lerameur said:
John Popelish a écrit :
I just want to understand how they work for now. My knowledge was to
put energize the chip (V++, V--) then by putting a voltage at the non
inverting input, gounding the inverting input, I should be getting V++
at the output right ? with any chip above, but i am not getting this
except with the LM 324.
The operating concept for both opamps and comparators is that the
output goes low whenever the + input is more negative than the -
input. However, this effect takes place, only when both inputs are
within the input common mode voltage range (in some cases, only one
has to be inside this range).
So, with the inverting (- input grounded, the output should pull low
whenever the + input is more negative than ground. But the input
common mode limit for these parts is 0.3 volts below the negative
supply rail, and the inputs are not allowed to go lower than this,
without damaging the chip.
In order to have a positive output voltage when the comparator is not
pulling down, you must provide some external pull up mechanism to the
output (a 10k resistor to the positive supply rail, for instance).
The follwing step (or problem) involves the circuit explained
originally (logic probe), if I try to use two OP amp (in one chip ) the
output go to high when theoretically they should be low.. just like I
show in my schematic.
I am still skeptical that you have the opamps connected properly. Can
you add a photograph of your assembly to the web page?