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StackBook Part 5 - Power Supply

01 09 09 - 22:36 I'm going to need 3.3v for the ethernet module, so I may as well build the power supply.



It's a rather simple design - two low-drop-out linear regulators - a LM3940IT-3.3 and a LM2940CT-5.0. Essentially, the voltage comes in via the DC socket, or terminal block, and is dropped down to 5v by the LM2940. The 3.3v regulator is then powered off the 5v regulator to provide 3.3v. This is done because the 3.3v regulator can only handle 7.5v on it's input terminals as an absolute maximum, but the 5v regulator is rated up to 26v - otherwise this would exclude powering it from standard 12v sources. Since the 3.3v regulator is a low drop out regulator, it can provide 3.3v with Vin down to 4.5v.

Yes, the board is upside down because I initially thought it would go on the left, forgetting the layout of the board.

No, that battery pack is not the final design. It's just the closest DC source with a 2.1mm plug (I need to find where the ends of my plugpacks all went - I have a quite suitable switchmode 3/4.5/5/6/7v plugpack which should supply quite nicely at 6v.

Next up is I guess getting the graphical LCD onto this board (you can see the 16-pin connector at the top there - that is the start of it).