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Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 11:03:15 AM UTC-4, John Devereux wrote:
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Nice,  thanks John  

George h.  

Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 11:17:06 AM UTC-4, George Herold wrote:
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These are the sorts I was thinking of:

http://katalog.we-online.de/media/images/v2/Family_WE-PBF.jpg

I'd forgotten all about the newer "chip" styles.

Cheers,
James

Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 11:03:15 AM UTC-4, John Devereux wrote:
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That is nice, thanks.  I guess I need to whack them more often--the
last one was a decade or two ago.

Cheers,
James Arthur

Re: beads and zero ohm resistors
snipped-for-privacy@yahoo.com writes:

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Perhaps the higher current / lower Z types would tend towards your alloy
strap model.


--  

John Devereux

Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 11:56:16 AM UTC-4, John Devereux wrote:
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The end of this unit's left terminal looks like a plated copper strap:
http://media.digikey.com/Photos/Wurth%20Electronics%20Photos/7427930.jpg

But it looks almost like that guy's strap was inserted into a completed
ferrite bead, then bent; the ferrite units in my stock look like the
ferrite was formed in place around the strap.  No seams.

Cheers,
James Arthur

Re: beads and zero ohm resistors
On Wednesday, September 28, 2016 at 11:38:21 AM UTC-7, John Larkin wrote:
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My reply here does not answer your question.  However, given the more general topic of "0 ohm resistors," I want to pass on some that I found.

http://www.rohm.com/web/in/datasheet/PMR50HZPJ000

An 0402 is less than 0.5 milli-Ohm and takes 20 A.

They are not inexpensive (cheap), especially the 0402.  

I found some parts from Stackpole that I thought were "equivalent," but the more I looked at them, I thought the metallic Rohm might be different in important ways.

Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 11:38:10 -0700, John Larkin

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As noted, I measured a cheap 0805 0r resistor and got around 6
milliohms with a positive TC around 3000 PPM/K.

One of my guys measured a ferrite bead:

https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/FB_1631008.txt

https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/FB_1631008.jpg

https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/FB_Cross.jpg


The background is that we are first-article testing a new resistor/RTD
simulator box. The 5-to-50 ohm range was expected to have a positive
tempco from some range-switching SSRs, and there's software correction
for that, but the measured tempco is almost twice the expected value.
I wanted to just frob the correction factor, but some people wanted to
understand why. Turns out that about half the error is in PCB traces
and the other half is in the ferrite bead. We could replace the bead
with a zero-ohm jumper, but we may as well leave it in (EMI
garlic-vampire mode) and correct for everything.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: beads and zero ohm resistors
Hello John,
...
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No.

Have a look at the video and the pics here:
http://www.we-online.de/web/en/electronic_components/produkte_pb/we-mpsb~1.php
to get an idea. I don't now how the produce the helix and how they fill  
the gaps with ferrite.
Some are at least produced as multilayer components, just like you would  
build a multilayer transformer coil or antenne on a PCB.

Cheers

Robert


Re: beads and zero ohm resistors
John Larkin wrote...
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 I have an inrush problem with some of my high-voltage
 pulser designs, which have electrolytics to deliver
 pulses up to 20A.  Large external capacitors are also
 allowed.  In my prototypes I hold off the HV until
 200ms after the low-V supplies settle.  This means
 the switching MOSFET must dissipate a substantial
 amount of energy, 1/2 C V^2, or up to 120J for the
 onboard caps, and much more for any outboard caps.


--  
 Thanks,
    - Win

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