Answer MET Question 17
Question : What are semiconductor devices? What are its advantages over thermionic devices? With respect to semi-conductor devices describe working principle and application of the following A. Zener Diode B. Transistor, C. Photocell, D. Thyristor
Answer:
A semiconductor device is an electronic component that utilizes the
electronic properties of semiconductor material, like silicon,
germanium, gallium etc., Semiconductor is neither a good conductor nor a
good insulator. Semiconductor devices have found wide applications
because of their compactness, reliability, and low cost. As discrete
components, they have found use In power devices, optical sensors, and
light emitters, including solid-state lasers. They have a wide range of
current- and voltage-handling capabilities, with current ratings from a
few Nano amperes to more than 5,000 amperes and voltage ratings
extending above 100,000 volts.
Doping a semiconductor with a small proportion of an atomic impurity, such as phosphorus or boron, increases the number of free electrons or holes within the semiconductor. When a doped semiconductor consists of excess holes, it is called a p-type semiconductor(p for positive electric charge); when it consists of excess free electrons, it is called an n-type semiconductor (n for negative electric charge). A majority of mobile charge carriers have negative charge.
Advantages of semiconductors over Thermonic devices:-
1. They have a very Low Power Consumption and No or negligible heat desipation.
2. Their operation is noise free and have longer life.
3. Fast action and quicker response.
4. Compact design of semiconductor thus less pron to physical damage.
5. They are able to handle multiple inputs and process
(A) Zener Diode- Zener diodes are normal PN junction diodes operating in the reverse biased condition. Working of the Zener diode is similar to a PN junction diode in forward biased condition, the special thingh that it can also conduct when it is connected in reverse bias above its threshold / breakdown voltage.
Application:It is used in rectifiers. circuits to get constant voltage at the output
It is used as a voltage reference
They are used in voltage stabilizers or shunt regulators
They are used in switching operations
They are used in clippers and clamper circuits
They are used in various circuit protections
They are used in Ammeters and voltmeters.
Doping a semiconductor with a small proportion of an atomic impurity, such as phosphorus or boron, increases the number of free electrons or holes within the semiconductor. When a doped semiconductor consists of excess holes, it is called a p-type semiconductor(p for positive electric charge); when it consists of excess free electrons, it is called an n-type semiconductor (n for negative electric charge). A majority of mobile charge carriers have negative charge.
Advantages of semiconductors over Thermonic devices:-
1. They have a very Low Power Consumption and No or negligible heat desipation.
2. Their operation is noise free and have longer life.
3. Fast action and quicker response.
4. Compact design of semiconductor thus less pron to physical damage.
5. They are able to handle multiple inputs and process
(A) Zener Diode- Zener diodes are normal PN junction diodes operating in the reverse biased condition. Working of the Zener diode is similar to a PN junction diode in forward biased condition, the special thingh that it can also conduct when it is connected in reverse bias above its threshold / breakdown voltage.
Application:It is used in rectifiers. circuits to get constant voltage at the output
It is used as a voltage reference
They are used in voltage stabilizers or shunt regulators
They are used in switching operations
They are used in clippers and clamper circuits
They are used in various circuit protections
They are used in Ammeters and voltmeters.
(B)Transistor
– Transistors consists of 3 parts ‘ a base, a collector, & an
emitter. The base is the gate controller device for the larger
electrical supply. The collector is the larger electrical supply, &
the emitter is the outlet for that supply. By sending varying levels of
current from the base, the amount of current flowing through the gate
from the collector may be regulated. In this way, a very small amount of
the current may be used to control a large amount of current, as in an
amplifier.
i. Various Applications and Uses of Transistor
ii. The core use of transistors include switching applications or both as amplification and switching.
iii. There is a kind of transistors which produce current flow depending on the amount of light shined upon them, those are known as photo-transistors.
iv. Bipolar Junction Transistors(BJT) can cause a greater current flow from the emitter to collector when a small amount of current is passed through the base.
v. Field Effect Transistors acts as voltage controlled devices. Field Effect Transistors (FETs) have very high input impedance and it helps to run very little current through them. This is helpful for not causing the power source to load down as they are not disturbing the original circuit power elements on which they are connected to. FETs are cheaper and easier to manufacture and cause less loading.
vi. Heterojunction Bipolar Transistors (HBT) can provide faster switching speeds and is used in analog and digital microwave applications. They are priceless to fabricate and can provide better lithographic yield. They are used in mobile and laser drivers as power amplifiers.
vii. Darlington Transistors has much higher ability to gain current. Because of its sensitivity, it can pick currents from human skin and that is why it is used in creating a touch-sensitive button.
viii. Schottky Transistors diverts high input currents and prevents the transistors from saturating.
ix. Multiple Emitter Transistors are used in Transistor-Transistor Logic (TTL) and NAND logic gates.
x. Dual Gate MOSFETs are used in RF mixers/multipliers, RF amplifiers where two controlled gates are required in a series.
xi. Avalanche Transistors has the capability of switching high currents in less than nanosecond transition times.
i. Various Applications and Uses of Transistor
ii. The core use of transistors include switching applications or both as amplification and switching.
iii. There is a kind of transistors which produce current flow depending on the amount of light shined upon them, those are known as photo-transistors.
iv. Bipolar Junction Transistors(BJT) can cause a greater current flow from the emitter to collector when a small amount of current is passed through the base.
v. Field Effect Transistors acts as voltage controlled devices. Field Effect Transistors (FETs) have very high input impedance and it helps to run very little current through them. This is helpful for not causing the power source to load down as they are not disturbing the original circuit power elements on which they are connected to. FETs are cheaper and easier to manufacture and cause less loading.
vi. Heterojunction Bipolar Transistors (HBT) can provide faster switching speeds and is used in analog and digital microwave applications. They are priceless to fabricate and can provide better lithographic yield. They are used in mobile and laser drivers as power amplifiers.
vii. Darlington Transistors has much higher ability to gain current. Because of its sensitivity, it can pick currents from human skin and that is why it is used in creating a touch-sensitive button.
viii. Schottky Transistors diverts high input currents and prevents the transistors from saturating.
ix. Multiple Emitter Transistors are used in Transistor-Transistor Logic (TTL) and NAND logic gates.
x. Dual Gate MOSFETs are used in RF mixers/multipliers, RF amplifiers where two controlled gates are required in a series.
xi. Avalanche Transistors has the capability of switching high currents in less than nanosecond transition times.
(C)
Photocell: It is a type of semiconductor which converts light into
electric energy. Photocells are sensors that enable you to detect light.
A Photocell is generally a resistor that changes its resistive value(in
ohms) depending on intensity of light.
When no light is present, they have a very high resistance that may be millions of ohms. In contrast, when light is present, their resistance lowers greatly to a few hundred ohms. This allows more current to flow inside the circuit.
They may be used with either alternating or direct currents. Photocells are small in size, but inexpensive and durable. Their versatility allows them to detect all kinds of light in all kinds of conditions. The range is from visible to infrared light.
Application:
Photocells are used as switches and sensors.
Widely used in automation where operation depends upon the light intensity change.
May be used in the place of variable resistors and photovoltaic cells.
Used in light meters and light controlled relays.
Used in counters, rpm sensors etc.
When no light is present, they have a very high resistance that may be millions of ohms. In contrast, when light is present, their resistance lowers greatly to a few hundred ohms. This allows more current to flow inside the circuit.
They may be used with either alternating or direct currents. Photocells are small in size, but inexpensive and durable. Their versatility allows them to detect all kinds of light in all kinds of conditions. The range is from visible to infrared light.
Application:
Photocells are used as switches and sensors.
Widely used in automation where operation depends upon the light intensity change.
May be used in the place of variable resistors and photovoltaic cells.
Used in light meters and light controlled relays.
Used in counters, rpm sensors etc.
(D)
Thyristor: A thyristor is a solid-state semiconductor device with four
layers of alternating P- and N-type materials. It acts exclusively as a
bistable switch, conducting when the gate receives a current trigger,
and continuing to conduct until the voltage across the device is
reversed biased, or until the voltage is removed.
Application:
Application:
Speed Controllers of AC and DC motors
DC and AC circuit breakers
Illumination and temperature controllers
Pressure control and liquid level regulators
Used in rectifiers, inverters, converters or Cyclo converters
Used in AVR.
Resistive welding and induction heating systems etc.
DC and AC circuit breakers
Illumination and temperature controllers
Pressure control and liquid level regulators
Used in rectifiers, inverters, converters or Cyclo converters
Used in AVR.
Resistive welding and induction heating systems etc.
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