I'm working with an LM339 comparator and a 5.1V 1N4733 Zener on a 12V supply intending to use the the zener as a constant reference to compare against. Realizing there needs to be a resistor from the supply voltage to the zener/comparator junction, I've downloaded datasheets on both ,(way over my head on that ), and googled the you know what outa zener diode circuits in an attempt to come up with the correct value.
All of which confused me but good!
The resistor will need to drop the 6.9V the zener doesn't need so all I need to figure out is how much current the zener and comparator combination need. 6.9 divided by the current should do it.
On the 339 datasheet from National Semi I see Typical Input Bias Current is 25 nA. nA? Isn't that a little small? That's @5VDC 25C BTW and I'll be on a 12V supply.
On the zener sheet from Surge Components other than the 49ma test current I haven't a clue .....
Any help?
SP
All of which confused me but good!
The resistor will need to drop the 6.9V the zener doesn't need so all I need to figure out is how much current the zener and comparator combination need. 6.9 divided by the current should do it.
On the 339 datasheet from National Semi I see Typical Input Bias Current is 25 nA. nA? Isn't that a little small? That's @5VDC 25C BTW and I'll be on a 12V supply.
On the zener sheet from Surge Components other than the 49ma test current I haven't a clue .....
Any help?
SP