A Comprehensive to 2N3819 N-Channel JFET

Numerous JFET types are available today, each offering distinct features and specifications suitable for various circuit applications. In this article, we will delve into the characteristics of the 2N3819 JFET. This particular device is adept at handling medium to high-frequency ranges, delivering high gain for wideband frequencies. Its capabilities include signal amplification, fast switching, and mixing, making it versatile for a multitude of applications. Additionally, the 2N3819 JFET is integrated into audio systems, contributing to enhanced sound quality.

Understanding the operation of this compact N-channel Junction Field Effect Transistor might initially seem complex. To simplify the comprehension process, this article has been crafted to guide you in the right direction. Let's embark on this exploration!

What is 2N3819 JFET?

The 2N3819 is an N-Channel depletion-mode JFET extensively employed in RF-based audio equipment for amplification and various applications. It specifically serves as a VHF/UHF amplifier. With a Drain-Source Voltage of 25 Vdc and a Drain-Gate Voltage of 25 Vdc, it operates effectively. The Gate-Source Voltage is set at 25V, and the 2N3819 is capable of delivering a Drain current of 100mAdc.

2N3819 Pinout

Pin Description of 2N3819 JFET

Features and Specification

• Category: N-Channel Depletion-Type JFET

• Drain-to-Source Voltage (VDS) = 25V

• Drain-to-Gate Voltage (VDG) = 25V

• Gate-to-Source Voltage (VGS) = 25V

• Drain Current (ID) = 0.1 A

• Gate-Source Cut-off Voltage (VGS(off)) = -8.0 Vdc (VDS = 15 Vdc, ID = 10 nAdc)

• Cut-off Frequency (Note 1) = 700 MHz (VDS = 15 Vdc, VGS = 0)

2N3819 Working Principle

The 2N3819 features a conduction path extending from the source to the drain. The regulation of charge flow through the channel path is achieved by adjusting the area of the channel.

Conduction in the channel is produced by a field effect. When a positive voltage is applied to the gate and source terminals, it induces reverse bias in the pn-junction. This reverse bias causes the depletion region around the gate terminal to expand, creating a gradient in the depletion region surrounding the pn-junction. Consequently, this constrains the current flow between the source and drain by narrowing the width of the conductive channel.

The flow of conductivity from the source to the drain stops when the depletion layer exceeds the width of the conduction channel, a phenomenon referred to as pinch-off. For instance, applying a negative voltage to the gate-source leads to the N-Channel JFET ceasing its functionality. However, it's important to note that exceeding the absolute value in stress can result in damage, and prolonged exposure to stress may impact its reliability.

Where to use 2N3819?

As mentioned earlier, the 2N3819 is primarily designed for VHF and UHF applications. Thanks to its low noise characteristics, it finds utility in amplifying various low-level signals, whether they are audio signals or other electronic signals. Additionally, it serves as a reliable switch with a maximum load capacity of 10mA. Furthermore, its high gain at 100MHz enhances its suitability for use in RF applications.

How to Choose a JFET?

1. Determine the JFET type based on the application requirements. For applications on the low side of the power path, such as in the case of the 2N3819 N-Channel JFET, it is the appropriate choice. Conversely, for high side switching applications, opt for a P-Channel JFET.

2. Compute the maximum Drain-Source voltage and the required Gate-Source voltage for the specific application. Select a JFET with Drain-Source and Gate-Source breakdown voltages exceeding the application's needs. The 2N3819, for instance, provides a 25V Drain-Source breakdown voltage and a 25V Gate-Source Breakdown voltage.

3. Determine the maximum Drain Current. Choose a JFET capable of handling a Drain current greater than what is actually needed for the application. The 2N3819, for example, can accommodate up to 100mA of continuous Drain current (ID).

2N381 - Interfacing Diagram

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

C1 serves as the coupling capacitor, while C2 acts as the DC blocking capacitor where the output is extracted. RC represents the collector resistor, and adjusting its value will alter the circuit's frequency response and control the DC gain by managing the collector current. R1 and R2 function as a voltage divider to bias the JFET.

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

2N3819 Circuits Examples

N-Channel JFET as a Switch

The DC voltmeter, linked between the drain and source terminals, gauges voltage. Once the N-channel at the gate terminal receives zero voltage, the FET transitions into saturation mode, leading to a closed circuit. Consequently, the DC voltmeter will register nearly zero voltage at the drain terminal.

Introducing adequate negative voltage to the gate terminal prompts the FET to operate in the cut-off region, functioning as an open circuit. Simultaneously, the DC voltmeter will indicate the input voltage source (+25V) at the drain terminal.

Audio Mixer 2N3819

Both audio input channels connect to the transistor gate, accompanied by two capacitors and variable resistors. When input signals are applied to the mixer, it induces variations in gate voltage and drain current. Consequently, this modifies the voltage drop across the load resistor, amplifying the audio signal.

Each variable resistor plays a role in audio mixing. Adjusting the resistances enables control over the input channels, influencing both the amplified signal and the mixer output. As a result, this procedure yields different sound levels. Ultimately, the connection of a capacitor in the output ensures the delivery of a high-quality signal.

2N3819 JFET Alternative

The replacements for 2N3819 JFET are: 

• 2N4416

• NTE312

• 2N5638

• 2N5640

• 2SK162

• 2SK518

Applications of 2N3819 JFET

• VHF/UHF Amplifier systems

• Receivers and Transmitters

• RF Modules

• Tone control

• High-frequency amplifiers

• Low capacitance switches

• Amplification and analog switching

• Low-level signal amplification

• Sensor Circuits

• Audio Amplifier Stages

2N3819 Package

2N3819 Datasheet

Download 2N3819 datasheet PDF.

Conclusion

In general, the 2N3819 JFET device is designed for low-level signal amplification and switching functions. It proves beneficial for enhancing signals in electronic circuits, particularly in VHF/UHF mixer applications. Moreover, it is noteworthy that the 2N3819 is equipped with a 25V Drain-Source and Gate-Source breakdown voltage, providing ample capacity for applications that demand a breakdown voltage beyond the minimum requirement. The device functions by regulating the flow of current between the source and drain pins, achieved through the narrowing of the conductive channel.