What is a Step Down Transformer : Construction & Its Working

A transformer is a static device because it doesn’t have any moving parts. The main function of this is to transmit the electrical power from circuit to circuit by changing the voltage-current but not frequency. The classification of the transformer can be done based on the functionalities like a step-up transformer and step down transformer. A step-up transformer is used to increase the voltage from low to high whereas a step-down transformer is used to decrease the voltage from high to low. So this article discusses an overview of a step-down transformer-working with applications.

What is a Step Down Transformer?

Definition: A transformer that converts the high output voltage using less current to low output voltage through high current is known as a step-down transformer. There are two types of windings in this transformer namely primary as well as secondary. Primary winding includes moiré turns as compared with secondary. The Step-down transformer diagram is shown below.

Step Down Transformer
Step Down Transformer

For example, the range of voltage used by the power circuit is 230v to 110v, but in electrical devices, it is less like 16v. So to overcome this voltage issue, a step-down transformer is used so that it can be reduced from 230v to 110V and finally to 16v.

Working Principle

The step-down transformer working principle of a step-down transformer is Faraday’s law of electromagnetic induction. In a transformer, mutual induction is necessary between two windings for transmission. In Faraday’s law, once the magnetic flux connecting a circuit changes, then an electromotive force can be induced within the circuit that is proportional to the flux linkage’s rate of change.

The induced electromotive force can be determined through the number of windings present in the transformer. So this is called turns ratio. The transformers voltage reduction ability mainly depends on this turns ratio. When the no. of windings present in the secondary coil is low as evaluated with the primary coil, then the linkage of flux to the secondary coil is also less as compared with the primary coil.

So, the electromotive force induced is low in the secondary coil, due to this reason the voltage is reduced at the secondary winding as contrasted to the primary winding.


The step-down transformer formula is

Ns/Np = Vs/Vp

Where the ‘Ns’ is no. of windings in secondary

‘Np’ is no. of windings in the primary

‘Vs’ is the voltage in secondary

‘Vp’ is the voltage in the primary

In this transformer, the no. of windings in secondary is always less as compared with the windings in the primary

Ns < Np

Types of Step Down Transformer

Step-down transformers are classified into three types like single phase, center phase and multi tapped.

  • Single-phase is used to step down the ratings of current as well as the input voltage to give less voltage & output current like 12V AC.
  • Center Tapped includes one primary & a center split within the secondary so it gives the output voltage with a center split like 12v to 0 to 12v.
  • Multi Tapped has numerous tapping within secondary winding and these are used to obtain the preferred output through secondary coils like 0 to12v, 0 to18v.

Construction of Step Down Transformer

The construction of a step-down transformer can be done using two or more coils wound on the transformer’s iron core. The efficient transformers mainly include the ferromagnetic core as this material turns into magnetized using the primary coil & transmits the energy to the secondary coil. A simple method to get a ferromagnetic coil is to discover 2-3 inches of big steel washer or a wrecking yard.

Step Down Transformer Construction
Step Down Transformer Construction

To make the coils in the transformer, any type of conducting wire can be used but the best one is a magnetic wire with 28 gauges. This is a thin copper wire with insulation coated. To make the primary coil, cover the wire strongly in the region of the washer. If required, wind it in the form of layers. Count the number of windings and note the number.

Once winding is done, maintain the two ends open to connect the power source & cover with masking tape in the region of the wires to maintain them in place. While designing this transformer, the windings in the secondary coil should be less. The actual amount mainly depends on the required voltage which can be calculated through the formula of the transformer.

Working of Step Down Transformer

The primary coil is connected to primary voltage whereas the other coil is connected to the load. So that the load draws the output alternating voltage like stepped up otherwise stepped down.

At the input of the transformer, the alternating voltage will excite the primary winding and an AC will circulate the winding. So the AC will result within an alternating magnetic flux to flow throughout the iron magnetic core to complete its lane.

When the secondary winding is connected to the alternating magnetic flux, then based on the Faraday’s Law, an emf can be induced within the secondary winding. The voltage strength at the secondary winding is mainly dependents on the no. of windings during which the flux gets supplied.

Therefore, without creating an electrical contact, in the primary winding, the alternating voltage will be supplied through the secondary winding.


The advantages of a step-down transformer include the following.

  • Durability is high
  • Reliability is high
  • Less cost
  • Efficiency is high
  • Used to step down the voltage so that transmission power making is cheaper as well as simple
  • Provides different voltage supplies


The disadvantages of the step-down transformer include the following.

  • It needs more maintenance
  • The rectification of fault takes more time
  • Instability within feedstock costs


The applications of a step-down transformer include the following.

  • Electrical Isolation
  • Voltage Stabilizers
  • Inverters
  • Power Distribution Network
  • TVs
  • In welding machines
  • Home Appliances
  • Transmission lines to step down
  • Adapters
  • CD players
  • Doorbells
  • Chargers

Thus, this is all about an overview of the step-down transformer. This is mainly used to decrease the voltage and thus it is used in approximately all electrical appliances in the household. At present, it is used in most electronic devices. Here is a question for you, what is the other type of transformer?