Ni-Cd charger circuit with pre-discharge for RC mode - Power Circuit - Circuit Diagram

1. During the charging and discharging states of the battery, various circuit modules operate to manage its state. Since the battery voltage varies significantly between these two states, two channels (VB and VB2) are utilized to enhance the detection efficiency and accuracy of the battery voltage. 2. Pin 14 plays a crucial role in controlling whether the load (such as a motor) is turned on or off. When this pin is pulled down by an external button, and the IC internally confirms via a logic circuit that the battery has sufficient power to drive the motor, the output at pin 18 is pulled low. This action allows the Q2 transistor to conduct, thus turning on the motor and connecting the battery to provide power. During operation, the IC continuously monitors the battery voltage via the VB2 pin. If the battery voltage falls below the threshold determined by resistors R5, R4, and R3 (specifically, when the voltage on the VB2 pin drops below 1.65V, which is related to Vee and set to 0.825*Vee), a 7-second low-voltage warning LED (pin 3) illuminates. The LED remains lit for 7 seconds each time the motor is turned off. If the battery voltage continues to drop to 0.80*Vee, the IC automatically shuts off the motor at pin 18 to prevent over-discharge and protect the battery. 3. Besides monitoring the -DV characteristic during charging, the IC also assesses other conditions of the battery, ensuring comprehensive protection mechanisms like maximum charging voltage limits, maximum charging duration, and overheat protection for the battery itself. 4. The aforementioned circuit provides excellent over-discharge protection. However, Ni-Cd batteries require not only reliable charging and discharging safeguards but also address their notable memory effect. To mitigate this issue, it's desirable for the charger to automatically top up any residual charge in the Ni-Cd battery before every charge. For further details regarding this feature, please refer to the subsequent section.