JP2998599B2 - Power supply for magnetron drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for driving a magnetron for use in a high-frequency heating device such as a microwave oven, or a device utilizing a microwave obtained from a magnetron such as a medical device, a drier, and a gas excitation device. is there.

[0002]

2. Description of the Related Art A conventional power supply for driving a magnetron includes a step-up transformer, a high-voltage rectifier circuit, and a magnetron. The step-up transformer boosts an AC voltage of 50 Hz or 60 Hz obtained from a commercial power supply, and converts the boosted AC high voltage. A high voltage rectifier rectifies the voltage to a DC high voltage to energize the magnetron and generate microwaves.

However, in such a configuration, the step-up transformer boosts the AC voltage of 50 Hz or 60 Hz, so that it is very large and heavy.
In order to reduce the size and weight of this step-up transformer,
Inverter-type electronics in Japan have been used to convert the 0-Hz or 60-Hz AC voltage into a high-frequency AC voltage of 20 kHz or higher, and to boost the high-frequency AC voltage to reduce the size and weight of the step-up transformer. Has been adopted in the range.

FIG. 6 is a circuit diagram of a magnetron driving power supply used in the inverter type microwave oven. The AC voltage of the commercial power supply 11 is rectified into a unidirectional voltage by a rectifier circuit, and is supplied to the inverter circuit 1 having the semiconductor switch element 2. The semiconductor switch element 2 is a bipolar junction transistor (BJ).
T), a transistor having a self-commutation function such as a MOS field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT), and a diode connected in anti-parallel to the transistor. The unidirectional voltage of the rectifier circuit is 20 k by this inverter circuit 1.
Hz. The boost transformer 3 constituting the inverter circuit 1 boosts the high-frequency AC voltage generated in the primary winding 4 and outputs a high-frequency high-frequency AC voltage. This high-frequency high-frequency AC voltage is supplied to a high-voltage rectifier circuit 12.
Is rectified and converted to a DC high voltage. The magnetron 7 is energized by the high DC voltage and emits microwaves.

[0005]

However, the magnetron driving power supply having such a configuration has the following problems.

When the frequency is increased by using the semiconductor switching element 2 as described above, a high-frequency AC current flows through the step-up transformer 3, so that the heat generated by the winding is very large. Therefore, it is necessary to forcibly cool with a cooling fan or the like.
FIG. 7 is a sectional view in which a power supply for driving a magnetron is mounted on an inverter type microwave oven. When the step-up transformer 3 arranged as described above is forcibly cooled by the cooling fan 8,
Since the cooling air passing through the step-up transformer 3 only passes above and below the primary winding 4, the contact area between the primary winding 4 and the cooling air is so small that cooling cannot be performed very effectively. . Further, the primary winding 4 of the step-up transformer 3 uses an electric wire called a litz wire in which a plurality of insulated wires are twisted to suppress an increase in AC resistance due to a high-frequency AC current. As described above, when the frequency is increased to several tens of kHz, an increase in the AC resistance is increased as shown in FIG. 8, and a desired effect cannot be obtained.

An object of the present invention is to solve the problems of the conventional power supply for driving a magnetron, and to provide a power supply for driving a magnetron which facilitates high output by suppressing a temperature rise of a winding of a step-up transformer. It is intended for.

[0008]

In order to achieve the above object, the present invention provides an inverter circuit for receiving the output of a unidirectional power supply and converting it to AC power, a control unit for adjusting the power converted by the inverter circuit, The inverter circuit includes a high-voltage rectifier circuit that receives AC power output from the inverter circuit and supplies high-voltage DC power to a magnetron, and a cooling fan that forcibly air-cools the inverter circuit, wherein the inverter circuit includes a step-up transformer, a primary winding of the step-up transformer, A resonance circuit configured by a resonance capacitor, and at least one semiconductor switch element that excites the resonance circuit, and the step-up transformer has a gap through which cooling air passes on at least one end surface of the primary winding ; And the primary winding of the step-up transformer
Twist multiple strands of insulated strands to further
Several strands were used.

Further, the primary winding of the step-up transformer pitch of combined φ0.18mm less and twist the wire diameter of the wire 25
mm or less.

[0010]

According to the magnetron driving power supply of the present invention, the following functions are provided.

[0011] That is, effectively, it is possible to cool the primary winding by providing a space for cooling air passes in at least one of the step-up transformer primary winding, further raising
Twist multiple wires with the primary winding of the voltage transformer insulated
A structure in which multiple twisted wires are further twisted together
Effectively reduces the proximity effect caused by high-frequency AC current
However, an increase in the resistance of the primary winding can be suppressed.

Further, the pitch of the wire diameter of the further plurality of twisted align structure of the plurality of twisted strands of wires that are insulated with the primary winding of the step-up transformer wires together less and twisting φ0.18mm When the thickness is 25 mm or less, the proximity effect due to the high-frequency AC current can be effectively reduced, and the increase in the resistance of the primary winding can be suppressed.

[0013]

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

FIG. 1 is a sectional view showing a magnetron driving power supply according to an embodiment of the present invention mounted on a microwave oven. The step-up transformer 3 has a ferrite core and magnetically couples a primary winding 4 and a secondary winding 5 wound around the same bobbin. The ferrite core has a gap for suppressing magnetic saturation, and the gap is arranged near the center of the primary winding 4. The bobbin of the step-up transformer 3 is provided with a gap 6 for passing cooling air sent from the cooling fan 8, and the gap 6 is directed to the cooling fan 8 so that the cooling air can pass through the gap 6 effectively. Are arranged.
For this reason, the primary winding 4 of the step-up transformer 3 and the cooling air come into contact with each other by the gaps 6 provided on the upper and lower sides of the winding and the bobbin, so that the contact area increases and the cooling of the primary winding 4 is effectively performed. Can be performed.

The primary winding 4 according to the present embodiment is the same as that shown in FIG.
As shown in (a) and (b), a plurality of insulated strands 4a are twisted, and then a plurality of bundles 4b of the twisted wires are twisted. With such a configuration, the increase in AC resistance due to the high-frequency AC current is as shown by the black triangle in FIG. 3, and the AC resistance in the operating frequency range (tens of kHz) of the inverter type microwave oven is smaller than that of the conventional electric wire. Effective reduction can be achieved.

The increase in the resistance value due to the high-frequency current can be explained as follows. That is, the force acting on the electrons e inside the adjacent copper wire is a force that draws the outer periphery of the copper wire as shown in FIG. 4 according to Fleming's law. For this reason, the current flowing through the copper wire concentrates on the outer periphery thereof, causing a bias in the current density distribution. Therefore, twisting the electric wires in a direction in which the force (vector F) received from the current flowing through the adjacent copper wire and the moving direction (vector v) of the electrons e reduces the bias in the current density and suppresses the increase in AC resistance. However, in the method of twisting a plurality of wires at once like a conventional stranded wire, the effect of twisting the wires is reduced because adjacent wires are parallel. However, by arranging a plurality of twisted bundles of electric wires as in the present embodiment, the number of adjacent electric wires in parallel decreases, and an increase in AC resistance can be more effectively suppressed. Becomes

FIG. 5 is a diagram showing the relationship between the temperature rise of the step-up transformer of the magnetron driving power supply of the present embodiment and the input power of the magnetron driving power supply. A black circle shown in FIG. 5 is a conventional product, a black triangle is a product of the present embodiment, and the product of the present embodiment is a bundle of electric wires 4b obtained by twisting a plurality of insulated wires 4a.
Are further twisted, and the strand has a diameter of φ0.
The twist pitch D of the stranded wire of 18 mm or less is set to 25 mm or less, which shows that the temperature rise of the winding is effectively reduced as compared with the conventional product.

[0018]

As described above, the magnetron drive power supply of the present invention has the following effects.

(1) An inverter circuit for receiving the output of the unidirectional power supply and converting it to AC power, a control unit for adjusting the power converted by the inverter circuit, and receiving the AC power output from the inverter circuit and applying a high voltage DC to the magnetron. A high-voltage rectifier circuit for supplying electric power and a cooling fan for forcibly cooling the inverter circuit, wherein the inverter circuit includes a step-up transformer, a resonance circuit including a primary winding of the step-up transformer and a resonance capacitor, and the resonance circuit. And at least one semiconductor switch element that excites
The step-up transformer has a configuration in which a gap for allowing cooling air to pass is provided on at least one end surface of the primary winding, so that the area where the primary winding contacts the cooling air can be increased, so that the primary winding is effectively used. Cooling , and one of the step-up transformers
The next winding is a stranded wire consisting of multiple insulated strands
In addition, a multi-strand structure enables high circumference
To effectively suppress the increase in AC resistance due to wave AC current.
To make it easier to increase the output of microwave ovens.
This has the effect.

( 2 ) In addition, the primary winding of the step-up transformer has a wire diameter of φ0.18 mm or less and a twisting pitch of 25 mm or less. It is possible to effectively suppress an increase in AC resistance due to current.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a magnetron driving power supply according to an embodiment of the present invention mounted on a microwave oven.

FIG. 2A is a front view showing a primary winding of the boosting transformer of the embodiment. FIG. 2B is a cross-sectional view of a primary winding of the boosting transformer of the embodiment.

FIG. 3 is a diagram showing an AC resistance increasing rate of a primary winding of the step-up transformer of the embodiment.

FIG. 4 is a diagram showing an electromagnetic action between adjacent conductors.

FIG. 5 is a diagram showing a temperature rise of a primary winding of the step-up transformer according to the embodiment of the present invention;

FIG. 6 is a circuit diagram of a conventional magnetron driving power supply.

FIG. 7 is a cross-sectional view showing a conventional magnetron driving power supply mounted in a microwave oven.

FIG. 8 is a diagram showing an increase rate of an AC resistance of a primary winding of a conventional step-up transformer of a power supply for driving a magnetron.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter circuit 2 Semiconductor switch element 3 Step-up transformer 4 Primary winding 4a Element wire 4b Bundle of stranded wires 6 Air gap 7 Magnetron 8 Cooling fan 12 High voltage rectifier circuit 13 Resonant capacitor 14 Control unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 62-10391 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 6/66

Claims (2)

(57) [Claims] An output of a unidirectional power supply is converted into AC power.
An inverter circuit, and an electric power to be converted by the inverter circuit.
A control unit for adjusting the force, and an output from the inverter circuit
Supply AC power and supply high voltage DC power to magnetron
A high-voltage rectifier circuit and a cooler forcibly cooling the inverter circuit.
The inverter circuit is a step-up transformer.
And the primary winding of the step-up transformer and the resonance capacitor.
And a small circuit for exciting the resonance circuit.
With at least one semiconductor switch element
The step-up transformer is cooled at least on one end face of the primary winding.
A magnetron driving power supply having a structure in which a gap for passing wind is provided and a primary winding of the step-up transformer is configured by twisting a plurality of insulated strands and further twisting a plurality of twisted wires. 2. The primary winding of a step-up transformer has a wire diameter of φ
0.18mm or less and twisted magnetron drive power supply according to claim 1, wherein the pitch was 25mm below.