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Test: PN Diode Switching Times


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10 Questions MCQ Test Analog Electronics | Test: PN Diode Switching Times

Test: PN Diode Switching Times for Electrical Engineering (EE) 2023 is part of Analog Electronics preparation. The Test: PN Diode Switching Times questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: PN Diode Switching Times MCQs are made for Electrical Engineering (EE) 2023 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: PN Diode Switching Times below.
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Test: PN Diode Switching Times - Question 1

 Diode acts as a short circuit when switched from forward to reverse bias for some time due to______

Detailed Solution for Test: PN Diode Switching Times - Question 1

When a diode is switched suddenly, it persists the conducting property for a short time in its reverse bias also. This leads to excess minority charge carrier settlement at potential barrier. Hence acts as a short circuit.

Test: PN Diode Switching Times - Question 2

Reverse recovery time for a diode is?

Detailed Solution for Test: PN Diode Switching Times - Question 2

The time period for which diode remains in conduction state even in reverse direction is called storage time. The time elapsed to return the non conduction state is called transition time. Their sum is called reverse recovery time.

Test: PN Diode Switching Times - Question 3

 Switching speed of P+ junction depends on.

Detailed Solution for Test: PN Diode Switching Times - Question 3

Switching leads to move holes in P region to N region as minority carriers. Removal of this accumulation determines switching speed. P+ regards to a diode in which the p type is doped excessively.

Test: PN Diode Switching Times - Question 4

Time taken for a diode to reach 90% of its final value when switched from steady state is______

Detailed Solution for Test: PN Diode Switching Times - Question 4

Time constant = RC. To reach 90% of the final value, time taken is 2.2 of RC. Time constant is the time required to discharge the capacitor, through the resistor, by 36.8%.

Test: PN Diode Switching Times - Question 5

Which of the following are true?
1) In reverse bias, the diode undergoes stages of storage and transition times
2) Minority charge carriers accumulation makes the diode as a short circuit
3) Storage time is the sum of recovery and transition times

Detailed Solution for Test: PN Diode Switching Times - Question 5

When a diode is switched from forward to reverse bias, storage and transition times takes place. The accumulation time or the life time of minority carriers makes it a short circuit. The conduction property is holds for a short period of time in reverse bias also.

Test: PN Diode Switching Times - Question 6

In a circuit below, the switch is at position 1 at t<0 and at position 2 when t=0. Assume diode has zero voltage drop and storage time. For 0<t<ts, the VR at 1k ohm resistor is given by_____

Detailed Solution for Test: PN Diode Switching Times - Question 6

At position ‘1’ when connected to +5V, the diode is forward biased and acts as a short circuit. So, VR is 5V. For 0<t<ts VR is -5V as the diode is in reverse bias. But it holds the conductive property within the storage time period. So, V is -5V.

Test: PN Diode Switching Times - Question 7

The switch is at position shown in the figure initially and steady state is from t=0 to t=to. The switch suddenly is thrown to the other position. The current flowing through the 10K resistor from t=0 is?

Detailed Solution for Test: PN Diode Switching Times - Question 7

Initially, the diode is in forward bias. When suddenly switched to reverse bias, upto a storage time limit, it conducts during storage time period.
We know that, current I=V/R=-20/10K=-2mA.

Test: PN Diode Switching Times - Question 8

 

A PN junction diode with 100Ω resistor is forward biased such that 100A current flows. If voltage across this combination is instantaneously reversed to 10V at t=0, the reverse current that flows through diode at t=0 is?

Detailed Solution for Test: PN Diode Switching Times - Question 8

At t=0, V=-10V. During storage time, current still flows.
We know that,
current I=V/R=10/100Ω=100mA from N to P region.

Test: PN Diode Switching Times - Question 9

The delay in switching between the ON and OFF states is due to _________

Detailed Solution for Test: PN Diode Switching Times - Question 9

When switched instantaneously it stays in a quasi state i.e.., temporary state which stores charges. The delay is produced due to this charge settlement. The diode needs to discharge these excess carriers in order to return the non conduction stage.

Test: PN Diode Switching Times - Question 10

The delay time can be reduced by?

Detailed Solution for Test: PN Diode Switching Times - Question 10

When the current increases the depletion layer decreases and the storage and transition time decreases. A decreased depletion layer can easily discharge the excess carrier and thereby lessens the delay time.

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