US3439257A

US3439257A - Magnetic core transformer with an adjustable coupling factor

Info

Publication number: US3439257A
Application number: US543926A
Authority: US
Inventors: Sigfrid Schweizerhof
Original assignee: Telefunken Patentverwertungs GmbH
Current assignee: Telefunken Patentverwertungs GmbH
Priority date: 1965-04-22
Filing date: 1966-04-20
Publication date: 1969-04-15
Anticipated expiration: 1986-04-15
Also published as: FR1476324A; SE318612B; DE1263852B; GB1141611A

Description

April 15, 1969 MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLING FACTOR Filed April 20, 1966 s. SCHWEIZERHOFY Sheet 014 l l/ I i [0 H SIGNAL. W APPLYING 1 9. l MEA NS 1 I le "11 OUTPUT SIGNAL 21V SIGNAL APPLYING /22 MEANS MEANS 6 l I I J l i k 1 Pl Ic 7: a l, 4, F/g. 2

INVENTOR Sigfrid Schweizerhof ATTORNEYS April 15, 1969 s. SCHWEIZERHOF' 3,439,257 MAGNETIC CORE TRANSFORMER WITH [KN-ADJUSTABLE COUPLIN G FACTOR Filed April 20. 1966 Sheet 2' 014 Fig. 4

mvsrvron Sigfrid Schweizerhof AT'TORN EYS April v 15, 1969 I s. SCHWEIZERHOF MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLING FACTOR Filed April 20, 1966 Sheet ATTORNEYS Filed April 1 20. 1966 w v. v w- V7(MV) s. SCHWEIZE RHOF 3,439,257 MA GNET IC LCORE TRANSFORMER WITH AN ADJUSTABLE COUPLING FACTOR Sheet 4 of 4 e; (A MPE RE -TUHV$) Fig.6

INVENTOR Sigfrid Schweizerhof ATTORNFYS us. Cl. 323-56 United States Patent 3,439,257 MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLING FACTOR Sigfrid Schweizerhof, Backnang, Germany, assignor to Telefunken Patentverwertungsgellschaft m.b.H., Ulm (Danube), Germany Filed Apr. 20, 1966, Ser. No. 543,926 Claims priority, appliction Germany, Apr. 22, 1965,

Int. Cl. H02p 13712; H02m 5/12 Claims ABSTRACT OF THE DISCLOSURE A magnetic core transformer, having an adjustable coupling factor which can be varied by means of a control current. The transformer has a magnetic core having four core zones made of the same material and arranged between four apertures. The core zones and the apertures are symmetrically arranged with respect to the center of the magnetic core. Also included in the transformer are an input and output winding, each penetrating two apertures which lie on diametrically opposite sides of the magnetic core center, and a control means for selectively magnetizing, up to saturation, two of the core zones that lie on diametrically opopsite sides of the core center. The control means includes a control winding and means for passing an adjustable control current through the control winding, so that in the absence of control current, there will be no inductive coupling between the input and output windings and as the control current is increased, the inductive coupling will increase.

The present invention relates to magnetic core transformers and to such transformers having a variable coupling factor which can be electronically regulated.

More particularly, the invention relates to magnetic core transformers wherein the coupling factor may be electronically regulated over a wide range by current means such as a control current, an adjustable direct current or current pulses, and such transformers have many uses, particularly in the communication art. For example, such transformers may be used for quickly establishing electrical connection in gate circuits for alternating currents or pulse signals. Also, this type of transformermay be used in electronic telephone exchange systems for testing the coil and busy condition of the subscriber lines and wherein the line current to be detected flows through the control coil of the transformer, causing the test signal which is electrically separate therefrom to be switched through the output of the transformer. The test signal may be in the form of a continuous alternating voltage or of a voltage pulse. The afore-described magnetic core transformers may also serve as modulators whereby the modulation of the input voltage is effected by varying the coupling between the input winding and the output winding. Furthermore, trans-formers having a coupling coefficient which can be electrically regulated may also be used as magnetic amplifiers if such transformers have a coupling factor which can be regulated within desired limits and with relatively low control power.

In the majority of applications for such magnetic core transformers, two factors are of primary concern. Thus, not only is the greatest possible variation in the coupling factor desirable, but above all, it is desirable to provide the transformer with complete decoupling between the input and output winding while maintaining adequate decoupling between these windings and the control winding.

Although prior art arrangements have attempted to provide each of these features in a single magnetic core transformer arrangement, it has previously been found that with the prior art arrangements only one desirable feature can be maintained at one time.

The prior art proposals include arrangements in which the degree of coupling between two coils is varied within certain limits by adjusting the permeability of the coupling ferromagnetic core through means of a separate bias magnetization winding arrangement as a result of which, the leakage inductance of the two windings is varied at the same time. These arrangements, however, have the decisive disadvantage for many uses in that a complete coupling and above all a complete decoupling between the input winding and the output winding is not obtainable, even with the aid of very large control fluxes. In addition, these arrangements also suffer from an undesirably large variation in the inductance of the transformer windings.

There have also been provided magnetic amplitude modulator arrangements in which the carrier signal is modulated by means of direct current bias-magnetized controllable inductors such as are shown in German Patent No. 1,050,839. However, the blocking to passing ratio of such inductors, which depend on the shape of the magnetization curve of the core material, is not very satisfactory and moreover, such arrangements generally necessitate the use of additional transformers.

Other arrangements are also known in which complex circuits having current-controlled inductors serve for precise modulation or signal transmission. Such an arrangement is disclosed in German Patent No. 910,671. However, the inductors only operate with resonant tuning and can therefore only be used for a specific carrier frequency and, in addition, a considerable expenditure for the arrangement is required due to the complex circuitry therefor.

Another known arrangement includes the use of superconducting materials. In this arrangement the coupling between two adjacent coils is varied in such a manner that an interposed plate is driven, by means of a controllable magnetic field, out of the superconducting state, i.e., complete magnetic shielding, into the normal conducting state, i.e., weak shielding. This method, however, has the disadvantage that it requires a complex and expensive lowtemperature cooling arrangement which uses, for example, liquid helium as the refrigerant, and furthermore, this method presents practical difliculties because of the very narrow transistion region between the two states of conductivity such that the desired coupling effect can not always be achieved.

It is therefore a primary object of the present invention to provide a magnetic core transformer which overcomes the disadvantages of prior art arrangements.

It is another object of the present invention to provide a magnetic core transformer having a coupling factor which can be regulated over a wide range.

It is a further object of the present invention to provide a magnetic core transformer which also provides for complete decoupling between the input and output windings while maintaining adequate decoupling between these windings and the control windings.

In essence, the objects of the present invention are achieved by providing a transformer having a core with four symmetrically arranged apertures wherein each of the input and output windings penetrates through two different non-adjacent apertures of the core. The arrangement is such that when the input winding is energized, the associated total magnetic flux provided thereby does not permeate the total turn area of the output winding and thereby provides zero coupling. A control winding is passed through all four apertures in such a direction that two non-adjacent of the four core zones, hereinafter referred to as control webs, situated between the apertures can be saturated by the control flux such that by means of a control current, the closed flux path of the input winding, to an adjustable extent, can be caused to pass through the turn area of the output winding for providing a coupling factor other than zero.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a simplified pictorial view of a magnetic core transformer arrangement according to the present invention.

FIGURE 2 is a simplified pictorial view of another embodiment of a transformer arrangement according to the present invention.

FIGURE 3 is a side view of a further transformer embodiment according to the present invention in which the core is formed from a plurality of pieces and the coils are shown in cross section.

FIGURE 4 is a plan view, partly in cross section, of the transformer arrangement of FIGURE 3.

FIGURE '5 is an exploded perspective view of a transformer arrangement including two disc-shaped cores as shown in FIGURE 1.

FIGURE 6 illustrates a curve of the output voltage versus control flux for the arrangement of FIGURE 5.

Referring now to the drawings, there is shown in FIGURE 1 a transformer arrangement including a disclike core 1 having four

circular apertures

2, 3, 4 and 5 respectively, with the centers of such apertures being arranged in the form of a rhombus in the plane of the core so that imaginary lines drawn between these centers would be perpendicular to one another and bisect one another to form a square. An input winding 6 having a signal applying means 20 connected thereto is arranged to pass through the core 1 by passing through the

apertures

2 and 4, thus surrounding the middle part of the core. An output winding 7 which is to be coupled to the input Winding also passes through the core by passing through

apertures

3 and 5 and forms a further winding about the center part of the core which is perpendicular to the input winding 6, the output winding having a signal receiving means 21 connected thereto. A control winding 8 which comprises two component windings 9 and 10 connected in series passes through all four apertures in the core and has a signal applying means 22 coupled thereto such that when a signal, for example, a variable direct current I is passed through the winding in the direction shown in the drawing, the control winding effects a change in the coupling factor. Due to the apertures, the core is formed with four core webs which separate the apertures and two of such webs are surrounded by the control winding and are shown hatched in the drawings. These webs are designated as control webs and are magnetically saturated to varying degrees by the control winding at their narrowest point:

It is readily apparent from the arrangement illustrated in FIGURE 1 that without the bias magnetization provided by the control current, i.e., I =0, the magnetic coupling between the input winding 6 and the output winding 7 will be zero for reasons of symmetry. However, the passing of a control current through the control winding causes the control webs to saturate and thus there will be provided a corresponding increase in the magnetic resistance, with the flux produced by the input winding 6, shown in broken lines in FIGURE 1, spreading to an increasing extent to the other webs of the core which are not saturated and result in the permeation of the turn area of the output winding 7. On complete saturation of the control Webs, the magnetic coupling between the input winding and the output winding substantially obtains the full coupling value of unity.

Although the core is shown as being disc-shaped in FIGURE 1 the core is not limited to such shape and may differ to a large extent therefrom. For example, as shown in FIGURE 2, although there is again provided a discshaped core 1, the apertures 2' to 5' therefore are provided with a sector-like shape which is more favorable for the blocking of the control webs by saturation. In this figure, the input and output windings and also the control windings correspond to those windings shown in FIGURE 1.

The core may also be produced from a plurality of parts in the interest of more simple production methods and winding techniques for the transformer and particularly for the purpose of using prewound coils which can be slipped onto the core. The core parts may be assembled, for example, with highly machined joints or in the form of an overlapped stacking of transformer laminations. Such a core is illustrated in FIGURES 3 and 4, in which FIGURE 3 is a side view and FIGURE 4 a top view thereof. As shown, the core 1 is in the shape of a square and comprises four component cores 1a, 1b, 1c and 1d which bear against one another at their highly machined surfaces. The two inner component cores 1b, and 1c, are constructed in the form of E-cores and the outer component cores 1:: and 1d in the form of U-cores. The finished windings which are wound on coil formers are mounted in the four apertures 2", 3", 4" and 5". The assembly of this transformer is effected by inserting the E-cores 1b and 1c laterally into the coil formers carrying the output winding 7 and the control winding component 9. Then, the coil former carrying the input winding 6 and the control winding component 10 is slid over these E- cores from above or from below, with the U-cores 1a and 1d being pushed laterally over the latter coil formers and the E-cores to complete the transformer assembly.

It is apparent from FIGURES 3 and 4 that the two component windings 9 and '10 which are connected in series to form the control winding 8 are arranged in different core apertures than that shown in FIGURES l and 2. However, the direction of the current in these component windings when penetrating the various apertures is such that the effect of the control windings on the input and output windings is the same in both cases.

In FIGURE 5 there is shown a further embodiment of the present invention for eliminating an undesired coupling which still exists between the control circuit and the transformer circuit in the arrangement of FIG- URE 1. As shown in FIGURE 5, there are provided two similar transformer assemblies as shown in FIGURE 1. These two assemblies are combined such that the voltages induced by the coupling of the transformer circuits and the control winding and vice versa, are compensated for, for example, by a series connection in opposition of the two control windings. Thus, two transformer cores 1 are arranged to lie closely one above the other, however, these cores are shown separated in an exploded view for reasons of clarity. The input winding 6 and output winding 7 are passed jointly about the two cores with these connections being shown by lettered connection points A to E for the sake of clarity. However, each core 1 is provided with a separate control winding similar to that shown in FIGURE 1. Therefore, the control winding 8 is provided with four

components

9, 10, 11 and 12, the components 9 and 10 being wound in series about the control webs on the top core and connected at the point G to the

components

11 and 12 which are wound in series opposition to the components 9 and 10. Accordingly, with this arrangement, the coupling between the transformer circuits and the control winding is eliminated.

The two cores shown in FIGURE 5 may, for example, be made from highly permeable ferrite plates having the following dimensions: an outside diameter of 45 mm., a thickness of 3 mm., an aperture diameter of 11 mm., and

a minimum control web width of 2 mm. The transformer input and output windings 6 and 7 each may comprise fifteen turns which are wound jointly over both cores with the control winding 8 comprising four component windings of fifty turns each which are wound separately over both cores.

In FIGURE 6, there is shown a curve representative of the output voltage V and its dependency on the number of ampere-turns for the controllable transformer of FIGURE having the above-mentioned dimensions. It should be noted that these dimensions are only illustrative and although a transformer constructed according thereto effects the desired decoupling between the control and transformer windings so as to satisfy the objects of this invention, these dimensions are not necessarily optimum. The measurements were taken with the transformer having a transmission ratio of 1:1 at a frequency of 100 kc.p.s. and with a loading of 150 ohms. As shown, FIG- URE 6 indicates a considerable variation in the output voltage V, which rises from very low values to essentially the full value of the input voltage V with an increase in the control number of ampere-turns 0,, The approximation to a zero output voltage in the decoupled state is, in practice, only limited by the asymmetries in the position of the core apertures and by the capacitative coupling between the transmitter windings. These factors, however, do not effect the principle of the present invention and the influence thereof can be reduced to a very great extent.

Thus, it is apparent from the above description that the magnetic core transformer according to the present invention not only provides a coupling factor which can be electronically regulated over a wide range, but above all, provides an essentially complete decoupling between the input and output windings and an adequate decoupling between these windings and the control winding. Accordingly, the magnetic core transformer according to the present invention has a great number of uses. For example, the transformer may be used for establishing connections through gate circuits and may also be used to advantage for amplitude modulation, for magnetic amplification and for measuring circuits. For providing an amplitude modulated signal, the signal applying means 22 applies a verying control signal to the control winding such that the input signal applied by means 20 would result in an amplitude modulated signal. In the case of a magnetic amplifier, a control signal for providing the desired amplification factor is applied. For use as a measuring circuit, a signal to be detected is applied to the control winding, such that given a predetermined input signal, the resultant output signal is indicative of the detected signal. It should also be noted that its use is not restricted to alternating current signals and that the transformer can be used for signals to be transmitted in pulse form and/ or control signals in the form of pulses.

The relationship between the coupling factor and the control current depends on the magnetization curve of the core material and on the magnitude and the crosssectional configuration along the control webs, and is therefore generally non-linear. In the case of transformers for switched through connections this provides no disadvantages since herein, it is only important to provide a sharp rise in the coupling with the control current. This rise can easily be achieved by means of a core material with a steep hysteresis loop and small remanence and coercive field strength and also by means of control webs having a small enough cross section so as to just permit the alternating current or pulse power to be transmitted. If the device is to be used for modulation purposes, the relationship between the control flux and the coupling factor may be made linear to a certain extent or it may be approximated to another desired function by the selection of a suitable core material and by appropriate shape of the control webs between the apertures. Furthermore, the operating point of the modulator may be favorably adjusted by means of additional bias magnetization.

As previously discussed, the core for the transformer may have different shapes and may be formed differently. For example, depending upon the frequency level to be transnntted or the shape of the pulses to be transmitted, the magnitude of the available control power and other conditions for a particular use of such transformer, the core may consist of a stack of transformer laminations or may be produced from soft magnetic ferrite materials. Ferrites with low saturation induction and high permeabil1ty are particularly advantageous when control power has to be very low with a low power to be transmitted, for example, in modulators or magnetic amplifiers. Furthermore, ferrites permit the transmission or modulation of high frequencies. Therefore, the transformer structure greatly depends upon the application for such transformer.

It will be understood that the above description of the present invention is susceptible to various changes, modifications, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A magnetic core transformer having an adjustable coupling factor which can be varied by means of a control current, said transformer comprising, in combination:

(a) a magnetic core having four core zones made of the same material and arranged between four apertures, said core zones and said apertures being symmetrically arranged with respect to the center of said magnetic core;

(b) an input winding penetrating through two of said four apertures which are arranged on diametrically opposite sides of said center;

(c) an output winding penetrating through the other two of said four apertures which are arranged on diametrically opposite sides of said center;

((1) control means for selectively magnetizing, up to saturation, two of said core zones which are arranged on diametrically opposite sides of said center, said control means including a control winding through which may be passed a control current, whereby, in the absence of said control current, there is no inductive coupling between said input and said output winding and, as said control current is increased, said inductive coupling increases.

2. The transformer defined in claim 1, wherein said magnetic core is entirely made of the same material.

3. A transformer as defined in claim 1 for providing high control sensitivity wherein the narrowest cross section of said two core zones situated between said apertures is sufficiently large for the maximum power to be transmitted.

4. A transformer as defined in claim 1 wherein the configuration of the cross section of said two core zones provides a desired relationship between the degree of coupling and the control current, the configuration depending upon the shape of the magnetization curve for 1 the core and upon the transformer uses.

5. A transformer as defined in claim 1 wherein for transmitting low powers with a high control sensitivity said core comprises highly permeable materials having a low saturation induction.

6. A transformer arrangement as defined in claim 1 and further comprising another of said transformers, said transformers being connected together for compensating for the voltages induced by coupling between the control windings and the input and output windings of the transformer arrangement.

7. A transformer arrangement as defined in claim 6 wherein the cores are mounted in a superposed relation and the input and output windings each pass jointly about each of the cores forming the transformer arrangement and the control winding is wound separately on each of said cores.

8. A transformer arrangement as defined in claim 7 wherein said control winding comprises four component windings, each of said component windings being wound about a respective one of said two core zones in each core with two of said component windings on one of said cores being wound in series opposition to the other two of said component windings on said other core.

9. In combination with the transformer as defined in claim 1, means for applying a signal to said input winding, and means for applying a varying control signal to said control winding for providing an amplitude modulated signal at said output winding such that said transformer serves as an amplitude modulator.

10. In combination with the transformer as defined in claim 1, a circuit arrangement including means for applying a signal to said input winding and means for applying a signal to be detected to said control winding for providing an output signal at said output winding such that said transformer serves as a measuring circuit.

8 V References Cited UNITED STATES PATENTS 7/1948 McCreary 321-68 11/1948 McCreary 321-68 2/1949 McCreary 32168 12/1952 McCreary 323-45 3/1953 Howlett 336212 X 3/1955 McCreary 332--51 8/1957 Dewitz 336171 4/1960 Cornell 336-212 FOREIGN PATENTS 4/1958 France.

WARREN E. RAY, Primary Examiner.

US. Cl. X.R.