Author Topic: (Back in Stock) DE/EU Simple LM399 Reference Board, improved second Version  (Read 5632 times)

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Offline RoadRunner

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Hi,

i have two boards and realised, that the 10 V output voltage varies in the 100s uV if the 15V input change in 100s mV below the 15V checkpoint.

Karsten


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Thanks for pointing, yes power supply need to be as close as possible to 15V.

Regards

Well the 10V board also makes a good thermometer :)

Attached is the board when the temperature is 24.5C and the voltage is 15.0+- 0.05V

10uV out which is much more like what I expected.  I'm going to build a new 15v board and wrap the ref board and stick it in it's own box but with my reference resistors as well :)

EDIT: Just read that....  So is it better to be 0.1V over than a little under?  OR as close as possible..... and just HOW close?

ALSO....  Is it safe to wrap it up in foam?  I don't want to damage it by overheating the board or anything like that.

Thanks


This is now in the range of ..... which is out, the reference or the DMM? :-)

One volt difference in Supply voltage makes around 180uV difference in output because of reference zener diode current.
 

Offline cowasaki

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Hi,

i have two boards and realised, that the 10 V output voltage varies in the 100s uV if the 15V input change in 100s mV below the 15V checkpoint.

Karsten


Gesendet von iPhone mit Tapatalk

Thanks for pointing, yes power supply need to be as close as possible to 15V.

Regards

Well the 10V board also makes a good thermometer :)

Attached is the board when the temperature is 24.5C and the voltage is 15.0+- 0.05V

10uV out which is much more like what I expected.  I'm going to build a new 15v board and wrap the ref board and stick it in it's own box but with my reference resistors as well :)

EDIT: Just read that....  So is it better to be 0.1V over than a little under?  OR as close as possible..... and just HOW close?

ALSO....  Is it safe to wrap it up in foam?  I don't want to damage it by overheating the board or anything like that.

Thanks


This is now in the range of ..... which is out, the reference or the DMM? :-)

One volt difference in Supply voltage makes around 180uV difference in output because of reference zener diode current.

In that case I need to build another power supply.  I've got one on KiCAD at the moment which would do it based on the LT3080ET.....  Maybe that's the way to go.
 

Online jpb

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My 15V was about 14.998V.

I used a LT3402 board from E-bay and a 150kohm Vishay resistor also from ebay (Note a LT3405 board provides more current but are about twice the price):

relatively expensive UK sourced which I used because I was in a hurry
https://www.ebay.co.uk/itm/LT3042-Ultra-low-Noise-Ultra-high-20V-200mA-PSRR-RFLinear-Regulator-Power-Module/142890461926?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
much cheaper straight from China
https://www.ebay.co.uk/itm/20V-200mA-Ultra-Low-Noise-LT3042-PSRR-RF-Linear-Regulator-Power-Module-K/283132638364?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

NB I had to desolder the setting resistor from the board and also connect the enable pin with the wire as shown in the picture on my earlier post.
https://www.ebay.co.uk/itm/Vishay-S102C-150K-0-01-Metal-Foil-Resistors/352563629910?ssPageName=STRK%3AMEBIDX%3AIT&var=621889264013&_trksid=p2060353.m1438.l2649
« Last Edit: March 09, 2019, 05:33:06 am by jpb »
 

Online kado

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jbp

thanks for the detailed information and links!

Bye the way: where could one buy those fine dual banana cables? Never find them until now.

Karsten


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Online jpb

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jbp

thanks for the detailed information and links!

Bye the way: where could one buy those fine dual banana cables? Never find them until now.

Karsten


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They are pomona ones - they are quite expensive new but I buy them if I see them going cheap on ebay - most of the time ebay is more expensive than digikey so beware!:
They come in different lengths e.g.
https://www.digikey.co.uk/product-detail/en/pomona-electronics/2BA-24/501-1696-ND/736429
 

Offline cowasaki

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It arrived today - thank you RoadRunner.

I've not insulated it but I've fed it through an LT3042 board I got from ebay to give it a low noise 15V supply.
My 2015 is dead on and my 2000 is reading between 2 and 3 in the last digit.

I'm very pleased though I'm not sure I like the power sockets which seem to require a fat probe to be stuck in rather than the thin wires I was trying to use - perhaps I'm using them wrong.

Sorry for the out-of-focus shot of the board.

Edit : the 2000 now seems steady at 2 and occasionally down to 1 in the last digit.

Do you have the schematic or other information regarding the ebay board?
 

Online jpb

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Do you have the schematic or other information regarding the ebay board?
I don't but it there is a lot of information on the LT3042 datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/3042fb.pdf
I think the board is pretty close to the schematic on the datasheet first page.

I just blundered around unsoldering resistors (and accidentally unsoldering and resoldering a capacitor!) until the output was determined by the external resistor I had soldered. The board is clearly labelled underneath as shown in the attached photo. I think it was R6 I had to unsolder. You can also follow the traces from the chip if your eyesight is up to it (mine is getting a little dodgy now-a-days!)

You also need to connect the enable to positive VIN (check on the datasheet).

It would be neater to just connect enable to VIN on the underside of the board.

I left the resistor legs very long for two reasons - one I thought I might want to use it for something else if it didn't work well on the board and secondly to avoid over-heating it when soldering (I also used a copper crocodile clip as a heat sink).

Of course, you can also fit a switch between VIN and Enable if you want to turn the thing on and off.
« Last Edit: March 17, 2019, 08:03:45 am by jpb »
 

Online jpb

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Offline grizewald

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I've cased mine as well, but as I always power the reference with a bench supply, I didn't need to add any other components, just a plug for the supply and a pair of 4mm plugs for the output.

The dimensions of the board are a little unfortunate as it doesn't fit inside any of the standard Hammond cases which are also tall enough. So, all I did was make a little foam igloo to keep the LM399 and it's leads warm and cosy and 3D print a couple of plastic rails to adapt the board to the case.

 

Offline alex-sh

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The dimensions of the board are a little unfortunate as it doesn't fit inside any of the standard Hammond cases which are also tall enough. So, all I did was make a little foam igloo to keep the LM399 and it's leads warm and cosy and 3D print a couple of plastic rails to adapt the board to the case.


Well, I am not so sure about unfortunate dimension. Did you measure it correctly?
This is the same LM399 board cased into Hammond 1455C1201. It is a tight fit though - I do not think you can squeeze in anything else.

« Last Edit: April 23, 2019, 08:54:01 pm by alex-sh »
 

Offline grizewald

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Well, I am not so sure about unfortunate dimension. Did you measure it correctly?

 ::)

With the insulation I added around the LM399 and allowing for the board to be held in the lowest slots on the inside of the case, the remaining 18.5mm in height was not enough. This is why I included the phrase "which are also tall enough".

Maybe your LM399 is mounted closer to the PCB than mine. Did you add any insulation around the reference to quickly stabilise the temperature and avoid convection effects?
« Last Edit: April 24, 2019, 02:08:49 am by grizewald »
 

Offline alex-sh

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Maybe your LM399 is mounted closer to the PCB than mine. Did you add any insulation around the reference to quickly stabilise the temperature and avoid convection effects?

I am not sure how close my LM399 is mounted to the board compare to yours.
Yes, mine is fully insulated. In fact I put in a lot of insulation material. However, the problem I had was not height. The problem I had was length. With the banana plugs I have used, it was difficult to put it all together.
 


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