Common ground OK or total isolation? Classic flyback with two winding inductor will do this either with common ground or fully isolated with eg optical feedback. Output switch off can be achieved with high side PNP or MOSFET. Classic buck/boost also does this OK (effectively a flyback with the inductor swapped over between input and output. R --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .