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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.
With a wide range of current ratings, the 1200-V family of IGBTs features the high-frequency “S” series, including the FGY75T120SWD, which is said to have the best switching performance in its class. Tested against currents of up to 7X the rated value, the 75-A IGBT also has a high degree of ruggedness against latch-up and other types of short circuits, which can create high current levels that damage the system.
The new family also includes the “R” series of IGBTs, which are ideal for medium-speed switch-mode power supplies (SMPS), including ones used in industrial motors, where conduction losses can take a serious toll on system performance. One of the first products in the R series is the FGY100T120RWD, which supports a saturation voltage (VCE(sat)) of 1.45 V at 100 A, a generational improvement of 0.4 V.
Onsemi said the IGBTs can operate at junction temperatures (TJ) of up to 175°C, which rivals the thermal management properties of SiC MOSFETs competing in high-voltage industrial and automotive-grade power supply designs. The FS7 family comes in a wide range of packages, including the TO247-3L and TO247-4L, as well as bare die, giving designers flexibility and design options, the company said.
The new Trench Field Stop IGBTs bring improvements in switching softness, too, which aids robustness, said onsemi. When IGBTs or other high-voltage power FETs are switched on or off, the switching occurs relatively fast. But it’s not instantaneous. The time it takes to transition between the on and off states results in wasted energy. Ultimately, such switching losses can limit the power system's operating frequency.
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 the 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 remains 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 results 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 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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