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.

Filter by
Sorted by
Tagged with
0
votes
3answers
164 views

Junction Field Effect Transistor

In terms of drain and source current P-channel JFET is similar to which BJT ? npn or pnp? kindly tell me about BJT's and FET's relation?
2
votes
1answer
171 views

DC-circuit with N-JFET transistor

My task is to decide RD and RS in this circuit: The properties of the N-JFET are Up = -3.5V and IDSS = 10mA. The criteria here is that the operating point should give UDS = 7V and ID = 5 mA. With ...
1
vote
2answers
711 views

JFET hidden wires detector

I want make hidden wires (AC, 220V) detector (circuit is below), based on Soviet p-channel JFET transistor КП103, but JFET's now is very rare. Can i replace this JFET by any low-power MOSFET? My ...
-1
votes
3answers
18k views

What is meant by pinch-off voltage? [closed]

When I read about junction field effect transistors I always get confused about pinch-off voltage in junction field effect transistors. Please explain what this is.
0
votes
1answer
2k views

Time domain of a Sine wave?

I am working on a lab in school with a common source JFET amplifier, and I needed to express \$v_{out}\$ in terms of time domain. If \$f\$ is the frequency and \$T\$ is the period, then I need $$v_{L}(...
1
vote
1answer
3k views

Replacement of 2N3822 and 2N5640 for a 0-12v adjustable power supply

I'm trying to make an adjustable 0-12v 0-500mA power supply. I'm using the following schematic as a base (I modified the 240Ohm resistor between Vout and Adj of LM317 2, and the RSC resistor): The ...
6
votes
1answer
5k views

VCA Using JFET and Op Amp

Just messing around with LTSpice I came up with this VCA that simulates shockingly good for what it is: I don't recall ever seeing the use of an op amp to mix the signal and control voltage in an ...
2
votes
1answer
1k views

Electret Mic Circuit Using JFET Bootstrap

I thought this circuit was clever so I'm sharing: The JFET current source is bootstrapping the electret and thereby providing 20dB of linearized gain. The bootstapping network also provides for some ...
0
votes
1answer
3k views

characteristics graph

I'm currently learning about Field Effect Transistors in my college class. And I'm having trouble understanding how to properly read characteristics curve graphs. I'm sure it's relatively simple, but ...
1
vote
2answers
9k views

Why can't I swap a TL071 with a 741?

I constructed this circuit as shown for use as a simple headphone amplifier. I was so happy with myself that I made a second one for stereo, as well as using a 3915 to make a very simple volume ...
5
votes
3answers
4k views

Why are MOSFETs used for VLSI IC fabrication instead of JFETs?

Why are MOSFETs used for VLSI IC fabrication instead of JFETs? What are some reasons the use of JFETs is not common?
1
vote
3answers
442 views

Audio FET Buffers and Negative Feedback

I am struggling to come to term with how negative feedback helps widen the scope of input signals coming into FETs (or OpAmps for that matter, but I am using J201 JFETs). I am aware that the largest ...
3
votes
1answer
8k views

Comparison between MOSFET, MODFET, and MESFET?

I am taking a course on semiconductor physics and am learning about MOSFETs, MODFETs, and MESFETs. I know the general structural differences between each one. A MOSFET is a metal, oxide, and ...
0
votes
1answer
1k views

Universal Voltage Divider Bias Circuit with both BJT and JFET

I am dealing with the following circuit: I am trying to understand if I can just assume that, much like in the JFET voltage divider circuit, V_G = 10/(40+10) * 16V , or if the presence of the BJT ...
0
votes
2answers
1k views

What is the output of a JFET op-amp?

I am trying to understand the way a JFET op-amp works. I have a circuit like this: You can see the LF347N chip I am using. The IN+ terminal is connected to a TTL switch providing 0V or 5V. The VCC+ ...
0
votes
1answer
2k views

P-channel JFET gate voltage

DC Circuit I drew this to try and understand why the gate has voltage on it when SW1 is closed. All I'm trying to accomplish is that when the gate has 0V, the 14V supply is connected to the 10k ...
6
votes
1answer
674 views

Role of capacitors in electric guitar's output to phone mic input converter

I want to build this electric guitar output to phone mic input converter: (source: altervista.org) From my limited knowledge on the subject, it looks like a simple JFET preamplifier (actually, I'...
0
votes
2answers
99 views

Is this node grounded?

I'm investigating a circuit with transistors. Below is part of the circuit where a JFET has been approximated with its g-parameters. The circuit continues to the left and right but that isn't relevant....
0
votes
1answer
2k views

Do P-channel JFET current go from source to drain?

For an N-channel JFET transistor, current moves from drain to source. I've read that a P-channel JFET works similarly, but with the voltages reversed. Does this mean that its current travels from ...
5
votes
1answer
1k views

Is operating point calculation the same for P-JFET and N-JFET with voltage-divider bias?

I've seen this calculation of operating point for N-JFET: Together with the relation \$I_D = I_{DSS}(1-V_{GS}/U_P)^2\$, it is possible to find \$I_D\$ and \$V_{SD}\$. This method doesn't take into ...
2
votes
4answers
2k views

Direct Coupling and No bias on JFET guitar preamp's

Why some of JFET preamp's for guitars don't bias the gate to Vgs(off)/2 and just reference it to ground? (Setting Zi) This also lead to just direct coupling the guitar output to the gate. As far as ...
3
votes
3answers
4k views

How can I make a simple voltage-controlled attenuator?

Having discovered just how awful the AC ripple is on some of my 5VDC wall-adaptors, I decided to make an Arduino program to calculate the RMS AC component and DC component of an adaptor under varying ...
0
votes
1answer
1k views

FET with high current ( power JFET) low VGSoff

I am looking for a N- channel JFET part number with IDmax > = 800 mA and low VGS(off) < -15 volts. I dont focus on the frequency As an inherent charactristics of JFETs is high working frequency ...
2
votes
1answer
2k views

Derivation of I_d of a self-biased JFET

I find that derivations of formulas are a lot more useful to me than just recitations of formulas. I'm looking at a self-biased JFET circuit, and I'm interested in deriving the quiescent state of the ...
9
votes
4answers
1k views

Is there a modern discrete component alternative to the JFET as preamplifier?

Please consider this schematic of an electret microphone capsule: (Source: Wikipedia) While considering something similar for signal conditioning of a 20 mVpp, 3k impedance output from a piezo ...
-3
votes
1answer
1k views

Electronics Books [duplicate]

I am earching for a good book for electronic devices and circuits. Details about 'dc' as well as 'ac' biasing are what I am interested in. If you could guide me to a good book, it would be wonderful. ...
1
vote
1answer
382 views

Measured VS Ltspice Difference in P-Chan JFET Attenuator

The following circuit is a slow switching +-15V audio signal attenuator: Why are the measured voltages (shown in white boxes) so different from the SPICE values (shown in the graph)? Note that ...
5
votes
3answers
4k views

Is it possible to design an amplifier with a given gain from a random discrete JFET?

A few weeks ago, I played around with a discrete JFET bass preamp design I found online (http://www.albertkreuzer.com/preamp.htm). One thing I realized from analyzing the circuit, running simulations ...
1
vote
1answer
844 views

How can you assure JFET Q-point?

As Beta changes from BJT to another, Vp and Idss also change from a JFET to another, but how can you assure that when the JFET changes, the Q-point does no change greatly?
2
votes
3answers
2k views

Bipolar Op Amp w/ Near Zero Offset?

My understanding is that if source resistance is low, a bipolar op amp has 10dB less noise than a JFET. I prefer the JFET op amps because the input offset is so low that you can eliminate coupling ...
0
votes
3answers
2k views

N-channel jfet fixed bias with high gain = 200

simulate this circuit – Schematic created using CircuitLab I would like to know if it is possible to produce an n-channel jfet connected in fixed bias configuration with a high gain of 200. If ...
1
vote
1answer
281 views

Turning the PN junction of JFET on?

I am going to use a N channel JFET as a normally-ON switch. I am wondering if it would cause any problem in the long term reliability having the PN junction forward-biased. In other words, would it be ...
3
votes
1answer
3k views

Depletion region in JFET transistor?

In this diagram of JFET transistor the depletion region is narrower at one end and wider at other end. Why is that so? Is it due to the voltages applied at gate and drain?
1
vote
5answers
10k views

Fet is named field effect transistor,why?

FET is named Field Effect Transistor while field effect is also producing in bjt. What are the factors/reasons that FET is called field effect while bjt is not? I have read textbook but it didn't ...
4
votes
2answers
305 views

odd JFET configuration

I was looking at figure 33 of the OP77 datasheet, and the JFET labeled D2 has an odd connection. Based on the way the circuit works that JFET must be a diode right? So why is the JFET connected as it ...
9
votes
4answers
27k views

Why JFET is called a voltage controlled device while BJT is called a current controlled device?

Why are JFET/FET called voltage controlled devices while BJTs are called current controlled devices. Both require a voltage to operate properly. In both an electric field is produced so what is the ...
7
votes
3answers
16k views

Why are JFET transistors used in circuits with high input impedances?

I read an introductory textbook to understand this but it doesn't tell the reason behind it. Is that because the JFETs require much less voltage to operate comparing to BJTs and one needs to drop ...
4
votes
2answers
4k views

Is pinch off voltage of JFET constant?

The drain current is related to gate to source voltage by the following equation: \$I_d = I_{dss} (1 - \frac{V_{gs}}{V_p})^2\$ Now, with changing \$V_{gs}\$, I think \$V_p\$ also changes. I am ...
8
votes
2answers
29k views

How to do a simple overcurrent protection/circuit breaker circuit for 12V 1-2A?

We're developing an I/O shield for Arduino (sort of) and having four FET controlled output connectors with approximated 12V 1-2A load each. I need all these four outputs to be short-circuit protected ...
8
votes
1answer
3k views

About JFET polarity

I often see the internal schema of a JFET transistor and it always look symmetrical. N-type channel that connect the drain and the source and P-type semiconductor on the gate for a N-JFET. I know that ...
34
votes
2answers
3k views

What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?

For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the on-...
3
votes
1answer
2k views

What's the 2N3904 / 2N3906 FET equivalent?

Is there a generic low-power switching FET that's multiply sourced, generally readily available, most simulators already have models for, etc.? I'm not looking for FETs that have similar electrical ...
20
votes
6answers
5k views

I don't quite understand this FET-BJT preamp circuit

I see this circuit a lot on electret microphone preamps, but I don't quite understand it. The FET is operated as a common source amplifier, so it has gain, inverts, and has relatively high output ...

1 2 3 4
5