VS-GP250SA60S IGBT suitability - no flywheel diode

[Unrealeous]

I've just come across some potentially cheap 2nd hand IGBT's for a small/medium DRSST build, but noticed that they don't have a flywheel diode.

Is this a deal breaker - or can I just add external diodes across the collector/emitter junction.

Here's a link to the datasheet https://datasheetspdf.com/pdf-file/1314335/Vishay/VS-GP250SA60S/1

[Unrealeous]

I'm not sure if the lack of response means that my question is a dumb one or if people generally don't have an opinion.

So, in the interests of science and the fact that I can't resist a bargain (I realise why those IGBt's are going cheap - they are now discontinued),  I've decided I'm going to add some some of these diodes and give it a go.   https://www.infineon.com/dgdl/IDW100E60_V2_1.pdf?folderId=db3a304412b407950112b408e8c90004&fileId=db3a304412b407950112b438da286bba

600V, 100A with 400A pulse...

I've built a few SSTC, this is my first attempt at a DRSSTC, so now doubt I'll blow a few things things up along the way.  Will report progress as it happens.

[AstRii]

I'm not sure if the lack of response means that my question is a dumb one or if people generally don't have an opinion.

I think there are none dumb question and if there were, this would surely not be one of them. Sometimes you just need to give it a bit more time.

Is this a deal breaker

It is a huge deal breaker, those diodes carry the primary energy back to bus capacitors during ring-down. They basically act as a full bridge rectifier (assuming full bridge of transistors).

or can I just add external diodes across the collector/emitter junction

I've seen people doing this in SSTCs, however I see no reason why it should not work for DRSSTC as well. Just make sure to place the diodes as close as possible to the IGBT (ideally directly on the terminals of the IGBT)

[Unrealeous]

Bridge is built.  Diodes are directly on the terminals of the IGBT as recommended.

[Hydron]

I also don't see why it wouldn't work, though I'd be very careful about using pulse skipping or any other modulation that puts extra stress on the diodes (beyond the rundown phase they're going to be active during regardless).

[davekni]

I also don't see why it wouldn't work, though I'd be very careful about using pulse skipping or any other modulation that puts extra stress on the diodes (beyond the rundown phase they're going to be active during regardless).

I certainly agree with avoiding pulse skipping etc.  Even in normal operation, be careful of high enable pulse frequency.  Diode power capability is <4W average without heatsinking.  Depending on primary current at end of enable pulse, ring-down duration, and enable pulse frequency, wouldn't be too hard to exceed 4W.