At 03:43 AM 11/24/2006, Peter P. wrote: >Dwayne Reid planet.eon.net> writes: > > > I'd use that nice aluminum box as the heatsink. No need to go to a > > switchmode regulator if power consumption is not an issue. > >Maybe that won't be necessary if the heat is spread a little by >adding one or a >few series resistors before the regulator. I like to think about the whole >picture. If a human must operate the box then the box cannot be over >40 degC. So >the input to a box is limited by the size of the box eventually, before forced >cooling becomes necessary. E.g. a handheld size box cannot take more >than about >3-5W input before becoming physically too hot to handle. Larger boxes scale >accordingly. A voltage regulator that runs 40-55 degC at normal load >and ambient >is not 'too hot' and does not normally mandate a radiator imho. Couple of minor points: 1) Box already exists and is already paid for. 2) That heat has to go *somewhere*. If you couple the regulator to the enclosure, the outside of the enclosure radiates that heat much more efficiently than if either resistors inside the enclosure or a separate heatsink has to radiate heat to the inside of the enclosure. 3) If the power dissipation is such that the enclosure would get as hot as 40C or above, a linear regulator is the wrong choice. I guess what I am saying is this: putting series resistors in front of the regulator doesn't reduce the TOTAL power dissipation. All it does is move it away from the regulator. But that heat is still inside the enclosure and the enclosure is still going to heat up. Mounting the regulator directly to the enclosure is a practical method of keeping it cool at very low cost. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 22 years of Engineering Innovation (1984 - 2006) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist