What is transformer? Mention the types of transformer in market.

Transformer is a device which is used to increase or decrease the voltage of an alternating current. It is of two types : step down transformer and step up transfer. 

A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. Transformers are most commonly used for increasing low AC voltages at high current (a step-up transformer) or decreasing high AC voltages at low current (a step-down transformer) in electric power applications, and for coupling the stages of signal-processing circuits.

A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding. A transformer is defined as a passive electrical device that transfers electrical energy from one circuit to another through the process of electromagnetic induction. It is most commonly used to increase ('step up') or decrease ('step down') voltage levels between circuits.

A transformer is not designed to convert AC to DC or DC to AC. The transformer can step-up or step -down current. A transformer that increases the voltage from the primary to secondary is called a step-up transformer.Transformers do not pass direct current (DC), and can be used to take the DC voltage (the constant voltage) out of a signal while keeping the part that changes (the AC voltage). In the electrical grid transformers are key to changing the voltages to reduce how much energy is lost in electrical transmission.