A step-down transformer has a power output of 50 W and efficiency of 80%. if the mains supply voltage is 200V. Calculate the primary current of the transformer.

A. 0.31 A
B. 3.20 A
C. 3.40 A
D. 5.00 A

Correct Answer:

Option A = 0.31 A

Explanation

Efficiency = (power output)/power input x 100%
= 1sVs/1pVp x 100%
∴ (80)/100 = (50)/IP x 200
I P = (50 x 100)/80 x 200 = 3.125 A