LM317: Dropout operatin of LM317

Hi Yokota,

I believe that the condition you are asking about is if Vin is less than the set output voltage for LM317 (Vout_nom).  If this is incorrect, please let me know.

In order to ensure a regulated output voltage, Vin should be equal to Vout_nom plus 3 V.  If Vin is less than Vout_nom plus 3 V, the output may drop out of regulation in which case it would track Vin as you described.

Very Respectfully,

Ryan