This post answers the question what is the power IGBT. IGBT is the combination of two discrete devices – MOSFET and BJT.

This approach to the semiconductor technology gives excellent output characteristics, great SOA and very good switching time, compared to discrete devices themselves. The power IGBT structure is depicted in Figure 1.

What is power IGBT

Figure 1. The electrical equivalent scheme of the IGBT.

A simplified structure of the device can be seen in Figure 1b. This vertical structure of the device offers the possibility to obtain the greater current densities and lower forward voltage drop. The p+n and p are combined in the BJT device. This device has low current gain. The operation of the power IGBT can be easily seen if we will operate the BJT with the voltage of the gate.

1. If the gate voltage is zero, and the collector voltage is positively biased, then the device is reverse biased.
2. If the gate is shortened to the emitter the device is OFF.
3. If the gate is positive, and bigger than the VTh, then the device is ON.

In addition, et’s look at the layer structure of the IGBT (Figure 2), the static characteristics of the drift region is expressed with the formula: WD=2εSVmaxqND, this depends on the charge carriers in the power IGBT, and other static characteristics. 

What is power IGBT
a – layer scheme of power IGBT

b – equivalent scheme of power IGBT

The power IGBT can be present with the following equivalent circuits, depicted in Figure 2.

Power IGBT characteristics

These characteristics are usually provided in the manufacturer’s datasheet, are:

  • Collector-emitter blocking voltage BVCES;
  • Emitter-collector blocking voltage BVECS;
  • Gate-Emitter voltage VGES;
  • Continuous collector current IC;
  • Peak collector repetitive current ICM;
  • Maximum power dissipation PD;
  • Junction temperature  Tj;
  • Clumped collective inductor current ILM;
  • Collector-emitter leakage current ICES;
  • Gate-emitter threshold voltage VGE(Th);
  • Collector-emitter threshold voltage VCE(SAT);
  • Forward transconductance gFE;
  • Total gate charge Qg;
  • Turn-on delay time td;
  • Rise time tr;
  • Turn-off delay time td(off);
  • Input and output capacitances Cies and Coes;
  • Reverse transfer capacitance Cres;
  • Safe-operation area SOA.
For instance, Digi-Key Electronics offers a big variety of IGBT.