Electrical Switch &Types Of Electrical Switch:
Introduction:
Electrical switches are nothing but it is semiconductor devices. These switches are more useful because of their low cost, small size, and reliability. Generally, this type of switch is used in integrated circuits (ICs), electrical motor drives, and HVAC applications and is also widely used as the digital output of the controller.
Types:
1) Relay
2) Bipolar Transistor
3) Power Diode
4) MOSFET
5) IGBT
6) SCR
7) TRIAC
Relay: 
Relay works on the principle of electromechanical, so this switch is also known as an electromechanical switch. When current pass through a coil, it will create a magnetic field around the coil. Relay is available in a wide range of voltage and current.
Bipolar Transistor:
Bipolar junctions transistor has three terminals; base, emitter, and collector. Transistors work on three regions; cut-off, saturation, and the active region. For switching purposes, an active region is not used.
If a sufficient amount of current is available at the base terminal, the transistor enters into saturation region and current will flow through the collector-emitter path and the transistor act as an ON switch. If the base current is not sufficient, the circuit is open, and the current cannot flow through the collector-emitter and transistor enters into the cut-off region. In this region, the transistor act as an OFF switch.
Transistor is used as an amplifier in electronics applications and is also used to make a gate like AND, NOT in digital circuits, and the transistor is also used as a switching device in an integrated circuit.
Power Diode:
Power diodes have two terminals; anode and cathode. A diode is made up of p and n-type semiconductor material and makes PN-junction, which is known as a diode.
When a diode is in forwarding bias current can flow through the circuit and in reverse bias blocks current. If the anode is positive with respect to the cathode, the diode is in forwarding bias and acts as a switch ON. Similarly, if the cathode is positive with respect to the anode, the diode is in reverse bias and acts as a switch OFF.
Power diodes are used in power electronics applications like rectifiers, voltage multiplier circuits, voltage clamper circuits, etc.
MOSFET:
MOSFET-Metal Oxide Semiconductor Field Effect Transistor. MOSFET has three terminals; gate, drain, and source. MOSFET works in two basic forms; Depletion type and Enhancement type.
If gate-source voltage (VGS) is not sufficient, MOSFET works as a depletion type and the depletion mode of MOSFET is similar to the OFF switch. If gate-source voltage (VGS) is sufficient, MOSFET works as an enhancement type and the enhancement mode of MOSFET is similar to the ON switch.
The range of switching of MOSFET is tens of neon seconds to a few hundred microseconds. MOSFET is used in the linear voltage regulator, chopper and audio frequency power amplifier, etc.
IGBT:
IGBT- Insulated Gate Bipolar Transistor. IGBT is a combination of BJT and MOSFET. IGBT has a high input impedance and high switching speeds as well as low saturation voltage.
IGBT has three terminals; Gate, Emitter, and Collector. IGBT can control with the use of a gate terminal. It can be switched ON and OFF by triggering and disabling its gate terminal. IGBT can block both positive and negative voltage same as GTO.
IGBT is used in inverters, traction motor control, induction heating, and switched mode power supplies.
SCR:
Silicon Controlled Rectifier. SCR has three terminals; Gate, Anode, and Cathode.
The working of SCR is the same as a diode, but SCR starts conducting when it is in forwarding bias and a positive clock pulse at the gate is also required. In forward bias, if the clock pulse of the gate is zero, SCR is turned off by forced commutation and in reverse bias, SCR remains in the OFF state same as a diode.
SCRs are used in motor control, power regulators, and lamp dimming.
TRIAC:
TRIAC is the same as two SCRs connected inversely parallel with the gate connected. TRIAC is a bi-direction device. TRIAC has three terminals; Main terminal 1 (MT), Main terminal 2 (MT2), and gate.
MT1 and MT2 terminals are connected with the circuit which we want to control and the gate is available for triggering pulse by positive voltage or negative voltage. When the MT2 terminal is a positive voltage with respect to the MT1 terminal and gate is also positive triggered, then SCR-1 of TRIAC triggers. When the MT1 terminal is a positive voltage with respect to the MT2 terminal and gate is also positive triggered, then SCR-2 of TRIAC triggers.
TRIAC can be used for both sources AC and DC but generally, TRIAC is used in AC applications like motor control, switching in lights, etc.
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