05 Thyristor Types Lakshmi S

7/29/2019 05 Thyristor Types Lakshmi S

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S. Lakshmi, MSRIT, Bangalore1

Thyristor Types

Phase-control Thyristors (SCRs).

Fast-switching Thyristors (SCRs). Gate-turn-off Thyristors (GTOs).

Bidirectional triode Thyristors (TRIACs).

Reverse-conducting Thyristors (RCTs).


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S. Lakshmi, MSRIT, BangaloreS. Lalshmi, MSRIT, Bangalore 22

Static induction Thyristors (SITHs).

Light-activated silicon-controlled rectifiers(LASCRs).

FET controlled Thyristors (FET-CTHs).

MOS controlled Thyristors (MCTs).


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Phase Control Thyristor These are converter thyristors.

The turn-off time tq is in the order of 50 to100sec.

Used for low switching frequency.

Commutation is natural commutation On state voltage drop is 1.15V for a 600V

device.


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They use amplifying gate thyristor.


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Bidirectional Triode

Thyristors (TRIAC)


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Mode-I Operation

MT2 Positive,Gate Positive

P1

N1

N2

P2Ig

Ig

MT2 (+)

MT1 ( )GV

(+)


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Mode-II Operation

MT2 Positive,

Gate Negative

P1

N1

N2N3

P2

Ig

MT2 (+)

MT1 ( )GV

Finalconduction

Initialconduction


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Mode-III Operation

MT2 Negative,

Gate Positive

P1

N1

N4

N2

P2

Ig

MT2 ( )

MT1 (+)G(+)


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Mode-IV Operation

MT2 Negative,Gate Negative

P1

N1

N4

P2

Ig

MT2 ( )

MT1 (+)

N3

G(-)


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Triac

Characteristics


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Gate Turn-off

Thyristors Turned on by applying positive gate signal.

Turned off by applying negative gate signal. On state voltage is 3.4V for 550A, 1200V

GTO.

Controllable peak on-state current ITGQ is thepeak value of on-state current which can be

turned-off by gate control.


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Advantages over

SCRs

Elimination of commutating components.

Reduction in acoustic & electromagnetic noisedue to elimination of chokes.

Faster turn-off, therefore can be used for

higher switching frequencies.

Improved efficiency of converters.


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Advantages over

BJTs

Higher voltage blocking capabilities.

High on-state gain. High ratio of peak surge current to average

current.

A pulsed gate signal of short duration only isrequired.


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Disadvantages of

GTOs

On-state voltage drop is more.

Due to multi cathode structure higher gatecurrent is required.

Gate drive circuit losses are more.

Reverse blocking capability is less than itsforward blocking capability.


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Reverse Conducting

Thyristors


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Anti-parallel diode connected across SCR on

the same silicon chip.

This diode clamps the reverse blocking voltage

to 1 or 2V.

RCT also called Asymmetrical Thyristor

(ASCR).

Limited applications.


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Static Induction

Thyristors

Turned-on by applying positive gate voltage.

Turned-off by applying negative gate voltage. Minority carrier device.

Low on-state resistance & low voltage drop.

Fast switching speeds & high dv/dt & highdi/dt capabilities.


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Light-Activated Silicon

Controlled Rectifiers

Turned-on by direct light radiation on silicon

wafer.

Gate structure is sensitive for triggering from

practical light sources.

Used in high voltage and high current

applications. Example: HVDC transmission,

Static reactive power compensation.


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Offers complete electrical isolation between

light triggering source & power circuit.

Rating could be has high as 4KV / 1500A.

di/dt rating is 250A / sec.

dv/dt rating is 2000V / sec.


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FET Controlled

Thyristors

Combines a

MOSFET & a

thyristor in parallel

as shown.

High switching

speeds & high di/dt& dv/dt.


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Turned on like conventional thyristors.

Cannot be turned off by gate control.

Application of these are where optical firing is

to be used.


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MOS-Controlled

Thyristor

New device that has become commercially

available.

Basically a thyristor with two MOSFETs built

in the gate structure.

One MOSFET for turning ON the MCT and

the other to turn OFF the MCT.


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Structure


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Equivalent Circuit

ON-FET

OFF-FET

Anode

Gate (G)

Cathode

Dn

+

n

n

n

p

p+

Q2

Q1p-

n+

p-

M1

S

DSM2


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Features Low on-state losses & large current

capabilities.

Low switching losses.

High switching speeds achieved due to fast

turn-on & turn-off.

Low reverse blocking capability.


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Gate controlled possible if current is less than

peak controllable current.

Gate pulse width not critical for smaller device

currents.

Gate pulse width critical for turn-off for larger

currents.


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S Lakshmi MSRIT Bangalore 30

Thank you .

05 Thyristor Types Lakshmi S

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