DE/EU Simple LM399 Reference Board, improved second Version

[RoadRunner]

A little while ago i made a quick LM399 based reference board and posted on the forum. Many people have made few suggestion.
So here the improved board.
Now it has reverse polarity protection using P-MOSFET with Power status LED

Good quality 1K Pot in series with 10PPM 20K register for output voltage adjust-ability.
Because LM399 initial tolerance is only 2% , feedback resistor value depend on LM399 initial calibration , it may range form 8.2K to 9.5K



PCB Gerber and source file are available here
https://github.com/circuitvalley/LM399_Voltage_reference

https://www.circuitvalley.com/2018/11/diy-open-source-lm399-V2-voltage-reference-10v-dmm-calibrate.html

There a little video description show you temperature plot over 17 hours with temperature ranging from 14 to 27 degree C.

[RoadRunner]

Here is one unit which was shipped to one forum member from previous batch.

[RoadRunner]

3 sold in one go , only two remaining

[RoadRunner]

Does any one want, Last one before Christmas?

[Iwanushka]

I will take it.

[RoadRunner]

I will take it.

Sorry , All Gone for now, next batch after Chirstmas.

[mk_]

I will take it.

Sorry , All Gone for now, next batch after Chirstmas.

 if Iwanushka is in a urgent need for the device then I will wait for the next batch even if the money arrived on your account during the next days.

[branadic]

If someone is looking for a LMx99 based 10V reference, I should receive some boards of a PWM based voltage reference soon, hopefully next week.

https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1955149/#msg1955149

-branadic-

[Iwanushka]

I will take it.

Sorry , All Gone for now, next batch after Chirstmas.

 if Iwanushka is in a urgent need for the device then I will wait for the next batch even if the money arrived on your account during the next days.

Mate, thanks for your kind offer, but I'm not in a hurry I can wait for the next batch.

[mk_]

Parcel arrived well packed, testing later this weekend

Thanks a lot

Michael

[RoadRunner]

Board is back in stock if someone needs one please drop a pm.

Thanks

[toastedcrumpets]

Pm sent, I'd like one please

[RoadRunner]

Pm sent, I'd like one please

you got one, Few still available.

[hellzakk]

I'll take one

[RoadRunner]

I'll take one

you got one

[nfmax]

Mine arrived safely this morning and is currently being tested. I'm using an HP 34401A which was last calibrated by Keysight on 8th January, and has a history of very good accuracy on the 10V range. At last calibration, it read 10.00002 V from a 10.0 V source (with an uncertainty of 0.000076 V). Allowing a couple of hours for the meter to warm up, then turning on the reference, gives me readings of around 10.00003V after 2 hours. It's varying a bit, but that is probably with room temperature. I'm logging that, and I will analyse the results later. The specification accuracy for the meter (10V range, 90 day) is 0.00025 V, so it is doing much better than it needs to!

[RoadRunner]

Mine arrived safely this morning and is currently being tested. I'm using an HP 34401A which was last calibrated by Keysight on 8th January, and has a history of very good accuracy on the 10V range. At last calibration, it read 10.00002 V from a 10.0 V source (with an uncertainty of 0.000076 V). Allowing a couple of hours for the meter to warm up, then turning on the reference, gives me readings of around 10.00003V after 2 hours. It's varying a bit, but that is probably with room temperature. I'm logging that, and I will analyse the results later. The specification accuracy for the meter (10V range, 90 day) is 0.00025 V, so it is doing much better than it needs to!

I am sure and happy that it matches the specs, Glad that you liked,
More boards available if anyone in need.

Few boards also available now with LM399H for and 42 EUR shipped within DE 45 EUR shipped worldwide. While LM399AH version priced at 50EUR DE and  53 EUR shipped worldwide.

[DC1MC]

Is it possible to to get one as close as possible to 10V ?

 Cheers,
 DC1MC

[RoadRunner]

Is it possible to to get one as close as possible to 10V ?

 Cheers,
 DC1MC

If i undstand correctly. You are asking about if output voltage is tunable? This is second version of the board. Previously there was no pot to for adjustment, now there a 1K pot to make fine adjusment to the low tempco gain resistors.  it is possible now tune voltage to 10.00000V.

Regards

[toastedcrumpets]

OK, I just received my purchase, the shipping was fast, you can see it took 11 days from saying I want one to it arriving!

I ordered the 50 euro board. I wanted a separate voltage reference to compare my recently repaired Fluke 3330B and my Keysight 34461A against.

However, between ordering this board and it arriving I actually upgraded from a 34461A to a DMM7510  This means i can do some serious testing of this reference.

I warmed up the DMM7510 for 90 mins and performed an ACAL. I then plugged the board into my bench PSU, first removing it from its anti-static bag, but returning it to its foam padding to reduce air currents and started logging! 5 NPLC and moving average of 20 points as recommended by the meter for maximum precision.

On startup there's a rapid transient followed by a slow drift upwards over time, but the voltage is accurate to 10ppm, which is quite impressive given its just been posted, ripped open and popped on.

Roadrunner, can you comment if you age these references at all? I'm going to leave it connected to my meter for a day or two and see what the performance is like over a longer time and will post again!

[RoadRunner]

OK, I just received my purchase, the shipping was fast, you can see it took 11 days from saying I want one to it arriving!

I ordered the 50 euro board. I wanted a separate voltage reference to compare my recently repaired Fluke 3330B and my Keysight 34461A against.

However, between ordering this board and it arriving I actually upgraded from a 34461A to a DMM7510  This means i can do some serious testing of this reference.

I warmed up the DMM7510 for 90 mins and performed an ACAL. I then plugged the board into my bench PSU, first removing it from its anti-static bag, but returning it to its foam padding to reduce air currents and started logging! 5 NPLC and moving average of 20 points as recommended by the meter for maximum precision.

On startup there's a rapid transient followed by a slow drift upwards over time, but the voltage is accurate to 10ppm, which is quite impressive given its just been posted, ripped open and popped on.

Roadrunner, can you comment if you age these references at all? I'm going to leave it connected to my meter for a day or two and see what the performance is like over a longer time and will post again!

All Boards were aged only around 4-5 days right before i calibrate and calibration is done right 1-2 days before i ship actually handover package to post.
I let board sit in free air, no any airflow arround but also with no extra insulation or anything like that.

[toastedcrumpets]

I let board sit in free air, no any airflow arround but also with no extra insulation or anything like that.

I believe insulation is a good idea as in free air any small oscillations in the air flow can carry over to the package surface temperature, then into the package itself. This causes oscillations in the power to the heater which then causes oscillations elsewhere (i.e. heating lines or resistors). With insulation, these oscillations are damped, and then you only have to deal with the slowly varying lab temperature changes, which hopefully are negated by your low tempco resistors.

[toastedcrumpets]

Just an update. The board has been on since it arrived and seemed to settle just below 10V at 9.99997.

I logged the voltage over night during a lab temperature change from 21 to 18C, with a humidity close to 25%.
You can see the drop in temperature quite clearly as a drop in voltage. I'm guessing it settled below 10V as you have a warmer lab than I do IIRC.

I'm quite happy with this performance and will now look to make a small insulated case for it to better reduce the dependence on lab temperature, then I'll trim the pot just a little to see if I can get it closer to my 10V.

One happy customer, thanks again!

[RoadRunner]

Just an update. The board has been on since it arrived and seemed to settle just below 10V at 9.99997.

I logged the voltage over night during a lab temperature change from 21 to 18C, with a humidity close to 25%.
You can see the drop in temperature quite clearly as a drop in voltage. I'm guessing it settled below 10V as you have a warmer lab than I do IIRC.

I'm quite happy with this performance and will now look to make a small insulated case for it to better reduce the dependence on lab temperature, then I'll trim the pot just a little to see if I can get it closer to my 10V.

One happy customer, thanks again!

Danke

[nfmax]

Mine arrived safely this morning and is currently being tested. I'm using an HP 34401A which was last calibrated by Keysight on 8th January, and has a history of very good accuracy on the 10V range. At last calibration, it read 10.00002 V from a 10.0 V source (with an uncertainty of 0.000076 V). Allowing a couple of hours for the meter to warm up, then turning on the reference, gives me readings of around 10.00003V after 2 hours. It's varying a bit, but that is probably with room temperature. I'm logging that, and I will analyse the results later. The specification accuracy for the meter (10V range, 90 day) is 0.00025 V, so it is doing much better than it needs to!

Finally got around to crunching the numbers & plotting the results! One vertical division on the volts axis is one LSD of the 34401A meter display. The meter had been on since about 11:00. At 12:15 or so I went into the lab and turned up the thermostat. I started logging both voltage and temperature at that time, but didn't turn the reference on until about 12:35. The thermostat timer turns the heating off at 18:00. Although the board was just sat on the bench, without a case or cover, it doesn't seem much affected by the room temperature.

There are a few spikes (e.g. around 17:50 & at 20:29) where I was at the bench. Some of them directly relate to turning other equipment and lights on & off. I made an initial zero test, with power off, and during this I observed that the board - specifically the input protection MOSFET - seems to be light sensitive. A bright desk light just above it gave a few microvolts output from the reference. Presumably the DS diode in the MOSFET was acting as a photodiode, and although the epoxy package is black, it's very thin. It is possible the offset voltage of the output amplifier may also be slightly photosenstive. Voltnuts may want to remove the LED before putting it in a screened, light-tight box!