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Biggles · 29th Jan 2016, 4:59 pm

The smaller 100mA versions are bad for this. Different manufacturers seemed to follow different pin outs, although the middle leg is usually common. I once wasted a bit of time when building a 13.2V power supply by using diodes to "jack up" the common leg of a 7812 which was fine out of the case but then returned to 12V every time I bolted it all up. Yes, you've probably guessed, I'd forgotten to isolate the tab and it was returning to 0V via the aluminium case. I now always tend to check the exact part number (prefix/suffix) and manufacturer of the 100mA ones against an RS or Maplin catalogue to confirm the pin out as I have had too many overheat and fail on switch on by idly guessing which is the input connection.
Alan

29th Jan 2016, 4:59 pm	#4
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Save yourself a quid or so... The smaller 100mA versions are bad for this. Different manufacturers seemed to follow different pin outs, although the middle leg is usually common. I once wasted a bit of time when building a 13.2V power supply by using diodes to "jack up" the common leg of a 7812 which was fine out of the case but then returned to 12V every time I bolted it all up. Yes, you've probably guessed, I'd forgotten to isolate the tab and it was returning to 0V via the aluminium case. I now always tend to check the exact part number (prefix/suffix) and manufacturer of the 100mA ones against an RS or Maplin catalogue to confirm the pin out as I have had too many overheat and fail on switch on by idly guessing which is the input connection. Alan