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Maharashtra State BoardHSC Science (Computer Science) 12th Standard Board Exam
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अभ्यासक्रम

Overview: Semiconductor Devices

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Topics

Estimated time: 56 minutes
Maharashtra State Board: Class 12

Definition: Rectification

The conversion of AC voltage into a DC voltage is called rectification. 

Maharashtra State Board: Class 12

Definition: Half-Wave Rectifier

The process of converting alternating current (AC) into direct current (DC) using only one diode, in which current flows only during one half cycle of the AC input is called a half-wave rectifier.

Maharashtra State Board: Class 12

Definition: Full-Wave Rectifier

A rectifier circuit that uses both half cycles of the AC input voltage to produce DC output is called a full-wave rectifier.

Maharashtra State Board: Class 12

Key Points: p-n Junction Diode as o Rectifier

  • A diode allows current to flow in one direction, so it converts AC to DC.
  • A half-wave rectifier uses only one half-cycle of AC, so its efficiency is low (40.6%).
  • A full-wave rectifier uses both half-cycles, resulting in higher efficiency (81.2%) and less ripple.
Maharashtra State Board: Class 12

Definition: Ripple

The unwanted AC component present in the rectified DC output is called ripple.

Maharashtra State Board: Class 12

Definition: Ripple Factor

The ratio of the root mean square (r.m.s.) value of the AC component to the DC component in the rectifier output is called the ripple factor.

Mathematically,

Ripple Factor = \[\frac{\text{r.m.s. value of AC component}}{\mathrm{DC~value}}\]

Maharashtra State Board: Class 12

Definition: Filter Circuit

A circuit that removes the AC component (ripple) from the rectifier output and allows only the DC component is called a filter circuit.

Maharashtra State Board: Class 12

Definition: Unregulated Power Supply

A power supply whose output voltage changes when a load is connected across it is called an unregulated power supply.

Maharashtra State Board: Class 12

Definition: Regulated Power Supply

A power supply whose output voltage remains constant even after connecting a load across it is called a regulated power supply.

Maharashtra State Board: Class 12

Definition: Zener Voltage Regulator

A voltage regulator circuit that commonly uses a Zener diode to maintain constant output voltage is called a Zener voltage regulator.

Maharashtra State Board: Class 12

Definition: Junction Breakdown

The sudden increase in reverse current of a p–n junction diode when the reverse voltage exceeds a critical value is called junction breakdown.

Maharashtra State Board: Class 12

Definition: Breakdown Voltage

The critical reverse voltage at which breakdown occurs in a diode is called breakdown voltage.

Maharashtra State Board: Class 12

Definition: Zener Breakdown

The breakdown occurring in a heavily doped p–n junction due to strong electric field breaking covalent bonds is called Zener breakdown.

Maharashtra State Board: Class 12

Definition: Zener Diode

A p–n junction diode specially designed to operate in the breakdown region is called a Zener diode.

Maharashtra State Board: Class 12

Definition: Zener Voltage

The voltage at which a Zener diode operates in the reverse breakdown region is called Zener voltage (VZ).

Maharashtra State Board: Class 12

Definition: Voltage Regulator

A circuit that maintains a constant output voltage despite variations in input voltage or load current is called a voltage regulator.

Maharashtra State Board: Class 12

Definition: Maximum Zener Current

The maximum current that can flow through a Zener diode at its rated voltage is called the maximum Zener current (IZ(max)).

IZ(max) = \[\frac {P_Z}{V_Z}\]

Maharashtra State Board: Class 12

Definition: Power Rating

The maximum power that a Zener diode can safely dissipate is called power rating.

PZ ​= VZ​ × IZ(max)​

Maharashtra State Board: Class 12

Definition: Zener Resistance

The opposition offered to the current flowing through a Zener diode in its operating region is called Zener resistance (Zener impedance).

Maharashtra State Board: Class 12

Definition: Photodiode

A special type of p–n junction diode that converts light energy into electrical energy is called a photodiode.

Maharashtra State Board: Class 12

Definition: Dark Current

The reverse current that flows through a photodiode even when it is not illuminated is called dark current.

Maharashtra State Board: Class 12

Definition: Saturation Current

The constant maximum reverse current reached at higher illumination levels is called the saturation current.

Maharashtra State Board: Class 12

Definition: Dark Resistance

The resistance of a photodiode when it is not illuminated is called dark resistance.

Maharashtra State Board: Class 12

Formula: Dark Resistance

Rd = \[\frac{\text{Maximum reverse voltage}}{\text{Dark current}}\]

Maharashtra State Board: Class 12

Key Points: Photo Diode

  • A photodiode operates in reverse bias, and its current increases when light falls on it.
  • Light creates electron–hole pairs in the depletion region, increasing current.
  • The reverse current increases with increasing light intensity.
  • It has a fast response and works over a wide range of wavelengths.
  • It is used in alarms, sensors, optical communication, and safety devices.
Maharashtra State Board: Class 12

Definition: Solar Cell

A device that converts solar energy directly into electrical energy using a p–n junction is called a solar cell or photovoltaic cell.

Maharashtra State Board: Class 12

Definition: Light-Generated Current

The current produced in a solar cell due to incident light is called light-generated current or photo-generated current.

Maharashtra State Board: Class 12

Definition: Short-Circuit Current

The current flowing through a solar cell when its terminals are shorted is called short-circuit current (ISC).

Maharashtra State Board: Class 12

Definition: Open-Circuit Voltage

The voltage across a solar cell when no external load is connected is called open-circuit voltage (VOC).

Maharashtra State Board: Class 12

Formula: Power Delivered to the Load

PL ​= V × I

At maximum power point:

PL ​= VOC ​× ISC​

Maharashtra State Board: Class 12

Definition: Light Emitting Diode

A p–n junction diode that emits light when forward biased is called a Light Emitting Diode (LED).

Maharashtra State Board: Class 12

Definition: Cut-in Voltage

The minimum forward voltage at which an LED starts conducting and emitting light is called the cut-in voltage.

Maharashtra State Board: Class 12

Definition: Electroluminescence

The recombination of electrons and holes releasing energy in the form of photons is called electroluminescence.

Maharashtra State Board: Class 12

Key Points: Light Emitting Diode

  • LED emits light when forward-biased due to the recombination of electrons and holes at the junction.
  • The intensity of light emitted increases with an increase in forward current.
  • LEDs are made from compound semiconductors, and different materials produce different colours.
  • LEDs are energy-efficient, long-lasting, fast-responding, and environmentally friendly.
  • LEDs are widely used in indicators, display systems, lighting, optical communication, and seven-segment displays.
Maharashtra State Board: Class 12

Definition: Bipolar Junction Transistor

A semiconductor device having two p–n junctions and three terminals (emitter, base and collector) is called a Bipolar Junction Transistor (BJT).

Maharashtra State Board: Class 12

Definition: DC Current Gain

The ratio of collector current to base current in DC operation is called DC current gain (βDC).

\[\beta_{DC}=\frac{I_C}{I_B}\]

Maharashtra State Board: Class 12

Definition: DC Current Amplification Factor

The ratio of collector current to emitter current in DC operation is called DC current amplification factor (αDC).

\[\alpha_{DC}=\frac{I_C}{I_E}\]

Maharashtra State Board: Class 12

Definition: Input Characteristic

The variation of base current (IB) with base–emitter voltage (VBE) at constant collector–emitter voltage is called input characteristic.

Maharashtra State Board: Class 12

Definition: Output Characteristic

The variation of collector current (IC) with collector–emitter voltage (VCE) at constant base current is called output characteristic.

Maharashtra State Board: Class 12

Definition: Input Dynamic Resistance

The ratio of change in base–emitter voltage to the corresponding change in base current at constant VCE is called input dynamic resistance (ri).

\[r_i=\frac{\Delta V_{BE}}{\Delta I_B}\]

Maharashtra State Board: Class 12

Definition: Output Dynamic Resistance

The ratio of change in collector–emitter voltage to the corresponding change in collector current at constant base current is called output dynamic resistance (ro).

\[r_o=\frac{\Delta V_{CE}}{\Delta I_C}\]

Maharashtra State Board: Class 12

Definition: Amplifier

A device used for increasing the amplitude of an alternating signal (voltage, current or power) is called an amplifier.

Maharashtra State Board: Class 12

Definition: AC Current Gain

The ratio of AC collector current to AC base current is called AC current gain (βAC).

\[\beta_{AC}=\frac{i_C}{i_B}\]

Maharashtra State Board: Class 12

Definition: Voltage Gain

The ratio of output voltage to input voltage in an amplifier is called voltage gain (AV).

AV = \[-\frac{\beta_{AC}R_L}{r_i}\]

Maharashtra State Board: Class 12

Definition: Power Gain

The product of current gain and voltage gain in an amplifier is called power gain (AP).

AP​ = βAC ​× AV​

Maharashtra State Board: Class 12

Definition: Digital Electronics

An electronic circuit that handles only a digital signal is called a digital circuit, and the branch of electronics which deals with digital circuits is called digital electronics. 

Maharashtra State Board: Class 12

Definition: Logic Gate

A digital circuit with one or more input signals but only one output signal is called a logic gate.

Maharashtra State Board: Class 12

Definition: Boolean Expression

The mathematical statement that provides the relationship between the input and the output of a logic gate is called a Boolean expression.

Maharashtra State Board: Class 12

Key Points: Logic Gates

  • A NOT gate has one input and one output; it produces the opposite (complement) of the input.
  • An OR gate gives output 1 when at least one of its inputs is 1.
  • An AND gate gives output 1 only when all its inputs are 1.
  • A NAND gate is the complement of an AND gate; its output is 0 only when all inputs are 1.
  • A NOR gate is the complement of an OR gate; its output is 1 only when all inputs are 0.
  • An XOR (Exclusive-OR) gate gives output 1 when the two inputs are different (odd number of 1’s).
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