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QUESTION #4 [25 Marks) a) Describe the holding current and latching current as applicable to an SCR. [5 Marks) b) For an SCR, the gate cathode characteristic is given by a straight line with gradient of 16 volts per amp passing through the origin, the maximum turn-on time is 4 us and the minimum gate current required to obtain this quick turn-on is 500 mA. If the gate source voltage is 15 V, i. Calculate the resistance to be connected in series with the SCR gate. (5 Marks] ii. Compute the gate power dissipation, given that the pulse width is equal to the turn-on time and that the average gate power dissipation is 0.3 W. [5 Marks] jii. Determine the maximum triggering frequency that will be possible when pulse firing is used. [5 Marks) c) The power (brightness) of a 100W, 110 V tungsten lamp is to be varied by controlling the firing angle of an SCR in a half-wave rectifier circuit supplied with 110 V a.c. What r.m.s. voltage and current are developed in the lamp at firing angle a = 60. (3 +2 Marks)