• A transformer has two sets of coils wrapped around a ring shaped core made of iron.
• The number of turns in the primary and secondary coils determines the voltage and current. If voltage increases in the secondary coil, the current must decrease in the same ratio.
• Figure A shows how a step-down transformer decreases voltage and increases current. In this example the primary coil has 400 turns, and the secondary coil has 100 turns. , To calculate the voltage you must divide 100 by 400. Then multiply your answer (0.25) by the voltage in the primary coil of 120 volts. The out voltage is reduced to 30 volts.
• Figure B shows a step-up transformer, where voltage is increased as current is decreased. In this example the primary coil has 100 turns, and the secondary coil has 400 turns, input voltage is 20. Therefore your output voltage will be 80 volts.