For my Convergent restoration, I decided to build an RASCSI to replace some failing SCSI hard drives. The RASCSI is a SCSI emulator built using a raspberry pi. Problem with these types of emulators is that if you carelessly power off the host computer (which was a perfectly acceptable thing to do back in the 80s), you end up also unsafely shutting down the pi — which can cause corruption of the SD-Card, loss of in-memory data, etc. Back when I built David Gesswein’s MFM Emulator, he included a supercapacitor UPS that provided power just long enough to safely shut down a beaglebone. I figured the same thing would work for a raspberry pi.
Years ago I heard about the OpenDPS project to give open source firmware to cheap and available chinese power supplies. These aren’t strictly whole power supplies, they are configurable CC and CV buck converters. That means that it needs a stable DC source to back it to be used as a bench power supply. Perhaps you may not want to do this if you intend to use the DPS as a battery charger run from a solar supply or something, but most people I see want to use them for bench supplies so that requires an existing DC supply. Today I finally finished mine.
We’re coming up on a confluence of two things: Nice weather, and relaxing of the Covid-19 lockdowns in much of the United States. This means more hams leaving their home shacks and taking their operating to the field. For some, this means climbing mountains and doing SOTA activations. For others, this means hiking on trails, and doing POTA activations. For yet others, this means gearing up for Field Day, or doing HF Pack operating, with a manpack station on their back. But no matter what they actually choose to do in the field and why, all of them have a similar need.
I saw an ad for a tiny chip1 that provides 5 volts2 of isolated power: You feed 5 volts in one side, and get 5 volts out the other side. What makes this remarkable is that the two sides can have up to 5000 volts between them. This chip contains a DC-DC converter and a tiny isolation transformer so there’s no direct electrical connection from one side to the other. I was amazed that they could fit all this into a package smaller than your fingernail, so I decided to take a look inside.
To test my LED Stair Lighting Controller boards I needed a 12V power supply that can deliver a lot of current. For this I chose a SP-320-12 from meanwell. However with the screw terminals it is not easy to use on a lab bench, also there is no display to monitor the output current. Therefore I build an enclosure around the PSU, and added a volt and ampere meter.
Another tech note from Richtek on power supply regulation with cable compensation. Link here
Cable compensation has been used to compensate the voltage drop due to cable impedance for providing a regulated charging voltage in battery charger applications. This application note uses a novel cable compensation method, which called cable minus compensation, as an example to describe the concept and design criteria for the cable compensation of a PSR flyback converter. The analytic results are also verified by the simulation results.