Back when Yoda was a Jedi-in-training, designing a power supply was relatively straightforward. We lived in a linear world: The front end of a typical power supply consisted of a transformer feeding a full-wave bridge rectifier followed by a large-value filter capacitor.
Incidentally, since Yoda was over 900 years old when this picture was taken (Fig. 1), the rectifier might have used vacuum-tube technology. But we digress.
1. “A difficult path it will be. Master many skills you must.” A switching power-supply designer must be familiar with a variety of disciplines, including magnetics, layout, thermal management, and digital control. (Source: Lucasfilm)
As described, a linear design is simple, reliable, and if an unregulated power supply meets your requirements, efficient, too. Add regulation, though, and the efficiency plummets. Linear regulators, as is well-known, control the output voltage by dropping it across the pass element (the power transistor), which dissipates copious amounts of heat and results in an efficiency as low as 60%.
Switching power topologies changed all that. Chopping up the incoming dc voltage into a high-frequency switched voltage and using that to produce the desired output voltage and current allows the power transistors to spend most of their time in the efficient “on” or “off” states, minimizing power losses.