Transformador razão de espiras

Transformer turns ratio

In an ideal transformer, the primary and secondary voltages, currents and turns all tie together through V₁ / V₂ = N₁ / N₂ = I₂ / I₁. Push the voltage up and the current drops by the same factor; do the reverse and the opposite happens. Power has to balance, after all: V₁ · I₁ = V₂ · I₂. Take a 230 V mains transformer feeding a 12 V output. Its turns ratio works out to 230 / 12 ≈ 19:1. Pull 5 A from the secondary at 12 V and the primary only sees about 5 / 19 ≈ 0.26 A. A step-up unit (N₂ > N₁) raises the voltage; a step-down one (N₂ < N₁) brings it down. Out in the real world there are copper and core losses, which is why efficiency usually lands somewhere in the 95–99 % range.

Applications

Power transmission: utilities push the voltage up to hundreds of kV to cut line losses (P_loss = R · I²), then bring it back down at substations and poles. Linear power supplies: 230 V → 12/24 V for electronics. Welding: a step-down transformer gives up voltage to get the very high current an arc needs. HV chargers and CRT TVs: a step up to several kV drives image tubes and other high-voltage loads.

FAQ

Does it work with DC? No. A transformer relies on magnetic flux that keeps changing. Steady DC gives you a static field and nothing gets induced in the secondary. You need AC, or at least pulsed DC.

Can I run a 110 V transformer on 220 V? Don't. The flux doubles, the core saturates, and the primary starts pulling enormous current until the windings burn out. Pick the correct voltage tap instead.

What about autotransformers? Here primary and secondary share one winding. That saves copper and weight, but you give up galvanic isolation. You'll find them in plenty of voltage-conversion adapters.