Voltage regulator question

[c d]

[mod note: thread moved from homework forum]

I have this Mouser voltage regulator

https://www.mouser.com/ProductDetail/STMicroelectronics/L7912CV/?qs=sGAEpiMZZMug9GoBKXZ75xbXFDWiKqpmvrbz5I0HaKg%3D

Wired according to datasheet https://www.mouser.com/ds/2/389/l79-974159.pdf see insert photo.

https://plus.google.com/photos/phot...0/6526650605024626690?authkey=CPTx7ezW74_OiAE

Would expect to see 12 V output. Input is 15.5 V Wired this a couple of times, get same output as input.

Before I go a lot further, am I on the right track? Your thoughts?

 

[NascentOxygen]

cd, do you have the red lead going to the negative terminal of the LiPo?

Interpreting your meter reading, is the O/P positive or negative with respect to ground?

 

[c d]

Red goes to positive of lipo and "input" terminal (middle of three wires) of voltage regulator, thanks for asking. btw, "input" is 15.5 V [positive] with respect to ground. Reading the "output" terminal with respect to ground and getting the same...

 

[Asymptotic]

Spec sheet calls for a C1 value of 2.2 uF for tantalum, but 10x or more when an electrolytic is used. Probably want to add a back diode across the output, too, but I don't think that's the problem. Negative regulators (more so than positive regulators) have a tendency to exhibit this symptom when under no load or lightly loaded (under 5 mA) conditions.

 

[Averagesupernova]

Why do you have the input positive with respect to ground on a negative voltage regulator?

 

[jim hardy]

Red goes to positive of lipo and "input" terminal (middle of three wires) of voltage regulator, thanks for asking. btw, "input" is 15.5 V [positive] with respect to ground. Reading the "output" terminal with respect to ground and getting the same...

79XX series are negative regulators. From what you say i'd guess you hooked the battery backwards. Likely it's shot now.

edit - average supernova and i crossed in the mail..

 

[CWatters]

The 7812 series are for +12V.