Same thing happens for the BJT transistor. When in conducting or switched ‘ ON’ mode the current flow from collector to emitter. The three terminals are shown as Gate, collector and Emitter.
As we can see, the symbol includes Transistor’s collector emitter portion and the MOSFET’s gate portion. In the above image, symbol of IGBT is shown. An IGBT’s gain is the ratio of output current changes with the input gate voltage changes.ĭue to high current capabilities, the BJT’s high current is controlled by the MOSFET gate voltage. Thus the gain is the ratio of output voltage changes with the input voltage changes.
MOSFET’s gate voltage changed the output current conduction. The MOSFET’s gate is isolated from the current conductions path. So, the same formula which is applied for calculating the gain of BJT’s, is not applicable for the MOSFET technology. β = Output Current / Input Currentīut, as we know, MOSFET is not a current controlled device it is a voltage controlled device, there is no input current across the MOSFET’s gate. In case of the BJT, we calculate the gain which is denoted as Beta ( ), by dividing the output current by the input current. This path is controlled by the N channel MOSFET. In the PNP transistor, collector and Emitter is conduction path and when the IGBT is switched on it is conducted and carry the current through it.
But in the case of IGBT transistor Pins, it is the Gate, which is coming from the N-channel MOSFET and the Collector and Emitter are coming from the PNP transistor. A standard BJT’s pin out includes Collector, Emitter, Base and a standard MOSFET pin out includes Gate, Drain and Source. N channel MOSFET is driving the PNP transistor. As we can see the above image, IGBT combines two devices, N channel MOSFET and PNP transistor. It’s same circuit structure used in Darlington Transistor where two transistors are connected exactly the same way. In the above image the equivalent circuit of IGBT is shown. Although, BJT is current controlled device but for the IGBT, the control depends on the MOSFET, thus it is voltage controlled device, equivalent to the standard MOSFETs. IGBT is a voltage controlled semiconductor which enables large collector emitter currents with almost zero gate current drive.Īs discussed, IGBT has the advantages of both MOSFET and BJTs, IGBT has insulated gate same as like typical MOSFETs and same output transfer characteristics. MOSFET has advantages of high switching speed with high impedance and on the other side BJT has advantage of high gain and low saturation voltage, both are present in IGBT transistor. It’s is a semiconductor device used for switching related applications.Īs IGBT is a combination of MOSFET and Transistor, it has advantages of the both transistors and MOSFET. IGBT is a short form of Insulated Gate Bipolar Transistor, combination of Bipolar Junction Transistor (BJT) and Metal oxide Field effect transistor (MOS-FET).
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