20. Input EMI Filter Inductor
1. Component Purpose
Switching converters and digital circuits on the board generate high-frequency noise that can travel back out through the 24V input power line. This conducted EMI (electromagnetic interference) can disturb other equipment connected to the same supply.
An LC filter at the input uses a series inductor and a shunt capacitor to ground. The inductor blocks high-frequency noise from passing through, while the capacitor shorts whatever noise gets past the inductor to ground. Together, they keep the power line clean.
Unlike a buck/boost inductor, this filter inductor carries only steady DC current (no large AC ripple), so the current and saturation margins are more relaxed.
Required: 10µH · ±20% · Irms ≥2A · Isat ≥2.5A · DCR ≤100mΩ · Shielded · SMD · −40°C to +125°C · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Inductors, Coils, Chokes → Fixed Inductors
Apply these filters:
- Inductance → 10µH
- Current Rating (Amps) → 2A or higher
- Current - Saturation (Isat) → 2.5A or higher
- DC Resistance (DCR) → 100mΩ or lower
- Shielding → Shielded
- Type → Wirewound
- Mounting Type → Surface Mount
- Part Status → Active
Tip: A shielded inductor is important in EMI filter applications. An unshielded inductor would radiate the very noise you are trying to contain, defeating the purpose of the filter.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Inductance | 10µH | Blocks high-frequency conducted noise. |
| Tolerance | ±20% | Standard for power inductors. |
| Current Rating (Irms) | ≥2A | Board draws up to 1.5A; margin for heating. |
| Saturation Current | ≥2.5A | Margin above 1.5A DC for transients. |
| DC Resistance (DCR) | ≤100mΩ | Low loss; avoids voltage drop on input rail. |
| Type | Shielded Wirewound | Contains magnetic field; prevents radiated EMI. |
| Temp Range | −40°C to +125°C | Industrial operating conditions. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide