Step-up and Step-down Transformers

Depending upon the number of turns in the secondary winding, the transformer can be called as a Step up or a Step down transformer.

The main point to be noted here is that, there will not be any difference in the primary and secondary power of the transformer. Accordingly, if the voltage is high at secondary, then low current is drawn to make the power stable. As well, if the voltage in the secondary is low, then high current is drawn so as the power must be same as the primary side.

Step Up

When the secondary winding has more number of turns than the primary winding, then the transformer is said to be a Step-up transformer. Here the induced EMF is greater than the input signal.

Step Down

When the secondary winding has lesser number of turns than the primary winding, then the transformer is said to be a Step-down transformer. Here the induced EMF is lesser than the input signal.

Turns Ratio

As the number of turns of primary and secondary windings affect the voltage ratings, it is important to maintain a ratio between the turns so as to have an idea regarding the voltages induced.

The ratio of number of turns in the primary coil to the number of turns in the secondary coil is called as the “turns ratio” or “the ratio of transformation”. The turns ratio is usually denoted by N.

N=Turnsratio=NumberofturnsonPrimaryNumberofturnsonSecondary=NpNsN=Turnsratio=NumberofturnsonPrimaryNumberofturnsonSecondary=NpNs

The ratio of the primary to the secondary, the ratio of the input to the output, and the turns ratio of any given transformer will be the same as its voltage ratio. Hence this can be written as

NpNs=VpVs=N=TurnsratioNpNs=VpVs=N=Turnsratio

The turns ratio also states whether the transformer is a step-up or a step-down transformer. For example, a turns ratio of 1:3 states that the transformer is a step-up and the ratio 3:1 states that it is a step-down transformer.