BJT under surge condition

[Jack// ani]

Hi all,

I'm reading power electronics...can't understand why this happens
so with a BJT.

Under surge condition Gate turn-off thyristor(GTOs) goes into deeper
saturation due to regenerative action. On the other hand, a bipolar
transistor tends to come out of saturation.

Please explain me.

Thanks

 

[Ken Smith]

In article <PuidnScE19-EHR_fRVn-1g@adelphia.com>,
John Popelish <jpopelish@rica.net> wrote:

Jack// ani wrote:
Hi all,

I'm reading power electronics...can't understand why this happens
so with a BJT.

Under surge condition Gate turn-off thyristor(GTOs) goes into deeper
saturation due to regenerative action. On the other hand, a bipolar
transistor tends to come out of saturation.

Please explain me.

Thanks

Do you have a data sheet of part number documenting this property?
The only reason I can imagine is one involving temperature rise.

IGBTs are a lot like MOS gated SCRs. In the N channel device, there is an
N channel MOSFET and a wanted PNP bipolar. There is also an unwanted NPN
structure in there. This NPN has a very low HFE and has a low resistance
path from its base to emitter but at high currents, it does start to add
some base drive to the PNP.

This slows the turn off a bit.


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