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In order to protect against ESD and overvoltage at a charger input, I would like to know if it is recommended to use TVS and Zener on the same circuit, if so, what would be the configuration?

The intention is to meet the requirement of IEC 61000-4-2, but also to protect the system if an unsuspecting person connects a charger of 12V or more, instead of 5V.

The Reverse Standoff Voltage of the chosen TVS is VRWM = 5V, and the Clamp Voltage for the TLP 16A graph is Vc = 11V.

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  • \$\begingroup\$ A TVS diode is essentially a zener, so having both is most likely unnecessary. You might want to consider having a polyfuse in series to protect the TVS diode in case of reverse or over voltage. Chose the TVS size so that it survives such conditions. \$\endgroup\$
    – Kartman
    Commented May 11, 2021 at 2:00

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This is a great question, I have asked a similar question before, but got no answers. With that said, that was a more philosophical question and yours is more to the point.

However: I have a solution that have been tested on multiple occasions to IEC 61000-6-2

(note; IEC 61000-4-2 is just the method; the actual requirements would be in a different standard)

The simple thing to do would be to protect the TVS diode, typically with a polyfuse, so that it can survive a DC overvoltage, but that defeats the entire purpose of the TVS: Any component in series with the TVS is going to face the full fury of the surge pulse. I have not found any polyfuse rated for surge currents of several hundred amperes.

My solution has therefore been to rate the TVS so that a destructive DC overvoltage is unlikely. In your case that would perhaps be 15V. Then you need to have a secondary overvoltage protection. You can do as you describe and use a zener and the previously mentioned polyfure, but I find it more elegant to use an overvoltage lockout. As you are working on 5V you have lots of options available in the form of Efuses.

With all that said I have claimed before on this site that a polyfuse is quite common to place infront of the TVS, (That claim was shot down the last time, yet it is the first comment here) so I am curious to get more input on this.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ You can put a cap in parallel to the fuse. Long term harsh DC inputs are still likely to kill the fuse though. \$\endgroup\$
    – tobalt
    Commented May 11, 2021 at 11:26
  • \$\begingroup\$ @tobalt Good point, that would certainly be useful against ESD and EFT, assuming it is suitably rated. I am uncertain if there are practical capacitors on the marked that can be of use during a surge puls. (There are capacitors, but the cost and dimensions of those puts them out of scope for most practical purposes) \$\endgroup\$
    – Arcatus
    Commented May 11, 2021 at 12:33
  • \$\begingroup\$ Thank you! I didn't know eFuses yet, I loved learning about them, and I feel more comfortable using them than putting a TVS and a Zener in parallel. Thank you for sharing your knowledge, it was of great help. \$\endgroup\$
    – Chelssinha
    Commented May 11, 2021 at 17:30

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