Abstract: Method for supplying a circuit unit (201) which is to be supplied with different supply voltages, in which the circuit unit (201) to be supplied is protected against overvoltages, having the following steps: application of at least two supply voltages (203a, 203b) with respect to a ground potential (210) to the circuit unit (201) to be supplied; connection of signal connections (208, 209) of the circuit unit (201) to signal lines (206, 207) for transmission of signals between the circuit unit (201) and external circuit units; emission of a reference voltage (204) from a control connection (212) of the circuit unit (201) to an overvoltage protective device (205), in that a supply voltage (203a, 203b) is passed on to the control connection (212) by means of a switching module (211); and tripping of the overvoltage protective device (205) on detection of an overvoltage which occurs with respect to the reference voltage (204) on at least one of the two signal lines (206, 207).