Lithium Batteries are indispensable. I have a few project like my own DIY Badge [Post Soon] or a Light Wand for Light Photography and an in-progress Mobile Rejuvenator which use lithium batteries ,usually those re-purposed ones that are sold in Local markets for Solar Lanterns with a capacity of 1100mAh.
The lazy me used to charge them with a diode drop of 0.7V from the USB Line making the constant charging voltage of 4.3-ish to get things done. Okay ! Okay ! I know this is the wrong way as there is a charging curve to be followed and over-voltage protection is required etc. and the most cumbersome part, you have to keep checking the battery voltage again and again to make sure its within the spec. Dahhh! To much work when you have a few of them to charge.
Li Ion Charger Required
There are tons of them available over ebay/dx/other maker sources but it all boils down to two chips :
- MCP73831 Tiny SOT23-5 Pkg and promise of 550mA Charging current
- TP4056 SOIC with T-Pad and 1A Charging Current
I went for the Easy to solder and higher charging current based TP4056 and turns out is was almost 40% cheaper too. Since both were linear (read as hot) so it might make SOIC better heat dissipater than SOT23-5 due to the area.
There are a lot of boards selling for 1.2$ a pop for this particular chip, ready to use. But, >Why buy, When it can be built.
Also none of the boards satisfied both my needs together:
- Control I/F with a MCU
- Micro USB
So, i went of to design my own based on the datasheet. The circuit is pretty easy and straight forward.
There were only the following changes:
- I provided a jumper for
CEpin to be connected either to a pin head (for MCU Control) or VCC (Auto)
- Extended the
!STBYto end to a pin head too.
- Provided a common ground to i/f
- Added micro USB and a 90degree pin header for my batteries.