JP2007192545A - High frequency heating device - Google Patents

Abstract

In a high-frequency heating device used in a device equipped with a magnetron such as a microwave oven, a high-frequency heating device including a power supply unit with good cooling efficiency is obtained.
A shunt resistor (30) used for measuring an output current of a unidirectional power supply unit (1) is disposed on a substrate (32) along a wind path of cooling air flowing on the substrate (32), and the diode bridge and The switching elements are arranged in substantially the same straight line.
[Selection] Figure 1

Description

  The present invention relates to a high-frequency heating apparatus suitable for use in equipment equipped with a magnetron such as a microwave oven.

Conventionally, in the above-described high-frequency heating apparatus, the current on the input side to which the commercial power is input is detected by a current transformer, and the electromagnetic wave output of the magnetron is constant by controlling the pulse width so that the input current becomes a predetermined value. Proposals have been made to adopt a configuration in which the current is controlled (for example, see Patent Document 1), or a configuration in which the secondary current of the step-up transformer of the high-voltage circuit is detected by the current transformer and the input current is controlled to be constant. (For example, refer to Patent Document 2). In these high-frequency heating devices, the current to be detected is detected by a current transformer.
Note that some conventional high-frequency heating devices include a cement resistor (a kind of winding resistance) for reducing the voltage of a commercial power supply after rectification and constant voltage to a predetermined voltage.

  FIG. 6 is a circuit diagram showing the configuration of the high-frequency heating device disclosed in Patent Document 2 above. The high-frequency heating device shown in this figure includes a unidirectional power supply unit 1, an inverter unit 2, a high voltage rectifier circuit 3, a magnetron 4, a switching rate detection unit 5, a secondary current detection unit 6, and a control unit 7. And current transformers 8 and 9.

The unidirectional power supply unit 1 is a diode bridge 1 that full-wave rectifies an AC power supply from a commercial power supply 20.
01 and a low-pass filter circuit comprising a choke coil 102 and a capacitor 103. In the unidirectional power supply unit 1, the above-described current transformer 8 is inserted on the AC input side of the diode bridge 101, and is used for detection of the input current. The inverter unit 2 includes a resonant capacitor 201, a step-up transformer 202, a transistor 203, and a commutation diode 204. The transistor 203 performs a switching operation by a switching control signal of 20 to 50 kHz supplied from the control unit 7. As a result, a high frequency voltage is generated in the primary winding of the step-up transformer 202.

  The transistor 203 is mainly formed integrally with the commutation diode 204 and is called an IGBT (Insulated Gate Bipolar Transistor).

  The high-voltage rectifier circuit 3 includes capacitors 301 and 302 and diodes 303 and 304, and generates a high-voltage DC voltage by rectifying the voltage generated at the secondary winding of the step-up transformer 202 by half-wave voltage doubler. Applied to magnetron 4. An AC voltage for the heater is also applied to the magnetron 4 from the heater winding of the step-up transformer 202. When the AC voltage for the heater is applied to the magnetron 4, the cathode is heated side by side to be in an emissionable state, and when a high voltage DC voltage is applied in this state, electromagnetic energy is generated. In the high-voltage rectifier circuit 3, the above-described current transformer 9 is interposed between the cathode of the diode 303 and the ground, and is used for detecting a secondary current.

  The switching rate detection unit 5 detects the on / off duty ratio of the transistor 203 of the inverter unit 3 and inputs the result to the control unit 7. The secondary-side current detection unit 6 detects the average value by full-wave rectifying the secondary current and inputs the result to the control unit 7. The control unit 7 multiplies the output signal of the switching rate detection unit 5 and the output signal of the secondary side current detection unit 6, and controls the on / off of the transistor of the inverter unit 3 so that the multiplication value becomes a desired value. I do.

  In this way, the commercial power supply 20 is converted into a unidirectional voltage by the unidirectional power supply unit 1, converted into a high frequency voltage by the inverter 21, boosted by the step-up transformer 202, and then double-voltage rectified by the high-voltage rectifier circuit 3 again. The high voltage DC voltage is converted to drive the magnetron 4.

In addition, although the description about the above-mentioned cement resistance is not found in the high-frequency heating device of Patent Document 2, if this is used, the DC output terminal of the unidirectional power supply unit 1 and the circuit to which it is connected (for example, the switching rate detection unit 5). , The secondary side current detection unit 6 and the control unit 7) are inserted between the power supply terminals, and the commercial power supply 20 is dropped to a predetermined voltage to be supplied to each circuit.
JP-A-8-96947 (page 7, FIG. 1) Japanese Patent Application Laid-Open No. 8-227791 (page 4, page 5, FIG. 1)

  However, the conventional high frequency heating apparatus has the following problems.

  In other words, a cooling fan is used to take measures against heat generation of the IGBT in which the transistor 203 and the commutation diode 204 are integrally formed in addition to the diode bridge 101 and the step-up transformer 202 on the printed circuit board. Since 8 and 9 hindered the flow of cooling air and cement resistance became a heat source, sufficient cooling efficiency was not obtained. In particular, since all components must be arranged in a limited space on the printed circuit board as the high-frequency heating device main body is downsized, improvement in cooling efficiency is desired.

  This invention is made | formed in view of the point which concerns, and it aims at providing the high frequency heating apparatus provided with the power supply unit with sufficient cooling efficiency.

  In order to solve the above-described problems, a high-frequency heating device according to the present invention includes a unidirectional power supply unit that converts a commercial power supply in a unidirectional manner using a diode bridge and at least one semiconductor switching element on at least a substrate. An inverter unit that converts power from the unidirectional power source unit to high-frequency power by turning on / off the semiconductor switching element, a step-up transformer that boosts the output voltage of the inverter unit, and an output of the step-up transformer In a high-frequency heating device having a high-voltage rectifying unit that doubles the voltage, the shunt resistor is inserted in series with respect to a location where the output current of the unidirectional power supply unit can be measured. The diode bridge and the switching element are disposed on the board along the air path of the cooling air flowing on the board. Characterized in that it is disposed substantially on the same straight line when.

  According to this configuration, the shunt resistor used for measuring the output current of the unidirectional power supply unit instead of the current transformer having a generally large shape is provided along the air path of the cooling air flowing on the printed circuit board. Since it is disposed above, the rate at which the shunt resistance hinders the flow of the cooling air can be minimized as compared with the current transformer, and the cooling efficiency can be improved.

  The high-frequency heating device according to the present invention is the high-frequency heating device according to any one of the above-described inventions, wherein a cement resistance for dropping the commercial power supply to a predetermined voltage substantially intersects the cooling air flow path. It is good also as what is arrange | positioned in the direction to do.

  According to this configuration, since the cement resistance accompanied by heat generation is arranged in a direction substantially intersecting the cooling air flow path, the cement resistance can be efficiently cooled.

  According to the high-frequency heating device according to the present invention, the shunt resistor used for measuring the output current of the unidirectional power supply unit is arranged on the printed circuit board along the air path of the cooling air flowing on the printed circuit board. The efficiency of cooling can be improved by minimizing the rate of obstructing the flow of cooling air.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a high-frequency heating device according to an embodiment of the present invention.
In this figure, parts common to those in FIG. 5 described above are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 1, the high-frequency heating device according to the present embodiment has a shunt resistor 30 for detecting an input current and a voltage generated in the shunt resistor 30 as an input current detection unit that replaces a conventional current transformer. And a buffer 31 for taking out. In addition, the high-frequency heating device of the present embodiment is configured to drop the DC output of the unidirectional power supply unit 1 to a predetermined voltage between the DC output end of the unidirectional power supply unit 1 and the power supply terminal of the control unit 7. A cement resistor 50 is provided.

The shunt resistor 30 is inserted in series with the negative output side terminal of the diode bridge 101 of the unidirectional power supply unit 1. When the shunt resistor 30 is mounted on the printed circuit board, the shunt resistor 30 is disposed along the air path of the cooling air flowing on the printed circuit board so as not to disturb the flow of the cooling air. The shunt resistor 30 includes a type attached to a heat sink, a cement mold type, or a bare resistance wire. In particular, when a bare resistance wire is used, space saving and cost reduction can be achieved.
On the other hand, the cement resistor 50 is interposed between the DC output terminal of the unidirectional power supply unit 1 and the power supply terminal of the control unit 7 as described above. In this case, when mounting on the printed circuit board, it is arranged in a direction substantially intersecting with the cooling air flow path in order to effectively cool the heat generation.

FIG. 2 is a diagram showing a mounting state of a part of the printed circuit board in the high-frequency heating device of the present embodiment. 3 is a view of FIG. 2 as viewed from the direction of the arrow Ya and obliquely from above, and FIG. 3 is a view of FIG. 2 as viewed from the direction of the arrow Ya.

  As shown in FIG. 2, the shunt resistor 30 is arranged on the printed circuit board 32 on substantially the same straight line as the diode bridge 101 and the IGBT 205 (configured by the transistor 203 and the commutation diode 204) attached to the heat sink 33. Has been. In this case, the cooling air flows from the mounting side of the step-up transformer 202 toward the mounting side of the cement resistor 50 as shown in FIG.

  In FIG. 3, the layout of the main components is roughly described. The step-up transformer 202 is disposed so as to be opposed to the heat radiating plate 33 so as to be opposed to the heat sink plate 33. The voltage components are mainly mounted on the printed circuit board 32 with control circuit components and weak electrical circuit components on the leeward side of the step-up transformer 202 (front side of the sheet).

  A part of the cooling air flows through the space between the heat sink 33 and the step-up transformer 202. Since the shunt resistor 30 is mounted on the printed circuit board 32 along the air path of this space, the cooling air is Most of them pass through without being blocked by the shunt resistor 30. In other words, the obstruction factor of the cooling air due to the shunt resistor 30 is minimized. Note that even if the shunt resistor 30 is arranged along the air path, there is a possibility that the area to which the cooling air hits will increase depending on its shape. In such a case, the area to which the cooling air hits will be minimized. A shunt resistor 30 may be disposed.

  Also, as shown in FIG. 4, the cooling air that has entered under the step-up transformer 202 and passes through the step-up transformer 202 reaches the cement resistance 50 on the leeward side. Since it is mounted in the crossing direction, the cooling air hits the entire side surface of the cement resistor 50. As a result, the cement resistor 50 is efficiently cooled.

Furthermore, some cooling air passes above the step-up transformer 202, and this cooling air hits the entire upper surface from the upper side of the cement resistor 50. Therefore, by arranging the cement resistor 50 in a direction substantially intersecting with the cooling air flow path, it is possible to cool the entire upper surface uniformly and reliably.
Note that even if the cement resistor 50 is arranged in a direction substantially intersecting the air passage, there is a possibility that the area hit by the cooling air may be reduced depending on the shape thereof. In such a case, the area hit by the cooling air is the maximum. The cement resistor 50 may be arranged in such a direction.

As described above, according to the high-frequency heating device according to the present embodiment, the shunt resistor 30 used for measuring the output current of the unidirectional power supply unit 1 is arranged along the air path of the cooling air flowing on the printed circuit board 32. Since it arrange | positions on the printed circuit board 32, the ratio which inhibits the flow of cooling air can be suppressed to the minimum, and the improvement of cooling efficiency can be aimed at.
In addition, since the cement resistor 50 is disposed in a direction substantially intersecting the cooling air flow path, the heat generating cement resistor 50 can be efficiently cooled.
The arrangement configuration of the shunt resistor 30 and the cement resistor 50 enables efficient cooling even if the space saving associated with the miniaturization of the high-frequency heating device main body is performed.

Note that the arrangement of the shunt resistor 30 along the airflow path of the cooling air flowing on the printed circuit board 32 means that the cement resistance 50 is to be arranged on the leeward side of the shunt resistor 30. It is effective in terms of cooling efficiency, including the point of cooling.
In addition to the cement resistor 50, if there are parts that generate heat when energized, they may be arranged similarly.

  In the above-described embodiment, the cement resistor 50 is inserted between the DC output terminal of the unidirectional power supply unit 1 and the power supply terminal unit of the control unit 7 as shown in FIG. Instead of the configuration, the AC power source is rectified by inserting diodes 207 and 209 at both ends of the commercial power source 20, and then a cement resistor 50 is connected between the connection point of the respective diodes 207 and 209 and the power supply terminal portion of the control unit 7. It goes without saying that the same effect can be obtained even if the insertion is performed.

  As described above, according to the high-frequency heating device according to the present invention, the shunt resistor used for measuring the output current of the unidirectional power supply section is the printed circuit board along the air path of the cooling air flowing on the printed circuit board. Since it arrange | positions above, the ratio which inhibits the flow of cooling air can be made into the minimum, and the improvement of cooling efficiency can be aimed at.

  Moreover, since the cement resistance accompanied by heat generation is disposed in a direction substantially intersecting the cooling air flow path, it is efficiently cooled.

  Therefore, even if the mounting density of the electrical components arranged on the printed circuit board is increased due to the space saving accompanying the downsizing of the high-frequency heating device main body, the heat generating components can be efficiently cooled. In other words, space can be saved and the high-frequency heating apparatus main body can be downsized.

It is a circuit diagram which shows the structure of the high frequency heating apparatus which concerns on one embodiment of this invention. It is a perspective view which shows a part of printed circuit board with which each component of the high frequency heating apparatus of FIG. 1 was mounted. It is the perspective view which looked at the printed circuit board of FIG. 2 from diagonally upward of the arrow Ya direction. It is the front view which looked at the printed circuit board of FIG. 2 from the arrow Ya direction. It is a circuit diagram which shows the example of a change of the high frequency heating apparatus which concerns on one embodiment of this invention. It is a circuit diagram which shows the structure of the conventional high frequency heating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Unidirectional power supply part 2 Inverter part 3 High voltage rectifier circuit 4 Magnetron 7 Control part 30 Shunt resistance 31 Buffer 32 Printed circuit board 33 Heat sink 50 Cement resistance 101 Bridge diode 205 IGBT

Claims (2)

At least on the substrate, a unidirectional power supply unit that converts commercial power into a unidirectional using a diode bridge, and
An inverter unit having at least one semiconductor switching element, and converting the power from the unidirectional power source unit to high-frequency power by turning on / off the semiconductor switching element;
A step-up transformer for stepping up the output voltage of the inverter unit;
In a high-frequency heating device having a high-voltage rectifier that doubles the output voltage of the step-up transformer,
A shunt resistor interposed in series with respect to the location where the output current of the unidirectional power supply unit can be measured;
The high frequency heating apparatus, wherein the shunt resistor is disposed on the substrate along an air path of cooling air flowing on the substrate and is disposed substantially in the same straight line as the diode bridge and the switching element. .   The high-frequency heating device according to claim 1, wherein a cement resistor for dropping the commercial power source to a predetermined voltage is arranged in a direction substantially intersecting with the cooling air flow path.

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