Characteristics of DIAC

 

Lab: To Study The Characteristics Of DIAC.

Objectives:  After completing this experiment, you are expected to be able to: 1.  Display the characteristic of a DIAC on the oscilloscope. 2.  Determine the positive U (BR)F and negative U(BR)R breakdown voltage.

Introduction: A DIAC is a three-layer PNP with two output terminals. It is similar to a bipolar transistor except that the doping concentrations at the junctions are different. A DIAC has equal concentrations for the two junctions. A DIAC is able to turn on from the off-state to the on-state in both directions. This is because a DIAC has two symmetrical switching characteristics. Therefore a DIAC is often used as a trigger component to control a TRIAC in the dimmer circuit, motor control, heat control, etc. Figure shows the symbol, construction, and characteristic of a DIAC.

Apparatus: Main: Characteristic PTE-047-03 Container Box Section PTE-047-08 Auxiliary: Adjustable power supply 0 – 220VAC Digital multi-meter Storage oscilloscope

 

Procedure:  1.  Set up the circuit according to the schematic in Figure.

 

2. The schematic can be realized by arranging the panels as in Figure.

3.  Adjust the oscilloscope so that the traces are at the middle of the screen. Apply an AC input voltage of 28V AC to the circuit. The RM 1 k Ω resistor changes the sensitivity of channel 2 to mA/div.

 

4.  Sketch the oscillogram of channel 2 (axis-Y) against channel 1 (axis-X). Mark the point where the breakdown voltages occur in the forward direction U (BR)F and the reverse direction U(BR)R.

5.  Record the forward U(Br)F and reverse U(Br)R breakdown voltage. a. U(Br)F = __________ volt. b. U(Br)R = __________ volt.

Conclusion:  A DIAC can turn on from the off state to the on state on both directions, because it has bidirectional symmetrical directions switching.