The Si9100 high-voltage switchmode regulators are monolithic BiC/DMOS integrated circuits which contain most of the components necessary to implement high-efficiency dc-to-dc converters up to 3 watts. They can either be operated from a low-voltage dc supply, or directly from a 10- to 70-V unregulated dc power source. The Si9100 may be used with an appropriate transformer to implement most single-ended isolated power converter topologies (i.e., flyback and forward),