Consumer Electronics

Difference between jfet and mosfet?

Answer

Wiki User
06/27/2010

hi

Main differences are,

Bipolar Junction Transistor:

switching speed is low;switching loss is more; conduction loss is less; frequency of switching is less

we can use as amplifier;Current control; conduction due to electron & holes

Junction field Effect Transistor:

it an unipolar; switching speed is high;so loss is less

voltage control;

Metal oxide semiconductor fet:

it nothiug bt fet, most of time v used for switching device in Smps do to power range

A BJT is a bipolar transistor in the sense that there are two types of charge carriers in them. In npn trnsistor the primary carrier in the hole and in pnp the electron. In JFET there is only one type of carrier. In n-channel case the carrier is elctron and in p-channel hole. So JFET is unipolar in that sense.

BJT is a current controlled device as the input current is amplified subjected to the mode of operation. For example in CE mode the input current is base current and output current is emmiter current which is (β+1) times amplified. The drop of this current across the load voltage is the output signal voltage. But a JFET is a voltage controlled device. The chalnnel conductance is determned by the voltage supplied at the gate terminal and depending on this the drain current flows.

MOSFET is one kind of voltage controlled device like JFET where there is metal oxide in between the gate and the channel. Depending on the voltage supplied on the gate terminal a voltahe is 'induced' by electrostatic induction in the isolated channel. The channel therefore behaves as a capacitor where due to the voltage some charges are induced. These charges shrink or extend the effective chanel width. For example in Enhancement Mosfet the channel width effectively increases and in depletion mosfet it decreases. Depending on this the drain to source current increases or decreasesA BJT is a bipolar transistor in the sense that there are two types of charge carriers in them. In npn trnsistor the primary carrier in the hole and in pnp the electron. In JFET there is only one type of carrier. In n-channel case the carrier is elctron and in p-channel hole. So JFET is unipolar in that sense.