Ultra Low Noise Lab Power Supply Extender for your existing lab supply

[branadic]

Hi,

I wanted to have an "Ultra Low Noise Lab Power Supply" for experiments with voltage references and instead of having a bunch of batteries (remember your green finger print on this earth) and instead of always using a low noise regulator for each quick and dirty voltage reference setup I decided to build a power supply for this and similar purpose.

LT3042 and LT3045 are available for a while and page 23 of the datasheet gave me exactly what I needed. It took its time to grow this idea and meanwhile some guy on DIY audio came across with a ready to go pcb for a first setup.

The price of 12€ for an audiophile white looking board seemed okay to modify it to my needs. It's a two channel, fixed current board paralleling 3x LT3045 giving up to 15V and up to 1.5A per channel, more than enough. Instead of the 10way trimmpots on this board I added Bourns multiway pots in 100k and 100k with 100k in parallel for the voltage setting of up to 15V.
Further I bought an 50VA, 12Vac toroidal transformer and some panel meters for voltage and current. The panel meters are supplied by the rectified voltage at the input of the voltage regulators.

The case was planed using Schaeffer front panel designer, exported as dxf and lasered at a local company. I decided to use a proMa EG2 aluminium profile (103mmx56mmx168mm) based chassis, but with wider front and back panel instead of standard 103mm and thus wider top and bottom plate.

It works pretty well, even though I seem to have some minor issues with mains hum coupling somewhere into the output. I'm currently investigating on that and ordered some self-adhesiv mu-metal foil to wrap it around the transformer. Further I will replace cables by shielded ones.

One the other hand without the transformer it is a pretty nice extender for existing lab power supplies, forming them into a low noise supply for the bench. So this is the idea. Let me ask, is there any interest in a group buy of bare boards and the aluminium chassis parts? All other parts can be easily bought in the bay and at your local electronic store or distributor. I plan to redesign the board with additional current limit setting, which is currently missing.

Meanwhile the guy with the pcb cracked up and sells assembled boards with fixed output current to the audiophile community for big bucks. 

EDIT: Added a first picture of my build.

-branadic-

[Henrik_V]

branadic, if you put some effort into a clean powersource, how about a better decoupling and guarding from mains?
DMM power supplies transformers from Fluke/HP use two shieldings , one for PE and one for guard...

[mzzj]

branadic, if you put some effort into a clean powersource, how about a better decoupling and guarding from mains?
DMM power supplies transformers from Fluke/HP use two shieldings , one for PE and one for guard...

That what I was also thinking. Toroidal transformer is bad if you want to avoid coupling to mains borne noise and one without shield screens is extra bad.

18650 Li-ion battery pack and LT3045 would avoid all the ground loops and conducted noise..

[branadic]

That's an effort I can spend, but I'm sure most of the people here on the board are not willing to pay the resulting price. Thus the idea of an ultra low noise power supply extender for existing cheapo lab supplies
But noone said that I won't do both.

-branadic-

[prasimix]

How are you going to shield noise that comes from cheapo power supply? Did you already try to connect LT3045 and check result? I presume that you are well aware how ambitious is your title (i.e. ultra low noise).

[BravoV]

Whats the low noise target in numbers or measurable metrics ?

[branadic]

How are you going to shield noise that comes from cheapo power supply? Did you already try to connect LT3045 and check result? I presume that you are well aware how ambitious is your title (i.e. ultra low noise).

The LT3045 has pretty good PSRR, so no worries whatsoever. You just connect the extender with banana jacks to your common cheap power supply.
Yes, I already connected the board to my lab power supply (PPS5330) and measured noise (0.1Hz - 10Hz) in the order of 2µVpp @ 1V and 20µVpp @ 10Vdc. Yes, be sure that I got infected by metrology in almost every fashion

Whats the low noise target in numbers or measurable metrics ?

See answer before, take a look at the datasheet of LT3045 and remember that three are paralleled.

-branadic-

[prasimix]

Great, now I noticed in your signature that you're well equipped. I never been in position to measure anything below 440 uV that shows my "super-duper" Rigol DSO with input grounded .

[branadic]

Simply add a low noise amplifier to convert your Rigol into a low noise measurement system

Added a first picture to the first post.

-branadic-

[prasimix]

That make sense . First I have to find one which I can build (I believe there is a bunch of them someplace on this forum).

[T3sl4co1l]

I wonder how much emissions those LED displays give off.

I have a few, I should check.

In short: you can call it whatever you like, but it is not low noise unless you've MEASURED IT SO!

Tim

[branadic]

In short: you can call it whatever you like, but it is not low noise unless you've MEASURED IT SO!

I'm sure you can read and I already stated that I measured ~2µVpp (0.1 - 10Hz) @ 1V and ~20µVpp @ 10V in configuration as an lab extender. I didn' state that I measured it in configuration as a stand-alone lab supply.

I received some mu metal foil (0,1mm) today and wrapped it around the transformer (configuration as stand-alone lab suplly). I'm currently waiting for my low noise amplifier to load the input cap to 10V output.

-branadic-

[T3sl4co1l]

In short: you can call it whatever you like, but it is not low noise unless you've MEASURED IT SO!

I'm sure you can read and I already stated that I measured ~2µVpp (0.1 - 10Hz) in configuration as an lab extender. I didn' state that I measured it in configuration as a stand-alone lab supply.

Oh, in a reply lower down.  Hard to see at a scan.

What about 10Hz to 10MHz, say?

Tim

[branadic]

What about 10Hz to 10MHz, say?

Step by step. Currently I measure it in the stand-alone solution, first 0.1 - 10Hz, next 10Hz - 100kHz as I have an amplifier for that too.

-branadic-

[branadic]

First impression in stand-alone configuration (with transformer powered from 230V mains line) and 10V output voltage. One division equals 5µV (0.1x setting on the scope, 80dB noise amplifier).

-branadic-

[branadic]

Did some further measurements in both configurations and it seems that there is no difference between Lab Supply Extender and Stand-Alone version, low frequency noise (0.1 - 10Hz) is in the order of 2µVpp per volt.

Next step is to measure 10Hz - 100kHz region.

-branadic-

[branadic]

It turned out that the hum that I measured was due to the cable between DSO and ULNPS supply I used for measuring. Replaced RG58 coax by twisted teflon cable and picked up hum is now much smaller but not fully vanished.
Attached is a picture of the inside and a picture of the preliminary front panel (a piece of printed paper laminated and attached with double-sided adhesive tape).

-branadic-

[jpb]

An interesting project.

What is the position on the boards? I have more power supplies than I need really (an Agilent, a Hameg and a TTi) but I like the idea of being able to add an ultra low noise front end and perhaps use the same approach for dedicated power supplies to other projects (OTT but hobbyists don't need to comply with the constraints put on commercial engineers!)

Given that the meters display down to less than a mV and the current can be up to 1.5A a useful addition might be sense inputs on the front panel but I guess for your purposes you don't plan to use the higher currents and don't particularly need the accuracy.

[branadic]

The voltage meters measure the voltage at the output jacks and are just as accurate as they come from asia. Technical parameter are given as below:

Weight: 16g
Display mode: Five 0.36 LED digital tube
update rate: > 3s/time
Physical size: 48 x 29 x 22 mm (L*W* H)
Opening size: 45 x 26 mm (L*W)
Supply voltage: 3.5-30V
Lead wire length: 14 cm（4 lines）
Measurement range: DC 0-4.3000-33.000V
Operation temperature: -10 degrees~65 degrees
Measurement accuracy: (0.3‰+ 2words) {means the table worst case maximum error of less than 10mv normal within error 2mv}
Red line 1:Power Supply + Black line 1:Power Supply -
Red line 2:VIN + Black line2: VIN -

They are powered from the rectified transformer voltage. Similar for the ammeter:

Color: Black
Display: 5 digits 0.36" LED
LED color: Blue
Working voltage: DC 3.5-30V
Current measuring range: 0-3.0000A
Current measuring accuracy: ±(0.5‰+2digits)
Working temperature: -10°C~+65°C
Dimension: 48 x 29 x 22 mm
Cable Length: 140mm

It measures the current from the negative jack to the regulator board. The regulator board is the white one on the left side with the blue heat sink.

-branadic-

[Wolfgang]

Hi,

I have some suggestions for improvements of your design:

- Make shielded compartments, one for the input filter, transformer, rectifier and first filter caps, and seperate ones for the other stuff
- separate power supplies for the DMMs, also in a shielded box
- User a preregulator before the final ones, also in an shielded box
- Final regulators also in a shieled box, preferably with coaxial output
- Use feedthru caps for the connection between boxes

Am I paranoid ? Yes. 

I was trying to make absolutely quiet power supplies for noise measurement preamps. The problem I had is that most RFI is coming from outside, from LEDs, IOTs, Mobile phones, PLC, ... To kill all that is difficult and needs RF building techniques.
As a last resort, I made battery powered supplies as well, they are the best so far ...

https://electronicprojectsforfun.wordpress.com/power-supplies/battery-operated-power-supplies/

[Richard Crowley]

The photo of the insides of the enclosure look surprisingly conventional. I see no evidence of shielding or even wire routing that one would expect in a low-noise design.  Aren't the digital displays noisy?

[branadic]

Well, you can solve a problem from the direction of panic (top down), which ends up in an expensive piece of kit or you can solve a problem bottom up, build something and improve it until you reach your goal. I always choose the latter
Noise from the panel meters can be easily filtered as it is high frequency. Couldn't find a problem till now, but if it turns out to be a problem I will perform some required steps on that.
Up to now there was no need to use panic shielding. Well at least, as I'm not sure if the mu metal shield around the transformer was really necessary. But since this is a self-adhesive tape one I won't remove it anymore. Instead the classical way is:
- to twist all AC cables
- avoid ground loops, even shielded cables can create them, when shield is connected on both ends

If really necessary I will replace some cables by twisted shielded ones, but therefor I need to make further measurements to see if this is required here.

-branadic-

[Wolfgang]

Your approach is just as valid as mine. I have more effort, but your probably have more redesign steps.

Hint: If you want rocket science or extreme performance, try to exclude as many errors as you can beforehand. There will be enough pitfalls left for you to fix. Murphy never sleeps. 

[branadic]

You are right Wolfgang, but what is critical for the stand-alone supply is less of an issue for the lab extender, as you don't have the 50Hz hum and the related problems as a source inside you device. But obviously there is not much interest in such a lab supply extender. Would have thought the resonance is much bigger.

Finished the first measurements on my stand-alone solution in the 10Hz - 100kHz range and can now see the advantages that needs be addressed next.

-branadic-

[Wolfgang]

Hi Branadic,

if you just want to finish off the noise and ripple of an existing PSU, have you seen the tricks from Charles Wenzel with his active noise killer circuits ?

http://www.wenzel.com/documents/finesse.html

Maybe this helps, when mounted close to the circuit to be powered.

Maybe a comparison of voltage regulator chips is also interesting:

https://www.bartelsos.de/dk7jb.php/rauschen-von-spannungsreglern

Another great source of tricks and infos is the reverse engineering of old HP power supplies with top performance.
I am looking for one of those on eBay just to have a look inside. Manuals are probably available at the BAMA archive.

Regards
  Wolfgang

[branadic]

Hi Wolfgang,

I do know both websites and also made some measurements and simulation using ideas from both.

-branadic-

[Wolfgang]

Hi,

I just had a look at it, but one questions remains - the LM317 is a really bad regulator regarding noise - the performance would probably a lot better if you had used an LM723 with PNP pass transistor and a Wenzel cleanup shunt afterwards - did you try this one ?

Regards
   Wolfgang

[Andreas]

Hello Branadic,

I had a bad experience with 50 Hz hum.

I was measuring 1/f (0.1 - 10 Hz) noise as usual of a battery powered reference with my 4th order band pass filter cirquit.
The output looked quite plausible: around 4uVpp for a 10 V reference.
But the signal looked somewhat "fuzzy" against similar measurements.
So I did a FFT analysis which revealed a strong 50 Hz (and 150 Hz) signal.
When zooming in you can also see a 0.8uVpp 50 Hz amplitude in the raw signal.
(Ok I should have done a noise floor measurement before actually measuring noise.)

Root cause was a switched on HP34401A near my "cookies box (tinned can)" where I put in my references and the amplifier.
Usually I would think that a 6.5 digit DMM has enough shielding around the transformer but obviously this is not true.

Also other transformers I have to put away for more than 0.5m to get no influence above noise floor.

So I would use e.g. a 12V AC wall wart with enough distance to my low noise supply or split the design into 2 boxes.

https://de.rs-online.com/web/c/stromversorgungen-transformatoren/netzteile/steckernetzteile/?searchTerm=12VAC

with best regards

Andreas

[carl0s]

That's a curious ruler. I'm trying to decide if I could use one of those, or if a tape-measure is better.

[branadic]

Wolfgang, this is about a power supply extender with variable voltage setting based on TL3045, not LM317, LM723 or fixed voltage regulators. The measurements I performed in the linked thread was about LM317 and since I had the components and the noise amplifier laying around and was interested in the answers I simply did it.

Andreas, thanks for the input. I haven't observed 50Hz hum in my 0,1 - 10Hz noise measurement yet, maybe due to 14s record time? I activated FFT on the scope, but saw nothing, so I will have a look on that. But I can see mains line hum in my 10Hz - 100kHz measurement and will need to improve the build for stand-alone configuration with the transformer in the same case as the regulator board. I do have some rf sheet metal from former rf projects to create some case seperators.

About shielding of dc rail cables, what would you suggest? Twist positive and negative rails and add a shield connected to the case or would you go for coax? I was curious to see, that a high quality coax cable between dc output jacks and DSO picked up quite a lot of mains hum, while a twisted cable reduced this significant. So I tend to use twisted but shielded cables.

However for the lab supply extender you only have to keep away mains line from it.

-branadic-

[Andreas]

Hello Branadic,

I would go for twisted pair against 50 Hz (magnetic) hum.
The reason is simple: The shield of a coax is simply not thick enough for magnetic shielding. So twisting is the more effective measure.
Low frequent (magnetic) shielding is done by the skin effect: the field generates a current in the shield which produces a counter magnetic field.
But at 50 Hz and copper you will need many multiples of 9.4 mm as shield thickness to get a effective shielding.

https://www.adt-audio.de/ProAudio_Grundlagen/Skineffekt/Eindringtiefe.html

Of course a additional shield is not completely useless: it helps against capacitive coupling.

with best regards

Andreas

[Wolfgang]

Hi,

the plausible reason for the 50Hz is that the 34401A (and successors) are always averaging over an integer number of line cycles, so this influence is averaged out and a perfect transformer shielding is not needed. This is also found in the spec sheet of the meters.

If line interference is cumbersome, you could try:

- twisted wires so that magnetic influence cancels out (works better than coax)
- maximize distance between the source of magnetic fields and the sensitive circuitry
- you could optimize stray fields by changing transformer mounting and direction
- never load transformers to the max because stray fields rise when cores approach saturation
- use toroids instead of classic transformer cores
- check rectifiers for no snap effects (use schottky or soft-recovery, snubber circuits, ...)
- soft iron boxes (or mu-metal) can shield some magnetics fields quite well.

To branadic,

OK, the LT3045 is a regulator with impressive data, I never used one of them due to the max voltage being too low. This plus a shunt noise canceller could yield good results, why not. I can try when I am back home at my lab in September.

Much luck !

[branadic]

Twisted all cables and also added MKS2-100nF on the output jacks, this gave a slight improvement in noise, but not good enough.
A seperate compartment for keeping out 50Hz hum would require at least a 1.5mm steel case. The rf sheet metal I have is only 0.5mm, not the perfect choice. So currently I stuck and can't go on.

-branadic-

[Echo88]

The only cheap source of shielded transformers i was able to find were transformers for tube-amplifiers, for example: https://www.ebay.de/itm/Rohrengleichrichter-Netztrafo-355/123279036514?hash=item1cb400d062:g:3EgAAOSw7t1a-pQz

Can someone suggest a source for double shielded transformers,preferably toroids, like Henrik mentioned?

[branadic]

The only thing I know are R-core transformers, but can't say nothing about their performance.

-branadic-

[Messtechniker]

I'd put the transformer, then not necessarily a torroid, with mains input filter, bridge rectifier
and a large cap + a small cap and a bit of series inductance in a separate metal box you can keep nicely
far away (2 to 3 m or more, use shielded cable) from your low noise regulation box. Saves you
all that possibly expensive shielding effort which even so may be insufficient.

If still not satisfied you might try two back-to-back transformers with careful
passive filtering (100 Hz low pass) in between to get rid of high frequency mush
coming from the mains.

A power transformer with a shield between primary and secondary would be preferable,
but these are expensive custom designs* often for medicinal equipment.
And might be salvaged from such..... Good of a one off but not so good if others
want to build your circuit.

Just a few ideas.

*) just ask Pikatron or Haufe in Germany for a quotation

[branadic]

Thanks, but I will go a different way:
First, because it's relative easy for me to manage, make a steel tube (1.5 - 2mm thickness) with steel washers for both ends and magnetically encapsulate the toriod transformer. Yes I know, there are some more cables carrying the mains line hum, thus...
Second, design a steel case (1.5 - 2mm) for the regulator part, laser it, weld the single parts together (for such reasons I bought kweld) and install it inside the aluminium chassis.
Third, I already ordered R-core transformer for comparison and will measure differences in different orientations, which could also be interesting for further projects.
Normal transformers have the disadvantages that they are big and don't fit into my chassis.

This will take some time for the material to arrive, but it's worth learning.

-branadic-

[Wolfgang]

Just a thought - tinplate (Schubert) boxes could be easier to handle; and they have good RF shielding properties.

[branadic]

Just a thought - tinplate (Schubert) boxes could be easier to handle; and they have good RF shielding properties.

That's correct, but since it's only tin plated steel you need a certain thickness to surpress 50Hz/60Hz. Following the picture below this gives 2mm @ 100Hz.



The curve in the above diagram uses μr=460 for steel AISI 1010 and a specific resistance of 6.9e-7 ohm*m. Other formula indicate at least 1.5mm for ST37. Now you might understand why the cases of good instruments are that massive around the transformators.

-branadic-

[mzzj]

Just a thought - tinplate (Schubert) boxes could be easier to handle; and they have good RF shielding properties.

That's correct, but since it's only tin plated steel you need a certain thickness to surpress 50Hz/60Hz. Following the picture below this gives 2mm @ 100Hz.

https://rfantennas.files.wordpress.com/2013/12/eindringtiefe2.png
The curve in the above diagram uses μr=460 for steel AISI 1010 and a specific resistance of 6.9e-7 ohm*m. Other formula indicate at least 1.5mm for ST37. Now you might understand why the cases of good instruments are that massive around the transformators.

-branadic-

Wrong pic or you extrapolated from graph? Your graph shows 60 micrometers at 100 kilo-hz?

AFAIK its even worser than that when you are trying to suppress (magnetic) near-field:

[Wolfgang]

Hi branadic,

I am not sure if the Schubert boxes are really made of steel. To me it looks like a very soft iron alloy (Weißblech). They can make steel ones, too, but you have to order them explicitely. How well do your curves fit to soft-iron alloys ?

[branadic]

Correct, I extrapolated to 100Hz but also checked with a µr of 250 for steel. Maybe an optimistic assumtion, there is not much on the net about it. I don't want to surpress near field but low frequency from mains line.

As far as I know tinplate is just tin plated steel, nothing fancy and I couldn't find any hint on carefully treatment, which would indicate some special grain orientation of the steel.

Meanwhile I started to upgrade my 10Hz - 100kHz 80dB AN83 amplifier. Since now I had 330µV/10V SMD tantalum installed, which was fine for measuring voltage references. I now upgraded to 3x AVX Corporation FFB54D0117KJC, so that I'm able to measure over the full output voltage range of the power supply and up to 75V.

-branadic-

[Harm314]

Hi Branadic,

The power supply extender sounds interesting, but I'm not certain from your posts what you intend to deliver: PCB only, PCB + parts, or fully built module.

If I read the demo board sheet correctly it is built using a four-layer PCB. That is beyond my design skills.

[branadic]

One the other hand without the transformer it is a pretty nice extender for existing lab power supplies, forming them into a low noise supply for the bench. So this is the idea. Let me ask, is there any interest in a group buy of bare boards and the aluminium chassis parts? All other parts can be easily bought in the bay and at your local electronic store or distributor. I plan to redesign the board with additional current limit setting, which is currently missing.

Wrote the answer in the first post. It will be a dual layer board only. The aluminium chassis parts get cheaper the more people are coming together. But up to know only two persons are interested.

Back to the stand-alone solution:
Found some shield from industrial cables today. Which cables should be shielded? DC cables? AC cables? What to connect shield to? GND (for DC cables) or earth (for both)? Do we have some experts on that or is it just try and error by measuring the resulting noise?

-branadic-

[branadic]

Received some goodies today 

-branadic-

[BravoV]

Received some goodies today 

Whats the SCN wire stands for ?

Btw  where did you buy it ?

[Cody Turner OKC]

woah, intresting production date on those... hahah

[Gerhard_dk4xp]

That means 9th of April in Europe.

I'd like to know if there are more to be sourced?

I have just put an 650 VA isolation transformer into a 4 height units 19" box
with some outlets and lots of filters to feed my scope and a NGT20
power supply or two. There is no safety ground on the secondary,
but lots of ferrite. It seems, my worst ground loop problem is gone.

Cheers, Gerhard

[2N3055]

Received some goodies today 

Whats the SCN wire stands for ?

Btw  where did you buy it ?

That is the screen to minimize capacitive coupling.
I'm interested how this transformers will perform...

[branadic]

Received some goodies today 

Whats the SCN wire stands for ?

Btw  where did you buy it ?

SCN (green-yellow) means, as 2N3055 already mentioned, screen and has to be connected to earth.
It's already all there and linked in the #msg1740833

-branadic-

[mzzj]

I have been eyeing(eying?)  those small R-core transformers also for similar projects.

Would be interesting if you measure pri-sec parasitic capacitance for the R-cores and your toroid.
WAG that toroid is 10 times worse.

[splin]

Are you sure the screen is a proper electrostatic screen? Looking at this similar transformer:

 https://www.ebay.co.uk/itm/115V-230V-30W-R-Core-Shield-Transformer-Audio-Amplifier-DAC-12V-12V-9V-9V/323400748432?hash=item4b4c2fcd90:g:xmsAAOSw~SlbHIxm

I wouldn't be surprised if the 'screen' connection was to the overall copper wrap which would be worse than useless by increasing the inter-coil capacitance.

How would a proper screen be arranged on an R-core transformer given that it would need to be placed between each coil and the core as well as between the cores. There clearly isn't a screen fully encapsulating each winding as the ends of the windings are clearly visible in the photos.

Is it not usual to have independent primary and secondary screens?

[mzzj]

Are you sure the screen is a proper electrostatic screen? Looking at this similar transformer:

 https://www.ebay.co.uk/itm/115V-230V-30W-R-Core-Shield-Transformer-Audio-Amplifier-DAC-12V-12V-9V-9V/323400748432?hash=item4b4c2fcd90:g:xmsAAOSw~SlbHIxm

I wouldn't be surprised if the 'screen' connection was to the overall copper wrap which would be worse than useless by increasing the inter-coil capacitance.

How would a proper screen be arranged on an R-core transformer given that it would need to be placed between each coil and the core as well as between the cores. There clearly isn't a screen fully encapsulating each winding as the ends of the windings are clearly visible in the photos.

Is it not usual to have independent primary and secondary screens?

AFAIK r-core transformers are usually/often wound with primary and secondary on separate legs/bobbins. This gives good isolation and low interwinding capacitance but larger leakage inductance and stray magnetic fields.
Usually you have to select balance between interwinding capacitance and leakage inductance, on 50 Hz operation and low noise measurement equipment I rather have low capacitance.

Super easy to also add your own static screen between bobbins, just don't make it shorted turn 
For best results you can also consider grounding the core.

OT: didn't know how the R-core transformers are wound, pretty cool:

edit: after more googling I think the primary is split between both bobbins. Shielding between windinds  is still easy compared to toroid transformer.

[splin]

AFAIK r-core transformers are usually/often wound with primary and secondary on separate legs/bobbins. This gives good isolation and low interwinding capacitance but larger leakage inductance and stray magnetic fields.

The direct interwinding capacitance might be quite low due to the bobbin spacing but both coils will have relatively high capacitance to the core so they are in series. Grounding the coil will help stop mains noise coupling to the secondary but not mains earth borne noise.

However, inserting screens between each coil and the core might not be too difficult? As I understand it the primary shield is normally grounded and the secondary is connected to guard?

[branadic]

Time to go on...
Attached a comparison of the new R-core transformer (65VA) with ring core transformator (50VA) type RKT 5012 with additional mu metal shield.

-branadic-

[splin]

Hi branadic, what is the screen wire connected to on the R-core? Is is to a copper foil wrapped around the transformer or does it have a proper electrostatic screen(s)?

Are you able to measure the primary to secondary capacitance easily?

[branadic]

post 12bit

Hi branadic, what is the screen wire connected to on the R-core? Is is to a copper foil wrapped around the transformer or does it have a proper electrostatic screen(s)?

Are you able to measure the primary to secondary capacitance easily?

I can't tell you what the screen wire is connected to. I would need to remove all tapes to see that, as it's not visible and would thus damage the transformer.
The only thing I currently have at hand to measure capacitiance is a VNWA. If you give it a few days I can measure it at work at a reasonable instrument.

-branadic-

[branadic]

Measured capacitance of the toroidal vs. R-core transformer...

toroidal transformer with additional mumetal shield
- 99.7pF

R-core transformer
- black to brown1:37.4pF
- black to brown2: 63.1pF
- black to yellow1: 41.7pF
- black to yellow2: 60pF

- red to yellow1: 43.6pF
- red to yellow2: 71.6pF
- red to brown1: 43.5pF
- red to brown2: 76.1pF

- black to screen: 66.9pF
- red to screen: 82.5pF

Measurements were proven to be reproducible and performed @ 1MHz.

-branadic-

[Zorc]

Very interesting project, thank you!
Have you made any more modifications and are you satisfied with the final result?

I've been considering building a power supply based on the LT3045 as well with a few fixed voltages but with adjustable current limit (and current display)

[Wolfgang]

post 12bit

Hi branadic, what is the screen wire connected to on the R-core? Is is to a copper foil wrapped around the transformer or does it have a proper electrostatic screen(s)?

Are you able to measure the primary to secondary capacitance easily?

I can't tell you what the screen wire is connected to. I would need to remove all tapes to see that, as it's not visible and would thus damage the transformer.
The only thing I currently have at hand to measure capacitiance is a VNWA. If you give it a few days I can measure it at work at a reasonable instrument.

-branadic-

Hi Branadic,

For an ultrastable, ultra low phase noise oscillator project I needed a *really* quiet PSU. After some homebrew attempts, I ended up with a Keysight B2962 SMU with ultra low noise filters. This part does make a difference, but it is expensive.
Maybe you can clone the output filters to improve your design ?

Regards
  Wolfgang

[branadic]

Hi,

didn't make any further modification to the setup, but am using the power supply now and then.

-branadic-

[niner_007]

branadic, can you share pictures of your bare LT3045 PCB? I’m currently working on a low noise supply based on LT3042, the topology is inout filtering and EMI - transformer - rectifier - capacitors- LT3081 pre-regulator - LT3042 regulator; one PCB with input filtering, pre-regulator, another PCB, stacked on top, with filters and connectors for the two independent LT3042 PCBs, eventually I plan separate metal cans for transformer, pre-regulator, and LT3042; attached is two of the PCBs

[Vovk_Z]

These LED pane meters powered from the same line will make output noisy (somewhere at kHz or tenth on kHz).

[niner_007]

I believe the adjustable resistor and long wires to it, also introduces noise. The reason I asked for the bare PCB, was because LT3042 requires special layout considerations, LT/AD, documents the layout guidelines in the data sheet, if you treat it as a normal regulator it won’t have the advertised performance.

[branadic]

Just some update.
I noticed quite large noise injected by the blue LED panel meters, they are based on ADCs and powered by the rectified and unregulated input voltage to LT3045, not by their regulated output voltage. Thought, PSRR should do it, but the ADCs themself introduce noise.
Thus, I've replaced them with analog panel meters. It looks ugly, but that's how you're doin' to achieve low noise.
Now, even a DIY 10V reference based on LTZ1000CH shows low noise.

-branadic-