I'm looking at using a series voltage reference to drive a resistive load.
I have no experience with these other than "powerless" uses such as providing Vref to an opamp. But it seems there are some parts out there that can handle some mA's of current. The example part I'm looking at is TI's REF3012 which provides 1.25V out at 25mA max load.
http://www.ti.com/lit/ds/symlink/ref3012.pdfAs an example, if I have an output load of 125 ohm (for easy math), that will draw 10mA current at 1.25V.
My input supply to the REF3012 will be, say, 5V. What's the current draw from the 5V input?
Is it simply power in = power out, plus the quiescent current?
That would mean, 1.25V * 10mA output, divided by 5V input; 1.25V*10mA/5V = 2.5mA draw from 5V? Plus the 42 uA quiescent current for a total draw of ~2.542mA @ 5V
This seems to give an efficiency of 42uA/2.542mA = 98% ? Seems too good to be true.
FWIW, I'm thinking of using this to provide the filament supply for a 6418 vacuum tube, stepping down the voltage from rechargeable AA's. If I have the math correct, it looks like it's a low cost, low component count, and very efficient solution. What am I missing?
Tube datasheet:
https://frank.pocnet.net/sheets/127/6/6418.pdf