Author Topic: LM399 based 10 V reference  (Read 536763 times)

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Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #675 on: March 20, 2018, 11:30:53 pm »
Great work.  Can you post your schematic?  You may want to add a couple of capacitors (one for the op amp's supply, and maybe one across a feedback resistor).
LTZs: KX FX MX CX PX Frank A9 QX
 
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Offline IconicPCB

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Re: LM399 based 10 V reference
« Reply #676 on: March 21, 2018, 03:38:58 am »
Post the schematic as a PDF or jpg i dont have the cad package you are using to draw it
 
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Offline amspire

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Re: LM399 based 10 V reference
« Reply #677 on: March 21, 2018, 04:16:05 am »
Post the schematic as a PDF or jpg i dont have the cad package you are using to draw it
Just do a screen capture. Even with KiCad, you get this as you are using some custom schematic elements:
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #678 on: March 21, 2018, 04:52:51 am »
Hi Rafael, right now, the LM399 zener is using the 15V rail and the 7k5 resistor as a current source.  As the current through a zener changes, its output voltage will also change (by a smaller amount).  So if your 15V rail drifts a bit, or if the 7k5 resistor drifts a bit, that can affect your output voltage.

There is a zener technique you can use (I believe it is called "bootstrapping"), where the regulated output of the zener is used to drive current through the zener, which means the current through the zener is as stable as the zener itself.

Here's the basic idea: (attached).  This is the same technique used on the circuit which is on the first page of this thread.


Edit: You may also be interested in some of the posts in this thread: https://www.eevblog.com/forum/metrology/influence-of-resistors-in-lm399-reference-circuit/
« Last Edit: March 21, 2018, 05:20:42 am by cellularmitosis »
LTZs: KX FX MX CX PX Frank A9 QX
 
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Offline Rafael

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Re: LM399 based 10 V reference
« Reply #679 on: March 21, 2018, 10:40:28 am »
My humble apologies.

Now attached properly.

Hi Rafael, right now, the LM399 zener is using the 15V rail and the 7k5 resistor as a current source.  As the current through a zener changes, its output voltage will also change (by a smaller amount).  So if your 15V rail drifts a bit, or if the 7k5 resistor drifts a bit, that can affect your output voltage.

Thanks for the explanations, the theory is clear now!! :)

There is a zener technique you can use (I believe it is called "bootstrapping"), where the regulated output of the zener is used to drive current through the zener, which means the current through the zener is as stable as the zener itself.

Here's the basic idea: (attached).  This is the same technique used on the circuit which is on the first page of this thread.


Edit: You may also be interested in some of the posts in this thread: https://www.eevblog.com/forum/metrology/influence-of-resistors-in-lm399-reference-circuit/

I've read this post sometimes, my head and maybe the translation is not helping either. I accompany your discussion on this topic and in others for a long time, it is admirable the struggle of all here for precision and stability, so I am sure that I am in the right place. Often the difficulty in finding the perfect component (or combination of compenents) makes it a quest for the lost treasure.

Thank you for the patience.  :-+
« Last Edit: March 21, 2018, 02:54:43 pm by Rafael »
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Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #680 on: March 21, 2018, 01:36:34 pm »
No worries, sometimes the best way to understand is by doing. The LM399 circuit is cheap enough that you could just build both versions and then see how they behave.

I know that I didn’t really start to understand the LTZ circuit until I actually started building one.
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline Macbeth

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Re: LM399 based 10 V reference
« Reply #681 on: March 21, 2018, 02:07:07 pm »
Post the schematic as a PDF or jpg i dont have the cad package you are using to draw it
Just do a screen capture. Even with KiCad, you get this as you are using some custom schematic elements:
Best to use a PDF for schematics, or a PNG for graphics / charts you want to be seen embedded inline with your posts. JPG is great for photos but introduces artifacts due to its lossy compression which can be horrible for diagram type drawings.

If OP produced the PDF using his version of KiCad with his libraries then the missing symbols will turn out just fine. PDF output is available under the File -> Plot menu.
 
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Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #682 on: March 23, 2018, 07:17:53 am »
Hello,

Last year I made an LM399 board which was intended to be a basic/cheap LM399 "utility" board (e.g., it accepts a single or dual op amp).  Useful for quick checks, like binning LM399's by voltage, initial 1000-hour ageing, checking 1/f noise, etc.

In minimal configuration, it can be populated with LM399, op amp, 3 resistors and 2 capacitors.

I recently sent a few copies of this board to a friend, and realized I hadn't ever published this board.

Here it is: https://github.com/pepaslabs/basic-lm399/blob/master/kicad/releases/v1/README.md

You can get 10 boards for $12 at dirtypcbs.com, or 3 boards for $19 oshpark.
LTZs: KX FX MX CX PX Frank A9 QX
 
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Online Andreas

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Re: LM399 based 10 V reference
« Reply #683 on: March 24, 2018, 05:03:46 am »
Mhm,

the 100nF on the output is not in the cirquit diagram.
And I think this is one essential component to imrove EMI.
(But should be mounted kelvin sensed between output and LM399).

With my (thyristor pre regulated) power supply I have also found
that a 100nF across the heater pins improves stability.

If you use the 10V output I would also
a) use a series resistor to improve stability against capacitive loading.
b) put a kelvin sensed 100nF between 10V output and this series resistor.

I would also put the 15V stabilisation on the board. (or at least within the housing of the cirquit).
Just to have the same output independant of the external supply.

with best regards

Andreas
 
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Offline RandallMcRee

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Re: LM399 based 10 V reference
« Reply #684 on: March 26, 2018, 11:04:00 pm »

I've already said enough.  I want to keep breathing...
What, YOU, worrying?

Indeed, DiligentMinds is now gone--I hope he *is* still breathing.

DiligentMinds, wherever you are, we miss you.
 
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Offline zhtoor

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Re: LM399 based 10 V reference
« Reply #685 on: March 28, 2018, 05:33:15 pm »
hello friends,

here is an interesting variation on LM399 reference circuit as implemented in IWATSU 7510/11/12/13
LM399 represented by D1/R6

regards.

-zia
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #686 on: March 28, 2018, 06:24:41 pm »
Mhm,

but the ratio stability of R1/R2 affects the +/-6V reference. (additionally  to R3/R4)
Why not use +/- 6.95V as reference and avoiding the additional error?

with best regards

Andreas
 
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Online Kleinstein

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Re: LM399 based 10 V reference
« Reply #687 on: March 28, 2018, 06:33:28 pm »
The effect of R1/R2 is not very large (e.g. sensitivity should be around 1/7). Likely they want +-6 V and not +-7 V.
 

Offline Cerebus

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Re: LM399 based 10 V reference
« Reply #688 on: March 28, 2018, 10:15:07 pm »

Indeed, DiligentMinds is now gone--I hope he *is* still breathing.

DiligentMinds, wherever you are, we miss you.

I have some suspicions about what has happened to him.

His previous postings have been mostly considered and intelligent. Then recently he seemed to have some rather unorthodox opinions on the existence of the aether. OK, the odd eccentricity isn't that unusual and can easily be overlooked - we have one clearly knowledgable, experienced member who normally makes perfect sense but has clearly drunk some of the audiophool kool-aide and needs taking with a pinch of salt on that topic. But in short order after the aether came up,  DiligentMinds went on to tell us he previously worked at Area-51 and a few days later almost all his posts have gone, apparently at his own instigation.

Either he is playing one hell of a practical joke on us or I suspect he's had some sort of breakdown and is now hopefully being looked after and nursed back to full mental health.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline hwj-d

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Re: LM399 based 10 V reference
« Reply #689 on: March 29, 2018, 02:07:32 am »
OT:

Or he is simply offended that his subjective life experiences have been made over-ridiculous.

That he obviously had all his posts deleted rather does not argue that he didn't know what he is doing. Psychologically, this is more of a kind of "punishment" of the forum, or some of its members.

Please also note that everything about area51 has a military relevance, even if it is no longer up-to-date.
 

Offline Rafael

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Re: LM399 based 10 V reference
« Reply #690 on: April 03, 2018, 06:31:06 pm »
It's a great hobby to draw pcbs....  ;D
LTZ1000 for voltages, Emmett Lathrop "Doc" Brown for me.
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #691 on: April 03, 2018, 06:43:54 pm »
It's a great hobby to draw pcbs....  ;D

And one can do so many re-designs:

I fear that the heater current (change) will influence your output voltage.
Why do you refer the ground pin of the 20K resistor to the input and not to the output?

with best regards

Andreas
 
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Offline Rafael

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Re: LM399 based 10 V reference
« Reply #692 on: April 03, 2018, 07:01:36 pm »
It's a great hobby to draw pcbs....  ;D

And one can do so many re-designs:

I fear that the heater current (change) will influence your output voltage.
Why do you refer the ground pin of the 20K resistor to the input and not to the output?

with best regards

Andreas

Thanks for the tip...

I will update.
LTZ1000 for voltages, Emmett Lathrop "Doc" Brown for me.
 

Offline TiN

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Re: LM399 based 10 V reference
« Reply #693 on: April 03, 2018, 07:45:02 pm »
PCB fab will express great amounts of love to you for this one.  :=\
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Offline GigaJoe

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Re: LM399 based 10 V reference
« Reply #694 on: April 24, 2018, 02:58:30 am »
around 6 month under +160 C;  1-st step done, will set a drifting measurement now ...
under board a thick thing are copper wire; board a green pcb, resistors blue  :)
interesting oxidation of LM's legs, it actually from ebay ( seen as very beginning of leg are OK )


 
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Offline Cerebus

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Re: LM399 based 10 V reference
« Reply #695 on: April 24, 2018, 11:26:56 am »
interesting oxidation of LM's legs, it actually from ebay ( seen as very beginning of leg are OK )

Classic sign of salvaged parts, where the legs were re-plated or, in some cases, had additional length brazed/welded onto them.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline GigaJoe

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Re: LM399 based 10 V reference
« Reply #696 on: May 01, 2018, 03:16:50 am »
I'm wonder, if this circuit make sense ...
I'd like to combine 4 Vref, but worried about current flow, so adding buffer to each in assumption opamp will do it better ,
then probably not bad to try filtering a noise; so R10 + C6,C1 (electrolytic) appears, to decrease a current leakage.  And R2, R4 - in opamp loop for Vdrop compensation   ...
4  such units in parallel, ( not 2 )


then amplification module to +10V  ..
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #697 on: May 01, 2018, 06:55:08 am »
Hello,

In this configuration with the feedback resistors R1+R3 at the summing point the both OP-Amps will fight against each other.
With the high output resistors it is likely that one of them will fall out of regulation due to saturation.
So I fear it makes no sense for a precision cirquit.

So either you can add additional summing resistors (I would reduce R2 + R4 in this case)
or you take R1 + R3 directly from the output of the OPs (in this case C2+C3 make no sense).

with best regards

Andreas
 

Online Kleinstein

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Re: LM399 based 10 V reference
« Reply #698 on: May 01, 2018, 07:30:32 am »
The usual way to do averaging with Lm399 or similar sources would be to do the averaging right from the LM399, before the 1st (and only) OP. In this step one can also add some filtering with a capacitor to ground in combination with the averaging resistors.

The LM399 output impedance is rather low and thus loading it with averaging resistors (e.g. 1-10K range) is not that relevant.

Even with 8 of the LM399 in parallel the noise is still rather high compared to the usual OPs (e.g. OP07, OP177), so no real need to use more OPs.

If the refs show different noise levels (and low noise is aimed for), one can use different resistors for averaging - the higher the noise the higher the resistor. If done right even a noisy reference can reduce the average noise, though from a certain point it may not be worth it, as the contribution gets too small.
 

Offline GigaJoe

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Re: LM399 based 10 V reference
« Reply #699 on: May 01, 2018, 06:01:38 pm »
that is my misunderstanding:     (Kirchhoff's circuit laws)
will LM  working as supposed,  when it current sink, not a source ...
further - changing voltage  output for a single LM,  do affect all LMs  due to current change for all, or it insignificant ?
 


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