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  • PIC16F1509 Based Solar Powered LED Security Light Driver

  • Created: Aug 23, 2016

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This reference design highlights a circuit for charging a battery and driving LED lights. The circuit utilizes the PIC16F1509 microcontroller, which has an 8-bit CPU and 14KB of program memory as its main controller. The design of the circuit is based on a DC/DC buck/boost power supply for battery charging and LED drive. It has an efficiency of approximately 80% at 500mA charging current. The circuit can accept 9VDC-25VDC inputs from a solar panel. It is compatible with solar panels with 30-36 cells. The circuit provides 6.8VDC-7.2VDC at 500mA output for battery charging and 9VDC-24VDC at 350mA output for LED driving.

The circuit has three primary functions controlled by the PIC16F1509 microcontroller. The PIC16F1509 controls a buck circuit for charging the battery from a solar panel power source. It also controls the MOSFET that drives the LED lights and accepts the signal that comes from the PIR sensor conditioning circuit. The switching for the buck circuit and the LED driver are controlled by using a fixed on-time, variable frequency signal. This signal is generated by the internal numerically controlled oscillator of the PIC16F1509 microcontroller. The higher the switching frequency, the higher the duty cycle. Aside from those three primary functions handled by the PIC16F1509 microcontroller, it also monitors transition between day and night modes through the voltage across the VSENSE_IN port, which is generated by the solar panel. The PIC16F1509 microcontroller also monitors the battery voltage across VSENSE_OUT port, current through ISENSE_OUT port, and temperature across PGD/BATTEMP port. It also monitors the current consumed by the LED light across LED_ISENSE port.

The main application of this circuit is for security. When it is daytime, the solar panel provides the power for the whole circuit. Out of the three functions, only the buck circuit for charging the battery is active. When daytime is over, the power source is switched from the solar panel to the battery. The PIR motion sensor circuit and the LED driver are activated. If the PIR motion sensor detects motion, it sends a signal to the PIC16F1509 microcontroller and the PIC16F1509 will activate the LED driver to turn ON the LED lights.