Page 67 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Advantages of FET
1 Since they are voltage controlled amplifier this makes their input impedence very high
2 They have a low noise output. This makes them useful as preamplifiers where the noise must be very low
because of high gain in the following stages.
3 They have better linearity
4 they have low inter electrode capacity.
Typical applications of JFET

One very important characteristic of JFET is its very high input impedence of the order of 109 ohms. This
characteristic of FET, has made it very popular at the input stage of a majority of electronic circuits.
As discrete components FETS are mainly used in,

• DC voltage amplifiers
• AC voltage amplifiers(input stage amplifiers in HF and LF ranges)
• Constant current sources
• Integrated circuits of both analog and especially in Digital technology.

1 FET AC voltage amplifier
In the circuit at Fig 9, the amplification is determined by the design. it can be varied within certain limits of the
drain resistance and the source resistance are made variable. Potentiometer can be connected in series for this
purpose.

Fig 9

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CITS : Power - Electrician & Wireman - Lesson 60-69