The invention relates to a method for frequency control of a piezoelectric transformer (1), wherein a piezoelectric transformer (1) is excited on an input side (1a) with an alternating voltage of predetermined frequency, and phase information of the input impedance of the piezoelectric transformer (1) is detected in a return path. The detected phase information regarding a predetermined phase criterion is subsequently evaluated and the frequency of the alternating voltage is controlled according to the evaluated phase information. In addition, a switch arrangement is described for carrying out a corresponding frequency control.
