FIGURE 5.1 below shows block diagrams with different input and output states for three types of multivibrators - NSC Electrical Technology Electronics - Question 5 - 2023 - Paper 1
Question 5
FIGURE 5.1 below shows block diagrams with different input and output states for three types of multivibrators. Identify the multivibrator in each of the following b... show full transcript
Worked Solution & Example Answer:FIGURE 5.1 below shows block diagrams with different input and output states for three types of multivibrators - NSC Electrical Technology Electronics - Question 5 - 2023 - Paper 1
Step 1
Block X
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Block X represents a Bistable Multivibrator due to its stable states.
Step 2
Block Y
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Block Y operates as a Monostable Multivibrator because it has one stable state.
Step 3
Block Z
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Block Z is classified as an Astable Multivibrator, which continuously oscillates.
Step 4
State the purpose of variable resistor R2.
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The variable resistor R2 is used to adjust the frequency of the output by changing the charge and discharge time of capacitor C1.
Step 5
Explain how the LED will be affected if it is directly connected to pin 3 without resistor Rs.
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If the LED is connected directly to pin 3 without resistor Rs, it will draw excessive current, potentially damaging the LED due to the lack of current-limiting resistance.
Step 6
Explain how this circuit operates.
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This circuit operates as a timer using the 555 timer IC, where the capacitor C1 charges and discharges, generating a pulse width modulation effect. The output toggles between high and low states based on the threshold levels set by the resistors.
Step 7
State the discharge path of capacitor C1.
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The discharge path of capacitor C1 is through resistor R2 to ground when the timer resets and the output goes low.
Step 8
Determine the voltage at pin 3 (non-inverting input) when the switch is open.
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When the switch is open, the voltage at pin 3 is equal to 3 V, which is half of the supply voltage.
Step 9
State whether the output is high (6 V) or low (0 V) when the switch is open. Motivate your answer.
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The output is high (6 V) when the switch is open because the voltage on the non-inverting input is greater than that on the inverting input.
Step 10
Determine the voltage at pin 3 (non-inverting input) when the switch is pressed. Motivate your answer.
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When the switch is pressed, the voltage at pin 3 drops to 0 V because the capacitor discharges rapidly to ground.
Step 11
Describe the operation of the circuit with reference to the voltages on the two input terminals and the output of the op-amp when the switch is pressed.
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Upon pressing the switch, both capacitor plates instantaneously discharge. The voltage at the non-inverting terminal drops below the inverting terminal, causing the output to switch to low (0 V). This triggers the charging process of the capacitor again.
Step 12
Refer to FIGURE 5.3.6 below and draw the output waveform on the ANSWER SHEET for QUESTION 5.3.6.
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The output waveform will show a square wave corresponding to the charging and discharging of the capacitor over time, crossing the 6 V and 3 V thresholds.
Step 13
Determine the voltage at which the circuit will trigger. Motivate your answer.
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The circuit will trigger at 3 V, based on the thresholds set by resistors in the Schmitt trigger configuration.
Step 14
Name TWO uses of a Schmitt trigger.
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Schmitt triggers are used to clean up distorted signals in radio communications and to convert analogue signals into digital signals.
Step 15
Draw the output signal on the ANSWER SHEET for QUESTION 5.4.3.
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The output signal will be a clean square waveform, toggling between high and low based on the input signal.
Step 16
Determine the value of the feedback resistance (Rf) at X.
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The feedback resistance Rf at X is calculated by using the standard formula based on the configuration of resistors in the network.
Step 17
Calculate the gain at Y.
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The gain (Av) at point Y can be calculated using the feedback and input resistor values, yielding a gain of -10.
Step 18
Calculate the output voltage (Vout) at Z.
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Vout at Z can be determined using the formula based on the sum of the input voltages, resulting in an output of -4 V.
Step 19
Deduce from TABLE 5.5 the relationship between Rf and the gain.
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From TABLE 5.5, it can be deduced that increasing Rf directly increases the gain in an inverting summing amplifier configuration.
Step 20
Draw the output on the ANSWER SHEET for QUESTION 5.6.1.
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The output waveform will resemble a differentiated waveform, showing sharp transitions corresponding to the input signal peaks and zero crossings.
Step 21
Explain what determines the polarity of the output voltage.
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The polarity of the output voltage is determined by the relationship between the input signal's instantaneous voltage and the reference voltage at the inverting terminal of the op-amp.
