voltage regulation doubts

[chinnacreative88]

if my input is 4-5v can i get regulated output of 13.8v only by using lm317 regulator for battery charging .........If not for 13.8v output regulated voltage what should be the range of input voltage.

 

[Jack// ani]

Yes, you can get 13.8V output.

But for adjustable voltage regulator like LM317 there is no way you can feed in 4-5V and expect 13.8V at output.

Minimum input voltage to ensure 13.8V output has to be 13.8 + 1.7(Voltage drop across LM317) = 15.5V

Hope this helps

 

[karesz]

Hi,
the min 15.5V is very optimistic calculated, mostly need an LM317 >+2-2.5V, but thes is really detail...
In ythes case you need a switched regulator_a "step-up" typ.
You can go to w"w.national.com, select power>> "webench" & you have a good possibility to select/design with SW he optimal "Simple Switch Family" with minimal components count + BOM to end...
K.