An SCR having a turn ON time of 5 μsec, latching current

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An SCR having a turn ON time of 5 μsec, latching current of 50 mA and holding current of 40 mA is triggered by a short duration pulse and is used in the circuit shown in the figure given below. The minimum pulse width required to turn the SCR ON will be

1. 251 μsec
2. 150 μsec
3. 100 μsec
4. 5 μsec

Correct Option: A

i_R =	100	=	100	= 0.02 A
	R₂		5 × 10³

=	100		1 - e^{{-20t / 0.5}}		= 5(1 - e^-40t)
	20

Then, i_T = i_L + i_R = 0.02 + 5(1 – e ^{– 40t})
It minimum pulse width is T for i_a ≥ latching current.
Then, 0.02 + 5(1 – e ^{– 40t}) = 0.05
⇒ 5(1 – e ^{– 0.40t}) = 0.03
⇒ t = 150 μ sec.