4th February 2008, 10:05 #1
Newbie level 2
difference between bjt and mosfet
i want to know about the difference btween BJT , JFET and Mosfet
4th February 2008, 10:05
4th February 2008, 10:22 #2
Full Member level 4
difference between jfet and mosfet
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 decreases.
4th February 2008, 10:22
5th February 2008, 07:38 #3
Newbie level 4
difference between mosfet and bjt
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
Metal oxide semiconductor fet:
it nothiug bt fet, most of time v used for switching device in Smps do to power range