LearnTronics
LC Energy Exchange
Recipe #39 — lc energy exchange
After learning capacitors and inductors separately, combine them. An LC circuit can trade stored energy back and forth between an electric field and a magnetic field.
Start with C charged: the capacitor drives current through L. As capacitor voltage falls, inductor current rises. When C reaches zero volts, current in L is maximum and continues charging C with the opposite polarity. The process then reverses.
EC = ½CV² EL = ½LI²
Two different energy stores
The capacitor stores energy in an electric field. The inductor stores energy in a magnetic field. An ideal LC circuit can exchange energy between those fields repeatedly.
Another way to think of it
It resembles a pendulum trading gravitational potential energy for motion and back again. The capacitor is analogous to the energy at the ends of the swing; the inductor current is analogous to maximum motion through the center.
A real circuit eventually stops ringing
Wire resistance, core loss, capacitor ESR, radiation, and the connected load remove energy each cycle. Without an amplifier adding energy, the oscillation decays.