Solar Charger

Portable energy for people on the move

Published in issue 3/2011 on page 68

With renewable energy high on the agenda, this little project will appeal to everyone who would feel better charging their mobile or PDA from solar sources. A lithium-ion cell stores the sun’s energy in between charging sessions. Smart circuitry in the solar charger monitors the battery voltage and protects the battery from overcharging and deep discharge.

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Products

Components

Resistors
SMD0805, 0.125W, 1%, if not shown otherwise)
R1 = 270kOhm
R2 = 82kOhm
R3,R4,R9 = 220Ohm
R5,R10–R13 = 22kOhm
R6 = 4.7MOhm
R7 = 1.5MOhm
R8 = 560kOhm
R14 = 240Ohm
R15 = 1.2kOhm
R16 = 100Ohm
R17 = 3.3Ohm
Capacitors
C1,C3,C6–C9 = 100nF (SMD0805, 10%)
C2,C5 = 100µF 16V, 10%, tantalum, SMD
C4 = 10nF (SMD0805, 10%)
Inductor
L1 = 10µH, 2.47A, 0.066Ohm, 20%, ferrite core (e.g. Coiltronics DR74-100-R)
Semiconductors
D1 = 1N4007 (MELF), e.g. LL4007G or BAT85 (see text)
D2 = Schottky diode 3A, 60V (e.g. MBRS360T3G, On Semiconductor)
D3 = LED red, 25mA, SMD1206
D4 = LED yellow, 25mA, SMD1206
D5 = LED green, 20mA, SMD1206
T1, T2 = IRF7413 (International Rectifier)
T3 = BC847 SMD (e.g. BC847CLT1G, On Semiconductor)
IC1 = ATtiny13V-10SU (Atmel), programmed, Elektor Shop # 090190-41*
IC2 = LT1302 (Linear Technology)
IC3 = LM317LD (e.g. from ST Microelectronics)
Miscellaneous
K3 = USB-A connector, SMD (e.g. Lumberg 2410 06)
S1 = Micro slide switch, 2-pole changeover (e.g. Multicomp MCLSS22)
K5 = Connector strip 6-pin, twin-row, 2.54mm spacing (e.g. Tyco/AMP 1241050-3)
JP1 = 2-pin pinheader with jumper, 0.1 in. lead pitch
LiPo battery 2000 mAh, 15C, 3.7V, e.g. Kokam 200015-0101G (834374H)
ASI-OEM solar panel 4.8V/80mA or 5V/81mA or similar
Schottky diodes BAT85 for parallel connection of the panels (see text)
PCB, order code 090190-1