ISE Develops New Low-Voltage DC/DC Converter
The Fraunhofer Institute for Solar Energy Systems (ISE, Freiburg, Germany) recently announced the development of a low-voltage dc/dc converter that creates output voltages between 12 and 350V with a high efficiency from input voltages as low as 0.7V. According to ISE, the converter opens up new application possibilities for energy converters such as fuel cells, thermoelectric converters and solar cells.At the low-power range, the compact 10W prototype of the low-power converter is claimed to transform an input current of 15A at 0.7V to 12V with an efficiency value of 85 percent. Higher yields are possible for lower currents, according to ISE. At the medium-voltage range, the converter that has been constructed can transform 1.4V and 200A to 350V with an efficiency value of 90 percent. A series connection of only 10 fuel cells can result in a 1kW bank."We were simply irreverent and broke a taboo," stated project leader Tim Meyer. "Up to now, it was accepted that high currents at low voltages automatically meant high losses. We were able to disprove this idea with carefully selected components and new circuit concepts, and thus eliminate the associated restrictions in systems technology."According to the ISE, where many cells had to be connected in series to produce normal operating voltages, a single cell is now sufficient in the extreme case. A stack of, for example, 20 fuel cells is required to generate system voltages of 12V. Disadvantages include the complex task of electronically monitoring each individual cell; the requirement for additional ventilators to transport air to each cell via a complicated duct system; and space requirements for the stack, which can limit the application possibilities, particularly for portable appliances. With the new low-voltage converter, the electricity supply can be constructed of a single fuel cell while the whole system still provides the usual output voltages. In off-grid solar applications, many small cells must be connected if a converter is not used. The institute's dc/dc converter is claimed to reduce the amount of wiring and eliminates the need to have large cells cut up, at great expense, to make small cells in the first place.