faulty lm338k reg's or me ?

Thread Starter

cockatoo

Joined Dec 23, 2017
11
hi , i can't seem to get these 5A ic's to work .i am using the simple circuits off datasheets etc. i have not connected any capacitors ,but used protection diodes a couple of times ,thinking maybe spikes killing them .. most of them , [6 so far ] worked with no load , only had dmm connected . when i connect a 1.2A load [2 light bulbs ] there is nothing , no flash , clicks , pops , smoke or smells ,very disappointing .. after this ,the volt meter just jumps all over the place in the MVolt range... i am sure i have pins connected right ... with the last one , i tried with a 34Ma load [led] and it worked as its supposed to. until i tried 500Ma load,"died".. .these are branded with the national semiconductor logo , brought from 2 different sellers [ebay, yeah, slow learner ] they were marked with different "batch" #s ....surely they all could'nt be fakes, dodgy , faulty units .. heres a couple of pics ..oh, by the way , the resistor is 220R from Vout to adj and then to -neg via a1 or 2k rheostat....thanks in advance for any ideas....lm338k 002.jpg 338 connecct 006.jpg
 

ericgibbs

Joined Jan 29, 2010
18,848
hi c,
Can you mark up this LM338 image, showing the connections and the DC input voltage and Output voltage you expect.?

E
A001.gif
 

Thread Starter

cockatoo

Joined Dec 23, 2017
11
hi c,
Can you mark up this LM338 image, showing the connections and the DC input voltage and Output voltage you expect.?

E
View attachment 144825
hi ,eric , i don't know how to do that , but attached image of circuit i copy . i am only experimenting/learning atm ,but i am using 12-14V and 24-28V as input , depending on what voltage i want to get out. i use a higher value 2k pot on the 24V input . i will use one around the farm to equalize batteries up to 16Vreg.JPG i use a pot or rheostat for R2 ... thanks...dennis
 

ericgibbs

Joined Jan 29, 2010
18,848
hi Dennis,
Your circuit should be OK at 0.5A .
Are you sure you have the two pins on the LM338 correctly identified.?
If you plan running at high currents a heat sink will be required
Eric

OT: what's your farm arable or animals?

EDIT:
Looking at your photo, how are you are making a contact with the TO3 metal case.?
Where is the second resistor.?
 
Last edited:

LesJones

Joined Jan 8, 2017
4,189
If you are not using the recommended capacitors mounted close to the regulator pins it could be oscillating. Check the output with an oscilloscpe to see if it is oscillating. What is the reason for not wanting to use capacitors ?

Les.
 

Thread Starter

cockatoo

Joined Dec 23, 2017
11
the screws through the ic and heatsink connect the plastic socket output pin / tab . looking at the bottom view , the pins are offset towards the top hole with the Vin pin on the right. if you were to superimpose my photo over the top of your ic out line it would plug into my socket , if you get what i mean...if i rotate ic 180* in socket , the mounting holes wont line up with ic or heatsink. i am fairly sure my connections are right .these are rated to 5A , i think you made a typo? i just have a larger hobby farm and run a few sheep and cows ...thanks again eric. i better get some sleep ..dennis..



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