JPH04338615A - Inverter transformer - Google Patents

Abstract

PURPOSE:To suppress heat due to induction heating by reducing an influence of a magnetic flux leakage from a gap to a primary winding. CONSTITUTION:A primary winding 11 to be wound about the part of a gap 27 in a pair of cores 25, 26 is characterized in that it is so wound that the distance between the cores and the wiring around the gap 27 is made larger than the distance between the cores and the wiring around the cores 25, 26.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter transformer used in an inverter power supply.

0003

2. Description of the Related Art First, a conventional example of an inverter power supply for driving a magnetron for a microwave oven will be explained with reference to FIGS. 5 and 6.

In FIG. 5, 1 is a commercial AC power supply;
After the AC voltage from the commercial AC power supply 1 is rectified by a diode bridge 2, it is smoothed by a choke coil 3 and a smoothing capacitor 4 to obtain a DC voltage. 5 is a switching element, and a freewheeling diode 6 and a resonant capacitor 7 are connected in parallel between the collector and emitter of the switching element 5 to form a resonant switching circuit. Reference numeral 8 denotes a high frequency inverter transformer, which includes a primary winding 9, a secondary winding 12, and a filament winding 13. A DC voltage is supplied to the collector of the switching element 5 via the primary winding 9 of the inverter transformer 8 . The switching element 5 is turned on and off by the drive signal from the drive circuit 14, and the DC voltage is periodically switched to 20 to 30k.
It is converted to a high frequency of about Hz. At this time, a sinusoidal resonant voltage as shown in FIG. 6(b) appears between the collector and emitter of the switching element 5 constituting the resonant switching circuit. In FIG. 6(b), T1 is a period during which the switching element 5 is on, and T2 is a period during which the switching element 5 is off. The sinusoidal high frequency wave is supplied to the primary winding 9 of the inverter transformer 8, and the primary winding 9 is
A high-frequency current as shown in Figure 1 is designed to flow. Further, a voltage doubler rectifier circuit including a voltage doubler capacitor 15 and a high voltage rectifier diode 16 is connected to the secondary winding 12 . Inverter transformer 8-2 with voltage doubler rectifier circuit
The high frequency high voltage generated in the next winding 12 is voltage doubled and rectified to obtain a DC high voltage, and this DC high voltage is applied to the magnetron 1.
It is applied as an anode voltage between the anode and cathode of 7. A filament voltage from filament winding 13 is supplied to the filament of magnetron 17. A current transformer 18 detects the average value of the anode current of the magnetron 17, and the detected current value is input to the inverter control circuit 19. The inverter control circuit 19 controls the input power to the magnetron 17 to a constant value, and the switching element 5
drive timing is controlled.

FIG. 7 shows an example of the configuration of the above-mentioned inverter transformer 8. A pair of cores 25, 26, 1 made of the following type ferrite face each other through an air gap 27.
It consists of a bobbin 28 that holds the secondary winding 9 and a bobbin 20 that holds the secondary winding. The primary winding 9 is wound so that its substantially center is at the gap position. this is,
This is to prevent the inductance of the primary winding 9 from dropping suddenly and causing destruction of the inverter power supply circuit when the magnetic flux passing through the cores 25 and 26 is saturated. In addition,
In FIG. 7, the filament winding is omitted from illustration.

Since the inverter transformer 8 operates at a high frequency, the cores 25 and 26 are made of ferrite instead of silicon steel plate to reduce the weight and reduce the hysteresis loss and overcurrent loss. , it is also possible to downsize the device.

[0007]

[Problems to be Solved by the Invention] In the conventional inverter transformer, as shown in FIG. 8, the distance A between the core and the winding around the gap in the primary winding is the same as the distance B between the core and the winding around the core. It has become. Therefore, when the magnetic flux in the core increases and approaches saturation, the magnetic flux leaks from the gap and crosses the primary winding. Since the current flowing through the primary winding of the inverter transformer is a high-frequency current, this leakage magnetic flux may cause part of the primary winding to be inductively heated and reach a high temperature, which may exceed the winding's heat resistance temperature and lead to damage. There was a problem. Conventionally, countermeasures against this problem have been to raise the heat resistance of the strands or to increase the cooling capacity of the transformer cooling fan to prevent dielectric breakdown between the windings due to heat generation. However, with the increase in the output of microwave ovens and the like, the induction heating of the primary winding has further increased, and more expensive high heat resistant strands, large cooling fans, etc. have become necessary.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inverter transformer capable of suppressing heat generation due to induction heating by reducing the influence of magnetic flux leakage from the gap on the primary winding.

[Configuration of the invention]

0010

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a pair of cores facing each other through a gap,
A primary winding that is wound around the gap in the pair of cores and is supplied with a high frequency converted from a commercial frequency, and a secondary high frequency winding that is wound around one of the pair of cores and has a required voltage value. The primary winding is wound such that the distance between the core and the winding around the gap is larger than the distance between the core and the winding around the core. The gist is what happens when you turn the page.

[0011]

[Operation] Since the primary winding in the gap portion is wound away from the gap, the influence of leakage magnetic flux from the gap on the primary winding is reduced, and heat generation due to induction heating is suppressed.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention.

[0014] In the drawings showing each embodiment shown in Fig. 1 and Fig. 2, the same or equivalent members and parts as in Fig. 7 are indicated by the same reference numerals, and redundant explanations will be omitted. .

In this embodiment, a convex portion 21a having an arcuate surface is formed on the inner surface of the bobbin 21 that holds the primary winding 11 corresponding to the gap 27 position, and the primary winding 11 is positioned at the gap 27. The distance between the surrounding core and winding is core 2
The wires are wound so that the required distance is greater than the distance between the core and the windings around the wires 5 and 26.

As described above, in the inverter transformer of this embodiment, the primary winding 11 in the gap 27 portion is wound at a required distance from the gap 27. The influence of leakage magnetic flux is reduced, and heat generation due to induction heating is suppressed. Therefore, a relatively inexpensive winding with a low heat resistance grade can be used as the primary winding 11. Furthermore, since the amount of heat generated by the primary winding 11 is reduced, it becomes possible to use a smaller fan for cooling the transformer.

FIG. 2 shows a second embodiment of the invention.

In this embodiment, a convex portion 22a having a rectangular cross section is formed on the inner surface of the bobbin 22 that holds the primary winding 11, corresponding to the position of the gap 27.
, the distance between the core and the winding around the gap 27 is the core 25,
The wire is wound so that the required distance is greater than the distance between the core and the winding around 26.

The operation is almost the same as that of the first embodiment.

FIG. 3 shows a third embodiment of the present invention.

In this embodiment, the bobbin 23 holding the primary winding 11 is divided into two, and the primary winding 11 is divided into two layers so that the primary winding 11 is not wound at all near the gap 27. It is wrapped around.

Therefore, in this embodiment as well, substantially the same effect as in the first embodiment can be obtained.

FIG. 4 shows a fourth embodiment of the present invention.

In this embodiment, the inner surface corresponding to the position of the gap 27 in the bobbin 24 holding the primary winding 11 is formed into a convex surface 24a having an arcuate surface. Therefore, the primary winding 11 is wound such that the distance between the core and the winding around the gap 27 is larger than the distance between the core and the winding around the cores 25 and 26 by a required distance.

The operation is almost the same as that of the first embodiment.

[0026]

[Effects of the Invention] As explained above, according to the present invention,
Because the primary winding was wound so that the distance between the core and the winding around the gap was larger than the distance between the core and the winding around the core, the influence of leakage magnetic flux from the gap on the primary winding was reduced. This makes it possible to suppress heat generation due to induction heating. Therefore, it is possible to use a relatively inexpensive primary winding with a low heat resistance grade, and it is also possible to use a small transformer cooling fan.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of an inverter transformer according to the present invention.

FIG. 2 is a longitudinal sectional view showing a second embodiment of the present invention.

FIG. 3 is a vertical sectional view showing a third embodiment of the present invention.

FIG. 4 is a longitudinal sectional view showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional inverter power supply.

FIG. 6 is a waveform diagram showing high-frequency current flowing through the primary winding of the inverter transformer in the inverter power supply of FIG. 5;

7 is a longitudinal sectional view showing an example of the configuration of an inverter transformer used in the inverter power supply of FIG. 5. FIG.

FIG. 8 is a diagram for explaining a problem with the inverter transformer shown in FIG. 7;

[Explanation of symbols]

11 Primary winding 12 Secondary winding 20 Bobbins 21, 22, 23, 24 that hold the secondary windings Bobbins 25, 26 that hold the primary windings Pair of cores 27 Gap

Claims (1)

[Claims] 1. A pair of cores facing each other through a gap, a primary winding wound around the gap in the pair of cores and supplied with a high frequency converted from a commercial frequency; It is wound around one of the cores of the pair and has the required voltage value of 2
and a secondary winding for obtaining a high frequency on the next side, the primary winding having a core-to-winding distance around the gap larger than a core-to-winding distance around the core. An inverter transformer characterized by being wound like this.