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Analog Electronics Lab Experiments

Study of characteristics of DIAC


Study of characteristics of DIAC.

Apparatus Required:

Power supply, DIAC Characteristic, Connecting Leads, Ammeter, and Voltmeter.

Brief Theory:

Diac:A Diac is a two terminal & four layer bi-directional semiconductor switching device.‘Di means two (two terminal device) and ‘ac’ means alternating current hence diac is a switch .In fact, it is a device which can conduct in both the directions. Only when the applied voltage is more then its break over voltage. It is similar as if two latches are connected in parallel. During +ve half-Cycle, the right four layer diode conducts heavily. During –ve half-cycle, the left diode conducts heavily only when the supply voltage exceeds the break over voltage of the Diac.

Circuit Diagram:



  1. Make connection as per circuit diagram.
  2. Apply +ve supply to the circuit.
  3. Increase the voltage step by step & note down the corresponding current values.
  4. After a certain voltage, the diac enter in –ve resistance region.
  5. Now apply reverse polarity & repeat the whole procedure again.

Observation Table:

S. No DIAC Characteristics/I (mA)/V (Volts)



Result:The characteristics of DIAC have been plotted.


  1. Always connect the voltmeter in parallel & ammeter in series as shown in fig.
  2. Connection should be proper & tight.
  3. Switch ‘ON’ the supply after completing the circuit
  4. DC supply should be increased slowly in steps
  5. Reading of voltmeter & Ammeter should be accurate.


Q1:Define DIAC?

A1:It is a two electrode bidirectional avalanche diode.

Q2:Define VBO?

A2:The voltage before which DIAC acts as a open switch.

Q3:Write application of Diac?

A3:Heat control circuit.

Q4:Define inter base Resistance?

A4:The total resistance of silicon bar from one end to other end.

Q5:Define valley Point?

A5:Point beyond which if emitter current increases, device enters into saturation region.

Q6:Define peak Point Emitter Current?

A6:Min. current that is required to trigger the device.