[volt-nuts] Lm399 heater
pa4tim at gmail.com
Sat Sep 15 13:54:58 UTC 2012
Hi Mickle ( and the rest )
Thank for the answers. I only looked LM399 but looking for LM199 gives more info.
The LM399 is now running, just on its own without the buffer as test to know the excact voltage. It started after a few minutes at 7.031,321 and after an hour it was 7.031,345V. I must go on a visit now so it is turned off for now.
Allmost killed it. I'm glad I used my PM2811 psu with the max current set at 160 mA. The layout is very confusing. The plus fom the heater is at the anode side of the housing. I only looked at cathode and anode and because in all the schematics the plus and kathode are drawn on the same side i overlooked it. After this I was afraid I killed it but it looks OK. Draws around 140 mA during the first seconds and a few mA ( 30 or 40 i think, but I gave not calibrated the current reading of the psu yet) after this time.
Tommow I get in the garage and part out an old realy defect Fluke 8500. There are WW precision card types and other precision resistors in there. Maybe I'm lucky and some paralleled resitors, and one from them in series together with a 10 turn potentiometer , brings me to 10V plus/min 20 to 50 uV, so a full turn of the pot is 2 to 5 uV for finetuning. In that case the tempco and mechanical construction of the 10K or 2K pot will not give much deviation ( I think) and in that case I can skip one KV and a buffer) I can do that with the ( green vishay) resistors I have but those WW card types have lower tempco I think. I also have a few WW precision potentiometers like those used in lcr bridges. Are they a good choise ( awfull big alltough)
But I do not mind ordering resistors for this but there is so much choise I do not know what to choose and real low tempco ones are over 15 euro a piece. If I make a refrence using a LTZ1000 I will buy them.
Op 15 sep. 2012 om 08:52 heeft Михаил (Mickle) <timka2k at yandex.ru> het volgende geschreven:
> Hi, Fred!
> This is my version of the mobile reference with triple LM399 averaging and
> statistical 7-10 V step-up divider:
> Schematic diagram http://www.mediafire.com/?srlfhhydq22r347
> PCB http://www.mediafire.com/?667506m6usf6649
> Testing http://www.mediafire.com/?dag35byj16ms389
> Mickle T.
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