GB2146847A

GB2146847A - Electrical inductance device

Info

Publication number: GB2146847A
Application number: GB08423273A
Authority: GB
Inventors: Hazen Curtis; Richard Charles Walker
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1983-09-19
Filing date: 1984-09-14
Publication date: 1985-04-24
Also published as: JPS61500001U; JPH051049Y2; WO1985001387A1; DE8490152U1; GB8423273D0

Abstract

A choke coil (10) includes a thermoplastic resin bobbin (26) carried on the center post (22) of a ceramic ferrite E-core (14) and locked in position by four locking tabs (52) extending from one end of the bobbin (26) and grasping the remote edges of the base (16) of the E-core (14). The bobbin (26) carries two windings (54, 56) with separate connections to four terminal pins (44) extending from one side of the assembly for attachment to a circuit board. The center post (22) and the outer legs (18, 20) of the core (14) extend beyond the end of the outer winding (56) to provide mutual magnetic field coupling there without the need of an end piece and to thereby increase the inductance of the device without increasing the number of turns of the windings (54, 56). The vertical edges (24) of the center post (22) at the free end and the corresponding edges (30) inside of the bobbin (26) at the insertion end are chamfered to facilitate assembly. The winding wire may also serve as a fuse link for a circuit in which the choke coil is used.

Description

SPECIFICATION Electrical inductance device This invention relates to an electrical inductance device and more particularly to choke coils ofthetype particularly suited for mounting on elecctronic circuit boards.

Numerous electronic circuits require as one of their components an inductance element, generallyforthe performance of some filtering function. Such is the case for circuits in telephone receivers. These circuits are subject to various types of electromagnetic noise which is best filtered out by an inductance.

Thetypesofinductance elements commonly used forsuppressing noise in electroniccircuitsare gener- ally known as "choke coils". They are preferably designed so thatthey can be readily mounted on a circuit board along with the other circuit components presenton it. Sincethismounting procedure is separate from the processes for manufacturing the other circuit portions on the board, it is important that there be a minimum of complexity involved in the assembly process.Also, since most of the other components of the circuit are either of a printed nature on the board or are relatively small integrated circuits, and since for any apparatus of this type space and volumearelikelyto be at a premium, it is desirable thatthe distance such a choke coil protrudes above the surface ofthe board be keptto a minimum.

According to the present invention there is provided an electrical inductance device comprising a coil member having at least one winding with an opening through the center of the winding, a ferrite core member including an elongated center post and at least one outer leg parallel to, and spaced from, the center post and joined to it at one end by a base portion integral with the center post and outer leg, the center post being disposed in the coil member opening and the outer leg being disposed adjacent the outside of the winding, both the outer leg and the center post extending attheirfree ends a predetermined distance beyond the winding to provide magneticfield coupling between the leg and the center post.

In accordance with the present invention the leg and center post of the core member extend beyond the end ofthe coil member, so that magneticflux coupling between the leg and the post is sufficientto permit significantly reduced winding turns in the coil member. This makes possible a reduced thickness dimen sionforthecoil member, and hence for the entire device.

An exemplary embodiment ofthe invention will now be described reference being made to the accompanying drawings, in which: FIG. lisa perspective view of an electrical inductance device in the form of a choke coil assembly in accordance with a preferred embodiment of the invention.

FIG. 2 is a top view of the choke coil assembly of Fig.

1.

FIG. 3 is a perspective view of the choke coil assembly of FIG. 1 with the core disassembled from it.

FIG. 4 is a perspective view of a bobbin of the choke coil of FIGS. 1 and 2 shown separately.

In FIGS. and 2 there is shown a choke coil assembly 10 which includes a bobbin assembly 12 fastened to a core member 14. The core member 14 is shown removed from the bobbin assembly 12 in FIG. 3 ofthe drawings. The core 14 is an E-core made of a ferrite ceramic material, such as, for example, a material designated as LRM382-L1 manufactured by the Western Electric Company in North Andover, Mass., in 1983. The core 14 includes a base portion 16, two outer legs 18,20 and a center post 22. The vertical edges 24 at the end of the center post 22 are chamfered. The bobbin assembly 12 includes a bobbin 26 which is molded ofthermoplastic resin material. It is shown separately in FIG. 4. The bobbin 26 has a central guide opening 28 for receiving the center post 22 of the core 14.The outside vertical edges of 30 of the guide opening 28 are chamfered to facilitate horzontal alignmentwhen the bobbin assembly 12 receives the center post 22. Vertical alignment is provided by a pairoftongue-like lead-in members 31 extending out a short distance from the guide opening 28 and flaring out, awayfrom it. A pair of axially spaced end flanges 32,34 are attached to a central cyindrical portion 36 of rectangular crosssection. Spaced midway between the flanges 32,34 is partition 38 which axially divides the bobbin 26 into two winding spools. Each ofthe flanges 32, 34 is provided with two holes 40 in its plane which each receive a terminal pin 44. The terminal pin has a short coil wire wrap leg section 46 bent at a right angle and a mounting stem section 48.The mounting stem section 48 includes a swaged segment 50 which deforms the inside wall ofthe receiving hole 40 to rigidly hold the pin 44 in place after it is assembled to the bobbin 26.

Fourtongue-shaped locking tabs 52 extend from one flange 32. These are designed to engage the outer edges surface ofthe base 16 ofthe core 14when the bobbin assembly is pressed against the base 16 on assembly and to firmly hold the core 14 in place.

Referring now back to FIG. 2 the bobbin assembly 12 is shown with the terminal pins 44 in place and each of the winding spoolswoundwith awinding 54, 56of copper wire. The completed assembly of FIGS. 1 and 2 shows the ends ofthe windings 54,56 wire-wrapped about the terminal legs 46. The mounting stems 48 extend from the bottom ofthe assembly and are designed to readily attach to a circuit board.

The legs 18,20 and center post 22 ofthe core 14 are significantly longerthan the length of the guide opening 28 in the bobbin 26, so that they extend beyond the end of the outerwinding 56 a distance of about30% oftheirtotal length. This provides magneticflux coupling through the air gaps between the outside legs 18,20 and the center post 22 which significantly increases the inductance value of the choke coil assembly 10. Without th is feature it would be necessary, in order to obtain the same inductance value, to add moreturns ofwireto the windings 54,56, thereby increasing the diameter ofthewindings 54,56 and givingthe entire choke coil assembly 10a correspondingly greater thickness dimension. Since this thickness dimension is the dimension which determines the protrusion of the choke coil assembly 10 above the level ofthe circuit board to which it is mounted, this would be undesirable for many applications where space is at a premium.

It is anotherfeature ofthe choke coil assembly 10 thatthecopperwirewhichformsthewindings54, 56 is of such a thickness that it serves as a fuse Iinkforthe circuitin which the choke coil assembly 10 is used.

Most typically, this would be a telephone receiver circuit.

It is an advantageous feature ofthe bobbin 26 that its configuration is asymmetrical. It is therefore more readily handled by automated assembly equipment. It is well known that automatic assembly equipment is more readily designed to handle asymmetrical pieces than symmetrical ones because it is easierto orient and align such pieces. The same can be said ofthe core 14.

The distancedthatthe center post 22 and the outside legs 18,20 of the core 14 extend beyond the end ofthe outer winding 56 mayvarywithin a range feasiblefora particular application. Also, if the distanced is made much greaterthan about 30% of the total length ofthe legs 18,20, and the post 22, no appreciable inductance will be added to the structure, and the core 14is likelyto become much more susceptible to breakage in handling.

While the coil assembly 10 includes two windings 54,56, it will be readily apparent to those skilled in the artthatthe bobbin 26 could also be wound with a single winding or more than two. Moreover it could be readily modified to be specifically designed for a single winding.

While the core 14 of the coil assembly 10 is an E-core having two outside legs 18,20, a U-shaped core having only a single outer leg would also provide coupling in the airgap between the outer leg and the center post if these extended sufficiently beyond the outer winding. This would be an alternative structure which might be suitable forsome purposes.

Even a single locking tab can hold the bobbin in place on the core. However, a structure with two opposing locking tabs, or preferablyfouras in the abovessembly 10, will provide a more reliable and firm attachment. It may be advantageous from the standpoint of the molding operation ofthe bobbin 26 thatthere be just two locking tabs which are diagonal lyopposed, ratherthanthefouroftheassemblyl2.

Claims

1. An electrical inductance device comprising a coil member having at least one winding with an opening through the center of the winding, a ferrite core member including an elongated center post and at least one outer leg parallel to, and spaced from, the center post and joined to it at one end by a base portion integral with the center post and outer leg, the center post being disposed in the coil member opening and the outer leg being disposed adjacent the outside ofthewinding, both the outer leg and the center post extending attheirfree ends a predetermined distance beyond the winding to provide magneticfield coupling between the leg and the center post.

2. The device in accordance with claim 1, in which the core is an E-core having a second outer leg parallel to,coplanarwith,and spaced from the center post and joined to it at one end bythe base portion,the second outer leg being disposed adjacent the outside of the winding opposite the first outer leg and also extend ing the predetermined distance beyond the winding to provide magneticfield coupling between itandthe center post.

3. The device defined in accordance with claim 2, in which the coil member includes a bobbin with two end flanges with central openings for receiving the center post and a cylindrical hollow center portion,the winding being carried between the flanges and around the hollow center portion.

4. The device defined in accordance with any of claims 1-3, in which at least one locking tab extends from the face of one oftheflanges of the bobbin for engaging the outer edge of the base to hold the bobbin in place on the center post.

5. The device in accordance with claim 4, in which two pairs of opposed locking tabs (52) extend from the flange ofthe bobbin to eithersideofthecenterpost and engagethe edges ofthe base portion ofthecore member remote from the flange in locking fashion.

6. The device in accordance with claim 5, in which the base portion,the legs, and the center postofthe core member all have generally rectangular crossections.

7. The device in accordance with claim 6, in which the bobbin includes a partition spaced between the flanges and carries two windings, one on each side of the partition.

8. The device in accordance with claim 7, in which the flanges of the bobbin each contain at least one hole extending through them in the plane oftheflange and have a terminal pin inserted through the hole, one end of the pin being bent at right angles and having the winding connected to it, the other end extending from the bobbin for attachment to a circuit board.

9. The device in accordance with claim 8, in which two opposed edges of the center post at its free end are chamfered to facilitate insertion of the center post into the opening of the bobbin.

10. Thedevicein accordancewith claim 9, in which opposing inside edges ofthe opening in the flange from which the tabs extend are chamfered to facilitate insertion of the center post into the opening of the bobbin.

11. The device in accordance with claim 10, in which a pair of opposed tongue-like lead-in members areprovided,flaring outwardfromthe bobbin between the locking tabs at each side of the core.

12. An electrical inductance device substantially as hereinbefore described with reference to the accompanying drawings.