It might seems very complex with the Dave’s circuit. But stay with us, and believe us it is not. Basically what Dave’s trying to tell us is a simple voltage controller circuit with current limiter, which as most of the PSU having nowadays.
As you can see from the diagram, we are having only few major blocks to take a look into details. First, bear in mind this PSU will be operating by two 18650 type-batteries and certainly they need a battery charger circuit to revive the voltage level once it drains out. And also, battery voltage with 3.7v+3.7v is insufficient to operate the PSU especially when user switches to higher output voltage like 15V, so we need to boost up voltage for LT3080 according to user setting and thus we require a dc-dc boost up converter. Remember our maximum voltage output is 20V only.
[Update and Revise 21/9/2018]
By taking advantages of Espresso lite V2 on-board 3.3V regulator, two lithium batteries are connected in series instead of parallel to obtain 7.4V and this is sufficient to bring up 5V regulator. 5V power rail will fire up ESP8266 SoC and bring up on-board 3.3V regulator. 3.3V power rail will further distribute to logic ICs located in PSU space.
The circuit seems very complex when glance at the first sight but when we split them out piece by piece, they are actually simple circuits exactly from what we’ve learned in text book. The crucial part that combine them together is our programming flow. It determines how well these hardware circuits serve their role and the performance of whole system. But before we go into software part , we will need a prototype to make the first run. Stay tuned for Part III!