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:
10w Zener diode, but I have not been able to find one.
LM7805, But they require a higher input voltage than my panel produces, and have a ~1v voltage drop.
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 ?