why the value of alpha 1 and alpha 2 is increasing in two transistor model of scr
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If the gate current IG is increased from zero to some positive value, this will increase the anode current IA as shown by equation 6. An increase of IA which is an increase of IE1 would increase a1 as shown in figure 4.4 and also a2 since . The increase in values of both a1 and a2 would further increase the value of anode current IAwhich is a regenerative or positive feedback effect.
If a1 and a2 approach unity, the denominator of equation 6 approaches zero and a large value of anode current is produced causing the thyristor to turn on as a result of the application of a small gate current.
The capacitance of the pn junctions are shown in figure 4.5 below.
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