June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.

  • Solar Powered LED Light

  • Created: Sep 01, 2016

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This reference design features a solar powered LED light that can be used to replace AC powered outdoor lights. It utilizes the IS32LT3175P device to drive the LEDs. The IS32LT3175P is a single channel linear programmable current regulator that can be used as an LED driver. Its output current can be adjusted from 20mA to 150mA by varying the resistance of the resistor connected between its ISET pin and the ground. The device has an LED fade function that can be accomplished by applying a PWM signal to the PWM pin or pulling the EN pin to ground. The fade IN and OUT time is dependent on the resistance of the two resistors connected to the TSET_UP and TSET_DN pins. The IS32LT3175P operates with a voltage supply ranging from 5V to 42V with a maximum power dissipation of 1.96W.

The whole circuit in this design is made up of four IS32LT3175P LED drivers, an ATmega328P microcontroller, V7805-1000R switching regulator, 12V solar panel (two PRT-13782 6V solar panel connected in series), 12V battery, charge controller circuit, LEDs, etc. The ATmega328P microcontroller and the IS32LT3175P LED drivers draw its power from the battery. The V7805-1000R regulates the voltage from the battery to 5V to power the microcontroller while the IS32LT3175P LED drivers are powered by the battery through a MOSFET which is controlled by the microcontroller. During daytime, only the microcontroller, solar panel, and the charge controller are active. In this time, the microcontroller and the charge controller is focus on charging the battery. The microcontroller monitors the voltage coming from the solar panel and from the battery through port PC0 and port PC1. This is to limit the energy supplied to the battery by the solar panel by controlling MOSFET Q3 when the battery becomes fully charged and to disconnect the supply for the IS32LT3175P LED drivers by turning OFF MOSFET Q4 when the battery reaches low state of charge. The transition from daytime to nighttime is also monitored by the microcontroller through the voltage it senses from the solar panel. During nighttime, the microcontroller switches ON the MOSFET Q4 to turn ON the IS32LT3175P LED drivers.

The IS32LT3175P output current is determined by the resistor connected at its ISET pin. In this case, with a 15kΩ resistor, the maximum output current of the IS32LT3175P is 100mA. This output current can be varied from zero to 100mA by using the fade function of the device. In this design, the fade function is done through the PWM pin of the IS32LT3175P. The ATmega328P microcontroller automatically adjusts the duty cycle of the PWM signal it sends to the IS32LT3175P LED drivers when it senses that the battery is running out of power. The PWM frequency should be within 50Hz and 300Hz.