Buck Converter Inductor Selection

Question

Problem: Buck Converter Inductor Selection. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose

In a buck converter, the inductor is the core energy-storage element. During each switching cycle, the switch connects the input to the inductor, which stores energy in its magnetic field. When the switch turns OFF, the inductor releases this stored energy to the output.

The inductor smooths the pulsed current into a steady DC output. Without it, the output would be a noisy, pulsed waveform instead of a clean 5V DC rail.

Two critical current specs define whether the inductor works safely:

• Current Rating (Irms): the continuous RMS current the inductor can carry without overheating. Must exceed the DC load current (2A).

• Saturation Current (Isat): the peak current at which the inductor’s core saturates and inductance drops sharply. Must exceed the peak inductor current (DC load + half the ripple current). If exceeded, the inductor loses its ability to store energy and the converter fails.

Required: 22µH · ±20% · Irms ≥3A · Isat ≥3.5A · DCR ≤120mΩ · 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 → 22µH
Current Rating (Amps) → 3A or higher
Current - Saturation (Isat) → 3.5A or higher
DC Resistance (DCR) → 120mΩ or lower
Shielding → Shielded
Type → Wirewound
Mounting Type → Surface Mount
Part Status → Active

Tip: On DigiKey, "Current Rating" usually refers to the thermal (Irms) rating, while "Current - Saturation" is a separate filter. Make sure to check both.

3. Key Specifications & What They Mean

Specification	Required	Why
Inductance	22µH	Sets ripple current and converter response.
Tolerance	±20%	Standard for power inductors.
Current Rating (Irms)	≥3A	Load is 2A; margin for continuous heating.
Saturation Current	≥3.5A	Must exceed peak current to avoid core saturation.
DC Resistance (DCR)	≤120mΩ	Lower DCR = less I²R power loss and heat.
Type	Shielded Wirewound	Shielded reduces EMI radiated to nearby circuits.
Temp Range	−40°C to +125°C	Industrial range; inductor runs hot.
RoHS	Yes	Compliance required.

Important: Always check both Irms and Isat ratings. An inductor can have a high Irms (thermal) rating but a low Isat value — meaning it overheats slowly but saturates quickly. Both must have adequate margin.

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

5. Filtered DigiKey Link

➡ View Matching Parts — 22µH, Shielded, ≥3A, Isat ≥3.5A, DCR ≤120mΩ

18. Buck Converter Inductor Selection