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A new family of high-frequency 1200-V IGBTs from onsemi target the high-density power supplies at the heart of solar inverters, uninterruptible power supplies (UPS), energy storage, and EV charging stations.
The FS7 IGBTs, based on the seventh generation of its Trench Field Stop technology, are ideal for the boost stage of heavy-duty power supplies to increase input voltages to higher levels as well as high-voltage inverters to supply ac outputs.
“As efficiency is extremely critical in all high-switching-frequency energy infrastructure applications, we focused on reducing turn-off switching losses and providing the best switching performance with this new range of IGBTs,” said Asif Jakwani, senior vice president of advanced power at onsemi.
Supporting a wide range of current ratings, the 1200-V IGBT family features the high-frequency S-series, including the 75-A FGY75T120SWD, which is claimed to have the best switching performance in its class.
The R-Series of IGBTs are better suited for medium-speed power supplies, including industrial-grade motor controls, where conduction losses can take a serious toll on system performance. The IGBTs, housed in a host of different packages, including the TO247-3L and TO247-4L, support a saturation voltage (VCE(sat)) of 1.45 V at 100 A, a 0.4-V improvement over the previous generation.
Furthermore, the company said new IGBTs can operate at junction temperatures (TJ) of up to 175°C, which rivals the heat tolerance of SiC MOSFETs that are also competing for slots in high-voltage power supply designs. Tested against currents of up to 7X the rated value, the IGBTs have a high degree of ruggedness against short circuits and latch-up, which can lead to high current and damage to the device.
The new Trench Field Stop IGBTs bring improvements in switching softness to the table, too, which also aids robustness, said onsemi. When IGBTs or other high-voltage power devices are switched on or off, the switching occurs fast. But it’s not instantaneous. The time it takes to transition between on and off results in wasted energy. Ultimately, such switching losses can limit the operating frequency of the power design.
In hard switching, the device is forced to turn on and off by using current or voltage to control the FET. On top of being hard on the FET, hard switching leads to switching losses and excess electromagnetic interference (EMI).
In soft switching, the FET can be turned on and off when voltage is at or close to zero, keeping switching losses to a minimum. While hard switching is relatively easy to implement, soft switching presents more of a challenge.
No Future for IGBTs?
The new IGBTs complement the company’s 1200-V SiC MOSFETs that are claimed to handle even higher frequencies and smaller form factors as well as run cooler, further reducing weight and power losses in a system.
While SiC MOSFETs are becoming key building blocks for inverters and other high-voltage power electronics at the heart of everything from EVs to solar inverters, the market is still in the early stages.
Jinchang Zhou, head of product management for the new IGBTs, said the “IGBT still has its place in the power ecosystem,” due to its long presence in the power electronics market and the evolution of the underlying technology.
Improvements to the trench mesa in the 1200-V IGBTs reduce the switching losses they experience, including the turn-off energy. Low switching losses equate to higher switching frequencies, which in turn enables the use of smaller passive and magnetic components. It result in a boost in power density and cost reduction at a system level. The new construction of the Trench Field Stop IGBTs also cuts conduction loss, which is a boon to efficiency.
The barrier diode integrated in the IGBT is specifically designed to reduce forward voltage (VF)—the total voltage required to get current to flow through a diode—and save even more real estate on the PCB.
According to onsemi, the new IGBTs have a positive temperature coefficient, too, which enables them to be placed in parallel without one of the power devices hogging more of the current, causing excess losses.
IGBTs will remain widely used in markets where the availability of supply and cost matter as much as or more than their power-handling properties. One example is charging stations, which the world urgently needs to usher in the EV era.
SiC power FETs have a higher price point than silicon IGBTs. Despite its inherent advantages, SiC is one of the hardest materials in the world. Thus, mass-production is a challenge—and a very costly one relative to IGBTs, which are manufactured on widely available silicon wafers and possess economies of scale.
“The power semiconductor content in the system is growing significantly, which leads to higher gain of SiC not eroding the growth of Si power devices much. In short, they will coexist in the foreseeable future,” said Zhou.
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