Types of IGBT: Basics, Comparison

Types of IGBT:

Insulated Gate Bipolar Junction Transistor (IGBTs) are normally classified into two types.

They are namely
(i) Non Punch Through IGBT [NPT-IGBT]
(ii) Punch Through [PT-IGBT]

  • These IGBTs are also referred to as symmetrical and asymmetrical IGBTs.
  • These varieties of IGBT differ widely with regard to their fabrication technology, structural details etc.
  • The table given below shows the salient features of the two types of IGBT.
  • Before proceeding further it is strongly recommended to read about Basics of IGBT. Click here to know about the fundamentals of IGBT.
  • The important facts about IGBT are summarized below ( If you are already familiar with IGBT basics, just skip this paragraph and proceed to next section)
  1. IGBT has the advantage of high current capability of BJT and has the advantage of easy control like MOSFET. Actually this power semiconductor device emerged to overcome the drawback of transistor and mosfet. 
  2. It is a three terminal device namely Drain, Source and gate or Emitter, Collecter and base.

What is meant by NPT-IGBT and PT-IGBT?
IGBTs having n+ buffer layer is called Punch Through-IGBT (PT-IGBT) and IGBTs made without this layer is known as Non Punch Through-IGBT (NPT-IGBT).
It is good to know about the structure of this device, for proper understanding of n+ buffer layer. Click here to know about Structure of IGBT

Why are they called as Symmetrical and Asymmetrical IGBTs?
A symmetrical IGBT (NPT-IGBT) is one having equal forward and reverse breakdown voltages. Such devices are used in AC applications.

In the asymmetrical IGBTs (PT-IGBT) structure, the reverse breakdown voltage is less than the forward breakdown voltage. These types of IGBTs are useful for DC circuits where the device is not required to support voltage in the reverse direction.

                 NPT - IGBT             PT - IGBT
More rugged in short-circuit failure modeLess rugged in short-circuit failure mode
More thermally stableLess thermally stable
Turn-off loss is less temperature-sensitive. Practically it remains unchanged with temperature.Turn-off loss is more temperature-sensitive. It increases significantly at higher temperature.
Collector is lightly doped (P layer only)Collector is heavily doped (P+ layer)
The temperature coefficient of ON-state voltage is strongly positive.Small positive temperature coefficient of ON-state voltage.
So in this type of IGBT, the parallel operation is easyParallel operation requires greater care and attention
Manufactured using diffusion process technology which is less expensive process.Fabricated in an N- epitaxial wafer process which is more expensive.
Thick N base. Does not contain any N-buffer layer. Space charge spreads across the wide N- base to withstand the voltage. NPT structure provides bidirectional blocking capability.Thin N base. Contains an N-buffer layer. Penetration of depletion region into this layer avoids the use of a broad N- base. This IGBT has lower reverse blocking capability.
High carrier lifetime yields a low forward voltage drop.comparatively lower lifetime, so high forward voltage drop.
These types of IGBTs are useful for AC circuitsThese types of IGBTs are useful for DC circuits

Read Further:
Comparison of MOSFET with BJT
Power Electronics System: Introduction,Advantages, Disadvantages
Applications of Power Electronics in Various Fields

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