Electronics > Metrology

LM399 based 10 V reference

<< < (283/291) > >>

Alex Nikitin:

--- Quote from: iMo on September 15, 2024, 08:19:52 am --- The small differences you see while measuring the voltage vs. current come from a nonlinear characteristics of the circuitry around the zener (see the schematics in the datasheet).

--- End quote ---

Not as the result of a nonlinearity, only of a limited open loop gain.

Cheers

Alex

Birb:
Hmm, I think my real question should be about how the 0.2mA affects drift.
Is it really a big difference?
Also, how does it affect settling times of the references? Thanks
I mainly want to try to avoid any extra resistors as this can keep the entire setup simple and component count minimal.

Also, is it better to have multiple references in parallel or put the LM399s themselves in parallel with each other?
(The advantage of small units is several could be placed together to form a more accurate(?) unit.)
(Though I note the ratio of 3:7 is really idealized and as far as my "testing" is the voltage is more like 7.04ish, so that would be a bit higher than wanted.)

iMo:

--- Quote from: Birb on September 17, 2024, 09:37:25 am ---Hmm, I think my real question should be about how the 0.2mA affects drift.
Is it really a big difference?
Also, how does it affect settling times of the references? Thanks
I mainly want to try to avoid any extra resistors as this can keep the entire setup simple and component count minimal.

Also, is it better to have multiple references in parallel or put the LM399s themselves in parallel with each other?
(The advantage of small units is several could be placed together to form a more accurate(?) unit.)
(Though I note the ratio of 3:7 is really idealized and as far as my "testing" is the voltage is more like 7.04ish, so that would be a bit higher than wanted.)

--- End quote ---
1. No, 2. No, it does not affect,  3. you may put N 399s in "parallel" (it does not mean the zeners are all parallel, they have separate zener cathode rezistors) via N summing resistors into a single common 7->10V amplifier (if required), 4. the output noise will drop sqrt(N) times down, where the N is number of "paralleled" refs (like 4 refs will do aprox 2x less noise).

Kleinstein:
Instead of in parallel, I would consider the new ADR1399 for about half the noise, comparable to 4 x LM399 in parallel.

The actual voltage of the LM399 can vary quite a bit between units. They can be above or below 7 V. A parallel version would need extra resistors for averaging and separate paths for the current. One could do the averaging at the 7 V level or the 10 V level to also average over amplifiers and resistors.

Birb:
My idea is to average at the 10V level, which, while increasing costs, does allow for post selection of the better references, allowing for better combinations at the end.
I am using lm399 because it's what I have on hand, and should work well if chosen well.
If I'm not mistaken, output protection should come after averaging correct?
This might increase the risks of mishaps during testing, but oh well.
As for external trim, I might try the AD587 method.

Navigation

[0] Message Index

[#] Next page

[*] Previous page