Op-amp comparator
An operational amplifier (op-amp) has a well balanced difference input and a very high gain. This parallels the characteristics of comparators and can be substituted in applications with low-performance requirements.
In theory, a standard op-amp operating in open-loop configuration
(without negative feedback) may be used as a low-performance comparator.
When the non-inverting input (V+) is at a higher voltage than the
inverting input (V-), the high gain of the op-amp causes the output to
saturate at the highest positive voltage it can output. When the
non-inverting input (V+) drops below the inverting input (V-), the
output saturates at the most negative voltage it can output. The
op-amp's output voltage is limited by the supply voltage. An op-amp
operating in a linear mode with negative feedback, using a balanced,
split-voltage power supply, (powered by ± VS) its transfer function is typically written as: 
.
However, this equation may not be applicable to a comparator circuit
which is non-linear and operates open-loop (no negative feedback).
