Turn on and Turnoff Characteristics of GTO
The voltage and current wave forms of a GTO is show in figure below.The positive and negative pulses are shown.
When a positive signal is applied,GTO starts conducting.Before initiation of conduction anode current(iA)is zero and anode- cathode voltage VAK is the peak reverse voltage.When conduction starts rises iA to full value and the VAK becomes very small(equal to on state voltage drop which is about 1V or so).when a negative gate signal is applied,the anode current becomes zero and the VAK rises to peak reverse voltage.
The total turnoff time is composed of three distinct times,storage time(ts ),fall time(tf) and tail time(tt).
Initiation of turn off process starts immediately on the application of negative gate signal. The time elapsing between application of negative gate current till this current reaches its negative peak value known as storage time (ts ). During this period, the excess charge are removed by the -ve gate currentt and GTO gets ready to turn off. During fall time tf,the anode current decreases rapidly and anode cathode voltage rises.This time tf in most GTO is about 1μs.After tf is over,the current falls slowly to zero value durung tail time tt..The voltage gets a spike because of the present of elements R and C of the snubber circuit(for protection of GTO).At the end of the tail time,the anode current iA becomes zero and VAK becomes equal to peak reverse voltage.
Written by John on October 18th, 2008 with
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