Feedforward control of switching regulators

Abstract

Feedforward control is a conceptually simple, highly effective and extremely robust, but not very well known or appreciated, technique for improving the dynamic regulation of switching regulators. Feedforward control is also used for stabilizing the switching frequency or the loop gain of free-running converters. The paper presents an overview of feedforward control, starting with small-signal input-voltage feedforward and load-current feedforward in the basic dc-dc converters, both with voltage-mode and current-mode control. Then the extension of the feedforward concept to large input-voltage perturbations without or with load-current feedforward will be discussed. This will be followed by the introduction of feedforward pulse-width modulators. The paper concludes with a discussion of miscellaneous practical topics (implementing input voltage feedforward in isolated converters with secondary-side control, feedforward to the input of the error amplifier, and feedforward stabilization of the switching frequency or the dc value of the control-to-output voltage gain). © 2012 Springer Science+Business Media B.V.