How does a solar lawn light's charge management system shut down the load when the battery voltage is too low?

The charge management system of a solar lawn lamp shuts down the load when the battery voltage is too low, primarily through a built-in over-discharge protection circuit. The implementation of this feature usually relies on a specific chip, such as the CN 302, which monitors the battery voltage and takes action when it drops to a preset threshold. Here's exactly how it works:

Voltage monitoring: The CN 302 chip has an internal integrated voltage comparator that monitors the battery voltage in real time. When the battery voltage falls below a set downward threshold (e.g. 3V), the system recognizes that the battery is in an over-discharge condition.

Load Disconnect: Once the battery voltage drops to the over-discharge threshold, the CN 302 chip will output a low-level signal through its FTH pin, triggering a switching device (e.g., MOS tube) in the external circuit to disconnect the load circuit. In this way, the lawn lamp's LEDs or other loads are automatically turned off, preventing the battery from further discharging and causing permanent damage.

Resumption of operation: When the battery voltage returns to the preset uplink threshold (e.g., 3.3V), the CN 302 chip will output a high level signal to reconnect the load circuit and return the lawn light to normal operation.

Hysteresis Function: In order to avoid frequent switching of the battery voltage between over-discharge and recovery resulting in repeated switching of the load, the system is designed with a hysteresis function. This means that the battery voltage needs to reach a certain magnitude of change before triggering the switching of the load, which reduces unnecessary operations and protects the battery and load equipment.

In this way, the charging management system for solar lawn lamps can effectively protect the battery from over-discharge damage, ensuring long-term stable battery operation and reliable use of the lawn lamp.