# Tagged Questions

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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### What is the role of the capacitors C2 and C3 below?

I want to build this electric guitar output to phone mic input converter: From my limited knowledge on the subject, it looks like a simple JFET preamplifier (actually, I've simulated the circuit in ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### JFET “How to find resistance of the device”

I have this homework question that I can find one way to get the answer but I want to use a certain equation "attached" to find the answer also. I'm having a hard time understanding what to ...
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### 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 ...
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### 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. ...
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### 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 ...
501 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 ...
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### 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?
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### 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 ...
236 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 ...
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### 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 ...
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### 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?
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### Fet is named field effect transistor,why?

Fet is named field effect transistor 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 ...
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### 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 ...
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### Why JFET is called voltage controlled device while BJT is called current controlled device?

My question is why JFET/FET is called voltage controlled device while BJT is called current controlled as both required voltage to operate properly.In both electric field is produced so why is the ...
1k 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 ...
811 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 ...
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### 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 ...
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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 ...
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### 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 ...