Inductor DCR Power Loss

Formula

Description

Every inductor has DC resistance (DCR) from the winding wire, which dissipates power as heat proportional to the square of the current. This copper loss is the dominant loss mechanism in power inductors at low frequencies. At higher frequencies, AC resistance (from skin effect and proximity effect) adds additional loss beyond DCR. Selecting a low-DCR inductor is critical for efficiency in power converters, especially at high currents. A 10 mΩ DCR inductor carrying 5 A dissipates 250 mW continuously.

Variables

• P — Power dissipated as heat (W)
• I — RMS current through the inductor (A)
• DCR — DC winding resistance (Ω)

Practical Notes

DCR increases with temperature (copper has a positive temperature coefficient of about 0.393%/°C). At 100°C, DCR is about 30% higher than at 25°C. For accurate loss estimation at operating temperature, use: DCR_hot = DCR_25 × (1 + 0.00393 × (T − 25)). Total inductor loss includes core loss (from hysteresis and eddy currents) in addition to copper loss.