Explaining op-amps and comparators

They both compare two input voltages and drive their output high or low depending on which voltage is higher. An op-amp however also has a third mode when voltages are equal, holding the voltage level.

Comparators compare input voltages

Short explanation; if the positive input voltage is greater than the negative, the output goes high, otherwise low.

The two images above show the two states a comparator can be in, either drive the output high, or low, depending on the which of the input voltages is higher.

Op-amps can deal with equal inputs

If we feed the output to the negative input, it will follow the positive input

Consider the circuit above, when the op-amp starts, its output is at 0V, and because the negative input is connected to the output, the negative input is also at 0V.

Now the op-amps does what its made for, positive input is greater than the negative, so drive the output to high. I put a graph next to the circuit to show you the output voltage.

As soon as the output voltage hits the +2V level, both inputs are in balance, and so the output voltage holds at that level. If the positive input would change, the output would again follow it. This is a voltage-follower.

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