Satish Pradhan Dnyanasadhana College, Thane ( Academic Year 2017 – 2018 ) SEM-VI T. Y. B. Sc. Electronics Unit 1 by Dr. S. R. Bhagat Dr. S. R. Bhagat

Field Effect Transistors The current flow is controlled by electric field Unipolar Switch faster Dr. S. R. Bhagat

Field Effect Transistors JFET MOSFET (IGFET) n-Channel JFET p-Channel JFET FET Enhancement MOSFET Depletion MOSFET n-Channel EMOSFET n-Channel DMOSFET p-Channel DMOSFET p-Channel EMOSFET Dr. S. R. Bhagat

FET and BJT Unipolar Bipolar High input resistance No offset voltage Immune to radiations Less noisy Greater thermal stability Simple to fabricate less space Dr. S. R. Bhagat

Basic Ideas There are three terminals: Drain (D) and Source (S) are connected to n-cha Dr. S. R. Bhagat

Normal Biasing of JFET Dr. S. R. Bhagat

Schematic Symbols Gate Drain Source Gate Drain Source Gate Drain n-channel JFET Offset-gate symbol n-channel JFET p-channel JFET Dr. S. R. Bhagat

Drain Characteristics Dr. S. R. Bhagat

Drain Characteristics Dr. S. R. Bhagat

Transconductance Curve IDSS VGS (off)=VP Figure: Transfer (or Mutual) Characteristics of n-Channel JFET Dr. S. R. Bhagat

FET Parameters Drain Resistance (rd) Transconductance (gm) The dynamic a.c. resistance is defined as the ratio of infinitesimal change in VDS to the corresponding change in drain current ID at a constant value of VGS Transconductance (gm) The mutual conductance is defined as the ratio of the change in drain current to the corresponding change in VGS at a constant value of VDS Dr. S. R. Bhagat

FET Parameters The voltage amplification factor () It is the ratio of change in VDS to the corresponding change in drain current VGS at a constant value of ID where Dr. S. R. Bhagat

Gate Bias Dr. S. R. Bhagat

Self Bias Dr. S. R. Bhagat

Voltage Divider Bias Dr. S. R. Bhagat

Common Source Amplifier Dr. S. R. Bhagat

JFET Analog Switch Dr. S. R. Bhagat

Shunt Switch Dr. S. R. Bhagat

Series Switch Dr. S. R. Bhagat

JFET Analog Switch Multiplexer Dr. S. R. Bhagat

FET as VVR Dr. S. R. Bhagat

Enhancement MOSFET Dr. S. R. Bhagat

Enhancement MOSFET Dr. S. R. Bhagat

Biasing of MOSFET Depletion Type Dr. S. R. Bhagat

Biasing of MOSFET Enhancement Type Dr. S. R. Bhagat

MOSFET Switch The MOSFET switch is most popular type of switch. It is good for transmitting low level voltage signals (as opposed to high current). Output swing depends critically on RD (ID=IDSS for VGS=0). Current flows at all times. Dr. S. R. Bhagat

A JFET has a drain current 5 mA A JFET has a drain current 5 mA. If IDSS = 10 mA and VGS(off) =  6V, find the value of VP and VGS In a n-channel JFET potential divider biased circuit, it is desired to set the operating point at ID = 25 mA and VGS = 8 V. If VDD = 30 V, R1 = 1 M and R2 = 500 k, find the value of RS Given ] IDSS = 10 mA and VP =  5V The transconductance of a JFET used in a voltage amplifier circuit is 3000 mho and the load resistance is 10 k , calculate the voltage amplification factor assuming that rd >> RL For a JFET, IDSS = 9 mA and VP =  35V. Determine ID when VGS = 0 V and  2 V. Dr. S. R. Bhagat

A JFET amplifier employs voltage divider bias A JFET amplifier employs voltage divider bias. The resistances are of value R1 = 1 M and R2 = 1 M. . If VDD is 20 V and the drain current is found to be 2 mA for RS = 15 k find VGS. If VDS is one half VDD, what is the value of RD? Dr. S. R. Bhagat

SCR Dr. S. R. Bhagat

Working of SCR When Gate is open Dr. S. R. Bhagat

Working of SCR When Gate voltage is zero Dr. S. R. Bhagat

Working of SCR When Gate voltage is positive with respect to cathode Dr. S. R. Bhagat

Equivalent circuit of SCR When Gate is open and V < VBr (Breakover voltage) When gate voltage is positive Dr. S. R. Bhagat

Important terms for SCR Forward Breakover Voltage (VBr) It is the minimum forward voltage, gate being open, at which SCR start conducting heavily i.e. turned on. Holding Current (IH) It is the value of current below which the SCR switches from the conduction state to the forward blocking region under specified conditions Peak Reverse Voltage (PRV) It is the maximum reverse voltage that can be applied to an SCR without conducting in reverse direction Dr. S. R. Bhagat

Important terms for SCR Forward Current Rating It is maximum anode to cathode current that SCR is capable of passing without damage Circuit Fusing Rating It is the product of square of forward surge current and the time of duration of the surge Dr. S. R. Bhagat

V-I Characteristics of SCR Dr. S. R. Bhagat

SCR as a Switch Advantages of SCR switch over mechanical or electromechanical switches No moving parts, hence noiseless operation at high efficiency The switching speed is very high upto 109 operations/sec It allows control over large current upto 100 A in the load by means of small gate current It is solid state device and has small size, hence gives trouble free long service Dr. S. R. Bhagat

SCR as a Switch DC gate trigger SCR turns on when switch S is closed Dr. S. R. Bhagat

SCR as a Switch AC gate trigger SCR turns on when IG  IGT Dr. S. R. Bhagat

SCR as a Switch Anode current interruption to make SCR off Dr. S. R. Bhagat

SCR as a Switch Forced Communication Dr. S. R. Bhagat

SCR as a Half wave Rectifier Dr. S. R. Bhagat

SCR as a Half wave Rectifier with firing angle upto 180 Dr. S. R. Bhagat

Triac Dr. S. R. Bhagat

Triac Construction Dr. S. R. Bhagat

Triac Operation Dr. S. R. Bhagat

Triac Characteristics Dr. S. R. Bhagat

Applications of Triac Intensity control of high power lamp Dr. S. R. Bhagat

Applications of Triac Electronic changeover of transformer taps Dr. S. R. Bhagat

The Diac Dr. S. R. Bhagat

Applications of Diac Light Dimmer Dr. S. R. Bhagat

A half wave rectifier circuit with SCR is adjusted to have a gate current of 1 mA. The VBRF of SCR is 100 V for Ig = 1 mA If a sinusoidal voltage of 200 V peak is applied find ( i ) firing angle ( ii ) conduction angle ( iii ) average current. Assume load resistance 1 k and the holding current to be zero An ac voltage of v = 240 sin 314t is applied to an SCR half wave rectifier. If the SCR has a forward breakdown voltage of 180 V, find the time during which SCR remains off An SCR has a circuit fusing rating of 60 A2s. Determine the highest surge current value that SCR can withstand for a period of 20 ms. Dr. S. R. Bhagat