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.
Questions tagged [jfet]
316 questions
8
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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 JFET have a polarity but since the schema is…
mathk
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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 voltage at the input? I'm a bit confused.
user16307
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Two JFET circuit
I have come across this circuit with two JFETs as shown below. Does anyone know what is the purpose of these two JFETs?
user42423
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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:
(source: prenhall.com)
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 account that it's a N-JFET.…
Anna
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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 is in the figure?
David
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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 are susceptible to damage from forward…
MattHusz
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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-\frac{V_{GS}}{V_{GS(OFF)}})^2 \$
\$V_{GS} = -I_DR_s =…
across
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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 – Schematic created using CircuitLab
With power off,…
AaronD
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JFET Source follower input impedance
I want to derive the input impedance of this JFET circuit :
simulate this circuit – Schematic created using CircuitLab
What is the method in order to derive the input impedance of this circuit?
here is the small signal but I haven't been able to…
exolune
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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?
Leo
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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 MOSFET datasheets to determine substitution…
nsayer
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Transfer characteristic of JFET
I read that in transfer characteristics of JFET, Vds is kept constant and Vgs is varied. But when Vp for any device is constant and Vds is also constant then even Vgs should be constant.
Krishnpriya Sinha
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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?
Anas Elgaood
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What JFETS are used in electret mics?
Electret mics supposedly use current of 0.5mA to 1.5 mA. In all JFETs the current at VGS = 0V is around 10mA. What JFET is then used in electret mics to be able to be powered by a laptop for example at 0.5mA ?
LEXOR AI
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What would happen if I left the gate open in a self-biased JFET circuit?
In a self-biased JFET circuit, the gate voltage must be approximately zero so that the reverse voltage at the gate-to-source will be equal(but negative) to the voltage across the source resistance. This can be achieved by putting very large…
hontou_
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