The IC TDA 4605-1 controls the MOS-power transistor and performs all necessary regulation and monitoring functions in free running flyback converters. Since good load regulation over a wide load range is attained, this IC is applicable tor consumer and industrial power supplies. The serial circuit of power transistor and primary winding of the flyback transformer is connected to the input voltage. During the switch - on period of the transistor, energy is stored in the transformer and during the switch - off period it is fed to the load via the secondary winding. By varying switchon time of the power transistor, the IC controls each portion of energy transferred to the secondary side such that the output voltage remains nearly independent ot load variations. The required control information is taken from the input voltage during the switch-on period and from a regulation winding during the switch-off period.