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Old 30th May 2012, 04:38 PM   #23521
jcx is offline jcx  United States
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Some noise measurements for LEDs and zener diodes
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Old 30th May 2012, 04:38 PM   #23522
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Originally Posted by jneutron View Post
Work is fun..it has always been fun...


Those embedded in this discussion already understand terminology such as ESR and ESL.

And, it is important to stretch one's understanding. Questions are not wrong.

Think of e/m theory as a crossword puzzle.

j

ps...Is "ESL" considered polysyllabic??
O K E. S. L. not esselle. (As if that means much!)

There are folks that English is not the first words they used. (Names don't count.)

It was from Ads that I sent out to food store folks, that I found small words worked well. It can be hard to write with just monosyllabic phrases.

What I did learn is that for restauranteurs pictures worked best!

ES
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Old 30th May 2012, 04:39 PM   #23523
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Just like double blind tests need to be properly interpreted. '-)
Can't be too skeptical.
Thanks again, Ed Simon, for doing the test and putting up pictures here, of what you found.
It is a matter of anticipatory design practice that I decided to NOT use a center tap in the CTC Blowtorch, however, it is not always possible to avoid using a center tap. Then what? What about an air core inductor (5mH or so) in series with the center tap before it is connected to common?
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Old 30th May 2012, 04:41 PM   #23524
SY is offline SY  United States
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Ed, how long was the lead and the braid once they were separated and how were they dressed wrt to the circuitry under test? A photo would be nice, but probably too late for that.
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Old 30th May 2012, 04:45 PM   #23525
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Thank You for the info!

My interest is in not just the low frequency noise shown here but a more broadband approach. It is nice to note he did begin to understand that effective source resistance has a large influence on noise.
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Old 30th May 2012, 04:46 PM   #23526
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I answered to John, but hoped that Ed would rear it and comment.

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I have a scope. And when I short tip of the probe with it's ground crocodile near any wire that charges caps through diodes I see spikes.
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Old 30th May 2012, 04:48 PM   #23527
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Ed, how long was the lead and the braid once they were separated and how were they dressed wrt to the circuitry under test? A photo would be nice, but probably too late for that.
3" I'll try to include a pretty picture in the article. Of course all circuits were tested the same as quickly as possible to insure the source noise stayed the same.

I did have a video guy once try to spec audio wiring. He wanted at least 5" of shielded twisted pair stripped back and covered with heat shrink tubing, using a green piece for the drain lead.

John (N) couldn't have explained it to that guy, not even with pictures.
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Old 30th May 2012, 04:50 PM   #23528
SY is offline SY  United States
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Originally Posted by simon7000 View Post
My interest is in not just the low frequency noise shown here but a more broadband approach. It is nice to note he did begin to understand that effective source resistance has a large influence on noise.
An easier way to do it is what Morgan Jones and I have done- put 20 or 30 of them in series and feed them from a current source. The noise is then much easier to measure, and by dividing by sqrt n, the individual noise density can be obtained.
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Old 30th May 2012, 04:59 PM   #23529
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I answered to John, but hoped that Ed would rear it and comment.
Actually I thought I had nice diode switching pictures, but when I went to add them to the article I couldn't find them. So on my things to do list is to redo them.

I do have the "Magic" diodes that Digikey used to sell that have switching noise of 3 to 10 times the AC voltage. It was the introduction of these diodes that made just about everyone aware of diode noise. The manufacturer pointed out that noise was not a specified parameter and their diodes did meet all spec.s Of course they did fix their process. But once the superstitious folks found one bad source of diodes they went all out with diode fixes, even using them on quiet diodes.

Now I have enough pictures of the current through the rectifier diodes to show that the transformer voltage float extends the charging time to at least 30 degrees. As you know charging starts when the AC line goes above the stored charge. What is interesting is that the current demands are so high that the upward slope is compressed a bit. Then when the AC voltage begins to drop, the current demands drop also so the voltage drifts up to extend the charging time.

What this means is that the start of charging has a maximum surge current and the stop of charging is at a very low current.

So it is the turn ON noise that has more energy than the turn off! This goes against most folks theories of how to reduce diode noise. So a small resistor in series with the diode does a lot of good for noise reduction. A small inductor causes spikes like Steve Eddy wouldn't believe (At least not without pictures!)

So Wavey did I cover what you want to reveal to the uninitiated unworthies?
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Old 30th May 2012, 05:04 PM   #23530
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An easier way to do it is what Morgan Jones and I have done- put 20 or 30 of them in series and feed them from a current source. The noise is then much easier to measure, and by dividing by sqrt n, the individual noise density can be obtained.
Yes series works, but there are two assumptions that I don't think hold!

One is that diode noise is uniform diode to diode.

The second is that it is uncorrelated!

Now we get into a gray area of I.P.

Let me see if I can get permission to go a bit further.
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