Hello,
I m using thyristors in mixed rectifier for soft start, just after that i have a PFC stage.
I'm thinking to add an overcurrent protection ; for example in case of short circuit at PFC stage the DSP should turn off both thyristors,
do you think in this case i can damage the thyristors due to high voltage spike ? ( L*di/dt can be very high)
Thank you,

 

Thyristors are extremely rugged beasts. They can sustain abuse that would destroy most transistors.

Unfortunately...,,, You can turn on thyristors at your hearth's delight, but you cannot turn them off at will.
The thyristor will only be turned off when its Anode current is reduced to zero. That can take several milliseconds.

But anyways to your question: a very large di/dt usually has the effect of retriggering the thyristor. To reduce the ristime, a parallel snubber is used.

 

I assume this is a rectifier bridge with two SCR's? It is customary to place a fifth rectifier reverse biased on the bridge output.
ON Semi
Max.

 

Thyristors are extremely rugged beasts. They can sustain abuse that would destroy most transistors.

Unfortunately...,,, You can turn on thyristors at your hearth's delight, but you cannot turn them off at will.
The thyristor will only be turned off when its Anode current is reduced to zero. That can take several milliseconds.

But anyways to your question: a very large di/dt usually has the effect of retriggering the thyristor. To reduce the ristime, a parallel snubber is used.

Hi thank you for your answer,
But using GTO thyristors instead of normal ones,
using snubbers capacitors does cause current spikes at the moment of turn on,