I think the rationale behind requesting approved components for X capacitors is that in the past there have been some unpleasant failure modes in those capacitors. In the case of a short circuit in the isolation the resistance the capacitor does not become zero, but something in the 10 Ohm range. This caused the capacitor to heat up tremendously and finally catching fire.
Semiconductors normally become open or short, at least when they heat up beyond 250 degrees C. Then the fuse will blow. The fireresistance of resistors can be checked during the abnormal operation tests and normally they only get overheated when some other component gets broken. That is why normally for bridge rectifiers no certfied components are requested. ---------- > ±H¥óªÌ: Randy Stephens <[email protected]> > ¦¬¥óªÌ: [email protected] > ¥D¦®: Bridge Rectifier on AC Mains > ¤é´Á: 1997¦~3¤ë26¤é AM 02:54 > > I have a question about bridge rectifiers operated directly off of the > AC mains. This will be the first component off-line for a high power > SMPS (after fuses and a switch of-course). I have been reading a little > bit about components used directly off-line, and have read that > capacitors which are connected after a rectifier in a primary circuit of > a SMPS unit need not be seperately approved (as per IEC 950 > interpretations). But, I cannot find any information regarding the > rectifiers themselves. > Is there any IEC/VDE/CE/CECC/SEMKO/etc. standard which I need to follow > for using a bridge rectifier? I have looked in both distributors and > manufacturers catalogs and cannot find any bridge rectifier which has a > safety mark. The only thing close is a couple with UL safety approval, > but UL usually doesn't go to well when it comes to CE marking. If there > isn't any, then would I be safe in using a 600 Volt Peak Reverse Voltage > (lead to lead) bridge? Or should I step up to a 800 PRV, 1000 PRV, or > even higher? > The equipment this will be used in will be tested to IEC 1010-1. I know > that I can just test the part to the tests in IEC 1010, but I would feel > more comfortable if a European Approved part was used instead of no > approval marking. > Any help would be appreciated. > > Randy Stephens > Electrical Engineer > Trek, Inc. > Medina, NY
