On Thursday, 9 October 2014 14:37:26 UTC+1, M.J.Sangster wrote: > > My guess is the heat is coming from the 7805 - they tend to generate heat > with even modest current draw. I believe a simple linear voltage regulator > is around 40% efficient - the rest goes to heat. The circuit uses 2 74141 > type IC's, they draw a lot of current. If it was a problem (too much heat) > the regulator would shutdown. > > The power supply looks good, I'm guessing neither the FET or the inductor > even get warm. >
The 74141s take 25mA each - being generous, the whole circuit may take 70mA including the alarm and GPS LEDs - the CPU is an ultra-low-power one and almost everything else is driven from the 12V rail - with 12V in, 5V out that's a 7V drop in the 7805 @ 70mA which is only about 500mW of heat - a 7805 in a TO-220 case hast a theta JA of 19C/W so the case will get to maybe 10C above ambient (perhaps a bit more as its in a case), i.e. its unlikely to get very hot at all (unless its oscillating, but it does have input and output 100n ceramics). Nick -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8e40eebb-3d46-43ba-b94d-facf0439cfe9%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
