Electronic switch

In electronics, an electronic switch is a switch controlled by an active electronic component or device. Without using moving parts, they are called solid state switches, which distinguishes them from mechanical switches. Electronic switches are considered binary devices because they dramatically change the conductivity of a path in electrical circuit between two extremes when switching between their two states of on and off. Many people use metonymy to call a variety of devices that conceptually connect or disconnect signals and communication paths between electrical devices as "switches", analogous to the way mechanical switches connect and disconnect paths for electrons to flow between two conductors. The traditional relay is an electromechanical switch that uses an electromagnet controlled by a current to operate a mechanical switching mechanism. Other operating principles are also used (for instance, solid-state relays invented in 1971 control power circuits with no moving parts, instead using a semiconductor device to perform switching—often a silicon-controlled rectifier or triac). Early telephone systems used an electromagnetically operated Strowger switch to connect telephone callers; later telephone exchanges contain one or more electromechanical crossbar switches. Thus the term 'switched' is applied to telecommunications networks, and signifies a network that is circuit switched, providing dedicated circuits for communication between end nodes, such as the public switched telephone network. The term switch has since spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between logic states or connect different signal lines. The common feature of all these usages is they refer to devices that control a binary state of either on or off, closed or open, connected or not connected, conducting or not conducting, low impedance or high impedance. The diode can be treated as switch that conducts significantly only when forward biased and is otherwise effectively disconnected (high impedance).