Transformers are usually represented by the letter "T" in schematics.
A transformer is essentially two inductors wound together so that their magnetic fields are coupled together.
An alternating current in the primary winding will induce an alternating current in the secondary winding.
Transformers are usually used to change the voltage of an alternating current.
If the secondary has fewer windings than the primary, the secondary voltage will be lower than the primary.
The primarary to secondary voltage ratio is directly proportional to the turns ratio.
An unregulated DC power supply using a transformer, diode and capacitor:
Use a transformer that is rated "120 VAC primary : 12.6 VAC secondary".
Use a 1N4004 diode.
Use a 1000 uf capacitor.
Plug the primary winding into a 120 VAC wall outlet. Warning! 120 VAC is a shock hazard.
The AC voltage on the secondary will be approximately 12.6 VAC (or higher with no load).
The diode will convert the AC voltage to a DC voltage. The diode also drops the voltage by about 1 volt.
The DC voltage across the capacitor will be about 17 VDC.
Why is the DC voltage so much greater than the AC voltage?
The 12.6 VAC signal is a sinewave that changes voltage from moment to moment.
The 12.6 VAC rating is an "RMS" value that stands for "Root-Mean-Square".
The RMS value is the square root of the sum of the squares of a sampling of instantaneous values.
The RMS value is a way to equate the power of an AC signal to the power of a DC signal.
The 12.6 VAC signal will produce the same amount of heating in a resistor or heater as a 12.6 VDC signal.
The peak of a sinewave is the square-root-of-2 bigger than the RMS value.
The square root of 2 is 1.414, so the peak voltage of 12.6 VAC is 12.6 * 1.414 = 17.8 VDC.
120 VAC 60 Hz sinusoidal voltage from wall outlet:
Conversion to 17 VDC:
