Patent ID: 8018314

Claim:
A center-tapped transformer comprising: a tubular first spool having a first surrounding wall defining a spool axis, and having opposite first and second ends, a first pin-mounting wall extending radially and outwardly from a portion of said first end of said first surrounding wall, and a first pin set mounted on said first pin-mounting wall; a tubular second spool having a second surrounding wall having first and second ends, a second pin-mounting wall extending radially and outwardly from a portion of said first end of said second surrounding wall, and a second pin set mounted on said second pin-mounting wall; said second surrounding wall having an inner diameter larger than an outer diameter of said first surrounding wall, and permitting said second end of said first surrounding wall to be inserted into said second surrounding wall, said first and second pin sets being disposed at diametrically opposite sides of the spool axis when said first surrounding wall is inserted into said second surrounding wall; a primary winding unit wound on one of said first and second surrounding walls; and first and second secondary winding units wound on the other one of said first and second surrounding walls; wherein said first pin mounting wall is formed with a recess opposite to said first pin set along the spool axis, and said second surrounding wall is formed with a flange extending radially and outwardly from another portion of said first end of said second surrounding wall that is diametrically opposite to the second pin mounting wall, said flange engaging said recess so as to retain said first surrounding wall in said second surrounding wall when said first surrounding wall is inserted into said second surrounding wall.