LM393 Comparator Resulting Low Logic when Expecting High


I am trying out a set of LM393 comparators as part of a switch mode power supply.

As a benchmark test for these comparators, I wired them to compare two potentiometers.

The idea was that if the left potentiometer (as pictured below) was set to a higher voltage than the right potentiometer, the output LED would turn off.

When the right potentiometer was higher than the left, the LED would trun on.

However, when I power the circuit, the LED stays off even when the left potentiometer is set to less than the right.

Here is the picture for the curcuit (the resistor shown is 220 ohms for the LED):

Thank you for sharing anything you may notice about my wiring or theory...


Show us a good schematic of your circuit.
Show us a good image of your ‘actual’ wiring.
Give links to components.

This is my Schematic:

This is a link to my LM393 ic's:

Because of my computer having a notoriously bad camera, I will try and get a clearer photo on another device.

Here is my wiring.
I hope that his is at least a slightly clearer image.

The 393 is open collector so the LED cannot be powered while going to GND, you need to have it going to +Vcc.


Oh, thank you!

That actually explains a lot of what i have ben seeing both in real life testing as well as in my Tinkercad circuit simulations...

I have tried connecting the LED to 5v through a 1k ohm resistor and it is finally working!

Thank you so much for noting that aspect of this ic, however obvious it may seem...

I am still getting into component electronics like this, so hopefully I won't make this same mistake again...

It takes some time to learn these things.

The data sheet will usually show the equivalent circuit for inputs and outputs.

Its not obvious, which is why datasheets are there (hint: learn to read them!). Most comparators are open-collector, and the reason is probably so that they can work with a variety of supply voltages.

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