lm 338 ic is not providing more than 1 amp current!!!!

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jigisha

Joined Dec 19, 2015
6
Hii....

I am using lm338 ic to-220 package used to provide 5v , 1.5 amp output.........i am giving power form my variable power source........nd had mounted one input electrolite cap 1000uf-25V, and and one 0.1uf ceramic cap at input , and providing 100uf - 25v cap at out. ..nd providing 220ohm resistor at ouput to adj pin terminal....and variableof 22k at adj teminal...by varying this pot i can get 5volt.........bt output current is not going more than 1amp........ plz suggest m wt should i change!!!!!! nd using proper heatsink with ic 338....................:(
 

GopherT

Joined Nov 23, 2012
8,012
Hii....

I am using lm338 ic to-220 package used to provide 5v , 1.5 amp output.........i am giving power form my variable power source......

... using proper heatsink with ic 338....................:(
i am giving 16v from my variable power source.
So, think about this, my friend.

You are asking that LM338 to take 16V down to 5 volts (11 volt drop) at more than one amp. Since it is cutting out at 1 amp, that means you are getting thermal shutdown because your "proper heat sink" cannot dissipate 11 watts of power (11 volts @ 1 amp). You actually want 1.5 amps, 16.5 watts - a good sized heat sink will be required and good bonding to the heat sink.
 

spinnaker

Joined Oct 29, 2009
7,837
Use capitals, stop pressing that "." key more than needed and post a schematic.
my supply can provide upto 20amp of current.....
Seven posts later and you are still using those obnoxious periods, no capital letters. Lots of old people here we don't handle "texting" speak well.

And you still haven't posted a schematic. How do you expect your problem to be able to be understood?
 

MikeML

Joined Oct 2, 2009
5,444
Heatsink................. Heatsink................. Heatsink................. Heatsink.................

actually, lack thereof...

(16-5)V*1.5A = 16.5W

To keep the temperature inside of the TO220 <100°C, the total thermal resistance Θja from Junction to Ambient must be (100-25) °C/16.5W = 4.54 °C/W.

Since Θjc= 1°C/W, the Θhs bust be less than ~3°C/W.

Even large finned heatsinks (Like These) require forced air cooling (fan) to get rid of that much heat.
 
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