71. When UJT is used for triggering an SCR, the wave shape of the signal obtained from UJT circuit is
72. A 3-phase full convertor takes a voltage of 200 V. Calculate the supply power factor, if the charging current in the battery is 20 A. Given the power delivered to the load is $$3500\sqrt 2 {\text{ W}}{\text{.}}$$
73. When a UJT is turned ON, the resistance between emitter terminal and lower base terminal . . . . . . . .
74. What is the peak to average power ratio for the signal x(t) = Asin(ωt) with 50% duty cycle?
75. Consider the following statements:
1. In a silicon controlled rectifier (SCR), if the cathode gate is reverse-biased, then the SCR cannot fire at all.
2. The turn-on time of an SCR increases with temperature.
3. After an SCR is turned on, it can be made to turn off again by reverse biasing the gate.
4. Gate recovery time is the minimum time that the anode voltage must be maintained below holding voltage VH to turn off the SCR.
Which of these statements are correct?
1. In a silicon controlled rectifier (SCR), if the cathode gate is reverse-biased, then the SCR cannot fire at all.
2. The turn-on time of an SCR increases with temperature.
3. After an SCR is turned on, it can be made to turn off again by reverse biasing the gate.
4. Gate recovery time is the minimum time that the anode voltage must be maintained below holding voltage VH to turn off the SCR.
Which of these statements are correct?
76. It is required to deliver an output DC power of 500 W to a resistive load. The transformer rating required in case of half-wave, conventional full-wave and bridge rectifiers, respectively, is
77. A single phase full wave mid-point thyristor uses a 220/200 V transformer with central tap on the secondary side. The PIV per thyristor will be:
78. In dc chopper if Ton is the on-time and f is the chopping frequency, then output voltage in terms on input voltage, Vs is given by
79. Which semiconductor device acts like a diode and two resistors?
80. A triac is a . . . . . . . . switch
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