“This is a tiny module that allows users to charge small Li-ion batteries, CR2032 or equivalent, from a low power source such as a small photovoltaic cell. The project consists of the LTC3105 step-up DC-DC converter chip which features Maximum Power Point Control (MPPC) and 250mV start-up voltage which enables operational directly from low power, high impedance alternative power sources such as photovoltaic cells. A user-programmable MPPC set point maximizes the energy that can be extracted from any power source. Burst Mode operation, with a proprietary self-adjusting peak current, optimizes converter efficiency and output voltage ripple overall operating conditions. The circuit works with single-cell or dual-cell in parallel. The operating supply of this project is as low as 225mV and a maximum of 5V. Input supply should not exceed 5V DC. The module is programmed to output 4.1V which is important to charge the Li-On battery. Jumper J1 should be open for normal operation, close to disable the output.
MPPC The maximum power point control circuit allows the user to set the optimal input voltage operating point for a given power source. The MPPC circuit dynamically regulates the average inductor current to prevent the input voltage from dropping below the MPPC threshold. When VIN is greater than the MPPC voltage, the inductor current is increased until VIN is pulled down to the MPPC set point. If VIN is less than the MPPC voltage, the inductor current is reduced until VIN rises to the MPPC set point.
Trickle Charge: Trickle charging means charging a fully charged battery at a rate equal to its self-discharge rate, thus enabling the battery to remain at its fully charged level.
NIMH Battery Charging: charging NiMH battery is also possible with this module by changing feedback resistors value, R4 = 470K, R5= 0 Ohms. R1 and R2 remain unchanged. This change will provide 3.2V output and it’s sufficient to charge 2x NiMH batteries.”