A transformer is an energy transfer device. Electrical energy applied to the primary is converted to a magnetic field which in turn, induces a current in the secondary which carries energy to the load connected to the secondary. There are two main purposes for using transformers. The first is to convert the energy on the primary side to a different voltage level on the secondary side. The second purpose is to isolate the energy source from the destination. Transformers are generally divided into two main types. Power transformers are used to convert voltages and provide operating power for electrical devices, while signal transformers are used to transfer some type of useful information.