Gate Turn-Off Thyristor

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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.

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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

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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 gt
  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.

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The End

• Thank You .