LM317 is the most popular adjustable positive linear voltage regulator IC. Although it's an IC it looks like a transistor of TO-220 package. It has three terminals. Following is the pin diagram of the IC:

Symbol	Parameter	Value	Unit
Vout		1.25  – 37	V
Vin – Vout	difference	3  – 40	V
TJ	Operating junction temperature range	0 – 125	°C
IO(MAX)	Maximum output current	1.5	A
IL(MIN)	Minimum load current	3.5 mA typical, 12 mA maximum
PD	Power dissipation	Internally Limited	W
R?JA	Thermal resistance, Junction to ambient	80	°C/W
R?JC	Thermal resistance, Junction to case	5	°C/W