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GATE 2014 EE (EE2) – Question 65

Power Electronics · Static V-I characteristics and firing/gating circuits for Thyristor, MOSFET, IGBT · 2 marks · Numerical answer

The SCR shown has latching current 40 mA. A 50 µs gate pulse is applied. Find maximum R (Ω) ensuring successful firing.

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Correct answer: 6055 to 6065

Explanation

While the gate pulse is present,the RLbranch current rises as iL(t)=(100/500)[1−exp(−500t/0.2)]. At50µsit is0.0235006A. The totalSCRcurrent must reach40mAby pulse removal,so100/R≥0.04−0.0235006=0.0164994A. Therefore Rmax=100/0.0164994=**6060.82Ω**. SubsequentRLcurrent continues increasing,so the end of the pulse is the limiting instant.