Use CRO to observe the output waveform of half wave-controlled rectifier with resistive load and determine the load voltage

 

Lab Report: Observation of Output Waveform of Half-Wave Controlled Rectifier Using CRO

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1. Objective:

To observe the output waveform of a half-wave controlled rectifier with a resistive load using a CRO and determine the average load voltage.

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2. Apparatus Required:

• SCR (e.g., TYN612)
• Diode (for comparison if needed)
• AC Power Supply (0-230V, 50Hz)
• Resistors (100Ω to 1kΩ)
• Load resistor (resistive)
• CRO (Cathode Ray Oscilloscope)
• Function Generator (for gate triggering pulse)
• Breadboard and connecting wires

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3. Theory:

Half-Wave Controlled Rectifier:

• A half-wave rectifier allows current to flow only during the positive half-cycle of the AC supply.
• By controlling the gate pulse of the SCR, the conduction period can be delayed, altering the output waveform.
• The firing angle ($\alpha$) determines when the SCR starts conducting in the positive half-cycle.

Average Load Voltage ($V_{avg}$) Calculation:

$$V_{avg} = \frac{V_m(1 + \cos(\alpha))}{2\pi}$$

where:

• $V_m$ = Peak AC voltage
• $\alpha$ = Firing angle

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4. Circuit Diagram:

• Include the diagram showing SCR connected in series with the resistive load and AC power supply.
• Gate terminal connected to the function generator.

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5. Procedure:

1. Assemble the circuit on a breadboard as per the circuit diagram.
2. Connect the AC supply across the circuit.
3. Connect the CRO probes across the load resistor to observe the output waveform.
4. Set the function generator to provide gate pulses to the SCR.
5. Vary the firing angle ($\alpha$) by adjusting the gate pulse timing.
6. Observe and capture the waveform on the CRO.
7. Measure the peak voltage ($V_m$) and firing angle ($\alpha$) from the waveform.
8. Calculate the average load voltage using the formula.

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6. Observations:

Firing Angle ($\alpha$)	Peak Voltage ($V_m$)	Output Waveform Shape	Calculated Load Voltage ($V_{avg}$)

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7. Results:

• The output waveform varied with changes in the firing angle, demonstrating the controlled operation of the SCR.
• The calculated load voltage matched the waveform observations.

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8. Conclusion:

The experiment successfully demonstrated the working of a half-wave controlled rectifier with a resistive load. The firing angle directly influenced the output waveform and the average load voltage.

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