What is Step Down Transformer?

What-is-a-Step-Down-TransformerA Transformer is a static apparatus which transforms electrical power from one circuit to another with no moving parts. It performs its action with the changes in voltage and current and no change in frequency. The main function of a transformer is to transfer AC electrical power from one circuit to another circuit while keeping the frequency level constant but with altered voltage, which means it increases or decreases the voltage based on the requirement of the machines. Depending on the functionalities the transformers can be classified in 2 types: 1. Step up Transformer and 2. Step down Transformer.


Types of Transformer:


1. What is Step Down Transformer?

A step down transformer is the one which reduces the output voltage that means it functions for converting high voltage with low current power into a low voltage with high current. Let me elucidate it with an example, everyone knows that our power circuits carry a voltage between 230- 110 v right. But electrical equipments like the bell require only 16v to operate properly. So, the step down transformer acts upon the current and reduce the voltage from 230- 110 v to 16v. Depending on the different areas sometimes, voltages are stepped down to 230v or 440v for the safety reasons. But to make this reduction in voltages a reality, the number of turns on secondary winding or coils is kept less than the primary winding or coils that ultimately result in less voltage being induced at the secondary output of the transformer.


Where the Step Down Transformer can be used?

The applications of Step Down Transformer is varied but the main applications of Step Down Transformers are as follows:

  • It is used in the main adapters and chargers for cell phones, CD players and stereos
  • It can be used to step down the voltage level in transmission line
  • In welding machines it is used in reducing voltage and increasing current.
  • And it is to be used in televisions, inverters, voltage stabilizers etc


Working Principle of Step Down Transformer

Transformers work on the “Faraday’s law of electromagnetic induction” principal which states that “when the magnetic flux linking a circuit changes, an electromotive force is induced in the circuit is being proportional to the rate of change in the flux linkage”. Transmission action in a transformer is performed by mutual induction between the windings.

The number of turns in primary and secondary winding respectively determines the Electro Motive Force induced between the two windings and this ratio is called as Turns Ratio. But do you know what decides the voltage reduction capability of step down transformers? It depends on the turn ratio of the primary and secondary coil. The amount of flux linkage to the secondary coil of the transformer remains less compared to the primary coil as the number of windings in secondary coil is also less than the number of windings in primary coil.


As the consequence, the emf which is induced will be less in the secondary coil, which ultimately reduces the voltage at the secondary winding compared to primary winding.

Please have a look on the formula used to design a Step Down Transformer





  • Ns = No. of turns in Secondary Winding
  • Np = No. of turns in Primary Winding
  • Vs = Voltage in Secondary Winding
  • Vp = Voltage in Primary Winding


But remember to work a transformer as a “Step Down Transformer”, it is necessary that the number of turns in secondary winding should always be less as compared to the number of turns in the primary winding of the transformer that is, Np>Ns.

Let’s understand it with an example: There is a Step Down Transformer in which the secondary turns [Ns] are 400, primary turns [Np] are 8000 and the input voltage [Vp] is 240. Then the voltage at the secondary[Vs] can be calculated with the following formula:


Vs= Ns*Vp/Np

Putting values given in the formula:

Vs = 400*240/8000

Vs = 12 Volt

Hence, the voltage at the secondary winding of the transformer is 12V, and we can see that it is less than that at the voltage in the primary winding. Therefore, the transformer can be said the Step Down Transformer.


What are the Types of Step Down Transformer?

There are three categories of Step Down Transformer which are as follows:

  1. Single Phase Step Down Transformer
  2. Center Tapped Step Down Transformer
  3. Multi Tapped Step Down Transformer


Advantages of Step Down Transformer

Please have a look on the advantages of Step Down Transformers:

  • These are useful in stepping down the voltage. It thereby makes the transmission power easier and cheaper
  • These provide more than 99% of efficiency
  • These provides varied voltage requirements
  • These are Low in Cost, Highly Reliable and Durable


Application of Step Down Transformer

The voltage is around 20kV from the Power Plant or Power Generation Station. For being able to transfer this voltage over to long distances, it is stepped up to 440kV with the use of Step up Transformer supplied by Servo Transformer Supplier in India. This voltage is then transmitted to a distribution station. At the distribution station, the 440 kV is then reduced to 11kV with the help of a Step Down Transformer making the voltage ready for customer use.


The Power in a Step Down Transformer

The power in a transformer is measured by using the product of the voltage and the current. The power in a transformer is rated in Volt – Amps VA (or in kilo Volt – Amps kVA for larger transformer sets).

The power according to the design of the transformer is almost always constant which means the power available at the secondary end of the transformer is same as the power as the power at the primary end of the transformer.


This theory is even applicable in a step down transformer. But, in this case the voltage is at the secondary coil of the step down transformer is lesser than that at the primary coil, the current at the secondary coil increases to balance the total power of the transformer.


Uses of Step Down Transformers

The street transformers that we see near our homes are all step down transformers. Before installing the switching power supplies all low voltage wall adapters use step down transformers.


A premier Servo Transformer Supplier in Delhi- Servo Star offers a wide range of quality stabilizers and transformers that suit different types of domestic and industrial applications like for metal processing equipment, elevators, production lines, medical equipment, construction devices, air conditioners and many more.


2. What is Step Up Transformer?

A Step up Transformer has more number of turns or coils on the Secondary Coils or the Secondary winding than in the Primary Coils or the Primary winding. Therefore, in step up transformer the voltage that gets supplied into the secondary coil in is greater than the voltage supplied through the primary coil. So, the step up transformer converts low voltage with high current into high voltage with low current because of the principle of conversion of energy. That means the voltage has been stepped up. This is where this transformer gets its name from, “The Step Up Transformer“.


Where the Step Up Transformer can be used?

The uses of step up transformers are not limited as you can find these transformers located in various industrial sites near you like power plants, designed to function with megawatts of power. Apart from power plants one can find the step up transformers’ uses in local and smaller applications, for instance: in x- ray machines that require approximately 50, 000 volts to work efficiently or a micro- wave oven that requires a smaller version of step up transformer in order to operate smoothly.