Download 5 – Gate Turn-off Thyristor (GTO)

5 – Gate Turn –off Thyristor (GTO)
-GTO was developed to overcome the chief limitation of SCRs which can be turned on via gate
terminal but cannot be turned off via gate terminal.
Device Structure and Symbol:
G-gate
A-anode
K-cathode
GTOs are of two types :
1. Asymmetrical
2. Symmetrical
Asymmetrical GTO:
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The Asymmetrical type GTOs are the most common type on the market.
This type of GTOs are normally used with an anti-parallel diode.
They do not have high reverse blocking capability.
They are used in Voltage Fed Converters.
Symmetrical GTO:
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The symmetrical type GTOs have an equal forward and reverse blocking capability.
They are used in Current Fed Converters.
Operation:
-a positive gate pulse turns the device ON.
-if GTO is already ON and a negative pulse is applied to the gate terminal, the device will turn
off
5 – Gate Turn-off Thyristor (GTO)
Power Electronics Track 1 Lecture Notes
A. R. Sombilla
Page 1
Packaging:
I-V Characteristics:
-The GTO has asymmetric voltage blocking capabilities
-practically blocks current in the forward bias region only
VBR = 20 – 30 volts
5 – Gate Turn-off Thyristor (GTO)
Power Electronics Track 1 Lecture Notes
A. R. Sombilla
Page 2
Comparison with a thyristor:
Characteristic
Description
Thyristor (1600 V, 350 A) GTO (1600 V, 350 A)
VT ON
On state voltage drop
1.5 V
3.4 V
ton,Igon
Turn on time, gate current 8 µs,200 mA
2 µs,2 A
toff
Turn off time
150 µs
15 µs
Advantages of GTOs:
-higher forward breakover voltage
-gate has complete control over the operation of GTO
-low power loss in the on-state
-high ratio of peak surge current to average current
-high gain in the ON-state
Disadvantages of GTOs:
-requires large negative currents for turn-off
-very small reverse voltage blocking capability
-switching frequencies are very low
Applications:
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AC drives
DC drives or DC choppers
AC stabilizing power supplies
DC circuit breakers
Induction heating
And other low power applications
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5 – Gate Turn-off Thyristor (GTO)
Power Electronics Track 1 Lecture Notes
A. R. Sombilla
Page 3