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JFET Basics for Electronics Enthusiasts

The JFET is a type of field-effect transistor with three terminals. Applying a reverse bias voltage to the gate terminal pinches the semiconductor channel between the source and drain terminals, impeding or stopping electric current flow. JFETs rely on a depletion region that must be closed to allow current to flow, and can have an n-type or p-type channel.

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10 views1 page

JFET Basics for Electronics Enthusiasts

The JFET is a type of field-effect transistor with three terminals. Applying a reverse bias voltage to the gate terminal pinches the semiconductor channel between the source and drain terminals, impeding or stopping electric current flow. JFETs rely on a depletion region that must be closed to allow current to flow, and can have an n-type or p-type channel.

Uploaded by

inzy283
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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JFET

The j unction field-effect tra nsistor (J FET) is one of the si m plest types of field-effect tra nsistor.[1] J FETs
a re three-term i na l sem icond uctor d evices that ca n b e used as electronica l ly control led switches or
resistors, or to b ui ld a m pl ifiers.

U nl i ke b i pola r j unction tra nsistors, J FETs a re excl usively volta g e-control led i n that they d o not need a
b iasi ng current. Electric cha rg e flows throug h a sem icond ucti ng cha nnel b etween source a nd drain
term i na ls. By a pplyi ng a reverse b ias volta g e to a gate term i na l, the cha nnel is pinched, so that the
electric current is i m ped ed or switched off com pletely. A J FET is usua l ly cond ucti ng when there is zero
volta g e b etween its g ate a nd source term i na ls. If a potentia l d ifference of the proper pola rity is a ppl ied
b etween its g ate a nd source term i na ls, the J FET wi l l b e m ore resistive to current flow, which m ea ns less
current would flow i n the cha nnel b etween the source a nd d ra i n term i na ls.

J FETs a re som eti m es referred to as d epletion-m od e d evices, as they rely on the pri nci ple of a d epletion
reg ion, which is d evoid of m ajority cha rg e ca rriers. The d epletion reg ion has to b e closed to ena b le
current to flow.

J FETs ca n have a n n-type or p-type cha nnel. In the n-type, if the volta g e a ppl ied to the g ate is
neg ative with respect to the source, the current wi l l b e red uced (si m i la rly i n the p-type, if the volta g e
a ppl ied to the g ate is positive with respect to the source). Beca use a J FET i n a com m on source or
com m on d ra i n config uration has a la rg e i nput i m ped a nce[2 ] (som eti m es on the ord er of 10 10 ohm s), l ittle
current is d rawn from ci rcuits used as i nput to the g ate.

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