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Recently I discovered, that some IGBT transistors in IGBT modules have the second pin for an emitter, called auxiliary emitter.

enter image description here

In the picture above 2nd and 4th pins are auxiliary emitters. This is from the datasheet to FS100R17N3E4 module.

However, I did not find any information about what are these pins used for, except that IGBT gate driver is connected to both 1-2 and 3-4 pins, but I do not understand why.

Could someone please recommend any literature on this problem? I would like to have a strong understanding of IGBT transistors and their drivers.
Is there any difference between 2nd and 27, 28, 29 pins, since they are at the same potential?

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    \$\begingroup\$ 2 and 4 are for sure small signals, 27,28,29 are high current. It makes easier to mount and separate gate driver part from high current output. \$\endgroup\$ – Marko Buršič Feb 28 at 11:23
  • \$\begingroup\$ thank's for answering me! How is it possible, that current does not flow through 2 and 4 pins into gate driver? Does the gate driver have high input resistance? \$\endgroup\$ – litvinik Feb 28 at 11:30
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To measure the voltage at the junction without the lead voltage drop.

This is used so that the gate voltage can better be controlled.

Since IGB can have pretty high current, even a small lead resistance can cause significant voltage drop, you can make sure to drive the IGBT at its maximum switching capacity, without the risk of destroying it by having a voltage on that gate that is too high.

They are called Kelvin point, like on this device: datasheet.

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  • \$\begingroup\$ As I understand, measuring emitter voltage helps us in setting the Vge voltage to turn on-off IGBT, right? \$\endgroup\$ – litvinik Feb 28 at 10:30
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    \$\begingroup\$ Yes, since IGBT can have pretty high current, even a small lead resistance can have a significant voltage drop. With advanced control you can make sure you apply the maximum gate voltage to switch properly without risking to destroy it. \$\endgroup\$ – Damien Feb 28 at 10:36
  • \$\begingroup\$ Thank you so much! You helped me to understand the functionality of IGBT module \$\endgroup\$ – litvinik Feb 28 at 10:39
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    \$\begingroup\$ Welcome, I'd like to add as well that since it's a module connected with leads, you may have long leads and thus even increasing this effect. \$\endgroup\$ – Damien Feb 28 at 10:40
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    \$\begingroup\$ I remembered, that we studied the four-wire measuring, so I guess it is the same situation here with IGBTs \$\endgroup\$ – litvinik Feb 28 at 10:43
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These are used for measurement purpose and driver reference. Due to the high current and high transients you can have already quite noticeable voltage difference between the auxilliary emitter and the power emitter.

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    \$\begingroup\$ So auxiliary emitter is taken as the "real" emitter of IGBT, because power emitter pin has different potential due to the high currents, voltages and the resistance of the wire? \$\endgroup\$ – litvinik Feb 28 at 10:32
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    \$\begingroup\$ It's taken as reference point for measurement and gate control, don't know if it's right to call it "real" emitter. \$\endgroup\$ – po.pe Feb 28 at 10:35

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