first time here

I would like to ask what is the blown up device on the picture. I think its somekind of diode. I searched the ST site, but I didnt find anything with these markings. The board is from an APC BacUPS 600.

Picture of the device enter image description here

EDIT Thanks for the identification. Do you know of any parts that i can use to replace this one? Sucks that this one is obsolete.

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    \$\begingroup\$ Have a look at the datasheet for STTA206S. That has the marking T51. \$\endgroup\$
    – DiBosco
    Jan 3, 2018 at 15:09

2 Answers 2


As mentioned in the above comment by DiBosco, If you search for ST T51 diode, the datasheet catalogue for the STTA206S will come up.

As per the catalogue this is an ultra-fast high voltage diode.

enter image description here

  • \$\begingroup\$ Thanks for the answer, its obsolete. Can i just replace with some generic HV diode? \$\endgroup\$
    – user173589
    Jan 3, 2018 at 15:35
  • \$\begingroup\$ No problem, glad to help. Depends on the use case. I would suggest checking the main specifications from the above datasheet and comparing to your generic diode. \$\endgroup\$
    – rrz0
    Jan 3, 2018 at 15:36
  • \$\begingroup\$ Yes, well done for copying what I'd already posted. :p You should not just replace with any old diode. It's a superfast device and is probably specified for a reason. Seek out something with the same (or better) characteristics. \$\endgroup\$
    – DiBosco
    Jan 3, 2018 at 15:43
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    \$\begingroup\$ @DiBosco I can reference you in the answer, however I searched using the above keywords which led me to the same result ;) Also you are right in saying that any old diode should not be used, but this still depends on the use case, which the OP has not shared with us. \$\endgroup\$
    – rrz0
    Jan 3, 2018 at 15:46
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    \$\begingroup\$ @DiBosco: This is exactly why, if you're going to post an answer, you should make it an actual answer, not a comment. \$\endgroup\$
    – Dave Tweed
    Jan 3, 2018 at 16:16

Finding the fault that caused the part to fail may be more important than finding just finding a replacement. ST make many newer parts that will work, but I just happened to find one made by Diodes Inc.

Rectifiers 3.0A Ultra Fast Rec 25pF 1000 Vrrm 1.8V

This has lower capacitance and higher Vr (1000V) than original part (600V)