Differential Mode Filter Inductance
L = Z / (2πf)
Quick answer
This calculator solves L = Z_target / (2πf) for Inductance. With Target Impedance 0.47 kΩ, Frequency 10 MHz, the result is 7.48 µH. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Differential mode EMI filters use series inductors to block high-frequency noise currents while passing the desired DC or low-frequency signal. The required inductance is determined by the impedance needed at the noise frequency of interest. This formula rearranges the inductive reactance equation to find the inductance that presents the target impedance at the specified frequency. Higher inductance provides more attenuation but also introduces more DC resistance and potential saturation issues at high currents.
Variables
- L — Required filter inductance (H)
- Z — Target impedance at the noise frequency (Ω)
- f — Frequency of the noise to be filtered (Hz)
Practical Notes
For effective filtering, the inductor impedance should be at least 10× the source impedance at the noise frequency. Ferrite bead inductors are preferred over wire-wound inductors for EMI filtering because they are lossy at high frequencies, converting noise energy to heat rather than reflecting it back. Always verify the inductor performance with actual impedance vs. frequency curves from the datasheet.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| L | Inductance | µH | nH, µH, mH, H |
| Z | Target Impedance | Ω | mΩ, Ω, kΩ, MΩ |
| f | Frequency | MHz | Hz, kHz, MHz, GHz |
Step by step
- 1. What you know: Target Impedance 0.47 kΩ, Frequency 10 MHz
- 2. The relation: L = Z_target / (2πf)
- 3. Substitute: Z = 0.47 kΩ, f = 10 MHz
- 4. Result: Inductance = 7.48 µH
Nearest standard component values
| Series | Nearest value | Error |
|---|---|---|
| E12 | 6.8 µH | 9.1% |
| E24 | 7.5 µH | 0.26% |
Worked examples
Minimum range
Given: Target Impedance 1 Ω, Frequency 100 kHz
Result: Inductance = 1.592 µH
Low range
Given: Target Impedance 10 Ω, Frequency 1 MHz
Result: Inductance = 1.592 µH
Typical
Given: Target Impedance 0.47 kΩ, Frequency 10 MHz
Result: Inductance = 7.48 µH
High range
Given: Target Impedance 4.7 kΩ, Frequency 100 MHz
Result: Inductance = 7.48 µH
Maximum range
Given: Target Impedance 47 kΩ, Frequency 1 GHz
Result: Inductance = 7.48 µH
Solving for each variable
Solve for Inductance
Target Impedance 1 Ω, Frequency 100 kHz → 1.592 µH
Solve for Target Impedance
Inductance 100 nH, Frequency 100 kHz → 62.83 mΩ
Solve for Frequency
Inductance 100 nH, Target Impedance 1 Ω → 1.592 MHz
How Inductance changes with Target Impedance
| Target Impedance (input) | Inductance (result) |
|---|---|
| 47 Ω | 0.748 µH |
| 117.5 Ω | 1.87 µH |
| 0.235 kΩ | 3.74 µH |
| 0.3525 kΩ | 5.61 µH |
| 0.47 kΩ | 7.48 µH |
| 0.705 kΩ | 11.22 µH |
| 0.94 kΩ | 14.96 µH |
| 1.88 kΩ | 29.92 µH |
| 3.29 kΩ | 52.36 µH |
| 4.7 kΩ | 74.8 µH |
The same result in other units
| Unit | Value |
|---|---|
| nH | 7480 |
| µH | 7.48 |
| mH | 0.00748 |
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<p><a href="https://vbatpower.com/formulas/dm-filter-inductance/">Differential Mode Filter Inductance</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Differential Mode Filter Inductance?
Use L = Z_target / (2πf). With Target Impedance 0.47 kΩ, Frequency 10 MHz, Inductance works out to 7.48 µH.
How do you calculate differential mode inductance calculator dc?
Rearrange for Inductance: with Target Impedance 10 Ω, Frequency 1 MHz, Inductance is 1.592 µH.
What is the formula for Differential Mode Filter Inductance?
The formula is L = Z_target / (2πf). Differential mode EMI filters use series inductors to block high-frequency noise currents while passing the desired DC or low-frequency signal.
How do you find Target Impedance when you know the other values?
Rearrange for Target Impedance: with Inductance 100 nH, Frequency 100 kHz, Target Impedance is 62.83 mΩ.
How do you find Frequency when you know the other values?
Rearrange for Frequency: with Inductance 100 nH, Target Impedance 1 Ω, Frequency is 1.592 MHz.
What units does Differential Mode Filter Inductance use?
Inductance is shown in nH, µH, mH. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
All EMC / EMI formulas →Need more features?
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