Ferrite Inductor Tolerance
in [Design]
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From: Ian Bell on 12 Jun 2010 17:13 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%. Cheers Ian
From: Joerg on 12 Jun 2010 18:00 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Nico Coesel on 12 Jun 2010 18:18 Ian Bell <ruffrecords(a)yahoo.com> 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 >> > >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%. I'd expect more like tens of percents. Keep in mind that the inductance also varies with current. Thats why you always see air core inductors in loudspeaker filters. If you need accurate inductors you better to use a gyrator circuit. http://sound.westhost.com/dwopa.htm#inductor -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico(a)nctdevpuntnl (punt=.) --------------------------------------------------------------
From: Archimedes' Lever on 12 Jun 2010 18:34 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.
From: Joerg on 12 Jun 2010 18:48
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%. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |