Induction heated fusing apparatus having a dual function transformer assembly

Claim 1

An induction heated fusing apparatus having a dual function transformer assembly, the induction heated fusing apparatus comprising: (a) a pressure roller; (b) an induction heatable fuser roller having an electrically conductive layer, said heatable fuser roller forming a fusing nip with said pressure roller; and (c) a dual function transformer assembly for inductively heating said induction heatable fuser roller as a first function, and for increasing a supply frequency F1 of an AC power supply source to a desired inductive heating frequency F2 for said induction heatable fuser roller as a second function, said dual function transformer assembly including: (i) a closed loop magnetically permeable member comprising a transformer core having a first side surrounded with said induction heatable fuser roller as a secondary transformer coil, and a second side including a primary transformer coil winding thereover; (ii) an electrical circuit subassembly coupled to said primary transformer coil and connectable to the AC power supply source having said supply frequency F1, whereby said supply frequency F1 is increased to said desired inductive heating frequency F2, and said heatable fuser roller is inductively heated by said transformer assembly when said electrical circuit subassembly is connected to the AC power supply source, said electrical circuit subassembly including (i) a bridge circuit connectable to the AC power supply source for rectifying AC power therefrom to produce a DC power output, (ii) an auxiliary conductive coil winding around said closed loop magnetic flux carrying member; and (iii) a pair of transistors having their emitters connected to the output of said bridge circuit, their bases connected to opposite ends of said auxiliary conductive coil winding, and their collectors to opposite ends of said primary transformer coil, wherein said pair of transistors and said primary transformer coil are alternately driven by voltage changes across said auxiliary conductive coil winding.