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Old 5th Mar 2021, 5:44 pm   #1
Al (astral highway)
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Default Kelvin emitter pin on TO247 package?

Doing a bit more development on my inverter, so I've ordered some IGBTs with a pinout that I haven't seen before.

Power engineers, can you advise?

There are four pins. The unusual one, from my perspective, is the one labelled K for Kelvin. The others have the usual G, C, E labels for an IGBT.

Internally, the anode of the intrinsic (freewheeling) diode is bonded to the emitter pin. Externally, this is the fourth pin, labelled K.

In previous generations of IGBT's that I've worked with, the two are simply bonded internally and the Emitter pin is also common with the anode of the intrinsic body diode.

What should I do to safeguard the integrity of this device? It is not a standard TO-247 package. The full descriptor of this package is PG TO247-4-2.

I'm sensing that I should connect both the K and E pins together on the board, but I'm curious why this pinout exists?

Thanks in advance,
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Old 5th Mar 2021, 7:32 pm   #2
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Default Re: Kelvin emitter pin on TO247 package?

If it's of any interest, I found the answer in Infineon's application notes for their propietary 'Trenchstop 5' new generation of IGBTs: https://tinyurl.com/4ssn2n74

It's to separate the currents in the control loop from the power loop and to avoid problems related to parasitic inductance - specifically in the emitter lead.
"The newly introduced TO-247 4 pin package has an extra connection to the IGBT’s emitter, labeled E2 inFigure 3. This point shall be connected to the gate driver as shown in Fig. 3. Also known as Kelvin emitter terminal, this pin is not subject to the attenuation coming from the power loop. The current coming from the IGBT’s collector is solely conducted by the power emitter lead E ''

Simple and smart. Confusingly though, the application notes for this specific transistor call the pin K, not E2, as in the diagram below!
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Old 6th Mar 2021, 8:52 am   #3
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Default Re: Kelvin emitter pin on TO247 package?

Looks fun Al, so what does one do with the k terminal?

Andy.
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Old 6th Mar 2021, 10:20 am   #4
Ed_Dinning
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Default Re: Kelvin emitter pin on TO247 package?

Hi Gents Kelvin terminals were popular on some packages for a while. The reduce the small but sometime problematical resistance and inductance of the main emitter lead and it's load current flow. this allows more accurate current measurement and/ or better snubbering of the device

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Old 6th Mar 2021, 10:43 am   #5
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Default Re: Kelvin emitter pin on TO247 package?

High frequency components can create significant voltages across the inductance of bond wires and emitter pins. If the emitter pin is common to the input signal loop and the output signal loop, this is a form of feedback and reduces the gain the device achieves.

Having an alternate connection right onto the emitter metal on the die allows the input signal loop to have much less path in common with the output signal loop, and the gain thus can be extended higher in frequency.

The IGBT has two raisons d'etre. Bipolars can achieve higher current densities that power mosfets can, so for a given current capability, the IGBT die is smaller and therefore cheaper. Secondly, As a sort of Mosfet-bipolar Darlington, the gain of the bipolar section reduces the needed current capability of the MOSFET, and the smaller MOSFET has much lower gate capacitance, making it easier to drive.

The price paid is a higher saturation voltage

David
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Old 6th Mar 2021, 6:16 pm   #6
Al (astral highway)
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Default Re: Kelvin emitter pin on TO247 package?

Quote:
Originally Posted by Diabolical Artificer View Post
..so what does one do with the k terminal?

Hi Andy, the k terminal is in the control loop.

One side of this loop is the gate; the other side is the k terminal.

I had come across the concept before on IGBT modules, but then the terminal was called E2 to distinguish it from the emitter. This is the first time I've seen the concept in essentially a TO3-sized package.

The arrangement also puts C and E pins on one side of the package and K and G on the other side, separating high-voltage and control elements of the package. This makes it easier to avoid problems in the mechanical design.

Thank you @David and @Ed for your contributions.
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Old 8th Mar 2021, 7:05 am   #7
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Default Re: Kelvin emitter pin on TO247 package?

Ah, so it's it's like a four probe meter, Kelvin of physics fame not handbags and perfume.

Andy.
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