Lipo Protection Circuit Module designed as a shunt regulator to prevent individual cells exceeding 4.3V during charging from an external source. As the Seiko S8241/S8261, DW-01 and AIC1811 single cell protection ICs are difficult to source, a cheap comparator with integrated 0.2V voltage reference was used.
The MAX9646 has an internal 9mV Input Threshold Hysteresis. With the specified voltage divider and internal 0.2V reference, the load comprising of up to six 82 ohm resistors will switch on at 4.29V and turn off at 4.11V.
Each 82ohm resistor will apply a load of approximately 50mA. Add as many as required to bypass your charger's current. A LED indicates when the load is enabled for each cell.
Update 3rd October 2016: Board populated and tested. Each channel turns on at approximately 4.24V and off at 4.20V. Hysteresis is a little tighter than expected. Functions fine on a bench power supply, but observe oscillations (approx 4.5KHz) when running from a 7S Battery Pack. Extra hysteresis or better power supply coupling is required.
Q7, Q6, Q5, Q4, Q3, Q2, Q1
R62, R63, R64, R65, R66, R67, R52, R53, R54, R55, R56, R57, R42, R43, R44, R45, R46, R47, R32, R33, R34, R35, R36, R37, R22, R23, R24, R25, R26, R27, R12, R13, R14, R15, R16, R17, R2, R3, R4, R5, R6, R7
D7, D6, D5, D4, D3, D2, D1
U7, U6, U5, U4, U3, U2, U1
F1, F2, F3, F4, F5, F6, F7
R61, R51, R41, R31, R21, R11, R1
R69, R59, R49, R39, R29, R19, R8
YAGEO (PHYCOMP) RC0805FR-0718KL RESISTOR, RC12H 0805 18K
R70, R60, R50, R40, R30, R20, R10
R68, R58, R48, R38, R28, R18, R9
C7, C6, C5, C4, C3, C2, C1