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Parallel RLC Circuit Resonance Calculator

Calculate a parallel RLC (tank circuit) resonant frequency, quality factor (Q), and -3dB bandwidth from its resistance, inductance, and capacitance.

Resonant frequency (f₀)
5,032.92 Hz
Quality factor (Q)
3.162
Bandwidth (-3dB)
1,591.55 Hz
Half-power points
4,237.15 Hz – 5,828.7 Hz

How it works

A parallel RLC 'tank' circuit resonates at the same frequency as the series circuit this site already covers, f₀ = 1 ÷ (2π√(LC)) — reactance cancellation between L and C doesn't depend on how a third element is wired in. The quality factor behaves the opposite way, though: in a series circuit, R sits in the current's only path, so more resistance bleeds away more energy each cycle and lowers Q. Here, R sits in parallel with a lossless LC tank, acting as the only leak for the energy circulating between L and C — so a larger R leaks less and raises Q = R·√(C/L) (equivalently R ÷ (ω₀L) or R·ω₀C, all algebraically identical once ω₀ = 1/√(LC) is substituted in).

The -3dB bandwidth is still Δf = f₀ ÷ Q, the same relationship as any resonant circuit, and the (symmetric) half-power points are f₀ ± Δf/2. Electronics texts call series resonance 'voltage resonance' and parallel resonance 'current resonance': at resonance, each reactive branch in this tank circuit carries Q times whatever current the source supplies, the dual of how a series RLC circuit's capacitor and inductor each see Q times the source voltage.

FAQ

Why does raising R increase Q here, when it lowers Q in the series RLC calculator?

It comes down to where R sits relative to the energy that's circulating between L and C. In a series circuit, all the current has to pass through R, so a bigger R dissipates more of that energy every cycle and widens (lowers the Q of) the resonance. In a parallel circuit, R is a side path alongside the lossless LC loop — raising R makes that side path leak less current away, so more energy keeps circulating in the tank and the resonance gets sharper (higher Q).

What's a real example of a parallel RLC circuit?

The tuned 'tank circuit' in an oscillator or radio-frequency amplifier is usually a parallel LC combination with the surrounding circuit's finite input/output resistance modeled as the parallel R — which is exactly why parallel resonance matters in practice: that finite R sets how selective the tank actually is, not just the L and C values alone.

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