convert 150 - 300mV into 5Vdc

[Kevin Aylward]

If I was simulating it (im not) I'd bung in a resistor, and step its
value to see how much is needed to wreck the circuit. And I would
curse that I cant step a component in a logarithmic fashion, forcing
me do do multiple iterations by hand.

Not in SS

You can put lists of component values in a file and have all
combinations automatically done with one run button press.

I should add a direct log sweep mode though.

Murphy suggests that the critical winding resistance is 20% below
that of the transformer you choose

Without bothering to estimate its actual value, but if say Isat of
1mA is required then 150mV/1mA = 150 ohms, so Rwinding probably wants
to be < 50 ohms. The winding resistance varies in proportion to the
square of the number of turns (for constant winding area
utilisation), so it would be possible to design such a non-starting
transformer.

Worst case for this circuit is a bit tricky. The Idss will vary quite a
lot over device and temperature, as will the transformer saturation
point.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Jan Panteltje]

The winding resistance varies in proportion to the square of the
number of turns

I do not think so, if 1 turn = 1 Ohm, then 2 turns is 2 Ohm.
JP

 

[Spehro Pefhany]

I do not think so, if 1 turn = 1 Ohm, then 2 turns is 2 Ohm.
JP

... until you hit the second layer.

Best regards,
Spehro Pefhany

 

[Jan Panteltje]

.. until you hit the second layer.

Use a wider core!

 

[Terry Given]

Use a wider core!

To be pedantic:

Given the same core, with the same percentage utilisation of available
winding area, then the winding resistance IS proportional to the square of
the number of turns: double the no. of turns and you must HALVE the
cross-sectional area, so R-per-turn doubles, as does N - voila, R = kN^2

if the wire is very thin, it gets even worse - in this case the (constant)
insulation thickness eats a large chunk of the available winding area, so R
= kN^m where m > 2

of course "use a bigger core" might fix the problem. And it might not - go
read the historic paper on the influence of id/od ratio on the
characteristics of a toroid.....circa 1960 IIRC

cheers
Terry

 

[Jan Panteltje]

To be pedantic:

Given the same core, with the same percentage utilisation of available
winding area, then the winding resistance IS proportional to the square of
the number of turns: double the no. of turns and you must HALVE the
cross-sectional area, so R-per-turn doubles, as does N - voila, R = kN^2

if the wire is very thin, it gets even worse - in this case the (constant)
insulation thickness eats a large chunk of the available winding area, so R
= kN^m where m > 2

of course "use a bigger core" might fix the problem. And it might not - go
read the historic paper on the influence of id/od ratio on the
characteristics of a toroid.....circa 1960 IIRC

cheers
Terry

You can be pedantic all you want, I added 2x turns on my ferrite rod, and
the resistance doubled.
JP

 

[Fred Bartoli]

You can be pedantic all you want, I added 2x turns on my ferrite rod, and
the resistance doubled.

The key is : "with the same percentage utilisation of available winding
area", i.e. with the same total cross section of copper.

This is not what you're doing when just doubling your turns, keeping the
same wire.

Thanks,
Fred.

 

[Jan Panteltje]

The key is : "with the same percentage utilisation of available winding
area", i.e. with the same total cross section of copper.

This is not what you're doing when just doubling your turns, keeping the
same wire.

Thanks,
Fred.

Is this still true when you use flat copper?
JP

 

[Fred Bartoli]

Is this still true when you use flat copper?
JP

Sure. That's true whatever the wire cross section : for a given widing area,
double the number of turns and you'll have to halve the wire cross section
area, giving 4 time the DC resistance. Nothing you can do against this.

Thanks,
Fred.

 

[Jan Panteltje]

Sure. That's true whatever the wire cross section : for a given widing area,
double the number of turns and you'll have to halve the wire cross section
area, giving 4 time the DC resistance. Nothing you can do against this.

Thanks,
Fred.

OK, now I finally see what you guys ment!
Sorry it took me so long...
JP

 

[Jan Panteltje]

On a sunny day (Sun, 6 Jun 2004 00:24:03 +0200) it happened "Fred Bartoli"
<[email protected]>:JP

PS it is not true for superconducting wire.
JP

 

[Terry Given]

On a sunny day (Sun, 6 Jun 2004 00:24:03 +0200) it happened "Fred Bartoli"
<[email protected]>:JP

PS it is not true for superconducting wire.
JP

Are you sure? I thought that superconductors had finite resistance, albeit
very low - 10^-25 ohms or so. I know nothing about superconductors, but
would be very surprised if this resistance didnt vary as a function of
cross-sectional area and conductor length. But of course if the number is
still ridiculously low, who cares

IIRR there are also peak current limits - exceed this current and voila, no
superconductivity. Superconducting power transmission lines are beginning to
come into service (the first was in NY I think?)

cheers
TG

 

[Terry Given]

OK, now I finally see what you guys ment!
Sorry it took me so long...
JP

it doesnt really apply with a ferrite rod, as the available winding area is
kind of large (theoreticaly infinite . try winding a 60A CM choke on a
toroid and watch it assume paramount importance though (then thank the
people who invented pull winders for toroids - mechanized crochet hooks
Then try 600A.

Cheers
Terry

 

[Jan Panteltje]

Are you sure? I thought that superconductors had finite resistance, albeit
very low - 10^-25 ohms or so. I know nothing about superconductors, but
would be very surprised if this resistance didnt vary as a function of
cross-sectional area and conductor length. But of course if the number is
still ridiculously low, who cares

I have asked that question at an uni where they did these things, and they
told me that is was ZERO and ZERO,
that is why these magnetic fields keep in place once they injected a current.
But that was many years ago, so maybe memory gone astray.
I am no expert on that stuff.
JP

 

[Terry Given]

I have asked that question at an uni where they did these things, and they
told me that is was ZERO and ZERO,
that is why these magnetic fields keep in place once they injected a current.
But that was many years ago, so maybe memory gone astray.
I am no expert on that stuff.
JP

Hi Jan,

Im no expert either, but the closet physicist in me suggests nothing can be
zero - if for no other reason than measurement accuracy.

a quick google gave
http://cnls.lanl.gov/Highlights/1997-06/html/node4.html
which gives the resistivity as proportional to T^Q, ie non-zero. That there
is a resistivity backs up my original statement - its just bloody low. No
numerical data as yet

cheers
Terry

 

[Jan Panteltje]

Hi Jan,

Im no expert either, but the closet physicist in me suggests nothing can be
zero - if for no other reason than measurement accuracy.

a quick google gave
http://cnls.lanl.gov/Highlights/1997-06/html/node4.html
which gives the resistivity as proportional to T^Q, ie non-zero. That there
is a resistivity backs up my original statement - its just bloody low. No
numerical data as yet

OK, I have read that page, most of it I dunno anything about.
So I entered google, for 'superconductor resistance'
Looka here!
http://www.amsuper.com/html/aboutUs/super_fact.html

They say the same the guy in the uni told me, current lasts forever!
(infinite).
So what is what or if high temp superconductors are different... I dunno
JP

 

[John Larkin]

OK, I have read that page, most of it I dunno anything about.
So I entered google, for 'superconductor resistance'
Looka here!
http://www.amsuper.com/html/aboutUs/super_fact.html

They say the same the guy in the uni told me, current lasts forever!
(infinite).
So what is what or if high temp superconductors are different... I dunno
JP

The high-field (up around 20 T) magnets they use for NMR lose about 1
PPM of their field strength per day, mostly in very small jumps,
something about pinned current threads slipping or something. 1 PPM is
a *lot* to NMR, where the Qs run up around 1e9 and resonant
frequencies are proportional to field strength. The systems use
duterium locks and stuff to track the drift.

Could be that lower-current stuff doesn't decay at all.

John

 

[Terry Given]

The high-field (up around 20 T) magnets they use for NMR lose about 1
PPM of their field strength per day, mostly in very small jumps,
something about pinned current threads slipping or something. 1 PPM is
a *lot* to NMR, where the Qs run up around 1e9 and resonant
frequencies are proportional to field strength. The systems use
duterium locks and stuff to track the drift.

Could be that lower-current stuff doesn't decay at all.

John

Thanx John,

I did a bit of googling, and couldnt come up with any hard numbers - but
one site referred to the resistivity of traditional vs new superconductors.
I seem to recall around 10^-25 Ohms or so from first-year physics. Given
that 1uOhm is an astonishingly small number, another 19 orders of magnitude
effectively means they are "perfect" - 100 years = 3e9 seconds, so the
increase in time constant is such that an experimenter will die of old age
before seeing any real decrease. lets check: assume 1e-10 measurement
accuracy, then a measurable decrease will just occur in 33 years if R
reduces from 1uohm to 1e-25 ohms or so.

OK, the "zero" decay pretty much looks like that. To see something in say 1
day needs measurement resolution of about 1e-14 - thats a mighty fancy
meter.

Cheers
Terry

 

[Jan Panteltje]

The high-field (up around 20 T) magnets they use for NMR lose about 1
PPM of their field strength per day, mostly in very small jumps,
something about pinned current threads slipping or something. 1 PPM is
a *lot* to NMR, where the Qs run up around 1e9 and resonant
frequencies are proportional to field strength. The systems use
duterium locks and stuff to track the drift.

Could be that lower-current stuff doesn't decay at all.

John

Ah, good info.
Of cause Terry is right about 'no infinites' in nature..., or?
The big bang also started as a singularity, now they are talking about
what was before it.
'Infinite' or 'zero' often just means we have not been able to measure
that far.
I have learned on usenet not to use those terms ('like has no effect on'),
as some physicist will usually prove you wrong...
Yes a CD is sensitive to magnetic fields.... hehe
Regards
Jan

 

[John Larkin]

Thanx John,

I did a bit of googling, and couldnt come up with any hard numbers - but
one site referred to the resistivity of traditional vs new superconductors.
I seem to recall around 10^-25 Ohms or so from first-year physics. Given
that 1uOhm is an astonishingly small number, another 19 orders of magnitude
effectively means they are "perfect" - 100 years = 3e9 seconds, so the
increase in time constant is such that an experimenter will die of old age
before seeing any real decrease. lets check: assume 1e-10 measurement
accuracy, then a measurable decrease will just occur in 33 years if R
reduces from 1uohm to 1e-25 ohms or so.

OK, the "zero" decay pretty much looks like that. To see something in say 1
day needs measurement resolution of about 1e-14 - thats a mighty fancy
meter.

NMR is cool. You plop some water in a magnetic field and you get a
high-Q resonance that's precisely related to mag field strength, at
something like 4.3 KHz per gauss; the ratio is sort of a basic
property of the universe. Since we can measure this proton resonance
to 1 part in 1e9 or better, and since we can now measure frequency to
parts in something like 1e14, some pretty fine measurements can be
made. But, as I noted, this works best with high-field magnets which
are complex and very highly stressed, so aren't as stable as
lower-current stuff.

Here's a cute little magnet, complete with spiral staircase:

http://www.varianinc.com/cgi-bin/nav?products/nmr/spectromet/inova/900/index&cid=KPJKJJLFN

This drifts less than 10 Hz/hour at 900 MHz, which is about 0.3 PPM
per day. You leave all your credit cards down the hall when you visit
this puppy.


John