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BJT is a current-controlled transistor and JFET is a voltage-controlled transistor. JFET is similar to Lateral BJT which is usually used for BJT pnp devices, except the central region doping. The base doping in BJT is used so as to increase the beta, while the active region doping in JFET is used to adjust the threshold voltage. In BJT, Ie or Ib current is used to control Ic. In JFET, the reverse-biased Vgs is used to control Id.
First difference is in its production process... BJT is bipolar, JFET is unipolar.
JFET is Field Effect Transistor, so it controls drain-souce, Ids, current with its inverse PN voltage on its gate, Vgs.
Read the attachment, it has some of Sedra slides...
They are quite different:
- BJT is bipolar, JFET is unipolar transistor.
- BJT is current controlled, JFET is voltage controlled.
- At BJT, when increasing controlling current (Ib), then controlled current (Ic) increased and Vce decreased. Ic = 0 when Ib = 0.
At JFET, when increasing controlling voltage (Vgs), then controlled current (Id) decreased and Vds increeased. Id = max when Vgs = 0.
Actually the more precise question is how is BJT different from FET.. anyway, besides the fact that BJT is current controlled and FET is voltage controlled, BJT's are BIPOLAR devices and FET's are UNIPOLAR devices
every one has mentioned no of replies.all are correct.
bjt is current cont while jfet is voltage controlled devices.
jfets have higher input impedances than bjts. its v v important characteristcs,thats y we prefer to use jfets for increasing input impedance of amplifiers.
jfets can operate in enhancement modes....mosfets etc...
u can find a lots of material from following book
electronic devices and circuit theory
by bolysted
BJT:-
BJT stand for bi polor junction is a three terminal device that contains two PN diode sandwiched back to back.BJT is current control device
JFET:-
JFET is voltage controlled device.Their operation is governed by an electric field that control the electron current in an N-channel FET or the hole current in a P-channel FET.As indicated,the FET is a uni polar device using either holes(P-channel) or electrons(N-channel) as carriers
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