Superiority of the IGBT Compared to the MOSFET

The IGBT has certain advantages over the MOSFET at higher switching frequencies. However, at lower switching frequencies, the MOSFET typically exhibits lower total losses and a lower operating junction temperature. In this comparison, the selected IGBT and MOSFET devices have approximately the same die size and thermal impedance. This result may appear to contradict conventional wisdom, which often suggests that MOSFETs perform better at higher switching frequencies.

The observed performance advantage of the IGBT at higher frequencies can be attributed mainly to the significantly lower diode recovery loss component of the IGBT combined with a fast recovery diode (FRD). In addition, modern IGBT technology has achieved substantial improvements in minimizing tail current behavior. The reduced switching losses of the IGBT plus FRD, resulting from lower diode recovery losses, give the IGBT an advantage over the MOSFET at 20 kHz, which is considered a relatively high switching frequency for this type of application.

MOSFET switching losses, however, can be significantly reduced by using a gate driver with higher source and sink current capability, such as a driver with 2 A source and sink current. With improved gate drive performance, the total losses of the MOSFET can be reduced, allowing it to narrow the performance gap with the IGBT. The resulting higher dv/dt, however, may introduce undesirable effects such as high-frequency audible noise and increased levels of radiated electromagnetic interference (EMI).

At lower switching frequencies, where conduction losses dominate, the MOSFET benefits from the absence of a knee voltage in its forward conduction characteristics, along with its relatively low on-state resistance RDS(on). In this operating region, MOSFETs can achieve lower conduction losses compared to IGBTs.

While the IGBT remains the preferred device choice for this particular application example, the availability of MOSFETs with significantly lower RDS(on), improved diode recovery behavior, and stronger gate drive capability may begin to shift the balance in favor of the MOSFET. In such cases, the final decision often becomes a cost-to-performance comparison, commonly expressed as cost per ampere. In this regard, the IGBT typically maintains an advantage due to its much higher current density for a given die size.

Both IGBTs and MOSFETs are often available as viable options for a given application. It is therefore important to clearly understand the advantages and limitations of each device and to select the one that best meets the application requirements in terms of overall performance and cost. Although this is not always a simple task, greater familiarity with power semiconductor devices can greatly assist designers in navigating these complex design decisions.