JPH04283909A - High-frequecy high leakage reactance transformer - Google Patents

Abstract

PURPOSE: To form a high frequency high leakage reactance transformer through the use of flat windings, to provide both functions of the transformer with a controlled leakage reactance and an inductor to the high frequency high leakage reactance transformer, to reduce the number of components of a circuit using the transformer and to make the transformer small in size. CONSTITUTION: The high frequency high leakage reactance transformer 20 has a part 32 made of a low permeability magnetic material placed between a primate winding 28 and a secondary winding 30. The low permeability magnetic material part 32 forms a path for a control magnetic flux for leakage magnetic flux between the primary winding 28 and the secondary winding 30. A high efficiency operation is attained by preventing an excess eddy current from flowing to the flat windings. The high frequency high leakage reactance transformer 20 acts like both a transformer and an inductor to reduce the size of a fixture such as a resonance power supply or a ballast of a discharge lamp.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates generally to magnetic circuit components. More particularly, the present invention relates to high frequency transformers with controllable high leakage reactance.

0002

BACKGROUND OF THE INVENTION It is well known that the size of magnetic components can be reduced by increasing their operating frequency. However, as the frequency increases, winding loss increases due to eddy currents generated in the conductor. These eddy currents are caused by alternating current effects that increase at high frequencies, such as skin effects, proximity effects, and ambient magnetic fields from air gaps.

[0003] Typical windings at low frequencies are generally solenoidal or helical and made of circular, rectangular or foil conductors. However, at high frequencies, the AC to DC resistance ratio of such conductors increases significantly due to skin and proximity effects. In order to make efficient use of the cross-section of the conductor, it is advantageous to limit one dimension of the conductor to one or two skin depths. As a result, planar windings are often used to minimize the overall size of electrical components designed to carry a specified current at high frequencies, as opposed to at low frequencies. Unfortunately, other cross-sectional dimensions of the planar winding cannot be restricted in order to carry large currents, ie to obtain low resistance characteristics. Therefore, although the volumetric efficiency of conductors has been improved by the use of planar windings, eddy currents and their associated losses still remain, making reduction of such eddy currents a high concern.

Conventional magnetic structures, such as inductors, have a high permeability core with concentrated air gaps. Conventional cores also have winding windows that contain conductors wrapped in insulating material. The air gap in the core, which is small enough, is large compared to the overall window size so that the peripheral magnetic flux penetrates the conductor. Such magnetic field non-uniformity causes excessive eddy current losses. As a result, the AC resistance is much larger than the DC resistance.

One method for reducing AC winding losses without increasing the size of the winding window is described in the Power Electronics Specialist Conference Proceedings.
Specialists Conference Pro
ceedings), April 11-14, 1988,
1112-1119, K.D.T.Ngo and M.
．． H. ``Effects of Air Gap on Winding Loss in High-Frequency Planar Magnetism'' by Kuo).
Air Gaps On Winding Loss
in High-Frequency Planer
It has been proposed to distribute the air gap uniformly around the magnetic core, as described in ``Magnetics''. This distributed air gap effect can be achieved by constructing the inductor with a ferrite core that has a controllable low permeability. A low permeability core forms a closed loop structure surrounding a winding window containing a planar copper conductor wrapped in an insulating material. Although the low permeability core structure reduces AC winding losses, losses still occur due to non-uniform current distribution in the conductor resulting from magnetic field non-uniformities. In particular, regions of high magnetic field strength result from concentration of magnetic flux through the path of least reluctance near the corners of the core structure. This high field strength causes undesirable eddy current circulation in the outermost conductors of the windings.

Another method of reducing losses, also described in the above-mentioned article, is to use multilayer windings in the inductor with distributed gaps. Using multilayer windings not only improves the aspect ratio of the core geometry, but also reduces core losses. Furthermore, inductors with multilayer windings of the same current and frequency rating require larger winding windows than single layer ones, the use of which can reduce the negative effects of magnetic field inhomogeneities. Despite the above-mentioned advantages, the disadvantage is that overlapping conductors to form multilayer windings results in large proximity effect losses. However, the overall result is an inductor with an AC to DC resistance ratio equal to or slightly lower than that of a single layer distributed gap inductor.

US Pat. No. 4,943,793 discloses a dual permeability core structure for high frequency magnetic components with low winding losses and low AC to DC resistance ratio. A double permeability core surrounds a winding window that houses a planar winding, with a high permeability section and a low permeability section provided to generate a highly uniform or evenly varying magnetic field on the surface of the winding. It has a part. Magnetic structures such as those described in the aforementioned US patents are useful in constructing high efficiency inductors and transformers.

Certain high frequency circuit applications require the use of both inductors and transformers. for example,
Resonant power supplies generally use a resonant circuit with an inductor and an isolation transformer. Another typical application is as a ballast for discharge lamps such as fluorescent lamps. Therefore, it acts as both an inductor and an isolation transformer, reducing the size of the circuit and
There is a need to construct high frequency, high leakage reactance transformers using planar windings that increase the efficiency of the circuit.

[0009]

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a high frequency, high leakage reactance transformer using planar windings exhibiting low winding losses.

Another object of the invention is to use a planar winding, to have a controlled leakage reactance, and to be able to function as both a transformer and an inductor, a component of the circuit in which the transformer is used. The object of the present invention is to provide a high frequency transformer that can reduce the number and size of the transformers.

[0011]

SUMMARY OF THE INVENTION The above and other objects of the present invention are achieved in a new and improved high frequency high leakage reactance transformer using sections of low magnetic permeability material between planar primary and secondary windings. be done. The low permeability portion provides a controllable flux path for leakage flux between the primary and secondary windings. This prevents excessive eddy currents from flowing in the planar windings and substantially reduces capacitive coupling between the primary and secondary windings. High efficiency operation is thus obtained. Furthermore, the high leakage reactance transformer functions, for example, as an isolation transformer and also as an inductor. Such a combination structure can effectively reduce the circuit size and number of components.

The features and advantages of the invention will become apparent from the following detailed description of the invention, taken in conjunction with the accompanying drawings.

[0013]

DETAILED DESCRIPTION To illustrate the principles of the invention, FIGS. 1 and 2 are obtained by computer simulation for an E-shaped concentrated gap magnetic core 10 and a core 12 using a low permeability section 14 according to the invention, respectively. FIG. 3 is a diagram showing axially symmetrical lines of magnetic flux. Each core 10 and 1
2 is a planar conductor 16 representing the primary winding of a transformer carrying a current of 1 ampere passing through a portion of the core representing a winding window 18;
is shown as having In particular, the planar conductor 1
6 are wound around the respective axis of symmetry, i.e. the central leg 17, of each core. Each core 10 and 1
The influence of the secondary winding (not shown) on 2 is the same in each case, so the flux lines in FIGS. 1 and 2 do not extend above the legs of the core. Furthermore, each core 10 and 12
have the same inductance. For details, please refer to approximately 57
For an excitation energy of 9 μJ, the inductance of each core 10 and 12 is approximately 0.1158 μH. core 12
It is clear from the flux curves that the stray magnetic flux in the area of the winding window of is considerably less than that of the core 10. The eddy current losses in core 12 are significantly less than those in core 10 since eddy currents are approximately proportional to the square of the stray magnetic flux. In the particular example of FIGS. 1 and 2, the eddy current losses in core 12 are about 36% or less of core 10.

FIG. 3 shows one preferred embodiment of a high frequency high leakage reactance transformer 20 according to the present invention. In particular, the transformer of FIG. 1 has a pot core structure having a cylindrical housing 22 and a core post 24 extending between opposite ends of the housing and in concentric relationship with the housing. The cylindrical housing and core strut are each constructed of high magnetic permeability material. Inside the housing is a cylindrical winding window 26 that houses the primary winding 28 and secondary winding 30 wound around the core strut. In the pot core construction, the primary winding and the secondary winding are each preferably constructed of a planar conductor, ie a foil conductor. According to the invention, the primary winding and the secondary winding have a low magnetic permeability section 3 having a cylindrical inner wall concentric with the cylindrical peripheral wall of the housing 22.
separated by 2. This low permeability portion forms a control flux path for leakage flux between the primary and secondary windings. As a result, excessive eddy currents are prevented from flowing through the planar winding. Furthermore, capacitive coupling between the primary and secondary windings is substantially reduced due to the high resistance of the transformer core material in addition to the physical separation of the windings. In this way, high efficiency operation is obtained. Furthermore, a high leakage reactance transformer can function as both an isolation transformer and an inductor, for example. Such a combination structure is beneficial in reducing circuit size and component count.

In an alternative pot core construction shown in FIG. 4, each of the primary winding 34 and the secondary winding 36 includes a plurality of circular planar conductors stacked along the length of the core. Each winding has a hole through which a core post 24 passes during assembly. A suitable winding is described in U.S. Pat. No. 4,959,63.
No. 0 and US Pat. No. 5,017,902. According to the invention, the stacked planar conductors constituting the primary winding and the stacked planar conductors constituting the secondary winding are arranged in the winding window parallel to opposite ends of the cylindrical housing 22. They are separated by low permeability portions 38 which are separated by a low magnetic permeability portion 38.

Suitable high permeability materials are high permeability ferrites of suitable composition that have low losses at high frequencies, such as sintered ferrites of manganese-zinc ferrites. Suitable low permeability materials are, for example, mixtures of ferrite powder and organic binder or sintered ferrite. However, suitable low permeability and high permeability magnetic materials may be used. Typical high permeability and low permeability magnetic materials are described in the aforementioned US Pat. No. 4,943,793. Other suitable low permeability magnetic materials are available from Krystinel Corporation.
It is sold under the trademark KB6 by. A method of manufacturing a dual permeability magnetic structure is described in the above-mentioned U.S. Pat. No. 4,94
No. 3,793 and its divisional U.S. Patent Application No. 519,9
It is described in No. 97.

FIGS. 5 and 6 illustrate another preferred embodiment of a high frequency, high leakage reactance transformer 40 according to the present invention. Specifically, the illustrated transformer has a rectangular housing 42 made of high permeability magnetic material. Internal high permeability part 4
4 divides the winding window into two parts. A low permeability section 48a and 48b is provided within each portion of the winding window, with the low permeability section 48a and 48b being generally parallel to the internal high permeability section 44. A planar primary winding 50 with terminals 51 and 52 is wound around an internal high permeability section 44 . A planar secondary winding 54 having terminals 55 and 56 is wound around the primary winding 50, with low permeability portions 48a and 48b separating the primary and secondary windings. Alternatively, the positions of the primary and secondary windings may be reversed within the core if desired.

FIG. 7 shows yet another preferred embodiment of a high frequency, high leakage reactance transformer 60 according to the present invention. Transformer 60 has a generally rectangular housing 62 made of high permeability magnetic material. The high magnetic permeability portion 64 is a winding window 66
and is generally parallel to the top and bottom of the housing 62. Also, a low permeability section 68 perpendicular to the high permeability section 64 is disposed within the winding window 66 . A primary winding 70 having terminals 71 and 72 and a secondary winding 74 having terminals 75 and 76 are each wound around a high permeability section 64 and a low permeability section 68 is provided between the windings. ing.

The advantages of the transformer of the invention can be achieved over a wide range of operating frequencies, ie from at least 50 Hz to 30 MHz.

While preferred embodiments of the invention have been shown and described, it will be understood that such embodiments are shown by way of example only. Many changes, modifications and substitutions will occur to those skilled in the art without departing from the invention. It is the intention, therefore, to be limited by the scope of the claims that follow.

[Brief explanation of the drawing]

FIG. 1 is a magnetic flux line diagram in a concentrated gap magnetic structure.

FIG. 2 is a magnetic flux diagram in a transformer in which a low permeability section is provided between the primary and secondary windings according to the invention;

FIG. 3 is a cutaway perspective view of one preferred embodiment of a high frequency, high leakage reactance transformer according to the present invention.

FIG. 4 is a cutaway perspective view of another preferred embodiment of the high frequency high leakage reactance transformer according to the present invention.

FIG. 5 is a partially cutaway perspective view of another preferred embodiment of the high frequency high leakage reactance transformer according to the present invention.

FIG. 6 is a side sectional view of the embodiment of FIG. 5;

FIG. 7 is a partially cutaway perspective view of still another preferred embodiment of the high frequency high leakage reactance transformer according to the present invention.

[Explanation of symbols]

20 Transformer 22 Cylindrical housing 24 Core pillar 26 Winding window 28 Primary winding 30 Secondary winding 32 Low permeability part

Claims (8)

[Claims] 1. A high permeability housing having a winding window, a primary winding disposed within the winding window, a secondary winding disposed within the winding window, and a high magnetic permeability housing mounted on the housing. , at least one low permeability portion disposed within the winding window between the primary and secondary windings to form a leakage flux path between the first and second windings; , a high leakage reactance transformer. 2. The housing is generally cylindrical and has a cylindrical peripheral wall and two opposing ends, the housing further being concentric with the cylindrical peripheral wall and having a cylindrical peripheral wall and two opposing ends. 2. The transformer of claim 1, further comprising a high permeability core strut extending therebetween, and wherein said low permeability portion has a cylindrical inner wall portion concentric with said cylindrical peripheral wall portion. 3. The primary winding includes a planar winding wound around the core strut, and the secondary winding includes a planar winding wound around the cylindrical inner wall. 3. The transformer according to claim 2, comprising: 4. The housing is generally cylindrical and has a cylindrical peripheral wall and two opposing ends, the housing further being concentric with the cylindrical peripheral wall and having a cylindrical peripheral wall and two opposing ends. a high permeability core strut extending therebetween, the low permeability portion dividing the winding window into two separate portions and substantially parallel to the opposite ends of the housing; 2. The housing of claim 1, wherein each of said primary and secondary windings has a stacked planar conductor having an aperture for receiving said core strut and is disposed on one of said separate portions of said housing. transformer. 5. The housing has a top, a bottom and two
a generally rectangular structure having two opposing sides and further having a high magnetic permeability section generally parallel to the top and bottom, the transformer being disposed on opposite sides of the high permeability section and having a high magnetic permeability section; two low permeability sections substantially parallel to the high permeability section, the primary winding having a planar winding wound around the high permeability section, and the secondary winding having two low permeability sections substantially parallel to the high permeability section; Claim 1 comprising a planar winding wound around a winding, the windings being separated from each other by the low magnetic permeability portion.
Transformer listed. 6. The housing has a top, a bottom and two
a generally rectangular structure having two opposing sides and further having high permeability portions generally parallel to said top and bottom portions, said low permeability portions being approximately perpendicular to said high permeability portions, and said primary 2. The transformer of claim 1, wherein the and secondary windings each have a planar winding wound around the high permeability section and located on opposite sides of the low permeability section. 7. The transformer of claim 1, wherein said high permeability housing and said low permeability portion are each constructed of sintered ferrite. 8. The transformer of claim 1, wherein the high permeability housing is comprised of sintered ferrite and the low permeability portion is comprised of a mixture of ferrite powder and an organic binder.