IGBT Switching Characteristics

IGBT Switching Characteristics

The IGBT - Insulated Gate Bipolar Junction Transistor is a newly developed power semiconductor device which is almost replace the role of MOSFET in high voltage power electronics circuits. It contains the advantages of both MOSFET and BJT.

The Switching Characteristics of IGBT is explained in this post.
With the help of the above mentioned simplified circuit, we can understand the turn-on and turn-off process of IGBT.

It is recommended to know about Basics of IGBT and Structure of IGBT before proceeding further.


  • The voltage VGE  is normally negative. It is made into positive to turn-on IGBT.
  • As gate voltage is increased, VGE increases. When VGE = VGE(th) the collector current IC starts to flow.
  • Time taken for VGE to rise and reach VGE(th) (or) The time for IC to start increasing is called as "turn-on delay time tdn".
  • After VGE(th), the collector current IC starts to increase. The time for IC to rise and reach its max value is called as "rise time" for current(tri).
  • When IC reaches its max value, IGBT is in its ON state. When a device is in its ON state, it is said to be short circuited and so the voltage across it is equal to zero.
  • Therefore when IGBT is ON,  the VCE voltage starts reducing to a value nearly equal to zero. Here it falls to a value VCES(saturated value) or VCE(ON).
  • This time taken for voltage VCE to start to fall and reach its saturated value VCES is called as "fall time for voltage(tfv)".
  • Therefore the turn-on time tON = tdn + tri + tfv
  • These time delays are due to two reasons.
  • Gate-Collector capacitance will increase in MOSFET portion of IGBT at low VCE.
  • PNP transistor portion of IGBT travels (or) moves to the ON state more slowly than the MOSFET portion of IGBT.

Turn OFF:

  • IGBT is turned OFF by removing the gate voltage.
  • When Gate voltage VG is reduced, VGE starts to fall and VCE starts to increase.
  • Turn-off delay time(tdf) is the time between the VGE starts to decrease and the VCE starts to increase.
  • At the end of tdf, the VCE starts to increase and reaches its max value. The time taken for VCE to rise and reach its full value is called as rise time for voltage(trv).
  • As VGE decreases and reaches VGE(th) the drain current reduces to zero. Time interval tfi1 is the fall time for current. It is the turn-off interval of the MOSFET section of IGBT.
  • Here the current IC is not zero, but a small current flows due to the stored charge in n-- drift region. This is the internal BJT current.
  • This tailing of current (due to BJT internal current) takes place during the interval tfi2. It is the turn-off interval of the BJT section of IGBT.
  • The turn-off time TOFF = tdf + trv + tfi1 + tfi2

The Summary of Merits & Demerits of IGBT is given below:


  • Voltage controlled Device
  • Less On state loss
  • High switching frequency
  • No commutation circuit
  • Gate has full control over operation.
  • Flat temperature coefficient

Demerits of IGBT:

Thanks for reading....

You may also like...

3 Responses

  1. padam choudhary says:

    about SCR

  2. David says:

    Can somebody tell me how the CE-voltage would look like during turn off when considering a inductance in the switched circuit?

    Wouldn't there be a voltage overshoot?

    And what is the time of this overshoot?

    Thanks in advance for any comment 🙂

Leave a Reply

Your email address will not be published. Required fields are marked *