An isolation transformer is a transformer, often with symmetrical windings,
which is used to decouple two circuits. An isolation transformer allows an AC
signal or power to be taken from one device and fed into another without
electrically connecting the two circuits. Isolation transformers block
transmission of DC signals from one circuit to the other, but allow AC signals
to pass. They also block interference caused by ground loops. Isolation
transformers with electrostatic shields are used for power supplies for
sensitive equipment such as computers or laboratory instruments.