Rise Time (tr)
During rise time voltage falls from 90% Va to 10% where Va where Va is the initial anode voltage. In terms of current time taken by anode current to rise form 10% Ia 90 % I a is the final value of anode current. The turn on time of a thyristor mainly depends upon the rise time. If tr is high means ton will be high. To reduce the time tr should be kept low in limit. The rise time tr can be reduced by applying high and current pulses to the gate because is inversely proportional to the magnitude of Is and its build up rate. During tr Ia starts spreading from the narrow conducting region near the gate.