PIC16F1509 Solar Powered LED Security Lamp (Proof of Concept)

Design Highlights:

DC/DC Buck/Boost Power Supply
~80% Efficiency @ 500mA charging current
9 VDC – 25 VDC Input (compatible with 30-36 cell panels)
6.8 VDC – 7.2 VDC @ 500mA DC Output for Battery Charging
9 VDC – 24 VDC @ 350mA DC Output for LED Driving

PIC16F1509 Controlled Topology

Core Independent Peripheral Integration
Numerically Controlled Oscillator (NCO)
10-bit Analog to Digital Converter (ADC)
Maximum Power Point Tracking (MPPT) Solar Charging to Battery

Night sensing via solar panel
(2u) MCP6V02 OpAmp for current shunt amplification and motion sensing via Passive Infrared (PIR) sensor
MCP1790 High Voltage Regulator Boost LED Driver.

Theory of Operation

This proof of concept design is a solar DC/DC buck/boost power supply for battery charging and LED drive.

The design consists of 3 primary functions controlled by the PIC16F1509: buck solar powered battery charger, boost LED driver, and PIR sensor conditioning circuit. The switching is controlled using a fixed on-time, variable frequency signal generated by the NCO. The higher the frequency - the higher the duty cycle.

During daytime – the solar panel provides power, PIR motion detection is deactivated and only MPPT battery charging is active. During nighttime – motion detection is active and if triggered will start the LED driver for a specified time.

Transitions between day and night modes are based on solar panel voltage, with minimal loading for current testing.

Regulation Algorithms

Solar Maximum Power Point Tracking (MPPT) is used for charging the battery efficiently. The implemented MPPT algorithm is Perturb & Observe using a proportional loop to modify the panel operating voltage. Battery charging is done using a proper 3-stage CC/CV lead-acid charging algorithm with floating charge. Charge termination is triggered by either minimum current, flat current or a timer. LED current regulation is done by a proportional loop operating on the NCO frequency.

Contact your local sales representative to see a working demonstration of the Solar LED Driver.

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