Solar Powered USB Charger Using GaNFETs Marissa Burge1, Daniel Costinett2 Baylor University1 The University of Tennessee, Knoxville2 MOTIVATION Convert the variable power from a solar panel down to a constant 5V output to charge devices for use in developing countries. maximize efficiency minimize cost SOLAR PANEL Tested actual output of panel IV Curve of Panel Output LTSpice Model Using a current source Using the sun changed diode characteristics to match actual output of panel tested in full sun, partial sun, and full shade with 500Ω, 250Ω, and 50Ω loads. maximum power is 12.70W at 1000 W/m2 irradiance. Full Sun Voltage Resistance Power 50Ω 17.83V 49.3Ω 6.45W BUCK CONVERTER LTSpice Simulation Switch node voltage follows V1. Inductor charges and discharges each cycle. Build prototype GaNFETs L1 Efficiency is higher at higher frequency. Except for high and low duty cycles. 500Ω load C2 C1 7500Ω load Efficiency is higher with a lower load resistance. FUTURE WORK Factors affecting output The controller will get feedback from Vout and adjust the duty cycle to keep the output at a steady 5V. Controller Design Simulate in LTSpice Build prototype load Input duty cycle