Ferrite Inductor Tolerance
in [Design]
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From: Archimedes' Lever on 12 Jun 2010 18:56 On Sat, 12 Jun 2010 15:48:53 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Archimedes' Lever wrote: >> On Sat, 12 Jun 2010 15:00:59 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> You can get 5% catalog inductors from Delevan, Miller, TDK and several >>> others. If it needs to be more precise then you'd be off to boutique >>> lines, meaning $$$. >> >> >> Nobody needs to be that precise. Nobody here anyway. > > >Ahm, I have been. But that was in the RF world and done with active >laser trim. Sometimes down to 0.25%. Laser trim of an inductor? Small form factor maybe. Anything in the power realm has no need of that level of precision and there are few ferrite formulations that can hold any such tolerance, even merely sitting on the shelf.
From: John Larkin on 12 Jun 2010 19:01 On Sat, 12 Jun 2010 15:34:24 -0700, Archimedes' Lever <OneBigLever(a)InfiniteSeries.Org> wrote: >On Sat, 12 Jun 2010 15:00:59 -0700, Joerg <invalid(a)invalid.invalid> >wrote: > >> >>You can get 5% catalog inductors from Delevan, Miller, TDK and several >>others. If it needs to be more precise then you'd be off to boutique >>lines, meaning $$$. > > > Nobody needs to be that precise. Nobody here anyway. We buy 2% inductors and 1% capacitors to make LC clock oscillators in our digital delay generators. John
From: John Larkin on 12 Jun 2010 19:03 On Sat, 12 Jun 2010 15:00:59 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Ian Bell wrote: >> On 12/06/10 16:07, John Larkin wrote: >>> On Sat, 12 Jun 2010 10:22:59 +0100, Ian Bell<ruffrecords(a)yahoo.com> >>> wrote: >>> >>>> When winding modest inductors of a few hundred milliHenries on a ferrite >>>> core, given Al and a number of turns, what is the typical tolerance on >>>> the actual value of inductance when these are made in quantity? >>>> >>>> Cheers >>>> >>>> Ian >>> >>> An ungapped ferrite core could be all over the place. 25% wouldn't >>> surprise me. They will vary with temperature, too. You can buy gapped >>> pot cores in tolerances around 2-5%, I think. Or use a pot core with a >>> slug adjuster if you need 1% or better. See the datasheets. >>> >>> Powder-type cores can be bought with better tolerances. >>> >>> The people who wind inductors commercially get the exact number of >>> turns every time. >>> >>> John >>> >> >> >> It seems to me there are quite a few factors that could affect the >> actual inductance achieved and perhaps the least of them is the accuracy >> in counting the number of turns. I would expect there to be some >> tolerance in the Al value of the ferrite, that its exact dimensions >> would have an effect along with how neatly or otherwise the turns are >> wound. I have absolutely no idea if these are the major factors nor of >> the likely size of the actual major factors affecting the actual >> inductance. I am just trying to get a feel for the likely tolerance of >> ready made inductors. >> >> The reason I ask is am am designing some passive audio filters and I >> know exactly what tolerance of resistance and capacitance I can obtain >> but not a clue about inductance. It is no good me using 1% capacitors >> and resistors if inductors normally fail to achieve 5%. >> > >You can get 5% catalog inductors from Delevan, Miller, TDK and several >others. If it needs to be more precise then you'd be off to boutique >lines, meaning $$$. > >Example: > >http://www.delevan.com/seriesPDFs/1782.pdf > >But sit down before looking at prices for the F grade (1%), they can run >well north of $10 a piece in small qties and several months leadtime. >Hardly anyone does this stuff for audio anymore since DSPs became cheap. >Last time I designed an analog wideband audio phase shifter was ... ><scratching head> ... oh, about 20 years ago :-) > >If it absolutely has to be analog there's opamp gyrators, maybe that >could work? Sure would be cheaper. Active filters make more sense at audio frequencies. Inductors are big and expensive and have rotten Qs down there, so you have to do a predistorted filter design if you want any frequency response accuracy. PITA. John
From: Joerg on 12 Jun 2010 19:21 Archimedes' Lever wrote: > On Sat, 12 Jun 2010 15:48:53 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Archimedes' Lever wrote: >>> On Sat, 12 Jun 2010 15:00:59 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> You can get 5% catalog inductors from Delevan, Miller, TDK and several >>>> others. If it needs to be more precise then you'd be off to boutique >>>> lines, meaning $$$. >>> >>> Nobody needs to be that precise. Nobody here anyway. >> >> Ahm, I have been. But that was in the RF world and done with active >> laser trim. Sometimes down to 0.25%. > > > Laser trim of an inductor? Small form factor maybe. Anything in the > power realm has no need of that level of precision and there are few > ferrite formulations that can hold any such tolerance, even merely > sitting on the shelf. Well, Ian wrote that his app isn't power but precision audio. Different thing. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 12 Jun 2010 19:32
John Larkin wrote: > On Sat, 12 Jun 2010 15:00:59 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Ian Bell wrote: >>> On 12/06/10 16:07, John Larkin wrote: >>>> On Sat, 12 Jun 2010 10:22:59 +0100, Ian Bell<ruffrecords(a)yahoo.com> >>>> wrote: >>>> >>>>> When winding modest inductors of a few hundred milliHenries on a ferrite >>>>> core, given Al and a number of turns, what is the typical tolerance on >>>>> the actual value of inductance when these are made in quantity? >>>>> >>>>> Cheers >>>>> >>>>> Ian >>>> An ungapped ferrite core could be all over the place. 25% wouldn't >>>> surprise me. They will vary with temperature, too. You can buy gapped >>>> pot cores in tolerances around 2-5%, I think. Or use a pot core with a >>>> slug adjuster if you need 1% or better. See the datasheets. >>>> >>>> Powder-type cores can be bought with better tolerances. >>>> >>>> The people who wind inductors commercially get the exact number of >>>> turns every time. >>>> >>>> John >>>> >>> >>> It seems to me there are quite a few factors that could affect the >>> actual inductance achieved and perhaps the least of them is the accuracy >>> in counting the number of turns. I would expect there to be some >>> tolerance in the Al value of the ferrite, that its exact dimensions >>> would have an effect along with how neatly or otherwise the turns are >>> wound. I have absolutely no idea if these are the major factors nor of >>> the likely size of the actual major factors affecting the actual >>> inductance. I am just trying to get a feel for the likely tolerance of >>> ready made inductors. >>> >>> The reason I ask is am am designing some passive audio filters and I >>> know exactly what tolerance of resistance and capacitance I can obtain >>> but not a clue about inductance. It is no good me using 1% capacitors >>> and resistors if inductors normally fail to achieve 5%. >>> >> You can get 5% catalog inductors from Delevan, Miller, TDK and several >> others. If it needs to be more precise then you'd be off to boutique >> lines, meaning $$$. >> >> Example: >> >> http://www.delevan.com/seriesPDFs/1782.pdf >> >> But sit down before looking at prices for the F grade (1%), they can run >> well north of $10 a piece in small qties and several months leadtime. >> Hardly anyone does this stuff for audio anymore since DSPs became cheap. >> Last time I designed an analog wideband audio phase shifter was ... >> <scratching head> ... oh, about 20 years ago :-) >> >> If it absolutely has to be analog there's opamp gyrators, maybe that >> could work? Sure would be cheaper. > > Active filters make more sense at audio frequencies. Inductors are big > and expensive and have rotten Qs down there, so you have to do a > predistorted filter design if you want any frequency response > accuracy. PITA. > I did get nice results with discarded 88mH toroid inductors from Missy Bell though, built lots of filter with those back at college. Until one sunny day I looked in the box ... all gone :-( But you are right, if there is power available active is the way to go. Or DSP :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |