Sept- 24, 1946- H. D. GARRETSON _ 2,403,017 ELECTRICAL CIRCUIT ARRANGEMENT Filed May 5. 1943 HARRY D. GARRETSON INVENTOR. $1M ATTORNEK. i’ I Patented Sept. 24, 1946 2,408,017 UNITED STATES PATENT OFFICE 2,403,017 ELECTRICAL CIRCUIT ARRANGEMENT Harry Douglas Garretson, Whitestone, N. Y., as signor to Philips Metalix Corporation, New York, N. Y. Application May 5, 1943, Serial No. 485,769 5 Claims. (01. 171-119) 1 My invention relates to electrical circuit ar rangements and particularly to circuit arrange 2 Fig. 2 illustrates the circuit arrangement of the invention as applied to an adjustable voltage transformer in which the input and output wind ings are electrically insulated from each other. Referring to the drawing, the transformer of over bared turns of a transformer winding. The Fig. 1 comprises a rectangular magnetic core It invention is especially applicable to adjustable on two legs H and I2 of which are two windings voltage auto-transformers having a step-down l3 and M respectively, connected in series addi ratio and will be described in this connection. tive relationship to input terminals !5 and [6. A Transformers of the above speci?c type usually 10 continuously adjustable voltage is obtained at comprise an electrical winding having a ?xed ‘output terminals 13 and I9 from the winding [4 voltage portion and an adjustable voltage por» by means of a slider I‘! which contacts bared tion. In practice, the two portions of the wind portions of the winding I4. The voltage appear ing are spatially separated in order to provide ing at terminals 18 and 19 has a Value deter proper access of the adjusting slider and its op mined by the position of the slider I’! relative to erating mechanism to the adjustable-voltage per» the interconnection between windings l3 and M tion of the winding. In the case of transformers to which the terminal 19 is connected. comprising a rectangular magnetic core, the fixed As above pointed out, the leakage rectance voltage and the adjustable portions of the trans normally existing between windings l3 and [4 ments for adjustable voltage transformers have ing a variable output voltage continuously ad justable by a sliding member adapted to move former Winding are each Wound on a separate leg of the magnetic core. While this construction simpli?es the mechan~ ical design of the transformer, I have found that it introduces certain electrical disadvantages, more particularly, this construction produces a transformer having a high leakage reactance and characterized by poor voltage regulation. It is an object of the invention to obviate the above electrical disadvantages. causes the transformer to exhibit poor voltage regulation. In accordance with the invention, the leakage reactance of the transformer is ef fectively reduced by means of a tertiary widing 20 which is connected in shunt with the Winding I4. Winding 20 is 50 coupled to winding l3 that substantially all of the magnetic lines induced in the transformer leg H by the winding [3 are linked with the winding 20, Such a close cou pling is obtained by superimposing the winding A more speci?c object of the invention is to 30 20 over the Winding I3. provide novel circuit arrangements for trans The number of turns of the winding 20 is so formers of the above described type by which the determined that under no-load conditions the effective leakage reactance of the transformer is voltage induced in the winding is equal to the reduced without sacri?cing the mechanical ad voltage appearing across the winding M. vantages of the transformer construction. In usual practice, the transformer of Fig. 1 A further object of the invention is to provide has a step-down ratio of 2 to 1, i. e. the maximum simple and economical expedients for improv voltage obtainable across the terminals l8 and I9 ing the voltage regulation of adjustable volt is equal to one-half the voltage applied to ter age transformers. minals l5 and I6. In such a case, the windings These and further objects of the invention will 4.0 l3 and H! are symmetrical and to obtain the im appear as the speci?cation progresses. provement in regulation in accordance with the In accordance with the invention, I effectively invention a Winding 20 is used having the same reduce the high leakage reactance between the number of turns as the windings I3 and [4. ?xed-voltage and the adjustable voltage portions The transformer illustrated in Fig. 2 com of the windings by means of a tertiary Winding 45 prises a rectangular magnetic core 30 having a which is closely coupled to the ?xed-voltage por winding 3| positioned about a leg 32 of the core tion and which is electrically connected in and connected to input terminals 35 and 36. P0 shunt with the adjustable-voltage portion. sitioned about a leg 34 of the core is an output The invention will be described in greater de winding 33 one end of which is connected to out tail with reference to the appended drawing in 50 put terminals 31. The output voltage of the which transformer is adjustable by means of an ad Figure 1 illustrates the circuit arrangement of justable slider 39 adapted to contact bared por the invention as applied to an adjustable volt tions of the winding 33 and connected to a ter age auto-transformer having a step-down ratio minal 38. Windings 3| and 33 are electrically in between the input and output terminals, 55 sulated and their turns ratio may be step-up or 2,408,017 ‘a step-down as desired depending on the require ments to be met by the transformer. In accordance with the invention, the leak age reactance existing between the windings 3| said core, a second winding on another portion of said core, and so positioned with respect to said first winding that a substantial amount of leakage reactance exists between the windings, a slider member adapted to contact bared por and 33 is elfectively reduced by means of a ter tions of said second winding, and means to re tiary winding dill which is connected in shunt with duce the effective leakage reactance between the winding Winding Mi is superimposed on said windings, said means comprising a tertiary the winding 3! and so coupled to it that substan winding on said core tightly coupled magnetically tially all of the magnetic lines of force induced in leg 32 are linked with the winding 43. The 10 to said first winding and connected in shunt with said second winding. number of turns‘ of winding 40 is so determined 4. An adjustable voltage transformer compris that the voltage induced in this winding is the same as the voltage induced in winding 33. ing a rectangular magnetic core, a winding on It should be well understood that while the invention has been described in connection with transformers having a continuously adjustable said core having a portion positioned about one leg of the core and a second portion positioned voltage output, the invention is equally applic able to transformers in which the output voltage is adjustable by means of a plurality of taps of the output winding. While I have described my invention by means of speci?c examples and in speci?c embodiments, I do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention. What I claim is: 1. An electrical transformer comprising a mag netic core, two magnetically coupled windings on said core and so positioned with respect to each other that a substantial amount of leakage reactance mists between. the windings, and a ter~ tiary ‘wins. on said core tightly coupled mag netically to one of said two windings and con nected in shunt with the other of said two wind ings. 2. An electrical transformer comprising a mag netic core, a winding on a portion of said core, a second winding on another portion of said core, and a tertiary winding on said core superim l. i) posed on said ?rst winding and connected in shunt with said second winding. 3. An adjustable voltage transformer compris ing a magnetic core, a winding on a portion of about another leg of said core and interconnected in series relationship with said first portion, a slider member adapted to contact bared portions of said second winding for providing an adjust able voltage proportional to the part of said sec ond winding portion between the slider contact and the interconnection between the winding portions, and a winding on said core superim posed on said ?rst winding portion, connected in shunt with said second winding portion and having an induced voltage equal to the induced voltage of said second winding portion. 5. An adjustable voltage transformer compris ing a rectangular magnetic core, a winding on a leg of said core, a second winding positioned on a second leg of said core, electrically insulated from said ?rst winding and so positioned with respect thereto that a substantial amount of leak— age reactance exists between the windings, a ter tiary winding on said core superimposed on said ?rst winding and connected in shunt with ‘said second winding, said third winding having an induced voltage equal to the induced voltage of said second winding, and means for contacting selected portions of said second winding for pro‘ viding an adjustable voltage proportional to the portion of the winding interposed between said means and the end of the winding HARRY DOUGLAS GARRETSON.