This is one of the voltage regulator types.
Part Number : 7812
Function : 12V, Voltage Regulator
Package : TO-220 Type.
Manufactures : National Semiconductor
See the preview image and the PDF file for more information.
The 7812, LM78XX series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. One of these is local on card regulation, eliminating the distribution problems associated with single point regulation. The voltages available allow these regulators to be used in logic systems, instrumentation, HiFi, and other solid state electronic equipment. Although designed primarily as fixed voltage regulators these devices can be used with external components to obtain adjustable voltages and currents. […]
1. Output current in excess of 1A
2. Internal thermal overload protection
3. No external components required
4. Output transistor safe area protection
5. Internal short circuit current limit
6. Available in the aluminum TO-3 package