Silicon Controlled Rectifier (SCR) :
An SCR is a controlled rectifier made up of p-type and n-type semiconductor material belonging to the thyristor family. It consists of three terminals anode, cathode, and gate, and works similar to a diode when a pulse is applied to the gate terminal. It is a unidirectional device that can conduct current only in one direction.
Bipolar Junction Transistor (BJT) :
A BJT is also a semiconductor device with PN junctions that can amplify the signals. It is also a three-terminal device emitter, collector, and base. BJTs are mainly used in switching and amplifier circuits that increase the strength of a weak signal, whereas SCRs are used in rectifier and power control applications.
Metal Oxide Semiconductor Field Effect Transistor (MOSFET) :
MOSFETs are similar to BJTs used in switching and amplifier circuits. It is a three-layer, three/four-terminal (drain, source, and gate) unipolar device. The main difference between BJT and MOSFET is that BJT is a current-controlled device whereas the flow of current in MOSFET is controlled by voltage i.e., it is a voltage-controlled device.
Insulated Gate Bipolar Transistor (IGBT) :
An IGBT is formed by combining the characteristics of BJT and MOSFET. It combines the low ON-state losses of BJT and the very simple gate drive of MOSFET. The structure of IGBT is similar to MOSFET. It has high voltage and current handling capabilities with high-speed switching and low gate current performance.