The shrinking ac/dc supply

摘要

Changes in power supply design are rarely revolutionary. Rather, they are evolutionary and depend on a host of component and manufacturing technologies that, for the most part, develop at a modest pace. Broadly speaking, switchers up to 150 W tend to use flyback topologies in which the energy is only transferred to the load during the off time of the switching element Above this rating, forward converters—also called buck converters—are normally adopted. Here, the converter can operate in two states: continuous, where the input inductor current never falls to zero, and discontinuous, where the inductor current falls to zero at the end of each cycle. Both topologies (see Fig. 1) usually use an input transformer to provide isolation, necessary for medical power supplies.