Thanks for the reply! First a bit of background:
The first use case for this will be to replace an RV-style converter/charger. It's a CC/CV battery charger that stays "on" in a float mode. It's clearly built for SLA type batteries (which I have) but it's not very flexible. This converter charger is one component of a cobbled together DIY UPS I have for my home network rack. The whole system is a double conversion online topology. RV converter/charger charges the AGM battery bank, then an inverter runs full time to provide power. The inverter is powered from the converter/charger when AC mains is present, or the battery when not. It's built this way because I had the batteries and the inverter already, so adding the converter/charger was the only thing thing I needed.
To this converter/charger -> battery bank -> inverter setup, I have added a Arduino Pro Micro clone running some code and a few external boards/modules to do AC on/off detection and DC voltage sensing. Over the USB port, the Arduino appears to be a HID Power Device (aka a UPS) to a
NUT server, so I can have various devices react when the AC mains goes away. As an example, my NAS shuts down after 15min to increase the time-on-battery of the rest of the network rack). None of this is critical, but it's been a fun project. It was inspired because I realized I could get an Internet connection even when my entire block was off power if I could just power my "modem" and router.
I said all this for a few reasons:
* I have a working system. I don't "need" to do this. I'm thinking about building because I need an Arduino anyway for the UPS reports over USB and that got me thinking about more flexible battery charger / adjustable power supply in general. I want the challenge of the project, but I don't have a "solve this as easily as possible" need.
* The converter/charger works, and I also have a cheap bench top PSU which I've used it for charging various things in the past. I also have a few fairly flexible battery chargers typically used by folks in the R/C hobby. I have things that will do the job, all would need the addition of my Arduino for UPS reports over USB.
* One of the longer term goals of doing this would be to reduce the "number of boxes" in my DIY UPS system from two to one. Practically, this means I'd need to contain both the AC/DC and the inverter side in the same box. A may not do that right away, if/when I do I would use something like the EGS002 driver board.
I assume your point about not controlling DC/DC conversion with an MCU means "don't have the MCU directly drive the transistors or MOSFETs with PWM". That seems reasonable, so "build it myself" should be an IC with some adjustment pin I can control from the MCU (which would also run my user interface and the the existing "UPS reports over USB" functions.
I guess another option is to buy a pre-built DC-DC conversion module that has an analog pot for adjustment, and then use the MCU and a simple circuit in place of the pot.