Practical Design of a Buck Converter by Dennis L. Feucht
Controller Design
We have completed derivation of the design formulas for the power switching part of the converter. Output voltage regulation is achieved by the controller. It inputs Vo and outputs D. Vo is scaled with a resistive divider, then compared to a commanded value. For fixed-voltage converters, this is a stable and accurate reference voltage. If Vo is low, D is increased; if high, D is decreased.
Various IC controllers are commercially available. Two classic low-cost 8-pin ICs that are useful for reference designs are the UCC3842 and the NE5561 (or variants). Newer parts typically have smaller packages, more features and performance, and a higher price. In choosing a controller IC for long-term use, it is best to select one that has won a long-term reputation in the market and will continue to be available in future years. For short-term designs, any commercially available IC that can be bought in lifetime volumes is also a possibility.
