Yes, that's the temperature of the silicon itself, and unless you're really pushing the chip hard you can pretend that the case temperature and Tj are the same. For simple applications you can run it slightly out of range, but if you're really interested in making certain it is within its operating range, put a 2W resistor nearby and insulate the resistor and regulator. Calculate the resistor to run of the unregulated voltage with 1/4W heat output and you should be fine. Also kee in mind that while the ice is at a nice cool -10C, it is very unlikely that the air high off the ice is at that same temperature - though it can get down there - especially when the rink (and therefore your device) is in use. Consider mounting the power supply outside the rink. Alternately, get the LM317A which has a much larger temperature range and then don't worry about it. -Adam On 12/21/07, Rikard Bosnjakovic wrote: > I'm having a couple of LM317:s which I'm about to use in a hockey > arena (with ambient temperature around -10 degrees Celcius). In the > datasheet - maximum ratings section - for the 317, I find "T_op > Operating junction temperature: 0-125". > > I'm a bit confused by "junction" in this statement. Does this mean > that an ambient temperature of -10 will make the LM317 unable to work, > or does it mean that it will be fine as long as the junction is no > colder than 0 degrees? > > > -- > - Rikard - http://bos.hack.org/cv/ > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist