Schematic for Overcharge Protection & RGB LED Charge Meter for 6V NiMH Eneloop Pack

The discussion centers on designing an external 6V NiMH battery pack using 5x AA Sanyo Eneloop cells for mobile phone charging, with a focus on implementing overcharge protection and a charge level indicator using an RGB LED. The original plan involved using a 7806 IC to step up 5V USB input to 6V for charging the battery pack and a TA48M033F regulator to step down from 6V to 5V for phone charging. It was clarified that overcharge protection is not accessible from the phone itself and must be integrated externally for the battery pack. Recommendations include researching NiMH fast-charge management ICs and battery level indicator ICs or circuits. The 7805 regulator is unsuitable due to its dropout voltage; a low dropout regulator (LDO) like the TA48M05F is preferred for maintaining 6V output. Linear Technology’s LTC3558 demo board was suggested as a ready-made solution offering boost and buck charging with built-in overcharge protection and status indicators, though it lacks a full battery gas gauge. It was noted that no single IC commonly combines both fast-charge management and charge level monitoring for NiMH batteries, so separate ICs or circuits may be required. Battery University was recommended as a resource for charging principles.
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