The IC TDA 4605-3 controls the MOS-power transistor and performs all necessary control and protection functions in free running flyback converters. Because of the fact that a wide load range is achieved, this IC is applicable for consumer as well as industrial power supplies. The serial circuit and primary winding of the flyback transformer are connected in series to the input voltage. During the switch-on period of the transistor, energy is stored in the transformer. During the switch-off period the energy is fed to the load via the secondary winding. By varying switch-on 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 of 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. A new cycle will start if the transformer has transferred the stored energy completely into the load.