EP1023736B1 - Radio interference suppression choke - Google Patents

Description

The invention relates to a choke for radio interference suppression and a process for its manufacture.

In clocked power supplies, especially in switching power supplies, it occurs during very steep voltage or current edges the switching operations of the power supply to electromagnetic Disorders. These so-called "broadband radio interference" are undesirable, however. Their frequencies are in the range a few hundred kilohertz into the megahertz range. According to the norms of electromagnetic compatibility (EMC) are these radio interference at the point of origin, that is, to eliminate within the device.

The most effective method for radio interference suppression lies in the Use of so-called single-line chokes. conductor chokes are chokes for radio interference suppression, which are ring-shaped, on a wire or a pin of a circuit component attachable magnetic tape cores are formed. such Chokes for radio interference suppression are from the data book Toshiba Corporation, Material & Components, Technical Data, "Amorphous Noise Suppressor, AMOBEAD ™, Serial No. E-63001, January 30, 1988.

Single-line chokes assign to other components Interference suppression, such as an RC low pass, the advantage of large inductances even with large choke currents as well as a broadband interference suppression in the range of 10 kHz to 30 MHz. Furthermore, they have a special high insertion loss even in the lower frequency range. After all, they have low overall losses and small component sizes on.

In the above document are so-called single-line chokes in the form of small wound magnetic tape cores made of amorphous alloys, specified in particular on a cobalt basis. The wobbled Magnetic tape cores become conductors that conduct electricity of the component causing the fault is postponed or attached. There they act as saturable chokes, with their Help high-frequency interference during a switching operation can be effectively combated. Following the Switching takes place through the saturation of the magnetic material of the magnetic tape core, however, no influence on the one to be protected Circuit more.

In the manufacture of such a magnetic tape core from a However, amorphous alloys usually do this entangling band on a winding shaft made of tool steel in usually fixed by spot welding. After welding the magnetic tape core with the desired geometric Data wrapped. Finally the tape ends again by spot welding on the outer circumference of the magnetic tape core attached. After completing the welding process, the Magnetic tape core sheared off the winding shaft. The resulting one annular magnetic tape core can then be known Be processed further. In particular, the Magnetic tape core subjected to a heat treatment and then covered with a passivation layer.

However, such single-line chokes are used in the manufacture, since the ring-shaped components are manually operated via the connection pins, for example a transistor or a diode Need to become. The adjustment of the annular single-conductor choke around the connecting pins a large one Role and requires additional assembly effort.

Another major disadvantage arises from the very poor thermal contact of the magnetic tape core to the Pins of the circuit and the defective caused thereby Dissipation of the heat loss from the magnetic tape core. For example, magnetization leads to the saturation at frequencies in the range of a few hundred kilohertz resulting heat loss usually to a component heating of over 100 ° C. Because of these high temperatures and the magnetic field generated by the operating current in the winding direction Tempering occurs, which is unfavorable causes a rectangular hysteresis loop that again the magnetic field is strengthened in the winding direction. This high temperatures are caused by the alloys used however in the long run not coping, which leads to an aging of the Material of the magnetic tape core with corresponding changes of the magnetic properties of the alloys. This usually require a further increase in magnetic reversal losses, which ultimately leads to the thermal failure of the Throttle can lead.

EP A 0655754 describes an inductive component where a magnetic film is tight around a lead wire to one Magnetic tape core is wound. This document discloses a choke for radio interference suppression according to the preamble of claims 1 and 2.

The object of the present invention is therefore a throttle to specify radio interference suppression, with as much as possible low assembly effort can be produced and for removal the heat loss from the magnetic tape core is very good has thermal contact of the magnetic tape core to the circuit.

According to the invention, this object is achieved by the features listed in the characterizing parts of claims 1 and 2.

Become radio interference suppression by the choke according to the invention both mentioned assembly difficulties avoided, as also the problem of the thermal coupling of the choke the rest of the circuit solved. All other benefits mentioned in particular the very good damping properties remain received without restriction.

In the choke for radio interference suppression according to the invention Manufacture of magnetic tape cores using a lead wire which serves as a winding shaft for the magnetic tape core. The material The connecting wire is made of an alloy that is both spot weldable for welding the magnetic tape to be entangled, as well as solderable for later assembly of the Component. The used as the winding shaft of the magnetic tape core The lead wire remains after the core winding in the magnetic tape core and then serves as the electrical conductor of the Component.

After winding, the magnetic tape cores are removed if necessary a heat treatment to adjust the magnetic properties subjected. Then a wrapping is offered of the magnetic tape core, for example through a common varnish or a shrink tube. Then as a varnish Epoxy powder paint can be used. However, it would also be conceivable the magnetic tape core with a thermoplastic or thermosetting To encase molding compound.

The component then present is a conventional one on the outside Resistance comparable and can be taken for granted as such by appropriate placement machines such as they are common in printed circuit board manufacturing become. It is particularly advantageous if the chokes according to the invention for radio interference suppression as SMD components are executed.

Advantageous refinements and developments are the subject of subclaims.

Figur 1

eine erfindungsgemäße Einleiterdrossel, die als gestiftetes Bauelement ausgeführt ist;

Figur 2

eine erfindungsgemäße Einleiterdrossel, die als SMD-Bauelement ausgeführt ist;

Figur 3

ein Temperaturzeitdiagramm, das die Bauteilerwärmung einer erfindungsgemäßen Einleiterdrossel (b) im Vergleich zu einer Einleiterdrossel nach dem Stand der Technik (a) zeigt.

The invention is explained in more detail below on the basis of the exemplary embodiments indicated in the figures of the drawing. It shows:

Figure 1

a single-conductor choke according to the invention, which is designed as a donated component;

Figure 2

a single-conductor choke according to the invention, which is designed as an SMD component;

Figure 3

a temperature-time diagram showing the heating of the components of a single-conductor choke (b) according to the invention in comparison to a single-conductor choke according to the prior art (a).

In Figure 1, 1 denotes a connecting wire. The connecting wire 1 can be a circular, rectangular, or have a similar cross-section. It would also be conceivable that the connecting wire 1 is band-shaped. Around the connecting wire 1 around a magnetic tape core 2 is arranged. The Magnetic tape core 2 typically consists of a thin one Tape or a thin film, the coil-like around the connecting wire 1 is wrapped around. In addition, advantageously a protective coating to protect the magnetic tape core 2 3 is provided in the area of the magnetic tape core 2 his.

The connecting wire 1, the magnetic tape core 2 and the protective coating 3 then form a single-line choke 4. The ends of the connecting wire 1 can serve as a connector. Typically, however, the ends of the lead wire 1 soldered into the circuit of an integrated circuit.

Figure 2 shows a further single-line choke 4, which here as so-called SMD component (surface mounted device component) is executed. The same elements are corresponding in FIG. 2 Figure 1 provided with the same reference numerals.

The inductor 4 in Figure 2 differs from that in Figure 1 essentially by the housing design. This one SMD component shown is for surface mounting on a Circuit board suitable. The connecting wire 1 is not in here from the magnetic tape core 2 covered area L-shaped. It would also be conceivable, as shown in the example in FIG. 2, that the areas not covered by the magnetic tape core 2 of the connecting wire 1 angled several times L-shaped are.

In addition, a circuit board is designated by 5 in FIG. The single-line throttle 4 is developed on the L-shaped Ends of the connecting wire 1 with a solder connection 6 the circuit board 5 connected.

For the manufacture of the single-line chokes shown in FIGS. 1 and 2 4, the following manufacturing steps are required.

First a wire is cut to a predetermined length, which then forms the connecting wire 1. For the production of the magnetic tape core 2 first becomes an amorphous thin ribbon or a thin magnetic sheet at one end on the lead wire 1 welded. Then this thin tape becomes spool-like wound around the lead wire 1 to a magnetic tape core 2. The second end of the tape is then also by spot welding on the outer circumference of the wound Coil attached. This is typically how you get an annular magnetic tape core (2). Particularly advantageous it is when the annular magnetic tape core (2) is closed Ring is formed.

A heat treatment step then typically closes on. The heat treatment is typically carried out in the Run. The throughput speed is chosen so that the thin band for a heat treatment time 0.5sec ≤ t ≤ 120sec to a temperature of 450 ° C ≤ T ≤ 550 ° C. This heat treatment step serves, among other things, the mechanical one Relaxation treatment of the magnetic tape core 2. Die Permeability and thus the correlated insertion loss can be optimized in the desired way become. Finally, the magnetic tape core 2 in one Magnetic field treated to set the desired hysteresis.

After the wound magnetic tape core 2 as described above was further treated, it is particularly advantageous in the area of the magnetic tape core 2 to apply a protective coating 3. The protective coating 3 serves in particular the mechanical Protection of the magnetic tape core 2.

An epoxy powder coating or a serve thermoplastic or thermosetting molding compound. It would be but also conceivable, the single-line choke 4 with a simple Cover shrink tubing.

It is essential to the invention that the material of the connecting wire 1 is both weldable and solderable. Furthermore, it is essential that the material used for the connecting wire 1 a sufficiently high electrical conductivity as well as a has high thermal conductivity. It's also imperative required that the material of the connecting wire 1 itself is non-ferromagnetic. Otherwise it could be in use the single-conductor chokes 4 through eddy current effects to one extreme heating of the connecting wire 1 come.

These requirements for the material of the connecting wire 1 will be ideally met by copper-based alloys. To achieve spot weldability here are resistance increasing Elements such as nickel, beryllium, Chromium, zircon, manganese or similar elements have been added. The most common are commercially available resistance alloys such as copper-nickel alloys or copper-manganese alloys.

A sufficiently good spot weldability of the lead wire 1 with the ferromagnetic materials of the magnetic tape core 2 is achieved with an alloy for the lead wire, which is composed of the formula CU _100- (a + b) Ni _a Mn _b . Here a and b are given in% by weight and meet the following conditions: 6≤a≤80 and 0≤b≤12.

The best results are achieved with a relatively low alloyed nickel content of approx. 6% by weight or manganese content of approx. 3% by weight. The upper limit of the nickel content of these alloys is on the one hand due to the decrease in the electrical conductivity with increasing nickel content and on the other hand due to the achievement of ferromagnetic compositions. The preferred composition is in the range of approx. 6 to 50% by weight of nickel with additions of 0 to 6% by weight of manganese. For example, the commercial alloy CuMn ₃ from the copper manganese system can be used.

Another alloy for the connecting wire 1 with good spot weldability is achieved with an alloy which is composed of the formula Cu _{100- (a + b)} Nn _a Ge _b . Here a and b are also given in% by weight and meet the following conditions: 3≤a≤6 and 0≤b≤6.

It is essential for the function of the choke for radio interference suppression necessary that the material of the magnetic tape core 2 from an amorphous or nanocrystalline, highly permeable, ferromagnetic Alloy. It is particularly advantageous if this alloy is made of soft magnetic material.

It is particularly advantageous if an amorphous cobalt-based alloy or a nanocrystalline iron-based alloy is used as the material here. These alloys typically have a saturation magnetostriction | λ _s | ≤ 5 ppm.

The simplest form of the protective coating 3 the single-conductor chokes 4 provide the sheathing. It is in Area of the magnetic tape core 2 the component by means of a powder coating coated. In this way you get conventional on the outside Resistances of comparable designs during assembly applied in a donated form on the circuit board 5 and to be soldered.

Another very interesting for later assembly Design can be achieved by overmolding the area of the magnetic tape core 2 with a thermoplastic or thermosetting molding compound in cuboid shape and then cut to length and embossed of the leader. In this way you get so-called SMD components that form part of a component assembly lead to a significant reduction in technical effort and more cost-effectively are producible.

The thermal connection to the surrounding area is available in both designs Circuit comparably good, so that here regarding the Application properties no serious differences are expected.

In accordance with the exemplary embodiments shown below the use of an amorphous cobalt alloy copper nickel lead wires different composition. With magnetic tape cores 2 without heat treatment, alternating field permeabilities become reached at 1 kHz of approx. 3000. At higher Measuring frequencies in the range of 1 MHz reduce the alternating field permeability to values around 1700. However, they will Magnetic tape cores 2 subjected to a heat treatment so improve the magnetic properties become clear. The alternating field permeabilities increase to values of approx. 250,000 (1st kHz) or 7000 (1 MHz).

FIG. 3 shows a temperature-time diagram that shows the heating of the components of a single-line choke (b) according to the invention in comparison to a single-line choke according to the prior art (a). To ensure comparability, two identical inductors were used for the investigation of the magnetic tape cores. The magnetization takes place at a current of I _eff = 4.5 A at a frequency of 100 kHz. Under these conditions, the single-line throttle according to the prior art reached a final temperature of 84 ° C., while the single-line throttle according to the invention warmed up to a maximum of 68 ° C.

Thus, in addition to the automatable further processing due to the proposed design also an optimal thermal Contact of the magnetic tape core 2 over the as live Conductor-connected connecting wire 1 to the printed circuit board 5 reached. This can result in a magnetic core 2 Overheating to tolerable for the alloys used Values are reduced. That way the problem can aging, which is functionally dependent on temperature, be drastically minimized.

LIST OF REFERENCE NUMBERS

1

connecting wire

2

Magnetic tape core

3

protective coating

4

Radio interference suppression choke

5

Circuit board, circuit board

6

solder

Claims (14)

1. Radio-interference suppression choke, comprising

   a connecting wire (1) consisting of an electrically conducting, heat-conducting, non-ferromagnetic first alloy and

   a strip-wound magnetic core (2) consisting of a ferromagnetic second alloy, which includes a thin strip wound into a coil around the connecting wire (1) and rigidly joined to the connecting wire (1) at its inner end,

   characterised in that the first alloy consists of a material suitable for soft-soldering and welding and has a composition given by the formula Cu_100-(a+b)Ni_aMn_b, where a and b are specified in % by weight and satisfy the following conditions: 6≤a≤80 and 0≤b≤ 12.
2. Radio-interference suppression choke, comprising

   a connecting wire (1) consisting of an electrically conducting, heat-conducting, non-ferromagnetic first alloy and

   a strip-wound magnetic core (2) consisting of a ferromagnetic second alloy, which includes a thin strip wound into a coil around the connecting wire (1) and rigidly joined to the connecting wire (1) at its inner end,

   characterised in that the first alloy consists of a material suitable for soft-soldering and welding and has a composition given by the formula Cu_100-(a+b)Mn_aGe_b, where a and b are specified in % by weight and satisfy the following conditions: 3≤a≤6 and 0≤b≤6.
3. Choke according to one of the preceding claims, characterised in that the second alloy consists of a soft-magnetic material.
4. Choke according to one of the preceding claims, characterised in that the second alloy consists of a high-permeability, amorphous or nanocrystalline material.
5. Choke according to one of the preceding claims, characterised in that the second alloy is an amorphous cobalt-based alloy having saturation magnetostriction |λ_s|≤5 ppm after heat treatment.
6. Choke according to one of the preceding claims, characterised in that the second alloy is a nanocrystalline iron-based alloy having saturation magnetostriction |λ_s|≤ 5 ppm after heat treatment.
7. Process for the production of a choke according to one of claims 1 - 6, comprising the following steps:

   a) a connecting wire (1) is cut to length;

   b) the thin strip is fixed at one end to the connecting wire (1) by means of a first weld;

   c) the thin tape is coiled around the connecting wire (1) to form a strip-wound magnetic core (2), and

   d) the other end of the thin strip is fixed to the outer circumference of the magnetic core by means of a second weld.
8. Process according to claim 7, characterised in that the strip-wound magnetic core (2) is subjected to heat treatment in order to improve the magnetic properties and for mechanical stress relief.
9. Process according to claim 8, characterised in that the heat treatment is carried out continuously and that the throughput rate is selected in such a manner that the thin strip is heated to a temperature of 450°C ≤ T ≤ 550°C for a heat-treatment time of 0.5 sec ≤ t ≤ 120 sec.
10. Choke according to one of the preceding claims, characterised in that the choke has a protective coating (3) for protecting the strip-wound magnetic core (2).
11. Choke according to one of the preceding claims, characterised in that the two ends of the connecting wire (1) are bent in an L-shaped manner.
12. Choke according to claim 11, characterised in that the choke (4) is what is referred to as a surface-mounted device.
13. Choke according to one of the preceding claims, characterised in that a closed toroidal core is provided as the strip-wound magnetic core (2).
14. Use of a choke according to one of the preceding claims in a switched-mode power supply.

Images