JPH07109797B2 - High frequency heating device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for capturing a door opening / closing signal of an inverter type high frequency heating device.

2. Description of the Related Art A high-frequency heating device must be configured so that power supply to the magnetron is stopped when the door is open. Therefore, the conventional heating device has a door switch 27 and a door signal switch 28 as means for controlling the supply of electric power to the high-voltage transformer 26, as shown in FIG. It is connected to the power line and mechanically switches the power line on and off by opening and closing the door. Further, the door signal switch 28 is arranged in the drive circuit of the relay 29 that controls the power supply to the high-voltage transformer 26,
It is connected in series to the operation coil 30 of the relay 29. Therefore, when the door is open, no current flows in the operation coil 30, the contact of the relay 29 is separated, and the door switch 27
At the same time, the power line will be cut off. On the other hand, the control unit 31
The door opening / closing information to and from the door signal switch 28 is transmitted by a door signal circuit including a resistor 32 connected to the operation coil 30 of the relay 29 and a zener diode 33. Further, a short switch 34 is provided as a protection circuit for short-circuiting the power line when the door is opened.

Next, FIG. 6 shows a configuration in which a semiconductor element such as a triac 35 is used as a means for controlling the power supply to the high voltage transformer 26. The semiconductor device is less safe than the relay in terms of its failure, and it is not sufficient to simply install a door signal switch in its drive circuit as in the case of the relay. The door switch 3a of No. 1 is inserted into the power line on the opposite side, and a double door monitor configuration is adopted. On the other hand, the door signal switch 28 is a control unit independently of the semiconductor drive circuit.
It is connected to 31 and inputs the open / closed state of the door to the control unit 31. Therefore, in the case of the semiconductor control means, four switch means for monitoring the movement of the door are required: the first and second door switches 3a and 3b, the short switch 34, and the door signal switch 28. .

In the above conventional example, 17 is a lamp 15 and a fan motor.
16 control relay, 20 control resistor transformer,
With the rectangular wave signal corresponding to the power cycle of the AC power supply and the power supply clock / low voltage power supply unit that supplies power to the cooking control unit,
Reference numeral 31 is a control unit composed of a microcomputer or the like. 36 is a relay for giving a triac trigger signal.

FIG. 7 shows the state of attachment to the switch body 37.

Problems to be Solved by the Invention Even in the inverter type high-voltage power supply circuit, since the semiconductor element is used as the switching element, four switches for monitoring the door states are required as described above. As a result, the cost of the extra door switch is increased, and the number of switches is increased from three to four, increasing the frictional resistance between the door lever and the actuator part of the door switch when opening and closing the door. The force becomes heavy and the operability is significantly reduced.

The present invention solves the above-mentioned conventional problems, and realizes saving of parts without impairing safety and also improves door operability.

Means for Solving the Problems The inverter type high frequency heating apparatus of the present invention uses a phototransistor output signal for detecting the voltage across the magnetron drive transformer and a power supply clock signal synchronized with the cycle of the AC power supply to open and close the door. Is to monitor.

Operation The inverter type high voltage power supply converts the commercial primary power supply into a DC voltage once, and then the semiconductor switch element chops this DC voltage at a chopping frequency of several tens of KHz and applies it to the magnetron drive transformer.
The power is converted from the secondary side to the secondary side. At this time, a switching transistor is used as a means for chopping a DC voltage at several tens of kilohertz, and minimizing the loss during switching of this transistor greatly affects its life.

For this purpose, a circuit for detecting the voltage across the coil of the magnetron drive transformer is provided to detect the timing when the voltage applied to the switching transistor is the minimum. A resistance voltage divider circuit is used as this detection circuit, and it is connected in parallel to the DC power supply.Therefore, when the door is closed, a constant current is constantly flowing, and on the contrary, when the door opens and the DC power supply loses its charge. , The current flowing there becomes zero.

The door opening / closing signal means of the present invention detects the change of the current by the phototransistor connected in series to the resistance voltage dividing circuit, and when the door is closed, a current flows through the diode of the phototransistor, and as a result, the phototransistor. The output side transistor of becomes "ON",
On the contrary, when the door is open, it is configured to be in the "OFF" state, the signal level of this phototransistor is input to the cooking control section of the entire cooking, and both the power clock signal synchronized with the cycle of the AC power supply is supplied. The door opening / closing information is obtained by determining the state of the signal.

Therefore, according to the door signal inputting means of the present invention, a dedicated door switch is not required, cost can be reduced by saving parts, and smooth performance at the time of opening and closing the door can be dramatically improved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an external view of a high frequency heating apparatus according to an embodiment of the present invention. The opening / closing information of the door 1 is transmitted to the door switches 3a, 3b shown in FIG. 1 installed on the power supply line by the actuator 2 attached to a part of the door 1.

Next, referring to FIG. 1, the configuration for taking in the door signal information will be described. The current entered from the power plug 4 enters the rectifier diode 5 through the first door switch 3a. Then, it enters the magnetron drive transformer 8 and the switching transistor 9 through the smoothing capacitor 6, the choke coil 7 and the like, and again passes through the rectifier diode 5, the current transformer 10, and then the second door switch 3b and returns to the power source. By the way, when the switch transistor 9 is turned on, the rectified voltage 142V of AC100V is applied to the magnetron drive transistor 8, and a current flows through the magnetron drive transformer 8 while the switch transistor 9 is turned on. Power conversion to the next side is performed. A custom IC is used as the switching control unit 11 that controls ON / OFF of the switching transistor 9.
An ON / OFF signal of the switching transistor 9 is output from the No. terminal and is applied to the base of the switching transistor 9 via the drive unit 12. Also, the voltage across the coil of the magnetron drive transformer 8 is input to the 2nd and 3rd terminals of the custom IC by the resistance voltage dividing circuits 13 and 14, and the custom
Due to the internal operation of the IC, the optimum ON / O voltage can be adjusted according to the voltage across this terminal.
Making FF timing. The DC voltage signal after rectifying and smoothing the output of the current transformer 10 is input to the 4th terminal, and the signal voltage according to the value of the primary side current is input to the 4th terminal of the custom IC 11. Inside the custom IC 11, the switching transistor 9 is controlled so that a predetermined primary current flows.
The ON / OFF duty is corrected based on the signal voltage from the current transformer 10 and feedback is applied so that it becomes a constant value.

On the other hand, control as a cooking device is performed by the microcomputer 38. Predetermined cooking is performed in response to a key input from the keyboard 38a. The R1 terminal of the microcomputer 38 is a control terminal of a relay 17 for turning on / off the oven lamp 15 and the cooling fan motor 16, and the R2 terminal is a terminal for outputting a start signal to the switching control section 11, and a phototransistor 18
By supplying a current to the diode side of the transistor, the transistor side becomes conductive, the switching operation is stopped, and the power supply to the magnetron 19 is interrupted.

Here, 20 is a low-voltage transformer that serves as a power supply for the microcomputer 38 and the power supply for the switching control unit 11, 21 is a power supply circuit for the microcomputer 38, and 22 is a switching control unit.
Power supply for 11.

By the way, the switching control circuit has the same potential as the AC120V line, but the entire control circuit of the cooking device such as the microcomputer 38 must be electrically insulated from the AC120V line. Therefore, the interface for exchanging signals is electrically insulated by using the phototransistor 18.

Next, the method of inputting door opening / closing information will be described.

As described above, when the door is closed, the contacts of the door switches 3a and 3b are closed, so that the output voltage of the rectifying diode 5 and the smoothing capacitor 6 is about DC142V, and this voltage is always the magnetron. Drive transformer 8,
Switching transistor 9 and resistance voltage divider circuit 1 which is a detection circuit for the voltage across magnetron drive transformer 8.
Applied to 3,14.

The resistance voltage dividing circuits 13 and 14 are provided at both ends of the drive transformer 8, respectively, and the first voltage dividing circuit 13 detects the voltage applied between the drive transformer 8 and the switching transistor 9 and outputs the second voltage dividing circuit. The voltage circuit 14 detects the voltage applied to the switching transistor 9. This resistance voltage divider circuit 13,1
The value of the combined resistance of 4 is about 50 K ohms, respectively, and a current of about 3 mA is always flowing by applying the DC142V.

Next, when the door 1 is opened, the door switches 3a, 3a
The contact point of b is opened, the power supply to the DC power supply of the rectifying diode 5 and the smoothing capacitor 6 is cut off, and the voltage of this DC power supply becomes OV after several tens of millimeters SEC. As a result, the current flowing through the resistance voltage dividing circuits 13 and 14 also disappears.

The door signal input terminal of the microcomputer 13 which controls the cooking by detecting the change in the current flowing through the resistance voltage dividing circuits 13 and 14 depending on the door open / close state by the phototransistor 25 connected in series to the first resistance voltage dividing circuit 13. It is input to K1 as "1" and "0" signals.

Next, the procedure for determining whether the door signal as described above is taken in the microcomputer 38 will be described.

In FIG. 3, when the door state A changes from closed to open, the microcomputer K1 input B changes from "L" (low) level to "H" (high).
Although it becomes a level, this input signal is once latched in the microcomputer, waits for the rising timing of the power supply clock waveform D generated from the AC power supply C, is processed programmatically in the microcomputer, and the recognition state E of the microcomputer is the door. The door opens when it is closed.

When the door is closed from the opening, the procedure is exactly the same, the microcomputer K1 input signal B is once latched,
Processing is performed in synchronization with the rise of the power supply clock waveform D. Therefore, as in the case shown in FIG. 4, when the door state A remains closed but the AC power source B has disappeared due to a momentary power failure, the microcomputer K1 input C has the door closed. However, it changes from "L" (low) level to "H" (high) level and changes as if the door was opened. However, as described above, this signal is temporarily latched inside the microcomputer and is processed only at the rising timing of the power supply clock waveform D. Therefore, unless this power supply clock is input due to an instantaneous power failure, the microcomputer recognition state E is The door remains closed and does not change.

In this way, by temporarily latching the signal from the phototransistor and processing it at the timing of fetching the power supply clock, it is possible to eliminate malfunctions during an instantaneous power failure.

Further, in the above description, the embodiment in which the processing is performed programmatically by using the microcomputer has been described. However, a sample hold circuit or the like may be used instead of the microcomputer, and the hardware can be naturally configured.

EFFECTS OF THE INVENTION As described above, according to the present invention, the following effects can be obtained with respect to the door signal capturing structure of the high-frequency heating device that also includes the inverter type high-voltage power supply.

(1) Paying attention to the fact that a constant current flows through the resistance voltage divider circuit that detects the voltage across the coil of the magnetron drive transformer only when the door is closed, and does not flow when the door is open. This change is detected by the phototransistor, and the door signal is detected. By substituting the switch, the parts for the door signal switch can be saved, and the total cost of the heating device can be greatly reduced.

(2) Since the door signal switch having a mechanical contact mechanism is eliminated, the operability at the time of opening and closing the door is lightened and the product value can be improved.

(3) By adopting a method of processing the output signal of the phototransistor in synchronization with the power supply clock waveform, it is possible to enhance the reliability and safety of the operation at the time of instantaneous power failure.

[Brief description of drawings]

FIG. 1 is an electric circuit configuration diagram of a high-frequency heating apparatus showing an embodiment of the present application, FIG. 2 is an external view of the apparatus, and FIGS. 3 and 4 are door signal acquisition processing according to an embodiment of the present application. FIG. 5, FIG. 5 and FIG. 6 are views showing the electric circuit configuration of the conventional heating device, and FIG. 7 is a perspective view showing the installation of the door switch and the like of the conventional example. 3a, 3b …… door switch, 5 …… rectifier diode, 6
...... Smoothing capacitor, 8 …… Magnetron drive transformer, 9 …… Switching transistor, 10 …… Current transformer, 11 …… Switching control section, 12 …… Drive section,
13,14 ...... Resistance divider circuit, 18 ...... Phototransistor, 3
8 …… Cooking control section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Suenaga 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masashi Yano, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co. 56) References Japanese Unexamined Patent Publication No. Sho 59-194384 (JP, A) Actual development Sho 60-85099 (JP, U)

Claims (1)

[Claims] 1. A high-frequency power supply section including an inverter circuit for driving a magnetron, a switching control section for controlling switching of the inverter circuit, an input voltage detecting means for detecting an input voltage of the inverter circuit, and heating control for cooking. A cooking control unit for controlling the whole, a power supply clock and a low-voltage power supply unit for supplying driving power for the cooking control unit together with a rectangular wave (clock) signal corresponding to the power supply cycle of the AC power supply, and an AC power supply side from the inverter circuit. Door open / closed state by a door switch provided on the door switch, a signal output from the inverter circuit input voltage detecting means in response to opening / closing of the door switch, and a rectangular wave (power clock) signal of the AC power supply. And a cooking control unit that controls heating control of cooking. Heating device.