Wednesday, 7 January 2015

How to make an h bridge using only comparators


I discovered I could easily make an H-bridge (or something that effectively behaved as one) by cross coupling the inputs of two op amps. So for op amps 1 and 2, 1+ is connected to 2- and 1- is connected to 2+. This worked great, but since I am not really amplifying a signal so much as comparing them, this seemed like a better job for comparators. However, when I tried the same thing with comparators, it did not work. After studying comparators a bit, I realized the problem had to do with the fact that a comparator's output cannot not reverse polarity like an op amp, but can only act as a switch. I get the feeling I would need four comparators for this to work, but I could use some help. Since I am using them in an odd way, the recourses online did hot help much.


My comparator is LM2903P. My op amp is TL082.


Here is the circuit I am using:


enter image description here



It is being used as a multivibrator. I would like to be able to get higher frequencies, so being able to use comparators would be useful.



Answer



Ideally comparators CAN switch output polarity.


Most real world ones can too.


If yours can't you may be using open collector / open drain ones like an LM393 or its cousin.


As usual, you need to supply a circuit diagram and par number to have best chance of people understanding what you are really doing.


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