Electronics > Projects, Designs, and Technical Stuff

DIY-SMU Project

<< < (18/53) > >>

ducreux92:
Hi,
I find opa2197 (opa197) which is much cheaper that opa2140 with similar caracteristics, but
architecture is CMOS not JFET amplifier - Is this amp suitable for the project ?

Kleinstein:
The OPA2197 has more low frequency noise, but is still  a good OP.  I like the low power consupltion for the speed.
Another cheaper replacement relatively close to the OPA2140 is the OPA1642  (mainly higher offset). It really depends on the positions - the OPA2140 may not even be a good choice in some places.

With hobby projects it is not so uncommon to use the parts you have at hand and know and this may than look odd.
Currently some parts may also not be avialable (or not from the favorite source) - this can also cause strange looking choices.

djerickson:
Thanks for the op amp substitute ideas for the OPA140/2140. I think JFET is the right choice, particularly for low bias current stages. Bipolar is generally higher input current, and CMOS is challenging for +/-15V, generally higher drift and noise. I don't trust the linearity (CMRR) of CMOS: they need circuit tricks to get wide input voltage range that sometimes compromise linearity.

I settled on OPA145/2145 as my go-to precision amp. Similar DC and noise specs to the OPA140/2140, slower (5.5MHz vs 11MHZ), better availability, and ~1/2 the cost.

I have built 2 complete DIY-SMUs so far. I'm getting ready to build the 'final' Rev2 Main boards and Rev3 Amp boards.

Jaromir has designed a very nice take on this project and has built a couple of units. His design uses an off-the shelf enclosure, and a custom AC transformer. And a simpler LED / buttons front panel similar to the original K236 instead of a touch screen.

If there is interest, I can get the new boards machine-assembled and can sell a few. At least the main board with its 175 parts. The Amp board (75 parts) is not bad to hand-build.

There are firmware additions and fixes that I plan:
   EEPROM based calibration. Currently requires recompile. A Python app does the hard part.
   Control of remote sense. Currently SCPI only
   Better Clamp control. Basically works, not accurate.
   Basic plotting page

Thanks,
Dave Erickson

DIY-SMU: www.djerickson.com/diy-smu
Jaromir's DIY-SMU: https://www.eevblog.com/forum/projects/how-i-made-my-smu/new/#new

ducreux92:
Hi,
Today impossible to find AD5686XX in tssop format.

Do you know an equivalent ?

djerickson:
Thanks for the heads-up on the AD5686. Last I checked 2 months ago some were available in TSSOP. Just not the most accurate grade.
I guess some options are to change to the harder-to-solder QFN, or add a footprint for the similar 8 channel AD5676.

Dave

Navigation

[0] Message Index

[#] Next page

[*] Previous page