Introduction to 2n3819

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Introduction to 2n3819

• 2n3819 is an N-Channel JFET(Junction Field Effect Transistor) which is mainly used for general purpose amplification and analog switching.
• It contains three terminals named as gate, drain and source.
• There are two types of JFET i.e N channel and P channel JFET. As it is an N-Channel JFET so conduction will be carried out by the movement of electrons.
• Unlike BJT(Bipolar junction transistor), this N-Channel JFET is a uni-polar device because conduction is carried out by single charge carriers i.e electrons.
• Three terminals source gate and drain are the analogous of emitter base and collector of BJTs.
• 2n3819 is a low-cost device which exhibits high performance at mid-to-high frequencies.
• It shows low leakage and noise and exhibits high gain at 100 MHz.
• Conduction will be achieved when electrons will emit from the gate and are collected by the drain terminal.

• There exists a conduction path between source and drain which is termed as channel.
• This JFET is also termed as voltage control device because small voltage at the gate terminal is used to control the conduction between source and drain terminals.
• The increase in initial input voltage at the gate terminal will help in increasing the channel path between source and drain terminals which ultimately increases the overall conductivity of the channel.
• This JFET can be used as voltage controlled resistors, amplifiers, and electronically controlled switches.
• It exhibits large input impedance up to thousands of ohm hence it doesn't effect the external components that we attach to its gate terminal.

2n3819 Pinout

• Current will from flow from source to drain.
• It is a voltage control device  and gate draws no current.

Working of N-Channel 2n3819

• There exists a conduction path between source and drain.
• The amount of electric charge can be controlled passing through the channel.
• By liming the area of channel path we can limit the charge flow from source to drain terminals.
• Conduction channel is made using the field effect. When a positive voltage is applied at the gate and source terminals it helps in reverse biasing the gate-source pn-junction, which ultimately enlarges the depletion region.
• Following figure shows the P-Type gate is diffused in the N-Type material which forms the reverse biased pn-junction. 

  

• This pn-junction will create a depletion region around the gate terminal.
• It is called depletion region because no charge carriers exist in this region.
• This depletion region will create a potential gradient around the pn-junction, and helps in limiting the flow of current between channel from source to drain by reducing the width of the conduction channel.
• N-Channel JFET sometimes referred as depletion mode devices when there is no voltage applied at the gate terminal.
• The conduction from source to drain will stop when depletion layer exceeds the width of the conduction channel.
• The point at which conduction stops is called pinch off region.
• Pinch off value is different for different transistors.
• In order to switch off this N-Channel JFET, negative gate-source voltage is required Vgs.

Absolute Maximum Ratings of 2n3819

• It is important to note that if stresses are exceeded from the given absolute value, they can harm the device.
• Also, if stresses are applied for extended period of time above the normal operating conditions, they can effect the device reliability.

Applications

• 2n3819 is widely used for high frequency amplifier.
• It can be used in low capacitance switches.
• For general purpose amplification and analog switching we use this N-Channel JFET.