For Astable-IC555 based multivibrator, TOFF = 0.69CR2. Between which pins of IC 555, R2 is connected :

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  1. 2, 7
  2. 5, 1
  3. 4, 7
  4. 3, 0

Answer (Detailed Solution Below)

Option 1 : 2, 7
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Detailed Solution

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Concept:

In an astable multivibrator configuration using the IC 555 timer, the output oscillates continuously between high and low states without requiring any external triggering. The timing of the high and low periods is determined by the values of two resistors (R1 and R2) and a capacitor (C).

The time for which the output remains low (TOFF) is given by:

\( T_{OFF} = 0.693 \times R_2 \times C \)

Calculation:

In the astable configuration:

  • Resistor R1 is connected between pin 7 (Discharge) and VCC
  • Resistor R2 is connected between pin 7 (Discharge) and pin 2/6 (Trigger/Threshold, which are connected together)
  • Capacitor C is connected between pin 2/6 and ground

Since TOFF depends only on R2 and C, and the discharge path goes through pin 7, R2 must be connected between pin 7 and the capacitor (which is at pin 2).

Therefore, R2 is connected between pin 7 and pin 2.

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