Gate Turn-Off Thyristor

M.S.P.V.L Polytechnic College,Pavoorchatram.

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Introduction

A Gate Turn-Off Thyristor (GTO) is a special type

of thyristor, a high-power semiconductor device.

GTOs, as opposed to normal thyristor, are fully

controllable switches which can be turned on and off by

their third lead, the GATE lead.

GTO thyristor can be fabricated with a reverse conducting

diode in the same package. These are known as RCGTO,

for Reverse Conducting GTO.www.ustudy.in

Circuit diagram of GTO

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GTO Diagram and Symbol

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Reverse BIAS

GTO thyristor are available with or without reverse

blocking capability.

Reverse blocking capability adds to the forward voltage

drop because of the need to have a long, low doped P1

region.

GTO thyristor capable of blocking reverse voltage are

known as Symmetrical GTO thyristor, abbreviated S-

GTO www.ustudy.in

Functions of GTO

Gate turn-off thyristor (GTOs) are four-layer PNPN devices

that act as switches, rectifiers, and voltage regulators.

Like other thyristor, GTOs can be turned on by the application

of a positive gate signal (g > 0); however, unlike other more

conventional devices that can be turned off only at a zero

crossing of current, GTOs can be turned off at any time by

the application of a gate signal equal to zero. 

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Functions of GTO

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Functions of GTO

Performance specifications for gate turn-off thyristor

(GTOs) include peak repetitive off-state voltage, peak

repetitive reverse voltage, peak cycle surge-on current,

maximum root mean square (RMS) current, and

holding current.

Peak repetitive off-state voltage (VDRM) is the maximum

instantaneous value of the off state.

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Cross section of GTO

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Operations of GTO

When a positive signal is applied, a GTO switches into

conduction state like the ordinary thyristor.

However in ordinary thyristor the current gains of NPN

and PNP transistors are very high so that gate sensitivity

for turn on is very high and on state voltage drop is low.

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Structure of GTO

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Operations of GTO

However in GTO, the current gain of PNP transistor is low

so that turn of its possible if significant current is drawn from

the gate.

When a negative gate signal is applied the excess carriers

are drawn from the base region of NPN transistor and

collector current of PNP is diverted to the gate.

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Operations of GTO

Thus the base drive of NPN transistor is

removed and this in turn removes the base drive

of PNP transistor and turnoff is achieved.

The End

…… Thank You …….

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