How the latest generation of 1,200 V IGBTs raises energy efficiency to a new level

The worldwide drive to achieve net zero in carbon emissions has prompted an astonishing build-out of energy infrastructure, such as wind farms, solar farms, and battery-based energy storage systems (ESS). The more efficiently this infrastructure operates, the more zero-carbon power it can supply to energy consumers. 

This is intensifying the competition among semiconductor vendors to reach new efficiency benchmarks for the crucial power components that determine how efficiently systems such as power inverters, converters and motors run. The latest such benchmark has been set by onsemi with the introduction of its new FS7 family of 1,200 V trench field stop IGBTs. 

Interestingly, the FS7 family consists of two product series, which meet the demands of different types of applications for the latest high-efficiency IGBTs: 

• High-frequency, high-power switching converters and inverters, in products such as solar power generators, ESS, welding equipment, and induction cookers
• High-power three-phase motors. This includes brushless dc motors, and both synchronous and asynchronous ac motors. 

In the first set of applications, a substantial contribution to power losses comes from switching; in the second set of applications, conduction losses have a larger impact. So onsemi has tuned the inherent IGBT trade-off between collector-emitter saturation voltage and turn-off energy differently in the two series of FS7 IGBTs: 

• The S series is optimized for low turn-off energy, to minimize switching losses in high-frequency converters and inverters
• The R series is optimized for low saturation voltage, to minimize conduction losses in motors, and in solid-state relays (SSRs)

 Fig. 1: The new FS7 field stop IGBTs from onsemi feature process enhancements including a trench narrow mesa and a proton implant multiple buffer. 

These new FS7 IGBTs benefit from a host of process and design enhancements which not only increase performance compared to earlier generations of 1,200V IGBTs, but also make the devices easier to control and more robust as shown in Figure 1. The new IGBTs include a co-packaged, optimized Gen 7 diode which produces a low forward voltage and optimizes switching softness. Their clean switching waveforms are shown in Figure 2. 

Ruggedness is demonstrated by the S series’ ability to avoid latch-up at up to seven times the device’s rated current, giving power-system designers very high confidence that it will continue to operate safely even under severe fault conditions. 

In addition, the R series IGBTs are rated for short-circuit, eliminating any concerns about the power switch’s operation in the event that a motor generates an extreme current spike. 

Fig. 2: Switching waveforms for the FS7 IGBT when turning on (top) and off (bottom). 

Efficiency performance steps up

Power-system designers commonly evaluate a new line of IGBTs for their impact on system efficiency. So how substantial an improvement does the FS7 family provide? 

 Fig. 3: Plot of the trade-off of saturation voltage against turn-off energy at 175°C for the FS7 family, the UFS (FS3) and FS2 families from onsemi.

For three-phase motor applications and SSRs, in which conduction losses must be minimized, the FS7 R series features a low saturation voltage of 1.65 V at 175°C, while its turn-off energy at this saturation voltage and temperature is 120 µJ/A.

For power conversion and inversion applications, which call for low switching losses, the FS7 ‘Fast’ S series offers very low turn-off energy of just 57 µJ/A.

As shown in Figure 3, there is a marked reduction in turn-off energy for the same saturation voltage between the earlier onsemi FS2 family and the new FS7 S series.

Broad portfolio of efficient IGBTs for multiple application requirements

The FS7 family of 1,200V IGBTs is available in four versions: 

• The S series 
  • FGY75T120SWD – 75 A current rating, housed in a power TO-247 three-lead package
  • FGY60T120SWD – 60 A current rating, housed in a power TO-247 three-lead package
  • FGHL40T120SWD – 40 A current rating, housed in a standard TO-247 three-lead package
• The R series 
  • FGY100T120RWD – 100 A current rating, housed in a power TO-247 three-lead package

onsemi has more FS7 devices under development with current ratings ranging from 40 A to 160 A:

• In a standard TO-247 three-lead package
  • R series: 40 A and 60 A current ratings
• In a power TO-247 three-lead package
  • S series: 100 A current rating
• In a power TO-247 four-lead package
  • S series: 75 A, 100 A, 140 A and 160 A current ratings

The power four-lead package includes a Kelvin source lead, the effect of which is to produce a substantial reduction in turn-on energy, making for even more efficient switching. onsemi also plans to supply FS7 IGBTs in bare die format. 

All FS7 IGBTs have a positive temperature coefficient for easy parallel operation. Every production unit is dynamically tested to give OEMs high confidence in the operation and reliability of the IGBT in their application. 

Design engineers who want to evaluate the new FS7 products can request a free sample from Future Electronics, where the large team of power electronics specialists will be pleased to provide advice on deploying these high-performance parts in new designs.