a simple and flexible battery charger for charging high voltage battery strings includes a dc - to - ac converter that drives the primary of a transformer having multiple secondaries . each secondary winding has a corresponding output stage formed of a rectification circuit , output inductor , and output capacitor . the output terminals of the output stages are connectable either in parallel or series . in either configuration , inductor current and capacitor voltage automatically balance among the output stage circuits . a controller normally regulates output terminal voltage by operating in voltage mode , but limits current by operating in a current mode when the average of inductor currents exceeds a specified limit . reconfiguration from parallel to series , or vice versa , is obtained physical reconnection of the output stage terminals and adjustment of a single voltage feedback scaling factor . connecting the output stages in series to produce a high voltage output reduces voltage stresses on the rectification circuits and enables use of schottky diodes to avoid reverse recovery problems .