*Switching is slower than for MOSFETs, but faster than that of bipolar transistors. By supplementing these deficiencies, an IGBT achieves high input impedance, fast switching*, and low on-resistance even with higher withstand voltage ratings. A bipolar transistor has a low on-resistance even with higher withstand voltage ratings, but drawbacks include a low input impedance and slow switching speeds. Because the gate of a MOSFET is insulated, it has the advantages of a high input impedance and relatively fast switching, but with the drawback that the on-resistance is higher with higher withstand voltage ratings. The operation and method of driving a IGBT will be explained separately.Īs stated above, an IGBT is a transistor that combines desirable aspects of MOSFETs and bipolar transistors. Like MOSFETs, an IGBT is a voltage-controlled device: when a positive voltage, relative to the emitter, is applied to the gate of an N-channel IGBT, there is conduction between the collector and the emitter, and a collector current flows. The gate is the same as in a MOSFET the collector and emitter are like those in a bipolar transistor.
The structure and other aspects will be described below in greater detail.Īn IGBT has three pins: the gate, the collector, and the emitter. The actual device is somewhat more complex, including the structure.
Some equivalent circuits provide more detail, but here a comparatively simple circuit is shown to aid understanding. IGBTs are of two types, N-channel and P-channel here we used in our example N-channel IGBTs, which are currently the mainstream.īelow are shown the circuit diagram symbol of an N-channel IGBT and the equivalent circuit of the device. As a hybrid of MOSFETs and bipolar transistors, they serve as power transistors that combine features of both. “IGBT” is an acronym of Insulated Gate Bipolar Transistor.
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