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LM3647 universal battery charger

A very simple universal battery charger electronic project can be designed using the LM3647 controller for Lithium-Ion (Li-Ion), Nickel-Metal Hydride (Ni-MH) and Nickel-Cadmium (Ni-Cd) batteries. The universal battery charger device can use either a pulsed-current charging or a constant-current charging technique. The device can also be configured to discharge before charging. Throughout the charging sequence the LM3647 monitors voltage and/or temperature and time in order to terminate charging.
In Ni-Cd/Ni-MH mode, four different charging stages are used: soft-start charge, fast charge, topping charge and maintenance charge .
In Li-Ion mode, four different charging stages are used: qualification, fast charge phase 1, constant current , fast charge phase 2, constant voltage , maintenance charge .
The charge current of the LM3647 is configured via external resistors, which in turn controls the duty cycle of the PWM switching control output.

The LM3647 automatically detects the presence of a battery and starts the charging procedure when the battery is installed. Whenever an error occurs (e.g., short circuit, temperature too high, temperature too low, bad battery, charge time over, etc.) the LM3647 will stay in error mode until the battery is removed or it gets within the allowed charging temperature range.

As you can see in the circuit diagram the user interface of this charger consists of up to three LEDs and one buzzer. The buzzer-circuitry turns the transistor Q3 on when the buzzer should sound. If the current consumption for the buzzer is lower than 0.3 mA then the buzzer may be directly connected to the BUZZER-pin. The BUZZER-pin does not generate a PWM-signal, therefore the buzzer must have its own oscillator circuitry.
The LEDs have four different states: On, off, slow flash (1 Hz) and fast flash (10 Hz). The buzzer has three different states: off, one short beep (100 ms) and one long beep (1s).
Use of the buzzer or the LEDs is optional, depending on design requirements.
It is possible to use the LM3647 with one, two or all three LEDs.
LM3647 universal battery charger schematic circuit

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