[1] The average output voltage(Vdc) of the full wave diode bridge rectifier is
(a) Vm/2
(b) 2Vm/p
(c) 3Vm/p
(d) 4Vm/p
[2] The typical ratio of latching current to holding current in a 20A thyristor is [GATE -2011]
(a) 5.0
(b) 2.0
(c) 1.0
(d) 0.5
[3] A half controlled single phase bridge rectifier is supplying an R-L load. It is operated at a firing angle (alpha) and load current is continuous. The fraction of cycle that the freewheeling diode conducts is [GATE -2011]
(a) 1/2
(b) [1-( a/p)]
(c) a/2p
(d) a/p
(a) Vm/2
(b) 2Vm/p
(c) 3Vm/p
(d) 4Vm/p
[2] The typical ratio of latching current to holding current in a 20A thyristor is [GATE -2011]
(a) 5.0
(b) 2.0
(c) 1.0
(d) 0.5
[3] A half controlled single phase bridge rectifier is supplying an R-L load. It is operated at a firing angle (alpha) and load current is continuous. The fraction of cycle that the freewheeling diode conducts is [GATE -2011]
(a) 1/2
(b) [1-( a/p)]
(c) a/2p
(d) a/p
Common Data for Questions [4] & [5]
In the 3 phase inverter circuit shown, the load is balanced and the gating scheme is 180 degree conduction mode. All the switching devices are ideal , Vd = 300V
[4] The rms value of load phase voltage is [GATE -2011]
(a) 106.1V
(b) 141.4 V
(c) 212.2 V
(d) 282.8V
Hint: VL = v(2/3) * Vs
[5] If the dc bus voltage Vd = 300v, the power consumed by 3 phase load is [GATE -2011]
(a) 1.5kW
(b) 2.0 kW
(c) 2.5 kW
(d) 3.0 kW
Hint: P = 3 * [(Vph * Vph)/Rph]
Common Data for Question 6 & 7:
10V Pulse Transformer (PT) is used to trigger the SCR in the adjacent figure. The SCR is rated at 1.5KV, 250A with IL=250mA, IH=150mA, and IGmax= 150mA, IGmin=100mA. The SCR is connected to an inductive load, where L=150mH in series with a small resistance and the supply voltage is 200V dc. The forward drops of all transistors/ diodes and gate- cathode junction during ON state are 1.0V.
[6] The resistance R should be
(a) 4.7K Ohm
(b) 470 Ohm
(c) 47 Ohm
(d) 4.7 Ohm
[7] The minimum approximate volt-second rating of the pulse transformer suitable for triggering the SCR should be: ( volt-second rating is the maximum of product of the voltage and the width of the pulse that may be applied
(a) 2000 �V-s
(b) 200 �V-s
(c) 20 �V-s
(d) 2.0 �V-s
[8] For an SCR with turn-on time of 5 �S, an ideal trigger pulse should have
(a) Short rise time with pulse width = 3 �S
(b) Long rise time with pulse width = 6 �S
(c) Short rise time with pulse width = 6 �S
(d) Long rise time with pulse width = 3�S
[9] Turn-on time for an SCRs is 10�S. If an inductance is inserted in the anode circuit, then the turn on time will be
(a) 10�S
(b) less than 10�S
(c) More than 10�S
(d) About 10�S
[10] On-state voltage drop across a thyristor used in a 250V supply system is of the order of
(a) 100 - 110V
(b) 240 - 250V
(c) 1 - 1.5V
(d) 0.5 - 1V
[11] In a SCR, ratio of latching current to holding current is
(a) 0.4
(b) 1.0
(c) 2.5
(d) 6.0
Hint: Usually the ratio is near to 3
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