Single Cell Lithium-ion battery charger

Posted on Jan 2, 2013

The rechargeable Li-ion, I began to intensely interested last summer, when I managed to bring a holiday without a phone charger. After several experiments involving originated in Figure 1, which has proved. Involvement of the stage provides a limited current charging and constant voltage. Charging current from the rectified voltage of the transformer through the transistor T1, diode D5, resistor R2 and the battery back to AC power. Current flow creates a voltage drop on R2, which opens T2. The transistor T2 controls the current through T1 - the current is regulated so that R2 was approximately constant voltage drop. The collector is connected LED1 T2, indicating the stage of charging current.

Single Cell Lithium-ion battery charger
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Single Cell Lithium-ion battery charger - image 1
Click here to download the full size of the above Image.

Resistor R1 is deliberately chosen a relatively small resistor that flowed much more power than you need to drive T1. Most of this current then flows through LED1 and T2. LEDs because the entire phase charging current of approximately constant bright light. Involvement LED1 limits the minimum output voltage at which the circuit operates correctly at about 1 V. Since the discharged battery voltage is still greater than 3 V, it is not at fault. Part of the circuit to stabilize the output voltage phase charging current does not apply. LED2 through the current small and poorly lit. Stabilizer TL431C to take effect in reaching the final tension. With increase of voltage the current starts to flow ICs, while the current of T2 is reduced. The final charging voltage is set divider R4, R5 and R6. Resistor R5 is used for precise adjustment of the output voltage. TL431C function circuit is very simple - increases when the input voltage of 2.5 V R, increases the current flowing between terminals C and A. The capacitor C2 and resistor R7 serves to ensure the stability of the controller. In constant voltage charging phase LED1 off (T2 is closed) and turns on LED2. It is thus very simple procedure indicated charging. When LED2 is lit, the article charged to more than 70%, and we use it. Conversely, left the article in the charger part is gradually recharged to 100% and charge current drops gradually to zero. Given that the batteries...

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