Basic and Physical Differences Between IGBT and MOSFET

After evolving side by side over the last three decades, Insulated Gate Bipolar Transistors (IGBTs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) now dominate the power semiconductor market. They are widely used in applications such as motor drives, uninterruptible power supplies (UPS), and solar inverters. A common design question is therefore where IGBTs provide the best fit and when it makes more sense to choose a MOSFET.

The IGBT is a power semiconductor device that combines the output characteristics of a bipolar junction transistor with the gate drive characteristics of a MOSFET. As a result, the IGBT is a minority carrier device with high input impedance and high current carrying capability. This allows it to handle high power levels efficiently while maintaining relatively simple gate drive requirements.

MOSFETs, on the other hand, are majority carrier devices. They offer very fast switching speeds and low switching losses, especially in low to medium voltage applications. However, as voltage ratings increase, the on state resistance of a MOSFET rises significantly. This increase limits efficiency and current handling capability at higher voltages.

Compared to MOSFETs, IGBTs are better suited for applications that require high current operation at higher voltage levels. Their bipolar conduction mechanism enables lower conduction losses at high voltages, making them more scalable for medium and high voltage power applications. This characteristic makes IGBTs a preferred choice in industrial motor drives, traction systems, renewable energy inverters, and high power UPS systems.

From a physical structure perspective, an IGBT integrates a MOSFET input stage with a bipolar output stage. This hybrid structure allows voltage controlled gate operation combined with high current density conduction. MOSFETs rely entirely on the electric field effect and therefore require larger die areas to support high current at elevated voltage levels.

In practical design terms, MOSFETs are generally preferred for low voltage applications, typically below 600V, where high switching frequency and efficiency are critical. IGBTs are typically chosen for applications above this voltage range, where high power density, robustness, and current capability are more important than extremely fast switching speed.