Power supply for voltage references

[dietert1]

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

[The Soulman]

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?

[dietert1]

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

[TiN]

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  .

[Kleinstein]

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.

[dietert1]

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

[TiN]

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.

[MegaVolt]

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.

[iMo]

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..

[branadic]

@ 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-

[dietert1]

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

[Kleinstein]

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. 

[TiN]

Branadic hardly a sales person  . 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.

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.

[TiN]

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.

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.

[View[+]Finder]

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.

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

[Gyro]

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.

[dietert1]

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

[Vgkid]

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.

[Kleinstein]

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.

[iMo]

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..

[Kleinstein]

The transformer for digital signal transfer is relative bulky and needs extra circuit - however there are new transformer based couplers also in chip form.

[KK6IL]

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

[Kleinstein]

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.

[iMo]

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..

[maxwell3e10]

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?