The current of the IGBT is one of the basic parameters of the device, and it is obvious that the FS450R12KE4 is a 450A 1200V IGBT module. This understanding is sufficient for day-to-day communication, but it is not enough for a design engineer, and the industry is full of misunderstandings and rumors.
Myth one
The maximum output current capability of the 450A IGBT module is 450A, and sufficient margin is required in the system design
450A is the nominal current of FS450R12KE4. So what is nominal current? The best way to get to the bottom of this problem is to go to the root of the problem and look for clues from the data sheets of Infineon chips.
Find the data sheet of the IGBT chip IGC142T120T8RM inside the FS450R12KE4, the strange thing is that there is no current information on the chip model, 142 is not the chip current, but the area of the chip, and its unit is square millimeters. Moreover, the DC current of the chip collector is not given in the data sheet, and the value is left blank, and the note states that this value is limited by the maximum virtual junction temperature TV Jmax and depends on the thermal performance of the assembly, which includes the IGBT product package and the thermal design of the system.
Table 1: Screenshot of the Trenchstop IGBT4 IGC142T120T8RM data sheet.
Although ICN=150A is indeed given on the first page of the chip data sheet, it is clearly stated that this is the application case FS450R12KE4 Econopack+ module, which is encapsulated in this power module at TC=100°C, at this time, the nominal collector of the chip is electric original Ziying Chen Infineon Industrial Semiconductors 2021-10-27 11:47Stream.
Table 2: Screenshot of the Trenchstop IGBT4 IGC142T120T8RM data sheet.
Notes in the data sheet.
From this we can conclude that:
Conclusion 1: The collector DC current of the IGBT chip depends on the heat dissipation, and the maximum virtual junction temperature should not exceed the limit of TV JMAX.
Based on the first conclusion, we should study the data sheet of the module, and it can be read in the data sheet of the module that the continuous collector DC current is related to the shell temperature, to be precise, the continuous collector DC current is defined at a given shell temperature, which can be guessed that this current is related to the loss under DC and the thermal resistance to the shell.
Table 3: Screenshot of the FS450R12KE4 Econopack+ module data sheet.
Definitions:
Follow the FS450R12KE4 datasheet and take a look at:
This is calculated as only 160oc, and you may wonder if it is better to define it according to 175oc? Wouldn't the CW collector DC current be greater? Not exactly, there are other factors to consider here.
Myth two
The peak current capability of the 450A IGBT module is 450A, and the output RMS current is much less than 450A
This is to study the pulse current capability of the IGBT, and we still start with the chip. In Table 1, IGBT4 IGC142T120T8RM data sheet can find the collector pulse current 450A, but the pulse width is limited by the maximum virtual junction temperature TV jmax, here is a note, this is the design value and passed the design verification, not tested in production. This is because the chip does not have a heat dissipation system, so it is not possible to test the current capability of the chip.
Looking at the module again, Table 3, screenshot of the FS450R12KE4 Econopack+ module data sheet, which clearly gives the collector repeated peak current ICRM=900A, which is twice the continuous collector DC current at the 100 degree shell temperature of the module, that is, the nominal current is 450A.
At the same time, the RBSOA of the reverse bias safe operating area is shown in the diagram, which represents the IGBT shutdown current capability, which means that Infineon's IGBT modules can reliably turn off 2 times their nominal current, and this important parameter is tested 100% in the factory inspection.
Conclusion 2: In the design of good heat dissipation, the 450A IGBT module can withstand the repeated peak current of 900A with a certain pulse width and shut down reliably, and the maximum working junction temperature does not exceed 150 in the design principle.
Myth three
In system design, exceeding the nominal current of the device reduces reliability and can only be done occasionally when overloaded.
Figure 1: Schematic diagram of an induction cooker.
2200W induction cooker generally uses 20A IGBT, such as IHW20N120R5 reverse conductive IGBT single tube. As can be seen from Table 4, the collector DC current is 20A at the shell temperature of 100 degrees, and the collector pulse current is 60A, which is three times the nominal current of the collector pulse current and RBSOA.
Table 4: Screenshot of the data sheet for the IHW20N120R5 retroconducting IGBT single tube.
Due to the quasi-resonant circuit, the voltage of the IGBT is very low when it is turned on, but due to the resonant capacitance, the pulse current is very large, nearly 50A, and there is a fairly high turn-on and conduction loss at this time; The turn-off voltage is zero, and although the turn-off current is as high as 60A, which has reached the limit of RBSOA, the turn-off loss is not large.
In the actual case, the system works at a resonant frequency of 23kHz, that is, the 20A IGBT continuously shuts off the 60A current at a frequency of 23kHz, under the condition that the loss is reasonable, the heat dissipation is good enough, and the junction temperature does not exceed the maximum allowable working junction temperature of 150 degrees.
Figure 2: Quasi-resonant current and voltage waveform of induction cooker, current red 20A DIV, voltage 200V DIV
Conclusion on IGBT modules:
The nominal current on the Infineon IGBT module model is the collector DC current calculated based on a certain shell temperature, which is not the same concept as the actual IGBT switching output current.
System Design Principle 1:The maximum operating junction temperature of an IGBT is not allowed to exceed the maximum operating junction temperature.
System Design Principle 2:The maximum current of IGBT depends on the pulse current capacity and the reverse bias safety working area, that is, the IGBT shutdown current capability, which is generally twice the nominal current, and the shutdown current in the design cannot exceed the reverse bias safety working area, then the system design is safe and reliable.