply circuit 4 while the output upper limit value setting means 17 decides the output upper limit value on the basis of the temp. sensed by the temp. sensor 20. This enables high frequency outputting over the rated output power as long as the temp. of the heat emission part is low. That is, high output value is set if there is no obstacle in terms of temp. compensation. The supplied power from the power supply circuit 4 is controlled by the output control means 17 so that the high frequency output of the magnetron 3 will become the output upper limit value. This increases opportunity of operation at the output upper limit value over the rated output value, and shortens the time for cooking.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a microwave oven improved to shorten cooking time.

(Prior Art) In a microwave oven, power is supplied to a magnetron to output high frequency waves, but at this time, the magnetron, particularly its anode, generates heat. Furthermore, in the power supply circuit for the magnetron, a large current flows particularly through the primary side of the high-voltage transformer, so this portion also tends to generate heat. Furthermore, in a power supply circuit equipped with an inverter, the switching elements generate heat.

Conventionally, microwave ovens have been equipped with fans, etc. to cool down the heat-generating parts mentioned above in order to suppress the rise in temperature, but the electrical components mentioned above are stored in a narrow space such as the machine room of the microwave oven. Because of this, heat tends to accumulate, and there is a limit to its cooling effect. Therefore, conventionally, the high frequency output is suppressed in advance to a constant value (rated output) so that the temperature of the heat generating part does not exceed a predetermined value when the microwave oven is operated continuously.

(Problems to be Solved by the Invention) Incidentally, there has been a long-standing demand for microwave ovens to be able to cook food in a short time. In order to shorten the cooking time, it is possible to increase the high frequency output, but this is not possible in the past because the output upper limit value is fixed at a constant value (rated output value) for temperature compensation.

The present invention has been made in view of the above circumstances, and its purpose is to provide a microwave oven that can change the high frequency output to higher than the rated output as necessary while ensuring temperature compensation, thereby shortening the cooking time. is to provide.

[Configuration of the Invention (Means for Solving the Problems) The present invention has been made with attention to the following points. That is, when the microwave oven is not used continuously or when it is not operated continuously for a long time, the temperature of the heat generating part of the microwave oven is often considerably lower than the limit value. In such a case, even if the rated output is determined, there is actually no difference in temperature compensation even if the device is operated at a higher output.

Therefore, the present invention provides a magnetron, a power supply circuit that variably supplies power to the magnetron, a temperature sensor provided to detect the temperature of a heat generating part in the magnetron or the power supply circuit, and An output upper limit value setting means for determining an output upper limit value based on a temperature detected by a sensor, and an output control means for controlling the power supplied by the power supply circuit so that the high frequency output of the magnetron becomes the output upper limit value. It is what it is.

(Function) According to the above means, instead of setting an output upper limit value uniquely, a temperature sensor and an upper limit output setting means are provided, and the temperature sensor detects the temperature of the heat generating part in the magnetron or the power supply circuit. Since the output upper limit value setting means determines the output upper limit value based on the temperature detected by the temperature sensor, if the temperature of the heat generating part is low, it is possible to achieve a high frequency output higher than the rated output. In other words, a high output value is set if there is no problem in temperature compensation. Since the output control means controls the power supplied by the power supply circuit so that the high frequency output of the magnetron becomes the output upper limit value, the chances of operation at the output upper limit value higher than the rated output value increase. Cooking time can also be reduced compared to conventional methods.

(Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

First, in FIG. 1, reference numeral 1 denotes a power plug, which is connected to a power outlet (not shown), to which power lines la and lb are connected, and one power line 1a A power switch 2 is interposed therein. 3 is a magnetron, and 4 is a power supply circuit that supplies power to the magnetron 3.

This power supply circuit 4 will be described. 5 is a DC power supply circuit consisting of a diode bridge 6 and a smoothing capacitor 7, which converts a 100V commercial AC power supply into DC power. The DC output from this DC power supply circuit 5 is transmitted to the transformer 8
The primary coil 8a, the resonant capacitor, and the semiconductor switch.
The voltage is applied to an input circuit 11 which is connected to a transistor 10 which is a switching element. A magnetron drive circuit 12 is provided on the secondary coil 8b side of the transformer 8, and this includes a capacitor 13 and a diode 14.
It consists of a half-wave voltage doubler circuit with

In the power supply circuit 4 as described above, the transistor 1
0 is controlled on and off by an inverter control circuit 15 to excite oscillation in the inverter circuit 11 and change the current flowing through the inverter circuit 11.

The inverter control circuit 15 is configured to turn on and off the transistor 10 at optimal timing based on a signal from a current sensor 16 consisting of a current transformer provided in the inverter circuit 11, and also controls a microcomputer. It is also possible to change the on-state period of the transistor 10 based on a control signal given from a control circuit 17 which is included and purchased. And the inverter circuit 11
When the on-time of the transistor 10 is changed, the anode current 1a of the magnetron 3 changes and the magnetron 6
The on-time of the transistor IO is changed and controlled by the control circuit 17 via the inverter control circuit 15. In other words, this control circuit 17 performs output control as described later. It also functions as an output upper limit value setting means.

The control circuit 17 is configured to receive various switch inputs from a switch operation section 18. In addition to a start switch, a cancel switch, and a cooking time setting switch, the switches in this switch operation section 18 include an output setting switch, and these output setting switches include:
There is a "range strong" setting switch and a "range weak" setting switch. The settings made by these switches and the cooking time are displayed on the display 19.

On the other hand, 20 is a temperature sensor made of, for example, a thermistor, which is fixed to a heat radiation fin for radiating heat from the anode of the magnetron 3.
A temperature detection signal of 0 is given to the control circuit 17 via the sensor circuit 21 and the A/D converter 22. A digital signal output from the A/D converter 22 is given to the control circuit 7 as the detected temperature. In this microwave oven, the output value when the detected temperature reaches the upper limit temperature, that is, the rated output value, is 600W.

Now, the operation of the above-mentioned ti戊 will be explained together with the control function of the control circuit 17 with reference to FIG. Now, when the control circuit 17 receives an input from the output switch (either the "Range Strong" setting switch or the "Range Weak" setting switch) by the user (step Sl), the output value corresponding to the setting switch is set ( Step S2). For example, "Range Strong"
If it is a setting switch, set the output to the maximum value that is higher than the rated output value for this microwave oven, and set it to "Microwave Low".
If it is a setting switch, set the output to r200WJ. When the cooking time is input using the cooking time setting switch (step S3), the control circuit 17 sets the input cooking time as an initial value of a built-in subtraction counter (step S4). After that, when the start switch is operated (step S5), the temperature sensor 20
The detected temperature is read (step S6). The control circuit 17 has data in which the output upper limit value is set linearly with respect to the detected temperature (anode temperature) set in the memory section, and the output upper limit value is set during continuous operation at the detected temperature or the rated output. It is determined as a guideline how much margin there is for the temperature (temperature that serves as a guideline for the limit).

The control circuit 17 then sets the output upper limit value based on the read detected temperature (step S7).

Next, if the above-mentioned output setting value by the user is equal to or higher than the automatically set output upper limit value (step S8), the following operating output value is determined as the output upper limit value (step S9).
, the following operating output values are determined as the output setting values (step S10). Then, the control circuit 17 outputs a control signal to the inverter control circuit 15 so that the determined operating output value is achieved.
5 adjusts the high frequency output by changing the on time of the transistor 10 of the inverter circuit 11. Therefore, if the determined operating output value is the automatically set output upper limit value,
The output is controlled to reach the upper limit value. Therefore, if this output upper limit value exceeds the rated output, the cooking time can be shortened compared to when operating at the rated output. Further, in this case, since the temperature of the anode of the magnetron 3 has not reached the upper limit temperature, temperature compensation can be achieved without causing an abnormal temperature. Note that if the operating output value determined in this way is larger than the rated output, cooking proceeds quickly, so it is preferable to correct the cooking time. However,
In such a case (determined in step 512), the cooking time is corrected (step S13). After this, if the cancel switch is not operated (determined in step 514), the cooking time is not exceeded (determined in step 515).
, steps 86 to 515 described above are repeated.

As a result, when operating in the "Range Strong" setting mode, the operating output value is higher than the rated output depending on the initial temperature of the anode, as shown by the solid and broken lines in FIG. ! value. When the anode temperature increases due to operation, the upper limit temperature is gradually set lower and approaches the rated output.

Here, the reason why the output upper limit value based on the detected temperature is set as the actual operating output value in the "Range Strong" setting mode is that the purpose of the "Range Strong" setting by the user is to request high output. Therefore, there is often no problem even if the actual operating output exceeds the rated output.

In the above embodiment, the temperature of the anode of the magnetron 3 is detected by the temperature sensor 20, but heat generating parts other than the magnetron 3 include the primary coil 8a of the transformer 8 and the transistor 1 which is a semiconductor switching element.
Since 0 is possible, these temperatures may be detected.

FIG. 4 shows a second embodiment of the present invention, and this embodiment differs from the first embodiment, particularly in the configuration of the power supply circuit and output upper limit value setting means, and the temperature detection location of the temperature sensor.

That is, the power supply circuit 31 connects the high voltage transformer 32 to the power plug 1 connected to the power outlet.
In addition, the magnetron drive circuit 33 on the secondary side of the high voltage transformer 32 is provided with a plurality of half-wave voltage doubler capacitors 34a, 34b, 3, each having a different capacity.
4c, and this capacitor 34a. 34b,3
4c is selectively controlled by a control circuit 35 serving as an output control means. In this case, each capacitor 34a,
Since the capacities of 34b and 34c are different, the charging voltage is different, and as a result, the anode current of the magnetron 3 can be changed. Further, the temperature sensor 36 is composed of a thermistor with a negative characteristic, and is provided so as to be able to detect the temperature of the primary coil 32a of the high voltage transformer 32.

The temperature sensor 36 includes a sensor circuit 38 consisting of a voltage dividing circuit including a resistor 37 between the DC power supply terminal Vc and the ground. The voltage Vs at the connection point 38a in the sensor circuit 38 exhibits a higher voltage value as the temperature detected by the temperature sensor 36 is lower.

3 is an output upper limit value setting circuit as an output upper limit value setting means, which is constructed by connecting a volume 45 for output setting to a bridge 44 consisting of resistors 40, 41, 42, and 43 as shown in the figure. ing. The illustrated connection points 39a of the three output upper limit value setting circuits are connected to the connection point 38a of the sensor circuit 38 through a diode 46 in the forward direction. In this output upper limit value setting circuit 39, the output voltage Vj is given to the control circuit 35 as the output upper limit value via the A/D converter 47.

This output voltage Vj increases as the slider 45a of the volume 45 is moved in the direction of arrow A.

In this case, the voltage Vj is at the connection point 3 of the sensor circuit 38.
It is restricted by the voltage Vs of 8a and the forward voltage of diode 46. That is, when the temperature detected by the temperature sensor 36 is low and the sum of the voltage Vs at the connection point 38a and the forward voltage of the diode 46 becomes higher than the voltage Vj, the diode 4
6 is off.

Further, when the detected temperature is high and the sum of the voltage S at the connection point 38a and the forward voltage of the diode 46 becomes lower than the voltage VJ, the diode 46 is turned on. Therefore, when the heat generation temperature of the primary coil 32a of the high voltage transformer 32 is low, the diode 46 is turned off and the output setting value set by the user (including a value higher than the rated output value) is set as the output upper limit value, and conversely, When the heat generation temperature of the primary coil 32a is high, the diode 46 is turned on, and the output setting value set by the user is reduced by the sensor circuit 38. Note that when the detected temperature reaches the upper limit temperature, even if the output setting value set by the user reaches the maximum value, the output value can be suppressed to the rated output value.

Therefore, the same effects as in the first embodiment can be obtained in this second embodiment as well.

In each of the above-described embodiments, the output upper limit value is determined for the output setting by the user, but for example, a type of microwave oven in which the output setting is not made by the user can also be applied.

In addition, the present invention is not limited to the above embodiments, and can be implemented with various modifications without departing from the spirit thereof.

[Effects of the Invention] As is clear from the above description, the present invention includes a magnetron, a power supply circuit that variably supplies power to the magnetron, and a temperature detecting section of the heat generating part of the magnetron or the power supply circuit. an output upper limit value setting means for determining an output upper limit value based on the temperature detected by the temperature sensor; and a power supply circuit configured to set the high frequency output of the magnetron to the output upper limit value. With this, the high frequency output can be changed to higher than the rated output as necessary while ensuring temperature compensation, thereby shortening the cooking time. This has the effect of making it possible to achieve the desired goals.

[Brief explanation of the drawing]

1 to 3 show a first embodiment of the present invention, FIG. 1 is an electrical configuration diagram, FIG. 2 is a flowchart showing the control contents of the control circuit, and FIG. 3 is a change in the output upper limit value. It is a figure showing an example. FIG. 4 is a diagram corresponding to FIG. 1 showing a second embodiment of the present invention. In the figure, 3 is a magnetron, 4 is a power supply circuit, 10 is a transistor, 11 is an inverter circuit, and 17 is a control circuit (
20 is a temperature sensor, 31 is a power supply circuit, 35 is a control circuit (output control means), 36 is a temperature sensor, 39 is an output upper limit value setting circuit (
output upper limit value setting means).

Claims (1)

[Claims] 1. A magnetron, a power supply circuit that variably supplies power to the magnetron, a temperature sensor provided to be able to detect the temperature of the heat generating part of the magnetron or the power supply circuit, and the temperature detected by the temperature sensor. A microwave oven comprising: an output upper limit value setting means for determining an output upper limit value based on the output upper limit value; and an output control means for controlling the power supplied by the power supply circuit so that the high frequency output of the magnetron becomes the output upper limit value.