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50uH PTKM series inductor OK for 70khz boost converter?

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treez

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Hello,
API Delevan dont provide delta B vs frequency graph for PTKM series inductors...will the PTKM50-894 be OK for use in a 70khz boost converter?

PTKM series inductors.
http://www.delevan.com/web/PDF/PowerInductor/RadialLeaded/PowerChokes/Page107_108_PTHF.pdf

Do you know if PTKM is ferrite or powdered iron, or other?

Am i right to assume that the lower the current in the PTKM inductor, the higher the inductance? In other words, the PTKM series are non-linear inductors.
 

Most of these types of chokes are designed to carry large amounts of dc, with very little ac voltage across the winding. In other words high frequency ripple reduction for dc filtering applications.

The fall off in inductance with rising dc current is typical of lower grades of powdered iron used in these types of applications, its an ideal material for high dc current, low ac voltage applications.

How well it will work in a boost converter largely depends on the ac voltage across the winding and the operating frequency, as core heating will be the limiting factor.

If its an unusually low voltage boost circuit, you might be in with a chance. If its running at a higher voltage, especially at 70 Khz, the core material will probably rapidly burn up from combined core losses.

You can always just try one in your circuit and see.
 
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Thanks very much Warpspeed, i now think we will have to just do a custom wound inductor on some off the shelf ferrite core pieces. we are boosting 9v to 300v over and over (cap discharge repetitively). There is about 1.5A of ripple pkpk and average current is 7A in the inductor. Its actually a cascaded boost, as used in the "down hole" industry for high step up ratios without transformers. This inductor is the upstream one.
 

300v at 70Khz is gapped ferrite territory.

You will probably need a suitably large cross sectional area to keep the turns down, to keep self resonant frequency high enough.
But its certainly doable, and need not be large or expensive.
 
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Power inductors need air gaps, gapped ferrite toroids are rather unusual so you can safely assume that the API toroid chokes are powder cores. According to other datasheet comments I expect a xx-iron alloy, similar to other major powder core vendors.

I wonder if API provides meaningful data on request, or if all customers are working on a creative trial-and error base?

Recently a customer of mine was really surprised by the high losses of industry standard powder cores and had to redesign a converter with ferrite cores. It's O.K. if you have sufficient time for empirical evaluation otherwise I would rely on quantitative core data.
 
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Sometimes from a photograph you can identify the core material by colour, assuming its a micrometals core, which is very often the case.

You can then use micrometals core loss data which provide some loss data for volt microseconds per turn for different materials. You may even be able to eyeball the actual turns from a picture, most of these are single layer windings of fairly thick wire.

The core losses are frighteningly high for the more common low cost materials.
I don't fancy your chances of being able to use these dc filter chokes for any high voltage high frequency application.

There are plenty of gapped ferrite core geometries to choose between, any of which should work for you.
 
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