I found a discarded Keithley meter with a burnt board. It had one of these voltage references (labeled SL40057, crossed to LM399) and some OP177 precision op-amps elsewhere on the board too (Similar to LT1001). So I pulled them off the board and built the 10V portable calibrator shown on the LM399 datasheet. Works perfectly, cost me nothing to make. Thanks for showing the guts of the device, quite interesting!
Great video! I appreciate you walking us through all the math associated with the data sheet and explaining the PPM and temperature drift factors. Definitely learning a lot on your channel! Thanks!
In my travels I found its baby brother, LM3999, in a TO92 plastic package. The zener and heater circuits both share a pin for V- which knocks accuracy down a bit, and boy does that thing run HOT!
Correct maybe, but there is a diode from pin 4 to pin 2 , heater resistor to zener diode ground inside the chip. I connect all vref voltage ouput ground direct, as short as possible, to pin 2 at LM399.
Nice video again. Can you check stability with heater off, also with the "topless" component if it still works? Perhaps blow cold air in it? I am very interrested in the results.
I'm going to have to go read the data sheet, mainly because I want to see how they built that opamp circuit to be stable enough to be a worthwhile buffer. Curse you, sir, for making me go do some research! 😀
made with Elf magic! @ Keebler! but in California, it's Parts Per Macintosh! did I learn something today? yes? I'm developing intelligence just watching U'r show's! good luck!
Well, the datasheet did say it was all on a monolithic substrate :) But before seeing it assumed it was a separate heater too. In fact I wonder if a separate heater would be better. Monolithic should have a steeper temperature gradient, no? ...and I could never bring myself so sell these beauties!
Is anybody knows, why are the zener diodes in that kind of precision component not bypassed by capacitors in the internal schematic? wouldn't that reduce the output noise?
