Small Signal Transistors
Small signal transistors are transistors that are used primarily to amplify low-level signals but can also function well as switches.
Transistors come with a value, called the hFE values, which represent how greatly a transistor can amplify input signals. Typical hFE values for small signal transistors range from 10 to 500, with maximum collector current ratings from about 80 to 600mA. They come in NPN and PNP forms. Maximum operating frequencies range from about 1 to 300 MHz.
As a design note, small signal transistors are used primarily to amplify small signals, such as a few volts. When using larger voltage and current, using many volts or amperes of current, a power transistor should be used.