How to publish analysis work of an approach worse that state-of-the-art? I am currently working on an engineering problem for which I have developed a new and quite effective solution.  My research field is electronics (if that matters).

The problem is quite complex as it revolves about using a single circuit configuration for multiple voltage ranges (conversion of ac voltage to high dc voltage).  State-of-the-art circuits offer unacceptable performance for input voltage range A and reasonable performance for input voltage range B.

My solution offers reasonable performance for voltage range A but the performance for voltage range B is slightly worse than state-of-the-art.

Since the problem can be broken to two individual parts (low voltage range and high voltage range), I plan to publish the first part on its own (e.g., novel high voltage step-up converter). However, I am debating how to publish the second part that on its own does not offer better performance than state-of-the-art. I have spent half a year developing, evaluating, and optimizing the circuit and I believe the engineering society would benefit from this work. 

I am thinking along the lines of "Analysis and optimization of ...".
Perhaps it would result in a paper that is too long to publish, but you might consider, at least, putting the two results into the same paper and giving an analysis of each case. 

Show how and why it works for one range, but, in a later section, show why it fails to work for the other. 

The overall suggestion here is that the analysis of the result and the possible insight it might bring to the general case is more important than each result individually. That is the perspective of a mathematician, anyway. The insight of the analysis/proof is more important than the theorem itself.