Multivibrators and 555 Timer

Q1: What is the difference between a retriggerable one shot and a nonretriggerable one shot?

A The nonretriggerable can only be triggered once.

B The retriggerable can be triggered many times.

C The output pulse can be stretched with a nonretriggerable.

D The output pulse can be stretched with a retriggerable.

Q2: An astable multivibrator requires:

A balanced time constants

B a pair of matched transistors

C no input signal

D dual J-K flip-flops

Q3: When a capacitor charges:

A the voltage across the plates rises exponentially

B the circuit current falls exponentially

C the capacitor charges to the source voltage in 5×RC seconds

D all of the above

Q4: Does the 74123 one shot have an internal timing resistor?

A yes

B no

Q5: A 22-k resistor and a 0.02-F capacitor are connected in series to a 5-V source. How long will it take the capacitor to charge to 3.4 V?

A 0.44 ms

B 0.501 ms

C 0.66 ms

D 0.70 ms

Q6: Which mode of operation is being used when a 555 timer chip has two external resistors and an external capacitor?

A monostable

B pulse stretching

C Schmitt triggering

D astable

Q7: Design a circuit using a 74121 to convert a 33-kHz, 30% duty cycle waveform to a 33-kHz, 60% duty cycle waveform.

A Rint = 2 kCext = 0.012 nF

B Rint = 2 kCext = 0.012 F

C Rint = 4 kCext = 0.012 nF

D Rint = 4 kCext = 0.012 F

Q8: With most monostable multivibrators, what is the Q output when no input trigger has occurred?

A LOW

B +5 V

C SET

D HIGH

Q9: What is the difference between an astable multivibrator and a monostable multivibrator?

A The astable is free running.

B The astable needs to be clocked.

C The monostable is free running.

D none of the above

Q10: Is there any limit to the number of times that a 74123 can be retriggered?

A yes

B no

Q11: What is another name for a bistable multivibrator?

A an on-off switch

B an oscillator

C a flip-flop

Q12: To obtain a 50% duty cycle in an astable 555 timer circuit:

A tLO = tHI

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

C capacitor voltage must rise above 1/3 VCC

D tLO = tHIRA = RB, and short RB with a diode during the capacitor charging cycle

Q13: An astable multivibrator requires:

A balanced time constants

B a pair of matched transistors

C no input signal

D dual J-K flip-flops

Q14: With most monostable multivibrators, what is the Q output when no input trigger has occurred?

A LOW

B +5 V

C SET

D HIGH

Q15: An astable 555 timer has the following number of stable states:

A 0

B 1

C 2

D 3

Q16: Triggering a retriggerable one shot during pulse generation will:

A time out the original pulse

B extend the pulse to this trigger width

C have no effect

D double the original pulse width

Q17: What controls the output pulse width of a one shot?

A the clock frequency

B the width of the clock pulse

C an RL time constant

D an RC time constant

Q18: The internal circuitry of the 555 timer consists of ________, an R-S flip-flop, a transistor switch, an output buffer amplifier, and a voltage divider.

A a comparator

B a voltage amplifier

C two comparators

D a peak detector

Q19: What is the function of the comparators in the 555 timer circuit?

A to compare the output voltages to the internal voltage divider

B to compare the input voltages to the internal voltage divider

C to compare the output voltages to the external voltage divider

D to compare the input voltages to the external voltage divider

Q20:
What is the output pulse width of the waveform at the output of the circuit in the given figure?

A 1.65 ms

B 18.2 ms

C 4.98 ms

D 54.6 ms

Q21: The monostable multivibrator circuit is not an oscillator because ________.

A its output switches between two states

B it requires a trigger to obtain an output signal

C it requires a sine wave input signal

D the circuit does not require a dc power supply

Q22: A crystal demonstrates the ________ effect when a mechanical force across the crystal causes a small voltage to be generated.

A photoelectric

B Co-pitts

C piezoelectric

D flywheel

Q23: The pulse width out of a one-shot multivibrator increases when the:

A supply voltage increases

B timing resistor decreases

C UTP decreases

D timing capacitance increases

Q24: In a typical IC monostable multivibrator circuit, at the falling edge of the trigger input, the output switches HIGH for a period of time determined by the ________.

A value of the RC timing components

B amplitude of the input trigger

C frequency of the input trigger

D magnitude of the dc supply voltage

Q25: If Vcc of a 555 timer circuit is set to +10 V what is the level of output voltage from the circuit?

A VOH = 10 V, VOL = 0 V

B VOH = 10 V, VOL = 0.1 V

C VOH = 8.5 V, VOL = 0 V

D VOH = 8.5 V, VOL = 0.1 V

Q26: 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?

A 290 ms

B 29 ms

C 33.3 s

D 290 s

Q27: Pulse stretching, time-delay, and pulse generation are all easily accomplished with which type of multivibrator circuit?

A astable

B monostable

C multistable

D bistable

Q28:
If a diode is connected across resistor RB (positive end up) in the given figure, what is the new duty cycle of the output waveform?

A 56%

B 44%

C 21.6%

D 17.4%

Q29: The ________ is defined as the time the output is active divided by the total period of the output signal.

A on time

B off time

C duty cycle

D active ratio

Q30: A monostable 555 timer has the following number of stable states:

A 0

B 1

C 2

D 3

Q31: An astable multivibrator requires:

A balanced time constants

B a pair of matched transistors

C no input signal

D dual J-K flip-flops

Q32:
Determine tHI and tLO for the circuit given below.

A tHI = 7.95 s, tLO = 6.24 s

B tHI = 6.24 s, tLO = 7.95 s

C tHI = 3.97 s, tLO = 3.21 s

D tHI = 3.21 s, tLO = 3.97 s

Q33: 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?

A 0.0 V

B 0.309 V

C 2.7 V

D 2.295 V

Q34: 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.

A 3

B 7

C 10

D 13

Q35: If the resistor in the Schmitt trigger astable multivibrator is a variable resistor, what part of the output voltage waveform will change when the resistance is changed?

A the shape of the waveform

B the amplitude of the waveform

C the period of the waveform

D none of the above

Q36:
Is the circuit given below an astable multivibrator or a monostable multivibrator?

A monostable

B astable

Q37: Which of the following is NOT a characteristic of a retriggerable monostable multivibrator?

A It is a dual multivibrator.

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

C It has no internal timing resistor.

D none of the above

Q38: The output of the astable circuit ________.

A constantly switches between two states

B is LOW until a trigger is received

C is HIGH until a trigger is received

D floats until triggered

Q39: What does the discharge transistor do in the 555 timer circuit?

A charge the external capacitor to stop the timing

B charge the external capacitor to start the timing over again

C discharge the external capacitor to stop the timing

D discharge the external capacitor to start the timing over again

Q40:
What is the duty cycle of the waveform at the output of the circuit given below?

A 78%

B 56%

C 50%

D 44%


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