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1. N Channel Transistor
2. N Channel Enhancement Mosfet Pdf

Comparison of N Channel and P Channel MOSFETs

N Channel Transistor

Major Brands BS250 N-Channel MOSFET Transistor, TO-92, 3 Pin, 5.2 mm H x 4.2 mm W x 4.8 mm L (Pack of 10) 5 $8 79 ($0.88/Transistor). Figure-4 depicts drain characteristics and transfer curve of enhancement type of MOSFET(N-channel). As shown in the figure-4 minimum threshold voltage is needed for the flow of drain current to start. This type of FET is ideal for switching application. This is due to the fact that no gate voltage is needed to keep the device in 'off' state.

• The P-channel enhancement MOSFETs were very popular, because it was much easier and cheaper to produce than the N channel device.
  But now a days these difficulties have overcome and mass production of N-channel MOSFETs becomes easier.
  Thus the N-MOSFETS have replaced PMOSs and P-MOSFETs have almost become obsolete.
• The hole mobility is nearly 2.5 times lower than the electron mobility.
  Thus a P channel MOSFET occupies a larger area than the N channel MOSFET having the same I_D rating.
  At normal fields, in silicon,
  the hole mobility is 500 cm^2/v.sec
  the electron mobility is 1300 cm²/v.sec.
  Therefore the P-channel ON resistance will be twice that of n-channel MOSFET ON resistance.

Remember:

1. ON resistance means the resistance of the device when I_D is maximum for a given V_DS. Its value depends upon μ of carriers.
2. P-channel device have holes as majority carriers.
3. N-channel device have electrons as majority carriers.

• At the same values of I_D and V_DS, if the ON resistance of P channel device were to be reduced/make equal to that of N-channel device, then the P-channel device must have more than twice the are of N-channel device. Thus the n -channel devices will be smaller is size.
  In other words the packing density of N-channel devices is more (R = ρ. l/ A)
• N channel MOSFETs are fast switching devices. The operating speed is limited by RC time constant of the device. The capacitance is proportional to the junction cross sections.
• The N channel MOSFETs are TTL compatible. As the applied gate voltage and drain supply are positive for an n-channel enhancement MOSFET.
• The drain resistance of P channel MOSFET is 3 times higher than that for an identical N-channel MOSFET.
• The N-Channel MOSFET has the higher packing density which makes it faster in switching applications due to the smaller junction areas and lower inherent capacitance.
• The N-channel MOSFET is smaller for the same complexity than P-channel device.
• Due to the positively charged contaminants, the N-channel MOSFET may turn ON prematurely, whereas the P-channel device will not be affected.

The summary of Difference Between N Channel and P Channel MOSFETs are listed in the following table.

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There are two types of MOSFETS: depletion-type MOSFETs and enhancement-type MOSFETs.

Enhancement-type MOSFETS are MOSFETs that are normally off. When you connect an enhancement-type MOSFET, no current flows from drain to source when no voltage is applied to its gate. This is why it is called a normally off device.There is no current flow without a gate voltage.

However, if a voltage is applied to the gate lead of the MOSFET, the drain-source channel becomesless resistive. As the gate-source voltage increases more and more, the current flowing from drain to source increasesmore and more, until maximum current is flowing from drain to source.

An enhancement-type MOSFET is so named an enhancement device, because as the voltage to the gate increases, the current increases more and more, until at maximum level.

An enhancement-type MOSFET behaves very similar in action to a bipolar junction transistor.

The other type of MOSFET, a depletion-type MOSFET, has the complete opposite behavior. Depletion MOSFETsare normally on devices. They conduct current at maximum level when there is no voltage applied to the gate lead. with a depletion-type MOSFET, as you increase the gate-source voltage, the drain-source channel of the transistor becomes more resistive and the current flowing from drain to source decreases, and if the gate-source voltage reachesthe cutoff level, the current completely ceases to flow.

N Channel Enhancement Mosfet Pdf