Hello,
some of my thoughts:
- where is the connection between GND and the negative star point?
- The usual stocked vishay resistors have 150 mils pin distance. The 200 mils are not so common.
- how do you mount the PCB within the housing?
- from where do you get the plastic cap? / will it also shield the soldering side of the PCB? Is there enough height in the housing?
- wouldnt it be better to place R4/R5 in direct thermal contact?
- I would put the voltage regulator within the housing (can be on a separate PCB) but D3 should be moved to the input of the voltage regulator.
(I use LTC1763 as voltage regulators which have a built in reverse polarity protection but are for maximum 20V input voltage.)
- after 3 accidents on unbuffered references (each time loosing 2-5 ppm + a horrible drift the next 6 months),
I appreciate the output buffer on my newer design.
- no EMI measures? (except the housing, but without line filtering)
with best regards
Andreas
-What advantage would using a voltage regulator over my current lay, bring?
Can you elaborate on your output buffer setup?
What would you suggest for EMI measures? I ran traces in tandem and tried to reduce loop area, atleast the ones I thought were necessary.
Possible output buffer attached. (other possibility see DATRON reference cirquit).
R23 is not populated in a 7V reference.
R25,C24 will be added in my next revision to improve behaviour in case of a short cirquit on the output of the buffer.
(be aware that many precision OPs have diodes between their inputs: so above 0.7-1.4V they are shorted against each other).
I use capacitors to do EMI filtering: see LTZ1000 thread
There was a few weeks there of headache due to wild TC's and instability because of the series zener I attempted to try to limit the power the heater would see at turn-on. That zener was removed and the circuit fell back more in line with how it should perform. In hindsight, I think I chose the wrong zener and the heater was being starved of the much needed current to properly ovenize the buried zener.
There was a few weeks there of headache due to wild TC's and instability because of the series zener I attempted to try to limit the power the heater would see at turn-on. That zener was removed and the circuit fell back more in line with how it should perform. In hindsight, I think I chose the wrong zener and the heater was being starved of the much needed current to properly ovenize the buried zener.
Since I've implemented the heater zener as an option on my board as well, I'm interested in which zener you saw problems with. I initially went with a 3.3V zener on a 15V VCC, which is pretty conservative.
Fantastic! I think this is the first post I've come across with this much detail on fiddling with the 400k resistor.
Any chance I could trouble you to render those graphs using the same Y scale?
At 3.3M you had the best results, did you test it with out the resistor populated?
Oh, nice, I see the CSV's here: https://xdevs.com/cm/teckit_test/
the funky jumps look like have something to do with the room temperature and the TC of 3458.
did you turn on your AC?