Here’s a sneak peak! I’m really interested to get the power boards in tomorrow and start testing. Most of these boost, buck and buck-boost boards you see on eBay for cheap actually aren’t all that bad. They generally follow the reference design fairly closely and mistakes or problems are easy to correct. For instance, the LM2596 boards I plan on using only have 35V electrolytic caps on them, which means the 32VDC max input rating on the boards are clearly not true (it would be true of the LM2596 itself, but you should generally double your max input voltage when picking caps, transients, surges and the like). Depending on the seller, the boards may have underrated input protection diodes (generally 1A max whereas these boards can do 1.5 or better with no additional heat dissipation and 3A with a small copper heatsink).
So anyway, here’s the larger of the two cases I’m contemplating. I’ve got a smaller one but it doesn’t have vents, so I’d have to manually cut holes. The board in the foreground will be the controller board (mounted on the underside of the cover most likely). The large chip at the top is a TLC5640 16 channel LED controller, that will be used to drive the RGB LEDs (seen in the background) which will be mounted over top of the six banana jacks (five of which will also have a 5.5x2.1mm [Type M] jack mounted underneath as well so you can easily use Type M to USB Micro / USB A Female adapters or extension cables.
The mid-sized chip is a TLC5616 8-channel LED controller, which we’ll be using as a generic PWM driver by hooking each channel to a PNP transistor and running the output through a simple low-pass filter; we’ll use them to vary the voltage on these switching regulator boards (by removing the potentiometer that comes with them). That’s the real secret to the whole operation.
The smallest chip is a simple 128 step digital potentiometer we’ll be using to trim the output voltage of the 150W step-up board which feeds the 5 LM2596 step-down modules when the desired output voltage is above VIN (nominally 12V). Each LM2596 module’s input comes through a relay; in the NC position it gets VIN, if we activate the relay it’s fed from the 150W step-up board (which will max out at 32V so the buck modules can provide a max of 30V). The idea is that the step-up board will be trimmed to 2V above whichever buck module is set the highest, this will give us the greatest efficiency and the least amount of heat. Obviously this isn’t the most nominal setup, but it’s an easy and inexpensive way to get a wide range of voltage on a lot of channels.
The “main” (sixth) channel will have two separate boards: A 150W buck converter module and a 150W boost converter module. Luckily they use compatible switching controllers, so I can wire the outputs together and use a dual op-amp and two filtered PWM signals to—in essence—create a buck/boost converter.
Lastly there’s a secondary microcontroller—go on, guess which one—that handles the LED control, monitors the voltage on VIN, the voltage coming from an additional LM2596 module [which supplies power for the Core, relays, MSP430, LEDs, etc.], the primary fuse, acts as a Watchdog for the Core and has the ability to kick it over and a few other small tasks.
Not shown is a serial to parallel shift register to control the 8 relays and a parallel to serial shift register to monitor the status of the 5 Type M jacks (with the 3 leftover inputs to scan up, down and enter buttons on the front panel).
As far as the display goes, I might just use a 16x2 LCD (serial backpack) as the main interface will be web based. Though I might use a 0.96" Color OLED to spice it up.
I still need to get the current monitoring figured out, but it won’t be too bad.
Some of the particulars are subject to change, but I think you get the idea. Damn, this ended up a lot longer than I intended it to be!
It’s funny, this all stemmed from me needing a beefy power supply to run multiple USB devices at once. Originally I was going to use an ATX power supply, but this will be a lot cleaner and more versatile. I know I could have just gotten one 150W step-down board, set it to 5V and hooked 10 outputs to it, but I figured for a bit more money I’d have something really useful! I already had a ton of the parts, so all I really needed were the switching modules, a relay card and some connectors. Building a similar unit from scratch would cost around $100 I estimate, but it should be great quality supply that’ll last you a long time once you’re finished.