Dostal's Designs: Buck-Boost Voltage Conversion, the Quiet Way (Download)
In many applications, voltages require upward and downward conversion. One example would be if an input voltage range of 6 to 24 V is available, and 12 V would be generated from it. Classical wide-range power supplies must be capable of such voltage conversions.
Different voltage-conversion architectures are capable of voltage conversion upward and downward. These are transformer-based topologies such as flyback regulators, a single-ended primary inductor converter (SEPIC) topology, and a 4-switch buck-boost topology.