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implementing multiple power sources

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How do I configure a device (~100mA) input so that it:

- powers the load from photovoltaic cells when light is available
- supplements solar power with a cell/battery power when available light is too low or not present
- prevents battery discharge in low light
- charges the battery with available solar energy when load is switched off.
- includes a buck/boost circuit to maintain charging/load voltage/MPP under low light/battery.
- ideally uses off-the-shelf components or even an IC that manages all the power

- Extra: uses externally applied voltage to simultaneous power the load and recharge the battery.

I discovered that those cheap solar lights for your garden contain ICs which are quite clever, but with one major drawback ... they only turn on when it's dark.
 
Quite an order. What kind of battery? I see some little buck/boost regulators on ebay.
 
It sounds like quite an order, but this sort of functionality should be ubiquitous. Calculators must employ very similar circuitry. I would go tear one apart to analyze how it's done, except they've become too miniaturized, complex, and often potted.

I picture using a rechargeable single cell lithium ion battery. Likely in a 18650 or 26650 package.

There are indeed prebuilt circuits that perform individual tasks, such as this convenient USB charger:
**broken link removed**
and this solar harvester:
**broken link removed**
The trick will be, how to tie everything together to make it behave like I described.
 
The "standard" way of doing things is to connect the load to the battery, so it is powered even if it's dark. The charger connects to the battery too and charges it when power is available. They don't interfere with each other. In a day time, the energy harvested by the charger goes directly to load and what's left goes to the battery until it's fully charged, at which point charger dials down its output so that net current to the battery is about zero. All solar chargers that I've seen work that way.

It's not worth doing MPPT for 100mA load. A simple switching charger (often called PWM charger) will work fine.
 
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