Semiconductor Diode — Part 1 MCQs with Explanations

In semiconductor diodes, the biasing conditions determine the direction of current flow. Let's analyze the options: Option A: Forward - When the crystal current (diode current) is large, it typically indicates that the diode is under forward bias . In forward bias, the voltage applied to the diode allows a significant current to flow through it. Option B: Inverse - When the diode is under reverse bias , the crystal current should be very low or negligible. Reverse bias means that the voltage applied to the diode is in the opposite direction of its normal operation, and it prevents significant current flow. Option C: Poor - The term "poor" is not commonly used to describe the biasing condition of a diode. It doesn't convey a specific biasing state. Option D: Reverse - While a reverse bias condition does restrict current flow in a diode, it is not the condition associated with a large crystal current (diode current). Therefore, the correct answer is Option A: Forward . When the crystal current (diode current) is large, the diode is typically under forward bias, allowing a significant current to flow through it.

A Zener diode is specifically designed to operate in the reverse breakdown region, known as the Zener breakdown region. Voltage Regulator: Zener diodes are commonly used as voltage regulators. They maintain a constant output voltage despite variations in the input voltage or load conditions. This is achieved by exploiting their ability to stabilize the voltage across their terminals when operating in the breakdown region. Amplifier: Zener diodes are not used as amplifiers; their primary function is voltage regulation. Rectifier: While Zener diodes can be used in rectifier circuits, their primary application is for voltage regulation rather than rectification. Multivibrator: Zener diodes are not used as multivibrators. Multivibrators are circuits used for generating square waves and timing applications, typically involving transistors or other components. Thus, Option B: a voltage regulator is the correct answer.

A zener diode is a type of diode that is designed to operate in the reverse breakdown region of its voltage-current characteristic curve. Reverse (Option A) is the correct answer because zener diodes are primarily used in reverse bias configuration where they maintain a constant voltage across their terminals when the voltage exceeds the breakdown voltage (zener voltage). This characteristic makes them useful for voltage regulation and protection in electronic circuits. Option B: Forward is incorrect because while diodes in general can conduct in the forward bias mode, zener diodes are not typically used in this mode for their intended purpose. Option C: Either reverse or forward is incorrect because zener diodes are specifically designed and optimized for operation in the reverse bias mode. Option D: None of the above is incorrect because zener diodes are indeed always connected in the reverse bias configuration for their intended applications. Therefore, the correct answer is reverse .

A centre-tap full-wave rectifier requires a specially designed transformer known as a centre-tap transformer . This transformer has a secondary winding with a tap at the center , which provides two equal voltages that are 180 degrees out of phase. These voltages are necessary to operate the two diodes in the rectifier circuit, enabling conduction during both halves of the AC cycle. Option A: half-wave rectifier – A transformer is optional. A half-wave rectifier can work directly on the AC mains without a transformer. Option C: bridge full-wave rectifier – It does not require a centre-tap transformer. It uses four diodes to rectify both halves of the AC input without needing a center tap. Option D: none of the above – Incorrect, as Option B clearly requires a transformer. Hence, a transformer is specifically required for a centre-tap full-wave rectifier.

In electronics, the type of filter circuit used in a power supply has a significant impact on its voltage regulation. The question is asking which type of filter circuit results in the best voltage regulation. A choke input filter (Option A) is known for providing the best voltage regulation among the given options. It offers a smoother and more stable output voltage by using an inductor (choke) to filter the rectified AC voltage. A capacitor input filter (Option B) is commonly used in power supplies but does not provide as good voltage regulation as the choke input filter. A resistance input filter (Option C) is not a common type of filter for power supplies and does not provide the best voltage regulation. So, the correct answer is Option A: choke input , which results in the best voltage regulation.

forward is the correct answer to “If the arrow of crystal diode symbol is positive w.r.t. bar, then diode is ___________ biased.”. This question is standard in competitive examination syllabi for Semiconductor Diode.

constant voltage is the correct answer to “In the breakdown region, a zener didoe behaves like a ___________ source.”. This question is standard in competitive examination syllabi for Semiconductor Diode.

increases is the correct answer to “If the temperature of a crystal diode increases, then leakage current ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

less than is the correct answer to “The d.c. resistance of a crystal diode is ___________ its a.c. resistance”. This question is standard in competitive examination syllabi for Semiconductor Diode.

one-half is the correct answer to “For the same secondary voltage, the output voltage from a centre-tap rectifier is ___________ than that of bridge rectifier”. This question is standard in competitive examination syllabi for Semiconductor Diode.

output is difficult to filter is the correct answer to “The disadvantage of a half-wave rectifier is that the___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

a rectifier is the correct answer to “A crystal diode is used as ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

42.5 V is the correct answer to “A half-wave rectifier has an input voltage of 240 V r.m.s. If the step-down transformer has a turns ratio of 8:1, what is the peak load voltage? Ignore diode drop.”. This question is standard in competitive examination syllabi for Semiconductor Diode.

sharp is the correct answer to “A zener diode has ___________ breakdown voltage”. This question is standard in competitive examination syllabi for Semiconductor Diode.

non-linear is the correct answer to “A crystal diode is a ___________ device”. This question is standard in competitive examination syllabi for Semiconductor Diode.

one pn junction is the correct answer to “A crystal diode has”. This question is standard in competitive examination syllabi for Semiconductor Diode.

electrolytic capacitor is the correct answer to “A 10 V power supply would use ___________ as filter capacitor.”. This question is standard in competitive examination syllabi for Semiconductor Diode.

400 V is the correct answer to “If the a.c. input to a half-wave rectifier is an r.m.s value of $$\frac{{400}}{{\sqrt 2 }}$$ volts, then diode PIV rating is ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

PIC rating is the correct answer to “When a crystal diode is used as a rectifier, the most important consideration is ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

one-half is the correct answer to “The PIV rating of each diode in a bridge rectifier is ___________ that of the equivalent centre-tap rectifier”. This question is standard in competitive examination syllabi for Semiconductor Diode.

linear is the correct answer to “When the graph between current through and voltage across a device is a straight line, the device is referred to as ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

barrier potential is the correct answer to “The knee voltage of a crystal diode is approximately equal to ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

forward is the correct answer to “A crystal diode utilises ___________ characteristic for rectification”. This question is standard in competitive examination syllabi for Semiconductor Diode.

1.21 is the correct answer to “The ripple factor of a half-wave rectifier is ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

40.6% is the correct answer to “The maximum efficiency of a half-wave rectifier is ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

bridge full-wave rectifier is the correct answer to “The most widely used rectifier is ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

one pn junction is the correct answer to “A zener diode has ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

in increased is the correct answer to “If the doping level in a crystal diode is increased, the width of depletion layer___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

protect the zener is the correct answer to “A series resistance is connected in the zener circuit to___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

0.7 V is the correct answer to “The forward voltage drop across a silicon diode is about ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

40000 : 1 is the correct answer to “The ratio of reverse resistance and forward resistance of a germanium crystal diode is about ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

lower than is the correct answer to “The PIV rating of a crystal diode is ___________ that of equivalent vacuum diode”. This question is standard in competitive examination syllabi for Semiconductor Diode.

is decreased is the correct answer to “If the doping level of a crystal diode is increased, the breakdown voltage___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

Ω is the correct answer to “A crystal diode has forward resistance of the order of ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

μA is the correct answer to “The reverse current in a diode is of the order of ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

using in electronic equipment is the correct answer to “Mains a.c. power is converrted into d.c. power for ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

a non-linear is the correct answer to “A zener diode is ___________ device”. This question is standard in competitive examination syllabi for Semiconductor Diode.

minority carriers is the correct answer to “The leakage current in a crystal diode is due to ___________”. This question is standard in competitive examination syllabi for Semiconductor Diode.

reverse is the correct answer to “A zener diode utilizes ___________ characteristics for its operation.”. This question is standard in competitive examination syllabi for Semiconductor Diode.

solid state is the correct answer to “___________ rectifier has the lowest forward resistance”. This question is standard in competitive examination syllabi for Semiconductor Diode.