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

Discussion in 'General Electronics Chat' started by jigisha, Dec 19, 2015.

  1. jigisha

    Thread Starter New Member

    Dec 19, 2015
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    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....................:(
     
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Use capitals, stop pressing that "." key more than needed and post a schematic.
     
    spinnaker likes this.
  3. ISB123

    Well-Known Member

    May 21, 2014
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    Current is determined by the load.
     
  4. Veracohr

    Well-Known Member

    Jan 3, 2011
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    What is your input voltage?
     
  5. jigisha

    Thread Starter New Member

    Dec 19, 2015
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    i am giving 16v from my variable power source.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What is the rated current your power supply can provide?
     
  7. jigisha

    Thread Starter New Member

    Dec 19, 2015
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    my supply can provide upto 20amp of current.....
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Change the 220 ohm to 120 ohm, and use a 470 ohms preset pot.

    Post pictures
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    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.
     
    absf likes this.
  10. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    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?
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    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.
     
    Last edited: Dec 19, 2015
  12. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    LOL

    I see you are posting in the SP's native language. Very kind of you.
     
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