• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 373 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISO5852S: Desaturation protection current value

Rajasekaran
Intellectual 945 points
Part Number: ISO5852S

Dear sir,

we are using ISO5852S gate driver for our inverter. 

Desaturation threshold voltage is 9V. 

Our IGBT saturation voltage is 1.85V. When Vce is above 1.5V,we wish to turn off the pulses. 

we are using 5qty of US1NWF-7 fast recovery diodes. As per the datasheet  of US1NWF-7, the forward votlage drop as 1.5V for 1A current. But when we measure the diode votlage drop using multimeter, we are getting 0.48V only. 

For desaturation detection, How much current will flow through the diodes and how many diodes may required to detect the desaturation condition of 1.5V. 

Thanking you.

Thanks & regards,

Rajasekaran.

  • 0
    TI__Expert 4875 points

    Hi Rajasekaran,

    The DESAT pin sources 0.5mA of current, so the forward current through the diodes is about 0.5 mA. So in this case the forward voltage will be very small just like you have measured. You would need many HV diodes in this case. 

    That seems to be a very low DESAT detection voltage. Can you please share the IGBT part number? The DESAT voltage threshold should be chosen based on the VCE voltage at the short circuit current, not the typical saturation voltage. Please see this related e2e thread which talks about choice of DESAT threshold voltage and how to reduce it if necessary.

    Regards,

    Audrey

  • 0 in reply to Audrey Dearien7
    Intellectual 945 points

    Dear sir,

    Our IGBT Module is FP75R12KT4.

    Our load current value is 20A and we wish to turn off the IGBT whenever the load current exceeeds 40 ~ 45A. 

    Kindly guide us to select the suitable zener + ultra fast recovery diode combination to protect the device from short circuit condition. 

    Thanking you.

    Thanks & regards,

    Rajasekaran. 

  • 0 in reply to Rajasekaran
    TI__Expert 4875 points

    Hi Rajasekaran,

    It is not recommended to perform overcurrent detection using the DESAT method, especially so close to the typical VCEsat level. There would most likely be false triggering with the threshold so so close to the typical voltage. The IGBT you have shared shows saturation at ~5V if you are using VGE of 13V. This would be a more suitable detection threshold to protect the IGBT. If you are just trying to sense overcurrent, I would recommend a current sense amplifier.

    To reduce the threshold from 9V to ~5V, you can use three STTH112A diodes in series. 

    Regards,

    Audrey

  • 0 in reply to Audrey Dearien7
    Intellectual 945 points

    Dear sir,

    Thanks for your support. now we can use the desaturation protection. 

    Thanks & regards,

    Rajasekaran.