Transformers are 2 or more inductors where the coils share the same magnetic field. This results in the current in one coil inducing a current in the other. They are commonly used to change the voltage from an AC source to a different voltage. We need much more description and information here. Would you add it?
"Ferrites? I don't know much about 'em, I only use ferrites in switching regulators." --National Semiconductor's Bob Pease
Can be replaced in many circumstances with an impedance inverter using only an opamp, a capacitor, and a few resistors.