The Ultimate Guide to 2N3819 N-Channel JFET

Numerous JFET variants are available in the current landscape, each endowed with distinct features and specifications catering to various circuit applications. One example is the 2N3819, an N-channel Junction Field Effect Transistor designed for general-purpose use. Functioning in depletion mode, this transistor necessitates reverse biasing for deactivation. Its operational capabilities extend to handling medium to high-frequency ranges, delivering substantial gain across wideband frequencies. Notably, it holds significance in VHF/UHF systems. Operating as a small-signal device, it excels in signal amplification and swift switching and facilitates mixing functionalities for many applications. Additionally, its utility extends to the integration within audio systems, contributing to an enriched auditory experience. In this article, we’ll explore the 2N3819 pinout, features, working, applications, alternatives and more details.

What is 2N3819 N-Channel JFET?

The 2N3819 is an N-Channel JFET. Finds its application in RF scenarios within the VHF/UHF spectrum, specifically in situations where amplification is a requisite. Tailored for RF amplifier and mixer applications, the accompanying graph illustrates the S-Parameters, offering insights into the common source characteristic of this JFET. Notably versatile, this JFET also proves valuable in switching-related applications.

Positioned as an economical, multipurpose JFET, the 2N3819 delivers commendable performance within the mid-to-high frequency range. Boasting attributes such as minimal noise and distortion, heightened gain and sensitivity, and top-notch signal amplification, it caters to a spectrum of applications, including very low-level signal amplification. Additionally, the transistor's aptitude as a switch shines through with rapid switching capabilities, proficiently driving loads up to 10mA. Furthermore, its prowess extends to providing substantial gain at 100MHz.

2N3819 Pinout

This transistor, comprised of epitaxial silicon, features a trio of pins. The pin on the left functions as the source, while the one on the right, designated as 3, serves as the drain. The intermediary pin assumes the role of the JFET's gate.

Pin Configuration

Pin No.	Pin Name	Description
1	Source	Source pin of the JFET
2	Gate	Gate pin of the JFET
3	Drain	Drain pin of the JFET

2N3819 Equivalents

2N3819 JFET equivalents include 2N4416, NTE312, 2N5638, 2SK162, etc.

• 2N4416: It is a JFET that shares similarities with the 2N3819, making it a suitable alternative. Renowned for its reliability and performance, the 2N4416 is often utilized in circuits requiring high input impedance and low noise levels, such as in audio amplifiers and RF signal processing.

• NTE312: It is a reliable substitute for the 2N3819 JFET. Recognized for its compatibility and consistent performance, the NTE312 is commonly employed in circuits where precise signal amplification and low noise are critical, making it an ideal choice for applications in communications and instrumentation.

• 2N5638: It is another JFET that serves as a substitute for the 2N3819. Valued for its versatility, the 2N5638 finds its place in various electronic designs, providing reliable amplification and signal-switching capabilities. It is often utilized in audio applications and low-frequency signal processing.

• 2SK162: It is a field-effect transistor (FET) that can be used as an equivalent to the 2N3819. Known for its high input impedance and low noise characteristics, the 2SK162 is frequently chosen for applications demanding precise signal amplification, such as in audio preamplifiers and instrumentation circuits.

How does 2N3819 Work

The 2N3819 incorporates a conduction pathway extending from the source to the drain. Regulating charge movement between these terminals involves adjusting the channel path's dimensions.

A field effect generates the conduction channel, with a positive voltage applied to the gate and source, inducing reverse bias in the pn-junction. This, in turn, leads to the expansion of the depletion region around the gate terminal, creating a gradient at the pn-junction. Consequently, the current flow between the source and drain is constrained by narrowing the width of the conductive channel.

When the depletion layer exceeds the width of the conduction channel, conductivity from the source to the drain halts. This cessation is known as the pinch-off region. For instance, when a negative voltage is applied to the gate source, the N-Channel JFET ceases operation. Nevertheless, exceeding the absolute value in stress conditions may result in damage. Furthermore, prolonged exposure to stress can impact the device's reliability.

2N381 Interfacing Diagram

The image below illustrates the standard utilization of the N-Channel JFET 2N3819 as an amplifier.

In this configuration, C1 is the coupling capacitor, while C2 is the DC blocking capacitor responsible for extracting the output. The collector Resistor (RC) holds significance, and altering its value affects the circuit's frequency response and controls the DC gain by managing the collector current. R1 and R2 act as voltage dividers to bias the JFET.

For a typical 12V operation, suggested values could be: R1 = 100k, R2 = 10k, RC = 10k, and C1, C2 can be 1uF ceramic capacitors.

How to Choose a JFET

1. Identify the appropriate JFET type for the intended application. For instance, the N-Channel JFET, such as 2N3819, is well-suited for the low side of the power path. In cases requiring high-side switching, opt for a P-Channel JFET.

2. Determine the maximum values for Drain-Source and Gate-Source voltages in the target application. Select a JFET with breakdown voltages for Drain-Source and Gate-Source that exceed the requirements. The 2N3819, for example, offers a 25V Drain-Source breakdown voltage and a 25V Gate-Source breakdown voltage.

3. Calculate the maximum Drain Current needed. Choose a JFET capable of tolerating a Drain current surpassing the actual requirement for the application. The 2N3819, in this context, supports up to 100mA of continuous Drain current (ID).

Where to Use 2N3819?

As mentioned, the 2N3819 is primarily designed for VHF and UHF applications. Its notable low noise characteristic renders it suitable for amplifying various low-level signals, whether audio or electronic. Additionally, it doubles as a switch with a maximum load capacity of 10mA. Furthermore, its high gain at 100MHz enhances its suitability for deployment in RF applications.

2N3819 Applications

• System for Amplification in VHF/UHF Range

• Transmitter and Receiver Components

• Module for Radio Frequency (RF)

• Control of Tone

• Amplifier for High Frequencies

• Switches with Low Capacitance

• Analog Switching and Amplification

• Amplification of Any Low-Level Signal

• Circuits for Sensors

• Applications in Audio

• Stages for Audio Amplification

2N3819 Example Circuits

N-Channel JFET as a Switch

The provided circuit illustrates the usage of the 2N3819 JFET as a switch. A DC voltmeter is linked between the Drain and Source terminals to gauge the voltage across the Drain terminal.

• When no voltage is applied to the Gate terminal of the N-channel JFET, the FET functions in saturation mode. It behaves like a closed circuit, and the DC voltmeter indicates nearly zero voltage across the Drain terminal.

• Conversely, applying a sufficiently negative voltage to the Gate terminal of the N-channel JFET shifts the FET into the cut-off region. It then acts as an open circuit, resulting in the appearance of the input voltage source (+25V) across the Drain terminal, observable on the DC voltmeter.

Field Detector Circuit 2N3819

The diagram above illustrates the configuration for an AC field detector:

It elucidates the 2N3819 N-Channel JFET's operation as a field detector. The source terminal of the transistor is linked to a power source supplying 6-12 Volts, thereby providing voltage to the 555 Timer IC. This IC is further connected to an LED that illuminates timer activation and a buzzer that emits a sound upon signal detection. An antenna connected to the gate of the 2N3819 serves to detect the AC field. The antenna transmits a voltage to the gate terminal whenever it perceives a charge or wave. The shift in gate voltage modifies ID, triggering the Timer IC. Consequently, the LED begins to flash, signaling IC activation, and the buzzer generates a sound to indicate the detection of a charge by the antenna.

Audio Mixer 2N3819

An audio mixer amplifies and blends audio signals to create diverse sounds and enhance overall audio quality. The schematic of an audio mixer is depicted below:

The transistor gate is connected to two audio input channels, followed by coupling capacitors and adjustable resistors. N-Channel JFETs are known for their high gain. The operation of a mixer closely resembles that of an amplifier, except for the variable resistors. When input signals are applied, the gate voltage changes, leading to variations in drain current. This, in turn, alters the voltage drop across the load resistor, amplifying the audio signal.

The variable resistors play a crucial role in audio mixing. By adjusting the resistances, we can regulate the contribution of each input channel to the output signal, resulting in a mixed and amplified audio signal with varying sound levels. The output is connected to a capacitor to ensure the quality of the resulting signal.

2N3819 Package

2N3819 Datasheet

Download 2N3819 Datasheet PDF.

Conclusion

In general, the 2N3819 JFET device offers capabilities for amplifying low-level signals and facilitating switching functions. This enhances signal quality within an electronic circuit, particularly beneficial for VHF/UHF mixer applications. Furthermore, the 2N3819 has a 25V Drain-Source and Gate-Source breakdown voltage support. This signifies its suitability for applications requiring breakdown voltages beyond the specified threshold. The device functions by regulating the current flow between the source and drain pins, which is achieved by narrowing the width of the conductive channel.

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