On 12/28/05, Howard Winter wrote: > > On Tue, 27 Dec 2005 21:05:31 -0500, Kenneth Lumia wrote: > > > I'm in the process of designing a PIC project that > > uses a switching regulator to convert 12Vdc from > > a "wall wart" supply to 5V. I'd like to leave out any > > fusing if possible. The wall wart is rated as a > > Class 2 device, which I believe also means that > > it is "inherently current limiting". > > I don't know if "Class 2" varies with geography, but over this side > of the pond it means it's double insulated, so doesn't need to be > Earthed. It says nothing about overcurrent protection. Actually I believe what Howard means by "Class 2" is actually called by " Class II" and is denoted by a double-walled square symbol. It means double insulation (with one fault, the device still has basic insulation) and has quite some other requirements depending on the product standard. What the OP mentioned by UL Class 2 power supply may well be totally different. It may simply means the output of the supply is below 60Vdc & 8A according to Google search result . /* Quoted from http://www.elpac.com/resources/faq.html */ 3. Q: Class 2 - what is this? A: "Class 2" is a UL definition for an output which is below 60Vdc (42.4Vpk) & 8A. Virtually all Elpac power supplies are class 2, however they are not tested and certified to class 2, and this is rarely needed by customers. 4. Q: Class II - what is this? A: " Class II" is a European definition for a 2 pin input WITHOUT Ground present, and as such the design has to be with Reinforced Insulation since it cannot rely on Ground for safety. Few Elpac products are Class II. Examples which are include WM1005 and W4012. /* End of quotation */ There are other Class II with different meanings in UL standards and other standards. Regards, Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist