Transistor

A transistor is an electronic semiconductor device, which is able to control and amplify electric currents and voltages. It is therefore referred to as an "active" component.

By the term "transistor" one generally thinks mostly of bipolar transistors. Other transistors are identified by an addition to the term (for example: field effect transistor).

Basically there are two types of bipolar transistors, the NPN- and the PNP transistor. This term is derived from the internal structure. Transistors have three terminals:

• Cathode,
• Emitter and
• Base.

Various transistors. (Enlarge)

Circuit symbol NPN transistor.

Circuit symbol PNP transistor.

The terminals are usually not marked on the component. For this you need the data sheets.

• BC 516
• BC 517
• BC 547
• BC 557