Electronic – How to determine what battery to use

batteriesbattery-operatedvoltagevoltage-regulator

I am making a project that requires two different voltage levels, 5V and 12V (although this can be lowered to 7V minimum). I have two voltage regulators as described by the schematics below:
12V regulator5V regulator

I want to have one power source that can supply enough current and last a decent amount of time to power both regulator circuits. I was thinking single A batteries in series but I'm not sure how many would be sufficient because the input for each says 3-40V, so technically I can get away with just two batteries in series or maybe two sets of two in series and those sets in parallel to get longer battery length. Or is a rechargeable battery better? The problem I'm having is I am not aware of a way to figure out what works and why because of my elementary electronics knowledge.

Thanks in advance

Best Answer

The LM317 is a linear regulator, which means the output voltage is always lower than the input voltage. As the 317 is quite old, it's at least 3 V lower than the input voltage.

The diagrams say '3-40 V' on the input. That's the rating for the LM317s, not the ratings for the circuits as shown. The 12 V circuit should say '15-40 V' on the input, the 5 V circuit '8-40 V'.

Your comment about using two A batteries suggests you were hoping that these were boost converters. It also suggests you are a long way from designing anything starting from components.

In which case, although knowing nothing about your loads, you may want to consider this as a starting point. Use a 5 V 'powerbank' as your single 'battery', and the supply to your 5 V load. They are easy to charge (usually from USB), have constant voltage out, and they are protected from all sorts of over- and under- abuse. Buy a 5 V to 12 V boost converter module from one of the online retailers, and use it to power your 12 V load.

If this isn't suitable, then we need to know more about your loads, application, and other constraints.