N Channel Enhancement type Mosfet  characteristics and working

Mosfet is a three terminal device which is a type of FET( Field effect transistor). It is suitable for high power applications as it can withstand large amount of currents. The output current is controlled by the input gate voltage. Hence, the field created by the input gate voltage often termed as Vgs controls the drain current Id. There are two types of MOSFET  N Channel Mosfet and P Channel Mosfet. N Channel Mosfet’s are further classified into Enhancement Type and Depletion type Mosfets. Here we will study N Channel Enhancement type Mosfet characteristics.

What is N Channel E-Mosfet (Enhancement)?

  • In E Mosfet a positive gate voltage is required to be applied which creates a channel between the source and the drain terminals. Therefore, this channel helps to induce drain current Id.
  • If there is no gate voltage, there is no channel created and hence there is no current flowing. Hence, this Mosfet is also called as Noramally Off Mosfet.

N Channel Mosfet Characteristics

There are two types of characteristics

  1. Drain Characteristics
  2. Transfer Characteristics

Diagram:

N Channel Mosfet Characteristics
N Channel Mosfet Characteristics

Drain Characteristics

  • In Drain Characteristics, the output current is plotted with respect to the Drain to source voltage VDS. We make VGS( Gain to source voltage constant). It helps us in understanding three regions of operation.

Drain Characteristics output

    Drain Characteristics output
  • On the X-axis we plot Drain to Source voltage while on Y- Axis we plot Id( Drain current).
  • We plot the current values for different values of Vgs. As in the above image we can see different plots of ID in red, blue, yellow, etc colors.
  • The plot in Yellow represents lowest Vgs value while the plot in green shows maximum Vgs value
  • As we can see the current remains constant after some drain voltage. Hence, minimum drain to source voltage is needed for Mosfet to work.
  • Hence, as we increase Vgs the channel width increases and it results in more drain current ID

 

Transfer Characteristics

  • Transfer characteristics is the graph of output current to input voltage.
  • Hence, we plot current ID( output) with respect to input voltage Vgs.
Mosfet Transfer Characteristics
Mosfet Transfer Characteristics
  • The above figure shows transfer characteristics. It is also known as transconductance curve.
  • Initially, when there is no Vgs( gate to source voltage) very less current flows. It is in micro amps.
  • When Vgs is positive, the drain current increases slowly.
  • After that there is a rapid increase in drain current corresponding to increase in vgs.
  • The drain current can be obtained by

Id= K (Vgsq- Vtn)^2.

  • The required values are provided in the Datasheets.

The above circuit is simulated in multisim. Check out the video below for Mosfet characteristics Simulation in Multisim.

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