Just for sharing
Because it is interesting and also because somebody ask me, i continue
to make some regulators noise measurements.
I have test the noise performance of :
LM2940CT-12 LDO regulator (NationalSemi)
The measurements methodology is same of my previous post.
(Vout=15V unless otherwise specified Rload=100 Ohms)
Results are (10Hz-100kHz bandwidth) :
LM317 -- 55ÂµVrms
LM2940CT12 -- 190ÂµVrms (Vout=12V)
LT1085 -- 40ÂµVms
These results show that the LM2940 sÃ©rie (Low dropout regulator) are the worst !
Finally for low budget, the best choice seem to be the LM317 with large decoupling capacitor in ref input.