How this 317 PS works?

[pftrvlr]

I am building a DAC kit, and this LM317 circuit is new to me. What are the pros? I guess it can provide more output current? But we are talking about low current DAC.

Also the open circuit output is 5.90v instead of 5.0v.

 

[TheMG]

Maybe this is designed for better ripple rejection and regulation.

This design only provides higher current if the regulator package or heat sinking is insufficient for a single regulator to dissipate the full voltage drop.

 

[leadbelly]

The technique is called a tracking preregulator. It has nothing to do with extra current. Read about it in the datasheet:

http://cache.national.com/ds/LM/LM117.pdf