Step Up vs Step Down Transformer: Key Differences

This page compares Step Up Transformers and Step Down Transformers, describing their differences with circuit diagrams and equations.

What is a Transformer and How it Works

Definition: A transformer is an electrical device that converts an alternating current (AC) of a certain voltage to an AC of a different voltage (either higher or lower).

Transformers operate based on two fundamental principles:

• When fluctuating current flows through a wire, it generates a magnetic field.
• When a magnetic field fluctuates around a piece of wire, it generates an electric current in the wire.

In a transformer, two coils are placed side by side, and a fluctuating or alternating current is applied to the first coil. As a result, current is generated in the second coil. This phenomenon is known as electromagnetic induction.

For efficient energy transfer between the two coils (primary and secondary), they are wrapped around a soft iron bar known as the core. If the number of turns in both primary and secondary coils are the same, the same amount of current is produced in the secondary coil as in the primary coil.

If the number of turns in the secondary coil are more or less compared to the number of turns in the primary coil, we can obtain step-up and step-down transformers, respectively.

Step Up Transformer

Image alt: Step Up Transformer

If the secondary coil has more turns compared to the primary coil, it’s called a Step Up Transformer. In this case, the secondary voltage is higher than the primary voltage, and the secondary current is smaller than the primary current. Figure-1 depicts the circuit of a Step Up Transformer.

Step Down Transformer

Image alt: Step Down Transformer

If the secondary coil has fewer turns compared to the primary coil, it’s called a Step Down Transformer. Here, the secondary voltage is smaller than the primary voltage. Figure-2 depicts the circuit of a Step Down Transformer.

Equations

The relationship between voltage, current, and the number of turns in the primary and secondary coils is described by the following equations:

$Vs/Vp = Ns/Np \quad \text{... Equation-1}$

$Is/Ip = Np/Ns \quad \text{... Equation-2}$

Where:

• $Vs$ = Secondary Voltage
• $Vp$ = Primary Voltage
• $Ns$ = Number of turns in secondary
• $Np$ = Number of turns in primary coil
• $Is$ = Secondary current
• $Ip$ = Primary Current