“It is a well-established but little understood fact that ac core losses increase when the ac ripple is dc biased – normal intuition says that dc bias does not increase ac cores losses because it is a static shift,” it said.
It is a situation found in buck regulators, for example, and can lead to unexpected temperature rise if not accounted for.
According to the company (see diagram):
The minor BH loop from the ac ripple follows along the general form of the major BH loop.
The permeability and hence inductance are proportional to the slope of the curves.
As the minor loop move closer towards saturation, the minor loop’s slope decreases.
This decreases inductance resulting in increased ripple current.
With the decreased slope and the BH loop becomes elongated, meaning more losses.
Thus, as dc bias is increased, the inductance will eventually start to decrease as it moves towards saturation which will in turn increase the ripple and the ac losses, the minor BH loop representing the hysteresis losses increases.
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