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User17669
Level 1
5 questions asked First question asked First reply posted
Level 1
Hi guys,

I am looking at the datasheet for IKW40N120T2. Can you please explain how to understand the parameters and conditions of the short circuit rating?

Thanks in advance,
nick
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_Klaus
Moderator
Moderator 10 replies posted First comment on blog 10 sign-ins
Moderator
Hi Nick,

the data sheet specification

4147.attach

basically says that the IGBT survives a low-ohmic short circuit for at least 10µs if all of the following conditions are met
*) the gate voltage is 15V
*) the bus voltage is <= 600V
*) the initial junction temperature is <= 175
(initial means prior to the SC event)

Please note that for higher gate voltages or bus voltages the short circuit withstand time reduces.

"Low ohmic" short circuit means that only the IGBT limits the short circuit current (no other inductance or resistance). Thus, the full bus voltage is on the IGBT while it is conducting the SC current. Since this means a (very) high power dissipation, the duration of the event is limited to 10µs. In this time, the short circuit needs to be detected and turned off in order to avoid a damage to the device.

More information can be found in this application note (p. 21-23)

Hope this helps!
Best regards,
Klaus

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3 Replies
_Klaus
Moderator
Moderator 10 replies posted First comment on blog 10 sign-ins
Moderator
Hi Nick,

the data sheet specification

4147.attach

basically says that the IGBT survives a low-ohmic short circuit for at least 10µs if all of the following conditions are met
*) the gate voltage is 15V
*) the bus voltage is <= 600V
*) the initial junction temperature is <= 175
(initial means prior to the SC event)

Please note that for higher gate voltages or bus voltages the short circuit withstand time reduces.

"Low ohmic" short circuit means that only the IGBT limits the short circuit current (no other inductance or resistance). Thus, the full bus voltage is on the IGBT while it is conducting the SC current. Since this means a (very) high power dissipation, the duration of the event is limited to 10µs. In this time, the short circuit needs to be detected and turned off in order to avoid a damage to the device.

More information can be found in this application note (p. 21-23)

Hope this helps!
Best regards,
Klaus
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User22501
Level 1
Level 1
Hello _Klaus,

When you write "bus voltage," do you mean

1. The voltage impressed across an individual IGBT, or
2. The DC link voltage of the network of two IGBT connected in a half-bridge.

Request you to clarify the same.
Thanking you,
Aditya
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_Klaus
Moderator
Moderator 10 replies posted First comment on blog 10 sign-ins
Moderator
Hi Aditya,

I assume you speak about a half-bridge configuration and not a multi-level converter. In such a half-bridge configuration you can have a short circuit condition, where both switches share the bus voltage fifty-fifty: a perfectly symmetric shoot through in one bridge leg (e.g. due to some mistake in the control). But it does not have to be like that:

  • Shoot-throughs do not have to be perfectly symmetric: certain tolerances (switch, gate voltage, ...) can lead to a more or less severe asymmetry in a shoot through; transient effects (e.g. a pull up of the gate voltage by several volts via Cres) can lead to a situation where the full bus voltage is present on just one device of the half-bridge.
  • A short circuit is not necessarily caused by a shoot through in one bridge leg - many other types are possible: ground shorts, winding failures, ...


We test according to standards such as the IEC 60747-9, for instance. Those standards do not consider a specific topology such as a half bridge - the full voltage is impressed on one switch. This corresponds to your case #1, see also page 20 of the AN2011-05.

However, thinking about all the potential short circuit situations, I strongly recommend to treat the specified voltage as DC link voltage in your design.

Hope this helps!
Best regards,
Klaus
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