Inductance, DCR and Operating Current: How to Read Inductor Specifications

Two inductors with the same nominal inductance may still not be suitable as direct replacements for each other. When reading a datasheet, look at the measurement conditions, winding resistance and current limits rather than comparing a single number on the label.

Inductance must come with measurement conditions

The inductance value must be read together with the tolerance and test conditions in the technical documentation. If the order documents give only a value without defining the measurement, the two sides may be comparing results taken under different conditions. Use the same agreed measurement procedure for sample approval and lot inspection.

DCR describes the DC resistance of the winding

DCR is not inductance. It is the resistance of the coil measured with DC, related to conduction losses. Distinguish between typical values and maximum limits, and note the temperature conditions of the measurement. Do not judge the efficiency of the whole component from DCR alone, as there are other loss mechanisms.

Saturation current and thermal limits are not the same concept

Saturation current is usually defined by a specified drop in inductance, whereas the thermal limit depends on temperature-rise criteria and test conditions. So when discussing a current rating for an inductor, specify which requirement it refers to and how it is measured; do not use these parameters interchangeably.

Evaluate together with the circuit and operating environment

Selection also depends on frequency, current waveform, circuit layout and cooling conditions. The design documents should state these conditions so components are evaluated on a consistent basis. Having the same size or the same visible number of turns does not prove that two samples have the same electrical characteristics.

Checklist before sample approval

Check inductance and tolerance, measurement conditions, DCR, current requirements, dimensions and terminations. State clearly which tests are the acceptance criteria for the order. When sending a request to ZINITEK, include the design documents or target specification sheet to discuss the sample and inspection scope.

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Technical reference: Coilcraft – Selecting the Best Inductor