1st Order Passive Filter Calculator

byee-diary •2/16/2022 10:49:00 AM • 2 min read

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Filter Calculator

Calculate Cutoff Frequency f_c

R — Resistance

C — Capacitance

Result — f_c

φ = 45° and X_c = R at cutoff frequency

Find R from f_c & C

f_c

C

Result — R

Find C from f_c & R

f_c

R

Result — C

Find R from Phase Angle φ

φ (degrees)

f_c

C

Result — R

Energy & Time Constants (τ)

V — Voltage (V)

R

C

Energy stored in C

τ — 63.2% of final value

5τ — within 0.01% of final value

Formulae — RC Low Pass Filter

Cutoff frequency:

f_c = 1 / (2π·R·C)

Capacitive Reactance at f_c:

X_C = 1 / (2π·f_c·C) = R

Time constant:

τ = R·C

Energy stored in capacitor:

E = ½·C·V²

Calculate Cutoff Frequency f_c

R (= X_L)

L — Inductance

Result — f_c

Find R from f_c & L

f_c

L

Result — R (= X_L)

Find L from f_c & R

f_c

R

Result — L

Formulae — RL Low Pass Filter

Cutoff frequency:

f_c = R / (2π·L)

Inductive Reactance at f_c:

X_L = 2π·f_c·L = R

Calculate Cutoff Frequency f_c

R (= X_C)

C — Capacitance

Result — f_c

Find R from f_c & C

f_c

C

Result — R

Find C from f_c & R

f_c

R

Result — C

Formulae — RC High Pass Filter

Cutoff frequency:

f_c = 1 / (2π·R·C)

Capacitive Reactance at f_c:

X_C = 1 / (2π·f_c·C) = R

Calculate Cutoff Frequency f_c

R (= X_L)

L — Inductance

Result — f_c

Find R from f_c & L

f_c

L

Result — R (= X_L)

Find L from f_c & R

f_c

R

Result — L

Formulae — RL High Pass Filter

Cutoff frequency:

f_c = R / (2π·L)

Inductive Reactance at f_c:

X_L = 2π·f_c·L = R

Tags: filter calculator

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