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I am struggling to understand how this circuit should work: enter image description here

I understand that inductor in this case is going to reduce the rate of changing current flowing through it, but I do not understand what is going to happen during the transient. Which device should react first?

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The MOV is fast, but not as fast as TVS. So, initally the spike comes to MOV, but it doesn't react. The TVS "opens" very fast and begins to conduct. The inductor limits the current rate of change in the meantime the MOV begins to conduct and absorbs the large portion of the energy. Once the MOV begins to conduct, the TVS is unloaded, so it "eats" only the very beginning of the spike.

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  • \$\begingroup\$ I don't believe it is that easy. I assume that due to the inductor TVS activation might be delayed or maybe never happen? \$\endgroup\$ – Nexy_sm Sep 17 '18 at 13:42
  • \$\begingroup\$ Doesn't care. If there is a residual voltage the TVS will conduct, the MOV has to take the sink the major energy because it can dump large energy, but is slow compared to TVS. TVS reacts quick, but also with small delay that's why an inductor is placed before, to delay the signal rise. The residual voltage is then almost the same as TVS rating, but then MOV wakes up and takes the rest. Without an inductor, even the TVS would leave a leading edge of the spike, because it has delayed reaction. \$\endgroup\$ – Marko Buršič Sep 17 '18 at 15:03
  • \$\begingroup\$ And how they should be dimensioned? MOV with lower breakdown voltage? \$\endgroup\$ – Nexy_sm Sep 18 '18 at 8:37

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