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 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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44 views

JFETs question about pinch-off voltage

Can the pinch-off voltage be equal to zero? In my opinion no, because the JEFT would be off all the time, isn't it?
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749 views

Simple MM Phono Preamp Design

I'v found myself in need of a new preamp for my turntable (the one built into my power-amp went out with a bang and tripped the breaker!). I'm using a moving magnet type cartridge with output around ...
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34 views

Confusing datasheet for JFET 113: Which value for IDSS applies?

I am trying to build a small amplifier with a JFET J113 to get a high input impedance. I have a problem with the datasheet: On page 3 it gives a value of IDSS=2mA for J113. However, on the following ...
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72 views

Why does the resistance of this JFET VCR change?

I'm trying to build an automatic gain control (compressor) for my audio amplifier. For this I'm using a 2N5458 JFET as a voltage controlled resistor. The circuit looks like this in LTSpice: The drain-...
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72 views

Multiple way to enable regulator

I want to know how can I enable the regulator in three different ways in correct way through the hardware. There is two PCBs in below picture. PCB1: 24V input plug (user plugged) 16V battery Charging ...
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50 views

Series current Feedback

I was tryig to build this circuit ("Series-feedback pair") from "Art of electronics" book (p. 150). Since I do not have the exact components I tried to model it in LTSpice with ...
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62 views

JFET Constant Current Source (CRD alternative)

Today I have build constant current source based on J111. To drain I connected VCC it's 24VDC from laboratory power supply, then I connected resitor 470Ohm between gate and source. To source pin i ...
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43 views

Quick JFET Datasheet Comparison/Analysis

In a previous question I asked for a replacement for the J402/LS3954 dual JFET that has gone out of production and increasingly expensive. (Mouser has them for $23 right now, what a deal) and I came ...
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43 views

Can anyone properly explain me the characteristic curve of the p-type JFET?

I know how a MOSFET works. But recently I wanted to know details about JFET. When V(GS) = 0 volts there will obviously a current flowing through the p-type channel. What confuses me is how the ...
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42 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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85 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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316 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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1k 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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221 views

Analogue multiplexer using JFET for small signals

I'm working on a circuit with a non-inverting amp and I would like to switch between two reference voltages, both with low output impedance. So in effect i want something like this: simulate this ...
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2k views

FET Push-Pull Amplifier

I'm curious about JFET/MOSFET circuit B class amplifier. When BJT is used we only have those (+/-)0.7V limiting the transistors and causing crossover distortion. But with adding FETs or MOSFETs to the ...
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279 views

Problem distinguishing BJT from JFET

I was testing few types of transistors on my newly acquired peak atlas pro and came across some N-channel depletion mode JFETs marked 2n3819. To my surprise the device indicated they are NPN BJTs. ...
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637 views

JFET transconductance vs. MOSFET transconductance

JFET's n-channel highest transconductance (from datasheets) is marked as In theory, the same value is defined as that applies for n-channel JFET. I haven't found equation which defines MOSFET's ...
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881 views

JFET Different Output Characteristics for different Vgs,off

Hi guys, I've been trying to design a simple amplifier with some gain. My first question is, why are there multiple output characteristic graphs (2 shown) for a single JFET? My first step in designing ...
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356 views

Photodiode JFET amplifier stage in pinch off?

In the circuit below, it seems that the JFET is biased in a regime with very low current (pinched off?). With respect to most designs I came across, this one uses rather large source and drain ...
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54 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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68 views

Design of a Frequency Mixer

I am quite new to this subject. I want to design a frequency mixer to mix a carrier frequency of 100 MHz with a 20 kHz signal. I found the attached circuit. It seems quite a simple circuit to multiply ...
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53 views

JFET question about operation

I have a question about the N-JFET.Assume it operates at the linear region and it acts like a voltage controlled resistor. Can we say that if Vdg(drain-gate voltage) is increased then the resistance ...
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Using an NPN transistor as a signal switch

I'm using this NPN switch to turn on and off a clean guitar signal (as part of a much bigger circuit not seen.) The base is connected to the switch, which gives the base 9V through a 1 megaohm ...
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106 views

Amplitude modulation with JFET

I have found a circuit that does AM modulation with a JFET transistor(2N5485.) I modified it slightly and ended up with the circuit below. A sample output is also given. I used Microcap 12 for the ...
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JFET circuit analysis

Below is the circuit in question: Below is my attempt, however, I feel there is something wrong because the value of Rd is not fixed.
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JFET biasing question

as we all know in order to work the JFET correctly, we need to have a Voltage across R_s which should be greater than the voltage across R_2. now I can make the voltage across R_s of my choice by ...
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Conditions for a JFET transistor to saturate

I have come across the relations: vDS > vGS – VP for n-channel JFET vDS < vGS – VP for P-channel JFET The two are given as the conditions for JFET to be in saturation. How can I arrive at these ...
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33 views

Relay to electronic switch change

I would like to change relay functionality in electronic switch. As per the concept, relay pole and NC position is short even there is no power applied to it. I need complete exact relay functionality ...
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79 views

Self-biased JFET - Midpoint bias: Why set the drain voltage to one-half of it?

To set a midpoint bias, I understand that ID = IDSS/2 (and by equation, VGS = VGS(off)/3.4). For calculating resistor values, why set VD = VDD/2?
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JFET RDS(on) Matching

Quick question here - I have a circuit that originally used a 2SK30ATM-GR JFET, with an RDS(on) maximum of 800 ohms. Most of the cheap JFETs I can find have a significantly smaller RDS value, ...
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492 views

Calculation of drain current in JFET

simulate this circuit – Schematic created using CircuitLab If IDSS= 10mA and Vp= -5V, when VDS=Vp, what is the value of ID and VGS? Lets say I apply KVL on drain-source loop. Then I get VDD-IDRD-...
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JFET switch circuit

I want to discharge capacitor when battery pack is disconnected. Will this work? In my project I use power source selector IC. Problem is, this IC does not recognize battery reconnection until ...
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321 views

How would you determine the Miller input and output capacitance for the amplifier in the figure?

When I calculate the Miller input and output capacitance I get; Cin(Miller) as 6.38pF and Cout(Miller) as 5.66pF. However, these values are incorrect.
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How to choose Drain current for a JFET Differential Amp

I have to design a JFET differential amplifier with a current mirror. I am unsure where to start and what to set the biasing current to. Any help will be appreciated to point me in the right direction....
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113 views

Common drain small signal analysis and unresolved question for fet

question: There is an amplifier circuit obtained between JFET and MOSFET. For the FET used in the circuit, IDSS = 8 mA, VGSoff = -3V and working point current is 1.42 mA. Use MOSFET parameters as ...
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119 views

Determining JFET substitution parameters

I have a design (see page 3) that uses a JFET to linearize the charge current for a capacitor used as an integrator. I've been using the BSR56, but that's been discontinued. I am used to looking at ...
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164 views

Replacement for E402/J402/LS3954 JFET?

I've come across old synthesizer schematics for an oscillator which makes use of a couple E402s. I am looking for a suitable replacement, and I don't think the specs have to be spot on at all, but I ...
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In jfet, how can VGS(off) be found with just IDSS and gm0?

Transconductance curve of jfet is a parabola. Given a point (0, IDSS) and gm0, which is the slope at VGS=0, how is it possible to find the VGSOFF ? One point and slope give a straight line, not ...
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91 views

SIPMOS as current source

I read this question and I have the same issue: acquire and protect an input with 5-24V range. I wonder if nowadays I can use a BSS126 as current source transistor. It's a depletion mode N-channel, I ...
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321 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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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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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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349 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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331 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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Need a switching circuit that is closed when Vgs is negative and open when Vgs positive, any ideas please?

I need a circuit that will be closed when Vgs is negative and open when Vgs positive. Basically the inverse of Enhancement mode MOSFETs or JFETs. I appreciate your help with this. Thank you!
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662 views

Phase Modulator with JFET

At the university we have seen this circuit as a Phase Modulator: simulate this circuit – Schematic created using CircuitLab where \$m(t)\$ is the message at audio frequency and \$v_p(t)\$ is ...
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JFET - transconductance, gain(mu) and internal resistance at the drain

Hello guys, here is such assignment: to determine gm, internal resistance at the drain and maximum gain (mu). 1) If Transconductance gm can be found from the formulas and graph. 2) How to determine ...
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Model for small signal - 3 transistors JFET

Could you tell me if the models for small signs are well made? And if they were not, you could tell me what I missed, please? Thanks. \$V_{dd}=17 \,V\$ \$IDSS= 8 \,mA\$ \$V_P=-3\$ \$r0=30 k\$ \$...
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572 views

Common Source JFET amplifier input voltage

I want to compare to different formulas which stand for same parameter/value. Here is common source JFET amplifier circuit schematic: Here is the first formula which should apply in general to all ...