LC Filter Calculator

Calculate cutoff frequency and design LC filter circuits

LC Filter Design Calculator

Allows low frequencies to pass, blocks high frequencies

Inductor value in circuit

Capacitor value in circuit

Filter Design Results

Cutoff Frequency

5032.92 Hz
In kHz:5.033 kHz
In MHz:0.005033 MHz
Frequency type:Audio Frequency

Circuit Components

Inductance (L):1 mH (1.000 mH)
Capacitance (C):1 μF (1.000 μF)
Filter type:Low-Pass Filter
Inductor in series, capacitor in parallel

Reactances at Cutoff Frequency

Inductive Reactance (XL):
31.62 Ω
Capacitive Reactance (XC):
31.62 Ω
At resonance:
XL = XC

Formula used: fc = 1 / (2π√LC)

Calculation: fc = 1 / (2π × √(1.000 mH × 1.000 μF))

Filter characteristics: Human hearing range (20 Hz - 20 kHz)

Filter Design Notes

🔧 Circuit configuration: Inductor in series, capacitor in parallel
📊 Frequency response: -40 dB/decade roll-off (second-order filter)
At cutoff frequency: Output voltage is -3 dB (70.7% of input)
🎯 Quality factor: Q = √(L/C) / R (depends on load resistance)

Example Calculation

Example: Audio crossover filter at 1 kHz

Given:

• Target frequency: 1 kHz

• Available capacitor: 47 nF

• Filter type: Low-pass

Calculate Required Inductance

L = 1 / (4π²f²C)

L = 1 / (4π² × (1000)² × 47×10⁻⁹)

L = 1 / (4π² × 10⁶ × 47×10⁻⁹)

L = 1 / (1.855 × 10⁻³)

L ≈ 0.539 H = 539 mH

Formula Reference

Cutoff Frequency
fc = 1 / (2π√LC)
Second-order filter
Inductance
L = 1 / (4π²f²C)
From frequency and C
Capacitance
C = 1 / (4π²f²L)
From frequency and L
Reactances
XL = 2πfL
XC = 1 / (2πfC)
At resonance: XL = XC

Filter Types

Low-Pass
L in series, C in parallel
Blocks high frequencies
High-Pass
C in series, L in parallel
Blocks low frequencies
Band-Pass
Series resonant LC
Passes specific band

Applications

Audio Crossovers20 Hz - 20 kHz
RF FiltersMHz - GHz
Power Supply50/60 Hz
EMI SuppressionkHz - MHz

Design Tips

🔧

Use standard component values for practical designs

📐

Consider parasitic resistance and tolerance effects

LC filters have sharper roll-off than RC filters

🎯

Quality factor Q affects bandwidth and selectivity

Understanding LC Filter Circuits

How LC Filters Work

LC filters use the frequency-dependent behavior of inductors and capacitors to selectively pass or block certain frequencies. Inductors have higher impedance at high frequencies (XL = 2πfL), while capacitors have lower impedance at high frequencies (XC = 1/(2πfC)).

Filter Configurations

  • Low-pass: Inductor in series, capacitor in parallel
  • High-pass: Capacitor in series, inductor in parallel
  • Band-pass: Series or parallel resonant circuits
  • Band-stop: Combination circuits for notch filtering

Design Considerations

Frequency Response:

• Cutoff frequency: fc = 1/(2π√LC)

• Roll-off rate: -40 dB/decade

• Phase shift: 90° per pole


Component Selection:

• Standard component values (E12, E24 series)

• Component tolerances affect accuracy

• Parasitic resistance affects Q factor

Practical Applications

  • Audio Systems: Speaker crossovers, equalizers
  • RF Circuits: Antenna tuning, channel selection
  • Power Electronics: EMI filters, noise suppression
  • Signal Processing: Anti-aliasing, smoothing filters