JP2803284B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device used for a microwave oven for home use, and more particularly, to a high-frequency heating device using an inverter circuit as a power supply. .

2. Description of the Related Art The configuration of a conventional high-frequency heating device will be described with reference to the drawings. FIG. 4 is a circuit diagram showing a configuration of a conventional high-frequency heating device. In FIG. 1, a commercial power supply 1 is exchanged for a direct current by a rectifier, and energizes an inverter circuit 2 including semiconductor switching elements such as inductors, capacitors, transistors, and diodes. The transformer 3 detects the voltage generated by the primary winding 4 for applying the output of the inverter circuit, the secondary winding 5 for generating a high voltage, the tertiary winding 6 for generating a low voltage, and the secondary winding. , And a separation plate 7 made of a metal conductor for separating the primary winding 4 and the detection winding 16 from the secondary winding 4 and the tertiary winding 6. If the housing of the high-frequency heating device is not grounded, for example, the bobbin around which the winding is wound for some reason is damaged, and the primary winding 4 and the detection winding 16 and the secondary winding 5 and the tertiary winding 6 When the high frequency heating device is in contact with the high frequency heating device, the housing itself of the high frequency heating device has a high potential substantially equal to the potential of the secondary winding 5. For this reason, even if the bobbin is broken, the separating plate 7 is connected to the primary winding 4 and the detection winding 16 and the secondary winding 5.
And to prevent the tertiary winding 6 from contacting. The high voltage generated in the secondary winding 5 is half-wave rectified by a capacitor and a diode and applied between the anode and the cathode of the magnetron 11. Since the anode is connected to the housing of the high-frequency heating device, the cathode has a negative potential with respect to the housing. The low voltage generated in the tertiary winding 6 is connected to the cathode and supplies current to heat the cathode. Therefore, the tertiary winding also has a high potential.

The magnetron 11 oscillates and generates microwaves when a high voltage of -4 kV or more is applied between the anode and the cathode and the cathode is sufficiently heated. The anode-cathode voltage after oscillation is clipped to about -4 kV due to the magnetron characteristics shown in FIG.

Immediately after the start of the inverter circuit, it takes some time until the cathode is sufficiently heated. For this reason, in order to reduce the time required from the start of the inverter circuit to the oscillation of the magnetron, a high voltage of about -7 kV is applied between the anode and cathode and a large current of about 13 A is supplied to the cathode as shown in FIG. The cathode is rapidly heated. The magnitude of the voltage applied between the anode and the cathode of the magnetron at the time of starting can be adjusted to an arbitrary voltage by adjusting a control signal from the control circuit 13 for driving the semiconductor switching element of the inverter circuit 2. .

For this purpose, the transformer 3 is provided with the detection winding 16 and the secondary winding 5 is provided.
The voltage generated by the secondary winding 5 can be set to an arbitrary value by detecting the voltage generated at the secondary winding 5 and feeding back the detection signal to the control circuit 13.

Input adjustment to the inverter circuit 2 after magnetron oscillation, input current is detected by inserting a current transformer 17 between the commercial power supply 1 and the rectifier, and input adjustment is performed by feeding back this detection signal to the control circuit 13. I have.

Problems to be Solved by the Invention Problems to be solved by the present invention are described below.

A primary winding and a detection winding provided in the transformer,
The separation plate for separating the secondary winding and the tertiary winding,
A cut portion is provided to prevent a closed loop, one end is connected to the housing of the high-frequency heating device, and the other end is open. If the cut portion is connected for some reason, a closed loop is formed and a short circuit occurs, a very large current flows, the separator plate becomes red hot, and there is a danger of causing a fire.

Also, a detection winding must be provided on the transformer to detect the transformer secondary winding voltage at the time of starting the inverter.
For this reason, the structure of the transformer becomes complicated, and the detection winding is separated from the secondary winding by a separation plate together with the primary winding.
The secondary winding must be located far from the secondary winding, which weakens the magnetic coupling between the secondary winding and the sensing winding, and makes it impossible to accurately detect the secondary winding voltage. .

Furthermore, since a means for detecting the input current is used to adjust the input to the inverter circuit, a current transformer is required, and there is a problem that the number of components is increased.

Means for Solving the Problems First, one end of a separation plate made of a metal conductor and having a cut portion for separating a primary winding from a secondary winding and a tertiary winding is connected to a casing of a high-frequency heating device. Connect to the body,
By connecting the other end to the voltage detecting means, the voltage induced on the separation plate during the operation of the inverter circuit is detected.

Secondly, an oscillation detection means for detecting the oscillation of the magnetron is provided by an output from the voltage detection means, and an output of the oscillation detection means is fed back to a control circuit for controlling a transistor of the inverter circuit, so that an anode of the magnetron is output. It is configured to adjust the high voltage applied between the cathodes.

Third, input power determining means for determining the input power to the inverter circuit based on the output from the voltage detecting means is provided, and the output of the input power determining means is fed back to the control circuit. Is adjusted.

Fourth, there is provided a short-circuit judging means for judging a short-circuit of the separation plate based on an output from the voltage detecting means, and the operation of the inverter circuit is stopped by an output of the short-circuit judging means.

Effects According to the present invention, the following effects are obtained.

First, the primary winding of the transformer and one end of a separation plate made of a metal conductor and having a cut portion for separating the secondary winding and the tertiary winding are connected to the housing of the high-frequency heating device,
Further, by connecting the other end to the voltage detecting means, it is possible to detect the voltage induced on the separation plate during the operation of the inverter circuit.

Secondly, by providing oscillation detection means for detecting the oscillation of the magnetron with the output from the voltage detection means,
The detection winding provided for detecting the secondary winding voltage of the transformer and determining the oscillation of the magnetron can be eliminated, and the structure of the transformer can be simplified.

Third, an input power determining means for determining an input power to the inverter circuit based on an output from the voltage detecting means,
By feeding back the output of the input judging means to the control circuit and adjusting the input power of the inverter circuit, it is possible to eliminate the input current detection current transformer necessary for adjusting the input power. Can,
The number of parts can be reduced.

Fourthly, by providing a short-circuit judging means for judging a short-circuit of the separation plate based on an output from the voltage detecting means, and stopping the operation of the inverter circuit by an output of the short-circuit judgment means, When the cut portion is short-circuited for some reason, a very large current flows, the separator plate becomes red hot and the temperature becomes high, and the danger of causing a fire can be eliminated, and the reliability can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a circuit configuration of a high-frequency heating device according to one embodiment of the present invention. In FIG. 1, a commercial power supply 1 is converted into a direct current by a rectifier, and energizes an inverter circuit 2 including semiconductor switching elements such as inductors, capacitors, transistors, and diodes. The inverter circuit converts DC from the rectifier into high-frequency AC having a frequency of 10 kHz or more. The control circuit 13 controls a semiconductor switching element of the inverter circuit 2. The transformer 3 includes a primary winding 4 for applying an output of the inverter circuit, a secondary winding 5 for generating a high voltage, a tertiary winding 6 for generating a low voltage, a primary winding 4 and a secondary winding 5. It is composed of a separation plate 7 made of a metal conductor that separates the tertiary winding 6. As shown in FIG. 2, the separating plate 7 has a structure in which a metal conductor such as copper is plated with tin or the like to prevent corrosion, and a cut portion 8 is provided. 9 and the other end is connected to the voltage detecting means 10. The separating plate 7 includes the primary winding 4
And the secondary winding 5, a voltage is induced when the inverter circuit 2 operates. The voltage detecting means 10 detects the voltage induced on the separation plate 7. Voltage detection means 10
In the case where the magnetron 11 is not oscillating when, for example, the inverter circuit 2 is started up and the magnetron 11 is not oscillating, the output waveform shown in FIG.
When 11 is oscillating, it has a waveform as shown in FIG.

In FIG. 1, an oscillation judging means 12 for judging the oscillation of the magnetron 11 receives the output of the voltage detecting means 10, judges the oscillation of the magnetron 11, and controls the control circuit of the inverter circuit 2.
Give 13 a signal. As described in the related art, in order to reduce the time required from the start of the inverter circuit 2 to the oscillation of the magnetron, a high voltage of about -7 kV is applied between the anode and the cathode of the magnetron, and a large voltage of about 13 A is applied to the cathode. An electric current is supplied to rapidly heat the cathode. The magnitude of the voltage applied between the anode and the cathode of the magnetron at this start is determined by the oscillation determining means 12 of the magnetron 11 receiving the output of the voltage detecting means 10, and a signal is given to the control circuit 13. The signal controls the on-time of the drive signal applied to the semiconductor switching element of the inverter circuit 2 to adjust the voltage between the anode and cathode of the magnetron.

The input power judging means 14 detects the voltage induced on the separator 7 after the magnetron 11 oscillates by the voltage detecting means 10 and receives the signal to give a signal to the control circuit 13 which controls the inverter circuit 2. The control circuit 13 controls the on-time of the drive signal given to the semiconductor switching element of the inverter circuit 2 by this signal, and adjusts the input power to the inverter circuit 2.

For example, when the input to the inverter circuit is increased, the exciting current flowing through the primary winding 4 of the transformer increases, and the voltage induced on the separation plate 7 having magnetic coupling with the primary winding 4 also increases. Therefore, by detecting the voltage induced on the separation plate 7, the input voltage can be known. Since the inverter circuit 2 operates at a frequency of 10 kHz or more, the output waveform of the voltage detecting means 10 shown in FIG. 2 has a similar frequency. For this reason, the input / output power determining means 14 is configured to rectify and smooth the output of the voltage detecting means 10 and obtain the average value.

If the separation plate 7 is short-circuited for some reason, the signal from the voltage detection means indicates that there is no induced voltage of the separation plate 7 even during the operation of the inverter circuit 2. In addition to receiving the signal from the controller, it judges the short circuit of the separation plate 7 and sends a signal to the control circuit 13 to stop the operation of the inverter circuit 2.

Effects of the Invention According to the present invention, the following effects are obtained.

By connecting one end of a separation plate having a cut portion which is a part of a component constituting the transformer to the housing of the high-frequency heating device, and connecting the other end to the voltage detection means, the primary winding and the secondary winding and The tertiary winding can be separated, and the voltage induced on the separation plate can be detected.

By providing the oscillation detection means for receiving the output from the voltage detection means and detecting the oscillation of the magnetron, it is possible to eliminate the detection winding conventionally provided in the transformer for detecting the oscillation of the magnetron.

By providing input power determining means for receiving the output from the voltage detecting means and determining the input power to the inverter circuit, the current transformer for detecting the input current, which has been conventionally used for determining the input power, is eliminated. be able to.

Short-circuit determination means for receiving an output from the voltage detection means and determining short-circuit of the separation plate is provided, and the operation of the inverter circuit is stopped by a signal of the short-circuit determination means. A large current flows through the device, preventing the risk of red heat and fire.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a separation plate of a transformer of the device,
FIG. 3 is a characteristic diagram of a magnetron, FIG. 4 is a circuit diagram of a conventional high-frequency heating device, and FIGS. 5 and 6 are characteristic diagrams of a magnetron. 1 ... commercial power supply 2 ... inverter circuit 3 ... transformer 4 ... primary winding 5 ... secondary winding 6 ... tertiary winding 7 ... separation plate 9 ... high frequency heating Equipment housing, 10…
... voltage detecting means, 12 ... oscillation determining means, 13 ... control circuit, 14 ... input power determining means, 15 ... short-circuit detecting means.

──────────────────────────────────────────────────の Continued on the front page (72) Takahiro Matsumoto, Inventor 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-63-271886 (JP, A) JP-A-61-188884 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B ⁶ /48- 6/50 H05B 6/66-6/68 H05B 11/00

Claims (4)

(57) [Claims] 1. A power supply unit obtained from a commercial power supply or a battery, an inverter circuit energized by the power supply unit, a control circuit for controlling a semiconductor switching element of the inverter circuit, and an output of the inverter circuit. A plurality of windings for boosting, a transformer formed of a separation plate made of a metal conductor for separating the plurality of windings, and a magnetron that is energized by an output of the transformer and generates a microwave, A high-frequency heating device having a cut portion on the separation plate, one end connected to a housing of the high-frequency heating device, and the other end connected to voltage detection means for detecting a voltage induced on the separation plate during operation of an inverter circuit. 2. A control circuit for controlling a semiconductor switching element of an inverter circuit, comprising: oscillation judging means for judging magnetron oscillation based on an output of a voltage detecting means connected to a separation plate of a transformer. The high-frequency heating device according to claim 1, which transmits the power. 3. An inverter circuit comprising: an input power determining means for determining the magnitude of power input to an inverter circuit based on an output of a voltage detecting means connected to a separating plate of a transformer; The high-frequency heating device according to claim 1, wherein the signal is transmitted to a control circuit that controls the semiconductor switching element. 4. A short circuit judging means for judging a short circuit of the separation plate based on an output of a voltage detecting means connected to a separation plate of a transformer, wherein the operation of the inverter circuit is stopped based on information from the short circuit judgment means. The high-frequency heating device according to (1).