As we have seen from the LM339 equivalent circuit picture above, the LM339 uses an open collector transistor Q8 in its output, therefore we have to use the “pull-up” resistor which is connected to the Q8 collector lead with the Vcc in order to make this Q8 transistor work. When the analog input on non-inverting is less than the analog input on inverting input, then the comparator output will swing to the logical low. The comparator circuit work by simply taking two analog input signals, comparing them and then produce the logical output high “1” or low “0“.īy applying the analog signal to the comparator + input called “non-inverting” and – input called “inverting“, the comparator circuit will compare this two analog signals, if the analog input on non-inverting input is greater than the analog input on inverting then the output will swing to the logical high and this will make the open collector transistor Q8 on the LM339 equivalent circuit above to turn ON. Comparison of Op-amp and Comparator Output Circuitry Basic Comparator Circuit Working Therefore, we could say that the comparator is the modified version of the Op-Amps which specially designed to give the digital output. Op-Amps can often be used as voltage comparators if a diode or transistor is added to the amplifier’s output) but the real comparator is designed to have a faster switching time comparing to the multipurpose Op-Amps. When we look closely at the comparator symbol, we will recognize it as the Op-Amp (Operational Amplifier) symbol, so what makes this comparator differ from op-amp Op-Amp is designed to accept the analog signals and outputting the analog signal, whereas the comparator will only give output as a digital signal although an ordinary Op-Amp could be used as the Comparators (Operational Amplifiers such as LM324, LM358, and LM741 cannot be used directly in voltage comparator circuits.