Showing posts with label Basic Electronics. Show all posts
Showing posts with label Basic Electronics. Show all posts

January 30, 2014

Some Basics of Electrical, Electronics and DLC

Some basics to help review your knowledge in electrical, Electronics and DLC. Suitable for ECE, EEE, EIE and related circuit branches.
(.zip - 9MB)

October 20, 2013

Animations | Electronic Devices and Circuits

To understand clearly how electronic devices and several electronic and digital circuits work, animations will be of great help and ease. Visit falstad.com
You would need Java plugin.

Index

September 12, 2013

EDC | FET | MOSFET | 2 Marks

Types of MOSFET
  • Depletion MOSFET (n-type, p-type)
  • Enhancement MOSFET (n-type, p-type)
Depletion MOSFET Vs Enhancement MOSFET

S. No.
D-MOSFET (n-channel)
E-MOSFET (n-channel)
 1.
Negative voltage at gate
Positive voltage at gate
 2.
Positive charges on the semiconductor site
Negative charges on the semiconductor site
 3.
Depletion of majority carriers
Inversion layer is formed
 

JFET Vs MOSFET

S. No.
JFET (n-channel)
MOSFET (n-channel)
1.
Between Gate and channel is a PN junction forming a diode
Between gate and channel is an insulating SiO2 layer forming a small capacitor
2.
Gate is reverse biased (negative voltage for n-channel)
Gate can be given positive or negative voltage depending on mode of operation required
3.
High input impedance due to reverse biased gate
Very high impedance due to insulated gate and capacitance effect
4.
Operated only in depletion mode
Operated in depletion and enhancement mode


 Yet to be updated!

September 11, 2013

EDC | FET | JFET | 2 Marks

FET (Field Effect Transistor)

FET is a  voltage controlled, unipolar, three terminal device.

Why FET is called a unipolar device?
In UJT, either holes or electrons is responsible for conduction of current (ID) through the channel and hence called unipolar device.
In n-channel JFET, free electrons (charge carrier) in the channel alone is responsible for flow of current (drain current) whereas in p-channel JFET, holes (charge carriers) present in the channel alone is responsible for flow of current.

Why is the term "Field Effect"?
In JFET, the drain current ID is controlled by electric "field" applied across gate and source.

Types of FET
  • JFET (Junction Field Effect Transistor)
  • MESFET (MEtal Semiconductor FET)
  • MOSFET (Metal Oxide Semiconductor FET)
JFET Biasing
  • Self bias
  • Voltage-divider bias
JFET Characteristics
  • Transfer Characteristics (ID Vs VGS)
  • Drain Characteristics (ID Vs VDS)
Pinch-off voltage
In drain characteristics,   at a constant VGS (VGS=0), the  value of VDS at which the drain current becomes constant for further increase in VDS is called pinch-off voltage.

Cut-off voltage
In drain characteristics, the value of VGS that keeps ID approximately zero is called cut-off voltage.

Characteristic parameters of JFET
  1. Transconductance (gm)
  2. Input resistance and capacitance
  3. Drain and source resistance (rd)
  4. Amplification factor (μ)
  5. Power dissipation (PD)
Applications of JFET
  • Can be used as switch or as amplifier as like BJTs.
  • Since input impedance is high and output impedance is low, it can be used as buffer in measuring instruments.
  • It has low noise capability ad hence can be used in RF amplifiers, FM tuners and other communication devices.
  • Input capacitance of FET is very low and hence usedd in cascade amplifiers in measuring and test equipments.
  • Used in oscillators, low frequency amplifiers and digital circuits.

September 07, 2013

EDC | SCRs | 2Marks

Latching current (IL):
During turn-on, the minimum value of anode current that must be attained so that the thyristor wil
l remain in conduction state even if gate signal is removed.

Holding current (IH):
When the gate is open, a certain value of anode current below which SCR will switch to OFF state is called holding current.
Methods to turn ON SCRs:
  1. Gate triggering - SCR can be triggered into conduction mode by gate pulse signal.
  2. Forward-breakover Voltage (VFBO) - When voltage across SCR (VAK) exceeds forward-breakover voltage (VFBO), SCR turns ON.
Methods to turn OFF SCRs:
  1. Reverse biasing anode-cathode terminals of SCR using external supply, called forced commutation.
  2. Interrupting or reducing the current through the SCR (Anode current, IA) below holding current
List of SCR ratings:
  1. Forward-breakover voltage, VFBO
  2. Holding current, IH
  3. Gate trigger current, IG
  4. Average forward current, IF(avg)
  5. Reverse-breakdown voltage, VRBO
List of SCR characteristics:
  1. Forward-blocking region
  2. Reverse-blocking region
  3. Forward-conduction region
Advantages of SCR as a switch over mechanical switch:
  1. Noiseless
  2. High switching speed
  3. Control over current with small gate current
  4. No mechanical movable contact, increasing life
Some applications of SCR:
  1. Speed control of motor, dimming of lights
  2. Power control
  3. Half-wave and full-wave rectifiers with current and power control 
Shockley Diode Vs SCR Vs TRIAC Vs DIAC

S. No.
Shockley Diode
SCR
TRIAC
DIAC
1.       
Uni-directional device
Uni-directional device
Bi-directional device
Bi-directional device
2.       
No gate terminal
Gate terminal is present
Gate terminal is present
No gate terminal
3.       
Basic 4 layer device
Shockley diode with gate terminal
Two SCRs in Inverse-parallel connection
Two Shockley diodes in Inverse-parallel connection
(OR)
Low current TRIAC without gate terminal
4.       
Terminals:
Anode and Cathode
Anode, Cathode and Gate
Main terminal1, Main terminal2 and Gate
Main terminal1 and Main terminal2
5.       
Break-over voltage cannot be controlled
Break-over voltage can be controlled with gate signal
Break-over voltage can be controlled with gate signal
Break-over voltage cannot be controlled
 

 

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