TI LiPo 9V battery pack for Vintage TI calculators

An extension to the TI59 Lipo project for old TI calculators requiring a boost to 9V from a lipo 3.7V.

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Inspired by this project :
I developed a battery pack to replace the BP7-BP8-BP9 packs (Generate 9V from and charge a Li-ion)
I also designed a 3D printable back lid to contain every thing.
I have to admit that this is my first project to publish here. All the design files will be stored on Github.

The electronics is designed with Altium Designer
The 3d CAD file with Autodesk Inventor.

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Nico Verduin wrote 02/05/2024 at 06:38 point

@tomcircuit Actuallay I missed the reason for both the diode and the Zener. I a next version I will remove them. I am also considering moving to USB-C. But still have a number of PCB to use first.

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tomcircuit wrote 01/26/2024 at 00:32 point

This is very nice, and these old BP-7/8/9 packs are all dead/leaking by now, so a replacement is long overdue. I notice that you include the MAX40203 (Ideal diode, U2) and 5.1V Zener (D2) in the circuit, but I am not sure why. 

In my TI-59 charger circuit the zener diode and MAX40203 were included to take care for the case when the original TI AC adapter was connected with the LiPo pack in place - the peak voltage from the AC adapter could be higher than the maximum rating of the MAX40203 and end up damaging it or, worse, finding a 'sneak path' and over-charging the LiPo.  

In the BP-7/8/9 packs, there is no AC charger connection anymore (the two-pin connector was on the old pack itself, not on the calculator body) so there is no possibility of an external high-voltage input. So, I think that you could safely remove D2 and U2, and jumper across pads 1 and 5 of U2. Your thoughts?

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George wrote 02/02/2024 at 05:29 point

My thoughts are I'm working on exactly this --> Using the original chargers, which are rated anywhere from 5 to 7VAC, requires rectification, smoothing, and a step down to operate a lipo charging IC. Battery (or the smooth input voltage) can be stepped up to 9VDC for the calculator. Quiescent is an issue but not worse than the original NiCad packs.

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