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V-I Characteristics of DIAC: Electronic Lab-2

The document summarizes the V-I characteristics experiment of a DIAC (bidirectional thyristor). It describes how a DIAC can be switched on from either polarity once the breakdown voltage is exceeded, after which it maintains a nearly continuous negative resistance. The experiment involves connecting a DIAC and measuring the voltages and currents across it as the supply voltage is increased in steps both normally and reversed, then plotting the V-I graphs to verify the characteristic Z-shaped curve.

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Abhishek
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2K views6 pages

V-I Characteristics of DIAC: Electronic Lab-2

The document summarizes the V-I characteristics experiment of a DIAC (bidirectional thyristor). It describes how a DIAC can be switched on from either polarity once the breakdown voltage is exceeded, after which it maintains a nearly continuous negative resistance. The experiment involves connecting a DIAC and measuring the voltages and currents across it as the supply voltage is increased in steps both normally and reversed, then plotting the V-I graphs to verify the characteristic Z-shaped curve.

Uploaded by

Abhishek
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Electronic lab-2

V-I Characteristics of DIAC


Jadav Gauri A.
92000221015
Aim: To plot V-I Characteristics of DIAC.
Apparatus: DIAC kit, multimeter, connecting lead.
Symbol:

Theory:
A diac is an important member of the thyristor family and is usually
employed for triggering triacs. A diac is a two-electrode bidirectional
avalanche diode which can be switched from off-state to the on-state
for either polarity of the applied voltage. This is just like a triac without
gate terminal, as shown in figure.
Its equivalent circuit is a pair of inverted four layer diodes. Two
schematic symbols are shown in figure. Again the terminal designations
are arbitrary since the diac, like triac, is also a bilateral device. The
switching from off-state to on-state is achieved by simply exceeding the
avalanche break down voltage in either direction.
Volt-ampere characteristic of a diac is shown in figure. It resembles the
English letter Z Because of the symmetrical switching characteristics for
either polarity of the applied voltage.The diac acts like an open-circuit
until its switching or breakover voltage is exceeded.
At that point the diac conducts until its current reduces toward zero
(below the level of the holding current of the device). The diac, because
of its peculiar construction, does not switch sharply into a low voltage
condition at a low current level like the SCR or triac.
Instead, once it goes into conduction, the diac maintains an almost
continuous negative resistance characteristic, that is, voltage decreases
with the increase in current.
This means that, Unlike the SCR and the triac, the diac cannot be
expected to maintain a low (on) voltage Drop until its current falls
below a holding current level.

Circuit diagram:
Procedure:
1. Connect the millimetre, DIAC, Voltmeter to the circuit.
2 . Switch on the power supply.
3. Increase the supply voltage in steps; note the corresponding currents
and voltages for each step.
4 . Plot the graph of V I Characteristics.
5. Reverse the terminal of DIAC. Increase the supply voltage in steps,
note the corresponding currents and voltages for each step
6 . Plot the graph of V I Characteristics.

Observations:

Result and discussion:


The V-I characteristics of DIAC is plotted on the graph which is true
according to theory.

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