Lab Report: Testing the Proper Functioning of DIAC and Determining Breakover Voltage

1. Objective:

To test the proper functioning of a DIAC and measure its breakover voltage (Vbo_{bo}), the voltage at which it begins conducting in either direction.

2. Apparatus/Materials Required:

  • DIAC (e.g., DB3, DB4)
  • DC Power Supply (0–30V)
  • Resistors (1kΩ to 10kΩ)
  • Voltmeter and Ammeter
  • Oscilloscope (optional)
  • Breadboard and connecting wires

3. Theory:

DIAC Characteristics:

  • DIAC (Diode for Alternating Current) is a bidirectional device that conducts current after the breakover voltage (Vbo_{bo}) is reached.
  • It does not have a gate terminal and functions symmetrically for both polarities of voltage.
  • Commonly used to trigger TRIACs in AC circuits.

4. Circuit Diagram:

Provide a simple circuit diagram:

  • Connect the DIAC in series with a resistor and the DC power supply.
  • The voltmeter should be connected across the DIAC, and the ammeter in series to measure current.

5. Procedure:

  1. Circuit Setup:

    • Assemble the circuit with the DIAC, resistor, DC power supply, and measuring instruments.
    • Ensure proper polarity connections in the measurement devices.

  2. Voltage Increment:

    • Gradually increase the voltage from 0V using the DC power supply.
    • Monitor the voltage across the DIAC and the current through it.

  3. Breakover Voltage Detection:

    • Observe the voltage at which the DIAC suddenly begins to conduct a significant amount of current.
    • This voltage is the breakover voltage (Vbo_{bo}).

  4. Record Data:

    • Note the voltage just before conduction and the corresponding current value.

6. Observations:

Applied Voltage (V) Current (mA) Breakover Observation
0 0 No conduction
... ... ...
Vbo_{bo} Significant Sudden conduction observed

7. Results:

  • Breakover Voltage (Vbo_{bo}) of the DIAC: [Insert value]
  • The DIAC conducted symmetrically after reaching this voltage, verifying proper functionality.

8. Conclusion:

The experiment successfully demonstrated the working of a DIAC and measured its breakover voltage. The symmetrical conduction property of DIAC makes it useful in AC phase control applications and TRIAC triggering circuits.