Electronic – Most efficient way to convert from 3.5-4.2V (singe cell LiPo) to stable 3.3V for currents up to 500 mA

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This question is hypothetical – there is no specific project, I just have an obsession with efficiency.

I use a lot of 3.3V modules, and have a bunch of single-cell LiPo batteries (which are amazing), so I'm wondering what would be the best way to combine the two if I were to make a project that would need to maximize battery usage efficiency. As far as I know, there are two options:

  1. Low dropout linear regulator (LDO) – not easy to find one with a dropout of 0.2V at 500 mA loads, but the bigger problem is that linear regulators turn the extra voltage into heat, making them very inefficient.
  2. Use a boost converter to bring that LiPo voltage to 5V, and then use a switching regulator to bring it down to 3.3V. I haven't found any modules on Ebay or Aliexpress that would do it with combined efficiency above 90%, unfortunately. And it appears that the switching regulators are very inefficient at low current draws, typical ones dropping down to 60% at 50 mA and below.

Are there any other ways? Is it possible to achieve an efficiency of at least 95% for such a small voltage difference?

Best Answer

I'd consider using a low-drop-out buck regulator that works almost down to the wire. Such as this one: -

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When the input voltage drops to 3.3 volts, the switch inside basically remains on hence, it acts as a regulator down all the way to virtually 3.3 volts.

There are probably several examples of this tech from the usual vendors. Note that the efficiency remains pretty much above 90% from currents as low as 1 mA to over 500 mA.

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