I have been looking for a center tap transformer for use in a dual +/-15 volt supply using 7815 and 7915 linear voltage regulators. I have obtained a transformer from an old stereo amplifier, which has a 52 volt coil with center tap, which will give me a nice solid 26 volts which I can rectify and feed my voltage regulators.
However, there is an additional coil on the transformer as seen in the diagram below from the service schematic of the amplifier. I measure about 50 volts across the orange and blue transformer output. I don't need the output from this second coil.
So the question is, what are the consequences of leaving this coil unconnected? Would this have any impact on power supply noise in my circuit?
Best Answer
There is no problem with leaving an unused secondary winding unconnected - but be sure to tape up the wires so that they will not accidently short to each other or to anything else.
The 26/26 volt secondary will give you about 36 volts DC, which is over the the Absolute Maximum input voltage of the 7815 and 7915 regulators, so this transformer is unsuitable for your application.