Author Topic: LM399 based 10 V reference  (Read 315864 times)

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Offline Andreas

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Re: LM399 based 10 V reference
« Reply #175 on: May 11, 2014, 01:19:37 pm »
Not perfect , but maybe usable

I have seen similar tea cups already but:
The silver reflector on the vacuum side is missing.

But perhaps its worth a try.
The dewars from Mickle seem to be no longer available.
Would be interesting if a thermal coffee mug
(stainless steel with vacuum) gives similar results.

With best regards

Andreas
 

Offline CaptnYellowShirt

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Re: LM399 based 10 V reference
« Reply #176 on: May 11, 2014, 03:54:12 pm »

Would be interesting if a thermal coffee mug
(stainless steel with vacuum) gives similar results.



I've been using 1 and 2 L coffee carafes as LN2 dewars now for a while. They silvered glass ones work great. All the others (stainless steel) not so great. Look for the word "Airpot" on ebay.
 

Offline macfly

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Re: LM399 based 10 V reference
« Reply #177 on: May 11, 2014, 08:19:36 pm »

Hello Mickle,

would you let the cat out of the bag, where we can buy S5-61 foil resistors?


Hello,

You could also order some VHP100/VHP103 or from the HZ series resistors from vishay and select for TC.
Most probably the S5-61 resistors are no longer manufactured. Otherwise you could google after them.

with best regards

Andreas

Andreas,

be sure, I studied the complete VISHAY precision resistor program, before I ask such a question.
Buying 10 or more VISHAY resistors of VHPxxx is nearly impossible for a hobbyist like me.
The russian resistors are military surplus, I think. Perhaps you can buy twenty S5-61 resistors for one VHPxxx?
They are also very interesting for applications with lower requirements.

Best regards,

macfly
Genius is one percent inspiration, ninety-nine percent perspiration (Thomas Alva Edison 1903)
 

Offline bingo600

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Re: LM399 based 10 V reference
« Reply #178 on: May 12, 2014, 06:11:12 am »
A bit of graphs (K2015 (blue) is the LM299) , red is the SVR-T

The LM299 sems quite stable , but it's strange that the board seems to have a negative tempco.
PCB is on the table aka. "open air".

I'll prob do as Andreas suggests , measure LM299 out and the 10v out.

/Bingo
 

Offline CaptnYellowShirt

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Re: LM399 based 10 V reference
« Reply #179 on: May 12, 2014, 03:23:03 pm »
I've had a raw LM299 hanging on magnet wire from a HP power supply for about a month now -- just swinging in the air over my bench. I've been really surprised how stable its voltage is for an unheated style of Vref. If I'm remembering correctly, the LM299 has a negative tempco.
 

Offline Andreas

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Re: LM399 based 10 V reference
« Reply #180 on: May 12, 2014, 07:31:30 pm »
If I'm remembering correctly, the LM299 has a negative tempco.

Hello,

from my LM399 most have a positive tempco see:

https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg422367/#msg422367

@bingo:
I do not think that the deviation comes from the LM299.
Except if you have a defective device.

In my ageing box I had also large deviations from one LM399.
The cause was a bad contact of the heater supply.

By the way: Do you use good thermal isolation for the LM299.
On both top and bottom side of the PCB?

With best regards

Andreas

 

Offline Andreas

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Re: LM399 based 10 V reference
« Reply #181 on: May 12, 2014, 09:27:59 pm »
Hello,

this is 2nd part of:
https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg441913/#msg441913

now I have measured LM399 #14.
 #14 is the one of my ageing box with the lowest voltage difference between unheated + heated.
Test setup is the same as previous post.
14V via 6K8 fix for the zener, 9-30V variable for the heater with variable series resistor.

There are some differences to mention:

PSRR (power supply rejection ratio) on #14 (60uV) is nearly 2:1 compared to #13 (34uV)
-> there seems to be no correlation between PSRR and TC (temperature coefficient)

 #14 works downto 9V heater voltage as specified in the datasheet. (#13 had some problems below 9.1V)

According to tempco (slightly negative on #14) the output voltage rises if heater voltage is too low with series resistor. (see unzoomed picture of 10R series resistor).

Again on the diagrams:
X-axis is heater voltage
left Y-axis is 2:1 divided zener voltage in mV (red dotted line)
right Y-axis is local PSRR gradient in ppm/V (green dots)

Results for 12-30V heater voltage change of LM399 #14

  0R: = 60uV
10R: = 64uV
22R: = 62uV
47R: = 67uV

So again any resistor on the heater seems to worse the PSRR slightly.

With best regards

Andreas

« Last Edit: May 13, 2014, 05:09:22 am by Andreas »
 

Offline CaptnYellowShirt

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Re: LM399 based 10 V reference
« Reply #182 on: May 13, 2014, 10:01:28 pm »
Well, its official.... I hate how the LM399's datasheet shows the example circuits in reverse to how the die is wired.    :palm:
 

Offline branadic

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Re: LM399 based 10 V reference
« Reply #183 on: May 14, 2014, 08:17:17 am »
Quote
When I look for dewar I only get to pages with LN2.
And the lowest cost dewar is around one HP34401A.
$10 sounds reasonable.

Hello Andreas,

I found dewar available from different suppliers:

https://www.thgeyer.de/store?PGM=search&GOTO=V1&OPEN=23233030303030333136&TICKETID=0012984908&randomseed=140514101031#opened (see 9.032 011, 100ml, also available without the blue jacket, so the price could be somewhat lower)

http://www.carlroth.com/catalogue/catalogue.do?lang=de-de&act=showBookmark&favOid=000000040000907600020023 (see LE85.1)

It's not that cheap compared to the disassembled TCXOs, but anyway available.

Regards, branadic
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline babysitter

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Re: LM399 based 10 V reference
« Reply #184 on: May 14, 2014, 11:51:49 am »
http://www.laborhaus.de/98/112/AD183/MTAxMQ==/KGW%20Isotherm%201011%20Laborhaus%20Scheller.html

The replacement glass part might save a few € against the full part and also the life of a poor nice oscillator !
I'm not a feature, I'm a bug! ARC DG3HDA
 

Offline branadic

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Re: LM399 based 10 V reference
« Reply #185 on: May 14, 2014, 06:35:23 pm »
Quote
The replacement glass part might save a few € against the full part and also the life of a poor nice oscillator !

Thats what I meant with:

Quote
(see 9.032 011, 100ml, also available without the blue jacket, so the price could be somewhat lower)

It could be cheaper to directly ask http://www.kgw-isotherm.de/ for a quote of a replacement glas as they are the original manufactor:

http://www.kgw-isotherm.de/produkte/dewar/00.html
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline branadic

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Re: LM399 based 10 V reference
« Reply #186 on: May 15, 2014, 06:00:26 pm »
Okay, it's exact the same price at KGW-Isotherm direct 35,51€. The plug itself is about 23,04€ pretty expensive.
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline babysitter

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Re: LM399 based 10 V reference
« Reply #187 on: May 15, 2014, 06:25:19 pm »
One could top it off with a Petri dish? At work I am using some customized thermostats out of - you guessed right - tuner boxes embedded in styrodur-like foam. In the 36 to 42 °C range I get the innards flopping around in a ~0.07° window.

I'm not a feature, I'm a bug! ARC DG3HDA
 

Offline doktor pyta

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Offline Andreas

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Re: LM399 based 10 V reference
« Reply #189 on: May 16, 2014, 08:16:09 pm »

I found dewar available from different suppliers:



The replacement glass part might save a few € against the full part and also the life of a poor nice oscillator !


Hello,

thanks for sharing.
This may be one of the next projects:
Either 4 LM399s or 1 LTZ1000 within a dewar.

With best regards

Andreas
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #190 on: May 23, 2014, 02:02:15 am »
I've really enjoyed these volt-nut threads and though I'm a newb, I've started down my own path of designing an LM399 reference.

The idea I'm exploring is to avoid any sort of trim on the output op-amp's voltage divider (just two fixed value resistors to set the gain).  Rather, I'll achieve trim by adjusting the current driven through the LM399 zener.

Not only that, but I'll control the current source for the LM399 zener via a DAC, so that you can calibrate it via software.  This means I can immerse the entire circuit in an oil bath and not have to crack it open while calibrating to tweak a pot, etc.

So, the first step down this path is coming up with a current source.

My first attempts were a traditional op-amp with current sense resistor on the low side.  However, I realized having the current sense resistor on the low side would introduce current error one way or another.

So I tried wrapping my brain around making a high-side current source, and this is what I came up with:



(Here, the DAC is represented by a voltage divider, and its reference represented by a simple zener).

Using this setup, a drift in the LM317 of +/- 0.1V results in a current source error of only 2.3 uA.  Not bad!

I'm initially choosing an LM317 target of 16.25V (using R values of 100 and 1200), as that allows operation from three 9V batteries discharged down to about 6.5V each.  (the batteries would be needed while e.g. putting the reference in a faraday cage -- I have terrible noise pickup at my house).

LTZs: KX FX MX CX PX Frank A9 QX
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #191 on: May 23, 2014, 02:19:51 am »
Hrmm, oops, 16.25 volts is too low for full range output of the DAC in this example.  That's partly because the LM399 is represented by an 8.2V zener, rather than a 6.95V zener.  So it looks like the minimum voltage supply I need is about 17.5V.

LTZs: KX FX MX CX PX Frank A9 QX
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #192 on: May 23, 2014, 04:09:50 am »
Uh oh, 10 minutes at the breadboard and I'm officially addicted to volt-nutting.  Even the most trivial LM399 circuit stops all the digits on my HP 3478A dead still!   The reading hasn't budget an LSB in 10 minutes now!

I fear I'll be justifying upgrading to a used 34401A all too soon...

Fun!
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline Andreas

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Re: LM399 based 10 V reference
« Reply #193 on: May 23, 2014, 09:50:59 pm »
Rather, I'll achieve trim by adjusting the current driven through the LM399 zener.
Good Idea: so you will have more fun at adjusting: Trim a bit, wait 15 minutes for thermally equalizing. Trim again. w. w. w.

Using this setup, a drift in the LM317 of +/- 0.1V results in a current source error of only 2.3 uA.  Not bad!
Too much: with 1 Ohms for the zener this is 2.3uV output voltage change.
Requirement of datasheet is 1mA +/- 0.1% for long term stability.

So I tried wrapping my brain around making a high-side current source, and this is what I came up with:
The LT1001 is no rail/rail OP. The cirquit violates at minimum the input common mode range below 2mA.

With best regards

Andreas
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #194 on: May 23, 2014, 10:22:08 pm »
Thanks Andreas

Requirement of datasheet is 1mA +/- 0.1% for long term stability.

Ah, I missed that part of the spec.  Do we know if they list this part of the spec simply because that is the only condition under which they tested long term stability, or are they saying that exactly 1mA is the sweet spot for long term stability because they've tested many different currents and found that to be best?
LTZs: KX FX MX CX PX Frank A9 QX
 


Offline echen1024

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Re: LM399 based 10 V reference
« Reply #196 on: May 24, 2014, 05:08:17 am »
I am using a double walled glass teacup I purchased in China. Seems to work quite well.
I'm not saying we should kill all stupid people. I'm just saying that we should remove all product safety labels and let natural selection do its work.

https://www.youtube.com/user/echen1024
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #197 on: May 25, 2014, 02:03:35 am »
I came across an interesting current source in the LM4050 datasheet:



I thought this arrangement might be interesting for use with driving an LM399:



This struck me as being interesting, because this greatly reduces the parts count, and also because the only pins which need to touch a voltage regulator are the op amp supply pins.

The 1000:1 ratio of the LT1029's 5V to R1's 5000 ohms translates into a 1000:1 ratio of LT1029 voltage drift to LM399 zener current, and also allows us to drive exactly 1mA through the LM399.

An R2 of 6.95k would allow us to also drive 1mA through the LT1029 (all of the stability specs in the LT1029 datasheet specify 1mA).  Welwyn makes a 0.1% 15ppm/C 6.98k resistor for $1.92.  http://www.digikey.com/product-detail/en/RC55Y-6K98BI/985-1056-1-ND/2401921

If we replace the zeners with voltage sources we can start to do some analysis.  It appears a drift of 1mV in the LT1029 would result in 200nA drift in our current source:



BOM costs thus far:
LM399A: $10
5k Vishay Foil: $20
LT1029A: $5
R2 (6.98k): $2
LT1001 (x2): $13

Total: $50.


This circuit seems to work, but I do admit I'm having a hard time convincing myself that it wouldn't suffer from start-up problems (what would prevent the op amp from just staying at 0V?).
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline fmaimon

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Re: LM399 based 10 V reference
« Reply #198 on: May 25, 2014, 02:09:06 am »
Read the first post of this thread. It's a better way to create a constant current as stable as the LM399 it is powering.
 

Offline cellularmitosis

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Re: LM399 based 10 V reference
« Reply #199 on: May 25, 2014, 02:48:13 am »
Read the first post of this thread. It's a better way to create a constant current as stable as the LM399 it is powering.

ah, taking another look at your schematic, I think I finally understand it :)
LTZs: KX FX MX CX PX Frank A9 QX
 


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