A transformer is an electrical device that changes the voltage of an alternating current (AC) supply. It does this without converting AC to direct current (DC). Think of it like a water pump that can increase or decrease the pressure of water flowing through a pipe. In a transformer, the “pressure” is voltage, and the “flow” is current.
When an AC voltage is applied to the primary winding, it creates a changing magnetic field in the core. This changing field induces a voltage in the secondary winding. The ratio of the number of turns in the secondary to the primary determines whether the transformer steps the voltage up or down.
| Symbol | Meaning |
|---|---|
| \$N_p\$ | Number of turns in the primary winding |
| \$N_s\$ | Number of turns in the secondary winding |
| \$V_p\$ | Primary voltage |
| \$V_s\$ | Secondary voltage |
The core relationship is:
\$\frac{Vs}{Vp} = \frac{Ns}{Np}\$
Suppose you have a 120 V supply (primary) and you need 12 V for a small appliance. Using the transformer equation:
\$\frac{Vs}{120\,\text{V}} = \frac{Ns}{N_p}\$
If we choose \$Ns/Np = 0.1\$, then \$V_s = 12\,\text{V}\$. This is a step‑down transformer because the secondary voltage is lower than the primary.
Transformers are designed for AC only. Using them with DC can damage the core and create safety hazards. Always check the specifications before connecting a transformer to a circuit.