LDO equivalent of LM338 and can that be used as CCS ?

[khankll]

hi
what are the LDO versions of LM338 (5 Amp) , LM 317
and does they work exactrly like their non ldo counter[parts .. except for the low droput..
and can they be used as CC souses like their non ldo couterparts are used ?

thanks

 

[khankll]

road is bumpy..

 

[(*steve*)]

what are the LDO versions of LM338 (5 Amp)

Not sure. I'd just search digikey and see what I found.

, LM 317

Again, I'd search digikey.

HOWEVER, LDO regulators typically use a PNP transistor as a pass element and the current out of the ground pin (of a 3 terminal design) is going to be large and dependant on the output current. This makes an adjustable 3 terminal LDO regulator pretty tricky.

Now, you *could* use a P channel mosfet as a pass element, however chip fabrication is an issue, as well as the additional stability issues generated by the capacitive nature of the gate.

and does they work exactrly like their non ldo counter[parts .. except for the low droput..

At some level of abstraction the answer is yes. However if one looks at their stability and frequency response you will find that LDO regulators differ considerably.

and can they be used as CC souses like their non ldo couterparts are used ?

Probably, but you're going to still have the issue of dropping the regulator voltage across a sense resistor so it makes sense to design something that doesn't have this.

LDO regulators almost always require output capacitors (sometimes quite tightly specified) to ensure stability and this may be a problem in a constant current application.

 

[khankll]

a bump // any one ? who can tell me any ldo which can repkace normal regulators ..

 

[(*steve*)]

Let me put it more bluntly.

Adjustable regulators rely on the current through the ground connection being both small and relatively constant (i.e. not determined by the load characteristics)

Low drop-out regulators employing a PNP pass element typically have high ground currents that are proportional to output current.

The two are incompatible (for three terminal regulators).

There are LDO adjustable regulators and they are used in a way that is very similar to three terminal regulators, but they have more than three terminals. The major differnce is that the ground pin is seperate from the adj pin