I am trying to built a circuit that will power two USB ports (both 5V and 0.5 amps) from the output of a solar panel that produces 20V at 0.2 amps. I have a voltage regulator that runs at 5v and 0.5 amps but I can't figure out the best way to boost the current up to 0.5 amps before I incorporate the voltage regulators.
If you want to power both USB ports at the same times, It might not be possibble. Your solar panel only supplies 2.24 Watts (20V * 0.2A) of power and you need to deliver 2.5 Watts (5V * 0.5A) to the ports. Subtracting any losses from your regulator(s), you will be WAY over your power budget. You will need more of a solar panel or less of a load.
The previous answer about wattage is correct, so this is your first problem. Try increasing the number of solar panels by connecting them in parallel. To answer your question about increasing current, a voltage regulator wastes energy to regulate voltage. You need somthing that is not so wasteful, and that is a DC-DC converter. You will need to buy a 20V-5V model. this will give you less voltage but more current than you origionally had with your solar panel. You can alter voltage and current capacity, but you cant increase power (watts) with a DC-DC converter.
