ADR1399 10V 5V 2.5V Reference Moddule - Page 1
Forum section: electronics / projects

author: Socke42
author_rank: Newbie
timestamp: January 30, 2025, 03:24:21 pm
content: Hello folks!I'm new to the forum and fairly inexperienced in analog electronics, but i'd like to learn more about this topic. So far i've mostly just played around with arduino and esp32, so mostly just digital circuits, and now i'd like to learn more about analog circuits.My longer term goal is to build a small benchtop multimeter and as a first project I would like to create a “precise” (not Voltnut-like) voltage reference module based on an ADR1399 with 10V, 5V, 2.5V outputs.During my research I found three different circuits that could be used for the 10V reference and I have some questions about them.(pdf)1.Do I understand correctly that in the normal LM399 circuit the weakest element is the resistor R8, because the current for the zener is only dependent on the supply voltage, the long-term stability and the temperature coefficient of this resistor?2.The circuit from The Art of Electronics eliminates the dependence on the supply voltage because the opamp feeds the Zener and only the resistor R20 limits the current?Is it a simplified version of JodelJony's circuit?3.I don't quite understand JodelJony's circuit. An explanation would be nice here.I only see an integrator driving a constant current source which in turn feeds the voltage divider and the zener plus the positive input of the opamp. the negative pin is fed by the divider output. R12 is probably only there for safety reasons.which circuit is best suited for my small project?Do the circuits have any other advantages or disadvantages?For the 2.5 and 5V I use a simple voltage devider with two buffer opamps. (KISS)Do you guys have any other comments, ideas, criticism or suggestions for improvement?best regards Stefan

author: iMo
author_rank: Super Contributor
timestamp: January 30, 2025, 04:29:10 pm
content: There is an error in your JodelJonny schematics.. (which is IMHO the best suited)

author: iMo
author_rank: Super Contributor
timestamp: January 30, 2025, 04:40:03 pm
content: JJ's original..

author: Socke42
author_rank: Newbie
timestamp: January 30, 2025, 07:09:06 pm
content: Thanks for the hint iMo!I have corrected the wiring diagram. Could you please tell me why you think the JJ circuit is best suited for this? I s the circuit less noisy, is it more stable or is it less sensitive to temperature than the others?Sorry for bugging you.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 30, 2025, 07:23:07 pm
content: The circuit is kind of the standard way to operate a LM399 or zener reference. The amplified ref. voltage is used to supply the zener current. This way one gets a rather stable zener current. The LM399 and ADR1399 are not even that critical with the current compared to more classic zeners, like 1N829.The extra transitor at the output helps to reduce the load to the OP-amp and thus thermal effects there. Depending on the load, one may not need it.The transistor also helps in making the circuit tolerant to capacitive load. The capacitor at the OP-amp is however a little on the high side, which makes the regulation a bit slow.One could consider some additional RC filtering. If this is wanted or good, depend on the application.The circuit is for a 10 V (or similar) reference. For smaller voltages it would need an additional divider and output buffer.The ADR1399 is already a bit in the voltnut direction. Especially for 2.5 V and 5 V there would be ready made reference chips and integer gain, like x 2 or x 4 is relatively easy.

author: WhatIf
author_rank: Newbie
timestamp: March 18, 2025, 11:12:52 pm
content: Hi all,I just signed up on the forum so please go easy on me!I'm a little puzzled by the corrected JodelJonny circuit. If I understand correctly the VISHAY resistor array is configured as a divider in the ratio 1:2 (bottom:top), whereas the nominal ratio required for 7V to 10 V would be 5:2, as in 7*(5+2)/5 = 9.8Am I missing something here? Could one of you give me the reference to the original JodelJonny information?Best wishes,Lew.PS I've just ordered the latest CircuitValley ADR1399 reference (TEN399 Version 3V1) and I'm considering upgrading the divide resistors using a resistor array.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 19, 2025, 05:52:46 am
content: The divider ratio is indeed a odd. the 2:1 ration would give 10.5 V nominal. One could than in a 2nd step divide down.The better ration for the divider would be a true gain of 10/7 with a resistor ratio of 1.5 : 3.5. This could be realized as 1 + 2 in parallel and 3+2 in parallel or an overall 8 resistors. One could have a tap to get 5 V nominal, but no 2.5 V. However this would be with the fine trim relative to the resistor array.

author: WhatIf
author_rank: Newbie
timestamp: March 19, 2025, 10:58:51 pm
content: Thanks Kleinstein,I really appreciate your reply. 1.5 : 3.5 would be much better than my 2 : 5.Meanwhile I have realised that I missed a connection in my original analysis, and the ratio in the JodelJonny circuit is actually 2/7 : 2/3, which is the same as 1.5 : 3.5. This is realised as 3 in parallel with 2 in series and 1 in parallel with 2 in series. I'm beginning to understand how flexible these resistor arrays can be!With the 20k resistor array used by JodelJonny, the choices are therefore 30k : 70k or 5.7k : 13.3 k. Which would you consider to be preferable for setting the gain of the OpAmp? I don't have a good appreciation of the most appropriate impedance level for that.Best wishes,Lew.