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4th September 2019, 22:16 #41
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5th September 2019, 16:07 #42
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Re: Inductor quality value for switching regulators
Easy peasy is obviously referring to AC resistance caused by skin and proximity effect of the winding.
1. You cannot define an AC resistivity because it depends on the geometry of the conductor. A foil or a cylinder with same crosssectional area will have different "resistance"
2. The skin depth is actually dependent on the DC resistivity this suggests that these two quantities cannot be independent parameters.
3. The terminology is wrong (IMHO); the wikipedia says: (Screenshot image)
4. it is rarely called AC resistance because it is also responsible for the inductance of the conductor.
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6th September 2019, 01:14 #43
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Re: Inductor quality value for switching regulators
it is rarely called AC resistance because it is also responsible for the inductance of the conductor.
for a single straight wire, AC resistance can be defined pretty exactly, as can it's self inductance,
AC resistance is called just that by the majority of power electronics engineers working in the field ...
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6th September 2019, 04:01 #44
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Re: Inductor quality value for switching regulators
for a single straight wire, AC resistance can be defined pretty exactly, as can it's self inductance,
Real part of the (complex) impedance is conventionally called the resistance but it has poor physical significance (because of the strong dependence on the geometry and other environment).
Unfortunately I do not have most of my old books.
Many power transformers use rectangular wires (some use thick foils) for winding; it is impossible (if my memory is correct) to derive any analytical formula for (the impedance) these cross sections. But the effect (the skin effect) is still there.
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6th September 2019, 08:25 #45
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Re: Inductor quality value for switching regulators
Please remember that the thread topic is about inductor quality values, or more generally speaking, about it's frequency dependent complex impedance. The contributions about "AC resistance" are clearly referring to the inductor impedance (in this case it's real part), not general properties of the conductor material. While skin effect describes the frequency dependent behavior of a straight wire, proximity effect handles the interaction with other parts of the winding.
There's a complete chapter in Snelling, Soft Ferrites about properties of the winding, see https://www.edaboard.com/showthread....ticproperties
Proximity effect in foil windings is overseeable, you can assume an almost uniform current distribution in many cases.
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