There are so many switches in your computer. It is not a hand-push switch that we commonly use. It is a switch operated by electrical signals. The computer counts numbers as ‘1’ and ‘0’ depending on the voltage level. High voltage is ‘1’, low voltage is ‘0’. Computers do binary calculations by default. When the computer adds or subtracts numbers, the electrical signals of ‘1’ and ‘0’ act as a switch in the ‘logic circuit’. This switch is a transistor.

The transistor behaves like a switch closes (connects) when a voltage above a certain voltage (about 0.6 to 0.7 V) is applied.

The structure of the transistor.

Most transistors have three terminals. These are called base(B), collector(C), and emitter(E).

  • base(B): This is a terminal that applies a weak electrical signal to operate the transistor.
  • collector(C): The collector(C) is normally blocked. If a weak electrical signal enters the base(B) terminal, a large current flows through the collector(C).
  • emitter(E): This is the terminal to which the currents from base(B) and collector(C) are combined.

A typical switch is lighted by pressing with a finger. The transistor is turned on when applying a voltage of about 0.6 ~ 0.7V or more to the base(B) terminal.