Voltage converter

The invention relates to a voltage converter of a Flußwandlertyp with respect to a transformer (17) secondary-side, self-controlled synchronous rectifier, wherein for driving an active switching element (V1, V2) of the synchronous rectifier, a capacitance device (C1; C1, C2) is provided, which by means of a secondary-side auxiliary winding (W1, W2) of the transformer and charged by means of a semiconductor element (D1, D2; 30, 32) is applied to a control terminal of the active switching element, wherein the capacitance device is formed so that the charge enables a synchronous switching operation of the active switching element.