Power electronics digital notes b. Tech III year

GTO (Gate Turn-off Thyristor)
GTO can be turned on with the positive gate current pulse and turned off with the negative gate current 
pulse. Its capability to turn off is due to the diversion of PNP collector current by the gate and thus 
breaking the regenerative feedback effect. 
Actually the design of GTO is made in such a way that the pnp current gain of GTO is reduced. A 
highly doped n spot in the anode p layer form a shorted emitter effect and ultimately decreases the 
current gain of GTO for lower current regeneration and also the reverse voltage blocking capability. 
This reduction in reverse blocking capability can be improved by diffusing gold but this reduces the 
carrier lifetime. Moreover, it requires a special protection. 
The symbol for GTO is shown in Fig.46. 
Figure: 1. 47. Symbol of GTO 
Overall switching speed of GTO is faster than thyristor (SCR) but voltage drop of GTO is larger. The 
power range of GTO is better than BJT, IGBT or SCR. 
The static voltage current characteristics of GTO are similar to SCR except that the latching current of 
GTO is larger (about 2 A) as compared to SCR (around 100-500 mA). 
The gate drive circuitry with switching characteristics is given in Fig. 48 and Fig. 49. 

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49 | 
P a g e
Figure: 1. 48. Gate Drive Circuit for GTO
 
Figure: 1. 49. Switching characteristics for GTO

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50 | 
P a g e
SCR Specifications and Ratings: 
The main specifications of the SCR are its voltage rating and current rating. In this post, let us see various 
ratings of thyristor. 
Voltage Ratings 
Peak Invese Voltage (V
PIV
)
The peak inverse voltage is defined as the maximum voltage which SCR can safely withstand in its OFF 
state. The applied voltage should never be exceeded under any circumstances.