Hi all, silly question. Dave's EEVblog was on... there was this bifilar wound coil (starts at ~39 minutes in)
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.
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
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.
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.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.
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.
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.
Without watching the video, you missed the mark.
Mikek
Why confuse the issue by throwing in a X-tal osc?
The inductor is out of a light dimmer.
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
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
OK that makes sense, so I think of it as an inrush current limiter?
George H.
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** Hold on a mo, Australians typically don't have ghastly accents or squeaky voices. David L Jones happens to be a short person, so has a higher pitch to his voice than most. Here is a vid where he has a guest presenter, Doug Ford whom I know well.Doug is not very tall either, but he is taller than Dave and I am taller than both at 5ft 9 inches.
Doug gives a talk about microphones, devices he dealt with a fair bit once when he worked as electronics designer for Rode Microphones here in Sydney.
.... Phil
The Amidoncorp.com website has a few books on magnetics, for rf.
Cheers
I'm using the SRF0703, 100 uH, as a mosfet gate driver.
My whine is that they don't ID pin 1. The only way to orient it is by the value screened on top. 101 looks a lot like 101 upside-down!
Luckily, it works installed upside down. But it's hard to convince QC of that.
You can do fun switcher tricks with a dual inductor.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Hmm, an interesting circuit. Momentarily shorting out your source signal? Part of your SSR monitoring scheme? That USB dpdt switch with enable is a cool part.
I'm surprised at your choice of 100V DPak MOSFET. You have about 4V gate drive, but that 270mR part wants 10V, is unhappy below 6V, at 4V it's Ron must be 10x higher!
Looking in my huge MOSFET table, I see a few 100V DPak parts rated at Vgs = 4.5 or 5V, e.g., FQD13N10L 200mR, IRLR3410, 125mR, DMN10H100SK3 100mR ...
Coupled inductor, John. Coupled is the word to use.
--
Thanks,
- Win
The current through the 1M sampling resistors is either switched to the shared test bus, or diverted to ground. If it wasn't grounded, some current would shoot through the switches of unselected channels.
(An undocumented problem in most cmos analog mux's is this effect, fets turning on when inputs go wrong-side of the rails.)
USB and digital bus switches are superb analog multiplexers, at a fraction of the price of official multiplexers.
The gate drive will be 10 or 12 volts. It's an open-loop flyback converter, driven by an open-drain output from a TPIC6595. The drive duty cycle sets the gate drive voltage. That's been breadboarded.
The 0.33r wirewound resistor absorbs the energy if the user puts a hard voltage across the SSR, and FPGA code monitors the situation and shuts down the channel before anything (including connector pins and PCB traces) blows up. First-article testing will be fun.
PCB design review on Monday.
I ignore the Word Police.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Interesting, even with 1M series resistance?
What size, p/n for the resistor? Your old IRFR120 type with 270mR max will be sharing a significant part of the load. The DMN10H100SK3 I mentioned has 80mR max Ron, and is cheaper, about 30 cents.
--
Thanks,
- Win
Yes. Before the ESD diodes turn on, the series fets can turn on when their sources are driven past the rails. My 70 uA of input current would shoot through into the other signal pins. This will happen at any current level. Some analog mux's specifically avoid this effect, but most don't.
I don't think that's the actual fet on the final BOM. That schematic is one that I have at home, not the final one. I think we're using some 8 mohm parts in real life. We did spend a lot of time thinking about protecting the SSRs. I tested several of the so-called self-protecting fets, and they were various sorts of terrible.
The bottom line is that almost all the fault energy goes into the resistor, not the fets.
I posted to s.e.d. about my resistor exploding experiments.
My best choice was a Vishay AC05 axial wirewound, reliable when pulsed at 15 joules.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Yes, that's the function that it seems to fill. Unlike a bifilar winding on a core, the transmission-line must be a single layer wound around that stick of ferrite (a second layer, NOT adjacent to the ferrite, would not be a continuation of the delay line). That's consistent with the odd one-layer winding on a stick (and 'inductor' function is less consistent).
It's a neat measurement problem to find a way to test the gizmo at sufficiently high current to see its 'normal' operating impedance and delay. You want a step of a few dozen volts and an amp or so of drive.
he called it "bifilar" seems more like "hairpin" wound to me.
You've got near-field interaction of the individual copper wires with the nearby bits of ferrite. and that's about it.
-- This email has not been checked by half-arsed antivirus software
-- John Larkin Highland Technology, Inc lunatic fringe electronics
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