Constant current battery charger with MPPT

Hoang Pham

Functional Requirements

• Max input = 160V
• Min input = 45V
• Max output = 33V
• Min output = 25V
• Max output power= 300W
• Target efficiency = 94%
• Output current regulation = +/- 10%
• Power point tracking efficiency = 80%

Schematic : https://github.com/goose1987/buck-CC-CV/blob/master/board/buck_160_28_300_sch.pdf

Key Design Areas

Switching frequency

GaN have very small surface area to dissipate heat. In addition, for high voltage step down in a buck, switching losses dominate. Goal is to operate at the highest frequency for the smallest passives. Max switching frequency is bound by max allowable loss of the high side FET

Comparing 3 200V eGaN devices shows EPC2010C as the best candidate for the application

Fsw ~= 425 kHz to allow for syncing higher to a max of 500kHz

max power point tracking

Solar array voltages, and the corresponding max power point voltage, are strong function of temperature. Use a small PTC to sense array voltage and add feedforward to the control loop. Converter will regulate input voltage and track power point based on array voltage. This assumes good knowledge of array temperature and pre-characterization of array voltage as a function of temperature. Pretty coarse but simpler than more advanced control like perturb and observe or incremental conductance