JPS62110293A - 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 improvements in high-frequency heating devices for so-called dielectric heating such as microwave ovens, and more specifically,
This invention relates to an improvement of a high-frequency heating device configured to use an inverter as its power source, generate high-frequency power by the inverter, boost the voltage with a step-up transformer, and drive a magnetron.

BACKGROUND OF THE INVENTION Various configurations of high-frequency heating devices of this type have been proposed in order to reduce the size, weight, or cost of the power transformer.

FIG. 6 is a circuit diagram of a conventional high frequency heating device. In the figure, the power of commercial power supply 1 is diode dob IJ
A unidirectional power source is formed. 3 is an inductor, and 4 is a capacitor, which serves as a filler for high frequency switching of the inverter.

The inverter includes a resonant capacitor 5, a step-up transformer 6, a transistor 7, a diode 8, and a drive circuit 9. The transistor 7 performs a switching operation with a predetermined cycle and duty factor (ie, on/off time ratio) by a base current supplied from the drive circuit 9. As a result, the primary winding 101C of the step-up transformer 6 has a collector current as shown in FIG. 8(a). and diode current! A current of 1 cd centered at d flows through the primary winding 10 as shown in Fig. 7(b).
A high frequency current IL flows. Therefore, the secondary winding 1
High frequency high voltage power and high frequency low voltage power are generated in the first and third windings 12, respectively. This high frequency low voltage power is supplied to capacitor 1
3.14 and choke coils 15.16 between the cathode terminals of the magnetron 17, while crystal frequency high voltage power is supplied between the anode and cathode as shown in the figure. As shown in U.S. Pat. No. 4,318,165, capacitor 5 and magnetron 17 are shown in FIG. 7(c).
, (d) flows, the magnetron 17 oscillates, and dielectric heating becomes possible.

With this configuration, transistor 7 is operated at 20KHz-10
When operating at a frequency of about 0 KHz, the weight and size of the step-up transformer can be reduced from a few minutes to a dozen times smaller than when boosting the voltage at the commercial power frequency, making the power supply section more compact.
It has the advantage of being able to reduce costs.

In particular, the high-frequency heating device shown in U.S. Pat. No. 4,318.165 has a so-called flyback converter circuit configuration in which the polarities of the primary winding 10 and secondary winding 11 of the step-up transformer 6 are as shown in the figure. As a result, the magnetron 17 can be driven without using a high-voltage diode normally used for high-voltage rectification, and a high-frequency heating device as shown in FIG. 6 is realized.

Therefore, there is no need for a high-voltage, high-frequency diode that is extremely expensive and large, making it possible to further reduce the size, weight, and cost of the high-frequency heating device.

FIG. 8 shows a sectional view of a conventional step-up transformer 6. E.I.
A primary winding 1o, a secondary winding 11, and a heater winding 12 are attached to a shaped core 18.

The transformer is a one-cage type transformer with a gap 13 in its core, and limits voltage fluctuations due to load fluctuation characteristics of the magnetron 17, which is a nonlinear element. transformer 6 no 2
The next winding 11 has line-to-line withstand voltage and is arranged and wound in multiple layers to save space. Varnish treatment is performed to increase the withstand voltage between each winding layer, and insulating polyester tape or the like is applied between each layer. Further, an insulating gap e was provided between the high-voltage part 14 of the winding and the core, and an insulating material 15 was sandwiched between them to form a high-voltage transformer.

Problems to be Solved by the Invention However, such conventional high frequency boosting devices have the following drawbacks.

The voltage between the anode and cathode of magnetron 17 is VAK
Since the load is large during the magnetron's non-conducting period, the current waveform has to have a large peak value.

As shown in FIG. 7(e), the waveform of VAK is at its maximum when a reverse voltage is applied to the magnetron. Here, the current IA flowing through the magnetron only flows when a voltage of approximately 3.5 KV or more is applied in the direction of magnetron D1, so in order to obtain a predetermined average current, the peak value of vAK must be large. I had no choice. Further, when the magnetron was started, a large VAK was also generated in the forward direction because the magnetron was not conductive until the cathode became hot.

Therefore, in order to increase the withstand voltage of the transformer, it is necessary to increase the insulation distance 111' between the core and the high voltage part of the winding.
This was an impediment to the miniaturization of transformers. In addition, in order to increase the insulation short period E, insulating materials are used.
There was a problem in that the insulation cost also increased. If high voltage countermeasures are not sufficient, corona will occur between the wire and the core, which will shorten the life of the transformer due to heat generation and carbonization of the winding coating, which will significantly reduce the reliability of the high frequency heating device. there were.

Means to Solve All Problems The present invention has been made to solve the drawbacks of the conventional high-frequency heating apparatus, and is a high-frequency heating apparatus constructed by the means described below.

That is, an inverter comprising a semiconductor switch such as a transistor and a resonant capacitor connected in series or in parallel to the semiconductor switch element, a single-cage single-voltage transformer connected in series to the semiconductor switch element, and the inverter. and a magnetron energized by the step-up transformer. The winding direction up to the tap and after the tap are opposite to each other, and the lowermost layer and the uppermost layer of the secondary winding are configured to have approximately the same potential.

Effects The present invention has the following effects due to the above configuration. That is, the high-frequency heating device of the present invention has a configuration in which the secondary winding of the leakage-type step-up transformer is arranged and wound in multiple layers to minimize the winding subane, and a tap is installed at a position approximately in the middle of the winding layers. The winding direction up to the tap and after the tap are opposite to each other, and the lowermost layer and the uppermost layer of the secondary winding are
In other words, the secondary winding is a coil consisting of the winding from the bottom layer to the middle tap, and a coil consisting of the winding from the top layer to the middle tap.
By connecting them in parallel, it is possible to configure the bottom and top layers of the winding layer closest to the core to have almost the same potential as the core, so the withstand voltage between the winding and the core is insufficient. This makes it easier to prevent corona outbreaks caused by coronavirus.

Since insulation measures only need to be applied to the end face portion of the winding close to the core, the amount of insulating material required to increase the withstand voltage can be reduced, making it possible to realize a low-cost and compact transformer.

EXAMPLE Hereinafter, an example of the high frequency heating device of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit configuration of a high-frequency heating device showing an embodiment of the present invention, and the same reference numerals as in FIG. 6 are corresponding components, and the explanation thereof will be omitted.

In FIG. 1, power from a commercial power source 1 is sent to a full-wave rectified DC power source 19 and supplied to an inverter 20. The inverter 20 is composed of a semiconductor switch 7 and the like, and energizes the step-up transformer 6 to supply high-voltage power to the magnetron 17.

The currents flowing through the transistor 7, the primary winding 10 of the transformer, the resonant capacitor 5, and the magnetron 17 are as shown in FIGS. 2(a) to 2(d), and the anode voltage VAK of the magnetron 17 is as shown in FIG. (e) This is because the oiliness of the primary and secondary windings of the 1-voltage transformer 6 is as shown in the figure, and that the 1-voltage transformer 6 is a leakage type transformer, and that the high-voltage capacitor 1a is This is due to the parallel connection to the Macnetron 17.

FIG. 3 shows a sectional view of a step-up transformer according to an embodiment of the present invention. Components with the same reference numerals as those in FIG. 9 are the same components, and their explanation will be omitted. In the figure, the core 18 of the transformer is grounded and has the same potential as the anode of the magnetron 17. The lowermost layer end 21 and the uppermost layer end 22 of the secondary winding 11 are at the same potential as the core 1B. Insulating material 2 is placed on the end surface of the secondary winding layer.
3 is provided. The number of turns of the secondary winding from the lowest layer end to the intermediate tap 24 and the maximum J: The number of turns from the layer end 22 to the intermediate tap 24-1 is assumed to be the same number as the lower layer winding.
The secondary winding is constructed by connecting the windings of the layered portions in parallel. Therefore, the cross-sectional area of the winding is approximately half that of a single winding.

Start winding the secondary winding from the bottom layer and wind it in the opposite direction from the middle tap position to the highest layer so that the inductance of the secondary winding does not cancel when the bottom layer and the top layer are at the same potential. There is.

One end of the heater winding is connected to an intermediate tap, and a high-voltage electric wire with an insulating coating is used for the heater winding. Litz wire is used for the primary winding 10 to prevent heat generation due to skin effect.

FIG. 4(a) shows the voltage distribution of the secondary winding in the dotted line portion of FIG. 3 with arrows, and also shows the winding voltage at the AA' line. FIG. 4(b) shows the voltage distribution and winding voltage of a conventional transformer. In FIGS. 4(a) and 4(b), the beginning part of the arrow is a ground potential which is the same potential as the core, and the end part of the arrow is a high voltage part. In the case of the conventional example (b), the potential difference between the core and the upper layer of winding is Vp, and insulation measures are required between them, but in the case of the present invention (a)
In the case of , since the potential difference between the core and the upper layer of the winding amount is 0, there is no need for insulation countermeasures in this part of the insulation pair area, and there is no need to take an insulation distance.

FIG. 5 shows another embodiment of the step-up transformer of the high-frequency heating device of the present invention. In the figure, the same components as in FIG. 3 are denoted by the same reference numerals, and explanations thereof will be omitted. In FIG. 5, the secondary winding 11 of the transformer includes an independent 1-belt winding 25 and a lower winding 2.
6, the layer winding 25 and the lower layer winding 26 are wound in opposite directions, and the winding end 27 of the lower layer winding 26 and the winding start 2 of the abdomen winding are connected. to form an intermediate tap portion. In this case, there is no need to reverse the width in the middle of winding the wire, and it is the same as conventional winding.

Available.

In addition to sandwiching an insulating material between the end face 29 of the winding layer and the core, is there a method of partially potting the secondary winding? There is a way to do it.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

The secondary winding of the step-up transformer has an aligned multi-layer winding structure, and a tap is provided at a position approximately in the middle of the winding layers, and the winding directions up to the tap and after the tap are opposite, and the lowest layer of the secondary winding and the winding direction after the tap are opposite to each other. Since the uppermost layer is configured to have approximately the same potential, (1) the insulation distance between the transformer core and the uppermost part of the winding can be shortened, making it possible to provide a compact high-frequency heating device with a smaller transformer.

ri) Since fewer parts need to be insulated, it is possible to create a high-voltage transformer at low cost. Since the structure can be changed, an inexpensive high-frequency heating device can be provided.

(3) Since the secondary winding has two wires arranged in parallel, thin wires can be used, and the heat generation of the wires due to the skin effect can be reduced even in the case of high-frequency impark sources.

(4) Since the voltage is high, there is little possibility of life deterioration due to corona discharge, etc., and a highly reliable high-frequency heating device can be constructed.

[Brief explanation of drawings]

Figure 3 is a cross-sectional view of the step-up transformer of the same device, Figure 4 (a)
is an explanatory diagram showing the voltage distribution of the winding of the step-up transformer of the device, FIG. 4) is a characteristic diagram showing the voltage distribution of the winding of the step-up transformer of the conventional high-frequency heating device, and FIG. A sectional view showing another embodiment of a step-up transformer for a high-frequency heating device,
FIG. 6 is a circuit diagram of a conventional high-frequency heating device, and FIG. 7 is a 1E current/voltage waveform diagram of each part of the circuit of the same device, tJ! , 8 shows the y1 voltage of the same device, 5... Resonance capacitor, 6
......Step-up transformer, 7...Transistor, 9...Drive circuit, 11...Secondary winding, 17...Magnetron, 19・・・・・・
Unidirectional power supply, 20... Inverter, 21...
...Bottom layer, 22...Top layer, 24...
··Tap. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (5)

[Claims] (1) A leakage type inverter comprising a semiconductor switch, a resonant capacitor connected in series or parallel to the semiconductor switch element, a drive circuit for driving the semiconductor switch element, and a leakage type inverter connected in series to the semiconductor switch element. a step-up transformer, a unidirectional power source that supplies power to the inverter, and a magnetron energized by the step-up transformer, and the secondary winding of the step-up transformer has an aligned multi-layer winding structure, and almost all of the winding layers are A high-frequency heating device having a configuration in which a tap is provided at an intermediate position, the winding directions up to the tap and after the tap are opposite, and the lowermost layer and the uppermost layer of the secondary winding are made to have approximately the same potential. (2) The high frequency heating device according to claim 1, wherein an insulating material is inserted between the layers of the secondary winding. (3) The high-frequency heating device according to claim 1 or 2, wherein the core of the step-up transformer and the lowest layer of the secondary winding are at substantially the same potential. (4) The high-frequency heating device according to claim 1 or 2, wherein an insulating material is inserted between the end face of the secondary winding and the core of the step-up transformer. (5) The high frequency heating device according to claim 1 or 2, wherein an insulating material is inserted between the primary winding and the secondary winding of the transformer.