Designing a voltage subtractor or Step down Circuit

Thread Starter


Joined Sep 8, 2020

I have a Li ion battery pack with a voltage output of 30 (discharged) - 42V (fully charged). On the other hand I have a level indicator which has four levels and works with an input voltage range of 0-12v. I am looking to design a simple circuit that would basically subtract 30v from the battery output so that I can feed it to the battery level indicator.

Would love to hear any suggestions.


Joined Feb 24, 2006
I think you should be thinking of taking the high input voltage and scaling it down by an appropriate factor (< 1) to put it in the range of your measurement device. This should be easy to do with a single supply opamp with a suitable common mode voltage range. For a cruder approximation you can do the scaling with a voltage divider and be done with it as long as the monior does not present an appreciable load to the voltage divider. Like this: