JPH0473911A - High frequency transformer - Google Patents

Abstract

PURPOSE:To obtain a transformer having the winding arrangement of less copper loss even with increases in frequency by interlaminating with respective layers of primary windings and secondary windings which use copper foils for connection of the respective layers in a state that adjacent primary winding and secondary winding layers are almost coincided in current density and by making the thicknesses of copper foils of primary windings and secondary windings less than specified values. CONSTITUTION:In a high frequency transformer where primary windings NP and secondary windings NS using copper foils are arranged alternately and fitted to a magnetic core 10, the ratio of turns of primary windings NP to secondary windings NS should be a natural number or fraction number, and respective layers of primary windings and secondary windings are interlaminated and connected in a state that the thickness delta of the copper foil of the primary winding NP and the secondary winding NS is delta<3XK/sq. rt. f. K is the constant of skin effect: 66[mn] in copper, and f is the frequency [Hz] of current applied to the winding. For example, when the ratio of turns is 1:10, primary winding NP is parallel winding whose one turn is 10 pieces, and the secondary winding NS is winding of 10 turns, where parallel windings are interlaminated with each turn of the secondary winding NS.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a high-frequency transformer suitable for use in electronic equipment that handles high frequencies of approximately several MHz, and particularly relates to improvements in reducing loss.

<Prior Art> When a sinusoidal AC voltage Vp of frequency I is applied to the primary side of a transformer, the magnetic flux density B induced in the core can be expressed by the following equation.

B=vp/(2z/nt・5eff)
(1) Here, nl is the number of primary windings, and S eff is the effective cross-sectional area of the core. Therefore, as the frequency I increases, the magnetic flux density B within the core decreases, making it possible to downsize the core. However, the distribution of the current flowing through the windings is biased due to the skin effect and proximity effect described below, and as the frequency becomes higher, the effective equivalent resistance increases, that is, the copper loss increases.

■ Skin effect Figure 12 is an explanatory diagram of the skin effect, where (A) is a cross section of a conductor, (
B) represents the current distribution in the diametrical direction.

The skin effect refers to the fact that as the frequency increases, current flows concentrated on the conductor surface.The skin thickness δ, which occurs when leakage magnetic flux around the conductor enters the inside of the conductor, is the constant K of the skin effect. It is given by the following formula using .

δ=to/J/[mml ■Here, I is the frequency. If f is IMHz and the conductor material is copper, K is 66.1 [mm], so δ is 66.1 μ.
m. Therefore, in the case of a single wire, the internal AC resistance can be reduced by making the wire diameter as thick as the skin. However, since there is a certain limit to the current density that can be passed through the conductor, the load current on the secondary side is limited, and the space factor decreases due to the subdivision of the winding.

■ Proximity Effect Figure 13 is an explanatory diagram of the proximity effect, where (A) shows the case where current flows in the same direction in two lined up conductors, and (B) shows the case where the current flows in the opposite direction. Proximity effect refers to the fact that when there is a current-carrying conductor in close proximity, the magnetic field created by this conductor is not uniform across the conductor's cross section, so the magnetic field inside the conductor is not completely canceled out and losses increase. When flowing in the same direction, the current is distributed on the outside, and when flowing in the opposite direction, the current is distributed on the inside. To alleviate this problem, the distance between adjacent conductors can be reduced to about the thickness of the skin, but there is a problem in that the shape of the transformer becomes larger.

In FIG. 14, the conductor is made of copper foil, and these two copper foils are located in parallel with a distance d between them. Figure 15 is the 14th
FIG. 3 is an explanatory diagram of AC resistance Rac in the arrangement shown in the figure. The vertical axis shows AC resistance RaC based on DC resistance RdC,
A distance d is placed between the horizontal glazes. The width W of the copper foil is 5m.
This is an example of calculation when m, thickness l are 100 μm, and frequency I is IMHz. Rac/Rdc is 1.5 for copper foil alone, but increases to 2.2 in the same direction (for example, in an inductor with a coil-shaped winding), and increases in the opposite direction (
For example, in a transformer with alternating primary and secondary windings, this decreases to 1.3.

<Problems to be Solved by the Invention> As mentioned above, as the frequency increases, copper loss increases due to the skin effect and proximity effect, leading to an increase in the temperature of the transformer, leading to breakdown of magnetic permeability and damage to the winding insulation. This caused deterioration. Furthermore, there is a problem in that miniaturization of the transformer is restricted when heat radiation is taken into consideration.

The present invention has solved these problems, and an object of the present invention is to provide a high-frequency transformer having a winding arrangement with low copper loss even when the frequency is increased.

Means for Solving the Problems> The present invention achieves the above objects by alternately arranging primary windings and secondary windings using copper foil on a magnetic core. This is a high frequency transformer with the following configuration.

That is, the turns ratio of the primary winding and the secondary winding is a natural number or a fraction, and each layer of the primary winding and the secondary winding is laminated alternately, and each layer of the adjacent primary winding and secondary winding is stacked alternately. The layers are connected in a state where the current densities of are approximately the same, and the thickness (δ) of the copper foil of the primary winding and the secondary winding is set to δ<3xK/J/: a skin effect constant, 66[-1] for copper.

12 Frequency of current applied to winding [H2].

It is characterized by the following.

<Function> Each component of the present invention has the following function. Since the primary and secondary windings are made of copper foil, and the thickness is equivalent to the thickness of the skin effect, AC resistance can be reduced.

In addition, since the primary and secondary windings are arranged alternately,
The direction of current flow is reversed, reducing the influence of the proximity effect and reducing copper loss.

<Example> The present invention will be explained below using the drawings.

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

In the figure, a core 10 is made of a magnetic material, such as BI type cocoa. The primary winding Np is the number of turns Np''
C″ is given by the design conditions.The number of turns of the secondary winding NS is Ns
Basically, they are stacked alternately with the primary winding NP.

FIG. 2 is an explanatory diagram in which the turns ratio is 1:1, (A) is a winding connection diagram, and (B) is a sectional view of the winding configuration, here showing the case of three layers. The primary winding NP has 3 layers per turn, and the secondary winding Ns has 3 layers per turn.As shown in the cross-sectional diagram, both are alternately wound in single layers, and the 3 layers are realized by wiring. There is.

FIG. 3 is an explanatory diagram when the turns ratio is 1=10, in which (A) is a winding connection diagram and (B) is a sectional view of the winding configuration.

The primary winding Np consists of 10 parallel windings (shunt winding), and the secondary winding Ns consists of 10 turns of winding, and the parallel winding is connected to each turn of the secondary winding Ns. They are layered alternately.

FIG. 4 is an explanatory diagram when the winding ratio is 2=3, where (A) is a winding connection diagram and (B) is a winding configuration cross-sectional view.

The secondary winding Np is composed of 6 layers of 2 turns and 3 parallel windings, and similarly the secondary winding Ns is composed of 6 layers of 3 turns and 2 parallel windings. Here, it is preferable to use one copper foil for one layer, and each copper foil is laminated alternately between the primary winding Np and the secondary winding Ns, and the desired winding ratio is achieved by wiring. There is. Generally, the turns ratio is n:m (m is a natural number of 2 or more, and n
), the primary winding Np and the secondary winding Ns are made of copper foil that is the least common multiple of n and rn.

For example, when the winding ratio is 2=3, the least common multiple is 6, so the primary winding Np and the secondary winding Ns are each made of six pieces of copper foil. Of course, the number of sheets may be 12, which is a natural number multiple of the least common multiple.

Next, analysis of AC resistance and current density distribution will be explained. FIG. 5 is a cross-sectional view of a multilayer transformer model as an analysis example. Here, 10 copper foils with a width of 5 mm and a thickness of 100 μm are used.
The sheets are stacked at intervals of 100 μm, and are vertically symmetrical with respect to the center.

FIG. 6 is a current density diagram of each copper foil when current flows in opposite directions in each layer, and FIG. 7 shows a current density diagram of each copper foil when current flows in opposite directions in the order of 3 to 2 layers from the top. Generally, the product of the current IP flowing in the primary winding of a transformer and the number of turns Nρ has the following relationship with that of the secondary winding.

Np-1p=Ns-1s (3) Therefore, when the current flowing through the entire copper foil is added, it becomes zero. In Figure 6, since the strength of the magnetic field on both the upper and lower sides of each copper foil is almost the same, the eddy currents induced thereby cancel each other out, reducing the AC resistance (conductor C0nduCter1 in Figure 2).
~5, the AC resistances are 1.05, 1.01, 1.
0G, 1.01, 1.06).On the other hand, in Fig. 7, the strength of the magnetic field becomes non-uniform, so eddy currents remain and AC resistance increases (corresponding to conductors 1 to 5). , AC resistance is 1.21, 1.4G, 1.97, 1
．． 44°1.24).

FIG. 8 is an explanatory diagram of the thickness of copper foil. Thickness δ of one sheet of copper foil and AC resistance Rac (expressed as a ratio to DC resistance RdC)
0 When the frequency I is IMHz, the thickness of the skin effect is 66 μm. 0 As shown in the figure, at a thickness δ almost equal to the thickness of the skin effect, the magnetic field distributed in the width direction of the copper foil This is because the eddy currents induced by this are canceled out. Therefore, if the thickness is three times or less than the skin effect thickness, the AC resistance is two times or less, which is preferable.

FIGS. 9 and 10 are explanatory diagrams of a transformer using such copper foil for winding. In FIG. 9, copper foil is wrapped concentrically around the central pillar of the El core. In this case, it is difficult to determine the length of the winding wire because the length of one round is different for each layer to be wound, which poses an obstacle in manufacturing. In FIG. 10, copper foil is formed into a disk shape and laminated, and although all the winding lengths are the same, there is a problem in that it becomes difficult to connect the windings to each other. This connection work requires each winding to be connected in a coiled manner, so care must be taken when soldering. Therefore, there has been a desire for a winding structure that allows for easy winding of copper foil.

FIG. 11 is an explanatory diagram of a tape-shaped copper foil winding, showing (1) to (4) in the order of work steps. First, an insulating layer is provided on a tape-shaped copper foil winding (FIG. 11 (1)).

This involves applying insulating tape to the top and bottom of the copper foil, or using chemical methods to fold it to fit the shape of the zero-order core (Figure 11C-(4)), and make the necessary turns. Obtain several windings. In this case, in order to realize the winding structure of the primary winding and the secondary winding explained in FIG. 1, it is preferable to wind two rows of copper foil tapes in a double spiral shape so as to overlap each other.

In this way, the manufacturing method is simple and easy to use on an automatic line, and even when manufacturing by hand, the copper foil winding work can be easily performed without requiring any special jig.

<Effects of the Invention> As explained above, according to the present invention, when copper foil is used for the primary winding and the secondary winding, both are tightly coupled to reduce the influence of vortices, and the copper foil is Since the thickness of the foil is approximately the thickness of the skin effect, the copper loss is small even at high frequencies, and therefore the temperature rise of the transformer itself is small, so there is an effect that a high frequency transformer that can be miniaturized is provided.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figures 2 to 4 are explanatory diagrams of the winding configuration and connections according to the winding ratio, and Figure 5 is a cross-sectional view of a multilayer transformer model as an analysis example. , Figure 6 shows the case where the current flows in the opposite direction in each layer, and Figure 7 shows the three layers from the top.
The current density diagram of each copper foil when the current flows in the opposite direction in the order of one sheet and two sheets, Figure 8 is an explanatory diagram of the thickness of copper foil, and Figures 9 and 10 are when copper foil is used for winding. Explanatory diagram of the transformer, 1st
FIG. 1 is an explanatory diagram of a tape-shaped copper foil winding. Fig. 12 is an explanatory diagram of the skin effect, Fig. 13 is an explanatory diagram of the proximity effect, and Figs. 14 and 15 are two copper foils placed in parallel! FIG. 3 is an explanatory diagram of AC resistance in the case of 10...Core, Np...Primary winding, Ns...Secondary winding. (A/) No.? Noah 70 core diagram (B) (A) series diagram CB), Takeyoshi Ichikara 7X3 Z; 1 3 pieces x 2 Diagram 9ih thick? [umj

Claims (1)

[Claims] A high-frequency transformer in which a primary winding and a secondary winding made of copper foil are arranged alternately and attached to a magnetic core, the transformer having a turn ratio between the primary winding and the secondary winding. A natural number or a fraction, the layers of the primary winding and the secondary winding are alternately laminated, and the layers are connected in such a way that the current density of each layer of the adjacent primary winding and secondary winding is approximately the same, and The thickness (δ) of the copper foil of the primary winding and the secondary winding is δ<3xK/√f K: skin effect constant, 66 [mm] for copper, f: current applied to the winding A high frequency transformer characterized by having a frequency [Hz].