Switching regulators for poets: A gentle guide for the trepidatious

Switching regulators, with their high efficiency and small size, are increasingly desirable as overall package sizes shrink. Unfortunately, switching regulators are also one of the most difficult linear circuits to design. Mysterious modes, sudden, seemingly inexplicable failures, peculiar regulation characteristics, and just plain explosions are common occurrences. Diodes conduct in a wrong way. Capacitors act like resistors; fuses do not blow and transistors do. The output is at ground, and the ground terminal shows volts of noise. The most common problem area in switching designs is the inductor, and the most common difficulty is saturation. An inductor is saturated when it can no longer hold any magnetic flux. As an inductor arrives at saturation, it begins to look more resistive and less inductive. Under these conditions the current flow through it is limited only by its DC copper resistance and the source capacity. A good way to approach designing a switching regulator is to break the problem into small tasks and then integrate everything. The combination of inductors, a sampled feedback loop, and high speed currents and voltages leaves much room for confusion.