Over the years, I have accumulated many used computer power bricks. Although I could just use them by themselves to power other electronics with similar voltage and current requirements, I thought I would combine a few of them together as the input to a linear regulator so that I can make a powerful lab power supply.
With the original schematic at hand I took the liberty to make a few changes. First of all I replaced two transistor-zener regulators with LM317L/LM337L. Circuits are calculated to produce 33V positive and 3V negative voltages. Thus total supply voltage for the opamps does not exceed 36V and therefor we may use standard ones. I also made changes in the LED drive circuit and a few other minor changes.
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.