SCR forward breakover

[Zman]

Hi

This may be an elementary question, but I haven't found a convincing answer in any reference book.  Why does the voltage across an SCR suddenly decrease after the forward break-over voltage?  As far as I understand, the middle junction breaks down at that voltage.  Why does the voltage across it drop to zero after it breaks down?

[Jerry]

Hi Zman,

You described it yourself when you said "the middle junction breaks down at that voltage".  Before the breakdown there is a barrier created by the PN junction.  This barrier is what impeeds the current flow.  Once the barrier breaks down then current flows freely.  If current flows freely then there would be a very low voltage drop, something near zero.  Read more about the SCR in this Data ebook on Talk Electronics.

[Jerome Trent]

For those of you who don't know, we have a Resources for Electronics Forum.  In this forum you can find a link to the data book that Jerry refers to, along with many, many other links to lots of electronic information.  The resources are here for your use.