about centre tap transformer.
The center tap is simply another wire which is typically connected somewhere in the middle of the secondary coil. For example, suppose you
had a transformer with 120VAC primary (2wires) and a 24VAC secondary (2 Wires at each end of the secondary coil). If you placed a center tap on
the coil, using the center tap and either end you would get 12 VAC if the center tap is truly in the center. This concept is used in
electronics to generate positive and negative voltages using the center tap as the ground.