Special Purpose Inductor

Question

Tonight as I studied a power supply circuit board I came across an unusual inductor. I can speculate that it is designed for high current and high frequency but I really don't know. I am hoping to learn more about it. Can anyone give me some insight into the reasons for the design characteristic which includes heavy multi-strand wire for the conductor (roughly 1.5 mm diameter 18 AWG?). Here are a couple pictures of the inductor which has a very stable inductance of 100 uH when tested up to 100 kHz.

In the circuit it was in series with the collector of a PNP MJE253 Power transistor.

Any insights would be educational.

Thanks John

Gough Lui · Answer

As far as I know, that would be a Litz wire inductor - part of the reason would be to operate at high frequencies (RF) and not succumb to skin effect issues. See https://en.wikipedia.org/wiki/Litz_wire - Gough

shabaz · Answer

Also, maybe their machines are old and cannot handle hard-to-bend wires : ) e.g. if it's easier to wind multi-stranded wire than thicker single-core. Sometimes I get curious about what goes on in factories.. for example someone gave me a box of 'Fox's' biscuits assortment (Fox's is the name of the manufacturer). I don't usually get them (I live in a town where there is a different major confectionery manufacturer). To me, the entire assortment tastes approximately the same, just different shapes : ) I guess they are re-using ingredients and maybe production runs on same bits of machines : ) The consumer wants variety in an assorted box, and this is a way (it feels to me) to kind-of fake it a little bit : ) Also reminds me (I could be wrong, I think I read it somewhere) that RCA did a lot of work in the development of LCD TFT technology... but then didn't do much with it, because they'd spent a load of money on machines to make TV tubes : ) They obviously must have regretted that decision a few years later..

DAB · Answer

Hi John, It is probably a high frequency choke filter. It would help the high frequency response of the device. DAB

jw0752 · Answer

Hi shabaz, Your biscuit story makes me think of Pasta. John

Gough Lui · Answer

I'm guessing it must have been an expensive piece of kit you managed to get it out of? I've actually not seen any such inductors for power supply stuff before either ... normally for things like RF or something needing high Q-factor - perhaps it was part of a tuned filter of some sort. Would the supply have been subject to/created a large amount of ripple at a particular frequency? (Just thinking out loud) - Gough

jw0752 · Answer

I found something similar from Wurth: https://www.newark.com/wurth-elektronik/74437429203101/inductor-100uh-8-8a-20-shielded/dp/50AC8073?scope=partnumberlookahead&ost=74437429203101&searchref=searchlookahead&exaMfpn=true&ddkey=https%3Aen-US%2FElement14_US%2Fw%2Fsearch John

michaelkellett · Answer

I think it's just a high current inductor. May be intended to operate at higher than 100kHz. It's a little strange to go for Litz wire and the open bobbin, saving loss with one hand and giving it away with the other. MK

Special Purpose Inductor

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