On 01/25/2016 01:33 PM, John Larkin wrote:> On Mon, 25 Jan 2016 13:13:12 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> 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. > > We like to start with a polyfuse (radial lead, not surface mount) > followed by a unipolar transzorb. Seems to protect against user > blunders, short of 120 VAC on a 24 volt bus. > > Lightning can be a nightmare in tropical climes and old buildings. > Horror stories about gear in Florida. Protect those RS485 chips, too. > >> >> 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. >> >> The bad news about regulated switchers is that they have negative input >> resistance, which may become a problem when the wiring runs get too >> long. (I can see somebody running the power on a spare CAT6 pair, 20 >> ohms per 1000 feet.) > > That recently confused our test folks. We have some bench supplies > that come up slow, and some products with purchased switcher bricks, > and the combo wouldn't start with the supplies set for apparently > reasonable current limits. We try to include UVLO and/or soft-start > when we design switchers. > >Even soft start won't help when the wiring resistance gets too high. A 2-W supply running off 24V has an input resistance of about R_in = 1/(dI_in/dV_in) = 1/(2W/24V - 2W/23V) = -276 ohms but that drops rapidly as the input voltage declines--it's 66 ohms at 12V input. Thus when the wiring resistance gets into the tens of ohms, life starts to get interesting, and of course when it gets above 72 ohms, it can't supply 2W into any load whatsoever. 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
Coupled Inductors--how coupled is coupled?
Started by ●January 25, 2016
Reply by ●January 25, 20162016-01-25
Reply by ●January 25, 20162016-01-25
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
Reply by ●January 25, 20162016-01-25
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 > > -LasseThanks. 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 -- 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 25, 20162016-01-25
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. 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 25, 20162016-01-25
On 01/25/2016 01:33 PM, John Larkin wrote:> On Mon, 25 Jan 2016 13:13:12 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> 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. > > We like to start with a polyfuse (radial lead, not surface mount) > followed by a unipolar transzorb. Seems to protect against user > blunders, short of 120 VAC on a 24 volt bus.I've also put unipolar TVSes in series with the ground pin of a PolyZen. You keep the super-fast switching action, which is great. You do have to be careful not to exceed the standoff voltage rating of the polyfuse part, of course. 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 25, 20162016-01-25
On Mon, 25 Jan 2016 14:34:34 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 01/25/2016 01:33 PM, John Larkin wrote: >> On Mon, 25 Jan 2016 13:13:12 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> 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. >> >> We like to start with a polyfuse (radial lead, not surface mount) >> followed by a unipolar transzorb. Seems to protect against user >> blunders, short of 120 VAC on a 24 volt bus. > >I've also put unipolar TVSes in series with the ground pin of a PolyZen. > You keep the super-fast switching action, which is great. You do have >to be careful not to exceed the standoff voltage rating of the polyfuse >part, of course. > >Cheers > >Phil HobbsThe radial polyfuses come in higher voltages than the surface-mount parts. They are kinda more predictable on current limiting, too. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 25, 20162016-01-25
On 01/25/2016 04:00 PM, John Larkin wrote:> On Mon, 25 Jan 2016 14:34:34 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 01/25/2016 01:33 PM, John Larkin wrote: >>> On Mon, 25 Jan 2016 13:13:12 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> 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. >>> >>> We like to start with a polyfuse (radial lead, not surface mount) >>> followed by a unipolar transzorb. Seems to protect against user >>> blunders, short of 120 VAC on a 24 volt bus. >> >> I've also put unipolar TVSes in series with the ground pin of a PolyZen. >> You keep the super-fast switching action, which is great. You do have >> to be careful not to exceed the standoff voltage rating of the polyfuse >> part, of course. >> >> Cheers >> >> Phil Hobbs > > The radial polyfuses come in higher voltages than the surface-mount > parts. They are kinda more predictable on current limiting, too. > >Not PolyZens--they're magic. The zener heats up the polyfuse super fast on any sort of large overload, so you don't have the problem of the diode unsoldering itself before the polyfuse switches. They aren't as fast for reverse voltage, but then you don't care as much since the diode isn't dissipating much. 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 25, 20162016-01-25
Phil Hobbs wrote...> > 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've measured quite a few types, not your p/n but similar ones. Like John says, they tend to be bifilar wound, and therefore with quite low leakage inductance. I've measured 0.3 to 0.5% of the magnetizing inductance.** So coupling = 0.96 to 0.98. One caution: They have more winding-to-winding capacitance than you'd normally expect. Easy to measure. ** using an HP 4192, from low-freq to 12 MHz. -- Thanks, - Win
Reply by ●January 25, 20162016-01-25
On Mon, 25 Jan 2016 13:14:34 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 01/25/2016 10:38 AM, mixed nuts wrote: >> On 1/25/2016 10:14 AM, 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? >> >> Looks too small to be anything far from unity - even with a small gap >> between ferrite bits - 0.998? >> >> The series mode inductance is spec'd to be 1880 (470*4)! ;) >> > >Plus or minus 20%, of course. ;) > >Cheers > >Phil HobbsDo you have a decent LC meter? Just short one winding and measure the other. TDR will work too, to estimate small inductance. Sometimes I use a function generator and a scope to measure small inductances. That helps resolve resonances, which confuse some meters. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 25, 20162016-01-25
On Mon, 25 Jan 2016 16:07:24 -0800, John Larkin <jjlarkin@highlandtechnology.com> Gave us:>On Mon, 25 Jan 2016 13:14:34 -0500, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 01/25/2016 10:38 AM, mixed nuts wrote: >>> On 1/25/2016 10:14 AM, 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? >>> >>> Looks too small to be anything far from unity - even with a small gap >>> between ferrite bits - 0.998? >>> >>> The series mode inductance is spec'd to be 1880 (470*4)! ;) >>> >> >>Plus or minus 20%, of course. ;) >> >>Cheers >> >>Phil Hobbs > >Do you have a decent LC meter? Just short one winding and measure the >other. TDR will work too, to estimate small inductance. > >Sometimes I use a function generator and a scope to measure small >inductances. That helps resolve resonances, which confuse some meters."coupled inductor" There is no such animal. If there is coupling it immediately becomes and is empirically defined as being a transformer. Turns count ratio and voltage transformation rules apply.
