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 one set the Q-point for a JFET cascode amplifier, and what are the correct "Idss" requirements for cascoded JFETs?
I am trying to teach myself electronics, and am currently attempting to learn about cascodes with the intent of building an RF amplifier that will amplify a microvolt signal up to line level with ...
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Design an AGC circuit for microphone using JFET
At the beginning of the circuit, I designed a 20Hz to 20kHz second-order Butterworth bandpass filter circuit, and then I tried to pass the filtered signal through an AGC circuit to achieve a smooth ...
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Design of a band-pass filter with automatic gain control using a JFET
I have implemented this circuit which is supposed to do AGC and filter out the signal between 20 Hz-20 kHz, but it seems have some problems. The bandpass filter works well, but the agc circuit doesn't ...
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Why does the FET input stage of op-amps still have an input current limit?
AFAIK, Igs of MOSFET/JFET is around 0.
That means that in MOSFET/JFET almost no current flows from gate to drain.
Modern FET input stage:
I read some op-amp datasheets, those op-amps have FET inputs, ...
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Can this switching schematic be simplified with digital control?
This is a portion of the schematic of an old (80s) audio synthesizer/effect (Roland Juno 6). The two inputs are triangle waves (opposite phase). The circuit shorted by TR8 and TR17 is not shown for ...
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Active load and current source purpose on NE5532
I'm trying to do some reverse engineering on the NE5532 schematic, but I can't understand how is designed the current source for the first stage. What I want to analyze now is in yellow on the picture....
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Gain of 0 dB for a common drain using JFET
I need to design a circuit that has a gain of 0 dB that allows a voltage attack on a 100 Ω load.
My first thought was to make a common-drain circuit since I had to use only JFETs. First I only used 1 ...
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JFETing op-amp inputs
My goal is to be able to use a high-speed, low-distortion, BJT-input op-amp having a much lower input current - that's why I'm trying to JFET the inputs. I don't want to cut DC with input cap, I want ...
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Schmitt trigger using JFET
I want to make a Schmitt trigger using a JFET instead of a bipolar transistor. I started by trying to understand how this circuit worked using a BJT and then moved on to try and replace them with ...
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Why do JFETs have such wide parameter spread?
I've noticed that in almost every JFET datasheet I've looked at, the values for Idss and Vto (also known as Vgs-off vary hugely.
A J111, for example, could have a Vto of anywhere from −3 to −10 volts ...
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FET Amplifier Output Distortion
I am new to electronics and still in learning phase. I have made an FET pre-amplifier (using n-Channel JFET) for electret microphone. The output distorts when input signal crosses 200 mV. The top of ...
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In-line switch for energy harvester
I have a seemingly simple problem.
I am developing a system that harvests energy from a piezo-electric vibration source. The harvesting circuit works well and I am happy with that, but I also want to ...
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Help biasing this JFET buffer
I'm trying to make a simple JFET buffer but I am struggling to find clear instructions on how to calculate the bias resistors.
I've built a circuit which nearly works, but I'm getting well below unity ...
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What is pinout of JFET in schematic. Is pin 1 really gate?
In the following schematic the J310 part, Q5 and Q6, are shown rotated.
If so shouldn't the pinouts show the gate as pin 3 instead of pin 1?
I thought he pinout of a J310 was 1-drain 2-source 3-gate.
...
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N-Channel JFET analog switch clarifications
I've read a few other questions on here which helped me understand analog FET switches better but I still have a couple of questions/clarifications which I'd like to understand better.
Consider a ...
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Maximum safe gate-source voltage (gate current) for JFET
I'm designing an AC-coupled low-noise preamplifier that will likely use parallel JFETs as the first amplifier stage.
One of the things I'd like to measure is the noise of very quiet regulators. JFETs ...
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What is the quiescent voltage of this circuit? [closed]
I am struggling to understand how the voltage on the capacitor C18 and at the gate of Q2 normalises to a quiescent state in the below circuit:
Specifically, I have two questions:
When the circuit is ...
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How to choose component values for a JFET common-source amplifier?
I am trying to design a simple common source jfet amplifier using a J109 transistor.
I'm using the J109 datasheet and equations from the book Electronic Devices by Thomas L. Floyd.
The issue is that I ...
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Why does voltage decrease as resistor increases?
As you can see in the images below, when I increase the resistor value from 200 Ω to 2 kΩ, the voltage at the node Vd suddenly decreases.
Why is this so?
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How to make an electret condenser microphone work?
This is the schematic. I've tried to build it and it doesn't work. Can someone please tell me where I've got it wrong?
The resistor value I used is 470 ohms and the Vsource is 9 volts.
The electret ...
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Why does the thermal noise of this large resistor not contribute to the input noise for this JFET-input inverting amplifier?
I'm interested in building a low-frequency, low-noise, AC-coupled preamplifier (mostly for measuring the noise of very quiet linear regulators). Several existing designs that I've seen use a matched ...
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Using Jfet as constant current source to drive a BJT
The circuit diagram below shows two simple voltage regulators, one of them is driven by constant current source using a Jfet and the second one also providing a constant current because the voltage is ...
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Unconventional use of a JFET: Potential pitfalls?
The idea is to (almost) replicate the soft power button on a modern PC, using an ATX power supply and some GPIO's from a microcontroller that's going to be there anyway:
simulate this circuit – ...
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Why does this JFET buffer perform so poorly at 82 MHz?
I made a Colpitts oscillator that worked well first time. Frequency about 82 MHz.
(nb. corrected diagram adding ground between series 68 pFcaps and corrected Vout)
I wanted to add a buffer and chose ...
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When to use discrete JFETs? [closed]
JFETs have lost importance and many parts are being gradually discontinued. However, due to the depletion type operation and other properties, I believe that even now in the 2020ies, there are still ...
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Troubleshooting simple JFET preamplifier design
The circuit shown below (with actual measured values) simulates correctly in as much that it provides some gain.
When I have built the circuit connected it to a signal generator using a 1mVp-p zero dc ...
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I don't understand JFET/this diagram Associate CET study guide
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I need help understanding JFET amplifier circuit I have a lot of questions that maybe basic questions I'm sorry.
This is a N-channel Jfet so it has negative voltage but what does that even mean “...
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Calculate JFET resistance
I'm exploring JFETs at the moment; I'd like to use them as a variable resistor and set the resistance with a control voltage. I'm using it to control a 1Vpp sine wave through ds.
I'm using a J201 JFET....
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Why does the polarity of voltage Vds have to be reversed for p-Channel JFET in comparison to n-Channel JFET?
I am trying to replicate the characteristics of n-channel and p-channel JFET, but I don't understand why voltage Vds has to be reversed in the p-Channel JFET for current to flow.
I have these ...
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LTspice JFET Voltage Divider Bias Configuration
I want to simulate this circuit in LTspice program and find Idss,Vp and Idsq,Vdsq but cannot. How can i simulate transfer characteristic?
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RC filters in JFET negative feedback
I saw a useful answer about JEFT negative feedback here and so I thought I'd ask for some help too!!
I'm attempting to create a JFET gain stage that uses a filter in a negative feedback loop to boost ...
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What Does This JFET Do If Vgs is Always 0V
I'm trying to understand this reference circuit that I found in the datasheet for a piezo accelerometer.
I don't understand what the purpose is if the gate and source are common. My best guess after ...
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JFET self bias, choosing source resistor so that the operating point is (1/2, 1/4)
When \$R_s=R_{DS} = \frac{-V_{GS(OFF)}}{I_{DSS}}\$, my textbook seems to suggest that \$I_{D}\$ equals \$\frac{I_{DSS}}{4}\$, but I'm not able to derive this. Any help?
My work:
\$I_D = I_{DSS}(1-\...
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What is the purpose of gate resistor in gate bias?
The input driving below circuit has only two states: \$-10V\$ for OFF and \$0V\$ for ON.
Why can't we apply this input directly to the gate? I mean removing the resistor \$R_G\$ doesn't seem to ...
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Why are regular diodes designed with ideality factors \$n\gg 1\$
(The question is at the end of the text.) In have a recurring application, where I want to clamp ESD strikes into a sensitive high-impedance into a guard node using antiparallel diodes.
simulate this ...
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What is the best way to find an RF FET device for a design?
I'm searching for a jfet or mosfet for a receiver front end, but there doesn't seem to be many options. Everything I find seems to be obsolete. The closest thing I've found to a component that matches ...
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JFET- circuit. Uds and Id dependency?
For a lab assigment I did measurements with the oszilloscope for the circuit below containung JFET BF245A.
I obtained those curves for Id (drain) in relation to Ugs (gate-source) for the Uds (drain-...
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Electret microphone: convert sound to current or resistance?
See this picture (from Wikipedia):
The electret microphone consists of a capacitor with a static charge and a JFET. I wonder how the electrical signal relates to the sound signal.
I understand that ...
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Why are JFETs used in voltage-controlled resistors instead of MOSFETs?
Voltage-controlled resistors (VCRs) are usually implemented using JFETs. JFETs are less common than MOSFETs, so, why not use MOSFETs in VCRs instead?
They both feature an Ohmic region.
Is this because ...
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Is the BS170 MOSFET the right candidate for the task?
I have 2 FETs in my arsenal, the BF256 and the BS170 and I want to reset an opamp integrator.
Is the BS170 the right part for the task? The datasheet doesn't tell a lot, except it seems to have "...
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Do the depletion regions meet during pinch off in JFET?
In an N-channel JFET, when the voltage across gate and source terminals is 0V and the voltage across drain and source terminals is increased, at a certain voltage (pinch off voltage), the depletion ...
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Adjustable voltage, 1 MHz capacitive biasing
I'm a budding physicist with little electronic design experience and am interested in driving an alternating E-field of adjustable strength within capacitive loads.
Buying a several thousand dollar ...
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Is my summary of transistor behaviour (on or off) in saturation mode correct?
In the following Table, I made a summary of my understanding of the configurations in which the various sorts of field-effect transistors are on or off, in saturation mode.
Is my summary of transistor ...
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Is the power consumption of field effect transistors lower than that of bipolar transistors, and why? [duplicate]
Is the power consumption of field effect transistors lower than that of bipolar transistors, and why?
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What is a suitable equivalent to 2N5459 JFET? [closed]
I am attempting to build an audio limiter circuit which has a JFET as part of the BOM. This JFET is obsolete and no longer manufacturered. Can someone recommend an equivalent JFET or a way of ...
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In a JFET, is the gate *always* connected to the bulk/substrate?
In a JFET, is the gate always connected to the bulk/substrate ?
Or is there "no rule" (sometimes it is, sometimes it is not)?
And what about the case of the MOSFET ?
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What happens when an audio JFET amplifier receives signals from two microphones?
I have seen this JFET amplifier circuit in my notebook.
It is very possible that it isn't a practical amplifier and that they just tried to teach me about JFET applications, but I have two questions ...
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Proving that this JFET + Bipolar source follower give back a linear output
I was reading about this source follower and wondered how the bipolar transistor makes Vgs somewhat stable.
I believe that what happens here is that when Vin is high more current flows through the ...
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Are there two sorts of *geometry* of JFET?
In some schematics of JFET, we see in the geometry that the source and drains are perpendicular to the position of the gate.
Example :
https://en.wikipedia.org/wiki/JFET
In some schematics of JFET, ...
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Where can I find the symbolic symbols of various bipolar, JFET, MOSFET in a *unified* style?
Where can I find the symbolic symbols of various bipolar, JFET, MOSFET in a unified style ?