This design uses the CN3722 chip as the maximum power tracking lithium battery charger, which can charge multiple batteries, the charging current can reach 5A, the charging efficiency is high, the heat is low, the size of the constant current can be set, with charging indicator and full Indicator light, chip with battery overvoltage and overtemperature protection and charging input voltage undervoltage protection.

R8 and R9 in the picture are the input voltage divider resistance MPPT is generally 1.04V, by modifying the resistance to adapt to different input voltage, this chip is generally used for solar charging, with temperature compensation inside the chip, the curve is the same as the solar charging board Called maximum power point tracking. OVER1 and CHRG1 are the charging and charging end indicators respectively. R10 is a negative temperature coefficient thermistor. When the temperature exceeds 50 degrees in the lithium battery, the charge is turned off. PMOS1, D3, D4, L3, R13, R14, R15, R17, U3 form a buck circuit. The resistance of R13, R14 determines the charging current. This circuit is set to 2A. R15 and R16 are used to set the output voltage.