ON OFF Switching

A switching device is any mechanical, electrical, magnetic, pneumatic or hydraulic device designed to open or close an electrical circuit (permit or interrupt the flow of electrons in a circuit).

Switches are essentially binary devices: they are either completely on ("closed") or completely off ("open").

For power applications, when closed, switches are required to carry a certain amount of continuous current without overheating, and in the open position they must provide enough insulation to isolate the circuit electrically.
Device capabilities are represented by some general parameters like power (max current, max voltage) and max speed (switching frequency) and also control flow: unidirectional or bi-directional.
The power capability propriety can be enhanced using parallel pairing or Darlington pairing.

Switch examples:

• Electromagnetic Relay 
• BJT - Bipolar junction transistor
• MOSFET - Metal–oxide–semiconductor Field-effect transistor
• TRIAC - Triode for Alternating Current 
• SCR - Thyristor, Silicon-controlled rectifier
• Solid State Relays
• UJT - Unijunction transistor
• GTO - Gate Turn-Off thyristor
• MCT - Metal–oxide–semiconductor Controlled Thyristor
• JFET - Junction gate Field-effect transistor 
• IGBT - insulated-gate bipolar transistor
• H bridge (Full-H or Half-H) (solid-state or mechanical)