Abstract: Embodiments of the present disclosure provide an active equalizer circuit, a battery management system, a power supply system and an electrical equipment. The active equalizer circuit comprises a plurality of switching transistors, a driving transformer, a multi-port converter, a buck converter, and a microcontroller. Each of the switching transistors is coupled to a battery cell in the series battery pack on a one-to-one basis. The multi-port converter comprises an equalizing transformer and a bridge converter, each secondary winding of the bridge converter is coupled to a corresponding plurality of battery cells. The buck converter has an input terminal coupled to an output terminal of the series battery pack and an output terminal coupled to an input terminal of the bridge converter.