A transformer has 400 turns in the primary and 100 turns in the secondary. The input voltage is 28 volts, 1 amp. What is the output voltage?

A transformer has 400 turns in the primary and 100 turns in the secondary. The input voltage is 28 volts, 1 amp. What is the output voltage?

• A. 14 volts
• B. 7 volts
• C. 28 volts
• D. 0.7 volts

Answer: (B)

Voltage output follows the turns ratio. The secondary has 100 turns and the primary 400, so the secondary voltage is a quarter of the primary: Vs = Vp × (Ns/Np) = 28 × (100/400) = 7 volts. In an ideal transformer, power in equals power out, so the output current would be 28 W / 7 V = 4 A. This shows the transformation: stepping down from 28 V to 7 V with a 4:1 turns ratio.

Voltage output follows the turns ratio. The secondary has 100 turns and the primary 400, so the secondary voltage is a quarter of the primary: Vs = Vp × (Ns/Np) = 28 × (100/400) = 7 volts. In an ideal transformer, power in equals power out, so the output current would be 28 W / 7 V = 4 A. This shows the transformation: stepping down from 28 V to 7 V with a 4:1 turns ratio.