The cable situation above and below by desk is as if the Vandals had come through. Outlet expanders plugged into outlet expanders. So many wall adapters. Many of them supplying the same voltage. 5V is the worst offender in terms of the number of redundant adapters.

This got me thinking... what if I could use one AC DC converter for all my 5V devices? One box, lots of cables coming out. Much cleaner.

In fact, what if I could put all my AC DC converters in one box? It would be great if I could have cables coming out with any type of connector on the end, and individually set the voltage on each cable.

Simple enough, right? Surely there's already a consumer product out there for this. Well... not really.

The closest thing is the good old benchtop variable voltage power supply. But for many reasons it's quite insufficient. It's bulky. It isn't designed to have multiple cables connected to one voltage source. The varieties with three or more output levels get very expensive very quickly. And part of the reason for that is that they're actually more precise than I need. A devices that takes 20V input in can deal with 19.9 just fine.

Since it's such a simple thing, it'll be no problem to just build it myself. Maybe I'll even sell it as a consumer product. Sure.

I decided to target a maximum power output of 9A at 20V for one output, as that is the rating of the AC DC converter which came with my device with the highest power needs, my CalDigit TS53 Plus docking station.

Happily, that is less than the 20V @ 5A maximum power draw required by USB-PD version 1.0, so that would be easy to support. I decided to have some USB ports on the device too. And now with two types of output, it would be nice if the case was configurable like a Framework laptop. So in v1, you'd start with a master board and a case with say 10 or 20 slots on it. Then you'd attach modules as you need for simple DC out or USB-PD.

Version 1 of the design was something like this:

I picked out a voltage regulator, the TPS55288 from TI, and designed and ordered a test board (very heavily inspired by TI's corresponding evaluation module).

It worked. However I learnt in the process that each of these modules were going to be expensive. With the TPS55288 voltage regulator at $6.03 on Digikey, a 10A-rated 4.7uH inductor costing ~$3 and the 4-layer v1 board coming in at $8 per unit, plus the connectors and MCU and little components, it was going to be ~$25-$35 per module just for parts. With just 10 outputs that would be far too expensive.

Additionally, although I had only been initially looking for a buck regulator to step down from 24V to whatever was required, the design I had actually supported boost as well. The high-power PSU being quite a big line item (UHP-200-24 from MEAN WELL being $52.45 on Digikey at time of writing), I thought, hey... what if the user could provide his own AC DC converter? Since my regulators could boost, if he had say 18V @ 10A power supply sitting around, he could plug that in and still get 20V output at high current.

So that's something else that was bouncing around in my head as I began coming up with v2. Which I will discuss more in my next post.

Please send comments to blogger-jack@pearson.onl.