The Effect of DC Bias on Inductance Measurements
As an inductor is magnetized with a DC current or high level of AC current the inductor core will eventually saturate. As current increases the value of inductance will reduce up to saturation to the saturation point when the inductance tends towards zero. This is particularly evident with applications such as power supplies, power amplifiers and EMC/EMI filters, the inductance value may be significantly modified as current increases and the inductor is used closer to magnetic saturation.
The magnetic design of a coil/choke must ensure that there is sufficient flux density design margin to avoid saturation with DC bias being applied. The following B-H (B = flux density, H = magnetic field strength) curve demonstrates this characteristic:
Magnetization Characteristic of Magnetic Material The "B-H Curve"
If a high power inductor is not tested as it will be used in a final application (under full load) then at best the inductor may cause system level performance issues including output noise, inefficiency and possible overheating or at worst complete failure at final test. This is because a measured inductance is only accurate under realistic DC load conditions. Thorough testing an inductor under realistic load conditions may also lead to a better optimized and possibly lower cost inductor design.