hb129 Posted July 8, 2009 Report Share Posted July 8, 2009 been trawling the internet trying to find a replacement to using a c64 psu to power a single core, dual 6581r4 midibox and i came across thishttp://www.circuitstoday.com/12v-5v-combo-power-supplyi'm not an expert but wouldn't the 7805 get really, really hot? Would a regular heatsink plus some ventilation be enough to combat this problem? can anyone see any other problems with this circuit? Quote Link to comment Share on other sites More sharing options...
nILS Posted July 8, 2009 Report Share Posted July 8, 2009 Depending on the load - yes. Seeing how much current you will have with an LCD and some blinky LEDs - this will cause some serious heat. Burning 7V @ 200-600mA... Quote Link to comment Share on other sites More sharing options...
hb129 Posted July 8, 2009 Author Report Share Posted July 8, 2009 Can I infer from this that the approximate current draw for a minimal stereo setup (with LCD and LEDs) is 200-600mA? It'd mean the 7805 would reach over 250C without a heatsink, more than twice its stated temparture tolerance!Would heatsinking something like this be straightforward and can anyone recommend a suitable heatsink? I've never heatsinked anything before, i'd be a bit concerned it would affect the function of the rest of the circuit somehow. Quote Link to comment Share on other sites More sharing options...
hb129 Posted July 8, 2009 Author Report Share Posted July 8, 2009 actually nils, i'm thinking of using your simple psu design but with a 7812 (with a decent heatsink, 4.2W is dissipated) instead of a 7809 and maybe a high power rated resistor before the 7805 to share the dissipation. I'm hoping this'll work out cos i really don't want to use a c64 psu.If anyone's got any recommendations/warnings for a heatsink and resistor combo, i'm all ears. Quote Link to comment Share on other sites More sharing options...
lylehaze Posted July 8, 2009 Report Share Posted July 8, 2009 78xx series regulators (the positive ones) have the tab at ground already. So if you have a metal case, you have a great heatsink already there. Just use a bit of thermal grease to help conduct the heat.DO NOT do this with 79 series (negative) regulators unless you get insulating hardware, as these tabs are NOT grounded.Have Fun,LyleHazeP.S. the board in the middle has the regulators. If you look close, you'll see 2 of them are bottom-mounted and screwed to the case (paint scraped way for better heat conduction) Quote Link to comment Share on other sites More sharing options...
hb129 Posted July 8, 2009 Author Report Share Posted July 8, 2009 i haven't got the enclosure sorted yet, but that sounds like a good idea. Quote Link to comment Share on other sites More sharing options...
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