Lossy LC tank explained

In ideal LC oscillators inductor and capacitor do not consume or dissipate any power. The energy is transferred back and forth between L and C without losses. However, real components and wires have parasitic resistances that cause energy losses. This circuit models parasitic resistances as a single 50 mΩ resistor. Flip the switch to charge the capacitor, then flip it again to start oscillation. Inductor current is plot versus capacitor voltage (update EC to 2.09 to see the plot). The plot shows that after every cycle some energy is lost as voltage and current become smaller. The trajectory spirals down to the origin until no energy remains. Try to adjust the resistance. A large value like 1Ω will dissipate most of the energy during the first cycle. A small value like 1 µΩ will dissipate little energy, and the trajectory becomes a closed orbit. The orbit plot makes it easy to understand energy transfer between L and C. When the trajectory crosses vertical axes (voltage is zero) all energy stored in the inductor. Capacitor stores all the energy when trajectory crosses horizontal axis (voltage is zero). So during one cycle the energy is completely transferred four times.

published 10 years ago