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Temp compensation for linear regulators

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smartsarath2003

smartsarath2003

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Hello,
I built a small LM338 regulator Ckt. The problem I am facing is the output voltage going down slowly when i leave the load ON. Is this happening because of temp. I connected a load of 220R at 24V output, so it not too much current actually. Does anyone have anyidea why is this happening and how can we prevent this :?:
I checked the LM338 datasheet and its given that the Vref , Iadj goes up by temp. From this can I conclude that the variation in Iadj is more than variation in Vref and thats why the regulator is pulling its output down to maintain 1.25V. Looks little bit confusing :roll:
Any Help Please.........................
Thanks
 

These voltage regulators, including LM338, are pretty good as far as temperature stability is concerned.
Try to use full configuration, with protective diodes and 10µF tantalum capacitor connected between ADJ pin and 0V .. (as per Fig3/page6: **broken link removed** )
 
Hai,
I used 10uf electrolytic cap between ADJ and GND and its made bit better So I tried with 1A load. At that load, still the 3rd digit in my meter going down slowly and after few minutes, The regulator enters thermal shutdown. I used a 10x5x0.2cm heat sink and confused a bit to seee the problem again. Is it just with the heat sink or anything else that i need to modify
Thanks
 

As you know 338 is a linear regulator so it will convert equivalent of (Vin-Vout) * I into heat.
One solution is to lower the input voltage to ≥Vout+3V ..
Other solution is to increase the size of the heatsink .. or use one of those computer heatsinks with a small fan .. in some cases natural convection is not enough to cool things down ..
 

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