Radio interference suppression choke

Inductor devices – Interlinked coils or windings – Coil surrounding linear conductor

Reexamination Certificate

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C336S208000

Reexamination Certificate

active

06310534

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to a choke for suppressing radio interference and is also directed to a method for the manufacture thereof.
In clocked power pack parts, particularly in switched power pack parts, electromagnetic interference occurs due to extremely steep voltage or, current edges during the switching operations of the power pack part. This so-called “broad band radio interference”, however, is undesired. The frequency of the radio interference the region of a few hundred kilohertz up into the megahertz range. In conformity with the standards of electromagnetic compatibility (EMC), this radio interference is to be eliminated at the point of creation, (i.e., within the device).
What is probably the most effective method for suppressing radio interference is the employment of what are referred to as single-conductor chokes. Single-conductor chokes are chokes for suppressing radio interference that are fashioned as annular magnetic tape cores that can be plugged onto a wire or onto a terminal pin of a circuit component. Such chokes for suppressing radio interference are known, for example, from the Data Book of the Toshiba Corporation, Material & Components, Technical Data, “Amorphous Noise Suppressor, AMOBEAD™, Serial No. E-63001, Jan. 30, 1988.
Compared to other components for suppressing radio interference, such as a RC low-pass, for example, single-conductor chokes have the advantage of high inductances even given high choke currents as well as a broad band interference suppression effect in the range from 10 kHz through 30 MHZ. Further, they also exhibit an especially high insertion attenuation in the lower frequency range. Finally, they exhibit low overall losses and low structural sizes.
What are referred to as single-conductor chokes in the form of small, wound magnetic tape cores of amorphous alloys, particularly on a cobalt basis, are discussed in the aforementioned document. The wound magnetic tape cores are slipped or, plugged onto the conductors carrying the current in the component part causing the interference. There, the chokes act as saturatable chokes with whose assistance high-frequency disturbances can be effectively combated during a switching event. Due to the saturation of the magnetic material of the magnetic tape core, however, influencing of the circuit to be protected no longer occurs following the switching event.
In the manufacture of such a magnetic tape core composed of an amorphous alloy, however, the tape to be wound is usually secured to a winding shaft made of tool steel with a spot weld. After the welding, the magnetic tape core is wound to desired geometrical configuration. Finally, the tape end is, in turn, secured to the outside circumference of the magnetic tape core with a spot weld. After the end of the welding process, the magnetic tape core is shorn from the winding shaft. The annular magnetic tape core that has been formed as a result can then be further-processed in a known way. In particular, the magnetic tape core is subjected to a thermal treatment and is subsequently covered with a passivation layer.
Such single-conductor chokes, however, are complicated to manufacture since the annular component parts must be manually attached over the terminal pins, for example of a transistor or a diode. The adjustment of the annular single-conductor choke around the terminal pins thereby plays a particularly large part and requires additional assembly outlay.
Another critical disadvantage derives from the extremely poor thermal contact of the magnetic tape core relative to the terminal pins of the circuit and an inadequate elimination of the unwanted heat from the magnetic tape core that is caused as a result thereof The dissipated heat arising, for example, given a magnetization into saturation at frequencies in the range of a few hundred kilohertz thus usually leads to a heating of the components of more than 100° C. As a result of these high temperatures and due to the magnetic field in winding direction generated by the operating current, a tempering occurs that, unbeneficially causes a rectangular hysteresis loop that in turn, intensifies the magnetic field in winding direction. Over time, however, the alloys that are utilized cannot overcome these high temperatures, this leading to an aging of the material of the magnetic tape core with corresponding changes in the magnetic properties of the alloys. These usually cause a further increase in the re-magnetization losses, which can ultimately lead to the thermal failure of the choke.
European reference EP A 0655754 discloses an inductive component, whereby a magnetic foil is tightly wound around a terminal wire to form a magnetic tape core.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to specify a choke for suppressing radio interference that can be manufactured with extremely little assembly outlay and that exhibits extremely good thermal contact of the magnetic tape core with the circuit for the elimination of the dissipated heat from the magnetic tape core.
This and other objects are inventively achieved by a choke for suppressing radio interference featuring
a terminal wire composed of an electrically conductive and thermally conductive, non-ferromagnetic, first alloy; and
a thin band composed of a ferromagnetic, second alloy that is wound around the terminal wire to form a coil and that has its inner end positively connected to the terminal wire.
As a result of the inventive choke for suppressing radio interference, said assembly difficulties are avoided and the problem of the thermal coupling of the choke to the rest of the circuit is also solved. All other said advantages, particularly the very good attenuation properties, are preserved unmitigated.
A terminal wire that serves as winding shaft for the magnetic tape core is employed for manufacturing magnetic tape cores given the inventive choke for suppressing radio interference. The material of the terminal wire is composed of an alloy that is capable of being spot welded for welding the magnetic band to be wound and that can also be soft-soldered for later assembly of the component. The terminal wire employed as winding shaft of the magnetic tape core remains in the magnetic tape core following the winding of the core and then serves as electrical conductor of the component.
After the winding, magnetic tape cores are potentially subjected to a thermal treatment for setting the magnetic properties. An enveloping of the magnetic tape core, for example on the basis of a standard lacquer or a shrink hose, is subsequently available. An epoxy powder lacquer can then be employed as lacquer. However, it would also be conceivable to envelope the magnetic tape core with a thermoplastic or duroplastic press compound.
The component part that is then formed is externally comparable to a conventional resistor and can, of course, be further processed like such a resistor with appropriate automatic equipping units such as those standard in printed circuit board manufacture. In particular, it is thereby advantageous when the inventive chokes for suppressing radio interference are implemented as Surface Mounted Device (SMD) components.
Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combination particularly pointed out in the appended claims.


REFERENCES:
patent: 5532910 (1996-07-01), Suzuki et al.
patent: 5815060 (1998-09-01), Matsumoto et al.
patent: 0 306 041 (1989-03-01), None
patent: 0 655 754 (1995-05-01), None
Toshiba Corporation Material & Components, Technical Data, Amorphous Noise Suppressor, AMOBEAD™, Serial No. E-63001, Jan. 30, 1988.
Patent Abstract of Japan: JP 01 081209 dated Mar. 27, 1989.
Patent Abstract of Japan: JP 02 292805 dated Dec. 4, 1990.
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