[sdiy] 7915 regulators

[Seb Francis]

Hi,

Slightly OT .. does anyone have the experience that 7915 regulators are very poor under low loads?  I've just built a simple bench power supply (I wanted it to be kind of a worst-case PSU, hence using cheap fixed voltage regulators).  The 7815 & 7805 give near enough perfect voltage with only the load of a DVM.  But with -30V in, the 7915 gives out -22V with no load, and -17V with a 10K load.  My friendly local electonics shop was kind enough to test their entire stock of 6 to try and find a good one, but they were all the same, giving out <-20V with -30V in and no load.

Should I put some kind of load across the output?  I've seen a few 78/9XX-based PSU circuits where a single indicator LED is across the -ve rail output - I always thought it was just a arbitrary choice to place the LED across this rail.

BTW, the 7915 in question (and the 78XXs) are all manufactured by ST, although they all come from different locations (Morocco, China, Malaysia!)

Perhaps I should try and get some NS or ON versions of the 7915?

Seb