comparator working

What is Comparator

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A comparator is a circuit that compares two input voltages or currents and gives output High or Low as per input signal. The Output is a digital form according to the input signal compared with the reference. Basically a comparator is used in electronics to compare the two Analog input signals given on both input terminals and we get the Digital output as High level or Low level.

Comparator is used to sense the signal of a predefined rich level. If I set a level to sense then I can use a comparator to sense it when the input signal of this level cross more or below the level, suddenly the output is changed from Low to high and high to low. The comparators are used for so many electronics instrumentation for automation and drive different logic circuits.

Difference between operational amplifier (op-amp) and comparator

The symbol of the operational amplifier and comparator are looked the same. But Op-amp is designed to accept an analog input signal and also give the output Analog signal. But the Comparator accepts the analog input signals but gives the digital output. Comparators are faster than the operational amplifier. An op-amp will works as the comparator if using the transistor at the output.

If the input is applied at the + pin, this is called non-inverting input

If the input is applied at the – pin then this is called the inverting input.


1. Non-inverting mode

If I connect the input voltage at the non-inverting input and set a reference voltage level at inverting input which is to be sensing. In this circuit, the voltage will compare with the reference. If the applied voltage is lower than the reference voltage then the output is LOW, and if the applied input voltage is greater than the reference voltage then the output will HIGH. Here High level means output is directly connected automatically with VCC and Low means Output is directly connected with Ground.

For example,  if we set the reference voltage at 6v, then when the input voltage increases to 6v then the output suddenly swings to HIGH and gives the voltage the same as VCC, Otherwise output gives the LOW or 0v voltage.

Input voltage > Reference Voltage – Output HIGH

Input voltage < Reference Voltage – Output LOW


comparator working comparator circuit diagram

2. Inverting Comparator (Inverting-Mode)

In inverting mode the input voltage is connected with the Inverting terminal and reference voltage is st at the non-inverting terminal. In this connection, the voltage at the Inverting terminal will be sensed and compared with the voltage at the non-inverting terminal which is the reference voltage. The inverting mode comparator works reverse to the non-inverting comparator. Means If the voltage at Inverting terminal is greater than the Reference voltage then the output will LOW, But If the Input voltage is Lower than the Reference voltage than the Output Will HIGH. This comparator gives output Inverted of input.

For example, Reference voltage adjusted at 6v, when the input voltage increases and goes to 6v then the output will suddenly swing to LOW or 0v. Otherwise, the output will HIGH and give the voltage the same as VCC.

comparator working

comparator circuit

The LM358 is the very popular comparator ic used for general purposes. This ic has 2 opamp comparator. LM324 is also a very popular and most using comparator ic. It has quad op-amp comparator.

LM 358

LM 324


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