Questions tagged [fet]

Field Effect Transistor, a transistor in which most current is carried along a channel whose effective resistance can be controlled by a transverse electric field. Commonly used types of FETs include the Metal Oxide Semiconductor FET (MOSFET), and less common in recent designs, the Junction Gate FET (JFET or JuGFET).

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How would one calculate the transconductance of the FETs in this circuit?

I was given formulas to find the transconductance (gm) of the FETs using IDSS, VP and VGS, however, none of the ways I tried them leads to the correct answer (given as 2,55mS).
423 views

Why do some JFETs oscillate and others don't?

Below is a simple JFET Clapp Oscillator, which works quite well. It starts oscillating at around 40us and gets into clean, stable oscillation by 100us: When I replace the J309 JFET with a more ...
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MOSFET feedback mechanism

I made an simple feedback circuit. R2 and R3 is voltage divider there so I'm setting them sufficiently big values. But in this setup, it works with 2N7002 and not IRFZ44N (gain is way less then I set ...
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Sure, here's your question translated into English: I'm working on developing a DC electronics load that I intend to discharge at up to 30V and 60A. For this, I'm using the FBSOA MOSFET IXTN200N10L2, ...
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What is the difference between using op amp and transistor for small signal amp? [closed]

I have a question. As you know, not only the transistor can be used for switching level or amplifying small signal (single or multiple stage design), but also op-amp can be used in same purpose. So ...
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is Vov of a nMos always VGS - Vt?

Looking at this graph from Analog Circuit Design Discrete and Integrated by Sergio Franco, is it always true that Vov = VGS - Vt? or is this only true at pinchoff point?
488 views

Using an N-channel FET as a switch

I want to use an N-channel FET as a pass gate SPST switch to let an FTDI reset signal through to to my microcontroller or not, based on an independent signal. simulate this circuit – Schematic ...
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LED indication for driven n-FET inputs

Given that I'm using a microcontroller (e.g. an ATtiny85) output pin to drive the gate of an n-channel FET (e.g. NTMD6N02R2G) acting in the role of an SPST switch, is there any issue with either of ...
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Small signal equivalent circuit of multistage amplifier

I've been trying to draw the small signal equivalent circuit of this circuit and derive the expression for voltage. Using the equivalent circuit I drew, I derived the voltage gain expression but I got ...
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Do FETs need to be biased?

From my knowledge, BJTs need to be biased to control its linearity and gain, usually with resistors on the base and collector. Suppose I want a FET in saturation acting as a high-side switch. Do FETs ...
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AC analysis of a Bias Tee

I am designing a bias tee here and wondered whether it actually works or not? Hence I conducted an AC analysis instead of S-parameters (after verifying that s parameters are okay). The bias tee has ...
170 views

Where is the body terminal of a FinFET connected usually in digital circuits and in analog circuits?

What is the usual practice in industry regarding the body terminal of a FinFET? Is it connected to the source to eliminate body effect? Or is it connected either to the ground(nfet) or the supply(pfet)...
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FET turn-on time in DC-DC converter

I am selecting a GaN FET for a buck-boost DC-DC converter application. The Vgs of the part I'm looking at combined with the gate charge and gate resistance lets me switch the FET on in about 5.3 ns. ...
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Difference between Kelvin and Celsius in dynamic thermal behavior of MOSFETs

I am trying to understand the temperature behavior at the junction level and this Application Note "AN_201712_PL11_001" from Infineon describes the process. The problem is that I have a hard ...
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Difference between IGBT and FET+BJT

What are the practical differences between a true IGBT and a combination of FET and BJT, apart from a more efficient production and packaging? Can I obtain a device of comparable qualities to IGBT if ...
91 views

op amp positive feedback Schmitt trigger

I have recently come across the op amp Schmitt trigger presented in 3rd edition art of electronics. I decided to build the circuit myself in circuit lab, and I have some questions regarding its ...
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High-side switch on N-MOSFET for 1-Wire

I have two devices that both control 1-Wire data line: The system is designed in a way that only one of devices will be working and another will be in power-off state. When device is turned off it ...
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Numbers on a Field-effect transistor

I'm looking for a transistor and managed to find a number of them online however there is also a number at the top which I don't know what it means. i.e this is what I found online: https://m.media-...
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How Series FET connected opposite to each other operates? [closed]

Two FETs are connected in series opposite to each other. See the following circuit diagram. I am confused here that when both FETs are turned on, How does it allow current to flow? but in the ...
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Transformer-coupled low noise amplifier

A rather common way to make a low noise amplifier with an equivalent input voltage noise density in the range of ~0.1 nV/rtHz, is to take a FET and place a step-up transformer in front of it. I have ...
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How can I identify an IC marked '32D FD'?

I need to find the IC name of this marking number. It looks to me SOT-23 package. It is most probably an FET IC used for PWM dimming control of an LED driver. I am attaching LED driver schematic from ...
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MOSFET current direction

What is the direction of conventional current in a N-Channel MOSFET? What I think is it's from Drain to Source inside the transistor which means externally(in the external circuit) it will be the ...
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I'm working on improving our system's mechanical brake control mechanism. Currently, the brake is controlled by relays, but there are issues with oscillations (because it is a sudden and not smooth ...
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What would happen to the drain current of a D-MOSFET at cutoff voltage when we are going to plot the tranconductance curve?

Here, $$I_{DSS} = 8 \,\textrm{mA}$$ $$V_P = -6 \,\textrm{V}$$ Equation for the drain current, $$I_D = I_{DSS} \left(1 - \frac{V_{GS}}{V_P}\right)^2$$ So, the cut-off voltage is where the Drain ...
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Pull-up resistor is running slowly (inverting MOSFET circuit)

There's a problem with my fan control circuit. It works well, but when I first power up the circuit, the fan runs for about 0.2 seconds. The reason seems to be the time until the pull-up resistor is ...
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FET driving by NPN issue (PWM)

I am having a few problems regarding a simple FET PWM driver. I am aware this circuit does not adhere to the best design practice, but I am in a situation where the design cannot be changed. I have ...
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Connecting FETs to make a push pull GPIO

We have a circuit that generates pulses via GPIO. We use FETs for the push-pull mechanism. Our schematic: Description of the ...
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To BJT or not to BJT: That is the question [duplicate]

Practically speaking, when is it better to use a BJT vs a FET for swtiching (not as a linear amp)? Given that FETs have both N-channel and P-channel forms, and BJTs come in NPN or PNP, it seems that ...
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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 ...
168 views

How to choose a "good" 3.3 V LDO and FET for low power applications?

I am trying to design my first low-power PCB using an ESP32 to switch a 12 V 1.2 A LED Strip. I purchased this module that charges a Lithium battery using a solar panel here. Hence that is where the 5 ...
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FET AM modulator

I have been meddling with a FET-based AM modulator. I implemented a basic circuit as attached here along with its output. Is the output as it should be? If not, what am I doing wrong, and how can I ...
481 views

Using a Zener diode MOSFET gate voltage control circuit

I have a little problem with my simple project. I want to control a 24V / 4A blower motor. It works okay, but the MOSFET gets too hot. I used a Zener diode to make the gate voltage above 12V, but it ...
1k views

FET amplifier from 100 kHz to 100 MHz

I studied electronics a long time ago (and forgot almost everything) but now I would like to make a FET amplifier up to 100 MHz of extremely small signals (e.g. 1nV or even smaller.) The signals are ...
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PMOS with floating source

I'm trying to understand this example schematic from the LTC4007 datasheet. It all makes sense for the most part. My question is around Q1, which is a PMOS. When ...
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Electret condenser bias voltage

I have an electret condenser from PUI Audio (https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf). The Vs is recommended to be 3V but my circuit and only supply maximum of 2.5V. The ...
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48 V phantom power backup: switch off the 9 V backup battery with FET

I found this device here on the site. I need something to switch to a 9 V backup battery when there is a 48 V phantom power outage. How can I change the FET to switch OFF the BAT1 (9 V) backup battery ...
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Transfer characteristics of a Toshiba DMOS FET

I am looking at the TBD62003A load driver, but it is very light on details about transfer characteristics. Are there characteristics curves available from a similar device? Specifically, I want to ...
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Calculating CMOS threshold voltage

I found this solution in a textbook, and I do not understand how they calculated Vth2 (typo written as 'Vth' at the bottom). More specifically, where does the 2Vm come from? I understand that Ids1 = ...
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Possible FET with SMD marking 2YJ33

I need to replace a SOT-23 SMD transistor with the marking 2YJ33 (image attached Q1 and Q2). Any idea what it could be?
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0-10V LED driver dimming with Raspberry Pi and FET

I'm a beginner, so please be gentle! I'm trying to dim the linked LED light fixture driver using a Raspberry Pi (RPi). I want to dim using PWM in conjunction with a FET. Before dimming I am trying to ...
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117 views

Is there a microscopic oscilloscope probe?

Does such a device exists to measure voltage and current in 14nm and below semiconductors?
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Mosfet Rdson inconsistency in datasheet? Or conceptual error?

I was checking the datasheet for the Allpower AP2012S and while checking the graphs to determine the Rdson in my point of operation I found what I think might be an inconsistency, however, I wanted to ...
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Controlling external device by tapping into existing transistor

I'm working on one project where I cannot figure out on how I can control my external device by tapping into some home appliance. Just to note, that I have very limited knowledge of electronics and I ...
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Help solve rds for pchannel FET from this datasheet

I would like to use a pchannel FET as a voltage controlled resistor in a circuit where my voltages are between 0 and 1.1 Volts. I'm hoping to use the J175 but truthfully I am having a difficult time ...
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Is it possible to make an OFET in a home lab?

Is there a way to build an OFET at home? (low tech, no deep vacuum and plasma, without toxic/hard to dispose chemicals) What can be the minimum budget for that? While conductive polymers are pretty ...
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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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Picking a FET for Logic Level

I've always been confused when picking a FET to be used for logic level signals. There are so many factors to look at for FETs, I get overwhelmed. In this case my supply voltage will be a 3 alkaline ...
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Which MOSFET should I use for high-voltage inverter circuit [closed]

I have an inverter circuit with 2 MOSFETs alternating, a capacitor, and a couple of resistors. When I supply 5 V I can see a high-frequency square wave, given the capacitor and resistors values. When ...