I bought a batch of five LM338T 5 amp voltage regulators from Ebay recently.
They all test as substandard, they act as a regulator but are not even able to supply as much current as an LM317T.
Photo of the faulty item.
These are my tests I carried out, the supply voltage after smoothing was just over 21 volts.
The first photo (LM338T no load.JPG) was taken with the voltage set to 13.08 volts and no load on the regulator circuit.
The second photo (LM338T 10 ohm load.JPG) was taken with a 10 ohm load, the current shows as 1.25 amps and negligible volt drop, 13.05 volts.
The third photo (LM338T 5 ohm load.JPG) shows the LM338T regulator has shut down (current limiting) and the output voltage has dropped to 7.66 volts, current shown is 1.41 amps.
The current should be about 2.5 amps when supplying a 5 ohm load at 13 volts.
The same test carried out on a LM317T showed the device could supply 1.75 amps into a 5 ohm load.
I notice that RS also seem to be selling the same items, according to the photos on their website.
So I have written to RS and suggested they may like to test theirs.
Mike
They all test as substandard, they act as a regulator but are not even able to supply as much current as an LM317T.
Photo of the faulty item.
These are my tests I carried out, the supply voltage after smoothing was just over 21 volts.
The first photo (LM338T no load.JPG) was taken with the voltage set to 13.08 volts and no load on the regulator circuit.
The second photo (LM338T 10 ohm load.JPG) was taken with a 10 ohm load, the current shows as 1.25 amps and negligible volt drop, 13.05 volts.
The third photo (LM338T 5 ohm load.JPG) shows the LM338T regulator has shut down (current limiting) and the output voltage has dropped to 7.66 volts, current shown is 1.41 amps.
The current should be about 2.5 amps when supplying a 5 ohm load at 13 volts.
The same test carried out on a LM317T showed the device could supply 1.75 amps into a 5 ohm load.
I notice that RS also seem to be selling the same items, according to the photos on their website.
So I have written to RS and suggested they may like to test theirs.
Mike
