A diode will behave as an open circuit if the voltage in the circuit is less than __________
a) cut off voltage
b) saturation voltage
c) leakage voltage
d) threshold voltage
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Answer: d
Explanation: The diode made up of semiconductor has a certain threshold voltage only after which it behave as closed circuit in the sense it performs some operation if the threshold voltage is greater than the voltage in circuit.
What will be the diode resistance if the current in the circuit is zero?
a) 0 ohms
b) 0.7 ohms
c) 0.3 ohms
d) 1 ohms
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Answer: a
Explanation: When the current in the circuit is zero there will be no flow of charges to resist hence the diode resistance will be zero.
The diffusion capacitance of a PN junction _______
a) decreases with increasing current and increasing temperature
b) decreases with decreasing current and increasing temperature
c) increasing with increasing current and increasing temperature
d) doesnot depend on current and temperature
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Answer: b
Explanation: CD =τ I /n0 VT
Where, I is the current and VT is temperature factor. The diffusion capacitance is directly proportional to current and indirectly proportional to the temperature.
Reverse recovery time for a diode is?
a) Time taken to eliminate excess minority charge carriers
b) Sum of storage time (TS) and transition time (TT)
c) Time taken to eliminate excess majority charge carriers
d) Time elapsed to return to non conduction state
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Answer: a
Explanation: 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.
Time taken for a diode to reach 90% of its final value when switched from steady state is______
a) 2.3*time constant
b) 2.2*time constant
c) 1.5*time constant
d) equals the time constant
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Answer: b
Explanation: 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%.
Avalanche breakdown in zener diode is ______
a) electric current multiplication takes place
b) phenomenon of voltage multiplication takes place
c) electrons are decelerated for a period of time
d) sudden rise in voltage takes place.
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Answer: a
Explanation: The carriers in transition region are accelerated by electric field to energies. That energies are sufficient to create electron current multiplication. A single carrier that is energized will collide with another by gaining energy. Thus an avalanche multiplication takes place.
What happens to a tunnel diode when the reverse bias effect goes beyond the valley point?
a) it behaves as a normal diode
b) it attains increased negative slope effects
c) reverse saturation current increases
d) beacomes independent of temperature
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Answer: a
Explanation: After the valley point is crossed, the tunnel diode obtains positive slope resistance. That is similar to the characteristics of a normal diode. So it behaves like a normal diode after beyond valley point.
In the forward bias condition, the resistance of point contact diode is_________
a) less than that of a general PN diode
b) greater than that of a general PN diode
c) equal to that of a general PN diode
d) varies exponentially than that of a general PN diode
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Answer: a
Explanation: The current flow of the point contact diode is not independent of voltage applied to the crystal unlikely to a general PN diode. This characteristic of contact diode makes its capacitance high at high frequency. A small capacitive current flows in the circuit.