The conversion from a high-input-voltage to a low-output-voltage with low-output-power and large efficiency is challenging, particularly if a limited voltage technology is considered for silicon integration. After presenting few criteria, the paper reviews possible topologies for silicon integration of active devices. A preliminary demonstrator is experimentally analyzed to draw conclusions and prepare the specifications of a future integrated circuit.

The design of a low-cost 800V-to-12V, 4 W isolated DC/DC converter for automotive applications is investigated. Such a converter is required to supply tiny systems directly from the high-voltage battery of an Electric Vehicle. In particular, a selected topology based on a Multi-Level Flying-Capacitor stage is analyzed. The converter operating mode selection is studied and simulation results reveal the interest of operating at the limit of the ZVS mode. The design of a planar transformer adapted to the application is described. Design considerations of an IC brick that includes the main blocks required to control the power stage are discussed. The performances of a 4 W prototype with two transformer designs validate the choice of the operating mode. The peak efficiency is 87.4% which confirms the interest of the selected approach compared to existing solutions

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