Download Power Electronics - Dr. Imtiaz Hussain

Power Electronics
Lecture-8
TRIAC & DIAC
Dr. Imtiaz Hussain
Assistant Professor
email: [email protected]
URL :http://imtiazhussainkalwar.weebly.com/
1
TRIAC (Triode for Alternating Current)
• The major drawback of an SCR is that it can conduct current only
in one direction.
• In AC systems it is often desirable to control both +ve and –ve
half cycles.
• For this purpose a TRIAC is used.
2
TRIAC (Triode for Alternating Current)
• Triac is a three terminal five layer semiconductor switching
device that can control flow of current of an ac load.
• Three terminals are designated as Main terminal 1 (MT1), Main
Terminal 2 (MT2) and Gate (G).
3
TRIAC Packages
4
TRIAC (Triode for Alternating Current)
• Following point may be noted about the triac.
1. The triac can conduct current (with proper gate current) regardless of
the polarity of the main terminals.
2. A triac can be turned on either with a positive or negative voltage at
the gate terminal.
3. Like the SCR once the triac is fired into conduction, the gate lose all
control. The triac can be turned off by reducing the circuit current to
the value of holding current.
4. The main disadvantage of triacs of SCRs is that triacs have considerably
lower current handling capabilities. Most triac are available in ratings
of less than 40A at voltages up to 600V.
5
Triac Operation
6
Triac Characteristics
• V-I characteristics of triac in the 1st and 3rd quadrants are essentially identical to
those of an SCR in 1st quadrant.
• Triac can be operated with either positive of negative gate control voltage. But in
normal operation usually the gate voltage is positive in 1st quaint and –ve in 3rd
quadrant.
7
Triac Phase Control Circuit
8
Triac Applications
High Power Lamp Switch
Change over of Transformer Taps
9
Example-1
• The triac shown in following figure can be triggered by the
gate triggering voltage 𝑉𝐺𝑇 = ±2𝑉.
a) How will you trigger the triac by only +ve voltage?
b) How will you trigger the triac by only -ve voltage?
10
Example-1
• Solution
a) How will you trigger the triac by only +ve voltage?
11
Example-1
• Solution
b) How will you trigger the triac by only -ve voltage?
12
Triac Gate Control Circuits
• RC triggering Circuit
13
Triac Gate Control Circuits
• Double RC triggering Circuit
14
Triac Gate Control Circuits
• Break over device in triggering Circuit
15
Triac Gate Control Circuits
• UJT triggering Circuit
16
Triac Gate Control Circuits
• UJT triggering Circuit
17
DIAC (Diode for Alternating Current)
• A Diac is a two terminal three layer bidirectional device
which can be switched from its OFF state to ON state for
either polarity of applied voltage.
18
DIAC Packages
19
DIAC Characteristics
20
DIAC Applications
• Diacs are used primarily for triggering of
triacs.
• Some of the circuit applications of diac are
– Lamp Dimmer
– Heat Control
21
DIAC Applications
– Lamp Dimmer
22
DIAC Applications
– Heat Control
23
Example-2
• A small gate triggering voltage 𝑉𝐺𝑇 = ±2𝑉 is required to fire
a triac. How will you raise gate triggering voltage level of
triac?
24
Example-2
• Solution
25
To download this lecture visit
http://imtiazhussainkalwar.weebly.com/
END OF LECTURE-8
26