Discrete modeling and analysis of switching regulators

A simplified method for finding and using discrete small-signal models for switching regulators is presented. With introduction of a new "straight-line" approximation, and application of root locus techniques, it is demonstrated that discrete models may be used accurately to predict wide bandwidth closed-loop behavior with methods simple enough to be useful in the initial design phase of a switching regulator. The principal result is a set of converter transfer functions comparable to the set derived by describing function techniques, but not subject to the low frequency restriction of describing function models. Also presented is a set of pulse-width modulator transfer functions which indicates that the potential small-signal transient behavior of a switching regulator is independent of the choice of modulator