Battery charger with constant voltage mode

A battery charger in constant voltage (CV) mode maintains a fixed output voltage while allowing the charging current.

How Constant Voltage Mode Works

• The charger sets its output voltage equal to the fully charged voltage level of the battery (e.g., 4.2 V for a single Li-ion cell).
• Initially, when the battery is not yet fully charged, the charging current is high.
• As the battery charges and its voltage nears the charger’s output voltage, current gradually decreases.

Charger Architecture (CV Mode)

Power Stage:

• DC-DC converter (e.g., buck or boost depending on battery/input voltage).
• Controlled to regulate the output voltage.

Voltage Feedback Loop:

1. Battery voltage is sensed.
2. Compared to a reference voltage (e.g., 4.2 V).
3. Error is processed by a PI controller.
4. Output adjusts PWM duty cycle to keep output voltage constant.