Designing acpl-337j desaturation circuitry

The ACPL-337j has it built in so you dont have to worry about it.

• Integrated Fail-Safe IGBT Protection
  • DESAT Detection, “Soft” IGBT Turn-off and Fault Feedback
  • Under Voltage Lock Out (UVLO) Protection with Feedback

https://www.broadcom.com/products/optocouplers/industrial-plastic/isolated-gate-drive-optocouplers/highly-integrated-sma…

Thank you for fast reply. I know thak acpl-337j has it implemented but I want to know what diodes should I use as DESAT diodes and false fault prevention diodes (last page of datasheet). Correct me please if I'm wrong but I assumed that theese diodes are additional external components between pins 14 and 13 (false fault protection diodes (schotky and zener)) and betwen pin 14 and IGBT colector (regular diode and zener diode).

Thank you.

DESAT protection is built in to trigger a fault condition at 7V - Vf. Additional diodes can be added if you wish to change this fault condition.

If you wish to change the fault condition you would have to specify what your new fault condition is before selecting diodes and then work them out with the value sums on that page of the datasheet.

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datasheet quote

The value of VCE  that triggers DESAT to signal a FAULT condition is nominally 7  V –  VF. If desired, this DESAT threshold voltage can be decreased by using multiple DESAT diodes or low-voltage Zener diode in series. If n is the number of DESAT diodes, the nominal threshold value  becomes VCE,FAULT(TH)  = 7 V – n  × VF. If a Zener diode is used, the nominal threshold value becomes VCE,FAULT(TH)  = 7 V  – VF  – VZ.  When using two diodes instead of one, then diodes with half of the total required maximum reverse-voltage rating may be chosen.

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I think the built in protection is pretty general purpose, you would need to know what your expected fault condition was before you start adding diodes.

Oh, great! Looks like my reading skills are my largest promlem. So conclusion is that for driving some general purpose IGBTs and MOSFETs no diodes are required at all. Additional diodes are required only for cases where specific DESAT threshold is required. So is it ok if I wire everything up without diodes and look at short circuit current waveform (over IGBT) with scope and then if too large current is present for too long, I then put some diodes to reduce treshold.

Thanks.

Yes thats the way I'd go about it some people prefer doing the math for everything in the system but the hands on approach of wiring it up and testing is more fun!

I will try then. Thanks a lot!

I will try then. Thanks a lot!