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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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GAN FET gate current requirement

I'm looking for advice in making sure the FET driver I've chosen is capable of driving the FETs I've chosen with turn on time as low as possible. I'm going to use the LMG1210 and EPC2020 with 12V ...
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P-Channel MOSFET Flipped on Schematic

I'm designing a circuit which has a bluefruit nrf52832 micro controller built into it. When referencing the schematic provided by Adafruit I noticed that they had +VBAT going to the drain of the p-...
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LED drive circuit (PFET) turning ON by itself

I thought 10k pull-up would prevent LED from turning on, but when I connect +VBAT (4V) and have D_LED_S_W floating the LED turns on slowly (in few seconds). When this happens the gate voltage starts ...
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BeagleBone Black Driving NFETs w/GPIO

In short, I want to drive some NFETs directly from some of the BBB's GPIO. 3 of the NFETs will pass 1-3 Amps of D-S current and 1 NFET will pass <1 Amp from the D-S. As you may know the BBB's ...
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37 views

How does the current pass through FET when its gate is unbiased/grounded in AC analysis?

My first question is how does the drain voltage increase V(drain) when the source voltage V(source) is increased for the below common gate FET: And secondly and most importantly in AC analysis they ...
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15 views

Profet Smart Highside Power Switch Output Always 'High'

I bought the Infineon Smart Highside Power Switch - PROFET BTS442E2, in order to switch a ~16V supply using a logic level PIR sensor. BTS442E2: http://www.mouser.com/ds/2/196/Infineon-BTS442E2-DS-...
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261 views

Why are the advantages of JFET over MOSFET, or why are JFET still used?

I saw JFET in an electret mic circuit, and it is quite recent, so I'm wondering why. Since we are looking for the highest gate impedance, MOSFET would seem to be a better choice. I've also read that ...
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Why does a single AND gate need 60 transistors?

Looking at the datasheet for the MC74VHC1G08, under the features section, it states Chip Complexity: FETs = 62. Why does this IC need 62 transistors, while an AND ...
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Weird FET results for noob

Wisdom states that the load is connected to the drain, and the source connected to pos or 0v dependant on P or N channel. However ... I have a "2N3820" (a p-channel in TO92 package), so pin out (...
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54 views

P-channel FET and CNY17-3 opto isolator

Long story short, I want to have a relay turn OFF when the output of a 4017 goes high. So I installed an opto-isolator, connecting the LED to the output of the 4017, ie "on" until the ouput goes high....
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57 views

Simple push-pull problem

I've made a circuit based on the schematics below, which works fine at simulation. The goal is to add some extra oomph on the output of a LT1210 opa (V1) to drive a piezo element at higher voltages ...
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69 views

Converting a non-electret condenser microphone circuit to electret?

I'm trying to convert an MXL 603s circuit, which has a non-electret capsule, to an electret version. I'm pretty certain that the only real difference between the two would be the fact that the non-...
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59 views

Why is this transistor failing?

I have a Sharp LC-19SB24U Monitor that tends to blow a fuse on the power supply. Every time it does, the FET (FQP8N60C) has also gone bad. So I replace the FET (with thermal paste) and the blown ...
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388 views

Logic-level converter FET

I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side. ...
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JFET Voltage Divider design question

I've been trying to get this question done for a couple of days now and no matter how much I try I've been unable to get it done. Your help in this question is greatly appreciated.
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188 views

how to reduce current to power LEDs

I am replacing a microscope lamp with a motorcycle LED headlight. The light is 20W, 9-85V DC; the driver built in and a complete black box to me. I power it with a 65W power supply (18.5V/3.5A). For ...
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108 views

Voltage drop when switching FET

I am working on a project which will be switching LED strips with a max of 2A. As a test I have connected a 20W hallogen light. When I try to switch it I get a voltage drop as can be seen in the ...
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35 views

replacing obsolete HEMT and differences between Package/Case and Supplier Device Package

I've been designing an amplifier, with ATF33143 as my HEMT in mind. Yet, I just found out the said HEMT went obsolete. So I started looking at SKY65050-372LF as a possible replacement. On the DigiKey ...
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146 views

Why does a MOSFET enter saturation?

From all my browsing, it has become clear that as drain-source voltage increases, we eventually reach saturation. Mathematically, Vds>Vgs-Vt is the condition we look at. But when I try to understand ...
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2k views

Is it good practice to run large amounts of current through a MOSFET?

I have been looking for a good way to control the flow of a lot of current in my project. This may at some points be 40-50 amperes at 12-15 V. While relays are a good choice, they are mechanical ...
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71 views

Filtering current spikes in photodiode transistor selector

I am building a circuit for sensing photocurrent from a photodiode. The diodes are manufactured with selection transistors to form an active matrix and below is a model of a single pixel consisting of ...
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2answers
151 views

Momentary Switch NAND Latching IC Burning and (Possibly) Faulty Logic

Problem: My issue is that the momentary switch with NAND latching logic that I have designed is not functioning consistently. It does work as intended at first, but then fails to work after repeated ...
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116 views

JFET saturation current

Is it possible to analytically calculate Idss for JFET? I tried by setting voltage gate-source to zero, and then finding the drain current, but it doesn't seem to match with the given value?
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124 views

Start/ stop 5v motor from headphones jack

I would like to make the jaw of a plastic skull open/close based on words spoken by a Raspberry Pi. I can make the Pi send the audio to the headphone jack, and would like to use this output to run 5v ...
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69 views

What is a good Field-Effect Transistor Model?

Hi guys I'm writing an electronics circuit simulator and I need a very simple and straightforward model for a field-effect transistor (as simple as the Ebers-Moll model for a BJT). I can use resistors,...
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100 views

What kind of diode should I use across the load?

I'm designing a circuit using an ST VN7020AJ high side driver. The application diagram recommends placing a diode from VCC to ground. The document doesn't provide any recommendations on the type of ...
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30 views

How to do thermal analysis of a P channel high side drive circuit.

I have to design a PCB where one of the features is such that every time a stepper motor is moving a fan switches on. A high side P channel FET driver has been suggested as shown below: I just need ...
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71 views

Transfer function of loop-back bias circuit for RF amplifier

I am trying to implement a current mirror as part of a bias circuit for a RF amplifier. I want to do a transfer function of the bias circuit since it creates a loop from the amplifier fet drain to ...
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1answer
245 views

Negative Gain and in a common gate FET amplifier [closed]

We conducted an experiment involving frequency response in common gate FET amplifier. The results at different frequencies from 10Hz to 1MHz are obtained and we got a negative result in the first few ...
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1answer
135 views

What is the purpose of this FET load?

I'm used to seeing a load resistor in the place of the yellow highlighted (Q2) section of this FET amplifier circuit. This is the input section of a guitar overdrive effect, so any distortion created ...
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4answers
359 views

FETs: When does Input Capacitance and Gate Charge matter?

My question is this: Besides frequency response (i.e. filter effect), does input capacitance every matter? When does gate charge matter? Obviously these have effects on the graphs in the datasheet, ...
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74 views

Current consumption of PWM controlled MOSFET [closed]

I'm trying to design an application in which a DC/DC converter with limited output current capabilities drives the gate of one or more transistors in PWM mode. My question is, how can I estimate the ...
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2answers
612 views

MOSFET with 5 V logic, 24 V VDS / VGSS

I am trying to select a MOSFET that will work as a logical switch on a 24 V power rail, toggling on/off as signaled by a GPIO on an Arduino. The Arduino pin that will connect to the gate on the FET is ...
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1answer
91 views

How to choose right transistor? [closed]

I have been trying to design a differential amplifier for EEG. How can I choose the right bipolar transistors and FETs according to my aims ? Any guide will be appreciated. Thanks in advance.
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2answers
88 views

Turn gate on and off while on rising edge of a signal

I am measuring a voltage which looks something like the positive half of a sine wave and I want to drive the gate of a FET while this voltage is inbetween two certain points. So for example the ...
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59 views

JFET I drain vs V gate to source curves

Why there are several curves on next image (datasheet for 2SK170)? What condition changes to use one or another curve?
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1answer
56 views

Power Amplifier inside an OPAMP

Here is a simplified schematic diagram of one of the operational amplifiers inside a TL08x. The Diagram I wonder why a power amplifier is used ? (on the right side) What is it good for ? Thanks in ...
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121 views

Is the FET gate resistance counted on the RC time constant?

As I understand, a logic "1" output to an input of another IC can be modeled like this : simulate this circuit – Schematic created using CircuitLab with C1 representing output capacitance, R1 ...
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146 views

Resistor Divider PMOS Example Problem

From Razavi's Design of Analog CMOS Integrated Circuits, question 2.6a asks to plot \$I_x\$ vs. \$V_x\$ as \$V_x\$ varies from 0 to 3 V in the circuit below. The solution manual states that: $$V_{sg} ...
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2answers
45 views

Can a ITS4100S-SJ-N High side power switch be used to switch AC/DC load

I have seen a PLC which uses the ITS4100S-SJ-N component to switch (just on/off) a 24V DC, 2A max. load. I was asking if those components can also be used to switch 24V AC? Datasheet: https://www....
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195 views

What role does a FET play when working with GPIO pins on a Raspberry Pi?

I recently asked this question where I'm trying to wire up this momentary switch to my Raspberry Pi 1 Model A such that: The switch is normally open; and When pushed down: it closes the circuit, ...
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1answer
28 views

MOSFET drain current parametrized to distance

In Id-Vgs Mosfet curves, sometimes, current is parametrized to a distance in micrometers. What is this parameter? Gate length, effective gate length, or width of the transistor.
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Current drop a certain vds in a transistor

I am measuring the I-V characteristics in a transistor using a 2 channel source measurement unit (SMU) when I change the \$V_{ds}\$ and measure the current while connecting the gate and the source to ...
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2answers
324 views

Can you turn on a NMOS with a lower voltage than at the drain?

So, a NMOS can be turned on if the \$V_{GS}>V_{TH}\$. If the circuit is such as below: simulate this circuit – Schematic created using CircuitLab So, say that the \$V_{TH}\$ is quoted as ...
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1answer
62 views

High Side Switch Flicker during Power Up

I have some problem with a P-channel mosfet used as high-side load switch. Everything works fine beneath the power up moment. You can find the schematic in the picture below. During Powering the ...
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1answer
123 views

Troubleshooting a PWM-field effect transistor driver board

I'm an untrained hobbyist trying to fix this motor driver circuit and was looking for some guidance or help with troubleshooting, or reconstruction. The circuit is from a handheld vacuum cleaner that ...
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1answer
360 views

Swap FET TO-220 pinout

I messed up my PCB design when I made a change of FET-model. Now the Drain and the Source pins are swapped and it seems that there are no TO-220 models made this way (1-Gate, 2-Source, 3-Drain). Are ...
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2answers
51 views

Need help finding the transconductance author of this book is referring to

I am reading a book "Practical Electronics for Inventors" and I was trying to understand the FETs, at several places the author has mentioned about the trans conductance that he has noted with gm. I ...
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841 views

Solenoid valve FET

I would like to drive a proportional solenoid valve (PVQ31 24V model from SMC) using a high frequency PWM. I followed Olin Lathrop's advice to open a new topic. He suggested to build a circuit ...
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88 views

What is the name of the maximum source to drain differential for a FET? [closed]

I'm working with high voltage, high power motor applications, and it's slipping me right now; what is the name for the maximum voltage between the drain and source of a FET? Edit: sorry for the ...