555 IC Timer Interview Questions and Answers:

1. What is 555 timer?

Ans. The 555 timer is a highly stable IC that can produce accurate and highly stable time delays or oscillation. The frequency of oscillation and duty cycle are accurately controlled by only two external resistors and a capacitor.

2. What do you mean by a grounded load?

Ans. When the load is connected between the output terminal (pin 3) and grounded terminal (pin 1), it is called grounded load, this is also sometimes called the normally off load.

3. Why normally control terminal of 555 timer is connected to ground through a 0.01 μF bypass capacitor?

Ans. Normally control terminal (pin 5) of timer is connected to ground through a 0.01 μF bypass capacitor so as to prevent noise coupled onto this pin from causing false triggering.

4. What are the two basic modes in which the 555 timer operates?

Ans. The 555 timer basically operates in one of the two modes-either as monostable or as an astable multivibrator.

5. Name the CMOS version of the 555.

Ans. 7555.

6. Why is it possible to operate MMV for a frequency-divider application?

Ans. MMV operation as a frequency-divider is possible because the MMV cannot be triggered during the timing cycle.

7. Why is it possible to operate MMV for pulse stretching application?

Ans. MMV operation as a pulse stretcher is possible because the output pulse width of MMV is of longer duration than the width of the negative going trigger pulse. This output pulse can be viewed as a stretched version of the narrow input pulse.