Cadmium nickel battery charging circuit composed of CD4040

Cadmium nickel battery charging circuit composed of CD4040

The nickel-cadmium battery charger composed of CD4040 counter chip is shown in the figure. It can charge four nickel-cadmium batteries with a capacity of 500mA in series, the charging current is 50mA, the charging time is 1.5 hours, and it has the function of automatically powering off after charging is completed. The 555 time base circuit constitutes a clock signal generator and generates a l0Hz square wave signal with a period of 6 seconds. When the power is turned on, pin ③ of IC2 outputs a low level, which turns on the semiconductor tube VT1 and makes the relay Kl work. The contact K1-1 is closed and the switch S is in self-protection. At this time, the charging current flows to the battery and starts charging the battery. The status indicator LED is lit, indicating that charging is in progress. CD4040 counter constitutes frequency divider and charging circuit. When the power is turned on, the clock signal generated by ICl is input to pin ⑩ of IC2, and IC2 starts counting. Since IC2 is connected as a frequency divider of 8192:1, only when the count pulse reaches 8192, the ③ pin of IC2 will change from low level to high level, causing VTl to cut off, Kl to stop working and release the contact K1-1, causing it to become disconnected, thereby stopping charging. VD2 is used to prevent battery current from flowing back into the circuit.