Author Topic: Power supply for voltage references  (Read 38150 times)

0 Members and 6 Guests are viewing this topic.

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2255
  • Country: br
    • CADT Homepage
Re: Power supply for voltage references
« Reply #100 on: January 18, 2021, 08:25:43 pm »
Have seen those in a Keithley 213 quad isolated DAC. They have low coupling capacitance as they are. And the advantage that you have access to the core. I remember bending up a corner of the uppermost core sheet and soldering a wire to it to connect the core to guard.

Regards, Dieter
 

Offline The Soulman

  • Frequent Contributor
  • **
  • Posts: 961
  • Country: nl
  • The sky is the limit!
Re: Power supply for voltage references
« Reply #101 on: January 19, 2021, 07:17:01 pm »
Any drift for both the meter and the ltz1000 should be down in the noise for such a short time and temperature range.
Did you let everything warm-up (for several hours) before starting the measurement/data-logging?
 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2255
  • Country: br
    • CADT Homepage
Re: Power supply for voltage references
« Reply #102 on: January 20, 2021, 07:15:04 am »
Your reference output voltage increased by about 1 mV. In your own words this is bad. To get anywhere near the expected results, one would use voltage regulators between batteries and reference board. As far as i remember that HP 3458A reference board needs bipolar supply to work properly.
Also i was wondering, whether that BNC cable on your black box is the reference voltage output.

Regards, Dieter
 
The following users thanked this post: View[+]Finder

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Power supply for voltage references
« Reply #103 on: January 20, 2021, 08:16:49 am »
Something is awfully wrong. Ditch the LiPo (it's there just waiting you to short something by accident and blow stuff up) and use 36313A PSU to test first.
At first glance you seem to forgot connect heater supply or returns to the PSU, as that could be nearly only possible explanation to this insane instability. Tempco of most A9 boards is beyond what any of the 6.5d DMMs can measure in small temperature swings (<10°C).

Why you don't show more photos showing exact setup , connections, wiring etc? It's not year 2005 when you had to pay $$ for every megabyte of internet data on dialup  ;).
« Last Edit: January 20, 2021, 08:19:01 am by TiN »
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 
The following users thanked this post: View[+]Finder

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14511
  • Country: de
Re: Power supply for voltage references
« Reply #104 on: January 20, 2021, 08:58:48 pm »
The ground to the heater power must be connected to the main ground - just keep the output separate. It is just inside the DMM circuit that heater ground and power ground use separate paths, but they are still connected on the PCB.

The negative voltage is only used to reduce the ground return current - this is not so much an issue here. For testing only the reference, one should get away without using it: one mainly misssed the extra heat source.
It would help to have a regulated voltage for the main part. The heater may use the same battery pack with a separate regulator or even before the regulator.
 
The following users thanked this post: View[+]Finder

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2255
  • Country: br
    • CADT Homepage
Re: Power supply for voltage references
« Reply #105 on: January 20, 2021, 09:56:45 pm »
Heater current 0.045 mA means the oven is inactive. The LTZ1000 datasheet recommends 0.1 to 0.3 W heater power. Depending on heater voltage it should take at least 10 mA or so.
And the schematic in the image shows the heater minus separate from the reference Gnd, so in case of using two separate supplies one should make an external connection.

Regards, Dieter
 
The following users thanked this post: View[+]Finder

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Power supply for voltage references
« Reply #106 on: January 20, 2021, 11:12:41 pm »
Either LTZ chip is blown open now, or power is not properly supplied. Normal heater currents for A9 are about 25-29mA for heater and few mA for signal ground.

As pointed out, ground MUST be connected as PSU end. Easy to check if heater works by looking at control temperature input (1/13k divider tap output) and control feedback (opamp output for oven control). Both should be same voltage around 0.4** V-ish. You should have four wires going to PSU which are +12...+15V for signal power (opamp, etc), signal ground return, +15 or so power for heater in, heater return to PSU-. Then short circult jumper between returns at PSU LO ports, if your PSU has isolated outputs (like E36313A does).
Then you have your sense lines for zener+ and zener- from A9 to voltmeter.
« Last Edit: January 20, 2021, 11:15:25 pm by TiN »
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 
The following users thanked this post: View[+]Finder

Offline MegaVolt

  • Frequent Contributor
  • **
  • Posts: 928
  • Country: by
Re: Power supply for voltage references
« Reply #107 on: January 21, 2021, 07:44:18 am »

If you click on the virtual display 6500 there is an option to save only the screen. In my opinion, this is more convenient than saving entire screenshots.
 

Offline iMo

  • Super Contributor
  • ***
  • Posts: 4938
  • Country: vc
Re: Power supply for voltage references
« Reply #108 on: January 21, 2021, 11:43:03 am »
The first thing I would do - I would replace that cheapo LT1013 dil8 socket with precision one. I had many problems decades back with digital stuff not mentioning analog while messing with those sockets.. Unless the precision socket is not suitable there because of different plating..
 
The following users thanked this post: TiN

Offline branadicTopic starter

  • Super Contributor
  • ***
  • Posts: 2417
  • Country: de
  • Sounds like noise
Re: Power supply for voltage references
« Reply #109 on: January 21, 2021, 05:02:06 pm »
@ ViewFinder

Would be great if you would either open a new thread or chose another one, as this thread is intended to address power supplies for voltage references and your specific problem has nothing to do with it, as far as I can see. *no hijacking*

@ exe
The plastic I used for the shield is Proto Pasta, the shield itself is 3D-printed

Still waiting for components, while I already build a second transformer.

-branadic-
Computers exist to solve problems that we wouldn't have without them. AI exists to answer questions, we wouldn't ask without it.
 
The following users thanked this post: TiN, Jacon, Okertime

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2255
  • Country: br
    • CADT Homepage
Re: Power supply for voltage references
« Reply #110 on: January 22, 2021, 08:20:21 pm »
I think the engineering approach you propose is completely valid. Maybe the OP is a salesman and his thread title was really meant as "Look at this power supply for voltage references". Then people like you and me make it into a wild collection of personal taste, belief and knowledge. A true mishap.

Regards, Dieter
 
The following users thanked this post: View[+]Finder

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14511
  • Country: de
Re: Power supply for voltage references
« Reply #111 on: January 22, 2021, 09:40:54 pm »
The demand on the power supply is mainly low injetion of common mode signal, low capacitance and good EMI compatibilty.  It is relatively hard to tel how a reference circuit reacts to EMI - there can be resonances. In addition the reference is not alone, but it would be connected to some meter or similar and these may to be sensitive.

It is still a good question on how to quantify the quality - there are different frequencies involved and the capacitance from the output side  to ground can make a difference. Chances are it would be more the current to a low impedance connection that would matter, not so much the open ciruit voltage, with little extra capacitance. 
 
The following users thanked this post: View[+]Finder

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Power supply for voltage references
« Reply #112 on: January 22, 2021, 11:57:30 pm »
Branadic hardly a sales person  :-DMM. And thread started for PSU design talk and sharing results, not for fixing particular altered and possibly damaged LTZ ref.

Before going EMI rabbit hole it is better to apply requirements expected from voltage reference application. If its going to be measured by floating DVM and null-meters against other references then major required feature of PSU is low leakages and common rejection to avoid ground loops. If reference is used as a part of bigger system (like A9 3458A module) it have different requirements for PSU. Above shown A9 module is very sensitive for pickup and grounding. It is essentially useless as transfer reference on ppm level. Just turning common LED lamp with crappy SMPS will ruin your A9 output stability and noise. No matter if powered by nude virgin custom ppmium transformer or  fire breathing lithium pack. And thats offtopic here, we already have excellent RFI\EMI test thread right here.

I really don't understand View[]Finder's resistance to make own thread named "Experiments with DMMs and references" and post all stuff there, people will be much happier to help and suggest things when it's all in one dedicated spot, instead of guessworking thru 5 different hijacked threads on what is going in. Threads creation does not require payment or anything  :) PPMs also nothing to do with external data, that is completely wrong, just like saying percents are anything to do with calibrations. It's just a convenient tool to do the opposite - remove absolute values from measurands and outline the deviation of one set with arbitrary selected point(s) against another.

Quote
to find a way to have a $200 standard perform as well as a $2,000 one
$200 standard will stay such, no matter what magical power is used to power it. Noise is least of the problems in voltage references, compared to much harder issues like stability, temperature/humidity/pressure dependence, jumps and stress factors, robustness during transport, etc.
« Last Edit: January 23, 2021, 12:17:21 am by TiN »
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 
The following users thanked this post: Andreas, View[+]Finder

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4543
  • Country: ua
    • xDevs.com
Re: Power supply for voltage references
« Reply #113 on: January 23, 2021, 03:22:05 am »
Threads are designed as tool to organize things. This one is about power supplies for voltage references. Not about references themselves or how to measure/analyze them as ultimate goal. It is nice and respectable to keep metrology section (and any other section same way) organized and structured, instead of having all threads go in random directions, also to help newcomers to find information easier. Branadic got into power supply design reference by study on modules he got, and its quite interesting direction. Your results with A9 board seem to be all over and so far unique to your setup/equipment/case/device. I can't speak for everyone here, but instead of trying to reply to your posts in every somewhat remotely related threads about this I would be more inclined to spend time helping you rectify issues in separate dedicated thread. From posts it is visible that you misunderstand some key concepts (nothing wrong with that!, we all learning here) so those warrant to be separated from power supply design or repair of my 3458A U2 as well. PPM means parts per million. It does not mean parts per ideal 10V, you don't subtract anything to calculate ppm deviation of value A to B.

Quote
others' offers of advice were welcome and I would gladly have accepted a suggestion to relocate that discussion. None was offered.
I've suggested to create your own thread twice in two different threads already. I think you just trolling now.
Why make it hard on people to navigate thru multiple offtopic discussions? To save an entry in forum database? :-//

The reason why EEVBlog is one of the best forums about electronics is variety of topics and all different people who have shared engineering knowledge about those things in all those threads. Trying to keep it structured is least we can do before we drown in huge pile with everything mixed in a single thread. I'm done, sorry all.
« Last Edit: January 23, 2021, 03:32:24 am by TiN »
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 

Offline View[+]Finder

  • Supporter
  • ****
  • Posts: 186
  • Country: us
    • Sparks! A Learning Place for Curious Minds
Re: Power supply for voltage references
« Reply #114 on: January 24, 2021, 07:31:27 pm »
Threads are designed as tool to organize things. This one is about power supplies for voltage references. Not about references themselves or how to measure/analyze them as ultimate goal. It is nice and respectable to keep metrology section (and any other section same way) organized and structured, instead of having all threads go in random directions, also to help newcomers to find information easier. Branadic got into power supply design reference by study on modules he got, and its quite interesting direction. Your results with A9 board seem to be all over and so far unique to your setup/equipment/case/device. I can't speak for everyone here, but instead of trying to reply to your posts in every somewhat remotely related threads about this I would be more inclined to spend time helping you rectify issues in separate dedicated thread. From posts it is visible that you misunderstand some key concepts (nothing wrong with that!, we all learning here) so those warrant to be separated from power supply design or repair of my 3458A U2 as well. PPM means parts per million. It does not mean parts per ideal 10V, you don't subtract anything to calculate ppm deviation of value A to B.

Quote
others' offers of advice were welcome and I would gladly have accepted a suggestion to relocate that discussion. None was offered.
I've suggested to create your own thread twice in two different threads already. I think you just trolling now.
Why make it hard on people to navigate thru multiple offtopic discussions? To save an entry in forum database? :-//

The reason why EEVBlog is one of the best forums about electronics is variety of topics and all different people who have shared engineering knowledge about those things in all those threads. Trying to keep it structured is least we can do before we drown in huge pile with everything mixed in a single thread. I'm done, sorry all.
Please accept my apologies for the confusion this has caused--particularly to those who have offered me assistance in the past--and I assure you that I have no intent to "troll" on this or any other forum. I remain interested in contributing to the discussion centers on measurement, analysis and reduction of errors in voltage as measured by the kind of instruments I own: former premium-grade Keithley, Keysight and Fluke products. I believe that is consistent with the interests of the general readership. Of course I will be happy to start another thread. Would it be asking to much to request suggestions for a title and, please, may I place it under the Metrology section?

Best regards,
Donal B. Botkin

 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 9773
  • Country: gb
Re: Power supply for voltage references
« Reply #115 on: February 06, 2021, 06:44:24 pm »
I hesitate to post this as it's a completely off the wall idea.

As it happens, I had the same toothbrush in my disposal pile!

So some quick approximate measurements with DMM6500 in Digitize Current mode measuring from one side of the battery inside the toothbrush to PE on the back of the DMM6500.

DMM6500 noise floor: 0.005uApp
Without charge base nearby/on: 0.4uApp
Without charge base nearby/on, inside thick steel box section grounded to PE through 1M resistor: 0.2uApp
Whilst on charge base: 1.5uApp

As is, no good; the modifications you suggested would be a good start but not something I'm interested in doing at the moment.

Edit: I'm unsure if there might be some interaction with the DMM6500's own leakage (0.14uApp)

Wow, some impressively quick measurements, thanks!

As you say, it sounds like no good as it stands, but scope for experimentation. There's certainly enough physical gap, without the toothbrush body to implement some sort of primary screen, and a separate guard screen on the secondary.

https://youtu.be/JJgKfTW53uo?t=1320 :). This, of course, rerpresents only one model from one brand. Other may do it better.

Thanks exe, I hadn't realised that Dave had done a teardown, well of the toothbrush side, I think all of the charging bases are potted internally for waterproofing. The one that I've pulled apart is a single winding with a bridge rectifier rather than a lower loss 2 winding two diode full wave arrangement.

Dave showed some interesting waveforms, interesting about the 800Hz charge pulsing - I had assumed that they were 'dumb' HF oscillators but maybe there's some (unreachable) intelligence in there.

I will report back any findings.

Just a quick follow-up. I just posted a quick teardown of the charging base for a Lidl torch in Dave's original Braun toothbrush teardown discussion thread... https://www.eevblog.com/forum/blog/eevblog-284-braun-toothbrush-teardown/msg3451180/#msg3451180

It seems to have similar power output capability to the Braun but operates at a higher frequency, in the region of 150kHz, and without the severe ringing that Dave observed. Surprisingly it's just a single transistor oscillator circuit. I was expecting something a bit more complex to cope with the inductive load difference between zero load (removed) and full charging load.

Hopefully of some interest for a high isolation supply anyway if it is quieter. The higher operating frequency might be easier (or more difficult!) to filter out.
Best Regards, Chris
 

Online dietert1

  • Super Contributor
  • ***
  • Posts: 2255
  • Country: br
    • CADT Homepage
Re: Power supply for voltage references
« Reply #116 on: February 09, 2021, 07:04:18 am »
Yesterday i found this image taken by ve7xen in a Datron 1081 multimeter. Those guarded transformers look like the solution i arrived at in my study of the "Art of electronics" proposal. Except each of those transformers includes a single turn winding (green wires). How does that work?

Regards, Dieter
« Last Edit: February 09, 2021, 07:06:47 am by dietert1 »
 

Online Vgkid

  • Super Contributor
  • ***
  • Posts: 2722
  • Country: us
Re: Power supply for voltage references
« Reply #117 on: February 09, 2021, 08:13:11 am »
Those look like isolation transformers for the digital side. They were widely implemented before the use of opto-isolators Here is an example in the HP 3456A.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14511
  • Country: de
Re: Power supply for voltage references
« Reply #118 on: February 09, 2021, 08:43:33 am »
The circuit is like 2 transformers in series: First some 2x10 to 1 turn and than back 1 to 2x10 turns. One turn helps to reduce the capacitance of a single transformer and the 2nd transformer halves the capacitance and brings the signal back to a level were one wants it.

The transformer with 2 cores close by and one coupling winding is a similar principle, just a few more windings for coupling and less distance. The closer coupling reduces stray magnetic fields, that can be more of an issue with a power transmission than with just a digital signal transfer in the old meters.
 

Offline iMo

  • Super Contributor
  • ***
  • Posts: 4938
  • Country: vc
Re: Power supply for voltage references
« Reply #119 on: February 09, 2021, 09:21:52 am »
First time I can see TTL chips made in El Salvador.. Interesting..
PS: the transformer solution looks better to me - no LED brightness degradation over time..
« Last Edit: February 09, 2021, 09:32:05 am by imo »
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14511
  • Country: de
Re: Power supply for voltage references
« Reply #120 on: February 09, 2021, 04:22:08 pm »
The transformer for digital signal transfer is relative bulky and needs extra circuit - however there are new transformer based couplers also in chip form.
 

Offline KK6IL

  • Regular Contributor
  • *
  • Posts: 56
  • Country: us
Re: Power supply for voltage references
« Reply #121 on: February 10, 2021, 10:26:50 am »
Quote
The transformer for digital signal transfer is relative bulky and needs extra circuit - however there are new transformer based couplers also in chip form.

Some magnetic couplers, such as the NVE IL26x series, power up in an unknown state(BTDT). 5 pF isolation. The Silicon Labs Si866x does not require startup sequence, in to out C not specified.  Note those devices are for data transmission, not power, as are the transformers in the photo Vgkid posted.

John
 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14511
  • Country: de
Re: Power supply for voltage references
« Reply #122 on: February 10, 2021, 11:36:48 am »
Those ring transformers shown by Vgkid may also be OK for low level power transmission, but in the 3456 and other old meters they were used to data transfer.

The 2 transformers shown in the picture are one side only - so there are 2 more similar transformers at the other side. So the 2 don't belong together, they are 2 separate data channels.
 

Offline iMo

  • Super Contributor
  • ***
  • Posts: 4938
  • Country: vc
Re: Power supply for voltage references
« Reply #123 on: February 10, 2021, 12:47:56 pm »
The transformer for digital signal transfer is relative bulky and needs extra circuit - however there are new transformer based couplers also in chip form.
There are about 4-5 TTL chips at the both sides usually - no problem to put all the stuff inside a smallest cpld or an fpga. Thus you would need the 2 small FT37-43 toroids (an example) and maybe 2 resistors to limit the current into the transfromer winding. With two cores per channel (one is at tx, one is at rx side) the coupling capacitance gets to a half and the max isolation voltage doubles..
« Last Edit: February 10, 2021, 01:03:34 pm by imo »
 

Offline maxwell3e10

  • Frequent Contributor
  • **
  • Posts: 870
  • Country: us
Re: Power supply for voltage references
« Reply #124 on: October 23, 2022, 08:39:38 pm »
I am wondering if anyone has suggestions for reducing small sharp spikes in a simple linear power supply that are associated with rectifier diode bridge. The spikes are synched to AC line and last 20-50 microsec. I am not sure how they propagate to the rest of the circuit, perhaps magnetic or capacitive coupling. They occur when the diodes turn on, so the exact phase depends also on the power supply load. Are there perhaps better diodes to use or putting some sort of filter to smooth out the turn-on transitions?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf