Method for generating a regulated D.C. voltage from an A.C. voltage and power supply device for implementing said method

The invention relates to a method for generating a regulated direct voltage (U G ) form an alternating voltage (U w ) using a step-down transformer (S 1 , D 1 , D 2 , C 0 , L), a step-up transformer (S 2 , D 2 , C 0 , L), an inductance coil (L) and a control device ( 11 ) that controls the transformer in a step-down or step-up transformation mode. According to the invention, an inductance coil voltage measuring signal (I) is compared with three limiting values (A, B, C) with the purpose of simplifying said method, wherein A corresponds to zero, B lies between A and C and B and C correspond to the direct voltage (U G ). Switching from the step-down to the step-up transformation mode is effected when the increasing voltage measuring signal (I) drops after reaching B and A is not reached again and increases to C instead. Switching from step-down to step-up transformation mode is effected when the decreasing voltage measuring signal (I) increases after reaching A and B is not reached and drops to A instead. In the power supply device for implementing the method, the control device ( 11 ) comprises three comparators ( 15, 16, 17 ) for comparing the limiting values (A, B, C) with the voltage measuring signal (I) of a voltage measuring device ( 5 ), wherein at least B and C are dependent upon regulation deviation (X w ).