US2288120A - Iron-cored coil - Google Patents

Description

June 30, 1942.

w. s. CHALLIS 2,288,120

IRON-CORE]? COIL Filed Nov. 18, 1959 INVENTOR WILL/AM S/OA/E) CHALL/S I BY ATTORNEY Patented June 30, 1942 IRON-CORED COIL William Sidney Challis,

Hayes, England, assignor to Electric & Musical Industries Limited, Hayes,

Middlesex, Britain England,

a company of Great Application November 18, 1939, Serial No. 305,108 In Great Britain November 10, 1938 1 Claim.

tionate direct current to flow in a coil, the value of" said direct current determining the permeability of the iron core on which is wound a coil which is connected in the local oscillator circuit, the circuit being such that departure of the intermediate frequency from its assigned value causes the constants of the coil which is connected in the local oscillator circuit to alter in such a manner that the intermediate frequency produced approaches closer to its assigned value.

It has previously been proposed to vary the constants of a circuit connected to a coil in which high frequency currents are adapted to flow by utilising the Variations in direct current adapted to flow through another coil, both the coils being wound on iron cores ferent materials, the coil in which high frequency currents are adapted to flow being wound on a core formed from high frequency powder core material.

It has been found, contrary to what would normally be expected, that low frequency core material may satisfactorily be employed in connection with the coil adapted to carry high frequency current, and it is the object of the present invention to make use of this fact.

According to one feature of the present invention there is provided a circuit including a coil arrangement comprising two coils arranged about an iron core of low frequency material wherein one of said coils is adapted to carry direct current and is connected to a direct current circuit and the other of said coils is adapted to carry high frequency current and is connected to a high frequency circuit, the arrangement being such that when a change in the direct current occurs the permeability of the core is changed so as to produce a change in the constants of the high frequency circuit.

According to another feature of the present invention there is provided a coil arrangement comprising a coil adapted to carry direct current and a coil adapted to carry high frequency current said coils being disposed about an iron core of low frequency material formed in two opposing groups of laminated E-shaped stampformed of dif ings, the core forming a closed path around said coils which are spaced apart and surround the centre limbs of said core, the arrangement being such that a change in current in the coil adapted to carry direct current causes the permeability of the core to change so as to enable a change to be produced in the constants of a circuit associated with said coil adapted to carry high frequency current.

In order that the present invention may be clearly understood and readily carried into effect it will now be described with reference to the accompanying drawing in which Fig. 1 illustrates a longitudinal section along the line of Fig. 2, and Fig. 2 illustrates aplan of a present preferred embodiment of the invention by way of example.

The iron-core consists of a series of laminated E-shaped stampings composed of the two series having reference numerals l and 2, the laminated stampings of each series being face to face and both series being maintained adjacent one another with the limbs of one series overlapping the limbs of the other series. The laminated stampings of each series may, if desired, be alternately interleaved but this method of packing the stampings introduces air gaps at the nonoverlapping portions of the stampings. Surrounding the centre limbs and enclosed by the outer limbs of the stampings there is a coil former or bobbin of insulating material comprising the two parts 3 and 4 made in one piece, the part 3 having wound therein a coil 5 adapted to carry direct current, while the coil 6 adapted to carry high frequency current is Wound on the part 4 of the coil former, the coil 6 surrounding only the centre limbs of the series of laminated stampings 2.

It will also be seen from Fig. 2 that the portion of the core material associated with the coil 5 has a larger area of cross section than the portion of the core material associated with the coil 6. Further, although the limbs of the stampings I may extend further towards and beyond the coil 6 as compared with the position shown in the accompanying drawing, the relative positions there shown, with the limbs of the stampings I not encroaching upon the space occupied by the coil 6, are preferred.

The distance between the adjacent ends of the coils 5 and 6 should be greater than a minimum value, below which minimum value the arrangement is bound to be inefficient, and the maintenance of this minimum value may be assured by making the portion 1 of the coil former sufficiently wide. In one particular case in which the iron core is 1 in length, and has approximately the same dimension for its overall width, the central limbs of the stampings being approximately A" wide, a convenient value for the spacing between the coils 5 and 6 is 1%" The number of turns on the coils does not appear to be of primary importance in this connection, as the same value for the spacing between the coils 5 and 6 is adopted in arrangements wherein the coil 5 has about 3000 turns, or about 500 turns, and the coil 6 has up to about 40 turns.

The series of laminated stampings indicated at I and 2 of which the iron core is composed is made of metal such as is usually used for the cores of low-frequency transformers in radio receivers, for example that known under the registered trade-mark Mu-metal, and'the coils may be tapped so that different portions of the coils may be utilised in different circuits in any desired manner. The "central limbs'o'f the laminated stampings 2 are made to lie as close as possible to thecentral -portionof the coil 6 by making the "portion of thecoil former '4 which lies adjacent-the central portion of the stampings 2 as thin as convenient. The 'tappings to the coils *5 and ii may be'brought outto terminals aflixedto a piece of insulating material 8 which is shaped so as to be held in position by the stampings 2 and the outer portion of the part 4'0f the former. The wire used in the coil 6 may be-wire specially suitable for-carrying high frequency currents,'such as litz wire.

'The series of laminated stampings I and 2 are maintained rigidly positioned with respect to each other by-clips indicated at"9 made of copper,

fixed to the adjacent ends of the laminated stampings I and 2, and by a wedge I0, made of insulating material, partially inserted into the interior of the coil former 3 and thereby held rigidly against the inner limbs of the laminated stampmgs.

It may be desirable to bias the core comprised of the series of laminations I and -2 by giving it a definite permeability value, and for this purpose'a biassing coil may be arranged on the iron core in addition to the coils 5 and 6, and this biassing coil may, for example, be wound on the inner part of the former carrying the coil 5.

A coil arrangement according to the present invention may be utilised in any circuit wherein the change in permeability of an iron core due to variations of current in one coil are required toinfiuence the constants of a circuit associated with another coil, but has been primarily designed for use for the automatic frequency control of radio receivers.

In arrangements wherein the coil 5 is connected in a valve circuit, such as the cathode or anode icircuit of a valve, the said coil will be supplied with a definite amount of current dependent upon the circuit conditions. If it is required to have a permeability bias in the iron core of a required value, then such a permeability bias may be obtained by providing the coil 5 with an appropriate number of turns. With the coil 6 connected to the local oscillator circuit of a receiver, it is desirable to obtain as great a change as possible in frequency of the local oscillator for a given change in current in the coil 5, and this may be achieved by increasing the number of turns in the coil 5. However, if this increase in the number of turns alone were effected, the permeability bias of the core would be varied from the required value. In order to offset this change in the permeability bias of the core the aforesaid biasing coil may be used or a further coil employed, either of these latter coils being given a suitable number of turns and supplied with a suitable current so that the permeability of the iron core is restored substantially to its required value, although the original coil 5 has an increased number of turns. Such further coil may be wound on the same former as the original coil 5, and may be supplied with direct current from a separate source or from the same source as the high tension supply of the valve in the circuit of which the original coil 5 is connected.

By this means of providing an. increased number of turns in the coil 5, and another coil to offset the permeability bias change in the iron core from its required value, an increased frequency change is obtained for a given change in the current in the original coil 5, the permeability bias of the core being maintained substantially at the required value.

I claim:

In a variable high frequency inductance device, a direct current control winding, 2. high frequency inductance winding made of a wire suitable for carrying high frequency currents, an iron core composed of low frequency material forming a closed magnetic path around said winding said iron core being made up of a pair of laminated E-shaped auxiliary cores mounted face-to-face adjacent one another and with their respective limbs partially overlapping, said control Winding being wound around that portion of the central limb of said iron core which includes at least a part of the un-overlapped portion of the central limb of one of said auxiliary cores and the overlapped portion thereof, said high frequency winding being in axial alignment with said control winding, said high frequency winding being spaced from said control winding by a distance exceeding a predetermined minimum value and wound around only the'un-overlapped portion of the central limb of the other of said auxiliary cores, a cylindrical coil support for said control winding concentric with said central limb portion, said support being provided with a spacer flange located between said two windings, said flange having a thickness to provide said minimum value spacing, "the arrangement being such that a change in current in the direct current winding causes the permeability of the core to change and thereby produce a change in the inductance of the other winding, the portionof the iron core associated with the direct current winding having a greater cross-section area than the portion of the iron core associated with the high frequency induct-

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