AC2 Fundamentals Unit 3 – Parallel Resonance
This response curve shows that as frequency increases, the circuit current (IT) decreases until it
reaches a minimum point, then it increases again. The relationship between impedance and line
current in a parallel resonant circuit is exactly opposite to the relationship between impedance
and total current in a series resonant circuit. At resonance, circuit current and voltage are in
phase (impedance is resistive) for series and parallel LC circuits.
Parallel resonant circuits are used in tuning and filtering circuits because they provide a high
impedance at the resonant frequency and a low impedance at all other frequencies.
As in series resonant circuits, the Q determines the selectivity of a parallel resonant circuit, and
the bandwidth (B) is a measure of selectivity.