using negative linear reg for positive voltage

[mianchen]

i'm making a few (50) identical widgets that require +5v, ~50ma power supply. I only have 5 78l05, but 100+ 79l05. is there any potential problems if I use these 7905 as voltage reg? obviously I will connect the gnd pins of 7905 to the vcc of the widgets, and output pins to ground of th widgets.

I've tested it and it worked, but since i'm a noob, I'd like to ask before I design the pcb and start making the lot. thanks

[Simon]

It's possible, I can't remember the implications, probably that you loose your common ground but if this is not a problem it might well be ok.

[SeanB]

No problem just remember a 7905 requires a little more capacitance on input and output, as they can oscillate if there is not enough. Refer to data sheet for recommended values.

[Short Circuit]

Anybody to service these widgets in the future will probably hate you for saving these 10 cents.

[mariush]

I agree, not worth the price. You can get them the next day from Farnell.

You can get 50 of those for less than 9 pounds... maybe not 7805, but these would be just as good, for 50mA it doesn't matter: http://uk.farnell.com/nxp/nx1117ce50z/ldo-5-0v-1-25-sot223/dp/2057286

7805 are also cheap enough: http://uk.farnell.com/fairchild-semiconductor/ka78l05az/ic-v-reg-5-0v-78l05-to-92-3/dp/1014073