What must be checked before using the RL low-pass filter relation?

Identify the filter type, fc and load effect on H(jω).

8. Filters and frequency response

RL low-pass filter

Formula

H(j\omega)=\frac{R}{R+j\omega L}

Detail

The RL low-pass has the same first-order Bode shape as the RC low-pass.

Explore the idea

Variables

$H(j\omega)$ dimensionless
$\omega$ rad/s
$f_c,f_0$ Hz
$R,C,L$ Ω, F, H
$Q$ dimensionless.

Conditions

Linear time-invariant filter; light load unless stated.

Intuitive explanation

For “RL low-pass filter”: |H(jω)| shows the passband and fc marks the −3 dB Bode point.

Worked example

With

R=100\,\Omega

L=15.9\,\mathrm{mH}

and

f=1\,\mathrm{kHz}

\omega L\approx100\,\Omega

and

|H|\approx0.707

Common mistakes

using ωc in place of fc or the reverse
forgetting load shift of the cutoff
mixing dB with linear gain

Frequently asked questions

What must be checked before using the RL low-pass filter relation?: Identify the filter type, fc and load effect on H(jω).

Also known as

low-pass filter, cutoff frequency, Bode plot, −3 dB

Conventions

dimensionless, Hz or dB

Last reviewed: 2026-09-19

Found an error? Contact us.

Related formulas

8. Filters and frequency response

RL low-pass filter

In 8. Filters and frequency response

Formula

H(j\omega)=\frac{R}{R+j\omega L}

Detail

The RL low-pass has the same first-order Bode shape as the RC low-pass.

Explore the idea

Variables

$H(j\omega)$ dimensionless
$\omega$ rad/s
$f_c,f_0$ Hz
$R,C,L$ Ω, F, H
$Q$ dimensionless.

Conditions

Linear time-invariant filter; light load unless stated.

Intuitive explanation

For “RL low-pass filter”: |H(jω)| shows the passband and fc marks the −3 dB Bode point.

Worked example

With

R=100\,\Omega

L=15.9\,\mathrm{mH}

and

f=1\,\mathrm{kHz}

\omega L\approx100\,\Omega

and

|H|\approx0.707

Common mistakes

using ωc in place of fc or the reverse
forgetting load shift of the cutoff
mixing dB with linear gain

Frequently asked questions

What must be checked before using the RL low-pass filter relation?: Identify the filter type, fc and load effect on H(jω).

Also known as

low-pass filter, cutoff frequency, Bode plot, −3 dB

Conventions

dimensionless, Hz or dB

Last reviewed: 2026-09-19

Found an error? Contact us.

RL low-pass filter

Tags

Detail

Explore the idea

Variables

Conditions

Intuitive explanation

Worked example

Common mistakes

Frequently asked questions

Also known as

Conventions

Related formulas

RL low-pass filter

Tags

Detail

Explore the idea

Variables

Conditions

Intuitive explanation

Worked example

Common mistakes

Frequently asked questions

Also known as

Conventions

Related formulas