Forums

little pcb-mount CTs

Started by John Larkin May 4, 2015
On Tue, 05 May 2015 17:34:03 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2015-05-05 4:55 PM, whit3rd wrote: >> On Monday, May 4, 2015 at 4:40:20 PM UTC-7, John Larkin wrote: >>> On Mon, 4 May 2015 16:26:02 -0700 (PDT), whit3rd <whit3rd@gmail.com> >>> wrote: >>> >>>> On Monday, May 4, 2015 at 3:17:18 PM UTC-7, John Larkin wrote: >>>>> Anybody know of a source for a small (1 amp range) PCB mount current >>>>> transformer? Frequency will be around 400 Hz. >> >>>> Any transformer, with a shunt resistance on the secondary, is a current transformer. >>>> Why not go with Coilcraft LPR6235 series >> >>> The ones with low primary DCRs also have low L/R time constants, so >>> wouldn't work very well at 400 Hz. >> >> I don't get it. In-circuit, the input impedance is ohmic (winding factor and output >> load resistor) plus some small DC resistance; there's no dependence on >> energy storage in an inductor, no L/R time constant involvement. >> >> How does any problem occur 'at 400 Hz', in a transformer? >> > >Not enough inductance. The old rule of thumb among RF guys is Z=4x the >impedance of the circuit it's connecting to, at the desired frequency. >When the Z of a winding is only 2-3ohms and you want a 400ohms burden >resistor that's a wee problem :-)
With a 100 ohm burden resistor, the 100:1 version of the Coilcraft LPR6235 is down 3 dB at about 900 Hz, and -8 dB at 400 Hz. There's not much to be gained from reducing the burden resistor, because the secondary copper is over 300 ohms. If I was running at exactly 400 Hz, I might almost use it and cal around the error. Or resonate the secondary or something. But my range is maybe 300 to 1KHz. A 0.1 ohm resistor and my little ISDN transformer looks like it would work. I'll need an opamp to add some gain ahead of the ADC. But that's all parts that we have. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Wed, 06 May 2015 07:39:55 +1000, "David Eather" <eather@tpg.com.au>
wrote:

>On Wed, 06 May 2015 07:31:14 +1000, John Larkin ><jlarkin@highlandtechnology.com> wrote: > >> On Tue, 05 May 2015 13:58:40 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2015-05-05 1:15 PM, John Larkin wrote: >>>> On Tue, 05 May 2015 10:13:52 -0700, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>> On 2015-05-04 6:22 PM, John Larkin wrote: >>>>>> On Mon, 04 May 2015 17:28:12 -0700, Joerg >>>>>> <news@analogconsultants.com> >>>>>> wrote: >>>>>> >>>>>>> On 2015-05-04 5:20 PM, Joerg wrote: >>>>>>>> On 2015-05-04 5:00 PM, John Larkin wrote: >>>>>>>>> On Mon, 04 May 2015 16:47:14 -0700, Joerg >>>>>>>>> <news@analogconsultants.com> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On 2015-05-04 3:17 PM, John Larkin wrote: >>>>>>>>>>> >>>>>>>>>>> Anybody know of a source for a small (1 amp range) PCB mount >>>>>>>>>>> current >>>>>>>>>>> transformer? Frequency will be around 400 Hz. >>>>>>>>>>> >>>>>>>>>>> There are switcher current sense CTs, but I don't know if they >>>>>>>>>>> will >>>>>>>>>>> work that low. >>>>>>>>>>> >>>>>>>>>>> Or maybe I could use a shunt and a voltage-mode (audio) >>>>>>>>>>> transformer. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> How about this one? Lots of stock. >>>>>>>>>> >>>>>>>>>> http://www.digikey.com/product-detail/en/CSE187L/237-1103-ND/242546 >>>>>>>>> >>>>>>>>> That one is nice. The 500:1 ratio, makes 2 mA RMS out with 1 amp >>>>>>>>> in. >>>>>>>>> That's 100 mV RMS into a 50 ohm burden resistor. >>>>>>>>> >>>>>>>>> The alternative is to use a 0.1 ohm shunt and a step-up audio >>>>>>>>> transformer. That could give me more voltage for my ADC, but, >>>>>>>>> then, >>>>>>>>> opamps are cheap. >>>>>>>>> >>>>>>>> >>>>>>>> If you never have more than 1A maybe use a larger burden resistor? >>>>>>>> The >>>>>>>> datasheet says 4Vrms max on the output which is probably where the >>>>>>>> core >>>>>>>> begins to saturate when operated at 50Hz. You'd have to check the >>>>>>>> bandwidth though. >>>>>>>> >>>>>>> >>>>>>> P.S.: Regarding audio transformers I'd avoid those in case this >>>>>>> remains >>>>>>> in production for many years. I had my comeuppance a few months ago. >>>>>>> Needed med-grade audio isolation transformers for the audio range. I >>>>>>> thought I'd just order the same ones I did a decade ago but now ran >>>>>>> out >>>>>>> of. When I looked it was like visiting an old building and >>>>>>> discovering >>>>>>> that ... it had become a parking lot. >>>>>> >>>>>> I was just testing an ISDN transformer that we have in stock. That >>>>>> would work OK down to 300 Hz, if I keep the voltage reasonable. >>>>>> >>>>> >>>>> Thing is, ISDN has never really caught on in the US and I believe it's >>>>> on its last leg. I wouldn't want to use ISDN products in new designs. >>>>> DSL, yes. >>>>> >>>>> Another item that could work well is the current sense inside GFCI >>>>> receptacles. That's a rock-bottom priced scenario and due to code >>>>> requirements they won't go away as long as wel live. Since these are >>>>> also needed on aricraft, companies such as Rockwell make GFCI breakers >>>>> also for 400Hz. >>>>> >>>>> >>>>>> Inductors and transformers are *such* a nuisance. >>>>>> >>>>> >>>>> I like them. The project I am working on today would be impossible to >>>>> do >>>>> without. It gets to be really interesting when working with tapped >>>>> inductors in a resonant configuration. >>>> >>>> They are indispensable, but hard to spec and buy. There are very few >>>> standard transformer footprints or specs, and it's hard to find things >>>> in stock. Some of the "dual inductors", which are really 1:1 >>>> transformers, are multi-sourced and usually stocked. >>>> >>>>> >>>>> Maybe I am biased because I grew up in the world of RF where almost >>>>> nothing ever works without inductors. >>>> >>>> Standard 1603-1206 inductors are easy to get. But a lot of cool RF >>>> inductors are sole-source. >>>> >>>> We use tons of Talema 1:1:2:2 ISDN transformers... about 14K so far, >>>> 3K in stock. In dc/dc converters, mostly, or as pulse transformers, >>>> occasionally signal transformers. I did a coolish 120 VDC supply with >>>> one recently, to power a photodiode. >>>> >>>> Delivery is slow, from India, but no supply issues so far. I know that >>>> I can get custom-built equivalents, if I ever need to. >>>> >>> >>> I found these guys to be very customer-oriented: >>> >>> http://www.xfmrs.com/ >>> >>> Giving back and thinking worldwide for that is what I like most: >>> >>> http://www.xfmrs.com/NewsDetail.aspx?id=25 >> >> We donate about $40K a year. One of my charities is The Fistula >> Foundation, which repairs broken ladies. I'm approaching 100 repairs >> now. >> >> > >That is one of the great charities. If no one else has said it, "thanks >John".
As long as I can do some real good for some real people, I can be obnoxious on s.e.d. ! -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 5 May 2015 18:44:44 -0700 (PDT), Bill Sloman
<bill.sloman@gmail.com> Gave us:

>On Wednesday, 6 May 2015 05:24:22 UTC+10, DecadentLinuxUserNumeroUno wrote: >> On Tue, 05 May 2015 10:13:52 -0700, Joerg <news@analogconsultants.com> >> Gave us: >> >> >Thing is, ISDN has never really caught on in the US and I believe it's >> >on its last leg. I wouldn't want to use ISDN products in new designs. >> >DSL, yes. >> >> As a consumer access method perhaps, but ALL switches are 100% ISDN >> (for YEARS, literally). >> >> Otherwise ALL DSL would not even function. Much less high end dial-up >> modems. >> >> Cop a clue, child. >> >> DOH! > >IncandescentLinuxUserNumeroUno may not be > AlwaysWrong, but he does make some dumb > choices. Dissing me may not be particularly > stupid, but dissing Joerg is exceedingly foolish. > >IncandescentLinuxUserNumeroUno shares this > much with krw - he can't imagine that his own ideas > on a subject could possibly be incorrect.
He is an idiot, and so are you. I said nothing about "a DSL transformer". What I said was that ISDN most certainly IS still in WIDE USE. You also need reading comprehension course work. AND you are still a Goddamned, retarded line length dumbfuck.
On 6/05/2015 12:13 PM, DecadentLinuxUserNumeroUno wrote:
> On Tue, 5 May 2015 18:44:44 -0700 (PDT), Bill Sloman > <bill.sloman@gmail.com> Gave us: > >> On Wednesday, 6 May 2015 05:24:22 UTC+10, DecadentLinuxUserNumeroUno wrote: >>> On Tue, 05 May 2015 10:13:52 -0700, Joerg <news@analogconsultants.com> >>> Gave us: >>> >>>> Thing is, ISDN has never really caught on in the US and I believe it's >>>> on its last leg. I wouldn't want to use ISDN products in new designs. >>>> DSL, yes. >>> >>> As a consumer access method perhaps, but ALL switches are 100% ISDN >>> (for YEARS, literally). >>> >>> Otherwise ALL DSL would not even function. Much less high end dial-up >>> modems. >>> >>> Cop a clue, child. >>> >>> DOH! >> >> IncandescentLinuxUserNumeroUno may not be >> AlwaysWrong, but he does make some dumb >> choices. Dissing me may not be particularly >> stupid, but dissing Joerg is exceedingly foolish. >> >> IncandescentLinuxUserNumeroUno shares this >> much with krw - he can't imagine that his own ideas >> on a subject could possibly be incorrect. > > He is an idiot, and so are you.
AlwaysWrong, in vintage form. I'm well aware that Joerg isn't an idiot, as is everybody who can understand his occasional posts about the more demanding circuits than you can comprehend.
> I said nothing about "a DSL > transformer". What I said was that ISDN most certainly IS still in WIDE > USE.
But decreasing, as Joerg was pointing out. It's an obsolescent technology, just like the antique news-reading software to which you are sentimentally attached.
> You also need reading comprehension course work.
We don't all share your problems
> AND you are still a Goddamned, retarded line length dumbfuck.
And from my point of view, you are addicted to antiquated news-reading software. -- Bill Sloman, Sydney
On Wednesday, 6 May 2015 11:55:47 UTC+10, John Larkin  wrote:
> On Wed, 06 May 2015 07:39:55 +1000, "David Eather" <eather@tpg.com.au> > wrote: > > >On Wed, 06 May 2015 07:31:14 +1000, John Larkin > ><jlarkin@highlandtechnology.com> wrote: > > > >> On Tue, 05 May 2015 13:58:40 -0700, Joerg <news@analogconsultants.com> > >> wrote: > >> > >>> On 2015-05-05 1:15 PM, John Larkin wrote: > >>>> On Tue, 05 May 2015 10:13:52 -0700, Joerg <news@analogconsultants.com> > >>>> wrote: > >>>> > >>>>> On 2015-05-04 6:22 PM, John Larkin wrote: > >>>>>> On Mon, 04 May 2015 17:28:12 -0700, Joerg > >>>>>> <news@analogconsultants.com> > >>>>>> wrote: > >>>>>> > >>>>>>> On 2015-05-04 5:20 PM, Joerg wrote: > >>>>>>>> On 2015-05-04 5:00 PM, John Larkin wrote: > >>>>>>>>> On Mon, 04 May 2015 16:47:14 -0700, Joerg > >>>>>>>>> <news@analogconsultants.com> > >>>>>>>>> wrote: > >>>>>>>>>> On 2015-05-04 3:17 PM, John Larkin wrote:
<snip>
> As long as I can do some real good for some real people, I can be > obnoxious on s.e.d. !
It doesn't work that way. You being obnoxious on s.e.d. incurs a different sort of karmic debt that the kind you pay off by helping strangers who are in real trouble. The two axes are orthogonal. -- Bill Sloman, Sydney
On Wed, 06 May 2015 12:34:10 +1000, Bill Sloman <bill.sloman@ieee.org>
Gave us:

>But decreasing, as Joerg was pointing out. It's an obsolescent >technology, just like the antique news-reading software to which you are >sentimentally attached.
AGAIN! NO IT IS NOT! EVERY telcomm switch house has it on EVERY line, you absolute fucking idiot. The system will not work without it, and that includes DSL.
On Wednesday, 6 May 2015 13:04:36 UTC+10, DecadentLinuxUserNumeroUno  wrote:
> On Wed, 06 May 2015 12:34:10 +1000, Bill Sloman <bill.sloman@ieee.org> > Gave us: > > >But decreasing, as Joerg was pointing out. It's an obsolescent > >technology, just like the antique news-reading software to which you are > >sentimentally attached. > > AGAIN! NO IT IS NOT!
"Is" isn't "will be".
> EVERY telcomm switch house has it on EVERY line, you absolute fucking > idiot. The system will not work without it, and that includes DSL.
Anything that works is obsolescent. The telephone system uses a lot of DSL parts now, but it's going to go over to optical fibre for new installations - the businesses involved know that they were in telephony, but they know that they are now in communications, and DSL is a rather narrow pipe. ISDN is even narrower. -- Bill Sloman, Sydney
On Tue, 05 May 2015 23:04:27 -0400, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

>On Wed, 06 May 2015 12:34:10 +1000, Bill Sloman <bill.sloman@ieee.org> >Gave us: > >>But decreasing, as Joerg was pointing out. It's an obsolescent >>technology, just like the antique news-reading software to which you are >>sentimentally attached. > > > AGAIN! NO IT IS NOT! > > EVERY telcomm switch house has it on EVERY line, you absolute fucking >idiot. The system will not work without it, and that includes DSL.
If you google ISDN TRANSFORMER you can find pages of manufacturers. They are really nice little transformers: low copper resistance, super low leakage inductance, nice wide bandwidth, standard surface mount footprint, rugged, cheap. You can do all sorts of fun tricks with the 1:1:2:2 version. If the ISDN market dries up, there will be tens of millions of them around in warehouses. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 6/05/2015 2:37 PM, John Larkin wrote:
> On Tue, 05 May 2015 23:04:27 -0400, DecadentLinuxUserNumeroUno > <DLU1@DecadentLinuxUser.org> wrote: > >> On Wed, 06 May 2015 12:34:10 +1000, Bill Sloman <bill.sloman@ieee.org> >> Gave us: >> >>> But decreasing, as Joerg was pointing out. It's an obsolescent >>> technology, just like the antique news-reading software to which you are >>> sentimentally attached. >> >> >> AGAIN! NO IT IS NOT! >> >> EVERY telcomm switch house has it on EVERY line, you absolute fucking >> idiot. The system will not work without it, and that includes DSL. > > If you google ISDN TRANSFORMER you can find pages of manufacturers. > They are really nice little transformers: low copper resistance, super > low leakage inductance, nice wide bandwidth, standard surface mount > footprint, rugged, cheap. You can do all sorts of fun tricks with the > 1:1:2:2 version. If the ISDN market dries up, there will be tens of > millions of them around in warehouses.
Only if IncadescentLinuxUserNumeroUno is involved. If the market dries up, the rational manufacturers will stop making them, and any sensible people running the warehouses will sell their surplus stock on E-bay. -- Bill Sloman, Sydney
On 2015-05-06, DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote:
> On Wed, 06 May 2015 12:34:10 +1000, Bill Sloman <bill.sloman@ieee.org> > Gave us: > >>But decreasing, as Joerg was pointing out. It's an obsolescent >>technology, just like the antique news-reading software to which you are >>sentimentally attached. > > > AGAIN! NO IT IS NOT! > > EVERY telcomm switch house has it on EVERY line, you absolute fucking > idiot. The system will not work without it, and that includes DSL.
You're saying it's part of the FXS? -- umop apisdn