CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@Naman Agarwal • 02 Sep, 2012
why gate terminal is always kept near the cathode terminal?? why not near anode terminal??
@[Prototype] • 02 Sep, 2012
[​IMG]

See the layer diagram of SCR I've made above.

An SCR is nothing but a P-N junction diode & an NPN transistor combined together. There's no significance of gate being near to the cathode side, its just the normal base terminal of an NPN transistor which is being used as GATE in SCR. Since the PN junction doesn't have a 3rd terminal & NPN transistor is used, the GATE automatically happens to be near the cathode.
@arunchary • 03 Sep, 2012 • 1 like its because we know the simple concept of current,cathode have a more no.of electrons to drive then anode.little bit of gate current which leads to drive and then it will starts conducting.....
@Jeffrey Arulraj • 14 Oct, 2012 • 2 likes Sorry to say this guys both have hinted on a wrong tone

The prime reason is to provide an addtional voltage to the reverse biased PN junction (2nd junction) and thus we get a breakdown before the actual reverse bias break down voltage (say 30 V this is supplied partly from AK voltage and partly from the Gate voltage so earlier BD for lesser AK voltage )

If the Gate is connected nearer to the Anode more voltage will be needed to trigger the SCR as higher voltage will be required to breakdown the reverse biased diode in junction 2
@Vishal Sharma • 14 Oct, 2012 Just now learned the topic in college. I totally agree with jeffrey
@[Prototype] • 14 Oct, 2012
jeffrey samuel
Sorry to say this guys both have hinted on a wrong tone

The prime reason is to provide an addtional voltage to the reverse biased PN junction (2nd junction) and thus we get a breakdown before the actual reverse bias break down voltage (say 30 V this is supplied partly from AK voltage and partly from the Gate voltage so earlier BD for lesser AK voltage )

If the Gate is connected nearer to the Anode more voltage will be needed to trigger the SCR as higher voltage will be required to breakdown the reverse biased diode in junction 2
I always thought there was no functional significance of that. Thanks for enlighting. Guess my attention was somewhere else when this thing was taught.
@Vishal1485 • 31 Oct, 2012 practically this terminals are arranged in sequence cathode, anode & gate
@Jeffrey Arulraj • 31 Oct, 2012 • 1 like
Vishal1485
practically this terminals are arranged in sequence cathode, anode & gate
That is only in a chip or in the pin diagram of the SCR which you use in lab not in the internal structure friend
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