Multivibrators and 555 Timer MCQs

Question 1

The monostable multivibrator circuit is not an oscillator because ________.

Accepted Answer

it requires a trigger to obtain an output signal

Answer

its output switches between two states

Answer

it requires a sine wave input signal

Answer

the circuit does not require a dc power supply

Question 2

A retriggerable one shot has a pulse of 10 ms. 3 ms after being triggered, another trigger pulse is applied. The resulting output pulse will be ________ ms.

Accepted Answer

13

Answer

3

Answer

7

Answer

10

Question 3

What is the pulse width of the output of a 74123 if an external 4.7-k resistor and a 0.022-F capacitor are used?

Accepted Answer

33.3 s

Answer

290 ms

Answer

29 ms

Answer

290 s

Question 4

To obtain a 50% duty cycle in an astable 555 timer circuit:

Accepted Answer

tLO = tHI

Answer

RA = RB and short RB with a diode during the capacitor charging cycle

Answer

capacitor voltage must rise above 1/3 VCC

Answer

tLO = tHI, RA = RB, and short RB with a diode during the capacitor charging cycle

Question 5

An astable 555 timer has the following number of stable states:

Accepted Answer

0

Answer

1

Answer

2

Answer

3

Question 6

Which mode of operation is being used when a 555 timer chip has two external resistors and an external capacitor?

Accepted Answer

astable

Answer

monostable

Answer

pulse stretching

Answer

Schmitt triggering

Question 7

A 0.3-F capacitor has an initial charge of 2.7 V. If it is discharged through a 10-k resistor for 6.5 ms, how much voltage will be left across the capacitor?

Accepted Answer

0.309 V

Answer

0.0 V

Answer

2.7 V

Answer

2.295 V

Question 8

Which of the following is NOT a characteristic of a retriggerable monostable multivibrator?

Accepted Answer

It has an active-HIGH reset, which terminates all timing functions.

Answer

It is a dual multivibrator.

Answer

It has no internal timing resistor.

Answer

none of the above

Question 9

The pulse width out of a one-shot multivibrator increases when the:

Accepted Answer

supply voltage increases

Answer

timing resistor decreases

Answer

UTP decreases

Answer

timing capacitance increases