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Power Electronics

11.

A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is

Answer: B

No answer description available for this question.

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12.

A DIAC has two terminals, anode and cathode.

Answer: B

They are designated as T1 and T2 because diac can conduct in both directions.

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13.

A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is

Answer: B

Freewheeling diode conducts for a° in each half cycle.

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14.

In single phase half wave regulator, the average current over one full cycle

Answer: D

The input current during positive half cycle is less than that during negative half cycle.

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Answer: B

It is a four layered PNPN device without a gate terminal. Its characteristics is similar to that of SCR with zero gate current. It is acting as a trigger switch for Thyristor.

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16.

The number of leads in a power semiconductor diode are

Answer: A

A diode has 2 leads irrespective of its rating.

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17.

A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, the turn on time will be

Answer: C

Inductive load increases the turn on time.

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18.

When thyristors are connected in series and parallel, it may be necessary to have :

Answer: C

Thyristors in series do not share the voltage equally and require voltage derating. Thyristors in parallel need current derating.

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19.

The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode)

Answer: B

Discharge current flows through Re .

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20.

A semi converter operates in two quadrants.

Answer: B

It operates only in quadrant.

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