Signal generation unit and method to generate a data signal in a control unit of a power system device

A signal generation unit and a method for generating a data signal in a control unit of a power system device, especially of a tap changer drive unit, are provided. The signal generation unit comprises a signal relay (6) to alternately open and close at least one relay contact thereby performing a switching operation between two different output voltages and a protection circuit in parallel with the at least one relay contact for protecting the at least one relay contact against overvoltages. The at least one relay contact corresponds to two relay output terminals (8). In order to allow the signal generation unit to be used for different DC output voltages and up to a maximum rated inductive load the protection circuit comprises a transistor switch (10) in parallel with the two relay output terminals (8) and a switch control unit (11) for closing the transistor switch (10) before opening the at least one relay contact and opening the transistor switch (10) after the at least one relay contact is opened.