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Monday, September 11, 2017

Designing a single Li-ion cell UPS for the Raspberry Pi

A friend and I set out on a quest to design a UPS for the RPi that really worked for higher power applications.

Most designs, even the ones I have listed on this blog, suffer from a lack of true output power for the more power hungry RPi Models, like the Model 3, or when there are enough devices feeding off the USB port bus.

You will be hard pressed to find UPS designs, even commercial ones, that are able to supply and sustain more than 1 Amp to the Rpi. I purchased a couple, and all of them ended up in the "salvage for parts" bin. They were useless.

I designed several ones myself over the past years, and currently use the last version every day on several of my classic Model B's. I used it for my file server and web server and also while I'm doing designs and tests. It helps to protect my work and the SD card, of course.

This latest version is described here: rpi-power-supply-with-1-button-start
However, as with so many others, it is limited in the amount of power it can supply. As I said, most of them max out at about 1 Amp. I can only use it on an almost idling Model 3.

There are a few major challenges you need to overcome. One is the booster design, the amount of current and then there is the heat factor. Consider that at a minimal 3V Li-Ion cell voltage, the booster needs to get upwards of 5A from the cell to be able to supply 2.5A at 4.8V to the RPi.

My mouse-pal friend Bud Bennet (an ex analog chip designer from Linear Technologies) and I (no qualifications to speak of), set out to design a solution. In the process, we actually designed a few and stumbled several times to get it right.

Here is the blog with all the details:



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