Junction Field Effect Transistor , By

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JFETJunction Field Effect Transistor

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Introduction (FET)Field-effect transistor (FET) are important devices such as BJTs Also used as amplifier and logic switches What is the difference between JFET and BJT?

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BJT is Current-controlled

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FET is Voltage-controlled

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Types of Field Effect Transistors (The Classification) JFET MOSFET (IGFET)n-Channel JFET p-Channel JFETn-Channel EMOSFET p-Channel EMOSFET Enhancement MOSFETDepletion MOSFETn-Channel DMOSFET p-Channel DMOSFET FET

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High input impedance (M) (Linear AC amplifier system) Temperature stable than BJT Smaller than BJT Can be fabricated with fewer processing BJT is bipolar – conduction both hole and electron FET is unipolar – uses only one type of current carrier Less noise compare to BJT Usually use as an Amplifier and logic switchIntroduction.. (Advantages of FET over BJT)

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Disadvantages of FETEasy to damage compare to BJT

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There are 2 types of JFET n-channel JFET p-channel JFET Three Terminal Drain – D Gate -G Source – SJunction field-effect transistor..

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SYMBOLSn-channel JFETp-channel JFET

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N channel JFET: Major structure is n-type material (channel) between embedded p-type material to form 2 p-n junction. In the normal operation of an n-channel device, the Drain (D) is positive with respect to the Source (S). Current flows into the Drain (D), through the channel, and out of the Source (S) Because the resistance of the channel depends on the gate-to-source voltage (VGS), the drain current (ID) is controlled by that voltage N-channel JFET

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N-channel JFET..

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P channel JFET: Major structure is p-type material (channel) between embedded n-type material to form 2 p-n junction. Current flow : from Source (S) to Drain (D) Holes injected to Source (S) through p-type channel and flowed to Drain (D)P-channel JFET

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P-channel JFET..

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Water analogy for the JFET control mechanism

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JFET Characteristic for VGS = 0 V and 0

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JFET for VGS = 0 V and 0

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Pinch-off (VGS = 0 V, VDS = VP).

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ID versus VDSJFET Characteristic Curvefor VGS = 0 V and 0

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(Application of a negative voltage to the gate of a JFET) JFET for

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JFET Characteristic Curve..For negative values of VGS, the gate-to-channel junction is reverse biased even with VDS=0 Thus, the initial channel resistance of channel is higher. The resistance value is under the control of VGS If VGS = pinch-off voltage(VP) The device is in cutoff (VGS=VGS(off) = VP) The region where ID constant – The saturation/pinch-off region The region where ID depends on VDS is called the linear/ohmic region

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p-Channel JFET

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p-Channel JFET characteristics with IDSS = 6 mA and VP = +6 V.

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Characteristics for n-channel JFET

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P+++Characteristics for p-channel JFET

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Last Updated: 8th March 2018

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