PFD7 vs IGBTS for Inverter Circuits

[EslamAlfawy]

Hi everyone,

On today’s blog I will argue on the features of CoolMOS™ PFD7s vs IGBTs in inverter circuits.

To give you a quick background story, last week I was talking to a colleague of mine who happened to be working on a campaign on CoolMOS™ PFD7 and asked me on whether I think CoolMOS™ PFD7 or IGBTs are more efficient as inverter circuits. Frankly, it took me a minute to come up with an answer on the pros and cons of both products and on today’s blog, I decided to share with you a more elaborated answer to my colleague’s question.

Designers often face the challenge of selecting either an IGBT or MOSFET for a given application and set of operating conditions. In the case of three-phase variable speed motor which drives up to 300 W rated power range, utilizing a DC bus voltage in the 300 to 400V range, 600 to 650V rated IGBTs have traditionally been the preferred device from an overall performance perspective. But with the availability today of high switching speed, low RDS (on), and relatively fast reverse recovery body diode in 600 to 650 V rated power MOSFETs, the question of whether it is time for the IGBT to give way to the MOSFET has arisen.

From results of different motor drives manufacturers, the IGBT has the advantage over the MOSFET at higher switching frequencies. But at lower switching frequencies, the MOSFET has the lower overall loss and lower operating junction temperature. This is in some ways counter to conventional wisdom where it is often argued that MOSFETs perform better at higher switching frequencies.

However, the lower switching loss of the IGBT due to a significantly lower diode recovery loss component gives it the advantage over the MOSFET at a relatively high switching frequency.

Interestingly, at lower switching frequencies where conduction loss dominates, the MOSFET benefits due to the lack of a “knee" in its forward characteristics, in conjunction with a relatively low RDS (on) especially in partial load conditions where the MOSFET has a lower on voltage drop compared to IGBT, which results in lower conduction losses

Now, there are a variety of MOSFETs and CoolMOS™ PFD7 is the latest generation of super junction technology offered by Infineon. A super-junction structure is a structure in which multiple vertical PN junctions are arranged, as a result of which an even lower ON-resistance RDS(ON) and reduced gate charge QG are realized while maintaining the high blocking voltage with improved ultra-fast diode recovery behavior, this could start tilting the balance towards the MOSFET.

Having said that, choosing which device is best for a given application depends on a lot of things, such as for example the cost/performance ratio ($ /Watt), switching speed, size and so forth.

On one hand, in cases where layout flexibility and thermal performance optimization play a major role, a discrete 600V IGBT RCD2 or CoolMOS™ PFD7 solution are the right choice. On the other hand, for highly integrated drives, the CIPOS™ family of IPMs is the most suitable choices. All of these products are compatible with microcontroller iMOTION™ products for motor control. To spice things up, Infineon has enhanced the performance and robustness of the power portfolio with power management IC controllers CoolSET™.

Let us know in the comment section below about your thoughts on this topic!

Until next time, take care! 🙂