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IGBT Features: Comparisons with MOSFETs and Bipolar Transistors

2023.07.19

Points of this article

・The features of IGBTs, MOSFETs, and bipolar transistors should be understood, so that they can be used selectively according to the application.

IGBT Features: Comparisons with MOSFETs and Bipolar Transistors

In applications requiring power transistors, the various options such as IGBTs, MOSFETs, and bipolar transistors are used selectively based on an understanding of their strengths and weaknesses. The following is a summary of the features of these different kinds of power transistors.

	MOSFET（N-channel）	Bipolar Transistor（NPN）	IGBT
Basic Structure
Control	Gate voltage	Base current	Gate voltage
Allowable Current	△	○	◎
Switching Speed	◎	△	○
ON Resistance	△	○	◎

※◎, ○, △: Respectively best, better, good

●MOSFETs

MOSFETs are voltage-driven and have a high input impedance, so that little power is needed to control them; and because they are unipolar transistors, with either electrons or holes as carriers, they also have the advantage of fast switching speeds. However, a conductivity modulation effect such as that in bipolar transistors cannot be used, and so MOSFETs have the drawback of higher on-resistances with higher withstand voltage ratings.

●Bipolar Transistors

Bipolar transistors have the advantage of a low on-resistance* even with higher withstand voltage ratings. During operation of a bipolar transistor, both holes and electrons move, and due to the conductivity modulation effect in which the resistance falls due to the entry of holes into the N- layer, the device has a characteristic in which voltage drops are suppressed. Bipolar transistors are current amplifiers, and so a larger current than the applied current can be passed. Drawbacks of these devices include a low input impedance, the large amount of power consumed for device control, and the slow switching speed due to the use of carriers of both polarities.
*The relevant parameter is the saturation voltage.

●IGBTs

IGBTs are a hybrid device that combines the structure of a MOSFET in the input section and a bipolar structure in the output section, thereby combining the advantages of MOSFETs and bipolar transistors. The input impedance is high and the device can be driven using minimal power, and amplification to large currents is possible. Moreover, the on-resistance* can be kept low even with higher withstand voltage ratings. Switching speeds are not as fast as those of MOSFETs, but are faster than those of bipolar transistors.
*The relevant parameter is the saturation voltage.

＜Summary＞

MOSFETs, bipolar transistors, and IGBTs have been compared. Advantages of IGBTs include low losses even with higher withstand voltage ratings and relatively fast switching. However, the different types of power transistors each have their advantages, and so in essence they should be selected for use according to the application. Regarding the range of application and selective use of the different power transistor types, please refer to “Range of Application of IGBTs” and “Applications Using IGBTs.

【Download Documents】 Basics of IGBTs

IGBTs are one of the typical power devices and are used in a wide range of applications including motor drives. This handbook provides a basic understanding of IGBTs, including their application scope and application picture based on their features, their structure and principle of operation, and how they compare with and use other power devices.

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IGBT

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IGBT IPM: Protection Functions and Operation Sequences ＋

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