Transformers

Introduction

A transformer is a passive electronics component and consists of a pair of wire coils coupled together with an iron core. The input coil is called the primary coil and the output coil is called the secondary coil.

Circuit symbol:

An ac signal on the primary coil produces a signal on the seconday coil at the same frequency. The voltage and current of the secondary coil is related to the voltage and current of the primary coil by the following relationships:
V_s = V_p(N_s/N_p)
I_s = I_p(N_p/N_s)
where the p and s subscripts refer to the primary and secondary coils, respectively.

Transformers are used to either "step up" or "step down" the voltage from an ac power source to a different voltage. They are also used to isolate a circuit from the noise in the ac power line.