Transformers and Impedance

Review Two types of current: –ac –dc Two fundamental principles: –Moving electrons create magnetic fields –Moving or changing magnetic fields cause electrons to move

AC Wave Vocabulary Review

The Inductor (Review) Coil of wire. –Stores energy in a magnetic field Value of inductance depends on: –Number of turns. –Spacing of turns. –Size of the wire. –Material of the core.

The Transformer Two inductors –Parallel and close together. –Iron core facilitates transfer. Two basic functions 1.Voltage transformation. 2.Impedance transformation.

How a Transformer Works

Transforming Voltage The ratio of the number of turns in the primary and secondary determine the voltage change. –Step up (increase) –Step down (decrease)

Impedance Defined Resistance is the opposition to the flow of current. –Capacitors and inductors react differently in opposing the flow of ac current than they do in opposing the flow of dc current. –Resistance to the flow of ac is called reactance. –Resistors react the same for ac or dc. Impedance is the opposition to the flow of ac current. –Includes the both components of opposition: resistance and reactance –Measured in Ohms –Symbolized by the letter Z

Importance of Impedance If there is an impedance mismatch between the source and the load, there will not be maximum transfer of power or energy. –i.e., speakers (generally 8-ohms impedance) operate most efficiently if connected to an 8-ohm impedance amplifier. Transformers serve to transform or match the impedance between the source and the load.

Transforming Impedance The ratio of the number of turns in the primary and secondary determine the impedance change –Step up (increase) –Step down (decrease)

Your Turn 2250 turns in the primary, 500 turns in the secondary, 120 volts ac applied to primary. What is the output voltage? 600 ohms output impedance of an amplifier, 4 ohm speakers. What is the turns ratio of the impedance matching transformer required?