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[SOLVED] The maximum voltage rating of Buck converter Inductor

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francis29

francis29

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Hello,
Buck converter.jpg

Let's consider this buck converter has 300V as input and designed to have 50V as output.
What is voltage rating of the inductor I should use?
During the ON time of the MOSFET the Inductor experiences 300V-50V=250V. So should I use
inductor that has voltage rating of 250V or more?
I have seen some reference designs ( tested as well ) that uses lesser voltage
rating inductor ( Ex: uses 120V rating for 500V input and 15V output buck converter ).
 
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Maximum voltage is 300V at startup, in case of doubt the inductor should be rated for it.

Do you have inductors with voltage rating? Most off-the-shelf sorage inductors don't have any voltage rating. A few are explicitely specified for high voltage operation.
 
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Yes, the offtheshelf ones rarely have voltage rating.....but since they are almost all wound with standard enamelled copper wire, you tend to assume that they are rated for at least a few hundred volts. So 300V would be fine for any of them. Note of warning though...some fine wire enamel of a certain type is not rated highly in voltage at all...you just have to hope your inductor doesnt use this.......other way is to wind your own inductor...using your own spec'd enamel copper wire.

See the LNK302 literature from power integrations....they have inductors listed there for the 400V rating thats needed for their application
 
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Search for high voltage rated inductors, a very few of the manufacturers rate then to 300 - 500V

It is a common fault in dishwashers etc that only use a buck supply off the mains, after a few years the L breaks down and the psu gives up the ghost ....
 

    francis29

    francis29

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Thank you all for your valuable comments. So my understanding from this is, when we have to use inductor for high voltage the only concern is the isolation resistance of copper wire coating and isolation between the two pins of the inductor.

I think even though the inductor experience high voltage as a whole, between the each turns there won't be much of a potential difference ( if there is too much number of turns ), correct me if I am wrong.

If possible can you please suggest some high voltage rated ( 400V, 900V ) inductor series?
 

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Hi
francis29 said:
between the each turns
Click to expand...
But from layer to layer the voltage is much higher. And the isolation is rather thin.

And it's not the resistance that's the problem, it's the possible arcing.

Klaus
 

    francis29

    francis29

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The below shows voltage rating of various sizes of enamelled copper wire...

Technical Data by Size | ELEKTRISOLA

www.elektrisola.com www.elektrisola.com

...the voltage ratings seem unbelieveably high, but it must be correct i guess.......the coating of enamel of a 0.1mm enamelled wire must by absoliutely microscopic...so its amazing that it has a breakdown of some 500-1300v, depending on its "grade".

The one inductor shown kindly by FvM in post #8 is the only inductor offtheshelf with a voltage rating....i know this because we found out when we did a LNK302 buck, and we had to use that family of parts.
 

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    francis29

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