Hey everyone! Hope you all are doing great. Today, I am going to give you the details on the Introduction to 2n4391. It is a simple N type JFET (Junction field effect transistor) which consists of three terminals called drain, source and gate and are denoted by D, S and G receptively. It is mostly used in analog switches and current limiters. I am going to give you a brief details on this transistor. Let’s get started.

Introduction to 2n4391

  • 2n4391 is a field effect transistor that consists of three terminals known as drain, source and gate.
  • It is called field effect transistors because static field performs as important part in the operation of this transistor.
  • Unlike normal transistors, it is a voltage controlled device as it doesn’t require any biasing current to control large amount of current.
  • It conducts, when current flows between drain and source terminals.
  • A JFET is considered fully ON as long as no potential difference appears between source and gate terminals. Similarly, applying a negative gate-source voltage will turn off JFET.
  • It restricts the flow of current if there appears any potential difference between source and gate terminals.
  • A JFET comes in two types, N type and P type channel. 2n4391 is a N type JFET where voltage at the source terminal is greater than the voltage at gate terminal.
  • 2n4391 is composed of semiconductor material which contains negative charge carriers such as electrons.
  • In JFET, the flow of current is handled by limiting the channel through which current is flowing.
  • Current also has a large effect on the electric field between drain and source.
  • 2n4391 comes with high speed analog circuit performance and low error voltage.
  • It has excellent accuracy, good frequency response that eliminates the additional buffering.
2n4391 Pinout

Pinout of field effect transistor 2n4391 is shown in the figure given below:

2n4391 consists of three terminals

1: Drain 

2: Source

3: Gate

  • It will conduct when current flows between drain and source terminals.
  • In this N type FET voltage at the gate terminal is used to handle the current flowing through the device.
Working of 2n4391
  • Movement of election plays an important role in the operation of all transistors.
  • Conducting channel in this N type JEFT is made by field effect process.


  • In N-type JFET, flow of electrons between source and drain is restricted by the number of holes in the gate terminal.
  • However, an electric filed is generated when we apply positive voltage at the gate terminal. It results in the flow of electrons from source to drain terminal, that ultimately switches on the transistor.


  • Current is generated by the addition of “field effect”, that’s why these transistors are named as field effect transistors.
  • Coating silicon layers with metal oxide gives this component a different name called MOSFET ( Metal Oxide Semiconductor Field Effect Transistor).


Absolute Maximum Ratings of 2n4391

Absolute maximum ratings of this N type JFET is given in the figure below.

  • Gate-Drain and Gate-Source voltage is -40V.
  • Gate current is 10mA.
  • It is important to note that ratings more than given on the above table can damage the device at large.
  • These are the stress rating that can be implied duration the operation of this JFET.
  • Similarly, if these rating are implied more than given time period, they can effect the reliability of device.
Comparison between JFET and Bipolar Junction Transistors
  • JFET are like normal transistors with some exceptions. In case of JFET, layers of N-type silicon material are coated with metal and oxide and they are placed in a different way than normal transistors.
  • Normal junction transistors are bipolar transistors i.e. they will conduct by the movement of electrons and holes in transistors.
  • JFET are uni-polar transistors, i.e. they either conduct with the movement of electron in N type transistors or movement of holes in P type transistors.
  • Both junction transistors and JFET come with great accuracy, show instant operation and both are robust and cheap.
  • However, in most of the electronic application JFET evidently replace bipolar transistors.
  • It is a good choice for specialized amplifier circuits and analog switching application.
  • It is mostly used in commutators and choppers.

That’s all for today. I hope you have got a clear idea of this N type JFET. However, if still you feel any doubt or have any question regarding this FET, I’d glad to help you in this regard. Your suggestions and feedbacks will be highly appreciated. Stay tuned!

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