LM317: LM317T/NOPB & LM317KCT

Hello,

Thank you for your question.

Have you tested with more than one part? This seems like it could be a damaged part. We recommend testing with another part and letting us know if you get different results.

Are you getting the same output voltage on both parts?

This also could be a problem with the leakage current occurring at the transistor level during operation, which is causing the reference to be higher than expected. Additionally, there could be leakage current at D2 causing the reference to be slightly higher than expected.

Best,

Hannah

Thankyou for your replay,

yes, I have tested more than one part and in my circuit I haven't used D1, D2, Cadj. i used Cin & Cout as 220uF 65V for the same resistance and Vin mentioned above & getting the REF voltage as 1.25V for LM317T/NOPB and for the same setup I'm getting 1.66V for LM317KCT.

There could still be leakage current from your input and output capacitors. 

What is the insulation resistance and the voltage rating of the capacitor you have selected? To calculate the leakage current yourself, you can use this equation:

Leakage current = Voltage Rating (V) / (Insulation Resistance)