Since J2 is in reverse bias there will not be any current flow inside the IGBT(from collector to emitter). Due to the voltage source V CC the junction J1 will be forward-biased whereas the junction J2 will be reverse biased. Consider other voltage source V CC connected across The Emitter and the Collector, where Collector is kept positive with respect to the Emitter. To understand the working of the IGBT, consider a voltage source V G connected positively to the Gate terminal with respect to the Emitter. The structure of IGBT is shown in the figure below. The junction between the p+ layer and n- layer is called the junction J2 and the junction between the n- layer and the p layer is called the junction J1. The layer closer to the collector is the p+ substrate layer above that is the n- layer, another p layer is kept closer to the emitter and inside the p layer, we have the n+ layers. IGBT is constructed with 4 layers of semiconductor sandwiched together. IGBT has three terminals attached to three different metal layers, the metal layer of the gate terminal is insulated from the semiconductors by a layer of silicon dioxide (SIO2). The different names of IGBT are Insulated Gate Transistor( IGT), Metal Oxide Insulated Gate Transistor (MOSIGT), Gain Modulated Field Effect Transistor (GEMFET), Conductively Modulated Field Effect Transistor (COMFET). Since IGBT is the combination of MOSFET and BJT they are also called by different names. The outcome obtained from this combination delivers the output switching and conduction characteristics of a bipolar transistor, but the voltage is controlled like a MOSFET. IGBT combines the low saturation voltage of a transistor with the high input impedance and switching speed of a MOSFET. IGBT can be constructed with the equivalent circuit that consists of two transistors and MOSFET, as the IGBT posses the output of the below combination of the PNP transistor, NPN transistor, and MOSFET. The Collector and the Emitter are the conduction terminals and the gate is the control terminal with which the switching operation is controlled. The symbol of the IGBT also represents the same, as you can see the input side represents a MOSFET with a Gate terminal and the output side represents a BJT with Collector and Emitter. The typical symbol of IGBT along with its image is shown below.Īs mentioned earlier an IGBT is a fusion between a BJT and MOSFET. These devices are mostly used in amplifiers for switching/processing complex wave patters with pulse width modulation (PWM). It is a three-terminal semiconductor switching device that can be used for fast switching with high efficiency in many types of electronic devices. IGBT is the short form of Insulated Gate Bipolar Transistor. In this article, we get familiar with the basics of IGBT, how they work, and how to use them in your circuit designs. You can think of IGBT as a fusion between BJT and MOSFET, these components have the input characteristics of a BJT and output characteristics of a MOSFET. So, we moved another popular power electronic switching device called the IGBT. But, both these components had some limitations to be used in very high current applications. We have already discussed in detail about the working of BJT and the working of MOSFET and how they are used in circuits. The most popular and commonly used power electronic switch devices are the Bipolar Junction Transistor BJT and the MOSFET.
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