This circuit uses an MCP73871 Lipo charger and an AVR controller to track the solar panel output power. Input voltage is 6V MAXIMUM so no more than 12 solar cells in series should be connected. Charge current of up to 1A is supported, though thermal limits might make that impractical. The ZXLD DCDC converter is used to Step up the 3.2-4.2V Lion/Lipo battery to either 7V ( 2 series LEDS) or 11.5V ( 3 series leds) @ 350-750 ma. Note that 3 LEDS at .750mA (8.5W) might be a stretch for the device... 2-5W of LED is more realistic. The TPS Buck boost converter is used to create a 5V USB charging port for a cell phone or tablet. It will detect a plugged in USB device and then start the DCDC converter. Running the charger and the light may exceed the Thermal envelope and firmware might be needed to not allow full light and charging. The two buttons at the bottom are the on/off/ brighness control.. Pressing "on" once turns the light to full brightness.. Pressing "off" turns the light off ( from full brighness) . Once on, holding the on button down for 1 second places you in dim mode. the off button now lowers the brighhtness and on raises it. after 10 seconds the buttons go back to normal, off is then off and on is back to full brightness. Teh back side of the board is left empty so that a heatsink can be attached. Significant heat from the LEDS and the converters/charger is generated. A board sized finned aluminum heatsink is recomended. But for simple construction we are looking into a heatsink fabricated from common scrap metal. ( angle iron and such)