can i use lm150 o/p(12V/3A) to 7805 to get (5v/1A)?

[anuradha bulakh]

I want 12V/2A and 5V/1A power supply.
I am thinking to do as- use one single X'mer 0-15V/3A to LM150 .To adjust LM150 as it gives 12V and next 7805 to get 5V/1A.And O/P of LM150 12V/2A.
Can I think it?

One more, while using adjustable regulator that variable resistor are reliable?
Or for final product design I should replace that var res. by required fix one?

please help me.

 

[karesz]

Hi,
Thes is possible, but not the best for energy efficiency! :-(
LM150-350 has max. ca. 2.5-2.7V droout, thes with your 3A=minimum 8-10W dissipation.
The case "K" hase a therla res. Rja=<35degre/A, self with the minimal needed 2.6V Udrop it will be eventally on the thermal limite! You have very clear to dimensionate the input voltages...
Im not a friend of switxhers, but for such powers their are better, or you have to select moderner analog (low_or extrem low_Dropout reglers.
Micrel has i.e. good types for some Ampers too...
Variabel resistors are enough reliable for most apps(multiturns are better), but evrybody has a need to rotate on a trimmer resistor if will see it; so I did never design trimmers in a commercially produced supply_if its possible!
With that aspect are fixed resistors (applyed psychology) surly more reliable .
K.