Posted: March 11th, 2023

Reply to the following questions below

As you said, these are  voltage-controlled devices. whereas BJTs are current controlled device.   Requiring no input control current is a major advantage of IGBTs.

“. . . used in applications such as induction heating . . .”

I have one of those induction-heated water pots for tea.  They heat scary fast and they have IGBTs in the base plate.

IGBT

IGBT, or Insulated Gate Bipolar Transistor, is a combination of MOSFET and BJT. It has four layers of semiconductor forming a PNPN structure. The emitter is between the N and P layers, while the collector electrode is attached to the P-layer. The IGBT collector and emitter terminals are used to conduct electricity, while the gate controls the IGBT. The working of the IGBT is based on biasing between the Collector-Emitter and Gate-Emitter terminals.

The collector-emitters are connected to the Vcc in a way that the collector is kept at a positive voltage than the emitter. Junction j2 becomes reverse-biased while junction j1 becomes forward-biased. The IGBT remains switched off as junction j2 is reverse-biased. No current flows between the emitter and collector. When a gate voltage Vg that is more positive than the emitter is applied, negative charges accumulate beneath the silicon oxide layer because of capacitance. Increasing the gate voltage increases the number of charges that form a layer when the gate voltage exceeds the threshold voltage in the upper region.

IGBT is in a non-conductive state when voltage is not applied to the gate terminal. If the gate voltage is increased, negative ions are accumulated on the upper side while positive ions are accumulated on the lower side. This leads to the insertion of negative charge carriers on the p region. The formation of a channel between the J2 junction allows current flow from the collector to the emitter.

The Insulated Gate Bipolar Transistor is used in applications such as induction heating, traction motor control, and switched-mode power supplies. IGBTs are also used in AC and DC motor drives and inverters. They are used for combining isolated-gate FET for the control input and bipolar power transistor as a switch in a device.

REFERENCES

“A Brief Overview of IGBT – Insulated Gate Bipolar Transistor” Components. Retrieved from 

https://components101.com/articles/what-is-igbt-working-operation-symbol-and-types

“What is IGBT? Construction, Types, Working and Applications” Electrical Technology. Retrieved from 

https://www.electricaltechnology.org/2021/08/igbt.html