An important detail of those efficiencies is that they only apply when the converter is working in continuous mode. In disc mode eff goes down, but sometimes it is necessary to operate in that area due to the low load power requirement
Yeah I noticed that in many switching I.C datasheets, as the current output goes down, the efficiency significantly worsens, sometimes below 50%.
There's no practical use-case for me to look into this at this time, but I have been curious about whether there are switching I.C's which remain 80%+ efficiency across a wide current range (ex. 1mA-5A). Maybe this just isn't possible however, due to the associated components of the switching regulator (I'm thinking the inductors + resistors would greatly influence the efficiency at lower currents). Anyway lol
This is a somewhat rare requirement with some exceptions. The chip companies make whatever customers need. The MAX797 is a third generatioin synch buck that did pretty well in this respect.
The exception, eluded to above is when uP's sleep etc. Mentioned elsewhere, modern power supplies often go into PFM or skipping modes to maintain efficiencies at light loads. The difficulty of these non continuous modes is ripple and noise.
The other thing to wrap your head around is to realize that efficiency isn't so important at light loads, its in the medium and heavy current regimes of operation. If you're 20% efficient at 1 mA, this is much less important efficiencies much less 90 at heavy loads. Notebooks use a linear regulator in deep sleep modes.(they don't put coin cells in notebooks anymore). Of course, there are exceptions, if your whole life is light load except one mode where you're heavy. In this case, you make the supply to have peak efficiency at lower currents and not do so hot at high outputs. Its all engineerging and optimazation.