Hello All,
When I designed the schematic, my focus was, to get a configuration, that will be adjustable to 10V, regardless of the tolerances of the LM399 zener voltage and the tolerance of the available resistors. The zener voltage of the LM399 is specified to 6,95V +/- 2%. I made a excel sheet, where I calculated several resistor values, that will be available on stock at a distributor. Than I came to the conclusion, that with the values, represented in my schematic, I will be able to adjust the reference to 10.000V. I made an annotation of the schematic, that's why the parts may have different IDs compared of my last posing.
In the beginning I had thought, to bye a new set of 1N827 zener diodes, but when I looked at the schematic of the original reference circuit, there are several resistors marked with "SAF" (Set At Factory) to be able to settle the tolerances of the of the Zener diodes and to set the output voltage to really 10.0000V. Due to the fact, that the resistors with low TK are relatively expensive and I do not have a stock of those, especial many different values, I decided to replace the original reference with one based on LM399.
The fixed resistors I used for my schematic are Vishay 102 series resistors with TK of 2ppm°C. The trimpot is also a Vishay (series 1202) part with a low TK of 10ppm and based on metal foil. The cosponsoring TK of the resulting resistor 2x5k parallel to the trim pot will be lower then the TK of the trim Pot but higher the the TK of the two fixed resistors.
The simulation with the C parallel to to the LM399 zener is very interesting. I did not really thought about this parallel C, it is just like something, that I always place a C in parallel to a zener diode or similar circuits. I'm using Altium - is it possible, to use the Model you posted also in Altium, or do I have to install LT spice for this?
@Kleinstein:
I made a photo of the used resistors from Vishay - see below. Here is also a link to this series of foil resistors:
http://www.vishaypg.com/foil-resistors/list/product-63001/. The spacing between the pads is 3,81mm ( 0,15inch) . The heater of the LM399 gets its own tacks of course - have a look at the PCB screen shot.
So have a nice week Guido