Question

The “power cube” transformer for a portable CD player has an output of 4.5 V and 500 mA (both rms) when plugged into a 120V/60Hz outlet. Part A If the primary coil has 1220 turns of wire, how many turns are on the secondary coil? I found the answer to part A: N=46 turns. Part B What is the peak current in the primary coil?

Answer 1

Apply in a transforner

Ns/Np = Vs/Vp = Is/Ip

where NS ans Np are seconda dr and primary tunrs

Vs and Vp are secondary and primary volatges

Is and Ip are secondary and prianry currents

also in ideal tansformer output P = input P

so VsIs = VpIp

part A: Np/Ns = Vp/Vs

Ns = Vs/Vp * Np

Ns = 4.5 * 1220/120

Ns = 46 turns

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use Ip = Is * Ns/Np

Ip = 500 * 46/1220

Ip rms = 18.85 mA

Ip peak = 1.414 * 18.85 = 26.65 mA or 27 mA