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Isat and Irms

Isat (Saturation Current) - is the current required to decrease the inductance value by the specified

maximum amount (given as a percentage of the nominal inductance value).

Irms - is the current required to increase the temperature of the part a maximum specificed amount

(given as a temperature rise in °C).

In some instances Isat and Irms are shown separately with a maximum decrease in inductance speci-

fied at one current rating (Isat) and a maximum temperature rise specificed at another current rating

(Irms). In other cases one current value is given for both (specified as Idc) and represents the current at

which a specified maximum inductance decrease and a maximum specified temperature rise can occur.

The graph below illustrates change in inductance and temperature as current increases.

Based on the above graph Isat and Irms could be expressed as follows:

1. Isat and Irms can be shown as separate current values. The Isat current is a value of current that

could potentially produce a specified maximum inductance change (-5%, -10%, -20%, etc. of the nominal

value). In this case a 1.0A current has produced a -5% inductance change so 1.0A could be specified as

the inductor's Isat current rating. The Irms could be expressed as the current that produces a +40°C

temperature rise which in this case is about 1.18A.

2. Both Isat and Irms can be expressed using one current value (Idc). In the above graph 1.18A could be

specified as the Idc for the part noting that at 1.18A a potential +40°C temperature rise (equivalent to

Irms) and a -10% change in inductance (equivalent to Isat) could occur.

NPI & NPIS Series