555 Timer IC Questions and Answers for Viva - 555

Answer-1: The 555 IC is a highly stable device that can be used for generating accurate time delays or oscillations. The 555 timer is an integrated circuit specifically designed to perform signal generation and timing functions. The mode of operations and desired outputs can be obtained by different circuits using external resistors and capacitors.

Answer-2: 555 Timer is used in: Astable multivibrators, Monostable multivibrator, Missing pulse detector, Linear ramp generator, Frequency divider, Pulse width modulation, FSK generator, Pulse position modulator, Schmitt trigger etc

Answer-3: In monostable mode of operation, 555 timer is used in missing pulse detector, Linear ramp generator, Frequency divider and Pulse width modulation.

Answer-4: In monostable mode of operation, 555 timer is used in FSK generator and Pulse-position modulator.

Answer-5: The basic blocks which constitutes 555 Timer IC are a relaxation oscillator, RS flip flop, Two comparator and Discharge transistor.

Answer-6: 555 Timer has two basic operating modes: monostable and astable. It is available in three packages. 8 pin metals can, 8 pin dip, 14 pin dip. It has very high temperature stability.

Answer-7: It is the CMOS version of the IC 555.

Answer-8:
Astable multivibrator time period, T = 0.69 * (RA + 2RB) * C
Monostable multivibrator, T = 1.1 * R * C.

Answer-9: An astable multivibrator is a multivibrator which has no stable states.
Monostable multivibrator is a one-shot multivibrator which has one stable state.
Bistable multivibrator is a multivibrator which has two stable states, that is both the states are stable.

Answer-10: The ratio of high output and low output period is given by a mathematical parameter called duty cycle. It is defined as the ratio of ON Time to total time.

Answer-11: A voltage controlled oscillator is an oscillator circuit in which the frequency of oscillations can be controlled by an externally applied voltage.

Answer-12: The Reset pin of the 555 is an active-low input, that is the IC resets when this input is connected to low state. So in a normal condition, it is connected to the +Ve terminal of the supply which always maintains a high state at the input.

Answer-13: The threshold and triggering voltages can be overridden by adjusting the voltage at the control pin. So as to eliminate noise, fluctuations control pin is connected to ground through a 0.01?F bypass capacitor.

Answer-14: It has a Wide supply voltage range (10-24V). It very linear modulation characteristics and has high temperature stability.

Answer-15: A PLL is a basically a closed loop system designed to lock output frequency and Phase to the frequency and phase of an input signal.