If the primary current is 3 A in a transformer with a 4:1 turns ratio, what is the approximate secondary current?

If the primary current is 3 A in a transformer with a 4:1 turns ratio, what is the approximate secondary current?

• A. 12 A
• B. 6 A
• C. 3 A
• D. 9 A

Answer: (A)

In a transformer, the voltage ratio equals the turns ratio, and the currents are inversely related to that ratio to keep power roughly constant. With a 4:1 turns ratio, the primary has four times as many turns as the secondary, so Vs ≈ Vp/4. To conserve power in an ideal transformer, the secondary current is Is ≈ Ip × (Vp/Vs) = Ip × 4. If the primary current is 3 A, the approximate secondary current is 12 A. This assumes an ideal transformer; real devices have small losses but the result is a good approximation.

In a transformer, the voltage ratio equals the turns ratio, and the currents are inversely related to that ratio to keep power roughly constant. With a 4:1 turns ratio, the primary has four times as many turns as the secondary, so Vs ≈ Vp/4. To conserve power in an ideal transformer, the secondary current is Is ≈ Ip × (Vp/Vs) = Ip × 4. If the primary current is 3 A, the approximate secondary current is 12 A. This assumes an ideal transformer; real devices have small losses but the result is a good approximation.