Transformers

What is a Transformer?

A transformer is a passive device that transfers electrical energy between two or more circuits through electromagnetic induction. It consists of two (or more) coils of wire — called windings — wound around a shared magnetic core. A changing current in the primary winding creates a changing magnetic field in the core, which induces a voltage in the secondary winding.

How a Transformer Works

• •AC flows through the primary winding, creating a changing magnetic field.
• •The magnetic field is concentrated by the iron or ferrite core.
• •The changing field passes through the secondary winding, inducing a voltage across it (Faraday's Law).
• •The ratio of primary to secondary voltage depends on the ratio of turns in each winding.

The Turns Ratio

The turns ratio (N_p / N_s) determines how the voltage is transformed. If the primary has 1,000 turns and the secondary has 100 turns, the turns ratio is 10:1, and the voltage is reduced by a factor of 10 (step-down). Conversely, if the secondary has more turns, the voltage increases (step-up).

Step-Up vs Step-Down

• •Step-down transformer — More primary turns than secondary (N_p > N_s). Reduces voltage. Example: mains 230 V → 12 V for a power supply.
• •Step-up transformer — Fewer primary turns than secondary (N_p < N_s). Increases voltage. Example: power station generators stepping voltage up to 400 kV for long-distance transmission.
• •1:1 isolation transformer — Equal turns. Voltage stays the same, but primary and secondary are electrically isolated. Used for safety.

Power Conservation

An ideal transformer doesn't consume power — it transfers it. Power in = Power out (P_p = P_s), which means V_p × I_p = V_s × I_s. If a transformer steps voltage down by 10×, the secondary current is 10× higher than the primary current. Real transformers have some losses (typically 2–10 %) due to core losses and winding resistance.

Types of Transformers

• •Power transformer — Large, heavy, laminated iron core. Used in mains power supplies. Steps 230 V (or 120 V) down to lower voltages.
• •Audio transformer — Matches impedance between audio stages. Smaller than power transformers.
• •Pulse/signal transformer — Small, ferrite core. Used in digital signal isolation and gate drive circuits.
• •Current transformer (CT) — Measures AC current by sensing the magnetic field. The wire carrying the current passes through a ring core.
• •Toroidal transformer — Doughnut-shaped core, very efficient and low electromagnetic radiation. Used in high-end audio and medical equipment.

Safety & Isolation

One of the most important roles of transformers is electrical isolation. The primary and secondary windings have no direct electrical connection — energy transfers through the magnetic field only. This means if someone touches the secondary side, they are not directly connected to the mains. Isolation transformers are essential for safety testing, medical equipment, and protecting sensitive electronics.

Real-World Transformer Losses

• •Copper losses (I²R) — Resistance of the wire windings dissipates heat. Thicker wire reduces this.
• •Core losses (hysteresis + eddy currents) — Energy lost in magnetising and demagnetising the core each cycle. Laminated cores reduce eddy currents.
• •Leakage flux — Not all magnetic flux links both windings. Better core design minimises this.
• •Typical efficiency: 90–98 % for well-designed power transformers.