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SMPS and grounding

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11 minutes ago, R1200CL said:

 

As I was staring to write you a long explanation, I suddenly understood I have no idea why I did ?

 

As of cause ? these current leakage doesn’t care about what signal is traveling through either the DC cable, nor the Ethernet cable. 

 

Thanks for notice...(my stupidity)

 

To defend you, I can say that I am all the same. An assumption is enough to get my brain working on high speed. I can tell you that all the things that pass through my brains nerve centers is not always that sensible! ?

However, like Einstein said coriousity has it's own reason to exist! ?


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1 hour ago, Superdad said:

 

You are conflating frequency with impedance and that is not correct.  In other words, there is high-impedance leakage and low-impedance leakage--and both have both high and low frequency components.

 

 

Actually the LPS-1 already completely blocks low impedance leakage.  And the SMPS grounding trick (I am now trying to source units that are already grounded--they exist--or get Mean Well to supply a custom version for us) is completely effective at shunting (getting rid of) the high-impedance leakage.

Due to our use of transistors (instead of large, expensive, noisy relays) to alternate between banks of ultracaps, there is a very small amount of capacitance across power domains in the LPS-1 (less than 100pF) which is enough to allow some high impedance leakage through.

 

To prove to everyone how effective the grounding trick is, here are 3 graphs--directly measuring leakage versus frequency.  (do not try to compare these to anyone else's measurements--scales and units are different; and these are in dBM not dBV, that's 13dB difference right there).

 

Here is the leakage (just up to 1KHz, John has done wider bandwidth measures as well) from a stock Mean Well GST40A:

MW40_1khz_0929.thumb.gif.59a646e8b689fee585ef61185c6d1105.gif

 

Here is the same Mean Well unit with its DC zero-volt ("ground") tied to the ground pin of its IEC320-C14 inlet this way:

59f3a12e91eb9_MWGST40groundedcopy.thumb.JPG.95cfee84264067b6277a79e6ef6ab26d.JPG

MW40_1khz_internalgnd_0929.thumb.gif.89f1766cd8262b961cd6d3f8bee361aa.gif

 

What you see remaining is all the low-impedance leakage. (Again this is the leakage measurement of just the grounded GST40A.)

 

And here is the leakage (not output noise; these are all common-mode leakage tests which John can explain) from an LPS-1 being powered by the same modified Mean Well:

MW40_1khz_internalgnd_lps1_0929.thumb.gif.6b97e417231ac2f45511c8b84715986d.gif

You can see how all the low impedance leakage is now blocked.

 

So yes, this is our admission that LPS-1, when used with an SMPS whose DC output is not grounded to AC mains, will let high-impedance leakage though (that's a different graph that I don't presently have from the same test set up).  How did we allow this to happen?  

a) The test set up to see this properly was not made; 

b) Power supplies used during development may have been grounded units;

c) We were not looking at high-impedance leakage or at these frequencies;

d) We were concentrating on other aspects of performance: Isolation, ultra-low noise, ultra-low impedance;

e) While John purposely chose transistors with the lowest possible capacitance, the spec sheets all specify capacitance only with the transistor in its "on" state, whereas in our application it is the capacitance of the part in its "off" state that is letting a little leakage through.  (He has since built a special board/jig to measure these transistors, and while he found a couple of parts that have both a little lower capacitance and meet the various functional current/voltage requirements, there will always be some; Even if we cut the total capacitance in half the high impedance stuff can still get through; The ground/shunting solution is simpler and totally effective.)

 

I hope this clears things up for those who are interested.  And yes, I have egg on my face for all those months during which I insisted that the choice of "energizing"/charging supply would make zero difference to the output of an LPS-1.  Of course noise, output impedance, and other aspects of our "floating" supply's isolation are not affected.  But yes, based on our choice of bundled SMPS for charging, some leakage current gets through--unless you ground/shunt it. Too bad the Mean Well GST25A-07 we chose was not the sort that already was grounded in this fashion (no safety or emissions violations come from it as far as we can tell; and other certified SMPS units are already built that way).

 

Happy Friday.  Have a great weekend everyone,

--Alex C.

 

 

Sorry about conflating impedance and frequency and thank you for explaining more thoroughly.

 

That being said, how does one block the low impedance component? 

I have already added the grounding umbilical to the output of the two LPS which I am using per John's guidance.

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3 hours ago, Superdad said:

And the SMPS grounding trick (I am now trying to source units that are already grounded--they exist--or get Mean Well to supply a custom version for us) is completely effective at shunting (getting rid of) the high-impedance leakage.

This is promising.  Is there an SMPS product line that's already grounded with a variety of volts/amps that might help me replace my other SMPS (the ones not powering an LPS-1).  Since I don't do DIY and find iFi's $50 kit obscenely priced, this would be great.


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14 hours ago, Superdad said:

 

Hi BigGuy:

Can you be more specific?  

a) What power supplies are you using?  

b) What components are they powering?

 

My post was only discussing SMPS (switch mode power supply) leakage and its relation to our UltraCap LPS-1.  Our LPS-1 always blocks low-impedance leakage.

 

And since LPS (linear power supply) units in general do not have much leakage current (high or low impedance), there is usually never a need to ground their outputs. 

There is the somewhat separate topic of Ethernet switches and grounding of a power supply feeding one.  However, if one is feeding an Ethernet switch from an LPS (ours or someone else's), grounding of that supply's zero-volt leg is not useful--unless you are using a specific Ethernet switch (such as the NetGear FS105/108) that John tested and found to also block leakage coming in from other Ethernet devices (by grounding).  

 

As for blocking the low-impedance leakage component of SMPS units, for that you need to either use an UltraCap LPS-1 or ditch the SMPS.  

I defer to John as to if there are actually any low impedance leakage currents making it into a switch from other networked components.  I suspect that the magnetics at every EN jack already blocks that.

 

Sorry this is so confusing.  O.o

--Alex C.

Yes, this impedance issue IS confusing so I appreciate you and John having the patience to simplify so more of us can understand.

 

To your questions...

 

One LPS is an old desktop "brick" from HP used to power laptops where I am using the 5V tap to power the ADNACO Glass/USB device <http://www.adnaco.com/products/s3a/>  

 

The second is a DIY LPS designed by a member of our audio society.  It is adjustable but I am using it to output 9V to a USB dongle similar in concept to the REGEN.

 

Both LPS are AC powered from a PS Audio P300 regenerator.

 

I recognize that John's grounding umbilical is more relevant to SMPS which by nature have more of an impedance issue than LPS but do remember him saying that it could/would help LPS as well.  I figured what the hey.

 

Having treated the high impedance component, I was looking to address the low impedance.

 

Thanks.

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2 hours ago, JohnSwenson said:

Theoretically you could do the same with USB, BUT USB is not just AC, it requires DC connectivity through the data pair, so a transformer will not work. This has made series blocking very difficult to deal with. There are a few solutions, but none of them block the high impedance components, so you still need to shunt the all the high impedance source before they get to the USB cable if you want to stop ALL the leakage from getting through to a DAC

 

Hi John, epic explanation.

 

Does this mean even the Intona fails to block high impedance components?

 

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1 hour ago, JohnSwenson said:

Yes, that is correct.

 

John S.

 

Thanks John. I guess the challenge now is how to shunt the high impedance components from a computer's non-grounded SMPS, before it gets to the Intona/ISO REGEN etc.

 

Is the USB adapter that comes with the iFi Groundhog a good solution? Using that in the computer's USB port?

 

iFi-Groundhog.thumb.png.dcdc3d6dd2912b8a70d8c51fa08bfe5d.png

 

 

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6 minutes ago, Em2016 said:

Thanks John. I guess the challenge now is how to shunt the high impedance components from a computer's non-grounded SMPS, before it gets to the Intona/ISO REGEN etc.

 

 

Many Desktop PC's do have their SMPS grounded.


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Just now, sandyk said:

 

Many Desktop PC's do have their SMPS grounded.

 

Laptops with 2-pin plugs don't though (like my Macbook).

 

Of course you can run off batteries but that can be impractical and add cycles to the battery.

 

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On 10/27/2017 at 5:38 PM, Superdad said:

 And yes, I have egg on my face for all those months during which I insisted that the choice of "energizing"/charging supply would make zero difference to the output of an LPS-1.

 

"Again this is not about measurements.  I am under zero obligation to sell our products to hostile people who seek only to defame us."

 

Is this a position you could find yourself climbing down from?

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@JohnSwenson nice investigation ;) 

 

Help a simple country boy out please: the term “high impedance leakage current” is making me a little dizzy as I try to drink my coffee on this Sunday AM. Impedance isn’t a term normally used to qualify a current so perhaps we should rename this before it takes on a life of its own — you mean “high voltage/impedance” = current ... what is a better term? 

 

Also these currents are going to be way more important at higher frequencies. I think if a circuit were made available to precisely illustrate the excellent point you are making here (this is all about parasitic capacitances and inductances) this frequency point will be better illustrated. (Yes— high impedance probes are essential when working with RF)


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or is it this: the solid state “relays”/MOSFET switches in the power supply have very high impedance when “off” and connected to the input SMPS so transmit this leakage?

 

yeah I think these are parasitic capacitances on the package, mosfets etc and really do pass much more current at higher frequencies — and grounding the SMPS does provide a low impedance path to ground.


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14 hours ago, sandyk said:

 

Many Desktop PC's do have their SMPS grounded.

IF the LPS or SMPS is grounded with a 3-prong plug, does this mean a grounding umbilical on the output is superfluous?

 

Any electronic downside to using one even with 3-prong?

 

 

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3 hours ago, jabbr said:

@JohnSwenson nice investigation ;) 

 

Help a simple country boy out please: the term “high impedance leakage current” is making me a little dizzy as I try to drink my coffee on this Sunday AM. Impedance isn’t a term normally used to qualify a current so perhaps we should rename this before it takes on a life of its own — you mean “high voltage/impedance” = current ... what is a better term? 

 

Also these currents are going to be way more important at higher frequencies. I think if a circuit were made available to precisely illustrate the excellent point you are making here (this is all about parasitic capacitances and inductances) this frequency point will be better illustrated. (Yes— high impedance probes are essential when working with RF)

@Jabbr,

 

Great minds question alike (except one of them hasn't finished his Dual Bank Floating Supercap Supply DIY board yet... hint, hint!).

 

SO I asked pretty much the same question a few weeks ago:

 

On 10/1/2017 at 10:57 AM, gstew said:

John,


I don't understand the context & meaning of 'high impedance and low impedance components' of the SMPS noise.

 

I've never heard of noise having an impedance.

 

Can you provide some background and definition on that?

 

TIA!

 

Greg in Mississippi

 

AND John gave one of his textbook clear answers... even a DIY tech like myself understood:

 

On 10/2/2017 at 2:19 PM, JohnSwenson said:

Any electrical signal (useful or noise) has a "source impedance". You can think of this as a resistor the signal has to go through before it gets to where you are looking at it. It is an impedance because it can vary with frequency.

 

As a concrete example, lets say your source has an impedance of 1k ohms, if you apply that to a 1k ohm resistor to ground, the signal level will be cut in half. That is actually how you usually measure output impedance, run the input through a known resistance to ground and measure the level across the resistor, the output impedance acts as a voltage divider with the known resistor, from the resulting voltage you can calculate the source impedance.

 

For any given "noise source" there is at least one mechanism generating that noise. The mechanism will have a particular impedance associated with it. In many cases more than one mechanism is involved with generating noise, each of these mechanisms may have a different output impedance. There may also be different frequency response issues with the different mechanisms.

 

This seems to be the case with SMPS, there seems to be at least two different mechanisms that cause the leakage and they seem to have very different impedances. I don't know what those mechanisms ARE, i have not spent time in figuring that out, I'm not really interested in building my SMPS so I don't really care what actually causes it, especially since it will take a LOT of work to find out and I would much rather spend my time working on other things.

 

Leakage current causes issues in audio systems when it flows through a conductor, creating a voltage across that conductor which causes something to not behave the way you would like it. In some cases this is just directly creating noise on the shield of an interconnect and the receiving circuit sees this as noise. In a DAC this can show up as noise developed on a ground plane that can modulate an oscillator causing increased jitter on the clock.

 

There are two ways you can attenuate the leakage noise, you can put a resistance in series with it, or you can shunt it. Lets cover both of the separately.

 

The series resistor form works like this: you have the source impedance and you stick a resistor in series. Lets look at some possible values and outcomes. Say 100 ohm output impedance and you put 1 mega ohm in series, that is going to attenuate the noise drastically. But what if the source is 100 mega ohms, then that 1 mega ohm resistor is not going to do very much (a VERY slight attenuation). So for high impedance series resistor works good for lower impedance source, but not well for high impedance source.

 

The shunt form works by shunting the source around your source around the "test point", frequently to ground. Say you have the 100 ohm source and you shunt with 1 mega ohm, nothing happens, but of the source is 100 mega ohms, that 100 mega ohm shunt will dramatically decrease the amplitude.

 

I know the output of the SMPS is a combination of impedances by running a bunch of these shunt and series tests with different values and seeing what I get. The only way to get the results I saw is if the source consists of both high impedance and low impedance components at the same time.

 

The upshot is that it takes BOTH methods to get rid of the noise, both a shunt and a series.

 

John S.

 

 

 

 

 

I hope that helps!

 

Greg in Mississippi


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Tuning: Various stands/vibration control, noise filters on digital power and Ethernet cables, audio cables MIT reg or Shotgun, ALL gear modified or DIY'd, MOST supplies linear or LPS-1s (DVD players & amps have SMPSs)

 

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3 hours ago, jabbr said:

or is it this: the solid state “relays”/MOSFET switches in the power supply have very high impedance when “off” and connected to the input SMPS so transmit this leakage?

 

yeah I think these are parasitic capacitances on the package, mosfets etc and really do pass much more current at higher frequencies — and grounding the SMPS does provide a low impedance path to ground.

 

MOSFETs where?  There are none in the LPS-1.

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34 minutes ago, BigGuy said:

IF the LPS or SMPS is grounded with a 3-prong plug, does this mean a grounding umbilical on the output is superfluous?

 

No!  Just because a PS may have a 3-prong (and actually have that pin connected on the primary side), it does not mean that it is also connecting that ground to its DC zero-volt output side.

 

An example that is the 40 watt Mean Well I posted graphs and a photo of:  Unlike the 25W series MW (okay the 7V version is labeled 22W) the GST40A units do come with their C14 AC input ground pin connected to the primary side.  But they still need the mod (green wire in my photo or external accomplishment of the same) to shunt the high-impedance leakage back to ground as discussed.

 

See also my overdue reply to @rickca in my next post.

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12 minutes ago, Superdad said:

 

MOSFETs where?  There are none in the LPS-1.

Haha are you sure? Of course there are ;)

 

What “relays” are you using? Solid state or mechanical?

 

Hint: regardless, the parasitic capacitance in the “open” position determines your “high impedance” circuit ;) 


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On 10/27/2017 at 5:49 PM, rickca said:

This is promising.  Is there an SMPS product line that's already grounded with a variety of volts/amps that might help me replace my other SMPS (the ones not powering an LPS-1).  Since I don't do DIY and find iFi's $50 kit obscenely priced, this would be great.

 

Hi Rick:

Well the thing is, this is not something that any SMPS manufacturer specifies.  And it seems to vary some even within a brand's offerings.  So each one has to be tested (VERY easy: Just put a continuity checker across the ground pin--has to be a 3-wire unit of course--and the outer barrel of the output and hope for a beep.)

 

I have bought a few brands through normal distribution but don't thing we can draw any conclusions about who does and does not offer what we seek.

I confess that most of my sourcing research is focused on Chinese brands that have low cost models which meet our requirements (or for which the factory is willing to customize for us).  I am looking for pieces for $8-15 in quantity, not $22-28 or more.

 

But if anyone comes across units that display continuity (as above), please e-mail me with the brand and model.  Even if you don't discover a brand whose whole line is correct for us, maybe there will be a model or two.  It's worth knowing.

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