Low-volume buck converter with adaptive inductor core biasing

This paper introduces a digitally-controlled buck converter with adaptive core biasing that allows for minimization of the output capacitor as well as of the inductor core. The improved performances are obtained through adaptive relocation of the converter operating point on the B-H curve of the inductor core, with the help of a digitally controlled low-power biasing circuit and an extra inductor winding. During transients, the point is set in the saturation region, so the inductance is drastically reduced. As a result the inductor current slew rate and, consequently, load transient response are improved allowing output capacitor reduction. The biasing is also used to reduce flux density allowing the core volume minimization. Experimental verifications with a 3.3 V, 30 W, 500 kHz prototype show that the adaptive biasing system has about two times smaller voltage deviation than the conventional buck allowing for proportional reduction in the output capacitance and for about 40% reduction in the magnetic core size.