JP2010107110A - Electronic oven - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic oven that prevents deterioration in the usability for users, without being hypersensitive with respect to making apparatuses stop, as a protective function of high-durability electrical component, with respect to overvoltage, as compared with a semiconductor device. <P>SOLUTION: The electronic oven includes: a high-voltage power source of a high-frequency transmitter and a heater for heating foods; a cooling fan motor for cooling the electrical components and transformers for transforming power source voltage into a predetermined voltage which are connected to a power source in parallel; a voltage detection circuit for detecting power source voltage by the secondary-side voltage of the transformer; the voltage level of the voltage detection circuit; one or a plurality of set voltage levels stored, beforehand; a timer for measuring the time that exceeds the set voltage level; and a control circuit for controlling the high-voltage power source of the high-frequency transmitter, the heater and the cooling fan motor, based on the set voltage level and the time measured by the timer. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a microwave oven that controls a high-frequency oscillator and a heater and a cooling fan motor by a supplied commercial power supply voltage.

  FIG. 3 is a block diagram of a conventional microwave oven. A high frequency oscillator 102 for heating food is connected from a commercial power source through an inverter 101 that performs power control. Similarly, a commercial power supply is connected to a heater 103 that heats food and a low-voltage transformer 104 that supplies a predetermined voltage to the circuit.

  A rectifying element 105 that rectifies this output and a capacitor 106 that smoothes the rectified waveform are connected to the secondary side of the low-voltage transformer 104. A control circuit 108 is connected to a voltage detection circuit 107 that divides the voltage of the capacitor 106.

  The control circuit 108 controls a control signal to the inverter 101 and a relay 109 connected in series with the heater 103 by the input voltage from the voltage detection circuit 107.

  The control circuit 108 increases the ON / OFF duty of the relay when detecting that the power supply voltage is lower than the input voltage of the voltage detection circuit 107, and decreases the duty when the power supply voltage is higher than the input voltage of the voltage detection circuit 107. The power supply to the food is controlled to be constant.

  Further, in the case of automatic cooking programmed in advance, there is a microwave oven that performs power supply voltage correction so as to keep the quality of cooking constant by correcting the energization time of the heater 103 (see, for example, Patent Document 1).

Further, a power supply voltage detection means is provided in the inverter 101 itself that performs power control, detects an abnormal voltage due to external noise such as a lightning strike or an abnormal voltage generated at the time of spark, stops the switching element drive circuit, and switches the voltage current of the switching element. There is a microwave oven that prevents an increase in duty and prevents destruction of the inverter 101 itself (see, for example, Patent Document 2).
JP-A-7-35352 Japanese Patent Laid-Open No. 11-144860

  In the method described in Patent Document 1, a cooking condition is improved by correcting heating conditions in a normally used power supply voltage range. A high-voltage power supply that performs power control when an abnormal voltage is applied, a heater, and a cooling fan. It does not protect the motor.

  In the method described in Patent Document 2, a detection means for detecting an abnormal voltage is provided in an inverter that is one of high-voltage power supplies, and when the abnormal voltage is detected, the switching element drive circuit is stopped to increase the voltage / current duty of the switching element. This prevents the inverter from being destroyed.

  This is to prevent breakdown voltage breakdown of the switching element against an instantaneous abnormal voltage, and detects a transient change in voltage to stop the operation at or below the breakdown voltage breakdown voltage of the switching element.

  The present invention applies a long-time non-rated voltage to electrical components such as high-voltage power supplies, heaters, and cooling fan motors that do not lead to immediate failure even when a power supply voltage higher than that assumed in normal use is applied for a short time. It protects against malfunctions caused by

  The present invention relates to a high-frequency power source for a high-frequency oscillator that heats food, a cooling fan motor that cools an electrical component, a transformer that transforms a power supply voltage to a predetermined voltage, and a secondary side voltage of the transformer. A voltage detection circuit for detecting a power supply voltage, a voltage level of the voltage detection circuit, one or a plurality of preset voltage levels stored in advance, a timer for measuring a time exceeding the preset voltage level, a preset voltage level, A high-frequency power source for the high-frequency oscillator and a control circuit for controlling the heater and the cooling fan motor are provided according to the measurement time of the timer.

  According to the microwave oven of the present invention, a set voltage level and a measurement time can be provided for each load of the high-voltage power source of the high-frequency oscillator, the heater, and the cooling fan motor, so that control can be performed for each load. .

  In addition, the control circuit of the present invention sets a voltage level and a measurement time that exceed the power supply voltage assumed for normal use as one of the set voltage levels, and when the measurement time is exceeded, the high-voltage power supply and heater of the high-frequency oscillator The energization of at least one of the cooling fan motors is stopped.

  According to the microwave oven of the present invention, as a protection function of an electrical component having a higher resistance to overvoltage than a semiconductor element such as a high-voltage power supply or a heater or a cooling fan motor, it is sensitive to a single voltage abnormality caused by external noise such as a lightning strike. In addition, since the abnormality determination process can be omitted, it is possible for the user to maintain ease of use. Moreover, this predetermined time can be determined in view of the use conditions for each electrical component.

  According to the present invention, as a protection function for electrical components that are more resistant to overvoltage than a semiconductor element such as a high-voltage power supply or a heater or a cooling fan motor, it is highly sensitive to abnormal voltage detection due to external noise such as lightning strikes. Since the process can be omitted, it is possible for the user to maintain the usability.

  Moreover, it becomes possible to prevent the insulation material of the winding wire constituting the high-voltage transformer and the cooling fan motor from being broken due to abnormal heat generation against the application of the non-rated voltage for a predetermined time or longer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram of a microwave oven according to an embodiment of the present invention. In FIG. 1, a high frequency oscillator 3 is connected from a commercial power source to control food or via a relay 1 and a high voltage transformer 2 to heat food.

  Similarly, a heater 6 that heats food, a cooling fan motor 7 that cools electrical components, and a low-voltage transformer 9 that supplies a predetermined voltage to the control circuit 8 are connected from a commercial power source via relays 4 and 5. On the secondary side of the low-voltage transformer 9, a voltage detection circuit 10 is constituted by a rectifying element that rectifies the output, a capacitor that smoothes the rectified waveform, and a resistor that divides the voltage.

  In the present embodiment, the control circuit 8 is connected to and operates on the secondary side voltage formed by the low-voltage transformer 9. In the circuit diagram of the microwave oven according to the present embodiment, the description of the power supply circuit after the low-voltage transformer 9 is omitted.

  In such a configuration, when the food is heated by the heater 6, the control circuit 8 controls the relay 4 to turn the heater 6 on and off to heat the food in the heating chamber to a desired heating state. In the case of heating with microwaves, the relay 1 is turned on and power is supplied to the high-voltage transformer 2 to operate the high-frequency oscillator 3 to irradiate the food in the heating chamber with microwaves.

  The control circuit 8 controls the heating amount for the food by turning on and off the relay 1 to heat it to a desired heating state. The control circuit 8 turns on the relay 5 and operates the cooling fan motor 7 to cool the electrical components in the machine room when the temperature of the electrical room or the machine room storing the electrical components rises due to the heating operation of the food.

  FIG. 2 shows the relationship between the power supply voltage of the commercial power supply and the power supply voltage detection level obtained from the output of the voltage detection circuit 10. The control circuit 8 is connected in series with the high voltage power supply (high voltage transformer 2) based on the input voltage information (power supply voltage detection level) from the voltage detection circuit 10 in order to improve the quality of cooking against fluctuations in the power supply voltage. The ratio of the on / off time between the relay 1 and the relay 4 connected in series with the heater 6 is changed.

  When the power supply voltage is lower than the rated voltage (for example, AC100V), the ON time is lengthened by increasing the ON / OFF duty ratio, and when the power supply voltage is high, the ON time is shortened by decreasing the ON / OFF duty ratio. The food is controlled so that the amount of heating is kept constant, and the optimal cooking quality is achieved against differences in power supply voltage due to differences in the location of microwave ovens and fluctuations in power supply voltage.

  Such correction control by the voltage detection circuit 10 and the control circuit 8 relating to the quality of cooking generally functions with a power supply voltage within the operation guarantee range of the microwave oven (for example, within the range of AC90V to 110V).

  Further, when a power supply voltage outside the operation guarantee range of the microwave oven is input, a set voltage level preset in the control circuit 8 by the timer 11 based on voltage information detected by the power supply voltage detection circuit 10. Measure the time exceeding. When this measurement time exceeds a predetermined time, the control circuit 8 turns off the relays 1 and 5 that turn on and off the high-voltage transformer 2 and the cooling fan motor 7.

  The set voltage is set to a voltage level outside the operation guarantee voltage of the microwave oven. This set voltage can be changed according to the operating states of the heater 6, the fan motor 7 and the high voltage transformer 2. Moreover, the predetermined time to measure can also be set with respect to each of the heater 6, the fan motor 7, and the high voltage transformer 2. The predetermined time is set according to the tolerance of overvoltage application of the heater 6, the fan motor 7, and the high-voltage transformer 2 that are operated by a commercial power source.

  In the case of an electrical component composed of a semiconductor element, it is necessary to control to detect a voltage lower than the maximum applied voltage that can be applied to the semiconductor element and stop the voltage application instantaneously. An electric component composed of a resistor and a winding such as the high-voltage transformer 2 constituting the slab is more resistant to an applied voltage than an electrical component generally composed of a semiconductor element against an overvoltage application of several seconds to several tens of seconds. Is expensive.

  Therefore, even if a measurement time longer than that of an electrical component composed of semiconductor elements is set, the situation in which the corresponding electrical component fails immediately cannot be reached.

The surge voltage caused by lightning superimposed on the commercial power supply and the noise generated during operation of other devices connected to the commercial power supply are considered to be within several tens of ms. On the other hand, if the relay that drives the heater, fan motor, and high-voltage power supply (high-voltage transformer 2) is turned off, the relay is turned off at an unexpected timing, so the initially assumed heating amount cannot be maintained and the desired heating state cannot be achieved. .

  This can be corrected by the control circuit 8, but the control becomes complicated. In addition, since the number of times the relay is turned on and off increases, the life of the relay comes earlier than expected. In the present embodiment, this predetermined time is set to several seconds or more in view of the conditions on the left.

  For example, when the power supply voltage of FIG. 2 exceeding 90 V to 110 V in the operation guarantee range of the product exceeds the power supply voltage detection level c of 125 V for 10 seconds or more, the relays 1, 4 and 5 are immediately turned off to turn off the heater 6, cooling fan motor 7. Stop energizing the high-voltage transformer 2.

  The power supply voltage (125 V) and the predetermined time (10 seconds) are an example obtained from the tolerance of overvoltage of the electrical parts described on the left, and it goes without saying that they are set according to the specification environment of the electrical parts to be used and the microwave oven. That is.

  According to the present invention, as a protection function for electrical components that are more resistant to overvoltage than a semiconductor element such as a high-voltage power supply or a heater or a cooling fan motor, it is highly sensitive to abnormal voltage detection due to external noise such as lightning strikes. Since the process can be omitted, it is possible for the user to maintain the usability.

  In addition, even if an unrated voltage for a predetermined time or longer is applied, the insulation material of the windings that make up the electrical components shown on the left can be heated abnormally by applying overvoltage by stopping the application of voltage to the high-voltage transformer or cooling fan motor. Therefore, it is possible to prevent dielectric breakdown.

  As described above, the present invention is applied to a microwave oven, and as a protection function of an electrical component that is more resistant to overvoltage than a semiconductor element, it is possible to prevent the device from being stopped sensitively. For us, the usability can be kept intact.

The block block diagram of the microwave oven which concerns on embodiment of this invention A diagram showing the relationship between the power supply voltage and the power supply voltage detection level obtained from the output of the voltage detection circuit Block diagram of a conventional microwave oven

Explanation of symbols

1, 4, 5 Relay 2 High voltage transformer 3 High frequency oscillator 6 Heater 7 Cooling fan motor 8 Control circuit 9 Low voltage transformer 10 Voltage detection circuit 11 Timer

Claims (2)

A high-frequency power supply for a high-frequency oscillator that heats food, a cooling fan motor that cools the heater and electrical components, a transformer that transforms the power supply voltage to a predetermined voltage, and a power supply voltage that is based on the secondary side voltage of the transformer. A voltage detection circuit for detecting a voltage level, one or a plurality of preset voltage levels stored in advance, a timer for measuring a time exceeding the preset voltage level, and the preset voltage level; A microwave oven comprising a high-voltage power supply for the high-frequency oscillator, a heater, and a control circuit for controlling the cooling fan motor according to a measurement time of a timer. As one of the set voltage levels, a voltage level exceeding a power supply voltage assumed in normal use is set, and when the set voltage level is exceeded for a predetermined time, the high-frequency power supply, heater, and cooling fan motor of the high-frequency oscillator The microwave oven according to claim 1, further comprising a control circuit for stopping at least one energization.

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