I like these cool (but rather large) push-pull drivers, 751-1475-1-ND but I'm not driving logic level on the FET side. For 400 volts I'd probably use an SSR. Thanks, DougM On Fri, Jun 14, 2013 at 10:13 AM, Dwayne Reid wrote= : > Good day to all. > > I'm working on a project where I need to be able to turn OFF a relay > that is controlling AC Mains voltage at a precise point on the AC > waveform. The incoming AC is either 120 or 240Vac. > > Someone else had done a previous incarnation of this project and they > used a standard electro-mechanical relay. They compensated for the > release time of the relay with an adjustable timer. > > I'm leaning in the direction of using a pair of decent-sized MOSFETS > back-to-back with a photo-voltaic opto supplying gate drive and > another opto-isolator to either interrupt or short the gate drive to > the MOSFETS. This should give me sub-millisecond response and > eliminate the need for manually adjusting a timer. > > Digikey has a few photo-voltaic parts available and I'm just > automatically selecting one that has sufficient output voltage (8V) > and the maximum available output current (40uA) - its a Toshiba > TLP191BF. They also offer a 20uA version (TLP190BU) for a dollar less. > > Before I actually go and order these, I thought that I'd ask the > collected wisdom of the PIClist to see if there is something else > that I should be looking at. > > I'm not adverse to using something like a photo-MOS SSR instead of > rolling my own but I haven't found anything on Digikey that has a > decent current rating. > > This is currently only a one-off project but there is a possibility > that the customer may decide to roll these out to other > locations. That would bring the quantity up to perhaps a dozen or so. > > I'm also on the hunt for decent N-channel MOSFETs. Most of my old > standbys are Vgs to 10V minimum - the logic-level MOSFETs that I use > are only good up to 60V or so. > > I need a minimum 8A, 400V rating. > > I do see that Digikey shows that one of my old standbys (IRF840) is > shown as having a logic-level gate threshold - I need check that > because I was darned sure that is one of those parts wanting minimum > of 10V gate drive. But Digikey also shows part numbers that I > recognize from Fairchild and ST Micro, as well as some from somebody > whom I've never seen before: "Alpha & Omega Semiconductor Inc". > > Anyway, I'm about to order one of these parts but thought that I'd > also ask if anyone has any favorites. > > Many thanks! > > dwayne > > -- > Dwayne Reid > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > (780) 489-3199 voice (780) 487-6397 fax > www.trinity-electronics.com > Custom Electronics Design and Manufacturing > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=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 .