Conduction losses in DC/DC-Converters as buckboost/boostbuck synchronous rectifier types

In this paper are calculated the conduction-losses of DC/DC converters with step-down and step-up dc power supplies to know and improve the efficiency. Because of the low-output-voltage application for minimum losses the passive diodes are replaced by active synchronous rectifiers [1]. In maximum there are four MOSFETs in different positions. There is a cascade connection of first a buck-converter and second of a boost-converter or of first a boost-converter and second of a buck-converter. For less MOSFETs there are analyzed a buckboost-converter, also a boost-buck-converter (named after its inventor Cuk converter) and a Sepic (Single Ended Primary Inductance Converter). To reduce the switching losses the investigations are made with relatively low switching frequency of about 80kHz in this low power range. The inductors of the converters are fabricated of FE-based nano-crystalline soft magnetic core material, so that core losses are neglected. The low inductance and low loss capacitors are also neglected in the efficiency calculation. The conduction losses of the DC/DC converter then can be calculated by mains of the R-DS(ON) of the MOSFETs and R-L12 wire resistance of the chokes and the switch duty ratio. There are made own loss-measurements of DC/DC converters and it is given a comparison of the device TPS63001 (buck or boost) from TI with constant output-voltage 3,3Volt and variable input-voltage 1,8Volt - 5,5Volt.