IGBT

Hi guys today we shall go through one of the most popular power semiconductor devices “IGBT”.

As we all know, the power semiconductor devices have become more popular in the recent past the power semiconductors can be broadly classified into three categories.

•        Power diodes
•        Power thyristors
•       Power transistors

The device which we are discussing today comes under the last category “Power Transistors”.

First of all we shall discuss about the basic symbol of IGBT

What does IGBT stand for ? and what is its symbol?

The IGBT is the abbreviation of Insulated gate bipolar transistor, which is the latest device in power electronics. It is obtained by combining the properties of BJT and MOSFET. We all know that BJT has low on-state losses for higher values of collector current but the drive requirement is complicated. The drive of the MOSFET is very simple but has high on-state losses. Hence the gate circuit of the MOSFET and the collector emitter circuits of the BJT are combined together to form a new device called IGBT thus the IGBT has the advantages of both BJT and MOSFETs.

Symbol of IGBT:

The above image shows the symbol of the IGBT, it has three terminals : Gate(G), collector(C ), Emitter(E) . Current flows from collector to emitter whenever a voltage between gate and  emitter is applied. IGBT is said to be turned on if gate voltage is applied else turned off hence the gate has full control over the conduction of IGBT.

Structure of IGBT:

The P⁺ injecting layer is heavily doped. It has the doping intensity of10¹⁹ / cm³. The n⁺ layer has 10¹⁹ / cm³. P type body region has doping level of 10¹⁶ / cm³and the n^- layer is lightly dope with 10¹⁴/ cm³.

Punch through IGBT: the n⁺ buffer layer is not necessary for the operation of IGBT. The IGBTs which have n+ buffer layer are called punch through IGBTs. Such IGBTs have asymmetric voltage blocking capabilities. These have faster turn off times hence used in inverters and choppers.

Non-punch through IGBT: The IGBTs without n⁺ buffer layer are called non-punch through IGBTs. These IGBTs have symmetric voltage blocking capabilities. These are used for rectifier type applications.

VI characteristics of IGBT:

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