Types of Electrical Switch.
Electrical switches are nothing but it is a semiconductor device.
These switches are more useful because of their low cost, small size and reliability.
Generally, this type of switches is used in integrated circuits (ICs), electrical motor
drives, HVAC application and also widely used as digital output of controller.
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 electromechanical switch.
When current pass through a coil, it will create a magnetic field around the coil.
Relay are available in wide range of voltage and current.
Bipolar Transistor: Bipolar junctions transistor has three terminals;
base, emitter and collector.
Transistors are work on three regions; cut-off, saturation and active region.
For switching purpose, active region is not used.
If sufficient amount of current is available at base terminal, transistor enter in to saturation
region and current will flow through collector-emitter path and transistor act as an ON switch.
If base current is not sufficient, circuit is open and current cannot flow through the
collector-emitter and transistor enters in to cut-off region.
In this region, transistor act as OFF switch.
Transistor are used as an amplifier in electronics application and it also used to make a gate
like AND, NOT in digital circuits and transistor is also used as a switching device in integrated
circuit.
Power Diode: Power diode have two terminals; anode and
cathode.
Diode is made up of p and n type semiconductor material and make PN-junction, which is known
as diode.
When diode is in forward bias current can flow through the circuit and in reverse bias
blocks current.
If anode is positive with respect to cathode, diode is in forward bias and act as a switch
ON.
Similarly, if cathode is positive with respect to anode, diode is in reverse bias and act
as a switch OFF.
Power diodes are used in power electronics application like, rectifier, voltage multiplier
circuit and voltage clamper circuit, etc.
MOSFET: MOSFET-Metal Oxide Semiconductor Field Effect
Transistor.
MOSFET has three terminals; gate, drain and source.
MOSFET is works on two basic forms; Depletion type and Enhancement type.
If gate-source voltage (VGS) is not sufficient, MOSFET works as depletion type and 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 MOSFTE is similar to ON switch.
Range of switching of MOSFET is tens of neon seconds to a few hundred microseconds.
MOSFET used in 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 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 inverter, traction motor control, induction heating and switched mode power
supplies.
SCR: Silicon Controlled Rectifier.
SCR has three terminals; Gate, Anode and Cathode.
Working of SCR is same as diode, but SCR start conduction when it is in forward bias and
positive clock pulse at the gate is also required.
In forward bias, if clock pulse of gate is zero, SCR turned off by forced commutation
and in reverse bias SCR is remains in OFF state same as diode.
SCRs are used in motor control, power regulators and lamp dimming.
TRIAC: TRIAC is same as two SCRs connected in inversely
parallel with gate connected.
TRIAC is bi-direction device.
TRIAC has three terminals; 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 is at positive voltage with respect to MT1 terminal and gate is also positive
triggered, then SCR-1 of TRIAC triggers.
When MT1 terminal is at positive voltage with respect to MT2 terminal and gate is also positive
triggered, then SCR-2 of TRIAC triggers.
TRIAC can used for both sources AC and DC but generally, TRIAC is used in AC application
like motor control, switching in lights etc.
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