# Understanding a window comparator

I don't understand the output of the window comparator. How does the window comparator switch from HIGH to LOW? There is no transistor or anything else. Only two OPAMP which outputs are put together.

Can somebody explain it to me?

Here is a image of a window comparator:

Here is the description of the window comparator and the source of the image:

https://www.electronics-tutorials.ws/opamp/op-amp-comparator.html

• This question has been asked before. If you read the article: they are open collector op-amps. Mar 8 '19 at 9:39
• I dont see there open collector op-amps in this article. Do I need a special op-amp? I simuated it in orcad and used a LM324. And it works. But i dont know why...
– otto
Mar 8 '19 at 9:54
• @TobiasK you say there are no transistors or anything... What do you think is inside the op-amp? You used an LM324 in a simulation, the datasheet has an internal schematic. You can see the transistors in there. You don't need a special op-amp to make a window comparator, but for this particular configuration, you want an open-collector type. All of these terms can be Googled and then with the explanation of the window comparator in your linked page, it should all make perfect sense
– MCG
Mar 8 '19 at 10:05

They are not op-amps - they are comparators and comparators of this type have an open-collector output hence, the two outputs are wire-ORed i.e. they form a wired logic function when sharing the same pull-up resistor ($$\R_L\$$)