I have a Lithium battery pack circuit that converts 4.2V (two 4.2V cells in parallel) to 5V.
Another option is to use a step-down converter from 8.4V (two 4.2V cells in series) to 5V.
Considering both cited circuits are well implemented, which choice would be more efficient in terms of power dissipation?
I am looking for some general rule as "step-down is always preferable than step-up" or "the absolute voltage difference matters" etc.
Best Answer
Boost converters are typically less efficient than Buck converters, but not by much. The fundamental reason has to do with the inductor current flowing directly to ground during the on-time, instead of through the load, like it does on Buck converters. There is an EE-Times article that mentions this: Unscrambling the power losses in switching boost converters
Since the efficiency differences are not significant, you are probably better served deciding on additional criteria instead of regulator efficiency alone, including: