Battery Saver Badge

Some minimal Badge. Long Battery live due to efficient boost converter with no own functionality beside delivering Power to a SAO connector.

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This is minimal Badge with minimal functionality: It just powers one SAO-Connector. But this with high efficiency. Instead of connecting a 3V coin cell directly it uses a TPS61021A boost converter. The TPS61021A can generate 3.3V from an input Voltage as low as 0.5V. When the battery gets more drains and the voltage drops, you still get 3.3V. This results in in an extended battery life. You could also use batteries, which do not work in other badges anymore, because of to low voltage.


schematic rev0 PDF

Adobe Portable Document Format - 24.22 kB - 03/17/2019 at 13:20


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Jan wrote 03/18/2019 at 11:38 point

I recently did some extended research (including a PCB with the MCP16251 chip), also including this converter chip. Be aware of a few things:

1) When batteries reach their end of life, the internal resistance increases to sometimes many ohms, especially coin cells. At 0.5V you couldn't draw more than 1mA or probably less from the chip. Not even enough to light a single LED... In addition to that the converter won't start up with 0.5V. If it drops under that threshold while driving a heavy load it won't turn back on if the voltage is under 0.9V.

2) Coin cells are "really empty" when the reach 2V, no way you get any usable current from them below that or say 1.5V max.

3) The converter still draws 17µA with no load, so a UVLO should be used to prevent battery leakage.

4) Efficiency drops quite a lot the lower the input voltage. Together with the normal converter losses, don't expect to get a load more battery life than without the converter. With coin cells I'd be tempted to say battery life could be less...

Microchip has some really interesting infos on one battery DC/DC boost stuff in this datasheet:

That's the chip I used for my converter, it's very similar, not as powerful but with a few µA less quiescent current...

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Alex wrote 03/18/2019 at 21:49 point

Thanks for you comment! Some thoughts from my side:
- I would not expected to get a lot more energy from the cell
- One main reason for me is to get 3.3V instead decreasing 3V
- leakage is not realy a problem for me, because of the switch in between the cell and the regulator
- the MCP is new to me. Also quite suitable for this application. I specially like the sot23 packge option, would be much more useful for kits.

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Jan wrote 03/19/2019 at 18:23 point

I see! Should work nonetheless! If you're in Germany and want to try the MCP one, they have these at, so no need to buy from China or Mouser/Digikey...

Regarding my leakage comment: I like to implement this feature for forgetful people like me: Use badge, put it somewhere, forget about it, find it again after a few days, see green goo oozing from battery. You know what I mean :)

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davedarko wrote 03/18/2019 at 11:07 point

Uhh, I'll take three!

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Alex wrote 03/18/2019 at 21:49 point

You will get some

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