Question

A negative going trigger pulse is applied to pin 2 of the IC 555 timer, passes through the threshold level of

• A. \( \frac{V_{CC}}{3} \) and sets the Flip-flop
• B. \( \frac{V_{CC}}{3} \) and resets the Flip-flop
• C. \( \frac{2V_{CC}}{3} \) and sets the Flip-flop
• D. \( \frac{2V_{CC}}{3} \) and resets the Flip-flop

Hint:

The trigger input of the 555 timer sets the flip-flop when the voltage at pin 2 drops below \( \frac{V_{CC}}{3} \).

Answer 1

The Correct Option is A

In an IC 555 timer, when a negative-going trigger pulse is applied to pin 2, it needs to drop below \( \frac{V_{CC}}{3} \) to set the flip-flop and initiate the timing cycle. Once the trigger voltage is below this threshold, the flip-flop is set and the output goes high. Thus, the correct answer is option (1).