Method for switching over a reference voltage potential for overvoltage protection devices

1. A method comprising:

a) providing at least two supply voltages with respect to a ground potential to a circuit unit;

b) connecting signal connections of the circuit unit to signal lines for transmission of signals between the circuit unit and one or more external circuit units;

c) propagating a reference voltage from a control connection of the circuit unit to an overvoltage protective device, the overvoltage protective device connected symmetrically to two resistance element connections of the signal lines;

d) propagating a second reference voltage signal from a second control connection of the circuit unit to the overvoltage protective device, the second reference voltage signal derived from at least two further supply voltages with opposite polarity by means of a second switching module;

e) tripping the overvoltage protective device responsive to detection of an overvoltage on at least one of the two signal lines with respect to the reference voltage, thereby causing the overvoltage protection device to dissipate the overvoltage to the ground potential,

f) switching the circuit unit to select one of the at least two supply voltages using a mode switching module that is integrated in the circuit unit,

and wherein the reference voltage depends on the selected one of the at least two supply voltages.

2. The method of claim 1 , wherein c) further comprises employing a switching module to propagate the reference voltage.

3. The method of claim 1 wherein c) further comprises employing a switching module to propagate the reference voltage, the reference voltage comprising the selected one of the at least two supply voltages.

4. The method of claim 3 wherein the selected one of the at least two supply voltages is a negative voltage.

5. The method of claim 3 wherein the selected one of the at least two supply voltages is a positive voltage.

6. The method of claim 1 wherein step c) further comprises propagating the reference voltage from the control connection of the circuit unit to the overvoltage protective device, the overvoltage protective device further connected symmetrically to two temperature-dependent resistance elements having positive temperature coefficients.

7. The method of claim 1 wherein step c) further comprises propagating the reference voltage from the control connection of the circuit unit to the overvoltage protective device, the overvoltage protective device further connected symmetrically to two temperature-dependent resistance elements having positive temperature coefficients, each of the two temperature-dependent resistance elements connected in series with a corresponding of the two resistance element connections.

8. A circuit arrangement for supplying voltage to a circuit unit and having overvoltage protection, the circuit arrangement comprising:

a) at least one voltage source for provision of at least two supply voltages, which are related to a ground potential, with respect to a ground potential for the circuit unit to be supplied;

b) an overvoltage protective device connected symmetrically to two resistance connections of the signal lines, the overvoltage protection device configured to trip upon detection of an overvoltage which occurs with respect to a reference voltage on at least one signal line of the circuit unit;

c) a switching module for providing the reference voltage to the overvoltage protection device, the reference voltage corresponding to a select one of the at least two supply voltages;

d) a second switching module configured to propagate a second reference voltage signal from a second control connection of the circuit unit to the overvoltage protective device, the second reference voltage signal derived from at least two further supply voltages with opposite polarity by means of a second switching module; and

e) a mode switching module integrated into the circuit unit and configured to switch the circuit unit to the select one of the at least two supply voltages.

9. The circuit arrangement according to claim 8 , wherein the switching module is integrated in the circuit unit.

10. The circuit arrangement of claim 8 wherein the switching module is operable to propagate the selected one of the at least two supply voltages as the reference voltage.

11. The circuit arrangement of claim 10 wherein the selected one of the at least two supply voltages is a negative voltage.

12. The circuit arrangement of claim 10 wherein the selected one of the at least two supply voltages is a positive voltage.

13. The circuit arrangement of claim 8 wherein the overvoltage protective device is further connected symmetrically to two temperature-dependent resistance elements having positive temperature coefficients.

14. The circuit arrangement of claim 8 the overvoltage protective device is further connected symmetrically to two temperature-dependent resistance elements having positive temperature coefficients, each of the two temperature-dependent resistance elements connected in series with a corresponding of the two resistance element connections.