Rich, How about if an active circuit is placed between the SMPS and the load that will limit the maximum delivered power to <100W even in the case of a single fault?
Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Rich Nute Sent: Monday, April 26, 2004 9:49 AM To: [email protected] Cc: [email protected] Subject: Re: Limited Power Source - 100W is the limit? Hi Amund: > Looking for an external AC/DC adapter with output power rating up to > 100W/24VDC. Our equipment has a plastic enclosure (flame class /HB > material), and therefore need a power that is classified as Limited Power > Source, ref IEC60950 chapter 2.5 > > Question: > Has I interpreted the term "Limited Power Source" correct when I conclude > that a 100W power supply is the maximum rating for such a power source? LPS has two, independent requirements, 100 watts and 8 amperes. (For a 24-volt output, the 100- watt criterion is the critical criterion because it occurs at about 4 amperes.) Both requirements must be met under BOTH normal operating conditions and with a single fault in the regulator circuit. These requirements are NOT related to the output rating. Instead, they are measured with the worst-case load applied to the output terminals. Assuming a SMPS, under normal conditions, a 100- watt rated output will surely output much more than 100 watts into a worst-case load. Under single-fault conditions, the output will approach 200 watts, maybe more. As a general rule, for rated outputs up to about 100 watts, the measured output with worst-case load will be about twice rated output. LPS generally applies to power supplies rated up to about 60-70 watts. As the output approaches 100 watts, regulators cannot provide sufficiently accurate power discrimination, so the output must be fused in order to comply with LPS. Your 100-watt, 24-volt supply will be LPS if you put a 3-amp or 3.3-amp fuse in series with the output. Of course, you only get about 75-80 watts of useful power. Best regards, Rich > From [email protected] Sun Apr 25 14:04:26 2004 > Received: from sanrel1.sdd.hp.com (brand.sdd.hp.com [15.80.36.199]) > by hpsdlfsa.sdd.hp.com (8.9.3 (PHNE_26304)/8.9.3 SMKit7.02 sdd epg) with SMTP id OAA24494 > for <[email protected]>; Sun, 25 Apr 2004 14:04:04 -0700 (PDT) > Received: from ruebert.ieee.org (unknown [140.98.193.10]) > by sanrel1.sdd.hp.com (Postfix) with ESMTP id 14933293A3 > for <[email protected]>; Sun, 25 Apr 2004 13:54:28 -0700 (PDT) > Received: from ruebert.ieee.org (localhost [127.0.0.1]) > by ruebert.ieee.org (Switch-3.1.0/Switch-3.1.0) with ESMTP id i3PKK9hK021477 > for <[email protected]>; Sun, 25 Apr 2004 16:20:09 -0400 (EDT) > Received: (from majordom@localhost) > by ruebert.ieee.org (Switch-3.1.0/Switch-3.1.0/Submit) id i3PKK93D021473 > for emc-pstc-resent; Sun, 25 Apr 2004 16:20:09 -0400 (EDT) > Received: from hormel3.ieee.org (gemini4.ieee.org [140.98.193.189]) > by ruebert.ieee.org (Switch-3.1.0/Switch-3.1.0) with ESMTP id i3PKK8hK021461 > for <[email protected]>; Sun, 25 Apr 2004 16:20:08 -0400 (EDT) > Received: from mail45-s.fg.online.no (mail45-s.fg.online.no [148.122.161.45]) > by hormel3.ieee.org (Switch-3.1.2/Switch-3.1.0) with ESMTP id i3PKK6tw021770 > for <[email protected]>; Sun, 25 Apr 2004 16:20:07 -0400 (EDT) > Received: from oemcomputer (ti221110a080-1268.bb.online.no [80.213.4.244]) > by mail45.fg.online.no (8.12.11/8.12.11) with SMTP id i3PKK3Jo000222 > for <[email protected]>; Sun, 25 Apr 2004 22:20:04 +0200 (MEST) > From: <[email protected]> > To: <[email protected]> > Subject: Limited Power Source - 100W is the limit? > Date: Sun, 25 Apr 2004 22:20:13 +0200 > Message-ID: <[email protected]> > MIME-Version: 1.0 > Content-Type: text/plain; > charset="iso-8859-1" > Content-Transfer-Encoding: 7bit > X-Priority: 3 (Normal) > X-MSMail-Priority: Normal > X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) > Importance: Normal > In-Reply-To: <421cb3b9b2d2f645b548d213c0a90e55015a0...@edgmsmsg01.eu.thmulti.com> > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 > X-UCE-Filter-Settings: 90_OPT_OUT > X-Scanned-By: IEEE UCE Filtering Service > Sender: [email protected] > Precedence: first-class > Reply-To: <[email protected]> > X-Resent-To: Multiple Recipients <[email protected]> > X-Listname: emc-pstc > X-Info: Help requests to [email protected] > X-Info: [Un]Subscribe requests to [email protected] > X-Moderator-Address: [email protected] > X-EPG-Spam-Status: No, tests=bogofilter, spamicity=0.499966, version=0.13.7.2 > X-EPG-Spam-Branding: http://www.sdd.hp.com/go/epgspam > > > Hi all, > > Looking for an external AC/DC adapter with output power rating up to > 100W/24VDC. Our equipment has a plastic enclosure (flame class /HB > material), and therefore need a power that is classified as Limited Power > Source, ref IEC60950 chapter 2.5 > > Question: > Has I interpreted the term "Limited Power Source" correct when I conclude > that a 100W power supply is the maximum rating for such a power source? > > Best regards > Amund Westin, Oslo / NORWAY > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ieee-pses.org/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
