This article introduces a solar LED street light solution that automatically detects ambient light to control the street light's operation and supports Maximum Power Point Tracking (MPPT). It also includes maximum solar panel efficiency, constant current LED control, battery status output, and user-configurable LED operating time.

The controller's main functions include two aspects: battery charging and supplying battery power to the LEDs.

1. Battery Charging.

When the system detects sufficient ambient light, the controller enters charging mode. There are two important voltage values for battery charging: deep discharge voltage and float charge voltage. The former represents the battery's state when its energy is depleted under normal operating conditions, while the latter represents the maximum limiting voltage during battery charging. This information should be consulted in the battery product manual. In the circuit design, for a 12V battery, the deep discharge voltage is set to 11V, and the float charge voltage is set to 13.8V. Both values are at room temperature, and the software will add appropriate temperature compensation values to these values.

2. Battery Discharge.

When the system detects insufficient ambient light, it enters battery mode to provide power to the LEDs. The LED current flows through a high-current detection chip (TSC101AILT&#41). This sample is sent back to the MCU, which adjusts the PWMDRV duty cycle of the switching signal to obtain a constant output current. To achieve energy saving, the constant current value of the LED is adjusted based on the ambient light intensity detected by the system: as the ambient light dims, the system's output current gradually increases from a small value. When the ambient light completely darkens, the system's output current reaches the preset maximum value. In addition to controlling the LED output via ambient light, users can also enable a time control function by setting the states of switches DIP1~4. The system will control the LED according to the combination of DIP1~4 settings, with a time range from 5 minutes to 12 hours.

Furthermore, to improve system reliability, the circuit design adds protection functions to a range of hardware and software components (such as solar panels, batteries, and LEDs). Based on this system platform, system performance can be further optimized in three aspects: adding a smart LED operating mode, adding a communication module, and adopting a wind-solar hybrid system.