A power supply comprises a first coupled to receive AC mains power that provides a first power level, a second stage that receives the first power level and that provides a second power level, a third stage that receives the first power level that provides a third power level, and a pulse width modulated...http://www.google.es/patents/US6005781?utm_source=gb-gplus-sharePatente US6005781 - Two switch off-line switching converter
