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In shown schematic, I would like to know by any chance or cause if Zener D9 will get damaged. If yes what are all possibilities?

FSK signal consist of 3Hz and 6Hz signal all together.

  • \$\begingroup\$ @KingDuken, link Out will go out of the board to different board which is consist of FSK discriminator ( converting to digital ) and share the same GND. As I mentioned in schematic it will have load 500mA max wrt GND. \$\endgroup\$
    – Micro
    Commented Aug 22, 2019 at 15:33
  • \$\begingroup\$ It helps if you explain the background to your question. I'm guessing you've got boards where D9 keeps failing? The better the quality of your question, the better the quality of the answers you will attract. \$\endgroup\$
    – TonyM
    Commented Aug 22, 2019 at 16:17
  • \$\begingroup\$ I am doing FMEA, just making sure everything works correctly. \$\endgroup\$
    – Micro
    Commented Aug 23, 2019 at 8:49

1 Answer 1


If the output is suddenly shorted the zener current is not limited. It will carry the charge current of the 4.4uF level-shifting capacitance.

Something similar might happen if the higher supply voltage is suddenly applied and the load is low-Z.

  • 1
    \$\begingroup\$ Exactly same thing I was thinking, that't why I marked both caps. \$\endgroup\$
    – Micro
    Commented Aug 22, 2019 at 15:43
  • \$\begingroup\$ I am thinking to use TVS in place of zener here. \$\endgroup\$
    – Micro
    Commented Aug 29, 2019 at 14:33

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