One issue in the hybrid switch circuit will be ensuring the relay contacts = still get sufficient arcing to keep them clean and low resistance... aka we= tting current. For the size relay you're talking about (30A) a minimum swit= ching load might be 5V 1A. Add that to the design spec... dont turn the sem= i switch hard on, instead regulate it to give the relay it's minimum switch= ing load. Not 100% sure if that should apply equally to turn off as well as= turn on. -------- Original message -------- From: RussellMc =20 Date:01/03/2015 1:35 AM (GMT+12:00)=20 To: "Microcontroller discussion list - Public." =20 Cc:=20 Subject: [EE]:: Relay enhancing for "higher" voltage DC operation=20 Summary: What are the issues when using a semiconductor switch across an electromechanical contact to (seek to) obtain higher voltage operation than the mechanical contact would otherwise allow and substantially lower power dissipation than a a semiconductor switch alone will allow for a given all up cost? DC operation is of primary interest, but AC gains should also be p= ossible. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .