Characteristics and Specifications of Power Semiconductor Devices

1) Power Diodes

  • Two terminal device - cathode and anode.
  • Forward voltage drop between 0.5 to 1.2 V
  • General purpose diode, fast recovery (essential for high frequency switching), and schottky diode (low on-state voltage).

2) Thyristors

  • Three terminal device - anode, cathode, and gate.
  • When anode terminal is at a higher potential than the cathode, and a small current is passed through the gate terminal to cathode, the thyristor conducts.
  • Once a thyristor is in a conduction mode, the gate circuit has no control and thyristor continues to conduct.
  • During conduction mode, forward voltage drop is between 0.5 to 2 V.
  • A conducting thyristor can be turned off by making V_A <= V_K.

2a) Forced Commutated Thyristor

  • FCT is Turned off by an extra circuit called commutation circuitry.

2b) Line Commutated Thyristor

  • LCT is Turned off due to the sinusoidal nature of the input voltage.

2c) Reverse Conducting Thyristor

  • RCT is widely used for high speed switching, especially in traction application.
  • Can be considered as a thyristor with an inverse parallel diode.

2d) Gate Assisted Turn-off Thyristor (GATT)

  • GATT is widely used for high speed switching, especially in traction application.

2e) Light Activated Silicon Controlled Rectifier

  • LASCR is suitable for high voltage power systems, especially in HVDC.


  • Widely used for low power ac applications like simple heat controls, light control, motor control, and ac switch.
  • Characteristics are similar to two thyristor connected in inverse parallel and having only one gate terminal.
  • The current flow can be controlled in either direction.

2g) Gate Turn Off and Static Induction Thyristor

  • GTO and SITH is a self turned off thyristor.
  • Both can be turned on by applying a short positive pulse to the gate and turned off by applying a short negative pulse to the gate.
  • Both do not require any commutation circuit.
  • GTO are very attractive for forced commutation of converters While SITH are expected to be applied for medium power converters with a frequency of several hundred kilohertz and beyond the frequency range of GTO.

2h) MOS Controlled Thyristor

  • MCT is a self turned off thyristor.
  • Turned on by applying a short negative pulse to the gate (with respect to its anode) and turned off by applying a short positive pulse to the gate.
  • It is like a GTO, except that the turn off gain is very high.

3) Power Bipolar Junction Transistor

  • Power BJT is a three terminal device - base, emitter, and collector.
  • Normally operated as a switch in the common-emitter configuration.
  • As long as the base of an NPN transistor is at higher potential than the emitter and the base current is sufficiently large to drive the transistor in the saturation region, the transistor remains on, provided that the collector-to-emitter junction is properly biased.
  • The forward drop of a conducting transistor is 0.5 to 1.5 V.
  • If the base drive voltage is withdrawn, the transistor remains in the non conduction (OFF) mode.

4) Power MOSFET

  • Power MOSFET is used in high speed power converters.

5a) Insulated Gate Bipolar Transistor

  • IGBT is a voltage controlled power transistor.
  • faster than power BJT, but still not quite as fast as Power MOSFET.
  • Offer far superior drive and output characteristics to those of Power BJT.

5b) Static Induction Transistor

  • SIT is a high power and high frequency device.
  • Solid state version of the triode vacuum tube and is similar to a JFET.
  • Low noise, low distortion, high audio frequency power capability.
  • Normally on-characteristics and the high on-state drop limit its applications for general power conversion.
  • Used in audio, VHF/UHF and microwave amplifiers.


  • 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.

No comments

Powered by Blogger.