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I am building several slightly-differently-purposed Arduino + Xbee systems to monitor various things around my home and property. Some of these are line powered, while others must use solar.

Many LiPo solar + DC chargers exist, but most output 5 VDC. I'm hoping to find one that puts out 3.3 VDC, directly rather than having to then use an on-board linear regulator, and waste that power. Of course, with the addition of a large enough cell, a drop from (say) 4v to 3.3v is unlikely to waste much heat.

I believe I need about 250 mA to be safe, but for very short bursts. When the Arduino is sleeping along with the Xbee, I cannot even measure its current draw with the three meters I have on hand. The majority of the current draw comes from the Xbee's transmit power requirements of up to 205 mA. The Arduino itself should be fairly constant, so with the 8 MHz clock running and a nominal 3.3 V supply, it looks like the Arduino will draw under 10 mA.

My ideal system would have connections for a solar source input, a DC input (or USB) and have indicators I can read the status of, to have the Arduino report on its own power supply state.

I am assuming a single cell LiPo here, or a package with internal cell balancing. Also assume I am doing all the smart stuff (powering down the unused components on the Arduino, setting the clock speed to its lowest setting, sleeping and waking only when there is something interesting to do, and sleeping the Xbee unless there is something to transmit.) I can calculate the power requirements and size the solar / LiPo properly.

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  • \$\begingroup\$ What's the current requirements? \$\endgroup\$ – Passerby May 29 '13 at 5:42
  • \$\begingroup\$ While the sparkfun.com/products/11231 sparkfun powercell can do what you want (with a 5v or 6v solar cell input, and 100mA 3.3v output), I think what you want is just not a common need. They would require a regulator that does both step up AND step down, for the full range of the lipo is 3.7 to 2.6v or so. Charge Pump regulators often work for this, but the current is limited to a few 1 or 3 hundred mA, anything more than that is expensive, relatively. \$\endgroup\$ – Passerby May 29 '13 at 5:53
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    \$\begingroup\$ Look at buck-boost voltage regulators: Available pre-built fairly inexpensively on eBay.com and other sites, or you could build your own using a regulator IC such as the OnSemi MC34063, available for under 20 cents apiece. \$\endgroup\$ – Anindo Ghosh May 29 '13 at 9:21
  • \$\begingroup\$ I added the current requirements, which are 215 mA max, but I'd like a safety margin, so 250 or 300 total if possible. \$\endgroup\$ – Michael Graff May 29 '13 at 16:01
  • \$\begingroup\$ @MichaelGraff in that case, I think the best thing to do is get separate lipo charging and output regulator circuits. Just make sure you get one that does step up AND down, as well as voltage lockout. Alternatively, you could design your own. \$\endgroup\$ – Passerby May 29 '13 at 20:13
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So to confirm - you want a LiPo charger + a buck-boost regulator to 3.3V (primarily cause you want to be power efficient).

So you have a ton of options. If you want to go with the Microchip battery charger that comes with the Sparkfun breakouts (https://www.sparkfun.com/products/10217) or Adafruit breakouts (), there are a ton of buck-boost regulators you can put in the next stage. I personally use the TPS63031DSKT in one of my designs, and I'm using the exact same schematic as in the first page of the datasheet (http://www.ti.com/lit/ds/symlink/tps63031.pdf). The efficiency curve is great for the Iout range you are expecting.

However, if you are starting from scratch, I'd look for a PMIC that combines the two like the LTC3558 from Linear (http://www.linear.com/product/LTC3558). That will really help cut down on board space, and cost. Really great chip - all its missing is a battery gauge. I know that MAXIM makes similar PMICs but I can't find it right now.

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You can use lipo directly with the 3.3V pin of the arduino, no regulator, the ATMEGA328 can run with 2.7 to 5.5 V at 8 MHz.

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Adafruit may have what you need and then some. Here is the link https://www.adafruit.com/product/390 Actually no scratch that it has exactly what you need. Both DC Jack and Micro-USB connections

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If all your chips can take 3.0-4.2V safely you can just get away without a regulator and power your project directly with a LiPo.

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