23 May 2017

Switching Semiconductor Devices for Inverter

The semiconductor devices which are used for inverter circuit is given below. The SCR is used for high power rating inverter.

Bipolar Junction Transistor ( BJT )

  • The BJT was used as semiconductor device in the inverter circuit earlier. 
  • The BJT requires continuous base current in order to keep it on. When the base current becomes zero, the BJT turns off.

Metal Oxide Field Effect Transistor ( MOSFET )

  • The base current in the BJT controls the output voltage therefore it is called as current control device whereas the gate – source voltage control the output current in the MOSFET therefore it is called as voltage control device.
  • When the gate – source voltage exceeds the threshold voltage, the MOSFET turns on.  Similarly when the gate – source voltage below threshold voltage, the MOSFET turns off. 
  • As the MOSFET is voltage controlled device, it requires low power but it consumer high power due to high gate – source resistance. 
  • The capacity of MOSFET based inverter is in kW and less than 700 voltage.

Insulated Gate Bipolar Transistor ( IGBT )

  • The IGBT has combined characteristics of MOSFET and BJT. 
  • The input impedance of the IGBT is high. 
  • The switching and conduction losses in the BJT are very low. 
  • The IGBT is a voltage controlled device similar to MOSFET. 
  • The IGBT is used as semiconductor device when high output voltage and current requires. 

Gate Turn Off Thyristor ( GTO )

  • Once the SCR is switched on in the DC circuit, it requires commutation circuit to turn it off. 
  • The GTO is a semiconductor device which is turned on by positive gate pulse and turned off by negative gate pulse. 
  • The main disadvantage of the GTO is that it has higher voltage drop when it is in turned on condition.