power electronics lec 6 - triac gto

Power Electronics MUHAMMAD NAVEED IQBAL G.C UNIVERSITY LAHORE

Week Lecture Class Task

Week 1

Introduction to power electronics

Solid-state devices used in power electronics

Week 2

The Power Diode

Thyristors

Week 3

GTO Thyristors

Power Bipolar Transistors, Assignment 1 [OUT]

Week 4

The Power MOSFET

Insulated Gate Bipolar Transistor, DIAC, TRIAC

Week 5

Quiz 1 Assignment 1 [IN]

Diode Rectifiers

Week 6

Single-Phase Controlled Rectifiers

Three-Phase Controlled Rectifiers

Week 7

Twelve-pulse and Twenty-four pulse rectifiers;

DC to DC conversation, buck converter

Week 8

boost converter, buck-boost converters

Isolated converters, forward converters


Week 1

Introduction to power electronics

Solid-state devices used in power electronics

Week 2

The Power Diode

Thyristors

Week 3

Thyristors turn On and Off characteristics

Thyristors types, Assignment 1 [OUT]

Week 4

TRIAC, GTO Assignment 1 [OUT]

The Power MOSFET Insulated Gate Bipolar Transistor,

Week 5

Power Bipolar Transistors, Diode Rectifiers


Week 6

Single-Phase Controlled Rectifiers

Three-Phase Controlled Rectifiers

Week 7

Twelve-pulse and Twenty-four pulse rectifiers;

DC to DC conversation, buck converter

Week 8

boost converter, buck-boost converters

Isolated converters, forward converters


Week 9 Flyback converters

Quiz 2 [Mid Term]

Week 10 Single-Phase Voltage Source Inverters, 3-Phase Voltage Source Inverters

pulse-width-modulated (PWM) inverters

Week 11 Resonant Switch

Quasi-Resonant Converters

Week 12 Zero voltage switch Assignment 2 [out]

Three-phase inverters

Week 13 Single-Phase AC -AC Voltage Controller, 3-Phase AC-AC Voltage Controllers


Week 14 Cyclo-converters

DC=DC Conversion, Positive Ouput Luo-Converters

Week 15 Negative Ouput Luo-Converters

Double Output Luo-Converters

Week 16 Revision

Revision

TRIAC

• Developed by GE in 1964

• Two Thyristors connected in anti-parallel

• Bi-directional device can conduct current in either direction

• Structure is quite complicated

• Can be triggered when 𝑀𝑇2 is +ive with respect to 𝑀𝑇1 and positive gate 𝐼𝐺 is applied w.r.t. M𝑇1

• Can be triggered when 𝑀𝑇2 is -ive with respect to M𝑇1 and –ive gate 𝐼𝐺 is applied w.r.t. 𝑀𝑇1

Limitations

• For Thyristors, 𝑑𝑉

𝑑𝑡 during OFF state is shown

• Device may go in conduction mode due to 𝑑𝑉

𝑑𝑡 during off state

• When i= 0, V across it is very different from zero

• Has less time than Thyristors to recover its blocking power

•𝑑𝑉

𝑑𝑡 rating is lower

SCR Limitations

• SCR is nearly an ideal switch

• Require a sharp pulse to turn On

• Block +ive as well as –ive V

• High V and high I devices are available

• Rugged

• Inability to turn-off by application of a control signal at the gate

• Inclusion of turn-off, capability in Thyristors requires device modification with some compromise in operational capability

Gate turn-off Thyristors (GTO)

• Lower power rating GTO developed by GE in 1961

• 1981 2.5 kV and 1kA device manufactured by hitacht, toshiba

• Can be turned on by +ive 𝐼𝐺

• Can be turned off by –ive 𝐼𝐺

• Four layer structure

• Thickness of 𝑃2 < that is SCR

• 𝑁2 layer is remover by itching in place where gate contacts are situated

• These cells are surrounded by gate, they are brought together by a cathode plate

• GTO can be seen as a large number of GTO in parallel

• At large intervals n region penetrates P1 layer to make contact with n region

• Used to speed up the turn-off process

• No reverse blocking capability (only J2 can block –ive V, very low)

• GTO without anode short can block –ive V

Interdigitation

• High level of gate interdigitation results in

• Even a remote part of cathode region is very near to a gate edge

• Fast turn On speed

• Like SCR only the area of cathode adjacent to the gate electrode is turned on initially and then spreads

• Turn on area is large

• High di/dt

ON-state characteristics

• They are similar to SCR

• Gate signal can be removed if 𝐼𝐴 > 𝐼𝐿𝐴𝑇𝐶𝐻𝐼𝑁𝐺

• Recommended that +ive 𝐼𝐺 is not removed

• 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 𝐺𝑇𝑂 𝑖𝑠 > 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 of SCR

• Under transient condition if 𝐼𝐴 ↓ below 𝐼𝐻𝑂𝐿𝐷𝐼𝑁𝐺 some regions may be turned off

• Anode I now↑ at high rate

• Could be destructive

ON-state characteristics

• During turn ON,𝑑𝑖𝐺

𝑑𝑡 peak value of 𝐼𝐴 should be large enough to

ensure that all cathode islands begin to conduct & there is a sharing of anode I

• Otherwise, hot spots may result

• 𝐼𝐺𝑀 = 10𝐼𝐺𝑇

OFF-state characteristics

• When Thyristors (or GTO) is ON, both T1 and T2 are in saturation

• By ↓ 𝐼𝐵2, T2 can be brought out of saturation

• The total saturation current 𝑖𝑠 𝑖𝐴 =𝛼2𝐼𝐺+𝐼𝐶𝐵𝑂

1− 𝛼1+𝛼2

• 𝐼𝐶𝐵𝑂 = 𝐼𝐶𝐵𝑂1 + 𝐼𝐶𝐵𝑂2

• When GTO is in on state, 𝐼𝐺 is very small


• 𝐼𝐴 𝑜𝑛 =𝐼𝐶𝐵𝑂

1− 𝛼1+𝛼2 is the current required to turn off

• If 𝐼𝐴 = 0, there is a large gate current such that 𝐼𝐺 =−𝐼𝐶𝐵𝑂

𝛼2

•𝐼𝐴 𝑜𝑛

𝐼𝐺=

𝛼2

𝛼1+𝛼2 −1

• 𝛼2 should be high as possible for transistor N1 P2 N2

• i.e should have a high gain

• 𝑃2 layer should be very thin and 𝑁2 highly doped


• Gate is reversed biased w.r.t cathode

• Holes are extracted from P2

• V drop is developed in P-base region

• Eventually reverse biased the gate-cathode region and cut off injection of electrons

• As holes extraction continue P2 is further depleted

• Conduction area decreases


• Anode I flows through the area far away from gate

• May be high current density

• May lead to localized heating

• Should be controlled

• Device may fail

• Eventually device turn off


• Turn off of GTO is greatly influenced by turn off circuit

• Turn of gain is very low 6-15

• Anode current is 100 A than Ig be around 10A


• When gate current starts flowing out anode current remains constant for some time called storage time

• Snubber circuits must be used

power electronics lec 6 - triac gto

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