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 I1, then the current in the inductance will be continuous for all values of dc current greater than I1even 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 I1