Efficiency improvement of a DC-DC converter used in Series-Connected Boost Converters

Today's power converter industry is apparently heavily influenced by the need to achieve two important goals: high efficiency and small weight and size. Switching frequency of the converter is a factor that moves the mentioned desired characteristics to opposite directions, improving one and deteriorating the other. A higher switching frequency allows us to use smaller components, but in return it reduces efficiency. At full load, the use of high frequencies is an obligation, since it is the way to avoid excessive output ripple and core saturation. At light loads however, we can improve efficiency by reducing switching frequency. The practical implementation of such a variable switching frequency scheme is discussed for a Push-Pull DC-DC converter used in a Series-Connected Boost Converter (SCBC.) Various approaches to implement the technique are discussed, and experimental results are provided. It was finally shown through the experiments that efficiency improvements up to 15% can be expected at light loads when using variable switching frequency.