I'm building a USB solar charger for my tablet, which has so far worked well.
I'm using a 5 Volt, 5 watt solar panel (same as this one), which outputs about 4.5V and 0.6A in real use when charging my device, together with a 5.1V, 5w Zener diode (1N5338B) to regulate / limit the voltage, as it goes up to ~7V when not under load, which I presume could damage my tablet.
Now, I want to add a second identical solar panel (in paralell), to get more current to charge my tablet faster.
I need an appropriate voltage regulator, as this 5 watt zener diode would no longer work with (up to) 10w of power.
So far, I've looked into:
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10w Zener diode, but I have not been able to find one.
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LM7805, But they require a higher input voltage than my panel produces, and have a ~1v voltage drop.
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A DC-DC voltage converter, such as this one. Would this work ? Does it have a voltage drop ?
Any other possibilities ? What do commercially available USB solar chargers use ?
Essentially, I'm looking for an appropriate component to prevent the voltage from the solar panel going over 5V and damaging my device.
Any recommendations ?
Best Answer
My first reaction is to put the two panels in series, then use a off the shelf buck regulator chip. If the two panels can't even put out 6 V or so in series (3 V per panel), then there is so little power available that it doesn't matter if the output is just shut off.