1. 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