The winding ratio of which transformer type is 3:1?

The winding ratio of which transformer type is 3:1?

• A. Step-down
• B. Step-up
• C. Isolation
• D. Auto

Answer: (A)

In an ideal transformer, the voltage ratio equals the turns ratio: Vp/Vs = Np/Ns. A winding ratio of 3:1 means the primary has three times as many turns as the secondary, so the secondary voltage is one third of the primary (Vs = Vp/3). That is exactly what a step-down transformer does—reduces voltage. A step-up would require the inverse ratio (1:3) to raise voltage. An isolation transformer typically uses equal turns (1:1) to isolate without changing voltage. An auto transformer uses a single winding with a tap and can provide various ratios, but the fixed 3:1 setup described corresponds to a step-down arrangement.

In an ideal transformer, the voltage ratio equals the turns ratio: Vp/Vs = Np/Ns. A winding ratio of 3:1 means the primary has three times as many turns as the secondary, so the secondary voltage is one third of the primary (Vs = Vp/3). That is exactly what a step-down transformer does—reduces voltage. A step-up would require the inverse ratio (1:3) to raise voltage. An isolation transformer typically uses equal turns (1:1) to isolate without changing voltage. An auto transformer uses a single winding with a tap and can provide various ratios, but the fixed 3:1 setup described corresponds to a step-down arrangement.