Its looks like a letter Z due to symmetrical switching characteristics for each polarity of the applied voltage. ... This means that, unlike the triac and the SCR, the disc cannot be estimated to maintain a low voltage drop until its current falls below the level of holding current. A triac is a 4-layer semiconductor device with two power terminals (MT1 and MT2) and a gate terminal. It is used as a power control device for 50/60Hz AC mains applications. It is placed in series with the load connected across the mains. ... A disc is a similar 4-layer device but does not have a gate terminal. http://bit.ly/2PIOIQM

1. ATHEENA PANDIAN
Diode for Alternating
Current (DIAC)
and
Triode for Alternating
Current (TRIAC)
BasicsofElectronics

2. DISCUSSION OUTLINE
Report
Coverage
What is Diode?
Symbol of DIAC
What is TRIAC?
Symbol of TRIAC
Constuction of DIAC and
TRIAC
V-I Chracterisitics of DIAC
and TRIAC
Applications of DIAC and
TRIAC
1.
2.
3.
4.
5.
6.
7.
Comstech•Oct.15,2020

3. BASICS OF ELECTRICALS
What is
DIAC?
The DIAC is a diode that
conducts electrical current only
after its breakover voltage, VBO,
has been reached momentarily.

4. BASICS OF ELECTRICALS
Symbol of DIAC
DIAC

5. WHATISTRIAC? It is a bidirectional
device that can
pass the current in both
forward and reverse
biased conditions and
hence it is an AC
control device.
BasicsofElectricals

6. Basics of Electricals
Symbol of TRIAC

7. BasicsofElectricals
BASICS OF ELECTRICALS
DIAC and
TRIAC
Basically, the DIAC is a two
terminal device; it is a
combination of parallel
semiconductor layers that
allows activating in one
direction.This device is used
to activating device for the
triac.

8. CONSTRUCTIONOFDIAC

9. CONSTRUCTIONOFDIAC
The basic construction of
diac consist of two terminals
namely MT1 and MT2.
When the MT1 terminal is
designed +Ve with respect to
the terminal MT2, the
transmission will take place
to the p-n-p-n structure that
is another four layer diaode.
The diac can be performing
for both the direction.
Then symbol of the diac look
like a transistor.
1.
2.
3.
4.
Traic is a three terminal
device and the terminals of
the triac are MT1, MT2 and
Gate. Here the gate terminal
is the control terminal.
The flow of current in the
triac is bi directional that
means current can flow in
both the directions.
Here, in the structure of triac,
two SCRs are connected in
the anti parallel and it will
acts like a switch for both the
directions.
1.
2.
3.
CONSTRUCTIONOFTRIAC

10. CONSTRUCTIONOFTRIAC

11. V-I CHARACTERISTICS OF OF DIAC

12. V-I CHARACTERISTICS OF OF DIAC
The diac performs like an open-circuit until its switching is exceeded.
At that position the diac performs until its current decreases toward
zero.
Because of its abnormal construction, doesn’t switch sharply into a low
voltage condition at a low current level like the triac or SCR, once it goes
into transmission, the diac preserves an almost continuous –Ve
resistance characteristic, that means, voltage reduces with the enlarge in
current.
This means that, unlike the triac and the SCR, the diac cannot be
estimated to maintain a low voltage drop until its current falls below the
level of holding current.
1.
2.
3.
4.

13. V-I CHARACTERISTICS OF OF TRIAC
The V-I characteristics of
triac in the first and third
quadrants are basically equal
to those of an SCR in the first
quadrant.
It can be functioned with
either +Ve or –Ve gate control
voltage but in typical
operation generally the gate
voltage is +Ve in first quadrant
and -Ve in third quadrant.
1.
2.

14. Applications
of
DIAC and TRIAC
BasicsofElectricals
Diac is connected back to
back using two zener
diodes and the
main application of
this DIAC is, it is widely
used to help even
activating of
a TRIAC when used in AC
switches,
dimmer applications and
starter circuits for
florescent lamps.

15. Thank You
BasicsofElectricals