JPS63221582A - Radio frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-frequency heater in a magnetron-based device using an inverter-type high-voltage generating circuit.

Prior art magnetrons used in microwave ovens require high voltages on the order of 4KV. Conventionally, such a high voltage was boosted to about 2KV using a transformer using a silicon steel plate, and then a desired voltage of about 4KV was obtained using a voltage doubler circuit. However, the power of the transformer is about 1 kW, and the size and weight of the transformer are also quite large.

In order to improve these drawbacks, a high voltage generation circuit using one type of inverter has been proposed.

This method rectifies the commercial power supply using a diode.
After performing slight smoothing with a power supply capacitor, a resonant circuit is constructed with the primary winding of the high-frequency transformer and a resonant capacitor, and using this and a semiconductor switching element,
The high frequency transformer is driven at a frequency of 20 KHz or higher, which exceeds the human audible frequency, to obtain the high voltage of 4 KV required for the magnetron. As a result,
The transformer is advantageous because it can be made smaller. This system will hereinafter be referred to as an inverter one-way high voltage generation circuit.

Problems to be Solved by the Invention As mentioned above, by using an inverter-type high voltage generation circuit, the transformer can be made smaller;
A semiconductor switching element, a diode, two capacitors, an inverter control circuit for controlling the semiconductor switching element, and the like are required, which causes various problems as shown below. That is, (1) The number of parts increases.

(2) Semiconductor switching elements and resonant capacitors generate transient voltages 3 to 10 times higher than commercial power supplies, so sufficient insulation distance must be provided or insulation deterioration due to dust, moisture, etc. must be prevented.

(3) It takes time to connect the increased number of parts.

(4) It is necessary to efficiently cool semiconductor switching elements, diodes, etc.

(6) There are problems such as the need to prevent beats and the like due to high frequencies (subharmonics) of the oscillation frequency of the inverter.

Means for Solving the Problems The present invention solves all the problems of the prior art described above. That is, in the above-mentioned one-way inverter high voltage generation circuit, the main components through which the main power current flows, namely the rectifying diodes, smoothing capacitors, resonant capacitors, and semiconductor switching elements, are integrally molded with resin together with the metal heat sink. be.

Since it is integrally molded with working resin, there is only one part, and even if a transient voltage occurs, it is safe because it is filled with resin, and it is also integrated with the heat sink, so it can dissipate heat. It's easy to do, and since it's hardened with resin, it doesn't make any audible humming noises.

Embodiment FIG. 2 is a circuit diagram of a main part of an embodiment of the present invention and a one-way inverter type high voltage generation circuit when implemented in a household microwave oven. In the figure, 1 is a commercial power supply, 2 is an inverter module, 3 is a rectifier diode, and 4 is a smoothing power supply capacitor, which are connected in parallel to the DC output of the diode.

Note that, if necessary, a check coil may be inserted between the diode and the power supply capacitor to prevent unnecessary radiation. 5 is a resonance capacitor, which is connected in parallel with the primary side of the high frequency step-up transformer 6. 7 is a semiconductor switching element. This is connected to an inverter control circuit 9 through a control input terminal 8 . 10.11
is a control voltage terminal for inputting to the inverter control circuit.

The inverter control circuit 9 generates a control signal for turning on/off the semiconductor switching element, and the semiconductor switching element turns on/off in response to this. As a result, a high voltage is induced on the secondary side of the high frequency step-up transformer 60, and the magnetron 12 generates radio waves.

When used in a household microwave oven, the inverter-type high-voltage generating circuit needs to generate power close to approximately 1KW, and the commercial power supply is connected to both ends of the resonant capacitor.
Even in the case of ov, it reaches 500 to eoov. If these parts are connected using ordinary electric wires, not only will the number of parts become complicated, but the structure for holding all the parts will also become complicated. The present invention solves these problems, and one embodiment thereof is shown in FIG.

FIG. 1 is a perspective view of essential parts of an embodiment of the present invention.

In FIG. 1, reference numeral 13 denotes a heat dissipation plate on which comb-shaped unevenness is formed using an aluminum metal drawing method or the like.

14 is a case attached to the heat sink 111.

This includes the aforementioned rectifier diode 3. Power supply capacitor 4. A common camera capacitor 6 and a semiconductor switching element 7 are housed therein. Especially semiconductor switching element 7
The heat dissipation plate 13 is used for the diodes and diodes, which require heat dissipation.
It is installed in close contact with the 16 to 2o are terminals for connecting to an external circuit.

The semiconductor switching elements and rectifier diodes are attached to the heat sink in advance, and the necessary connections are made to other parts before molding each part, and then the parts are placed in an appropriate mold and resin molded.

Another method is to bond the semiconductor switching element and the power supply diode to the heat sink while remaining as semiconductor chips, resulting in a further heat dissipation effect. FIG. 3 shows a sectional view of a main part of an embodiment of this method.

In FIG. 3, reference numeral 13 denotes a metal heat sink, on which an insulating plate 21 made of ceramic is bonded, a semiconductor chip 22 is further bonded on top of this, and bonding wires are attached to terminals 24 having the same structure. Connect by 26. in addition,
The semiconductor chip is molded with a first resin so as to cover the semiconductor chip.

The entire body is then molded with a second resin. It is preferable to use a relatively soft resin as the first resin in order to prevent damage to the semiconductor chip due to thermal stress. By adopting such a configuration, heat dissipation from the semiconductor chip can be further improved.

Further, if the inverter control circuit is also housed within these resin molds, the number of parts and wiring can be further reduced, making it convenient.

It would also be a good idea to resin mold the parts wired on the printed circuit board.

As described in detail, the present invention has the following effects because the main components of the inverter high voltage generation circuit are molded with resin together with the heat sink.

(1) Since the parts are integrated, there is only one part, so the configuration of the device is simple.

(2) Since it is molded with resin, sufficient insulation is guaranteed, and there is no need to worry about deterioration due to dust or humidity.

(3) Since the semiconductor element is attached to a heat sink, heat radiation is good.

(4) All parts are fixed with resin, so there is no buzzing or chattering noise.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part of an embodiment of the present invention, FIG. 2 is a circuit diagram of a one-way inverter high voltage generation circuit, and FIG. 3 is a sectional view of the main part. 3... Rectifier diode, 4... Power supply capacitor, 6... Resonance capacitor, 7...
... Semiconductor switching element, 13 ... Heat sink, 26 ... First resin, 2 Ryo ... Second resin. Name of agent: Patent attorney Toshio Nakao and 1 other person3-
IE-&Kishidai ■-to-tz people Kotsugutsusu 14-11 Ke-people

Claims (2)

[Claims] (1) A diode that rectifies the commercial power supply, a power supply capacitor inserted in parallel with the DC power supply by the diode, and a step-up transformer that supplies the high voltage of the magnetron.
a resonant capacitor connected in parallel to the primary side of the step-up transformer, and a semiconductor switching element connected in series to a parallel circuit of the step-up transformer and the resonant capacitor;
A series circuit of the resonant capacitor and the semiconductor switching element is connected in parallel to the power supply capacitor, and at least the diode, the power supply capacitor, the resonance capacitor, and the semiconductor switching element are molded with resin together with a metal heat sink. A high-frequency heater featuring (2) Molding with soft resin so as to cover one side of the semiconductor chip constituting the semiconductor switching element,
The semiconductor element, a power supply capacitor, a resonant capacitor,
The high-frequency heater according to claim 1, characterized in that the diode is integrally molded.