Exam Questions Papers - Engineering

Q1:

With respect to the following 555 timer circuit what will be the value of RA and R such that the LED turns on for a duration of 10 ms every time it receives negative trigger pulse. LED operating current = 20 mA, Vf = 1.4 V, Vo on = 13.4 V and C = 0.22 nf

A 41.4 KΩ, 600 Ω

B 45 KΩ, 630 Ω

C 43.5 KΩ, 580 Ω

D 44.9 KΩ, 600 Ω

ANS:A - 41.4 KΩ, 600 Ω

Timer operated in mono, mode RAC = RA = 41.4 KΩ R = = 600 Ω.