LC Filter Calculator
Free calculate cutoff frequency for low-pass and high-pass lc filters from inductance and capacitance.
Input Parameters
Results
Enter inductance and capacitance to calculate
What is an LC Filter?
An LC filter is an electronic circuit consisting of an inductor (L) and a capacitor (C) that filters signals based on frequency. LC filters can be configured as low-pass or high-pass filters depending on component placement.
In a low-pass LC filter, the inductor is in series and the capacitor is in parallel. It passes low frequencies and attenuates high frequencies. In a high-pass LC filter, the capacitor is in series and the inductor is in parallel - it does the opposite.
LC filters are used in power supplies, RF circuits, audio systems, and signal processing to remove unwanted frequencies, reduce noise, and shape frequency response. They're more efficient than RC filters at higher frequencies.
LC Filter Formula
Where:
- • f_c = Cutoff frequency (Hz)
- • L = Inductance (H)
- • C = Capacitance (F)
- • π = 3.14159...
Note: This formula applies to both low-pass and high-pass LC filters. The cutoff frequency is the same, but the frequency response is opposite.
How to Calculate
-
1
Convert units to base SI units
Convert inductance to Henries (H) and capacitance to Farads (F).
-
2
Calculate LC product
Multiply inductance and capacitance: LC.
-
3
Calculate cutoff frequency
f_c = 1 / (2π√(LC))
Practical Examples
Example 1: Low-Pass Filter
L = 1 mH, C = 1 μF. Calculate cutoff frequency.
Solution:
L = 0.001 H, C = 0.000001 F
LC = 0.001 × 0.000001 = 1×10⁻⁹
f_c = 1 / (2π√(1×10⁻⁹)) = 1 / (2π × 3.16×10⁻⁵)
f_c ≈ 5,033 Hz ≈ 5.03 kHz
Example 2: High-Pass Filter
L = 10 μH, C = 100 nF. Calculate cutoff frequency.
Solution:
L = 10×10⁻⁶ H, C = 100×10⁻⁹ F
LC = 1×10⁻¹²
f_c ≈ 159 kHz
Applications
Power Supplies
Filtering ripple and noise from DC power supplies, smoothing output voltage, and reducing electromagnetic interference.
RF Circuits
Selecting specific frequency bands, removing harmonics, and tuning resonant circuits in radio frequency applications.
Audio Systems
Crossover networks for speakers, frequency equalization, and removing unwanted frequency components in audio signals.
Signal Processing
Filtering noise, selecting frequency bands, and shaping frequency response in communication and measurement systems.
Frequently Asked Questions
What is the difference between low-pass and high-pass LC filters?
Low-pass filters pass frequencies below f_c and attenuate above. High-pass filters do the opposite. The cutoff frequency formula is the same, but component placement determines the filter type.
How does the cutoff frequency affect filter performance?
At f_c, the signal is attenuated by 3 dB (50% power). Below f_c (low-pass) or above f_c (high-pass), signals pass with minimal attenuation. The roll-off rate is -40 dB/decade for LC filters.
What is the Q factor of an LC filter?
Q factor measures filter sharpness. Higher Q means sharper cutoff. Q depends on component quality and any resistance in the circuit. Ideal LC filters have infinite Q (no resistance).
Can I use this formula for band-pass or band-stop filters?
No, this formula is for simple low-pass or high-pass filters. Band-pass and band-stop filters require more complex calculations with multiple LC sections or different topologies.
What happens if I increase L or C?
Increasing L or C decreases the cutoff frequency (f_c ∝ 1/√(LC)). Larger values mean lower cutoff frequencies. This is useful for filtering lower frequencies.