JPH10326673A - High frequency heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple circuit structure so as to prevent the flowing of a relay entering current by controlling a relay driving circuit based on an operation time stored in a nonvolatile memory and a detected value from a phase detection circuit such that a relay operation timing is synchronized with the specified phase of a commercial power source. SOLUTION: An opening/closing switch 6 and a relay 2 are both in OFF states before a high frequency heater is operated. When an article to be heated is placed in the high frequency heater and a door is closed, the opening/closing switch 6 is turned ON. Then, when the heating start instruction switch of an operation switch group 13 is turned ON, a microcomputer 7 reads the operation time of the contact of the relay 2 stored in a nonvolatile memory 14. Then, based on information from a phase detection circuit 12 for detecting the voltage phase of a commercial power source 1, a signal is transmitted to a relay driving circuit 11 and the relay 2 is turned ON such that the operation time of the relay 2 reaches the highest point of a commercial voltage, i.e., a transient current becomes smallest. Thus, the entering current of the relay 2 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device, in particular, a high-frequency device for synchronizing the operation timing of a relay that opens and closes when a commercial power is applied to a high-voltage application circuit for applying a high voltage to a magnetron, to the voltage phase of the commercial power. It relates to a heating device.

[0002]

2. Description of the Related Art A high-frequency heating apparatus is generally widely used as an apparatus capable of heating an object to be heated in a short time. FIG.
FIG. 1 shows a simplified electric circuit of a conventional high-frequency heating device. In the figure, 1 is a commercial power supply, 2 is a relay for opening and closing the high-voltage power supply circuit 3 when the commercial power supply 1 is applied, and 5 is a magnetron.

In this circuit, the initial impedance seen from the commercial power supply side of the high-voltage power supply circuit has a characteristic substantially equal to the inductance. Therefore, when the commercial power supply 1 is applied to the high-voltage power supply circuit, the magnitude of the transient current flowing through the contact of the relay 2 is determined by the voltage of the commercial power supply at that time. The transient current is largest when the voltage of the commercial power supply is 0 V, and is smallest at the maximum voltage. For example, in the case of a high-frequency heating device with an output of 500 W,
The steady-state current is 10 A, but a rush current exceeding 200 A may flow during transition.

The relay contacts may be closed at the maximum of the commercial power supply voltage each time. However, as shown in FIG. The operation time from the application of the coil voltage to the closing of the relay contact varies. FIG.
Means that the voltage applied to the coil is the rated voltage (18 in this example).
V is a graph showing the relationship between the voltage applied to the coil and the operation time of the relay, with 100% being V). For example,
When a rated voltage of 18 V is applied to the coil, the operation time of the relay fluctuates from 10 to 12.5 ms.
When a voltage of 0% is applied, the variation is reduced to 7 to 8 ms.

From these facts, when the voltage applied to the coil of the relay is driven in synchronization with the commercial power supply,
Due to the characteristics of the voltage value applied to the relay and the operation time of the relay, there is a risk that a transient rush current flows every time the relay contacts are turned on. In such a case, the degree of deterioration of the contacts of the relay increases, the contacts are welded, the magnetron remains driven, and the heating cannot be stopped, and the performance of the high-frequency heating device becomes very unstable. Become. There is also a problem that when a large current flows, it adversely affects other electric devices and circuits in the same wiring.

Therefore, conventionally, a method in which the voltage applied to the relay is evenly dispersed with respect to the phase of the commercial power supply to uniformly disperse the danger that the current during the transition becomes maximum is called a random roll call of the relay. Things were used. However, in this method, the frequency at which the current during the transition becomes large is reduced, but is not completely eliminated.

As a method for solving such a problem, there is a method described in Japanese Patent Application Laid-Open No. Hei 1-3313886.
FIG. 7 shows the configuration. In the figure, 2a is a main relay,
2b is a sub-relay, 6 is an open / close switch provided on the door of the high-frequency heating device to turn on and off according to the opening and closing of the door, 7
Is a microcomputer, 8 is a transformer, 9 and 10 are stabilized power supply circuits, 12 is a phase detection circuit for detecting the phase of the commercial power supply from the commercial power supply voltage, and 13 is a cooking start instruction switch and a cancel switch (not shown). A set of operation switches, 20 is a main relay drive circuit that applies voltage to the coil side of the main relay 2a to drive the main relay 2a, and 21 is a sub relay 2b that applies voltage to the coil side of the sub relay 2b.
And 22 is a contact on / off detection circuit for detecting opening and closing of the main relay 2a.

First, when the cooking start instruction switch of the operation switch group 13 is turned on, the main relay 2a is turned on via the microcomputer 7 and the main relay drive circuit 20, and the contact on / off detection circuit 22 turns on the main relay 2a. Detect operating time. When the operation time of the main relay 2a is determined, the main relay 2a is turned off, and then the sub relay 2b is turned on. Next, the microcomputer 7 sends a signal to the main relay drive circuit 20 so that the operating point of the main relay 2a becomes the maximum point of the commercial voltage based on the information of the detection circuit 12 for detecting the voltage phase of the commercial power supply 1, Close 2a. By controlling the timing of the operation of the main relay 2a in this way, an inrush current during a transition can be prevented irrespective of the variation in the characteristics of the individual relays.

[0009]

As described above, the conventional high-frequency heating apparatus prevents the rush current at the time of transition as described above. However, in such a conventional configuration, the operating time of the relay is reduced every time the cooking is performed. This has to be confirmed, and there has been a problem that the circuit for that has to be complicated. The present invention has been made to solve such a problem, and an object of the present invention is to prevent a rush current from flowing through a relay with a simple circuit configuration, and to obtain a high-frequency heating device in which the relay is hardly deteriorated.

[0010]

A high-frequency heating apparatus according to the present invention opens and closes a magnetron, a high-voltage power supply circuit connected to a commercial power supply to drive the magnetron, and a connection between the commercial power supply and the high-voltage power supply circuit. A relay, a relay drive circuit that drives the relay, a nonvolatile memory that stores an operation time of the relay contact, a phase detection circuit that detects a voltage phase of the commercial power supply, and an operation that is stored in the nonvolatile memory. Control means for controlling the relay drive circuit such that the operation timing of the relay is synchronized with a predetermined phase of the commercial power supply based on time and a detection value from the phase detection circuit.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 shows an electric circuit of a simplified high-frequency heating device according to Embodiment 1 of the present invention. In the figure, 11
Is a relay drive circuit that drives the relay 2 by applying a voltage to the coil side of the relay 2. In this embodiment, the relay drive circuit is a constant voltage power supply circuit. Reference numeral 14 denotes a non-volatile memory that retains data even without power supply and that can electrically rewrite data. The operation time from when a voltage is applied to the coil side of the relay 2 to when the contact is closed. I remember. In addition,
The same components as those in the above-described conventional example are denoted by the same reference numerals, and description thereof is omitted.

Next, the operation will be described. Electric power obtained from the commercial power supply 1 via the transformer 8 is supplied to the microcomputer 7 by the stabilized power supply circuit 9 and is supplied to the relay drive circuit 11 by the stabilized power supply circuit 10. The microcomputer 7 has a nonvolatile memory 1.
The operation time of the relay 2 stored in 4 is read. Further, the voltage phase of the commercial power supply 1 is taken into the microcomputer 7 via the phase detection circuit 12.

The operation will be described in more detail with reference to the flowchart of FIG. Before the operation of the high-frequency heating device (initial state), the open / close switch 6 and the relay 2 are both OFF (S1). Put the object to be heated in the high frequency heating device,
When the door is closed, the open / close switch 6 is turned on (S2). Next, the heating start instruction switch of the operation switch group 13 is set to O
When N is reached (S3), the microcomputer 7 reads the operating time of the contacts of the relay 2 stored in the non-volatile memory 14 (S4), and reads the information of the phase detection circuit 12 for detecting the voltage phase of the commercial power supply 1. A signal is sent to the relay drive circuit 11 so that the operation time of the relay 2 becomes the maximum point of the commercial voltage, that is, the transient current is minimized, and the relay 2 is turned on (S5).

Next, a method of storing the operation time of the relay 2 in the nonvolatile memory 14 will be described with reference to FIG. In the drawing, reference numeral 15 is not incorporated in the high-frequency heating device, but is incorporated in a board tester for checking whether the control board of the high-frequency heating device is normal when assembly is completed, and detects whether the contact of the relay 2 is closed. This is a contact operation timing detection circuit. The board tester is used to detect component failures on the board and manufacturing defects that occur when soldering components to the board.The board tester has a built-in automatic inspection check program. When the operation is not normal, the operation is stopped at the location of the failure, a symbol or the like corresponding to the failure is displayed, and a warning is given by a buzzer.

A method of storing the relay operation time in the non-volatile memory will be described with reference to the flowchart of FIG. First, the microcomputer 7 is shifted to the board check mode by a special operation such as simultaneous pressing of a plurality of keys of the operation switch group 13 and complicated plural operations (S11). In this mode, the cooking time is operated at twice the normal speed or the like, so that the operation of assembling the board can be checked as quickly as possible. And this mode is the board assembly 1
When the microcomputer 9 is turned off, that is, when the microcomputer 7 is reset, the microcomputer 9 is released, so that there is no problem in normal use. Next, when the cooking start instruction switch of the operation switch group 13 is turned on (S13), the relay 2 is turned on via the microcomputer 7 and the relay drive circuit 11 (S1).
At the same time, the operation time of the relay 2 is detected via the contact operation timing detection circuit 15.

When the operation time of the relay 2 is determined,
If there is an operation to stop the heating of the operation switch group 13 (S1
6), the relay 2 is turned off (S17). Finally, the microcomputer 7 stores the operation time of the relay in the nonvolatile memory 14 (S18). Here, switch group 1
The ON / OFF request from 3 is performed by the board tester, and the board tester is programmed to request the OFF after the operation time of the relay 2 is determined.

As described above, the operation time of the relay 2 is measured at the time of inspection of the board operation. Therefore, the measurement circuit may be built in the board tester. Since a relay operation time measurement program is only stored in the memory, there is no need to measure and store the program. Further, it is not necessary to incorporate a circuit for checking the operation time of the relay every time heating cooking is performed in the high-frequency heating device.

If the operation time of the relay 2 is not stored in the non-volatile memory, the operation may not be confirmed by the board tester. It is good to do so.

[0019]

According to the present invention, with a simple circuit configuration,
It is possible to prevent a rush current from flowing through the relay and obtain a high-frequency heating device in which the relay is less likely to deteriorate.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a high-frequency heating device according to a first embodiment.

FIG. 2 is a flowchart showing an operation of the high-frequency heating device according to the first embodiment.

FIG. 3 is an electric circuit diagram when the operation time of the relay is stored in the nonvolatile memory according to the first embodiment.

FIG. 4 is a flowchart showing an operation of storing the operation time of the relay in the nonvolatile memory according to the first embodiment.

FIG. 5 is an electric circuit diagram of a conventional high-frequency heating device.

FIG. 6 is a graph showing a relationship between a coil applied voltage and an operation time of a relay.

FIG. 7 is an electric circuit diagram of another conventional high-frequency heating device.

[Explanation of symbols]

1 Commercial power supply, 2 relays, 3 high voltage power supply circuit, 5 magnetron, 7 microcomputer, 11 relay drive circuit, 12 phase detection circuit, 14 nonvolatile memory.

Claims (1)

[Claims] A magnetron, a high-voltage power supply circuit connected to a commercial power supply for driving the magnetron, a relay for opening and closing the connection between the commercial power supply and the high-voltage power supply circuit, a relay drive circuit for driving the relay; A nonvolatile memory that stores an operation time of the relay contact, a phase detection circuit that detects a voltage phase of the commercial power supply, and an operation time that is stored in the nonvolatile memory and a detection value from the phase detection circuit. Control means for controlling the relay drive circuit so that the operation timing of the relay is synchronized with a predetermined phase of the commercial power supply.