Bifilar inductor?

Started by George Herold January 4, 2018
Hi all, silly question.  Dave's EEVblog was on... there was this bifilar wound coil
(starts at ~39 minutes in)
https://www.eevblog.com/
(hmm latest video I guess, Mailbag #1049)  
My question is; how the heck does that do anything inductive?  

George H. 
On Thu, 4 Jan 2018 11:37:19 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound coil
(starts at ~39 minutes in)
>https://www.eevblog.com/ >(hmm latest video I guess, Mailbag #1049) >My question is; how the heck does that do anything inductive? > >George H.
I refuse to watch Squeaky's videos. A bifilar inductor is really a 1:1 transformer with both windings made at once from a twisted pair. So it has very low leakage inductance and lots of inter-winding capacitance. https://www.digikey.com/product-detail/en/eaton/DRQ127-3R3-R/513-1308-2-ND/667268 These are sometimes sold as transformers, sometimes as dual-winding inductors. They are inductors in the sense that the winding inductance is specified, with a tolerance. I love those DRQ-series gadgets. They are good for all sorts of things. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thursday, January 4, 2018 at 7:42:34 PM UTC-5, John Larkin wrote:
> On Thu, 4 Jan 2018 11:37:19 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > > >Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound
coil (starts at ~39 minutes in)
> >https://www.eevblog.com/ > >(hmm latest video I guess, Mailbag #1049) > >My question is; how the heck does that do anything inductive? > > > >George H. > > I refuse to watch Squeaky's videos.
I understand, he was pulling apart an ovenized x-tal oscilator someone sent him. Then this bifilar inductor appeared. Maybe 1.5" of ferrite rod with ~10 turns of paired wire, maybe 20AWG, not twisted. The schematic drew it as an inductor on the AC input line to some lamp power supply.
> > A bifilar inductor is really a 1:1 transformer with both windings made > at once from a twisted pair. So it has very low leakage inductance and > lots of inter-winding capacitance.
OK a 1:1 transformer wired top to bottom..(I don't know the right terms.) I guess my mind thinks that to first order there is no B-field. But of course there has to be some...My 2nd model has a bunch of alternating rings of current. OK and then a bunch of capacitance....It's a 50/60 Hz 2 pole band pass filter? That's not right, it doesn't block DC.
> > https://www.digikey.com/product-detail/en/eaton/DRQ127-3R3-R/513-1308-2-ND/667268
Huh, I never knew of such things. You can make each series or parallel connection in two ways... (I'll have to read the spec sheet... I wish I had some good book/app note for transformer/inductor things, I've used and made them, but unless I'm designing for some magnetic field, I don't know what I'm doing. I've read about coax/ toroid transformers in ARRL and such but never with any deep understanding. George H.
> > These are sometimes sold as transformers, sometimes as dual-winding > inductors. They are inductors in the sense that the winding inductance > is specified, with a tolerance. > > I love those DRQ-series gadgets. They are good for all sorts of > things. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
On Thursday, January 4, 2018 at 11:37:24 AM UTC-8, George Herold wrote:
> Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound
coil (starts at ~39 minutes in)
> https://www.eevblog.com/ > (hmm latest video I guess, Mailbag #1049) > My question is; how the heck does that do anything inductive?
It's a shorted transmission line. So, there's some delay, during which it has a characteristic impedance (ohmic) after which it's a short circuit. As you suggest, it only has inductive character on the scale size of the wire separation. So, the triac (which has a dI/dt limit) will see some nontrivial impedance for a few nanoseconds (the ferrite makes this a SLOW shorted transmission line). The turnon transient, then, even if there's a capacitive load, is under control. Because it's only active for a short time, the losses are insignificant.
On Thu, 04 Jan 2018 16:42:23 -0800, John Larkin wrote:

> I refuse to watch Squeaky's videos.
Such a shame he has that *ghastly* Australian accent, the squeakiness of which only exacerbates grating quality of. It's simply appalling and the only thing that could make it even worse is if he were a she instead. :( For Aussie Sheilas, the best investment in finding a husband would be elocution lessons.
On 1/4/2018 6:42 PM, John Larkin wrote:
> On Thu, 4 Jan 2018 11:37:19 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > >> Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound
coil (starts at ~39 minutes in)
>> https://www.eevblog.com/ >> (hmm latest video I guess, Mailbag #1049) >> My question is; how the heck does that do anything inductive? >> >> George H. > > I refuse to watch Squeaky's videos. > > A bifilar inductor is really a 1:1 transformer with both windings made > at once from a twisted pair. So it has very low leakage inductance and > lots of inter-winding capacitance. > > https://www.digikey.com/product-detail/en/eaton/DRQ127-3R3-R/513-1308-2-ND/667268 > > These are sometimes sold as transformers, sometimes as dual-winding > inductors. They are inductors in the sense that the winding inductance > is specified, with a tolerance. > > I love those DRQ-series gadgets. They are good for all sorts of > things. > >
Without watching the video, you missed the mark. Mikek
On 1/4/2018 7:43 PM, George Herold wrote:
> On Thursday, January 4, 2018 at 7:42:34 PM UTC-5, John Larkin wrote: >> On Thu, 4 Jan 2018 11:37:19 -0800 (PST), George Herold >> <gherold@teachspin.com> wrote: >> >>> Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound
coil (starts at ~39 minutes in)
>>> https://www.eevblog.com/ >>> (hmm latest video I guess, Mailbag #1049) >>> My question is; how the heck does that do anything inductive? >>> >>> George H. >> >> I refuse to watch Squeaky's videos. > I understand, he was pulling apart an ovenized x-tal oscilator > someone sent him.
Why confuse the issue by throwing in a X-tal osc? The inductor is out of a light dimmer. >Then this bifilar inductor appeared.
> Maybe 1.5" of ferrite rod with ~10 turns of paired wire, > maybe 20AWG, not twisted. The schematic drew it as > an inductor on the AC input line to some lamp power supply. >> >> A bifilar inductor is really a 1:1 transformer with both windings made >> at once from a twisted pair. So it has very low leakage inductance and >> lots of inter-winding capacitance. > OK a 1:1 transformer wired top to bottom..(I don't know the right terms.) > I guess my mind thinks that to first order there is no B-field. > But of course there has to be some...My 2nd model has > a bunch of alternating rings of current. > OK and then a bunch of capacitance....It's a > 50/60 Hz 2 pole band pass filter? > That's not right, it doesn't block DC. >> >>
https://www.digikey.com/product-detail/en/eaton/DRQ127-3R3-R/513-1308-2-ND/667268
> Huh, I never knew of such things. You can make each series or parallel > connection in two ways... (I'll have to read the spec sheet... > I wish I had some good book/app note for transformer/inductor things, > I've used and made them, but unless I'm designing for some > magnetic field, I don't know what I'm doing. > > I've read about coax/ toroid transformers in ARRL and such > but never with any deep understanding. > > George H. >> >> These are sometimes sold as transformers, sometimes as dual-winding >> inductors. They are inductors in the sense that the winding inductance >> is specified, with a tolerance. >> >> I love those DRQ-series gadgets. They are good for all sorts of >> things. >> >> >> -- >> >> John Larkin Highland Technology, Inc >> picosecond timing precision measurement >> >> jlarkin att highlandtechnology dott com >> http://www.highlandtechnology.com >
On 1/5/2018 1:44 PM, Chris wrote:
> On Thu, 04 Jan 2018 16:42:23 -0800, John Larkin wrote: > >> I refuse to watch Squeaky's videos. > > Such a shame he has that *ghastly* Australian accent, the squeakiness of > which only exacerbates grating quality of. It's simply appalling and the > only thing that could make it even worse is if he were a she instead. :( > For Aussie Sheilas, the best investment in finding a husband would be > elocution lessons. >
There is really no reason to hate an Australian accent. I guess you just want something to hate to make yourself feel superior. I suspect the feeling didn't last long. Mikek
John Larkin wrote...
> George Herold wrote: > >> Hi all, silly question. Dave's EEVblog was on... there >> was this bifilar wound coil (starts at ~39 minutes in) >> https://www.eevblog.com/ >>(hmm latest video I guess, Mailbag #1049) >> My question is; how the heck does that do anything inductive? > > I refuse to watch Squeaky's videos. > > A bifilar inductor is really a 1:1 transformer with > both windings made at once from a twisted pair. So it > has very low leakage inductance and lots of inter-winding > capacitance. > >https://www.digikey.com/product-detail/en/eaton/DRQ127-3R3-R/513-1308-2-ND/667268 > > These are sometimes sold as transformers, sometimes as > dual-winding inductors. They are inductors in the sense > that the winding inductance is specified, with a tolerance. > > I love those DRQ-series gadgets. They are good for all > sorts of things.
One point, they are universally called coupled inductors. Think of one winding as an inductor, e.g., used in an inverting dc-dc converter. It'll have -Vo, plus a diode drop across its coil as it makes a neg output. The other winding has exactly the same voltage, use it with a diode to make an identical positive voltage, +Vo. I like Bourns SRF0703 series, 0.3 x 0.3 inches (half the size of an DRQ127), only $0.13, inductances from 0.33uH to 1000uH. One dc-dc converter IC, get bipolar +/-15V, etc, nice! My MPX-16H high-voltage multiplexer DAQ board uses TPS64201 with a NTS4173P FET to make a 1W converter. -- Thanks, - Win
On Thursday, January 4, 2018 at 9:17:22 PM UTC-5, whit3rd wrote:
> On Thursday, January 4, 2018 at 11:37:24 AM UTC-8, George Herold wrote: > > Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound
coil (starts at ~39 minutes in)
> > https://www.eevblog.com/ > > (hmm latest video I guess, Mailbag #1049) > > My question is; how the heck does that do anything inductive? > > It's a shorted transmission line. So, there's some delay, during which it > has a characteristic impedance (ohmic) after which it's > a short circuit. > > As you suggest, it only has inductive character on the scale size of > the wire separation. > > So, the triac (which has a dI/dt limit) will see some nontrivial impedance for > a few nanoseconds (the ferrite makes this a SLOW shorted transmission line). > The turnon transient, then, even if there's a capacitive load, is under control. > Because it's only active for a short time, the losses are insignificant.
OK that makes sense, so I think of it as an inrush current limiter? George H.