On Tue, 26 Jan 2016 15:15:43 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 01/26/2016 12:46 PM, John Larkin wrote: >> On Tue, 26 Jan 2016 12:14:51 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 01/25/2016 02:24 PM, Phil Hobbs wrote: >>>> On 01/25/2016 02:21 PM, Phil Hobbs wrote: >>>>> On 01/25/2016 02:04 PM, Lasse Langwadt Christensen wrote: >>>>>> Den mandag den 25. januar 2016 kl. 19.13.25 UTC+1 skrev Phil Hobbs: >>>>>>> On 01/25/2016 12:10 PM, John Larkin wrote: >>>>>>>> On Mon, 25 Jan 2016 10:40:33 -0500, Phil Hobbs >>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>> >>>>>>>>> On 01/25/2016 10:37 AM, John Larkin wrote: >>>>>>>>>> On Mon, 25 Jan 2016 10:14:12 -0500, Phil Hobbs >>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>>>> >>>>>>>>>>> So in the continuing saga of cotton spark detection, I need to >>>>>>>>>>> make an >>>>>>>>>>> isolated 2-output DC-DC converter to power an RS-485 link and a >>>>>>>>>>> small >>>>>>>>>>> SBC--about 2W altogether. This isn't a terribly low-noise >>>>>>>>>>> application, >>>>>>>>>>> so I was thinking about using the Bourns >>>>>>>>>>> SRF0703-471M "coupled inductor" as a flyback. The question is, >>>>>>>>>>> what's >>>>>>>>>>> the coefficient of couping? There's no way to find out from the >>>>>>>>>>> datasheet. I'll get a few to try out, but in the mean time, does >>>>>>>>>>> anybody know the approximate value of k for these beasts? >>>>>>>>>>> >>>>>>>>>>> Thanks >>>>>>>>>>> >>>>>>>>>>> Phil Hobbs >>>>>>>>>> >>>>>>>>>> We've measured that. The short answer is "about 0.99" >>>>>>>>>> >>>>>>>>>> Most seem to be bifalar toroids, pretty good coupling. >>>>>>>>>> >>>>>>>>>> Here's some notes on a couple of Coiltronics parts: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Notes on leakage inductance: >>>>>>>>>> >>>>>>>>>> Part, OCL, SCL, K ( sqrt(1 - SCL/OCL) ) >>>>>>>>>> DRQ74-8R2, 8.03uH, 110nH, 0.993 >>>>>>>>>> DRQ74-150, 16.91uH, 270nH, 0.991 >>>>>>>>>> >>>>>>>>>> Measured on AADE LC meter. RG 16-Sept-10 >>>>>>>>>> >>>>>>>>>> DRQ127-151 150 uH 4 uH >>>>>>>>>> DRQ127-331 330 uH 5 uH >>>>>>>>>> DRQ127-102 1 mH 70 uH >>>>>>>>>> >>>>>>>>>> JL Mar 2012 >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>> Thanks. The Bourns ones I was looking at are the cheesy "shielded" >>>>>>>>> kind >>>>>>>>> with the big gap at the top of the core + cup, so I was hoping it >>>>>>>>> would >>>>>>>>> be around 0.95-0.98. >>>>>>>>> >>>>>>>>> Cheers >>>>>>>>> >>>>>>>>> Phil Hobbs >>>>>>>> >>>>>>>> The DRQs are like that. I may be wrong about the construction, but >>>>>>>> coupling seems pretty good. >>>>>>>> >>>>>>>> The ISDN transformers are bifalar toroids, very good coupling. We use >>>>>>>> one 1:1:2:2 part that is very versatile. >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> It's sort of an interesting case--very cost sensitive, but has to be >>>>>>> tough enough to withstand a monsoon thunderstorm in a cotton mill with >>>>>>> very iffy grounding and long runs of thin wire. We're going to bus >>>>>>> around +24V, panel ground, and a twisted pair for 200 kb/s RS485 data. >>>>>>> >>>>>>> So I'm looking at some combination of MOVs, TVS zeners, and depletion >>>>>>> MOSFETs on all four lines, plus fully isolated power and comms. >>>>>>> >>>>>>> The first thing I tried was a half-bridge driving two 150 uH >>>>>>> double-wound inductors (L1A + L2A in series, L1B + L1B in parallel for >>>>>>> the output), followed by bridges, filters, and LDOs. That worked >>>>>>> well >>>>>>> with no ringing or other nonsense, and managed to get to 5V okay, >>>>>>> but it >>>>>>> was a bit marginal at the low voltage limit. Using MOSFETs for the >>>>>>> bridge on the output helped some, but it was just getting too >>>>>>> complicated. >>>>>>> >>>>>>> I'll probably just put in one of those 27-cent A&O buck chips and then >>>>>>> drive a couple of 1:1 transformers. I can use the unregulated input to >>>>>>> power the high side gate, which helps some. >>>>>>> >>>>>> >>>>>> flybuck? >>>>>> >>>>>> http://www.ti.com/lit/an/snva674b/snva674b.pdf >>>>>> >>>>>> -Lasse >>>>> >>>>> Thanks. Thought of that--I've done it before, but it really only works >>>>> when the main supply is more heavily loaded than the isolated ones. I >>>>> need two isolated outputs and zero non-isolated ones. >>>>> >>>>> Also I can't be sure that one supply will always be drawing more current >>>>> than the other--a double terminated RS485 link can draw over 80 mA, >>>>> whereas it's much less with AC termination. The SBC can draw 160 mA >>>>> max, but there's no minimum specified. So it looks like a buck followed >>>>> by two 1:1 transformers, bridges, and LDOs. _Not_ the elegant solution >>>>> I was hoping for, but there you go. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>>> >>>> >>>> Belay that--with a _sync_ buck, you can balance the voltseconds even >>>> with no load on the non-isolated output--it's a half-bridge. >>> >>> The sync buck half bridge looks like a winner. I should be able to use >>> a couple of those 27-cent Bourns coupled inductors and a $1 Richtek >>> RT7272 to make two isolated 5V outputs. As a bonus, putting capacitors >>> in series with the primaries roughly halves the effective V_in, which >>> lets the buck's duty cycle be longer, which improves efficiency. >>> >>> The cross-regulation isn't great unless the coupling coefficient is at >>> least 0.995, though, so I'll need some scheme for feeding back from >>> whichever output sags the most. The usual scheme for one output is to >>> use a TL431 with the LED of an optocoupler in series with its anode, >>> with feedback taken from the phototransistor. I could use two of those >>> and diode-OR them into the feedback, I suppose, but depending on cost, >>> it's probably better to use some of those toroids of John's to get >>> better cross-regulation. >>> >>> Thanks, Lasse, for prodding me that direction. >>> >>> Cheers >>> >>> Phil Hobbs >> >> The Versa-Pac multi-winding inductors are cool, but not cheap, $3 >> range. We're lately paying around $3 for the 1:1:2:2 ISDN transformer; >> maybe ISDN is going out of fashion. Maybe one could take the feedback >> off an AC winding and get pretty good regulation. >> >> Coilcraft makes some really cool planar-winding transformers. >> >> I guess one might build a transformer into a PCB, with holes for the >> legs of a core. Cheap, but lots of engineering. >> >> You could buy a CUI dual-out surface-mount isolated converter for >> around $4. > >Yeah, but they're ratiometric, which won't fly in this case because of >the power supply wiring resistance. > >Bummer that the toroids are getting so expensive. We need this gizmo to >have a long production life, so something more generic is good. > >I'll play with the diode-OR trick. I'm not too worried about positive >excursions because there'll be an LDO on each. > >Cheers > >Phil HobbsSounds like you could use a flyback, maybe regulate off the primary side. But that would almost certainly involve a custom transformer, which is always a nuisance. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Coupled Inductors--how coupled is coupled?
Started by ●January 25, 2016
Reply by ●January 26, 20162016-01-26
Reply by ●January 26, 20162016-01-26
On 26 Jan 2016 11:38:48 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>Phil Hobbs wrote... >> >> I was thinking about using the Bourns >> SRF0703-471M "coupled inductor" ... > > Newark has those on closeout sale right > now; that particular value is $0.19 each.Does closeout = EOL? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 26, 20162016-01-26
On 26/01/2016 20:29, Phil Hobbs wrote:> On 01/26/2016 02:38 PM, Winfield Hill wrote: >> Phil Hobbs wrote... >>> >>> I was thinking about using the Bourns >>> SRF0703-471M "coupled inductor" ... >> >> Newark has those on closeout sale right >> now; that particular value is $0.19 each. > > I saw that, and ordered 50 of them, which in my line of work is probably > a career's worth. I've recently done the same with a lot of TO92 and > DIP packaged parts. It's probably a bit under $1k in extra inventory, > but I can do dead bug protos for the foreseeable future. > > Cheers > > Phil Hobbs >Get yourself an inductor selection kit, most suppliers will then top it up for free as you use parts.
Reply by ●January 26, 20162016-01-26
On 01/26/2016 03:55 PM, John Larkin wrote:> On Tue, 26 Jan 2016 15:15:43 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 01/26/2016 12:46 PM, John Larkin wrote: >>> On Tue, 26 Jan 2016 12:14:51 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 01/25/2016 02:24 PM, Phil Hobbs wrote: >>>>> On 01/25/2016 02:21 PM, Phil Hobbs wrote: >>>>>> On 01/25/2016 02:04 PM, Lasse Langwadt Christensen wrote: >>>>>>> Den mandag den 25. januar 2016 kl. 19.13.25 UTC+1 skrev Phil Hobbs: >>>>>>>> On 01/25/2016 12:10 PM, John Larkin wrote: >>>>>>>>> On Mon, 25 Jan 2016 10:40:33 -0500, Phil Hobbs >>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>>> >>>>>>>>>> On 01/25/2016 10:37 AM, John Larkin wrote: >>>>>>>>>>> On Mon, 25 Jan 2016 10:14:12 -0500, Phil Hobbs >>>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>>>>> >>>>>>>>>>>> So in the continuing saga of cotton spark detection, I need to >>>>>>>>>>>> make an >>>>>>>>>>>> isolated 2-output DC-DC converter to power an RS-485 link and a >>>>>>>>>>>> small >>>>>>>>>>>> SBC--about 2W altogether. This isn't a terribly low-noise >>>>>>>>>>>> application, >>>>>>>>>>>> so I was thinking about using the Bourns >>>>>>>>>>>> SRF0703-471M "coupled inductor" as a flyback. The question is, >>>>>>>>>>>> what's >>>>>>>>>>>> the coefficient of couping? There's no way to find out from the >>>>>>>>>>>> datasheet. I'll get a few to try out, but in the mean time, does >>>>>>>>>>>> anybody know the approximate value of k for these beasts? >>>>>>>>>>>> >>>>>>>>>>>> Thanks >>>>>>>>>>>> >>>>>>>>>>>> Phil Hobbs >>>>>>>>>>> >>>>>>>>>>> We've measured that. The short answer is "about 0.99" >>>>>>>>>>> >>>>>>>>>>> Most seem to be bifalar toroids, pretty good coupling. >>>>>>>>>>> >>>>>>>>>>> Here's some notes on a couple of Coiltronics parts: >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> Notes on leakage inductance: >>>>>>>>>>> >>>>>>>>>>> Part, OCL, SCL, K ( sqrt(1 - SCL/OCL) ) >>>>>>>>>>> DRQ74-8R2, 8.03uH, 110nH, 0.993 >>>>>>>>>>> DRQ74-150, 16.91uH, 270nH, 0.991 >>>>>>>>>>> >>>>>>>>>>> Measured on AADE LC meter. RG 16-Sept-10 >>>>>>>>>>> >>>>>>>>>>> DRQ127-151 150 uH 4 uH >>>>>>>>>>> DRQ127-331 330 uH 5 uH >>>>>>>>>>> DRQ127-102 1 mH 70 uH >>>>>>>>>>> >>>>>>>>>>> JL Mar 2012 >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> Thanks. The Bourns ones I was looking at are the cheesy "shielded" >>>>>>>>>> kind >>>>>>>>>> with the big gap at the top of the core + cup, so I was hoping it >>>>>>>>>> would >>>>>>>>>> be around 0.95-0.98. >>>>>>>>>> >>>>>>>>>> Cheers >>>>>>>>>> >>>>>>>>>> Phil Hobbs >>>>>>>>> >>>>>>>>> The DRQs are like that. I may be wrong about the construction, but >>>>>>>>> coupling seems pretty good. >>>>>>>>> >>>>>>>>> The ISDN transformers are bifalar toroids, very good coupling. We use >>>>>>>>> one 1:1:2:2 part that is very versatile. >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> It's sort of an interesting case--very cost sensitive, but has to be >>>>>>>> tough enough to withstand a monsoon thunderstorm in a cotton mill with >>>>>>>> very iffy grounding and long runs of thin wire. We're going to bus >>>>>>>> around +24V, panel ground, and a twisted pair for 200 kb/s RS485 data. >>>>>>>> >>>>>>>> So I'm looking at some combination of MOVs, TVS zeners, and depletion >>>>>>>> MOSFETs on all four lines, plus fully isolated power and comms. >>>>>>>> >>>>>>>> The first thing I tried was a half-bridge driving two 150 uH >>>>>>>> double-wound inductors (L1A + L2A in series, L1B + L1B in parallel for >>>>>>>> the output), followed by bridges, filters, and LDOs. That worked >>>>>>>> well >>>>>>>> with no ringing or other nonsense, and managed to get to 5V okay, >>>>>>>> but it >>>>>>>> was a bit marginal at the low voltage limit. Using MOSFETs for the >>>>>>>> bridge on the output helped some, but it was just getting too >>>>>>>> complicated. >>>>>>>> >>>>>>>> I'll probably just put in one of those 27-cent A&O buck chips and then >>>>>>>> drive a couple of 1:1 transformers. I can use the unregulated input to >>>>>>>> power the high side gate, which helps some. >>>>>>>> >>>>>>> >>>>>>> flybuck? >>>>>>> >>>>>>> http://www.ti.com/lit/an/snva674b/snva674b.pdf >>>>>>> >>>>>>> -Lasse >>>>>> >>>>>> Thanks. Thought of that--I've done it before, but it really only works >>>>>> when the main supply is more heavily loaded than the isolated ones. I >>>>>> need two isolated outputs and zero non-isolated ones. >>>>>> >>>>>> Also I can't be sure that one supply will always be drawing more current >>>>>> than the other--a double terminated RS485 link can draw over 80 mA, >>>>>> whereas it's much less with AC termination. The SBC can draw 160 mA >>>>>> max, but there's no minimum specified. So it looks like a buck followed >>>>>> by two 1:1 transformers, bridges, and LDOs. _Not_ the elegant solution >>>>>> I was hoping for, but there you go. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>>> >>>>> >>>>> Belay that--with a _sync_ buck, you can balance the voltseconds even >>>>> with no load on the non-isolated output--it's a half-bridge. >>>> >>>> The sync buck half bridge looks like a winner. I should be able to use >>>> a couple of those 27-cent Bourns coupled inductors and a $1 Richtek >>>> RT7272 to make two isolated 5V outputs. As a bonus, putting capacitors >>>> in series with the primaries roughly halves the effective V_in, which >>>> lets the buck's duty cycle be longer, which improves efficiency. >>>> >>>> The cross-regulation isn't great unless the coupling coefficient is at >>>> least 0.995, though, so I'll need some scheme for feeding back from >>>> whichever output sags the most. The usual scheme for one output is to >>>> use a TL431 with the LED of an optocoupler in series with its anode, >>>> with feedback taken from the phototransistor. I could use two of those >>>> and diode-OR them into the feedback, I suppose, but depending on cost, >>>> it's probably better to use some of those toroids of John's to get >>>> better cross-regulation. >>>> >>>> Thanks, Lasse, for prodding me that direction. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> The Versa-Pac multi-winding inductors are cool, but not cheap, $3 >>> range. We're lately paying around $3 for the 1:1:2:2 ISDN transformer; >>> maybe ISDN is going out of fashion. Maybe one could take the feedback >>> off an AC winding and get pretty good regulation. >>> >>> Coilcraft makes some really cool planar-winding transformers. >>> >>> I guess one might build a transformer into a PCB, with holes for the >>> legs of a core. Cheap, but lots of engineering. >>> >>> You could buy a CUI dual-out surface-mount isolated converter for >>> around $4. >> >> Yeah, but they're ratiometric, which won't fly in this case because of >> the power supply wiring resistance. >> >> Bummer that the toroids are getting so expensive. We need this gizmo to >> have a long production life, so something more generic is good. >> >> I'll play with the diode-OR trick. I'm not too worried about positive >> excursions because there'll be an LDO on each. >> >> Cheers >> >> Phil Hobbs > > Sounds like you could use a flyback, maybe regulate off the primary > side. But that would almost certainly involve a custom transformer, > which is always a nuisance.That's where I started on this thread. The sync-buck "flybuck" converter is basically a half-bridge version of a flyback, with the voltseconds zeroed out by a series cap (which would be the output filter cap on a normal buck). (You could also think of it as an AC-coupled forward converter.) The thing I was initially missing is that the sync buck allows the isolated supply to be more heavily loaded than the main buck (which needn't be loaded at all, in fact). Normal switch/diode bucks don't work like that, because there's no way to sink current from the output cap, so the isolated supplies are really only good for light-duty auxiliary power. I've done photodiode bias supplies that way, for instance, piggybacking off the free AC from an LM2594. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 26, 20162016-01-26
On 01/26/2016 03:56 PM, John Larkin wrote:> On 26 Jan 2016 11:38:48 -0800, Winfield Hill > <hill@rowland.harvard.edu> wrote: > >> Phil Hobbs wrote... >>> >>> I was thinking about using the Bourns >>> SRF0703-471M "coupled inductor" ... >> >> Newark has those on closeout sale right >> now; that particular value is $0.19 each. > > Does closeout = EOL?No sign of that on the Bourns website, and DK has lots. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 26, 20162016-01-26
On 01/26/2016 04:04 PM, JM wrote:> On 26/01/2016 20:29, Phil Hobbs wrote: >> On 01/26/2016 02:38 PM, Winfield Hill wrote: >>> Phil Hobbs wrote... >>>> >>>> I was thinking about using the Bourns >>>> SRF0703-471M "coupled inductor" ... >>> >>> Newark has those on closeout sale right >>> now; that particular value is $0.19 each. >> >> I saw that, and ordered 50 of them, which in my line of work is probably >> a career's worth. I've recently done the same with a lot of TO92 and >> DIP packaged parts. It's probably a bit under $1k in extra inventory, >> but I can do dead bug protos for the foreseeable future. >> >> Cheers >> >> Phil Hobbs >> > > Get yourself an inductor selection kit, most suppliers will then top it > up for free as you use parts.Thanks. I got one from one of Mike Engelhardt's seminars awhile back. They aren't the cheap kind, though. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 26, 20162016-01-26
Phil Hobbs wrote...> John Larkin wrote: >> Winfield Hill wrote: >>> Phil Hobbs wrote... >>>> >>>> I was thinking about using the Bourns >>>> SRF0703-471M "coupled inductor" ... >>> >>> Newark has those on closeout sale right >>> now; that particular value is $0.19 each. >> >> Does closeout = EOL? > > No sign of that on the Bourns website, > and DK has lots.I think it means Farnell (England) is dropping that product line, that's all. -- Thanks, - Win
Reply by ●January 30, 20162016-01-30
Phil Hobbs wrote...> Winfield Hill wrote: >> Phil Hobbs wrote... >>> >>> I was thinking about using the Bourns >>> SRF0703-471M "coupled inductor" ... >> >> Newark has those on closeout sale right >> now; that particular value is $0.19 each. > > I saw that, and ordered 50 of them ...Made some measurements with my hp 4192 LCR meter. DCR 5.00 ohms both sides (spec 5.64 ohms) L (100kHz) 480uH [each or parallel] (spec 470uH) L_series (100kHz) 1.97mH (spec 1.88mH) Lell (any freq) 6.6uH (1.4%, very good) SRF 550kHz (poor, but OK for 100kHz use) These will do well, even with unmatched loads. -- Thanks, - Win
Reply by ●January 30, 20162016-01-30
On 01/30/2016 12:07 PM, Winfield Hill wrote:> Phil Hobbs wrote... >> Winfield Hill wrote: >>> Phil Hobbs wrote... >>>> >>>> I was thinking about using the Bourns >>>> SRF0703-471M "coupled inductor" ... >>> >>> Newark has those on closeout sale right >>> now; that particular value is $0.19 each. >> >> I saw that, and ordered 50 of them ... > > Made some measurements with my hp 4192 LCR meter. > DCR 5.00 ohms both sides (spec 5.64 ohms) > L (100kHz) 480uH [each or parallel] (spec 470uH) > L_series (100kHz) 1.97mH (spec 1.88mH) > Lell (any freq) 6.6uH (1.4%, very good) > SRF 550kHz (poor, but OK for 100kHz use) > > These will do well, even with unmatched loads. > >Thanks, Win. So k~= 0.986 then. Looks like I can mostly get rid of the line regulation sag by putting a resistor from V_in to the feedback point, which makes it practical to use the flybuck topology with an LDO per output. At that level it does need a lightweight snubber to protect the Schottky rectifier, but it doesn't cost much power. Probably when I've done this a few times I can make it simpler, but this seems pretty good. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 2, 20162016-02-02
On Monday, January 25, 2016 at 10:14:23 AM UTC-5, Phil Hobbs wrote:> So in the continuing saga of cotton spark detection, I need to make an > isolated 2-output DC-DC converter to power an RS-485 link and a small > SBC--about 2W altogether. This isn't a terribly low-noise application, > so I was thinking about using the Bourns > SRF0703-471M "coupled inductor" as a flyback. The question is, what's > the coefficient of couping? There's no way to find out from the > datasheet. I'll get a few to try out, but in the mean time, does > anybody know the approximate value of k for these beasts? > > Thanks > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > > hobbs at electrooptical dot net > http://electrooptical.netAre you asking for a way to measure mutual inductance, i.e., how to measure the coupling coefficient ?
