Introduction/Basic Operation

In switching regulator applications the inductor is used as an energy storage device. When the semiconductor switch is on the current in the inductor ramps up and energy is stored. When the switch turns off energy is released into the load. The amount of energy stored is calculated by the formula Energy = ½L.I² (Joules), where:

• L is the inductance in Henrys

• I is the peak value of inductor current

The amount by which the current changes during a switching cycle is known as the ripple current. Ripple current is defined as Vl = L.di/dt:

• Vl is the voltage across the inductor

• di is the ripple current

• dt is the duration for which the voltage is applied

The following parameters need to be defined or calculated to select an inductor:

• Maximum input voltage

• Output voltage

• Switching frequency

• Maximum ripple current

• Duty cycle