Add charging status to simple lithium-ion charger

Like other simple, single-cell lithium-ion battery chargers, Microchip’s MCP73812 provides no means of indicating the charging status. You can remedy this situation by adding four components (Figure 1). Add one more LED, and you also get a charging-complete indication. This two-LED configuration has the added benefit that one of the LEDs is always on, providing an indication that the charger is powered.

Add charging status to simple lithium-ion charger

While the cell is in the constant-current charging mode, 401 mA flows through the 1N4001 diode, D1. The additional 1 mA is the supply current of the control chip. Because the 1N4001 conducts before the base-emitter junction of Q1, it prevents Q1 from turning on until the forward voltage across it reaches about 450 mV. Q1 then starts to conduct and turns on D2, a red LED that indicates charging. Because the forward-voltage drop for a green LED is typically higher than that of a red LED—2.1 versus 1.7V—the voltage across D2 and Q1 is less than the turn-on voltage of the green LED, D3, and it remains off.

For the last part of the charging cycle, the controller switches to constant-voltage mode. As the cell voltage gets closer to this 4.2V terminal voltage, the current through D1 drops, and at 15 to 40 mA, both LEDs illuminate.

For more detail: Add charging status to simple lithium-ion charger

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Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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