Electrical World

[1] The reverse recovery time of the diode is defined as the time between the instant diode current becomes zero and the instant reverse recovery current decays to (a) Zero (b) 10% of the reverse peak current (I RM ) (c) 25% of ( I RM ) (d) 15% of ( I RM ) Ans: C [2] The cut-in voltage and forward-voltage drop of the diode are respectively (a) 0.7V, 0.7V (b) 0.7V, 1V (c) 0.7V, 0.6V (d) 1V, 0.7V Ans: C [3] The softness factor for soft-recovery and fast-recovery diodes are respectively (a) 1, >1 (b) <1, 1 (c) 1, 1 (d) 1, <1 Ans: D [4] Reverse recovery current in a diode depends on (a) Forward field current (b) Storage charge (c) Temperature (d) PIV Ans:A [5] The three terminals of power MOSFET (a) Collector, Emitter, base (b) Drain, source, base (c) Drain, source, gate (d) Collector, emitter, gate Ans: C [6]The three terminals of IGBT (a) Collector, emitter, base (b) Drain, source, base (c) A...

Power Electronics Objective Questions with Answers: Part-5 1. SCR is the solid state equivalent of (a) Transistor (b) Thyratron (c) Vacuum diode (d) Crystal diode Answer: B 2. With gate open, if the supply voltage exceeds the breakover voltage of SCR, then SCR will conduct (a) False (b) True (c) For DC (d) For AC Answer: B 3. The SCR is turned off when the anode current falls below (a) Forward current rating (b) Break over voltage (c) Holding current (d) Latching current Answer: C 4. In a SCR circuit, the angle of conduction can be changed by changing (a) Anode voltage (b) Anode current (c) Forward current rating (d) Gate current Answer: D 5. The normal way to close a SCR is by appropriate (a) Gate current (b) Cathode current (c) Anode current (d) Forward current Answer: A 6. An SCR has ......PN junctions (a) Two (b) Four (c) Three (d) One Answer: C 7. If gate current is increased, the anode-cathode voltage at which SCR cl...

Power Electronics Objective Type Questions with Answers: Part-4 [1] In a SCR , (a) Gate current is directly proportional to forward breakover voltage (b) As gate current is raised, forward breakover voltage reduces (c) Gate current has to be kept on continuously for conduction (d) Forward breakover voltage is low in the forward blocking state. Answer: B [2] In a SCR, at switch on, there is a sudden increase of current, then (a) The tolerance limit of di/dt varies from 3 to 30A/us (b) di/dt upper limit is 3A/us (c) di/dt rating can be increased by having an inductive load (d) di/dt rating can be increased by a resistive load Which of the above statements are true? (1) a, c (2) c, d (3) a, b, c, d (4) a, b Answer: 1 [3] The following PNPN device has a terminal for synchronising purpose (a) SUS (b) DIAC (c) TRIAC (d) Schmitt trigger Answer: A [4] In single phase full wave controlled rectifier, maximum output voltage is obtained at conduction angle....

Multiple Choice Questions Based on Power Electronics and Drives [1] When a line commutated converter operates in the inverter mode (a) It draws both real and reactive power from the AC supply (b) It delivers both real and reactive power to the AC supply (c) It delivers real power to the AC supply (d) It draws reactive power from the AC supply Answer: C [2] A chopper operating at a fixed frequency is feeding an RL load. As the duty ratio of the chopper is increased from 25% to 75%, the ripple in the load current is (a) Remains constant (b) Decreases, reaches a minimum at 50% duty ratio and then increases (c) Increases, reaches a maximum at 50% duty ratio and then decreases (d) Keeps on increasing as the duty ratio is increased Answer: A [3] To turn off a SCR, the reverse bias should be applied for a period ....... the turn-off time of the SCR (a) Equal to  (b) Longer than (c) Less than (d) Irrespective of Answer: B [ 4] In class A and class B commutation ...

Power Electronics Multiple Choice Questions In Last Post we shared Power Electronics MCQ Part 1 [1] During forward blocking state, the SCR has (a)  Low current, medium voltage (b) Low current, large voltage (c) Medium current, large voltage (d)  Large current, low voltage Answer: B [2] Once SCR starts conducting a forward current, its gate loses control over (a)  Anode circuit current only (b)  Anode circuit voltage only (c) Anode circuit voltage and current (d) Anode circuit voltage, current and time Answer: C [3] In a SCRs (a)  Both Latching current and holding current are associated with turn-off process (b)  Latching current is associated with turn-off process and holding current with turn on process (c) Holding current is associated with turn-off process and Latching current with turn-on process (d) Both Latching current and holding current are associated with turn on process Answer: C [4] The SCR can be termed as (a) DC swit...

Power Electronics Objective Questions and Answers [Q-1] When an inductance is inserted in the load circuit of SCR (a) The turn on time of SCR is increased (b) Output voltage is reduced for the same firing angle (c) Conduction continues even after reversal of phase of input voltage (d) A free wheeling diode is connected in such circuits Which of the above statements are true? (1) a, d (2) b, c, d (3) a, b, c,d (4) c, d Answer: 3 [Q-2] Snubber circuit is used to limit the rate of (a) Rise of current (b) Conduction period (c) Rise of voltage across SCR (d) None of the above Answer:C [Q-3] The provision of a free wheeling diode across an inductive load is (a) To restore conduction angle on phase (b) To avoid negative reversal voltage drop (c) To reduce the PRV (d) None of the above Answer:A [Q-4] While working in series operation, equalising circuits are added across each SCR to provide uniform (a) Current distribution (b) Firing of SCRs (c)...

Hello Engineers. Q.1 If the current of an SCR increases, the forward breakdown voltage will A. Decrease B. Not be effected C. Increase D. Become zero Ans: A Q.2 If the gate current of an scr is increased, the forward breakdown voltage will A. Increase B. Decrease C. Not be affected D. Become infinite Ans: C Q.3 After firing an scr, the gate pulse is remove. The current in the scr will A. Remain the same B. Immediately fall to zero C. Rise up D. Rise a little and then fall to zero Ans: A Q.4 An scr conducts an appreciable current when the gate is negative and the a node is positive with respect to the cathode. A. Gate is negative and the anode is positive with respect to the cathode B. Anode and the gate are both negative with respect to the cathode C. Anode and the gate are both positive with respect to the cathode D. Anode is negative and the gate is positive with respect to the cathode. Ans: C Q.5 Pulse gate triggering is achieved by means of ...