A camera will be mounted outside and powered via POE to Aruba 2540 network switch. I don't want indirect lightning surge to travel into the network switch. I don't care if the camera gets destroyed.

The ethernet line to line voltage is 54V, and the requirement that I have is that the TVS should clamp lighting surge upto 2000V or 400Amps.

What kind of circuit would I need for lightning protection with a TVS?


1 Answer 1


A TVS diode is probably not going to be enough to protect your equipment from a surge caused by lightning. Generally you'll want to use gas discharge tubes to take the brunt of the surge, then either inductors or dedicated Bourns TBU surge protectors, followed by TVS diodes to minimize the residual surge. Here is a fairly standard surge protection scheme that is used all over the place for exactly this purpose:

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Obviously you'll need to change the values of the TVS diodes, but this should give you an idea. Also, if your system doesn't mind a slightly higher series resistance, replace the inductors with TBU surge protectors, as I mentioned earlier.


Note that this is a double-sided protection circuit, meaning it can protect against surges from either direction. If this protection circuit is to be placed right next to the device which is to be protected, you may eliminage L3, L4, and SA2. Keep TZ1, TZ3, and the earth connection between them though. The device being protected should then be connected where L3 and L4 used to be, across TZ2 and TZ3.

  • \$\begingroup\$ If I were to use any components , it will ask me for a clamping voltage. Do I measure the voltage between line to line or line to ground for Voltage clamping? \$\endgroup\$
    – Kasap23
    Oct 25, 2019 at 1:47
  • \$\begingroup\$ I measured the line to line voltage and found that it is 54V. Does that mean I need a component with 54V as its clamping voltage? \$\endgroup\$
    – Kasap23
    Oct 25, 2019 at 1:48
  • 1
    \$\begingroup\$ @Kasap23 Probably the reverse standoff voltage, not breakdown. TVS diode thresholds are not exactly precise so you want to ensure that it never breaks down in the normal operating range. Reverse standoff/holdoff voltage is what it is guaranteed to not break down. Breakdown is when it starts to conduct. And clamping is the voltage drop when it is conducting a specified amount of current. \$\endgroup\$
    – DKNguyen
    Oct 25, 2019 at 1:53
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    \$\begingroup\$ My apologies for the delay. The 230V label on the gas discharge tube is indicating the DC spark-over voltage, showing when the GDT is intended to start conducting. Once it conducts, the voltage seen by the rest of the protection circuit is simply the voltage drop across the arc within the tube, which is relatively low. This is how the GDT takes the brunt of the surge. As for the 7.5V TVS value, that is the reverse standoff (working) voltage of the device. Our product is designed to handle 7.5V, so we don't want the TVS conducting during normal operation \$\endgroup\$
    – DerStrom8
    Oct 25, 2019 at 10:37
  • 1
    \$\begingroup\$ @DerStrom8 Oh, that's the symbol for a gas discharge tube? I thought it was a mains plug lol. The really low TVS voltage makes more sense now. \$\endgroup\$
    – DKNguyen
    Oct 25, 2019 at 13:17

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