Types of switches - Electrical switch

In previous article we discussed about mechanical switch:

https://articleelectrical.blogspot.in/2017/12/types-of-switches.html

In this article we will discuss about different types of electrical switch:
Electrical Switches:

The electrical switches is a semiconductor device. These switches are useful compare to mechanical switches because of their low cost, small size and reliability. In this switch, semiconductor materials is used, i.e silicon (Si), germanium (Ge). The electrical switch is used in integrated circuits (ICs), automation, electrical motor drives, HVAC application and also widely used as digital output (DI) of controller. 

               1) Relay

               2) Bipolar transistor

               3) Power diode

               4) MOSFET

               5) IGBT

               6) SCR

               7) TRIAC

               8) DIAC

               9) GTO

1) Relay: The relay is works on the principle of electromechanical, and because of this reason relay is also known as electromechanical switch. When current pass through a coil of relay, magnetic field is induced around the coil. The amount of magnetic field depends on the amount of current passes through the coil. Arrangement of the contacts is done such a way that, if current is increased with curtain limit contacts are energised and change its position. Sometimes, relay uses bi-metallic strip to sense the temperature for safety purpose. Relay are available in wide range of voltage and current. The relay plays an important role in protection against fault in power system network. In industries also, relays are used as a protecting device.

2) Bipolar Transistor: The bipolar transistor has three terminals or lags which is known as base, emitter and collector. The transistor is works on three regions; cut-off region, saturation region and active region. Symbol of the transistor is as shown in below figure. For the switching purpose, active region of the transistor is not used. The transistor enter into saturation region if sufficient amount of current is available at the base terminal. In this region, the current will flow through collector-emitter path and transistor act as a ON switch. If the base current is not sufficient, the circuit will remains open and current cannot flow through the collector-emitter and transistor enters in to cut-off region. The transistor act as OFF switch in cut-off region. The transistors are used as an amplifier in electronics application and it also used to make a gate like AND, OR, NOT in digital circuits and the transistor is also used as a switching device in integrated circuit (ICs). The transistors are not useful in high power application because it has more resistive loss compared to MOSFET.

3) Power diode: The power diode have two terminals which is known as an anode and cathode. The diode is made up of p (positive) and n (nagative) type of semiconductor material and make a pn-junction, which is known as diode. Symbol of power diode is as shown in below figure. When the diode is in forward bias current can flow through the circuit (switch is ON) and in reverse bias blocks current (switch is OFF). If anode voltage is positive with respect to cathode voltage, the diode is in forward bias and act as a ON switch. If he cathode voltage is positive with respect to anode voltage, the diode is in reverse bias and act as a OFF switch. The power diodes are used in power electronics application like, rectifier, voltage multiplier circuit and voltage clamper circuit, etc.

4) MOSFET: MOSFET is stands for Metal Oxide Semiconductor Field Effect Transistor. MOSFET has three lags which is known as gate, drain and source. MOSFET is works on two basic forms; Depletion type and Enhancement type. If gate-source voltage (VGS) is not sufficient, n this condition the MOSFET works in the depletion type. The depletion mode of MOSFET is similar to OFF switch. If gate-source voltage (VGS) is sufficient, MOSFET works as enhancement type and enhancement mode of MOSFET is similar to switch ON. 

5) IGBT: IGBT is stands for Insulated Gate Bipolar Transistor. The IGBT is a combination of BJT and MOSFET. IGBT has a low saturation voltage (characteristic of BJT) as well as  high input impedance and high switching speeds (characteristic of MOSFET) . IGBT has three terminals; Gate, Emitter and Collector. IGBT can control with the use of gate terminal. It can be switched ON and OFF by triggering and disabling its gate terminal. IGBT can block both +Ve and -Ve voltage same as GTO. IGBT is used in the inverter, traction motor control, induction heating and switched mode power supplies.

6) SCR: SCR stands for Silicon Controlled Rectifier. SCR has three terminals; Gate, Anode and Cathode. Working of SCR is same as power diode, The difference is only that SCR start conduction when it is in forward bias (cathode is -ve and anode is +ve) and positive clock pulse at the gate is also required. If clock pulse of gate is zero, SCR turned off by forced commutation in forward bias and in reverse bias SCR is remains in OFF state same as diode. SCRs are used in motor control, power regulators and lamp dimming.

7) TRIAC: TRIAC is same as two SCRs connected in inversely parallel with gate connected. TRIAC is bi-direction device. TRIAC has three lags; Main terminal 1 (MT), Main terminal 2 (MT2) and gate. MT1 and MT2 terminals are connected with circuit which we want to control and gate is available for triggering pulse by positive voltage or negative voltage. When MT2 terminal of TRIAC is at +ve voltage with respect to MT1 terminal and the gate is also +ve triggered, then SCR-1 of TRIAC triggers. Similarly, when MT1 terminal is at positive voltage with respect to MT2 terminal and gate is also +ve triggered, then SCR-2 of TRIAC triggers.

8) DIAC: DIAC is stands for Diode AC switch. The DIAC has two lags. DIAC can operate in both direction so, DIAC is bidirectional switch. The symbol of DIAC is as shown in below figure. DIAC works on two regions; forward blocking or reverse blocking region and avalanche breakover region. When applied voltage is less than breakover voltage DIAC works in forward blocking or reverse blocking region. In this region DIAC act as OFF switch. Avalanche breakdown occurs when applied voltage is greater than the break-over voltage and DIAC act as ON switch. DIAC cannot switch sharply for low voltage and low current application as compared to TRIAC and SCR. DIAC used in light dimming, control of universal motor and heat control circuit.

9) GTO: GTO is stands for Gate Turn-off Thyristor. The GTO has three lags which is known as Gate, Anode and Cathode. As name suggest, this device can turn OFF through gate terminal. In symbol of GTO consists of two arrows on the gate terminal, which shows the bidirectional flow of current through the gate terminal. By applying a small positive gate current GTO can turn ON and turn OFF by negative pulse from the gate terminal. GTO used in inverters, AC & DC Drives, induction heater and SVC (static VAR compensation). GTO cannot use for turning inductive loads off, without the help of the snubber circuit.