Hello,

I built yesterday a new power supply based on a new LM338T. I used the attached schematic, downloaded from circuitstoday.
I found that when I powered a 40W/24V light bulb from the power supply, the output voltage of the LM338T decreased from 24V to about 20-21V. The current absorbed by the load was 1.5A.
I checked with a brand new LM338T, and the result was the same.
I took an old LM317T and I checked again, with the same power supply and the same load. This time, the output voltage decreased from 24V to about 23.7V.
The brand new LM338T was bought a few days ago from a well known vendor and it says that is made by TI.
Both LM338T and LM317T were dual gauge.

Both LM317T and LM338T were heatsinked on a 12x8x2cm aluminum heatsink.

Am I missing something ? I thought if I use LM338 the output current can be higher ...

 

Your circuit looks OK.
Have you fitted all the capacitors shown on the schematic?

 

Yes, all the capacitors were been installed on the PCB.
I also installed an 100nF more capacitor, on the output of the power supply.

 

Hello,

What is the input voltage when the 338 is loaded?

Bertus

 

The input voltage, when LM338 is loaded is 30.3Vdc.

 

The brand new LM338T was bought a few days ago from a well known vendor

Sounds like you have bought some knockoffs
I bought some LM338's from Amazon one time to use as a current limiter and they would not pass more then a couple of amps. Threw those away and went back to my default supplier which is usually Digikey.
How much did they cost?
SG

 

Sounds like you have bought some knockoffs
How much did they cost?
SG

The brand new 338 was 1.75 euro, and the old 338 was about 2.11 euro.

 

What vendor?
I see that Mouser has the part for 2.10 US and Digikey for 2.94 US.
SG