California Polytechnic State University

LED Lantern and Cell Phone Charger

Abstract

                The goal of this project was to design a PCB that would control and manage the power between the 2.5-W monocrystalline solar panel, the NiMH rechargeable batteries, and the high-brightness white LEDs. Using a power tracking battery management IC and a step-up/down DC-to-DC converter IC, the circuit is designed to safely charge the batteries from the solar panel, and using the store battery energy to drive two LEDs at a constant voltage and current. For this project a PCB was designed, manufactured and assembled.

Design

                The schematic, component patterns, and board layout were designed using the program DipTrace. By running auto-placement and making a few adjustments to the auto-traces, the PCB was designed to have a relatively small footprint. The 2.5mm barrel port for the solar panel plug and the right-angle USB port were designed to mount directly onto the PCB.

Hardware Description

                The PCB consists of two sub-circuits, each controlled by an IC. The two sub-circuits may be called the Battery Management circuit and the LED Driver circuit.

                Battery Management Circuit:

                LT3652 – Power Tracking 2A Battery Charger for Solar Power

This IC can charge a battery pack with float voltage up to 14.4 V at a maximum of 2000 mA of current. Due to the limitation of the solar panel, the circuit was designed to charge the batteries at 250 mA. The LT3652 has maximum power point tracking (MPPT) capability and operated over a 4.95 V to 32 V input voltage range.

                LED Driver Circuit:

                MC34063 – 1.5 A, Step-Up/Down/Inverting Switching Regulators

The MC34063 steps up the battery voltage to drive two LEDs wired in series. The LEDs run at approximately 250 mA throughout the life of the battery. The LEDs, running at about 1.3 W, produce approximately 150 lumens of light. This is roughly the equivalent of an incandescent bulb running at 10 W, or 10-15 burning candles.

Manufacturing

                Reflow soldering is used for the soldering of the two SMD IC chips. The LT3652 comes in an MSOP-12 package with a bottom ground plane, and the MC34063 is an SOIC-8 package. The remaining through-hole components were then soldered by hand.

Conclusion

            This has been a great project for gaining hands-on experience in circuit board design and manufacturing. The biggest challenges were customizing all the component layouts and placing components strategically so that the terminal blocks were easy to access and the two ports lined up perfectly. I also had to make sure all the holes were tolerances correctly so that the components fit. The project was successful because the board functions well and the PCB is well-integrated into the housing of the lantern.

Downloads: Schematic BOM Project Report