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I looked through a few inductors' datasheets and in none of them is the maximum voltage specified. Even Mouser does not let you filter inductors by voltage. Why is that? Is inductor voltage "not important"? How could I know, what voltage can be applied to this inductor?

I need >400V inductor, because I am building a boost converter. I already have reached >70V, but I stopped because of given reason.

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    \$\begingroup\$ Just as capacitors are specified for maximum voltage and not current, inductors are specified for maximum current and not voltage. \$\endgroup\$
    – Barry
    Sep 4, 2021 at 18:35
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    \$\begingroup\$ This is a really good Q. If you were making a line filter choke for example you’d want to know the insulation strength of the coil. Resistors have voltage ratings for the same reason. +1 \$\endgroup\$ Sep 4, 2021 at 18:45
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    \$\begingroup\$ @Barry Many capacitors do have a ripple current spec, though, relating to self-heating and ESR. \$\endgroup\$
    – Hearth
    Sep 4, 2021 at 19:55
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    \$\begingroup\$ Can you update your question to include the specific part number you are looking at? Datasheet is for a range of parts, and the datasheet link may go bad over time. Also, please update your question to explain where the 400 V will be applied (across the two terminals of the inductor, or from GND on the PCB to both terminals on the inductor, or where?) \$\endgroup\$
    – mkeith
    Sep 4, 2021 at 22:40
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    \$\begingroup\$ What voltage are you boosting up from? Boost ratios greater than around 6:1 are typically very difficult. You might look into using a transformer or an auto-transformer instead of a simple inductor. \$\endgroup\$
    – mkeith
    Sep 6, 2021 at 0:27

3 Answers 3

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If the inductor voltage is not specified, you can assume it's limited to 50 V or thereabouts of standard enameled copper wire.

An inductor that can handle the voltage you want will be explicitly specified for it. Look at some more data sheets, or contact the manufacturers directly.

Depending on the number of parts you want, you could also consider winding your own, using wire with an appropriately specified insulation.

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    \$\begingroup\$ It would be quite difficult to get 50V across adjacent turns of the coil, I think. \$\endgroup\$ Sep 5, 2021 at 15:39
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    \$\begingroup\$ Turns can be physically adjacent without being electrically adjacent \$\endgroup\$
    – Frog
    Sep 5, 2021 at 21:31
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How could I know, what voltage can be applied to "this" inductor?

If you are talking about the voltage across the inductor then you need to factor in the frequency of the applied voltage and the maximum current that the data sheet states.

$$V = L \dfrac{di}{dt}$$

So, do a little maths and work out what this voltage might be given the operating frequency (and therefore a strong hint to \$\frac{di}{dt}\$). You should also consider that this type of inductor will not be recommended for above a certain frequency (see self resonance) and this further constrains you in \$\frac{di}{dt}\$. If the self-resonance frequency isn't specified (or derivable) then my rule is (and I firmly stand by it) is don't use it.

And if you are still intent on using it and don't have the data, speak with the supplier.

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    \$\begingroup\$ The ask is similar to ‘hipot’ for a transformer. This has little to do with the voltage between the ends of the coil, and everything to do with the voltage between the coil and its surrounding environment. \$\endgroup\$ Sep 4, 2021 at 19:24
  • \$\begingroup\$ @hacktastical I disagree \$\endgroup\$
    – Andy aka
    Sep 4, 2021 at 19:25
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You likely don't have 400 V between the terminals of the inductor; perhaps you have 400 V between any terminal and another part of your circuit (ground ?).

The high voltage insulation capability of these inductors is not specified; in high voltage applications you will need to ensure through spacing and perhaps additional insulation that your specification (and safety requirements) are met. You must assume negligible performance of the plastic protection wrapper on the inductor.

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  • \$\begingroup\$ A boost converter applies the storage inductor across the full input voltage and across the difference between the input and the output voltage. In case the output is 400V, the optimal case would be an input of 200V, and the voltage across the inductor will be 200V during charge and discharge. 400V sounds like PFC, and in that application, the input voltage varies between 0V and 330V, so the inductor voltage will be between 70V and 400V. \$\endgroup\$ Sep 6, 2021 at 9:48

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