lunalight pcb rev 2.1
DESCRIPTION
LunaLight PCB Rev 2.1. Fully Integrated Solar-Rechargeable LED Lantern and Cell Phone Charger. Mike Deagen (MATE) IME 458 May 25, 2012. The LunaLight is the result of a multidisciplinary senior project in collaboration with the non-profit organization One Million Lights. - PowerPoint PPT PresentationTRANSCRIPT
LunaLight PCB Rev 2.1
Mike Deagen (MATE)IME 458
May 25, 2012
Fully Integrated Solar-Rechargeable LED Lantern and Cell Phone Charger
The LunaLight is the result of a multidisciplinary senior project in collaboration with the non-
profit organization One Million Lights
LunaLight debut in Kenya (April 2012)
A solar-rechargeable LED lantern and cell phone charger has three sub-circuits
IC Type Purpose
Battery Management Take the input power from the solar panel and safely charge the rechargeable batteries within the lantern
LED Driver Provide a constant current to the LEDs at the appropriate forward voltage
DC-DC Boost Increase the potential of the 3.7V Li-ion battery to meet the 5V USB standard voltage
Battery Management LED Boost Driver & DC-DC Boost for Cell Phone Charger
LT3652MSOP-12 packageCost: $4.36
MC34063SOIC-8 packageCost: $0.45
Rev 1.0 of the PCB had wires leading to the batteries, the LEDs, and the switch
The goal for the second revolution was to reduce overall assembly time by integrating
all the electronics onto a single board
Other GoalsUse mostly SMT components
Multiple brightness settings with a slide switchLi-ion battery instead of Nickel Metal Hydride
Ports and Switches
LEDs
Battery Holder
I modeled the thermal management to see if the LED junction could rise above Tmax = 150°C
Heat Generated = 0.84 WTotal Est. θ = 102°C/WΔT = 86°CIf T∞ = 25°C, Tjunc = 121°C
81% of Tmax
I used reflow soldering technique for SMT components (front side) and manual soldering
for thru-hole components (back side)
91% isopropyl rubbing alcohol removed the solder flux residue
The basic functions of the PCB were confirmed with simple verification tests
Illuminance from 12” away“HI” = 473 lux“LO” = 94 lux
Solar Li-ion battery chargingVbatt_chg = 3.96 V
Ichg = 212 mA
Testing the LED voltage drop over time indicated a junction temperature of 50°C
Temperature coefficient of voltage = -4.0 mV/°C [CREE XP-E datasheet]
For two LEDs in series, temperature coefficient of voltage = -8.0 mV/°C
0 200 400 600 800 100012001400 16001800 20005.6
5.65
5.7
5.75
5.8
5.85
5.9
5.95
6
time (s)
LEDVoltage
(V)
∆ 𝑇=∆𝑉
−8.0𝑚𝑉 /℃=5.75𝑉 −5.95𝑉−8.0𝑚𝑉 /℃
∆ 𝑇=−200𝑚𝑉−8.0𝑚𝑉 /℃=25℃
𝑇=𝑇 ∞+∆𝑇=25+25=𝟓𝟎℃
However, the temperature coefficient of voltage is
probably not linear!
Overall, I think the design was successful, and future LunaLight teams should consider
implementing a fully integrated PCB
Questions?