A while ago I bought a pair of these 12V 3W UV-C light bulbs to use to build an EPROM eraser:
-
There are more details in this listing:
-
SHORT STORY: ^^^^^^^^^^^^ One blew on 15VDC (did nothing on a lower voltage), the other blew on 12VAC (did nothing on 9VAC). How are you meant to power them?
LONG STORY: ^^^^^^^^^^^ In my ignorance, I assumed these would work like normal incandecent or halogen bulbs, so I mounted a bulb in a tin with a hole in one end covered in layers of hot glue to act as a hopefully eye-safe viewing window (I only view it indirectly as an added precaution). Then, unsure of whether the voltage specification was AC or DC (and frankly, assuming that it didn't matter), I slowly raised the DC voltage from my bench supply.
There was no light, and until I reached about 15VDC only a few tens of milliamps current. Then the current suddenly surged to amps (still no light) and even though I made a hasty attempt to cut the power, I found that one of the two vertically stretched filaments had blown.
DC clearly wasn't working out, so I tried AC, starting low with a 9VAC plugpack and the backup globe (multimeter in series to measure current). This gave me the same "no light, a few tens of milliamps" condition, so I moved up to a 12VAC plugpack (I don't have a variac unfortunately).
Now I finally got light and decent current (although around .6A of it, so more than 3 Watts). As it ran, the blue light got darker and apparantly less visible, seemingly as the globe warmed up. The current also slowly increased to .88A after two minutes, then dropped back to .81mA by 2m 30s with the light still looking good. But current rose again to .92A, then it seemed to go into thermal runaway at 3min 20 and rapidly spiked to over 1.2A before I could cut the power. Inspection revealed that one of the filaments had now blown in this bulb as well.
I tested one of the half blown bulbs on another 12VAC plugpack, this time only rated at 500mA instead of the 1.7A of the one I used before. I could fill a page with the weird behavior that it showed in regards to both light an current consumption, but the blue light never became very dark, and the data on two EPROMs I put in was unaffected (checksums matched) after forty minutes. Current varied between .25A and .4A during operation.
So I clearly don't know the right way to drive these bulbs. Does someone know how they're meant to be powered, or should I just give up and go with one of the flourescent UV bulbs (which are unfortunately awkwardly long for the small device I had in mind).
P.S. I know about the $20 EPROM erasers sold from China, but I have a strict policy of not buying mains powered devices direct from China. Especially devices that I'll be tempted to leave unattended during use.