A Spike in EVs Means a Spike in Insulated Gate Bipolar Transistors (IGBTs)
The Insulated Gate Bipolar Transistor (IGBT) has been a key player in the development of electric vehicles. What makes them so valuable?
According to the International Energy Agency, there will be 125 million electric vehicles on the road by 2030. Amongst other reasons, this increase in production is being driven by technological developments that have significantly reduced the cost and improved the quality (that is, the range) of EVs.
Global EV vehicle deployment forecast to 2030. Image used courtesy of the IEA
One piece of technology that lies central to the development of EVs is the insulated gate bipolar transistor (IGBT).
The IGBT: A Brief Background
The IGBT (PDF) is a device that combines the high input impedance and fast switching speeds of power MOSFETs with the high conductivity characteristics of a bipolar transistor. While distinct from a traditional BJT, an IGBT is constructed similarly to a MOSFET, having an insulated gate and a similar silicon layout. The main difference between a MOSFET and an IGBT is that the IGBT has an extra p+ layer on the collector side.
Comparison of the BJT, IGBT, and MOSFET. Image used courtesy of Toshiba (PDF)
In this setup, the IGBT current flows through the internal PNP transistor by turning on the internal MOSFET while voltage is applied between the collector and the emitter. AAC contributor Robert Keim discusses the differences between FETs, BJTs, and IGBTs in more detail in his technical article on which of these three devices is right for your power stage design.
IGBTs in Electric Vehicles
The importance of the IGBT in an electric vehicle is really in the motor inverter as a switch. Being a high voltage, high-current device, it is generally connected directly to the traction motor in an electric vehicle. Essentially, it takes DC from the car’s battery and, through the inverter, converts AC control signals to the high power needed to turn the motor.
Example of an IGBT inverter circuit. Image used courtesy of Renesas
The IGBT is a perfect component for 35 KW to 85 KW EV motors thanks to its high efficiency and fast switching. High-efficiency devices like IGBTs lead to less wasted power and, consequently, greater mileage.
It’s for reasons like this that Danfoss Silicon Power recently announced that it has commissioned ON Semiconductor to supply its high-power IGBTs and diodes for inverter traction modules.
SiC MOSFETs: a Notable Rival
I would be remiss to write an article about IGBTs in power supply systems and not mention its greatest competitor: the silicon carbide MOSFET (SiC MOSFET). In a recent article highlighting new advances in SiC technology, I write about the many seeming advantages of SiC MOSFET over IGBTs. In some cases, these new SiC MOSFETs can improve power consumption in power supplies by 85% compared to IGBTs.
This difference in power consumption has a lot to do with the low on-state resistances of the new SiC MOSFETs, which lead to lower conduction losses than the IGBT.
IGBTs' Future is Tied to the EV Market
The massive growth in the EV market is expected to drive growth in the IGBT market as well. IGBTs are an integral part of EV power supplies and further developments in the field will assist in the decreasing cost and increasing range of electric vehicles.
What specific pain points have you experienced when designing with IGBTs? What are their strengths? Share your experiences in the comments below.