Types of Inductors

 

An inductor is basically a coil of wire. The material around which the coil is formed is called the core. Both fixed and variable inductors are classified according to the type of core material used. Three common types are: the air core, the iron core, and the ferrite core. Each has a unique symbol, shown above. Inductors are made in a variety of shapes and sizes. Some are shown above. Small fixed inductors are encapsulated in an insulating material and have the appearance of a small resistor. Variable inductors usually have a screw type adjustment, to allow inductance to be changed. 

Series and Parallel Inductors

When inductors are connected in series, the total inductance, L_T, is the sum of the individual inductors. The formula is similar to total resistance in series and total capacitance in parallel.

 

When inductors are connected in parallel the total inductance is less than the smallest inductance. The reciprocal of the total inductance is equal to the sum of the reciprocals of the individual inductances. The formula is similar to the formula for total parallel resistance and total series capacitance.