Designing a Battery Cycling Circuit for 200µA Charge/Discharge Using LM334

The discussion centers on designing a battery cycling circuit capable of charging and discharging small batteries at a constant current of approximately 200µA using an LM334 current source. The main challenge is implementing automatic current direction switching when the battery voltage reaches defined thresholds (0 V discharge and 1 V charge). It is noted that discharging to exactly 0 V is problematic due to measurement inaccuracies and potential battery damage, especially for typical chemistries. However, for silicon-based Li-ion batteries tested against metallic lithium, voltages near 0 V are achievable and relevant. Several contributors recommend using a microcontroller (e.g., Raspberry Pi with ADC) to monitor voltage and control current direction, as analog comparators struggle to detect zero volts accurately without split power supplies. A proposed solution involves a window comparator and RS flip-flop circuit to toggle current direction between charge and discharge states, with adjustable voltage thresholds set by resistor dividers. Using a split supply or negative rails can improve zero-volt detection. Alternatives include employing a Keithley Source Measurement Unit (SMU) for precise current sourcing and sinking with PC control, though cost is a factor. The discussion also touches on logging charge/discharge time and capacity for battery life assessment. Memory effect is mentioned as a reason for deep discharge cycles in some battery types, but Li-ion batteries reportedly do not exhibit this effect.
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