Need help in analysing this LM317 ckt

[cameo_2007]

Hi,

Please have a look at this LM317 reg. I just find a kind of configuration on the ADJ pin of the chip.A voltage reference.
Any clue on what is that helping for, as the chip also has a 1.25V reference.



The data sheet for one of the component,TL431 can be found here http://www.datasheetcatalog.org/datasheet2/3/074yxfos2h5s8aukijk5yg8id7fy.pdf

 

[alexan_e]

There is something wrong with your attachment, when I click them I get "Invalid Attachment specified. If you followed a valid link, please notify the administrator"

Alex

 

[cameo_2007]

just corrected it. thanks.

 

[FvM]

Any clue on what is that helping for, as the chip also has a 1.25V reference.

The circuit possibly intends a better load regulation than achievable with a single LM317. It's however not obvious, that the feedback loop is stable at all.

 

[ea.arun]

generally an extra feed back by using a configurable reference like TL431 is added to achieve a lower output voltage by introducing a different feedback than generally done by feeding the output directly through a voltage divider(or to cheat the eror amplifier of the LDO:wink......here the purpose should be a better load regulation.....

 

[alexan_e]

This circuit is shown in page 30 of
https://focus.ti.com/lit/ds/symlink/tl431.pdf

described as Precision 5-V, 1.5-A Regulator but your resistor values are different so your get higher output

Alex

 

[ea.arun]

cameo : i found onw with a similiar configuration.....refer page number 8 with a different linear regulator.....they have explained the function but maynot be relevent for this application but as a reference....
**broken link removed**

 

[FvM]

This circuit is shown in page 30

So we should assume for the time being that the feedback loop is stable.