JP3229309B2 - Magnetic core for interface transformer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a core for an interface transformer for use in a digital transmission device.

[Prior art] 20mH at 20kHz with minimum coupling capacitance
An interface transformer of this kind having an inductance L in excess of
In the so-called S _o interface, used in the interface between the network terminating and each terminal device as a transformer.

ISDN is a new worldwide digital communication system. In ISDN, the connection between the digital local exchange and the network termination is made via the _Uko line interface. At that time, the distance between the digital local exchange and the network terminal can be up to 8 km. Up to eight terminal devices can be connected to one network terminal. The terminal device is, for example, a telephone,
Television phones, video tex, facsimile,
It can be a text fax, workstation or the like. The terminal device can be separated up to 150 m from the end of each network here. The interface between the network termination and the terminal device is called the _So user interface.

Request for such S _o interface is an international standard CCIT
Specified in T I.430 or the German Federal Post Office standard FTZ 1 TR 230. These standards define the impedance of the interface, for example, in relation to the frequency or pulse mask of the transmitted digital pulse. Here, the pulse mask means an allowable range where a pulse should exist,
When S _o interface transformer has a termination resistor of 5 [Omega, it refers to those defined as an allowable range that may be present when the rectangular voltage pulse with about 750mV amplitude and 5.21μs time was sent. For the requirements on the magnetic and electrical properties of the _So interface transformers based on these standards, see, for example, Schaffner Elek.
tronik), company publication PUBL in Lutherbach, Switzerland
1101E, ISDN by H. Hemphill
Using Pulse Transf for Applications
ormers for ISDN-Applications) ". FIGS. 2 and 3 of this publication show the requirements for impedance and pulse transmission according to the post office standard. The ability to transmit digital pulses within a predetermined pulse mask is primarily related to the transformer inductance and capacitance. The transformer inductance L mainly determines the top tilt of the transmitted pulse. Top tilt is an undesirable decrease that occurs during the pulsing of the transmitted pulse voltage. ISDN
Transformer inductance is about 20mH to meet the requirements of
Must be exceeded. The capacitance of the transformer is
In particular, the transition from the high level to the low level affects the signal shape of the transmitted pulse. Here, the lowest possible value is required for the coupling capacitance. Coupling capacitance refers to the capacitance between two different windings of a transformer. The coupling capacitance depends in particular on the number of turns provided and the winding arrangement. S _o core as said publication, for example, RM6 core for an interface transformer is shown. Ferrite is specified for the core material. When ferrite is used, the values for the magnetic permeability μ and the saturation magnetic flux density Bs are limited. Typical values for this are μ = 10000, Bs = 0.45T (Siemens SIFE
RIT (Diferito) T38).

The inductance of the transformer is directly proportional to the magnetic permeability of the core material. In particular, even in the case of DC initial magnetization of a transformer, a relatively large core area or a large number of turns is required in order for the values of the magnetic permeability and the saturation magnetic flux density of the ferrite to satisfy ISDN requirements regarding inductance. However, a large core cross section means an increase in the core size and thus in the volume of the transformer. However, parts that are as small as possible are desired. A large number of turns means an increase in the coupling capacitance and therefore a deterioration in the transmission characteristics. In order to avoid this, a complicated winding structure in which an insulating layer is interposed between the windings is required. This makes the manufacture of the windings complicated and expensive.

[Problems to be solved by the invention] An object of the present invention is to make it possible to manufacture a _So interface transformer based on ISDN requirements with a volume as small as possible, a simple winding structure and a small number of turns. Do is to provide a magnetic core for S _o interface transformer. In particular, it is intended to satisfy the requirements of ISDN in the case of DC initial magnetization of a transformer.

[Means for Solving the Problems] In order to solve the problems, according to the present invention, 20 kHz
In an interface transformer core of a digital transmission device having an inductance L exceeding 20 mH, an amorphous Co-based alloy is used for the interface transformer core. In addition to Co, the core is mainly composed of a total of 3 to 8 atomic% of Fe.
And Mn and 24-29 atomic% of metalloid, and optionally 15 atomic% or less of Ni and 1 atomic% or less of Mo and / or Cr and / or Nb.
An initial magnetic permeability of more than 0 and less than 95,000 is provided. Co-based alloys have very low magnetostriction values. This means that the decrease in magnetic permeability due to stress in the material is very small.

With the core according to the invention, a compact interface transformer with small dimensions can be manufactured. This interface transformer satisfies the requirements defined in the standard by a simple winding structure. In particular, this transformer
The required value for the inductance is also achieved in the case of the initial magnetization as expected based on the asymmetrical current distribution in the DN network. The required inductance can only be achieved with a relatively large core cross section or a large number of turns, since in the case of Co-base alloys with an initial permeability μ> 95000 the permeability is already significantly reduced for small initial magnetizations. You. If the initial permeability μ <25000, the required inductance is likewise achieved only by said means.

In the present invention, the lower limit of the initial permeability of less than 95,000 is a limit value derived from manufacturing technology when manufacturing a magnetic core. In order to obtain a flat BH hysteresis curve having as high an initial magnetic permeability as possible, the core must be cooled in a heat treatment in which a transverse magnetic field is applied. At this time, the initial permeability increases according to the logarithm of the cooling rate. In the annealing process with extremely high load in the annealing furnace, the cooling rate in the transverse magnetic field is only about 3 K / min. Therefore, the initial permeability has an upper limit of 95,000 for manufacturing reasons. In the present invention, the lower limit value 25000 of the initial magnetic permeability is a limit value of the magnetic permeability that can be compensated by increasing the number of windings. If the initial permeability is lower than 25,000, the number of windings must be extremely increased, but the winding and coupling capacitances will increase, which will increase the capacitive impedance drop and increase the interface transformation. Vessel fails to function.

In addition to Co, it has proven to be particularly advantageous to use a Co-based alloy which contains mainly 3 to 8 at.% Fe and Mn and 24 to 29 at.% Total metalloid. Amorphous Co-based alloys having a metalloid content in the range from 5 to about 35 at.% Are known, for example, from EP 21101 and DE-A 30 21 536. However, it has been found that Co-based alloys having a metalloid content of less than 24 at.% Or more than 29 at.% Do not meet the requirements for initial permeability. B, Si, C and P are problematic as metalloids.

A combination of B and Si has proven to be advantageous, where B can be partially replaced by C. Due to the addition of Mn, the core according to the invention also meets the ISDN standard of the _So interface even in the case of said initial magnetization as expected in a transformer at the end of the network. Further, the amorphous Co-based alloy can include one or more of 15 atomic% or more of Ni and 1 atomic% or less of Mo, Cr, or Nb. However, when the Mn content is at least 0.5 atomic%, the core having the maximum allowable value for the initial magnetization is Co-
Obtained by Fe-Mn-metalloid alloy. Extensive research and testing has found that this type of Co-based alloy is a particularly suitable core material for ISDN interface transformers. In this type of Co-based alloy, the metalloid content z is related to the initial magnetic permeability μ, the Fe content a, the Mn content b, the Ni content c, the Mo—Cr—Nb content d, and the B or C content x. And given by:

18 + 1.4 · loge + f <z <18 + 1.7 · loge + f where e = μ (1 + 0.25 (a + c)) f = 0.25 (ab) −0.2cd−3.2x If the magnetic core according to the present invention is used, The _S0 interface transformer can be manufactured with a core cross section of less than 0.2 cm ² for the end of the net and a core cross section of less than 0.1 cm ² for the terminal end.

Embodiment Next, the present invention will be described in detail with reference to the drawings and tables showing a plurality of embodiments of a magnetic core according to the present invention.

FIG. 1 shows an interface and an inductive device in ISDN. These are the _Uko line interface between the digital exchange 1 and the network terminal (NT) 2, and the _So user interface between the network terminal 2 and the terminal equipment (TE) 3. A _Uko interface transformer 4 is used for transmitting information between the digital exchange 1 and the network termination 2. The processing of the digital signal at the network terminal 2 is performed by the electronic device 5. Network termination further comprises a NT interface transformer 6 S _o interface. Transmission of digital signals between the network terminal 2 and the terminal device 3 is performed by transmission lines 7 and 8.
And receiving lines 9 and 10. In terminal device 3, TE
Signal conversion via the interface transformer 11 and processing by the electronic device 12 are performed. The terminal device further comprises a current-compensated radio interference prevention choke 13.

Core based on this invention is used in the NT interface transformer 6 and TE interface transformer 11 S _o interface. Power is supplied to the terminal device in part from the digital exchange via the _So user interface. This applies, for example, when the terminal device is a telephone. The remote power supply of the terminal device is not shown in FIG. Remote power is supplied through the center tap 14 of the NT interface transformer 6. In an ideal case that does not correspond to the actual situation, the supply current is distributed to the transmission lines 7, 8 or the reception lines 9, 10 at the same rate. However, in practice different current paths have different resistances. Possible reasons for this are, for example, different winding resistances of the transformer and different resistances of the plug contacts of the line or of the connecting cord of the terminal device. Such asymmetry of the current in the transmission lines 7, 8 or the reception lines 9, 10 is
Resulting in an initial magnetization NT interface transformer 6 or TE interface transformer 11 S _o interface. A thorough study and calculations for this have shown that the TE interface transformer 11 must take into account an initial magnetizing current of about 3 mA. In comparison, the expected maximum initial magnetizing current in the NT interface transformer 6 is very large. This is because up to eight terminal devices can be connected in parallel to one network terminal. For this reason, an initial magnetizing current of up to about 12 mA is expected.

In order to guarantee the required transmission of the digital pulses falling within a given pulse mask range, the transformer must have an inductance of more than 20 mH even for the initial magnetizing current. Furthermore, the coupling capacitance should be small. The upper limit for this can be considered about 100 pF.

In the following examples, the amorphous core material was manufactured in the form of a thin tape by a melt spin quench method. This process is well known and is not the subject of this invention. An annular core was wound from an amorphous band. The toroid was then heat treated in a transverse magnetic field, ie, a magnetic field parallel to the axis of rotational symmetry of the toroid. The core was heated for this purpose to a temperature of about 420 ° C. and subsequently cooled at a cooling rate of 0.1 to 3 K / min. The core according to the invention has a magnetostriction value of less than 0.3 · 10 ⁻⁶ . This means that the decrease in magnetic permeability due to stress in the material is very small. The interface transformer must have a flat BH hysteresis curve, while the flat hysteresis curve has the property of having a very constant permeability over a wide range of magnetic field strengths. This property is similar to other circular or right-angled B
Cannot be obtained with -H hysteresis curve. In order to obtain a flat BH hysteresis curve, it is necessary to heat-treat the magnetic core in a transverse magnetic field.

Example 1: Co-Fe-M alloy Alloy composition Co68.2 Fe4 Si16.8 B11 based on the above method
Was produced. Various cooling rates of 0.2, 0.4 and 1.0 K / mi were selected. Table I describes the saturation magnetic flux density Bs and the initial magnetic permeability μ measured at a frequency of 20 kHz, and the magnetic field strength Ho at which the magnetic permeability decreases to 70% of the value of the initial magnetic permeability. The magnetic field strength Ho, together with the initial permeability, gives information about the suitability of the transformer material in the presence of initial magnetization. A small Ho value means that it is suitable only for a small initial magnetization.

It has been found that the initial permeability increases with the cooling rate, while the magnetic field strength Ho decreases accordingly. To meet the requirements of the ISDN standard for digital pulse transmission over the _S0 interface, Ho
Is less than 70 mA / cm in the case of the NT interface transformer 6 and less than about 20 mA / cm in the case of the TE interface transformer 11. Therefore, this alloy is suitable for both interface transformers based on its Ho value.

Example 2: Co-Fe-Me-M alloy In Table I, alloys containing Mn in addition to Co, Fe, and metalloid are described as alloy Nos. 2.1 to 11.1. N
Cores according to o.2.1 to 2.3 have an initial permeability of more than 95,000 and are therefore not included in the claims. Corresponding
Since the Ho value is clearly less than 20 mA / cm, this core is not suitable for the interface transformer. In contrast, cores 3.1 to 10.3 all have an initial permeability in the range of 25,000 to 95,000. Also in the case of these cores, the heat treatment has the same effect on the magnetic permeability and Ho as in the case of the core of Example 1. However, the value of Ho always exceeds 20 mA / cm regardless of the cooling rate during the heat treatment. No. 11.1 describes a magnetic core having an alloy composition outside the scope of the claims. The metalloid content is 20 at.% In this example. Ho value is Ho = 50
With this core, the requirements for the interface transformer can only be met when the core cross section or number of turns is increased, since it is very high at 60 but the initial permeability is too low at μ = 1000.

Example 3: Co-Fe-T-M alloy Table II describes the magnetic values of a core made of an alloy not containing Mn. These alloys are supplemented with 1.5 atomic percent Mo
including. It is found by comparison that these cores have a smaller Ho value than the core containing Mn described in Example 2. Therefore, a magnetic core containing no Mn and doped with Mo can be advantageously used for the TE interface transformer 11. By a suitable heat treatment as shown in the core No. 14.1, it is also possible to achieve a particularly high Ho value such that this core can be employed in the NT interface transformer 6.

FIG. 2 graphically illustrates the relationship between metalloid content and initial permeability. The group values indicated by squares relate to alloys with the composition Co balance Fe3.2 Mn1 (Si0.6 B0.4) z. The value of the group indicated by the asterisk is the composition Co residual Fe3.8 Mo1.5
(Si0.6 B0.4) z alloy. From this graph, a particularly advantageous range limit for the metalloid content is shown in relation to the content of the other alloy components and the initial permeability μ. Alloy composition Co _balance Fe _a Mn _b Ni _c T _d (Si _1-x (B, C) _x ) _{z where} T is at least one of the elements Mo, Cr or Nb, and the individual magnetic cores according to the present invention Is expressed by the following equation.

3 <a + b <8, c <15, d <1, 0.3 <x <0.7 For the allowable metalloid content of the magnetic core, 18 + 1.4 · loge + f <z <18 + 1.7loge + f where e = μ (1 + 0 .25 (a + c)) f = 0.25 (ab) -0.2cd-3.2x FIG. 3 shows a magnetic core containing Mn according to the second embodiment and a magnetic core not containing Mn according to the third embodiment. The relationship between Ho and initial permeability is shown graphically. The graph shows that the addition of Mn increases the Ho value. Especially with the magnetic core containing Mn,
A Ho value clearly exceeding the Ho of the magnetic core not containing Mn can be achieved. Therefore, alloys containing Mn are advantageous core materials for loaded interface transformers. Therefore, especially for interface transformers with large DC initial magnetization, alloys containing Mn are advantageous as core material.

Example 4: In another extensive study, amorphous Co-based alloys containing various combinations of Fe, Mn, Ni and Mo loadings were investigated. The results are summarized in Table III. The initial permeability was again measured at a frequency of 20 kHz. The results show that these cores can achieve an initial permeability in the range of 25,000-95,000. This requires relatively high cooling rates, which are often technically difficult to achieve during heat treatment. Cr or Nb has the same effect as Mo. Therefore, suitable magnetic cores are Ni, M, in addition to Co, Fe, Mn and metalloid.
It can also be made with an amorphous Co-based alloy containing o, Cr or Nb. However, alloys which do not contain the last-mentioned alloying elements are advantageous.

Example 5 A transformer was completed with a magnetic core having the alloy composition described in Examples 2 and 3. The transformer had two windings with the same number of turns. The completed device is 9.8 x 6.8 x
It had a size of 5mm. L without DC initial magnetization
The transformer inductance and coupling capacitance C were measured for (0) and for the initial magnetization with I = 2.5 mA DC. The results are summarized in Table IV. Example 2
With the No. 3.2 magnetic core, an inductance exceeding 20 mH was obtained even with a 2.5 mA DC initial load when the total number of turns was already 2N = 34. The inductance could be increased by increasing the number of turns. At the same time, especially the coupling capacitance increased slightly.

The magnetic cores No. 5.3, 6.3, and 7.3 also provided a sufficient inductance and a small coupling capacitance. These cores have an initial permeability of 67,000 to 86,000. Ho value is 26-45
in the range of mA / cm.

Further, the transformer was manufactured with the Mn-free magnetic core of Example 3 No.1.12. This core has a Ho value of only 15 mA / cm. For this reason, the inductance required for a 2.5 mA DC initial load could not be achieved with a total number of turns of 2N = 34, 38 or 42. But 2N = 46, 50, 54
In the case of the transformer having the total number of turns, the specification was satisfied. However, these transformers are disadvantageous for economic reasons due to the large number of turns.

FIG. 4 is a graph showing the relationship between the inductance and the DC initial load for the transformer having the No. 3.2 and 12.1 cores. Each core has 2 × 19 turns. Transformers with core No. 3.2 containing Mn show significantly higher DC initial loads than transformers with core No. 12.1 without Mn. A transformer with a core No. 3.2 containing Mn satisfies ISDN requirements up to a DC initial load of about 5 mA in the above configuration. This core can therefore be used in particular as a TE interface transformer 11.

Example 6: A transformer was manufactured using the cores No.1.2, 7.1, 9.2, 10.2, 11.1, and 27.1. These transformers again had two windings with the same number of turns. The dimensions of the completed device were 14 × 7 × 6 mm. The inductance L (0) without initial magnetization and the inductance and coupling capacitance C with a DC initial load of 12 mA were measured. The measurements were performed at a frequency of 20 kHz. The results are summarized in Table V.

Transformers with cores No.1.2, 7.1, 9.2 and 10.2 already had very good values of inductance and coupling capacitance for a small total number of turns, for example 2N = 38. Thus these transformers meet ISDN requirements. Due to the high DC initial load capability of these transformers, they can be employed especially as NT interface transformers 6. The initial permeability of the core given as an example is 34000
Between ~ 39,000. Ho values are in the range of 90-108 mA / cm. Comparison with the values of Example 5 reveals that for relatively high DC initial loads, a core having a relatively low initial permeability and a relatively high Ho value must be selected. This also applies to the magnetic core No. 11.1 described in Table V.
And 27.1. With these cores not included in the scope of the invention, 120
Or, for a total number of 200 turns, the requirement for inductance is only met. However, this large number of turns again results in a very large combined capacitance. Therefore, these transformers require costly and therefore expensive winding structures, for example by inserting an insulating layer between the windings in order to reduce the coupling capacitance.

FIG. 5 shows the relationship between the inductance and the DC initial load for two transformers having the magnetic core No. 9.2 or 14.1. The transformer had 2 × 19 turns (2N = 38). Transformers with magnetic core No. 14.1 without Mn
Meets ISDN requirements for inductance up to 0 mA DC initial load. In contrast, transformers with No. 9.2 Mn-containing cores meet ISDN requirements for inductance up to a DC initial load of about 14 mA. Therefore, the latter can be employed as the NT interface transformer 6 for a given assembly size and number of turns. FIG. 5 again shows the superiority of the magnetic core containing Mn in the case of a high initial DC load.

Thus, with the core according to the invention, a very compact transformer meeting the requirements of ISDN can be manufactured. A magnetic core suitable for various DC initial loads can be easily selected by the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is a schematic wiring diagram of an ISDN interface, FIG. 2 is a graph showing a relationship between a metalloid content and an initial magnetic permeability of an alloy for a magnetic core according to the present invention, and FIG. 3 is a second embodiment of the alloy.
3 and 3 are graphs showing the relationship between the magnetic field strength Ho at which the magnetic permeability decreases to 70% of the initial magnetic permeability and the initial magnetic permeability, and FIG. 4 shows the inductance of the transformer made of alloy No. 3.2 and No. 12.1. And FIG. 5 is a graph showing the relationship between the inductance and the DC initial load of the transformer made of alloy No. 9.2 and No. 14.1. DESCRIPTION OF SYMBOLS 1 ... Digital exchange office 2 ... Network termination 3 ... Terminal device 6, 11 ... Interface transformer

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Deitmar, Gretztour Karl, Germany Königsberger Gäschjüterase 21 (72) Inventor Gieselher, Hertzer Hanau, Germany Hanau 1, Humphade Inkbäck 2 (72) Inventor Hans Rainer, Hilchinger Langenserbolt, Leipzig 65, Germany (72) Inventor Jörg, Petzold Württeg Köbel, Germany Alange Firasse Jutlase 2 (56) References JP-A-58-1223851 (JP, a) JP Akira 61-243152 (JP, a) JP Akira 60-24338 (JP, a) JP Akira 56-152941 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) H01F 1/14 C22C 45/04

Claims (5)

(57) [Claims] An interface transformer core of a digital transmission device having an inductance L exceeding 20 mH at 20 kHz, wherein the interface transformer core is amorphous.
A Co-based alloy is used, and the magnetic core is mainly composed of 3 to 8 atomic% of Fe and Mn and 24 to 29 atomic% of metalloid in addition to Co, and optionally further 15 atomic% or less of Ni and 1 atomic% or less. A magnetic core for an interface transformer of a digital transmission device, characterized by containing Mo and / or Cr and / or Nb, and having an initial magnetic permeability of more than 25,000 and less than 95,000 by heat treatment in a transverse magnetic field. 2. A Co-based alloy of the following composition Co remainder _{Fe a Mn b Ni c T d} (Si 1-x (B, C) x) has a _z, that time T is elemental Mo, and Cr or Nb At least one of them, the following formula is established for the alloy composition (atomic%): 3 <a + b <8 c <15 d <1 0.3 <x <0.7 18 + 1.4 · loge + f <z <18 + 1. 7 · loge + f where e = μ (1 + 0.25 (a + c)) f = 0.25 (ab) −0.2cd−3.2x The balance is Co and impurities, μ is the initial permeability, and log is e 2. The magnetic core according to claim 1, wherein the core is a common logarithm. 3. The ratio of Mn exceeds 0.5 atomic% (b> 0.5)
3. The magnetic core according to claim 2, wherein: 4. The magnetic core according to claim 2, wherein the magnetic core material does not contain Ni (c = 0). 5. The magnetic core material does not contain Mo, Cr or Nb (d =
0) The magnetic core according to claim 2, wherein: