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Questions tagged [jfet]

Junction Field Effect Transistor - A transistor whose channel is modulated by the application of an electric field that is the depletion region of a reversed biased diode that forms the gate electrode. Characteristic features of the device are low noise and low gate capacitance.

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How current is steady after pinch off voltage?

I was studying the JFET. In the books and other material it is mentioned that when the voltage between the drain and source is increased then drain current is also increased. After a certain point (...
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1answer
74 views

Circuit to save one battery when another battery is present

I have a battery powered system and I want to preserve the test batteries during setup and calibration. I want the system to use the setup batteries if they are present and use the test batteries if ...
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46 views

Single MOSFET current source (JFET like)

Is it possible to build MOSFET current source similar to JFET current source like this: simulate this circuit – Schematic created using CircuitLab With MOSFET it should be something like this: ...
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28 views

TO-72 package FET Case pin

I have 2N3823 JFETs in TO-72 package, which has 4 leads. No problems with Gate, Drain, and Source, but there is also a Case pin that I have been ignoring. Now I am putting together a PCB for a ...
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73 views

How can an electret microphone have a more or less flat response?

I've got two concerns. The first is that the voltage across the electret capacitor is proportional to \$\frac{1}{d^2}\$. For the voltage to be proportional to the pressure difference between both ...
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260 views

Why are the advantages of JFET over MOSFET, or why are JFET still used?

I saw JFET in an electret mic circuit, and it is quite recent, so I'm wondering why. Since we are looking for the highest gate impedance, MOSFET would seem to be a better choice. I've also read that ...
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174 views

What's the catch with these JFETs?

I'm designing a low-noise, high-bandwidth (100 MHz) pre-amp using JFETs. The choice for JFETs was because it needs to operate with large source impedances (>10 kΩ). I spent a while looking for a ...
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1k views

What kind of transistor turns on with 0.2 volts?

I need a circuit to turn on a LED with 0.2 volts. I want to do it with a transistor as a switch. What kind of transistor will turn on at this voltage?
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38 views

Why does the output voltage of my linear gain amplifier depend on the JFET gate voltage?

I am trying to build a linear gain voltage controlled amplifier using an N-channel JFET as a voltage variable resistor (see circuit below). As the circuit is set op now, I would expect Vout to be ...
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76 views

Voltage controlled amplitude problem - JFET circuit

I work on a function generator project. It generates waveforms such as sine, triangle, rectangle with PWM regulation, saw. I would like to digitally adjust the signal output amplitude. Input signals ...
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57 views

How does the biasing work in a JFET based triangle to sinewave converter?

To those who haven't see this cool little circuit it employs the non-linearity and symmetry of the JEFET to clip a triangular signal to make it more sinusoidal Can someone please explain to me how ...
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1answer
146 views

Origin of increased noise in BF862/OP27 charge amplifier

For the amplification of piezoelectric sensor signals I am currently building a charge amplifier with a low noise JFET frontend utilizing an NXP BF862. The amplifier design is based on application ...
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68 views

Converting a non-electret condenser microphone circuit to electret?

I'm trying to convert an MXL 603s circuit, which has a non-electret capsule, to an electret version. I'm pretty certain that the only real difference between the two would be the fact that the non-...
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113 views

JFET colpitts oscillator - very unstable

I've designed, simulated and build this simple JFET colpitts oscillator and I couldn't get it to work with real parts. I didn't have BF256B jfet model so I simulated it using some generic one. The ...
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59 views

JFET Voltage Divider design question

I've been trying to get this question done for a couple of days now and no matter how much I try I've been unable to get it done. Your help in this question is greatly appreciated.
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51 views

Why is the source voltage 1/4 of the supply voltage applied to the drain in a voltage-divider JFET circuit?

According to a Junction Field Effect Transistor (JFET) article in ElectronicsTutorial, the voltage across the source resistance is equal to 1/4 the supply voltage applied to the drain/gate for a class ...
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1answer
392 views

ERROR(ORPSIM-16492)

I am new to PSPICE as well as the community and i'm trying some circuits given by my professor for an assignment. I've completed most of them which helped me in understanding how the software works ...
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63 views

Can a JFET replace a IGFET? (A 3N139 IGFET)

it is my first question so please forgive my errors. I try to build the People Detector from Popular Electronics http://www.swtpc.com/mholley/PopularElectronics/Jun1968/PE_Jun_1968_pg28.jpg. The 3N139 ...
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36 views

Choosing a suitable FET for a design project

I'm currently working on a project to produce a high speed and high voltage pulse. I'm trying to find a suitable FET. I intended to supply a voltage of about 50v to circuit. And using the FET to go ...
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32 views

GaAs and GaN as low temperature carriers in transistor

I've been looking at HEMT to use at low temperatures. GaAs and GaN seem to be discussed often in the context of low temperature amplification. My questions are twofold. To be suitable for low ...
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21 views

drain voltage of JFET (N type depletion)

I am trying to figure out the drain voltage of the JFET (N type depletion) ATF33143, given the architecture shown in the image below. I understand that it's basically a voltage divider and that \$ V_{...
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502 views

BJT vs FET for VHF LC oscillator

In the ARRL (2011) section 9.3.1 about LC oscillator circuits it says that "[t]he N-channel JFET source follower shown appears to be the most popular choice nowadays", but does not explain the ...
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79 views

Determine transconductance of a JFET given only voltage gain and internal drain resistance

I have a homework question as follows: If a JFET having a specified value of rd=100 kΩ has an ideal voltage gain of Av(FET) = -200, what is the value of gm ? As far as I know, the closest formula for ...
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756 views

Common Source JFET Amplifier Gain

I would be thankful if someone could explain me what is the general formula used to calculate the gain of a common source jfet amplifier. I have the fallowing circuit: Since this circuit was taken ...
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35 views

JFET impact-ionization current

Can someone explain me what impact-ionization current means and when does it happen? As far as I'm concerned, it's about gate current leakage when operated with high Vds and Id. If I'm right, why does ...
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72 views

Help with JFET circuit analysis

Just having trouble analysing the following circuit with the information given. where k=0.16mA/volt^2, Vt = -1.7V and A = 1V. I believe you have to first find an expression for V_gs but the ...
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69 views

Can an N-ch JFET switch be positive-common-source?

I'm considering switching options for an HF (3-15 MHz) tuner network. Pin diodes are interesting but their surrounding control circuitry is somewhat inconvenient, and they require relatively high ...
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125 views

Line regulation of zener diode with jfet

How am I able to calculate line regulation (S=dUout/dUin) for zener diode with current provided by JFET with zero gate - source voltage? Schematic below Lets say it's typical BF256B as JFET and BZX84-...
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236 views

What is small signal. And what is small signal equivalent circuit

I am very new in electronics. And this topic is bothering me. I want to know what is small signal and how to draw a small signal equivalent of jfet with common source.
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153 views

How do I make a simple bidirectional current limiter

I want to connect two separate batteries together and let the highest voltage one charge the lower one not exceeding the desired current. I expect it to be a solid state solution without the need for ...
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1answer
96 views

Dealing with JFET parameter spread in voltage controlled resistor configuration

So I need to make a voltage controlled resistor to control a Q factor in RLC resonator, I'm using a P-channel JFET for this and I can't choose a JFET because datasheets show huge IDSS and VGS spread. ...
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50 views

Operation of Junction field effect transistor

Is Vds necessay for Drain current (Id) or we can get Id by Vgs also as in books it is written that Vds is necessary.
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284 views

Schematic Symbol Help Possible Antiquated JFET Symbol Conversion

This is an old schematic, and the MPF102 JFET in the picture is confusing me. Can someone help me identify the Gate, Source, & Drain connections to this symbol, please! My guess is that the ...
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202 views

Measuring Vackar Oscillator Output Amplitude and High Frequency Effects

This is somewhat related to my previous question regarding why I wasn't seeing a clamp biasing effect with my JFET Vackar oscillator. I think I figured it out and I'm wondering if you guys agree. ...
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177 views

Clamp-biasing at JFET Gate in RF Circuits

Reading the book Communications Circuits by Clarke and Hess, I came upon a chapter entitled "Clamp-biased Square Law Device" (Chapter 4 - 4.9). It took me a while to realize that they were ...
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119 views

Choosing an SMD JFET [closed]

I've prototyped a simple circuit for interfacing a ceramic mic to an iPad. It uses a 2N5457 JFET. I just happened to have that component on hand and it worked well. I'd like to implement this ...
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161 views

Why are there no power JFETs?

After doing a search on mouser, I found only 4 JFETs rated for more than 1A drain-source current, compared to almost 3,000 BJT and 11,000 MOSFETs. Is this because there is less of a market for a high ...
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356 views

How susceptible to ESD damage are JFET gates?

Are the gates of JFETs protected against ESD transients? Is it best to include back to back zeners like with MOSFETs?
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206 views

How do I know what power rating pots need?

EE novice here. In this post on reddit, the author wonders if 125mW-rated potentiometers are usable in the MFOS Noise Toaster. The Noise Toaster drives analog audio circuitry off a single 9V battery ...
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139 views

What are the benefits of this type of JFET biasing

The next schemtaic I was found as an input stage of ultra-linear phono amplifier. What are the benefits of that type of biasing? I don't see that 12V zener has 12V voltage drop on it (only 4.2V) and ...
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1answer
52 views

The value Of a Voltage Can someone help

So i was working on JFET networks and in the calculation of The output impedance (Solution from the book) I am stuck in the solution My question is How can Vrd = V0 + Vgs ? The solution picture
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88 views

Soft muting small speakers quickly

I'm running a small 3W speaker from an MP3 module, in order to save power I control the module with a MOSFET switch. The module itself can not go into an very effective low current sleep mode so I ...
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358 views

MCU Controlled JFET switch for negative voltage?

I have a JFET that requires negative voltage to the base in order to close and 0V to be open. I have the following power rails: 5V , -12V & GND (0V). What would be the simplest way to switch the ...
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1answer
186 views

What is the op-amp in this JFET-matcher circuit?

In the circuit diagram on this page, there appears to be an unspecified op-amp. Could anyone guess at a component I could use for this and/or explain why there is no specification? Background: I am ...
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136 views

Multisim virtual JFET saturation current

How I can set virtual JFET saturation current in Multisim. I can't find any parameter with appropriate name in model settings of virtual JFET?
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1answer
77 views

Question about JFET resistor connection

In the picture is a Photovoltaic mosfet driver. So I understand that the JFET is used to discharge the MOSFET gate to source capacitance to decrease its turn of time. Whats the function of the 2M ...
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1answer
230 views

JFET Q-point for use it as resistor

I'm trying to use JFET as resistor. For use it as a resistor DS voltage need to be less than Vp. Vp from datasheet of 2n4391 is equal to -VgsOff and equal to 4.0V. How I can to set scheme to view ...
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728 views

VGS(off) for JFET in AGC circuit

I want to use a well known AGC circuit (see below) with 3.3V instead of 5V. The description of the circuit can be found here, and state the following about the JFET: Other JFETs with VGS(OFF) of 5V ...
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182 views

For the same JFET why are there two curves in a Transfer characteristics graph?

I am trying to learn about n-channel JFETs from David. A. Bell's book. In the transfer characteristics graph, there seem to be two curves as shown. Note that VGS(off) = Vp As you can see, one curve ...
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1answer
539 views

What is the difference in performance of a JFET current source to a 741 Op Amp current source?

It is possible to build a circuit that provides a steady current source via these two methods: Screenshot of op amp circuit Screenshot of self-biasing JFET current source In the circuit using an op ...