Part of Lecture series on EE321N, Power Electronics-I delivered by me during Fifth Semester of B.Tech. Electrical Engg., 2012 Z H College of Engg. & Technology, Aligarh Muslim University, Aligarh Please comment and feel free to ask anything related. Thanks!

1. EE‐321 N
Lecture‐6
Other Types of Thyristorsyp y

2. IntroductionIntroduction
h d d f• Thyristor is a generic term and stands for pnpn
type of devices
• However, in most general sense thyristor
would mean SCR
• Devices to be discussed: Triac, Diac, GTO
217‐Sep‐12 EE‐321N, Lec‐6

3. TRIACTRIAC
• Stands for TRIode for AC
A TRIAC d t i b th di ti• A TRIAC can conduct in both directions.
• It can be considered as two SCRs connected in
antiparallel with a common gate connectionantiparallel with a common gate connection.
• It is normally used in ac phase control
applications such as ac voltage controllersapplications such as ac voltage controllers.
• Available ratings: 1200 V, 300 A (rms)
• Less dv/dt and more turn OFF time than SCR thus• Less dv/dt and more turn OFF time than SCR, thus
not preferred for inductive loads or high
frequency cktsq y
17‐Sep‐12 3EE‐321N, Lec‐6

4. Symbol & CharactersticsSymbol & Characterstics
17‐Sep‐12 4EE‐321N, Lec‐6

5. Physical AppearancePhysical Appearance
17‐Sep‐12 EE‐321N, Lec‐6 5

6. Contd...Contd...
• Since a TRIAC is a bidirectional device, its,
terminals cannot be designated as anode or
cathode.
• If MT is +ve with respect to MT the TRIAC can• If MT2 is +ve with respect to MT1, the TRIAC can
be turned ON by applying a +ve gate signal
between G and MT1.1
• If MT2 is –ve with respect to MT1, the TRIAC can
be turned On by applying a –ve gate signal
between G and MTbetween G and MT1.
• The triggering sensitivity is highest with the
above combinations and they are generally used.y g y
17‐Sep‐12 EE‐321N, Lec‐6 6

7. Operating Modes/Quadrantsp g /
17‐Sep‐12 EE‐321N, Lec‐6 7

8. DIACDIAC
• DIode for ACDIode for AC
• Sometimes, also called gateless triac
i l di d d i i• Equivalent to two diodes connected in anti‐
parallel
• Symmetrical i‐v characteristics
• Turn ON voltage is about 30 Vg
17‐Sep‐12 EE‐321N, Lec‐6 8

9. Symbol & CharactersticsSymbol & Characterstics
17‐Sep‐12 9EE‐321N, Lec‐6

10. Contd...Contd...
• When V12 > VBO1 structure pnpn will conductWhen V12 > VBO1, structure pnpn will conduct
• When V21 > VBO2, structure pnpn’ will conduct
17‐Sep‐12 10EE‐321N, Lec‐6