Simple Photovoltaic Charger – Solar Power module with Back-Up

A simple photovoltaic (PV) to Li-On battery charger project is described here. At low V_CC voltage, PV current flows to both the system at V_CC and the battery. When V_CC reaches the programmed float voltage (4.1V with ADJ floating), the LTC4071 shunts excess current not used by the load, limiting V_CC to 4.1V and effectively reducing the battery charge current to zero. If the PV cells stop supplying current, the battery supports the load at V_CC through the LTC4071. A diode in series with the PV cells prevents reverse leakage of the PV cells from draining the battery. If the battery discharges to the point where V_CC falls below V_LBD (3.2V with LBSEL tied to GND) – Jumper J1=GND the LTC4071 disconnects the load from the battery to protect the battery from over discharge. Typically, solar cells are inherently limited in current, but this circuit may require an external resistor in series with the LTC4071 input for high-current solar cells. Select a series resistor such that the LTC4071 never needs to shunt more than 50mA. Low Capacity, Li-Ion/Polymer Battery Back-Up, suitable for Thin Film Batteries.

Features

• Input Solar Cell Up to 5V max – 50mA
• Li-on Battery Small Size
• On Board NTC for Battery Over Temperature Detection
• Header Connector for Battery, Solar Cell, and Load
• PCB Dimensions 15.88 x 13.34 mm

Connections CN1

• Pin 1 = + Load
• Pin 2 = GND
• Pin 3 = Solar Cell
• Pin 4 = GND
• PIN 5 = GND
• PIN 6 = Li-On Battery
• Jumper J1 = GND
• Jumper 2 No Use

Schematic

Parts List

Connections

Application Diagram

Gerber View

Photos

LTC4071 Datasheet

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