About LT1931 power output NG

The input capacitor, C105, seems too light in value. Increase the value to at least 2.2uF, then, try again.

Good luck!

DV

I change input capacitor... but can't maintain voltage... The parts purchased in the past operate normally in this circuit. thank for your answer...

The schematic you posted appears normal, besides the value of the C105 capacitor. I would make sure the new parts you have are what they claim to be. 

For further support you would need to provide further details, such as scope waveforms, pin voltages, etc..

Previously purchased parts also operate normally on the current board. 

 no1 :  VIN     no2 : SHDN  no3 : NFB    no4 : OUTPUT

this wareform is a photo of a person replacing only parts in the same circuit with LT1931A. 

It was the capacity probleam of inductor. The capacity value of the ring coil was 330 uh. 
Thanks for your support.... 

Thanks for the feedback!

DV

Thanks for the feedback!

DV