Hi,
depends onthe accuracy you require over temp - also how stable is the volt source you are running the ref from? ) over temp..? )
Something like the REF102 (10V +-2.5mV) would be delightful, but returning to Planet Earth... I would like 10.000V at ~20ºC ambient, but again - not realistic. 9.990 to 10.010 would be good, allowing for ~ +-3mV ripple. Not sure if I'm overstretching ability and/or reality here.
Hadn't thought of voltage source stability. Have had to go from 1V ref/Voltage source to 10V ref/V source idea, as error will be less pronounced and easier to measure with a degree of confidence it's accurate, based on Saturday's demoralising breadboard test run of 1V +-10mV.
Was going to work off 4*1.5V AA batteries and LDO Vreg TPS73801 SOT-23 (it's good enough for my needs, could stretch to a Micrel 29502 TO-220 but seems a waste of a very good LDO on this low current circuit).
Supply will have to be a 230V mains-based 230AC to dual output 15VAC encapsulated transformer into the regulator (bridge rectifier and smoothing caps before the regulator, obviously), followed by the 10V reference. I'd considered Vreg 13 - 14V > Vref 12V > Vref 10V but I'm under the impression that is overkill/redundancy in action/using an extra reference to only achieve the same amount of buffering and voltage stability and the same temperature drift - isn't it?
I've seen a problem with stacking two 5V LM4040s - according to two different DMMs I have, it outputs 5.01V on a 10k load (actual load would be 1G + 10M in series) - two would make 10.02V...
Set a TL431 to 5.07V and compared to LM4040 5V and LM4040 seemed more stable (rarely moved to 5.02V from 5.01V) whereas 431 appeared to move up and down 10mV and sometimes even 20mV when blowing on them or cooling them a little. I assume that is the slow feedback it has or my (not home-made) DMM doing too many readings per second which in the end is somewhat unhelpful perhaps.
One thing is that the power supply on the cheap oscilloscope seems a bit poor - 5V is always ~4.76V and 12V is ~11.84, on tiny loads of a few mA (best not actually try to get the advertised 1A out of it!) and its own osc probe says it has a puzzling 130mV ripple.
To be honest, I think I may "risk it" with a TL431 set to 10V as I'd have more control over the output voltage and for e.g. maximum 5 mins use at a time (and allowing circuit to cool down if need be - this is for home use, not on an industrial scale 24 hours a day - it should be able to show me what I want to read about a resistor value to use it in a timing application to measure 10pF to 1nF capacitors.
I don't understand why it is considered a "low quality" reference when it's used so much. Although comparing $0.25/TL431 to $8/REF102 may be a good indication as to why you and asdf44 have said "
change to a better ref".