HereWhy we need Button Cell Charger?
In miniature circuits, the trend is away from expensive dry button cells and towards NiCd button types. These batteries are easy to maintain: however they may be with a constant current for a certain fixed period, normally 14-16 hours.
The usual NiCd battery charger are generally not suitable for charging button cells, as their minimum charging current is too high for these cells. However, the button cell charger described here operates from a 9 V mains adaptor and can charge from one to five button cells.
Button Cell Charger Circuit Diagram:
D1 is a protection diode, while R1 and C1 decouple the supply line to charging processor IC1, an economy model of the well-known U2400B. D3 is a safeguard against polarity reversal of the button cells. R4 limits the charging current to 5 mA. During trickle charging, a current of 0.5 mA flows through R4 and R5. The value of C2 determines the charging time. After the mains adaptor is plugged in, the cells are charged at full current for a period shown in the table (T1 is ON): after that period trickle charging takes place (T1 is OFF). The trickle charging current is always 1/10 of the full charging current.