TRANSFORMER
Solutions to the problems given last activity;
1. A power transformer is used to couple electric energy from a power-supply line to one or more components
of the system. In one type of power transformer, there are three separate secondary windings, each designed
for a different voltage output. The primary of the transformer is connected to a 120 V source of supply and
has 100 turns. Find the number of turns on each secondary.
2. A transformer whose primary is connected to a 110 V source delivers 11 V. If the number of turns on the
secondary is 20 turns, find the number of turns on the primary. How many extra turns must be added to the
secondary if it must deliver 33 V?
3. A 7:5 step-down transformer draws 2 A. Find the secondary current.
4. A transformer delivers 550 V at 80 mA at an efficiency of 90%. If the primary current is 0.8 A, find the power
input in voltamperes and the primary voltage.
5. The step-down autotransformer at a power factor of unity is designed to deliver 240V to a load of 5 kW. The
autotransformer’s primary winding is connected to a 600 V source. Find the current in a.) the load b.) the
primary winding, and c.) the secondary winding.
6. A 60:1 output transformer is used to match an output transistor to a 4 Ω voice coil. Find the impedance of
the output circuit.