What do the letters on a voltage regulator mean (e.g., 7805 vs 78L05 vs 78M05)?

Short Answer: The letters indicate package type and current rating — not voltage or functionality.

Detailed: The "78xx" series of positive voltage regulators comes in multiple packages. The numbers after "78" are the voltage (05 = 5V, 12 = 12V, etc.).

Prefix	Package	Current rating	Typical use
78xx	TO-220 (through-hole, metal tab)	1A (1.5A peak)	General purpose, can use heatsink
78Mxx	TO-252 (DPAK, SMD)	500mA	Surface-mount, moderate current
78Lxx	TO-92 (small plastic, like a transistor)	100mA	Low current, small devices
78Txx	TO-220 (higher grade)	3A	High current with heatsink
78Sxx	TO-220	2A	Medium-high current

Common 5V Regulators Compared

Part number	Package	Max current	Heatsink needed?	Cost
78L05	TO-92	100mA	No	$0.30
78M05	TO-252	500mA	Usually no	$0.60
7805	TO-220	1A	Above 300mA	$0.50
78T05	TO-220	3A	Yes, large	$2.00
LM2596 (switching)	Module	3A	No	$3.00

Voltage Suffixes

The last two digits (or three) are the voltage:

Suffix	Voltage	Suffix	Voltage
05	5V	12	12V
06	6V	15	15V
08	8V	18	18V
09	9V	24	24V

Example: 78L12 = 12V regulator in TO-92 package, 100mA max.