Step-Up Transformer — Magnetic Field Coupling

Step-up transformer principles. A transformer transfers electrical energy between circuits through magnetic coupling. The iron core provides a low-reluctance path for magnetic flux, linking primary and secondary windings.

How it works

AC current in the primary coil creates a time-varying magnetic flux in the core. This changing flux induces a voltage in the secondary coil proportional to its number of turns. More secondary turns = higher induced voltage.

Key equations

V_s/V_p = N_s/N_p — The voltage ratio equals the turns ratio. For a step-up transformer, N_s > N_p, so V_s > V_p.

I_s/I_p = N_p/N_s — Current steps down inversely. When voltage steps up, current steps down.

Quantities

• V_p — Primary (input) voltage
• V_s — Secondary (output) voltage
• I_p — Primary (input) current
• I_s — Secondary (output) current
• N_p — Number of primary coil turns
• N_s — Number of secondary coil turns
• Φ — Magnetic flux in the core (webers)

Energy conservation

Power is conserved (ideally): P_p ≈ P_s = V_p×I_p = V_s×I_s. When voltage steps up, current steps down proportionally.

Sources

All About Circuits: Transformers

Electronics Tutorials: Transformer Construction