US 3426305 A
Description (OCR text may contain errors)
f Feb- 4, 1969 J. M. KEBLE 3,426,305
CHOKE HAVING A WINDING OF' FOIL Filed June 6, 1967 vJOHN MERVYN KEBLE INVENTOR ATTORNEY United States Patent O 26,199/ 66 U.S. Cl. 336-178 Int. Cl. H01f 17/06, 27/28 Claims ABSTRACT 0F THE DISCLOSURE A choke having a laminated core comprising at least one leg with a plurality of evenly disposed air gaps in said leg and having a winding on said core consisting of a strip of metallic foil.
The invention relates to a choke having a Winding in the form of a strip of foil.
Chokes, as used, for instance, for electric discharge lamp circuits, normally have a wire winding on a core leg which has an air gap at one end. It has been found that if the wire winding is replaced by a spiral winding of a strip of foil, the air gap causes an uneven ux linkage across the foil resulting in a marked eddy current loss. The loss arises because the foil extends parallel to the core leg.
According to the present invention there is provided a choke having a winding consisting of a strip of foil and a core in which there is a plurality of evenly disposed gaps in a leg of the core.
We have found the replacement of the conventional single air gap by distributed gaps reduces the eddy. current loss.
The gaps may be slots in some or all of the laminations and may be in one or more of the legs. The invention can be used with cores of the core-type or shell-type construction.
Embodiments of the present invention will be described with reference to the accompanying drawings in which:
FIG. 1 is a diagrammatic cross section of a conven tional choke core with a foil winding, and
FIGS. 2 to 4 are cross sections of choke cores constructed according to the invention.
FIG. l shows a conventional choke core 1 with an air gap 2 at one end of the centre leg of the core. The choke is shown with a foil winding 3. When a current is passed through the coil a stray magnetic flux is generated as indicated the loops of llux 4 with the asymmetrical air gap causing a greater ux linkage on one side B of the ICC foil than on the other A. With an alternating current this difference in ux linkage will result in a voltage being generated between the edges of each turn of foil causing an eddy current. Because the wire of the windings is relatively narrow this eddy current only arisesin the case of a foil winding.
The embodiment of the invention which is shown in FIG. 2 is a choke in which the eddy current loss is substantially avoided. The centre leg 5 f the core 1 has three symmetrically arranged air gaps ,6. The stray magnetic ux produced by a current will 'ow link the foil in loops 4 delining three distinct regions 7, 8 and 9. In this embodiment the eddy currents are confined to each region and are much smaller. The effect bears some resemblance to that obtained by splitting the foil lengthwise into three parts.
The air gaps may be slots 10 occurring in some or all of the core laminations, as shown in FIG. 3, in which they recur in any or each of the legs. The invention may be applied to two-legged. cores, as in` FIG. 4, having a winding on each core, when either or both cores may have evenly disposed air gaps. Similarair gaps can also be used with shell-type cores and in any type of gapped core in which it may be desired to use foil winding.
1. A choke having a laminated core comprising at least one leg with a plurality of` evenly disposed air gaps in said leg and having a winding on said core consisting of a strip of metallic foil.
2. A choke as claimed-in lclaim 1 in which the core has three legs and the said leg is the centre leg.
3. A choke as claimed in claim 2 in which the other legs also have evenly disposed air gaps.
4. A choke as claimed in claim 1 having two legs each provided with evenly disposed air gaps.
5. A choke as claimed in clain'tl in which some of the core laminations have slots forming the said air gaps.
References Cited UNITED STATES PATENTS 2,175,927 10/1939 Steinert 336-165 XR 2,521,513 9/1950 Gray 336-165 XR 2,998,583 8/1961 Worcester 336-232 XR LEwIs H. MYERS, Primary Examiner.
THOMAS J. KOZMA, Assistant Examiner.
U.S. Cl. X.R. 336-232