Series-type charger with output voltage automatically regulated and hot swap

Since the traditional series-type charger has no function of hot swap, a new series-type charger with hot swap is presented herein. In this study, hot-swap battery and stopping charging battery are achieved by floating voltage detection and battery bypass detection. Furthermore, by means of controlling the voltage across the collector of the bipolar junction transistor (BJT) and the ground, the output voltage of the DC–DC converter can be automatically adjusted. Accordingly, the BJT can always work under the active region with a designed constant voltage across it for any number of batteries in the steady state, reducing undesired conduction loss. Also, one constant current control circuit is utilized, which is connected in series with the voltage and bypass detectors. Above all, unlike the traditional series-type charger with the active equalizer, there is no energy transferred among batteries in the proposed charger. Finally, the proposed series-type charger with four battery channels is designed and applied to charging 18650 Li-ion batteries. Via some experimental results, the effectiveness of the proposed charger can be verified.