Simple nickel-cadmium battery charger

This nickel-cadmium battery charging circuit can indicate whether the battery is fully charged. The circuit is as follows: Turn on the switch K, and the 220-volt AC mains power is transformed by transformer B. After rectification by D1-D4, it supplies GNY0.5 to 2 cells through R1 and D6. Type batteries (AA nickel-cadmium batteries) are charged at a current of 500mA. D6 lights up to indicate charging. At this time, the opening voltage of the control pin ⑤ of the TWH8778 switch integrated circuit is less than 1.6V, and the circuit cannot be conducted, so D5 does not light up. As charging continues. The GNY battery charging current gradually decreases, the battery terminal voltage gradually increases, and the control pin voltage of TWH8778 also gradually increases. When it is equal to 1.6V, the circuit is turned on, and D5 lights up, indicating that the battery is fully charged.