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Satish Pradhan Dnyanasadhana College, Thane

Understand the principles of Field Effect Transistors, including JFET and MOSFET, their parameters, biasing, switching, and applications. This guide covers SCR operation and characteristics as well.

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Satish Pradhan Dnyanasadhana College, Thane

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  1. 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

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

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

  4. 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

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

  6. Normal Biasing of JFET Dr. S. R. Bhagat

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

  8. Drain Characteristics Dr. S. R. Bhagat

  9. Drain Characteristics Dr. S. R. Bhagat

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

  11. FET Parameters • Drain Resistance (rd) • 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 VGSat a constant value of VDS Dr. S. R. Bhagat

  12. 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

  13. Gate Bias Dr. S. R. Bhagat

  14. Self Bias Dr. S. R. Bhagat

  15. Voltage Divider Bias Dr. S. R. Bhagat

  16. Common Source Amplifier Dr. S. R. Bhagat

  17. JFET Analog Switch Dr. S. R. Bhagat

  18. Shunt Switch Dr. S. R. Bhagat

  19. Series Switch Dr. S. R. Bhagat

  20. JFET Analog Switch Multiplexer Dr. S. R. Bhagat

  21. FET as VVR Dr. S. R. Bhagat

  22. Enhancement MOSFET Dr. S. R. Bhagat

  23. Enhancement MOSFET Dr. S. R. Bhagat

  24. Biasing of MOSFETDepletion Type Dr. S. R. Bhagat

  25. Biasing of MOSFETEnhancement Type Dr. S. R. Bhagat

  26. 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

  27. 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

  28. 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

  29. SCR Dr. S. R. Bhagat

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

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

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

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

  34. 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

  35. 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

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

  37. 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

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

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

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

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

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

  43. SCR as a Half wave Rectifierwith firing angle upto 180 Dr. S. R. Bhagat

  44. Triac Dr. S. R. Bhagat

  45. TriacConstruction Dr. S. R. Bhagat

  46. TriacOperation Dr. S. R. Bhagat

  47. TriacCharacteristics Dr. S. R. Bhagat

  48. Applications of TriacIntensity control of high power lamp Dr. S. R. Bhagat

  49. Applications of TriacElectronic changeover of transformer taps Dr. S. R. Bhagat

  50. The Diac Dr. S. R. Bhagat

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