How do I arrange my circuit so that the TVS diode can do its ESD/transient job, without being fried in the miswiring/overvoltage scenario?

I have an analog 0-5V output that needs protection from miswiring, transients and ESD. My understanding is that TVS diodes are good for transients/ESD because of the quick response time, and Zener diodes are good for overvoltage because of the greater power dissipation capability.

However, TVS diodes need to be as close to the edge of the board as possible, and are typically the first line of defense in circuits I've seen:

Analog Input protection circuit

In the circuits below, D1 is the Zener, D2 is a reverse voltage Schottky, and D3 is the TVS diode.

Circuit 1: If I place the TVS diode (D3) out front, the miswiring scenario will fry it.

Analog output protection with overvoltage and TVS:

Analog Output Protection with Overvoltage and TVS

Circuit 2: If I place the TVS diode (D3) next to the Zener (D1), it is protected from the DC overvoltage. But it seems useless since R2 will be hit with the ESD pulse and it will limit the current into D3.

Analog output protection with TVS protected by Zener:

Analog Output Protection with TVS protected by Zener

Circuit idea 3: Just eliminate the TVS (D3) since the resistor can limit the ESD pulse and D1 can handle it. Maybe throw a capacitor or inductor by D1 to slow things down?

Analog Output Protection with Overvoltage and TVS Simulation

Source for TVS circuit image above.

  • 1
    \$\begingroup\$ You would want to consider leakage current and the ‘knee’ of the zener curve - tvs and zeners aren’t on or off. As you approach the zener voltage the current increases. In an analog circuit this may cause errors. For protection purposes the TVS diode should be adequate. Like a zener, they are thermally limited. You might want to consider if the over voltage condition are handled by the clamp diodes and ESD by careful choice of capacitor. \$\endgroup\$
    – Kartman
    May 19, 2021 at 5:03
  • \$\begingroup\$ So if I add a capacitor by D1, the capacitor and R2 will slow down the transient enough that the slow Zener diode can clamp it? And then D3 the TVS is not needed? It seems to work in simulation: E.g. tinyurl.com/yevxsslz \$\endgroup\$ May 20, 2021 at 18:58
  • 1
    \$\begingroup\$ Note that if you put 15kV across the average ‘real’ resistor that it most likely will flash over and become very low ohm. Again, beware of the zener - 1mA across 1k equals 1 Volt. \$\endgroup\$
    – Kartman
    May 20, 2021 at 21:52
  • \$\begingroup\$ @Kartman is there a way to protect against both DC overvoltage and 15kV transients/ESD? Or do we have to choose one or the other? \$\endgroup\$ May 28, 2021 at 21:53
  • 1
    \$\begingroup\$ Of course you can have both, but the devil is in the detail - especially with an analog signal as leakage with zeners, TVS diodes and varistors needs to be considered. Circuit layout also needs to be considered. \$\endgroup\$
    – Kartman
    May 28, 2021 at 23:26


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