This circuit is design for Li-Ion battery charger that features a dropout voltage of less than one volt. This charger is a constant-current and constant-voltage charger. Here’s the figure of the circuit.
The operation in the circuit is constant-current mode at the beginning of the charge cycle and switches over to a constant-voltage mode near the end of the charging cycle. The circuit consists of two basic feedback loops. The first loop controls the constant charge current delivered to the battery, and the second determines the final voltage across the battery. With a discharged battery connected to the charger, (battery voltage is less than 8.4V) the circuit begins the charge cycle with a constant charge current. The value of this current is set by using the reference section of the LM10C to force 200 mV across R7 thus causing approximately 100 μA of emitter current to flow through Q1, and approximately 1 mA of emitter current to flow through Q2. The collector current of Q1 is also approximately 100 μA, and this current is flows through R2 developing 50 mV across it. This 50 mV is used as a reference to develop the constant charge current through the current sense resistor R1. [Circuit’s source: National Semiconductor Notes].
The operation in the circuit is constant-current mode at the beginning of the charge cycle and switches over to a constant-voltage mode near the end of the charging cycle. The circuit consists of two basic feedback loops. The first loop controls the constant charge current delivered to the battery, and the second determines the final voltage across the battery. With a discharged battery connected to the charger, (battery voltage is less than 8.4V) the circuit begins the charge cycle with a constant charge current. The value of this current is set by using the reference section of the LM10C to force 200 mV across R7 thus causing approximately 100 μA of emitter current to flow through Q1, and approximately 1 mA of emitter current to flow through Q2. The collector current of Q1 is also approximately 100 μA, and this current is flows through R2 developing 50 mV across it. This 50 mV is used as a reference to develop the constant charge current through the current sense resistor R1. [Circuit’s source: National Semiconductor Notes].
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