Sunday, 3-January-2021

Raspberry Pi - over voltage protection / Raspberry as “notebook”


Will start with the second part of the title : Raspberry as “notebook”. Well, to be honest it come a bit misleading. It is not close to notebook, or tablet but more as : home DIY pc..
I have some Notebook TFTs at home, and they can be used as screen with proper driver. For that part Aliexpress have quite some offers and I order one HDMI (input) to LDVI driver. It come with control buttons, backlight control board, IR remote and LVDI cable. So far so good. It required 12V power supply of at least 2A. My switchable supply has 12V option with 5A output, and is perfect for the job.
Next in the list was DC-DC step down converter, and again you can buy half kilogram on reasonable price over the internet. When prepare it for mount, the pot I replace with 5.6kOhm resistor and the output was steady 5.1-5.2V, and that is perfect for the Raspberry.
After all craft was finished, I`ve had that:


Now, on that picture you see one extra PCB board, but will come to that just in a minute. To finish my thoughts : after all was ready and tested it worked as charm. I install Game Emulator on it, raspberian, kodi.. No issues what so ever.

And one of the days I somehow push the screen by mistake, it almost start felling down, so I grab it, the resistor I solder instead the pot touch the inductor , 12V went straight to the raspberry and.. you can guess what happen. Damn..

And now we come to the first part of the title: overload protection. Better late than never. Was it that the saying?
After some web search, I drop on some popular schematic and make little change to suit my need:


What I change :
- the pot between 5V and 2.2kOhm, I replace with 470ohm
- between thyristor`s gate pin and ground I add 1kOhm resistor (the blue arrow show it)

For test purpose, the cathode pin (rounded with red) was not set to ground. Here you can see the test:

How it work you can see from the video. What fuse I use? Fast 3.15A - 230V and it look like doing the job very well. And now you know what is that extra board what stay in between the Pi and the DC-regulator.

And my ready PCB come to be something as that:


That`s all. Hope it will be in good use also to someone else. Enjoy