Semiconductor components are known for being sensitive to overvoltage. If the maximum rated voltages given in the data sheet are exceeded, the component might be destroyed. For this reason, the components have to be protected from any excess voltage that might occur in any of the circuits, i.e. the voltage surges have to be reduced to levels which are below the maximum rated values for the given component.
Resistors and capacitors (RC elements), as well as certain semiconductor components such as varistors and silicon avalanche diodes have proven to be a reliable way of ensuring this. The use of RC networks turns the inductors in a circuit into series resonant circuits, converting the steeply increasing voltage peaks into attenuated oscillations of low amplitude. As a result, the energy of the overvoltage is forced to decrease to a low level over an extended period of time, rather than within a brief period of time at high power.
The remaining aforementioned circuit components make use of the nonlinear resistance behaviour. Their internal resistances decrease as the voltage increases. In combination with the circuit resistors and inductors, these form non-linear voltage dividers which let through the low voltages almost without attenuation, while higher voltages above a certain level are strongly attenuated.
Here, too, the overvoltage energy is distributed over a longer period; it is almost fully absorbed by the damping components alone. The overvoltage protection components can be integrated on the AC side of the switch assembly, on the DC side, or parallel to the individual switches.
For more information, please read: