JPH0650684B2 - High frequency air core transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [PRIOR ART AND PROBLEMS] A transformer (also called a transformer) receives AC power from one circuit and is connected to one or more other windings magnetically coupled to the AC power. It is an electric component or a static device that obtains an output transformed by an electromagnetic induction action, and has a wide range of applications such as voltage conversion, insulation between circuits, and impedance exchange.

In recent years, electronics have been widely used from industrial products to household items such as toys. This electronic circuit has been remarkably miniaturized along with the progress of semiconductor integrated circuit (IC, LSI, VLSI, etc.) technology, and the power supply for its operation needs to be small and lightweight. Therefore, a switching regulator is widely used as a power source. In order to reduce the size, weight and efficiency of switching regulators, it is conceivable to increase the switching frequency, and from the current mainstream of 50kHz to the higher frequency of 500kHz to MHz switching regulator. , Efforts are being made.

The technical problem for realizing a high-frequency switching regulator is the development of high-speed switching elements (transistors, etc.) and especially small high-frequency transformers. In transformers for switching regulators, sufficient insulation between primary and secondary windings is required. In order to obtain a withstand voltage, it is customary to physically separate the primary coil and the secondary coil, or to wrap them by providing a sufficient insulating layer between the coils. However, in order to minimize the leakage inductance between both coils and the energy transfer loss, the two coils are magnetically coupled by a magnetic path having a high magnetic permeability such as ferrite. When a magnetic core is used, it is difficult to obtain a magnetic material having high magnetic permeability and low magnetic saturation, which has a small size and light weight of a transformer, has a limit in price, and can be sufficiently used even in a high frequency of MHz class.

[Object of the Invention]

An object of the present invention is to provide an inexpensive, compact and lightweight transformer suitable for a high frequency switching regulator and the like.

Another object of the present invention is to make the conductive foil films insulated from each other through an insulating film to be integrally polymerized, and to wind the coil without using a magnetic core, that is, in an air core state, thereby making it inexpensive, compact and lightweight. And to provide a highly efficient transformer that can operate at high frequency.

Yet another object of the present invention is to provide a transformer that is extremely efficient over a wide frequency range.

[Outline of Invention]

As a result of experiments on energy transfer characteristics of transformers of various shapes, in the high frequency band of MHz class, by devising the winding shape, without using a magnetic core,
That is, it was found that the air core substantially eliminates the loss to obtain a highly efficient transformer. That is, it has been found that the energy transfer characteristics at high frequencies become extremely high by superposing two conductive foil films by interposing an insulator between them and winding them in an air-core state. Conventionally, a strip-shaped or foil-shaped conductor is used as a winding wire of a transformer instead of a copper wire having a substantially circular cross section, or a transformer in which a foil-shaped conductor is wound around a magnetic core through an insulating film at the same time is Although already proposed (for example, US Pat. No. 2,521,513), the present inventor can obtain a sufficiently high energy transfer characteristic by devising the winding shape in the air core state in the high frequency band of MHz class. Was recognized for the first time by experiment.

Conventionally, in order to realize a transformer capable of operating at a high frequency of MHz class, we have been obsessed with the improvement of magnetic cores, and have been devoted to improving various characteristics of magnetic cores such as high permeability and high saturation magnetic flux density. However, in the present invention, the problem of increasing the frequency is
This was solved by devising the winding shape in the air core state, and it is a fundamental revolution of the concept of a conventional transformer in which it is not necessary to use a magnetic core in the high frequency band. It has been proved that a high frequency switching regulator of MHz class can be miniaturized by using the air core transformer of the present invention.

Example (A)

FIG. 1 is a schematic diagram showing the structure of an air-core transformer according to an embodiment of the present invention. Conductive foil films 10 and 12 have a thickness of 50μ
m, width of about 10 mm, length of 1650 mm, and an aluminum foil having a suitable size and length at both ends, such as iron or copper wire, or terminals or lead wires 18, 20 and 2
2, 24 are fixed by a well-known technique such as electric welding. Prior to this welding, it is preferable that the welded portion of the lead wire be flattened by a press or the like. This conductive foil film 10,
12 is superposed through plastic films 14 and 16 having a high dielectric constant such as polyethylene and Mylar and a high withstand voltage, and is tightly wound in an air-core state using a winding machine. In this case, 14 and 16 mylar films as an insulator have a thickness of 12 μm, a width of 15 mm, and a length of about 1650 mm.
However, it is preferable that the width thereof is made wider than that of the conductive foil films 10 and 12 to increase the withstand voltage between the conductive foil films.

The thickness of the films 14 and 16 can be determined by the required dielectric strength between windings of the transformer, and the number of turns of the conductive foil films 10 and 12 can be determined by the required inductance and the turn ratio.

In the embodiment (A) of the air-core transformer of the present invention manufactured based on the above manufacturing method, the number of windings was 52 and the inductance of about 16 μH, the capacitance of about 64 nF and the Q value of 0.79 were obtained.

FIG. 2 is an equivalent circuit diagram of the air-core transformer of FIG.
Primary winding W ₁ between the terminals 18-22 is formed by the guide Denhakumaku 10, the secondary winding to the terminals 20-24 W ₂ is electrically Denhakumaku 12
Is formed by. A substantially constant distributed electrostatic capacitance C ₀ is unavoidably formed between the windings W ₁ and W ₂ over the entire length facing each other.

FIG. 3 is an example of a completed perspective view of the air-core transformer of the present invention, in which the conductive foil films 10 and 12 and the insulating films or tapes 14 and 16 are wound and then used as they are, or an appropriate one. The pressure is applied to deform it into a substantially elliptical shape, and the entire part except the terminals 18 to 24 is coated with a resin such as epoxy to prevent characteristic deterioration due to moisture absorption or the like. In addition, since there is no magnetic core, it is easy to be pressed and deformed. Both windings W ₁ , W
It is very effective in making the coupling between the _two more dense and preventing a decrease in efficiency due to magnetic flux leakage.

[Characteristics measurement circuit]

FIG. 4 shows a characteristic measuring circuit diagram of the air-core transformer according to the present invention.

A constant amplitude sine wave signal generator (191 type manufactured by Sony Tektronix Co., Ltd.) 28 having an output resistance Ri of 50Ω is connected to the primary winding W ₁ of the air-core transformer according to the present invention, and the secondary winding W ₂ is connected to the secondary winding W ₂ . Connect a 50 Ω load resistance R ₀ to reduce the voltage drop across both ends to 1
A wideband oscilloscope (Model 2445 manufactured by Sony Tektronix Co., Ltd.) 30 is used for measurement through a 0: 1 probe.

〔Frequency characteristic〕

FIG. 7 shows the measurement circuit of FIG. 4 in which the output amplitude of the sine wave signal generator 28 is maintained constant and the frequency is changed from 50 kHz to 100 MHz to obtain the ratio eo / input voltage eo / input voltage ei.
This is a plot of ei measured with an oscilloscope.

The sample according to the above-described embodiment (A) (the turns ratio of the primary and secondary windings is 1: 1) exhibits the transformation characteristic shown in FIG. 7 (A), which is less than 1 up to about 2 MHz. 5MHz from 2MHz
It is worth noting that it has a high value of 1 or more up to z and above 1 up to about 100 MHz. It is considered that this high-frequency characteristic is due to the fact that the degree of coupling between the primary and secondary windings is extremely dense as a whole and that not only inductive coupling but also electrostatic coupling due to a large capacitance existing between both windings. Further, it is presumed that the transformation ratio of 1 or more is obtained at a high frequency due to the relatively low but gentle Q of this air core transformer.

(Comparative (B))

Next, in order to compare with the present invention, the same material as that of the example (A) was used, and each winding was separated to prepare a wound sample. That is, as shown in FIG. 5, aluminum foil having a thickness of 50 μm, a width of 10 mm and a length of 1650 mm is formed on the conductive foil films 10 ′ and 12 ′, and the Mylar film 14 ′, 1 which is the same as the embodiment (A).
6 ', the conductive foil film 10' is first wound 66 times to obtain an inductance of 17 μH and Q0.87 to be the input side, and the conductive foil film 12 'is further wound 33 times to have an inductance of 15.6 μH. , Q0.83 was obtained on the output side, the same experiment as in Example (A) was conducted using the measurement circuit of FIG. 4, and as a result, the characteristics shown in FIG. There is no frequency where / ei is 1 or more, and around 1MHz and 6
Although eo / ei showed about 0.6 to 0.7 near 0 MHz,
It was found that the energy transfer characteristics were so low that they were incomparable as a whole compared to (A). As described above, it can be seen that even in the high frequency band, good operation at high frequencies cannot be achieved unless they are polymerized and integrally wound as in Example (A).

Example (C)

Next, the characteristics of the air-core transformer according to the present invention are compared by the number of turns.

The conductive foil films 10 and 12 shown in FIG. 1 are 8 μm thick and 6 mm wide.
Aluminum foil and insulators 14 and 16 with a thickness of 6μ
The samples shown in Table 1 were prepared using a Mylar film having a width of m and a width of 7 mm.

As a result of conducting an experiment similar to that of the embodiment (A) using the characteristic measuring circuit shown in FIG. 4, as the number of turns increases, the inductance and the capacitance increase, as is apparent from Table 1, and FIG.
As shown in (a), (b) and (c), it was found that the transformation ratio characteristics of eo / ei spread to the low frequency band side, and it was found that the used frequency band can be arbitrarily selected.

[Linearity]

Next, FIG. 9 shows that the oscillation frequency of the oscillator 28 of the embodiment (A) is made constant (5 MHz and 1 MHz) by the measuring circuit of FIG.
It is the linearity which measured and plotted the output voltage eo in case the input voltage ei was changed to 0.1 to 5 volts by the oscilloscope, ie, a dynamic range characteristic curve diagram. As is clear from FIG. 9, the air-core transformer of the embodiment (A) of the present invention has extremely good linearity over a wide input voltage range. In addition, due to the test equipment used, it was not possible to experiment with higher voltage, but since it is an air core and there is no magnetic saturation factor, it can be easily estimated that a linear output can be obtained even for a larger input. .

[Change, transformation]

Although the preferred embodiment of the present invention has been described above, the present invention should not be limited to this embodiment at all, and various changes and modifications can be made. For example, two or more outputs may be obtained by winding three or more conductive foil films mutually via an insulating sheet. For example, as shown in FIG. 6, one of the two foils is divided into two foils 12 ″ a, 12 ″ b, and the terminals 20 ″ a,
20 ″ b may be connected. The thickness of each conductive foil film can be selected appropriately according to the magnitude of the current flowing through it, and there is no significant difference in characteristics due to that, as compared with FIG. 7 (A). It was also confirmed by the comparison of Fig. 8 (C) Further, the conductor foil film can be formed on both surfaces or one surface of the insulating sheet by electroless plating, vapor deposition or sputtering technique.

〔The invention's effect〕

Since the air-core transformer of the present invention does not use any air-core, that is, a magnetic core or an iron core, it can be made extremely small and lightweight without causing a problem with magnetic saturation, and has a very good energy transfer characteristic at a certain frequency or more. Present. Further, since the conductive foil film is used, tight coupling is possible, and therefore, there is little leakage flux, and a foil having a sufficiently large cross-sectional area can be used as compared with a copper wire having the same circular cross-sectional area, so that the current capacity can be increased, Moreover, the influence of the skin effect can be minimized even at high frequencies. Further, since each winding can be insulated by using an insulating film having an arbitrary thickness, the isolation between windings, that is, the withstand voltage is excellent.

Therefore, the air-core transformer of the present invention is used as a transformer of a switching regulator that operates at a high frequency of MHz class, and is particularly effective for the purpose of improving its efficiency, downsizing, and weight reduction. It goes without saying that it can be used for many purposes requiring pressure resistance.

[Brief description of drawings]

FIG. 1 is an exploded view of an embodiment of an air-core transformer according to the present invention, FIG. 2 is an equivalent electric circuit diagram of the air-core transformer according to the present invention, and FIG. 3 is an embodiment of an air-core transformer according to the present invention. FIG. 4 is a completed perspective view, FIG. 4 is a circuit diagram for measuring the characteristics of the air-core transformer of the present invention, and FIG. 5 shows a main part of another form of the air-core transformer to be compared with the air-core transformer of the present invention. Exploded view, No. 6
FIG. 7 is an exploded view showing a main part of another embodiment of the air-core transformer according to the present invention, FIGS. 7 and 8 are frequency characteristic curve diagrams of one embodiment of the air-core transformer of the present invention, and FIG. FIG. 4 is a characteristic curve diagram of linearity and dynamic range of the air-core transformer of the present invention. 10,10 ', 10 ", 12,12', 12" a, 12 "b ... Conductive foil film 14,14 ', 14", 16,16', 16 "... Insulator 18,18 ', 18 ″, 20,20 ′, 20 ″ a, 20 ″ b, 22,22 ′, 2
4,24 ′ …… Terminal

Claims (1)

[Claims] 1. An air-core winding body is formed by winding two strip-shaped conductive thin films, which are laminated so as to face each other with an insulating layer having a high dielectric constant such as polyethylene or mylar, in an air-core state. Then, a primary side terminal and a secondary side terminal are welded and connected to the vicinity of both ends of the band-shaped conductive thin film of the air-core winding body, respectively, and the air-core winding body is formed into a substantially elliptical shape, and the outer periphery is coated with epoxy or the like. A high frequency air core transformer characterized by being formed by