---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 12/24/13: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:17 PM - Soild State Relays (Eric M. Jones) ________________________________ Message 1 _____________________________________ Time: 12:17:47 PM PST US Subject: AeroElectric-List: Soild State Relays From: "Eric M. Jones" 1) International Rectifier sells "Intelligent Solid State Switches" These take most of the pain out of building simple and reliable SSRs. Google them. These are available in both "high side" and "low side" types. See attached. 2) Don't forget the heat sink. Assuming the mosfet is either fully on or fully off, the heat sink is merely I X I X Rds(on). Example: FDD8445S http://www.farnell.com/datasheets/49165.pdf, is a 25A, 40V Fet in a remarkably tiny D-pak. It's Rds(on) is 6.7 m (Typ), VGS = 10V (the gate drive voltage), Id=25A (50A at 50% duty cycle). So to keep the thing under 100 degC you need a heat sink that will dissipate 25 X 25 X 0.0067 = 4.2 W minimum. Really a simple thing to do. And it costs $1.00. 3) The discussion about "What is the most common failure mode...?" for SSRs neglected to ask "What is the most common method of abuse...?", but there is a general rule for these devices: Large over-currents (slowly applied) tend to cause "short" failures. Large over-voltages (suddenly applied) tend to cause "open" failures. But YMMV... -------- Eric M. Jones www.PerihelionDesign.com 113 Brentwood Drive Southbridge, MA 01550 (508) 764-2072 emjones(at)charter.net Read this topic online here: http://forums.matronics.com/viewtopic.php?p=416173#416173 Attachments: http://forums.matronics.com//files/high_side_low_side_fets_944.pdf ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.