What is an IGBT?

The insulated-gate bipolar transistor (IGBT) is essentially a three-terminal power semiconductor device typically used as an electronic switch in a wide range of applications. The IGBT combines the simple gate-drive characteristics of the MOSFET with the high-current and low-saturation-voltage capability of the bipolar transistor in a single device. While specific IGBT datasheets and application notes from manufacturers provide a wealth of useful information, navigating this content can be time consuming, particularly for circuit designers new to IGBTs. Fig. 1 shows the cross section, equivalent circuit and symbol for an IGBT.

Fig. 1. The cross section, equivalent circuit and symbol for an IGBT.

 

What are the differences (if any) in the gate drive requirements of an IGBT vs. a similarly rated power MOSFET?

In general, the gate-drive requirements of an IGBT are quite similar to that of a comparable voltage and current rated power MOSFET. This follows from the fact that both these devices have a MOS- (metal-oxide-semiconductor) type gate structure. However, there are a few key differences in terms of their gate drive requirements as noted below:

·     IGBTs typically have a higher gate-emitter threshold voltage compared to a MOSFET. Also, at elevated temperatures, a higher gate-emitter voltage is required to ensure the device remains in saturation at a given collector current. For both of these reasons, the IGBT’s applied VGE (gate-emitter voltage) should be at least 14 V (preferably 15 V). In case of similarly rated MOSFETs, an applied VGS of 10 V (gate-source voltage) is generally sufficient to ensure saturation across temperature and current.

·     As the gate-emitter capacitance of a similarly rated IGBT tends to be lower compared to that for a similarly rated MOSFET, the series gate turn-on resistor value is often preferred to be higher compared to that for the MOSFET (often twice, or even higher still). This helps limit the turn-on dv/dt and thus minimize the potential for ringing and resultant EMI.