3.1 Differentiate between bistable multivibrators and astable multivibrators with reference to the output states - NSC Electrical Technology Electronics - Question 3 - 2023 - Paper 1
Question 3
3.1 Differentiate between bistable multivibrators and astable multivibrators with reference to the output states.
3.2 FIGURE 3.2 below shows the circuit of an op am... show full transcript
Worked Solution & Example Answer:3.1 Differentiate between bistable multivibrators and astable multivibrators with reference to the output states - NSC Electrical Technology Electronics - Question 3 - 2023 - Paper 1
Step 1
Explain the function of R1 and R2.
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Answer
R1 and R2 are both feedback resistors in the bistable multivibrator configuration. They set up the stability of the output state when the circuit is triggered. R1 helps to control the input resistance while R2 provides the necessary feedback to maintain the state until the input is changed.
Step 2
State the polarity of the output when S2 is pressed.
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When S2 is pressed, the output will be in one of its stable states, which can either be high (+9V) or low (0V), depending on the previous state of the circuit.
Step 3
Explain the operation of the circuit when S1 is pressed.
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Pressing S1 changes the configuration of the multivibrator. It changes the state from one stable point to another, effectively flipping the output voltage state from high to low or vice versa, based on the circuit's previous output level.
Step 4
Describe the value of the output voltage when S1 is pressed.
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The output voltage will switch to the opposite state of what it was before S1 was pressed. If it was previously high (+9V), it will drop to low (0V), and if it was low, it will switch to high.
Step 5
Refer to the input in FIGURE 3.5 below and draw the output waveform on the ANSWER SHEET for QUESTION 3.2.5.
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The output waveform would be a rectangular pulse that mirrors the input pulse characteristics, reflecting the changes in voltage across the specified time intervals.
Step 6
State whether this circuit uses an active high trigger or an active low trigger to set the output.
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This circuit uses an active low trigger to set the output, meaning that the output state changes when the trigger voltage falls below a certain threshold.
Step 7
Determine the threshold voltage of the circuit.
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The threshold voltage of the circuit is the voltage level at which the output changes state. It can typically be calculated as half of the supply voltage, which would be 3V if using a 6V supply.
Step 8
Explain the operation of the circuit when the trigger is pressed.
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When the trigger is pressed and brought below the threshold voltage, the output changes state. For a monostable circuit, this will generate a single pulse of output for a specific duration determined by the RC time constant.
Step 9
State how you would eliminate any unwanted noise from the supply that might affect the timing of the circuit.
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To eliminate unwanted noise, decoupling capacitors can be used at the supply pins of the circuit. Additionally, using a low-pass filter can help smooth out any high-frequency noise that can affect the timing.
Step 10
Explain the term duty cycle with reference to multivibrator outputs.
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The duty cycle is defined as the ratio of the time the output is high to the total time period of the waveform, expressed as a percentage. A 50% duty cycle means that the output is high for half of the time interval.
Step 11
State whether the charging time of the capacitor or the discharging time of the capacitor is longer. Motivate your answer.
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The charging time of the capacitor is typically longer than the discharging time due to the exponential nature of the charging curve in RC circuits, where the voltage approaches the supply voltage at a slower rate compared to the rapid discharge.
Step 12
Draw the voltage waveform that appears across capacitor C1 for ONE full cycle on the answer sheet for QUESTION 3.4.3.
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The voltage waveform across capacitor C1 will show a ramp-up during charging and a rapid fall during discharging, reflecting a triangular waveform shape during each cycle.
