Droop-Sharing in a Compact Satellite Up-Link

May 10, 2008

Droop-sharing is often the easiest and most reliable method of producing a redundant bus onto a backplane of a rack-based system. The method not only eliminates the need for a complex and vulnerable communications bus between PSUs, but also allows the backplane bus voltage to be further stepped-down to lower voltages to remove the need for absolute and precise regulation. These advantages, in conjunction with Vicor VI DC-DC converters, are being used in a compact satellite up-link, capable of fitting into a 3U rack.

The up-link required a distributed bus of +7.2V at 12A and -7.2V at 6A , with two PSUs to provide higher system reliability. Since operation over a wide range of mains networks, and generator supplies, was essential, the designers chose a Vicor VI-27R-EW module and Vicor VI-J7R-EY module to provide a PSU with continuous operating from an 90-264Vac input. The outputs were trimmed down to 7.2V and then OR-ed together using IR low forward voltage drop schottky diodes. Good transient response times were achieved by using a suitable series sense resistor, and a resistor between positive sense and positive output. The result was a system which provided improved regulation, compared to using OR-ing diodes, as well as current-sharing to within 10% which ensured a good transient response.

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