Types of Power Electronics Circuits

Power electronics circuits (also known as converters) can be classified into four types:

1a) Diode Rectifiers

  • Also known as uncontrolled rectifiers.
  • Converts ac input voltage (single phase or three phase) into fixed dc voltage.
  • Application: Electric Traction, Battery Charging, Electroplating, Electrochemical processing, Power supplies, Welding, and Uninterruptible power supplies (UPS) system.

1b) AC to DC Converters

  • Also known as phase controlled rectifiers.
  • Converts constant ac voltage (single phase or three phase) into variable dc output voltage
  • Use line voltage for their commutation, hence called as line commutated or naturally commutated converter. 
  • Applications: DC drives, Metallurgical and chemical industries, and Excitation systems for synchronous machines (SM)

2) DC to DC Converters

  • Also known as DC Choppers.
  • Converts fixed dc input voltage into a controllable dc output voltage
  • Requires forced or load commutation to turn off the thyristors. 
  • For lower power circuits, Thyristor are replaced by power transistor. 
  • Classified according to the type of commutation and also the direction of power flow.
  • Applications: DC drives, Subway cars, Trolley trucks, and Battery driven vehicle.

3) DC to AC Converters

  • Also known as inverters.
  • Converts fixed dc input voltage into a variable ac output voltage
  • Output may be variable voltage and variable frequency. 
  • Use line, load or forced commutation for turning off the Thyristor. 
  • At present, conventional Thyristor are also being replaced by GTOs in high power applications and by power transistors in low power applications. 
  • Applications: Induction motor drives, Synchronous motor drives, UPS, HVDC transmission, and Induction heating.

4) AC to AC Converters

  • Converts fixed ac input voltage into variable ac output voltage
  • It is of two Types:

4a) AC Voltage Controllers

  • Also known as AC Voltage regulators.
  • Converts fixed ac input voltage directly into a variable ac output voltage at the same frequency. 
  • Employ two Thyristor antiparallel or a TRIAC and turn off of both the devices is obtained by line commutation.
  • Output voltage is controlled by varying the firing angle delay. 
  • Applications: Lighting control, Speed control of fans, and Pumps.

4b) Cycloconverter

  • Converts input power at one frequency to output power at different frequency through one stage conversion. 
  • Line commutation is more common, through forced and load commutation may be employed. 
  • Applications: Slow speed large ac drives like Rotary Kiln.


  • The power semiconductor devices can operate as static switches or contactors also.


  • M. H. Rashid, “Power Electronics: Circuits, Devices and Applications,” Prentice Hall India, Second Edition, 2006.
  • P. S. Bimbhra, "Power Electronics," Khanna Publishers, fifth edition, 2012.

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