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Q&A

MOV vs TVS diode

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Simple thing that I realized I should know but do not -- when is an MOV preferable to a TVS diode (with some associated network to really make it work, in both cases)? Is it even something to routinely check as an option in e.g. 24V DC systems?

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You really have to compare datasheets. There are some general differences, but you shouldn't go by those in specific instances.

MOVs usually have softer knees, are available at higher voltages, and are available for dissipating higher powers. Usually. One drawback of MOVs that they get "used up" a little bit each spike they absorb. On the other hand, they may be available at temperatures where TVSs can't go. Another parameter to consider is off-state leakage, and how that varies over temperature.

Again, look at what's available for your application. What is your threshold voltage? How much current must the device be able to conduct to clip the voltage? How much energy must it be able to dissipate each spike? Does off-state leakage matter? What temperature range will this need to work over?

Once you have candidates that match all your criteria, read the datasheets, check the prices and availability, and compare.

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  • MOV are bidirectional components suitable for both AC and DC circuits, TVS are most often unidirectional, despite bidirectional TVS are also available;
  • conducts more current compared to TVS diodes (in general);
  • dissipates energy in a solid material and not in a junction.

I would use a MOV where I need to dissipate a lot of power. But that's just a declaration of principle. The detailed answer of Olin is the right way.

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Comment regarding the first bullet. A unidirectional TVS protects in both directions, just not symmetrically. It clamps at a much lower voltage in the other direction. (On Semiconductor application notes AND8231/D and AND8424/D.) Nick Alexeev‭ 3 months ago

Of course, this is a stupid diode in the other direction, but that's not what is needed in general for AC circuit (otherwise, use a diode). coquelicot‭ 3 months ago

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