Differences between an op-amp and a comparator

[japlytic]

You may think op-amps and comparators are the same because they use the same schematic symbol, but they are not.
Op-amps (most of which can be used as a comparator where the totem pole output becomes "digital") have an analog totem-pole output which can source and sink current, whereas comparators have a digital-only output which can only sink current (open collector type) when the non-inverting input is lower than the inverting input.
An open collector output on a comparator is used to completely disconnect part of a circuit (enter a high impedance state).

Hopefully, this will put some clarity in your mind.

[PeteS in CA]

Re: Differences between an op-amp and a comparator

Two other things to remember about using op-amps as comparators. Many op-amps' outputs will not go all the way to the supply rails. Thus, the rails might be 0V and 12V, but the op-amp output might only go to 2V and 10V. Also, when an op-amp's outputs are as close to either rail as they can get, they are saturated. This means that there is an extra delay in changing states for the output to pull out of saturation.

[diodo49]

Re: Differences between an op-amp and a comparator

I only know that I know nothing.

[Longbow]

Re: Differences between an op-amp and a comparator

An op-amp is one component of a comparator, so there is no reason to ask the question. Op-amps come in many configurations and frequency response capabilities. Open collector output is just one specialized type of op-amp. It is not specifically designed for a particular type of circuit function. There isn't a special symbol for a comparator since it is not a logic block. Op-amps are, by nature, analog devices. But, they certainly can be a part of a larger logic system.

A comparator detects when an input signal goes higher or lower than a given reference voltage (or current). A small amount of positive feedback is often used to stabilize the circuit when the input is near the reference.

[zoids]

Re: Differences between an op-amp and a comparator

A comparator is just one application of an op-amp when the op-amp is operated in the saturation region. When the ideal output exceeds VCC, the actual output can not exceed Vcc it can only output up to Vcc, likewise in the negative side it can only go up to -Vcc. An ideal op-amp has infinite open-loop gain, so if you use it without a feedback, it will function as a comparator.