LM311 queries..

[Ankur]

hi,
Cant experiment this out at present so am asking u ppl the following
:

If i leave one of the input pins OPEN and apply an input voltage to
the other ... wht will b the output ?
Suppose , i leave pin2 open then wht will b the output when i apply a
+5V at pin3 (and a -5V at pin3) ??

 

[John Popelish]

Ankur wrote:

hi,
Cant experiment this out at present so am asking u ppl the following
:

If i leave one of the input pins OPEN and apply an input voltage to
the other ... wht will b the output ?
Suppose , i leave pin2 open then wht will b the output when i apply a
+5V at pin3 (and a -5V at pin3) ??

Look at the internal schematic on page 18 of the data sheet:
http://cache.national.com/ds/LM/LM111.pdf

The inputs are through PNP transistors that need a pull down bias to
turn them on. So an open input acts as a positive voltage at the most
positive end of the common mode voltage range. On page 4, the input
range is listed as high as 13.8 volts with the +- 15 volt supplies
indicated in note 15. So an open input (either one) looks like a
voltage about 1.2 volts below the positive rail.
--
John Popelish