For many years prior to the 1970s, engineers designed and built switch mode
power supplies (SMPSs) using methods based largely on intuitive and exper-
imentally derived techniques. In general, these power supplies were able to
achieve their primary goal of high-efficiency power conversion; unfortu-
nately, due to the lack of adequate theoretical analysis techniques, many of
these power supplies only marginally met their desired performance require-
ments. In many cases, they were considered to be unreliable.
