I am trying make a variable voltage supply using part of this circuit:
Instead of a transformer and a rectifier, I am using a solar panel, which gives 37 V (open circuit) and about 30 V with a load. I also skipped the capacitors. I used a heat sink on the LM338 (not very big but not very small, either.)
It all works fine and I can regulate the voltage.
The problem is, it gets VERY hot.
I used a load of 0.5 ampere (an LED 12 V lamp,) and regulated voltage to about 12 V. The temperature was 70°C.
Have I missed something? The LM338 is said to be able to give 5 amperes from 1.2 V to 30 V.