Extension for LiPo Charger

The ‘Simple LiPo Charger’ published in Elektor Electronics April 2005 is a small and handy circuit that allows you to quickly charge two or three LiPo cells. Especially in the model construction world are LiPo batteries used a lot these days, particularly model aeroplanes. It is usual to use a series connection of three cells with these models. Since working with these model aeroplanes usually happens in the field, it would be nice if the batteries could be charged from a car battery. We therefore designed a voltage converter for the LiPo charger concerned, which makes it possible to charge three cells in series.

Resistors:

R1 = 25m (e.g., Digikey # 2FR025-ND)

R2 = 100k

R3 = 10k

Capacitors:

C1,C4,C8 = 100nF

C2,C3 = 47µF 25V radial

C5,C7 = 100µF 25V radial

C6 = 100pF

Semiconductors:

D1 = 31DQ05 (e.g., Digikey # 31DQ05-ND)

IC1 = MAX1771-CPA (e.g., Digikey # MAX1771EPA-ND)

T1 = IRFU3708 (e.g., Digikey # IRFU3708-ND)

Miscellaneous:

K1,K2 = 2-way PCB terminal block, lead pitch 5mm

L1 =  47H high current suppressor coil, (e.g, Digikey # M9889-ND)

PCB.,ref. 054012-1