Presentation on theme: "FET ( Field Effect Transistor)"— Presentation transcript:
1 FET ( Field Effect Transistor) Few important advantages of FET over conventional TransistorsUnipolar device i. e. operation depends on only one type of charge carriers (holes or electrons)Voltage controlled Device (gate voltage controls drain current)Very high input impedance ( )Source and drain are interchangeable in most Low-frequency applicationsLow Voltage Low Current Operation is possible (Low-power consumption)Less Noisy as Compared to BJTNo minority carrier storage (Turn off is faster)Self limiting deviceVery small in size, occupies very small space in ICsLow voltage low current operation is possible in MOSFETSZero temperature drift of out put is possible.
2 Types of Field Effect Transistors (Classifications) JFETMOSFET (IGFET)n-Channel JFETp-Channel JFETFETEnhancement MOSFETDepletion MOSFETn-Channel EMOSFETn-Channel DMOSFETp-Channel DMOSFETp-Channel EMOSFET
3 The Junction Field Effect Transistor (JFET) Figure: n-Channel JFET.
5 Figure: n-Channel JFET and Biasing Circuit. Biasing the JFETFigure: n-Channel JFET and Biasing Circuit.
6 Operation of JFET at Various Gate Bias Potentials Figure: The nonconductive depletion region becomes broader with increased reverse bias.(Note: The two gate regions of each FET are connected to each other.)
7 Operation of a JFET Drain - N Gate P P + + - DC Voltage Source - N +
8 Figure: n-Channel FET for vGS = 0. Simple Operation and Break down ofn-Channel JFETFigure: n-Channel FET for vGS = 0.
9 N-Channel JFET Characteristics and Breakdown Break Down RegionFigure: If vDG exceeds the breakdown voltage VB, drain current increases rapidly.
10 Figure: Transfer (or Mutual) Characteristics of n-Channel JFET Transfer (Mutual) Characteristics ofn-Channel JFETIDSSVGS (off)=VPFigure: Transfer (or Mutual) Characteristics of n-Channel JFET
11 Biasing Circuits used for JFET Fixed bias circuitSelf bias circuitPotential Divider bias circuit
12 JFET (n-channel) Biasing Circuits For Fixed Bias CircuitApplying KVL to gate circuit we getandFor Self Bias CircuitWhere, Vp=VGS-off & IDSS is Short ckt. IDS
13 JFET Biasing Circuits Count… or Fixed Bias Ckt.
14 JFET Self (or Source) Bias Circuit This quadratic equation can be solved for VGS & IDS