An Improvement of the Critical Inductance Criterion

In an inductive input filter for a rectifier-type power supply, critical inductance is the minimum value of inductance which will maintain a continuous current in the inductance. In the usual development of the critical inductance criterion, a small signal, or linear, concept of inductance is implied. Consider a ``swinging choke'' in which the inductance is allowed to vary with current due to saturation of the core; in this paper we show that if the inductance of a coil exceeds the critical value for some dc current I
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, then the current in the inductance will be continuous for all values of dc current greater than I
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even though the inductance may drop below the critical value. Thus, the size and weight of the inductor can be reduced below that of a coil designed to exceed critical inductance for all current greater than I
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