Voltage surge protection
The use of RC networks turns the inductors in the circuit to series resonant circuits, converting the steeply increasing voltage peaks into attenuated oscillations of low amplitude. |
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Uncontrolled rectifier circuits
In uncontrolled bridge circuits, it is normally sufficient to include a snubber on the DC side only. It is often not needed to include any protection circuit as long as the maximum breaking voltage of the diodes is significantly higher than the operation voltage.
Controllable switches (thyristors)
Thyristors have to be protected not only from excessive non-permissible surges, but also - and more
importantly - from the steep rate of rise.
The use of a single-thyristor snubber is, however, limited because the capacitors discharge through
these networks during triggering and thus cause undesired stress with a steep current rate of rise
(di/dt stress).
In thyristor assemblies for low current densities and high voltages where relatively small capacitance
and high-ohmic resistances are sufficient, this di/dt stress is still relatively low, meaning that here a
single-switch snubber alone is often enough.
For higher current densities, however, the solution is to use an AC side snubber.
For very high power, in particular for parallel thyristor circuits, it can be of advantage to connect the
RC circuit via an auxiliary bridge.
Circuits
• Dimensioning guidelines for single-switch snubbers
Assumption: around half of the energy represented by the recovered charge Qrr is transferred to the
circuit in the form of an overvoltage.