Questions tagged [mosfet]

An transconductance (using voltage to control current) electronic component used for switching and amplification. Acronym for Metal-Oxide-Semiconductor Field-Effect Transistor. (from http://en.wikipedia.org/wiki/Transistor)

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Why pulsed drain current is higher than continuous drain current in MOSFETs?

Why is pulsed drain current higher than continuous drain current in MOSFETs? In MOSFET data-sheets, pulsed drain current is much higher than (by at least 2x) continuous drain current. What is the ...
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Why does CircuitLab have the MOSFET symbols it has?

CircuitLab has [used to have -- they have changed their symbols since this question was asked] these goofy things: simulate this circuit – Schematic created using CircuitLab My eyes are much ...
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Why can't this circuit work for an inductive load?

I am using a similar circuit to speed control a 60 W AC fan using phase control. Unlike a TRIAC, supply to fan is given at the start of the cycle. I thought it would minimize the switching noise ...
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NMOS FET selection for reverse polarity protection

I am working on a reverse polarity protection circuit, similar to that in Figure 2 of SLVA139: Reverse Current/Battery Protection Circuits. Here is my circuit: My case is slightly more complex due to ...
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5V ups circuit oscillating?

I'm trying to design a 5V UPS. Power to load should switch if line voltage falls below about 4V. Battery voltage may be from 3.8 to 5V. I'm simulating in LTSpiceIV. I'll be using mosfets to supply ...
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Do AC inverter H bridges ever get driven this way?

There's a google competition going on at the moment called the little box challenge. It's to design a very efficient AC inverter. Basically the inverter is fed a DC voltage of a few hundred volts and ...
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Circuit Analysis - Function of BJT?

I am referring to the following AppNote from TI. What is the purpose of transistors Q3 and Q2? Is it to turn the PFET "hard off" when the controller isn't turning it on? Thanks AJ
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MOSFET Switch w/ Fast Settle Time for Switching E-Field

Application: I have a copper mesh (10cm x 10cm square) in a vacuum chamber connected to a BNC connector by a 24-cm-long copper wire. The goal is to switch the mesh voltage (referenced to ground) from ...
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GaN pulsed operation

Does anybody have experience biasing and pulsing a microwave GaN HEMT? I've just ordered a 10 Watt S-band transistor. I know all about bias sequencing. This application is pulsed. I've read about ...
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Wilson current mirror

I built a super wilson current current mirror. The Iin is 4-20mA at 24Vdc. Iin to Iout accuracy was a really bad 5%. I put 100 ohm resisters on the source to ground, and that helped a little. How can ...
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High side driver and Low side driver [closed]

Can anybody help me understand, what exactly a high side and low side driver is? In which scenario would either of them be used?
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p-channel MOSFET switch

I want to use a MOSFET as a switch driven by my microcomputer. The original circuit using N-channel MOSFET is on the left side. Honestly, I do not understand the choice of the IRLZ44. The circuit ...
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For 3.3V microprocessors, what's the best way to power the gate of a MOSFET?

The new processors are all 3.3V and dropping. So while I am used to 5V arduinos being able to power the gate of a MOSFET, at least most of the way, this is not going to be true any more. And for an ...
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How can I tell if a MOSFET is enhancement-mode or depletion-mode?

Today, from ignorance I have fallen head-first into the world of MOSFET transistors. In my scramble to find some information on the MOSFET I will be using as a switch (HEXFET actually), I learned that ...
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Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?

I have an STM32 MCU at home. I was thinking of controlling a load with this MCU and a MOSFET. Let's assume this is my circuit: In this circuit, we use a resistor (R2) to discharge the gate of the ...
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Simple MOSFET switch question

I have an application where I want to pass a current of about 300mA through a load, which should be turned on/off via a 3V/0V signal. I thought of using a 2N7000 as the switch and have it set up on a ...
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Difference between Mosfet and Voltage Regulator?

I'm new to electronics and was wondering what was the difference between a Mosfet and a voltage regulator?
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Mosfet Driver not driving mosfet

I have the following circuit: The MCP1402 MOSFET driver should be driving the BUK7Y13 N-channel MOSFET at 12V, but I'm seeing a much weaker signal which oscillates around 0.7V, preventing the gate ...
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H-bridge MOSFET voltage drop

After realizing the l293d output won't suffice and the voltage drop of the l298 is quite high, I believe learning to construct a simple H-Bridge to suit would be beneficial. Before starting with tests,...
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Level Shifting 1.8V to 5V with N-channel FET

I am using BeagleBoard-xM GPIO outputs to drive some DC motors with the help of L293D IC. The problem is that there is a difference between voltage levels. The GPIO outputs only supply 1.8V while ...
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Low Drain-Source MOSFET Leakage

I've been looking at the SM74611 Smart Bypass Diode from Texas Instruments and am very impressed with the reported reverse leakage current (0.3uA at 25C). Considering the device has a N-Channel FET, ...
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P-Channel MOSFET Drain-Source Polarity in Power Switch Application

I'm looking at using the LTC4412 power switch in an application. From the datasheet, here is the typical application circuit: : In the application circuit, an FDN306P p-channel MOSFET is used. I'm ...
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Effective MOSFET cooling

We need to drive a motor with around 40 Amps. The mosfet has an Rdson of about 7 mohms at 90 degrees Celsius. That is a whopping 11.2Watts of heat generated on the poor mosfet. We are very space ...
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MOSFET Difference between Normalised On Resistance and Output characteristics

In the datasheet for STP36NE06, it has two graphs which seem to contradict each other: In the graph on the left, for Vgs=10v and ...
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MOSFET Rds(on) question

I have a question related to the Rds(on) property of a MOSFET (IRF630N). Once the MOSFET is turned on (Vgs > Vth) will Rds(on) vary with the increase of Vgs? Or it is not affected by the gate ...
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Reverse polarity protection - PMOS vs Schottkey diode

I have a circuit running from 2 AA cells in series, meaning I get 3.0V when fresh (or 2.4V if NIMH cells) and it goes down to 2.0V, that's when my circuit cannot function anymore (no DC/DC onboard). ...
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Ideal component to switch 84V DC?

I wanted to control a 84V LED strip using a ATtiny13a microcontroller with minimal power wasted. I just want to turn it on and off, don't need any PWM dimming. The strip uses 270mA current and is ...
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How does power dissipation for surface mount components work?

I know that with usual through hole components we can attach heatsinks etc. But how does it work with surface mount components? Is having a copper plate around the component the way to go? How do we ...
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Why is this MOSFET burning?

I have a system that powers a transformer via a line to line power supply of 115Vac(L-N) for a total of 200Vac(L-L) In order to control the ON/OFF of the transformer, the NEUTRAL line is used to ...
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I was explaining a transistor to someone, and I realized: I don't really understand several key concepts at a low level. Help?

(Surplus story removed.) I was explaining MOSFETs, CMOS, and logic gates to someone and realized I didn't grasp some concepts as well as I thought. It culminated when he drew a single transistor, ...
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What happens when a MOSFETs gate is left open?

I was working with an interface with a MOSFET and I ran into a case where high impedence might be an input to the MOSFET's gate, essentially leaving the gate open. Would the MOSFET exhibit the same ...
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Boost SMPS getting very hot. Why?

I tried to experiment with boost SMPS with multiple supply rails and I almost burned myself when touching parts when running. Here is the circuit and the part getting hot: simulate this circuit &...
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Strange behavior from n-channel MOSFET

I'm using BS170 N-channel enchantment enhancement mode MOSFET and have the following circuit: The idea behind it is that the MOSFET should act as a simple switch and turn the LED on and off depending ...
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What parameters are to be considered when choosing a MOSFET?

I have a circuit that uses a MOSFET to heat a nickel titanium wire (by switching of course). But I don't understand why does it use IRF740 specifically. What parameters do we look into when choosing ...
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How to increase mosfet switching speed, and decrease switching losses?

I hope this is not a too broad question, but what are the best practices to achieve fast switching on a MOSFET driven by a PWM signal? My current knowledge tells me I can do two things: 1 - To use ...
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Why have a bulk terminal at all? (MOSFET)

I must be overlooking something but I really don't see the need to have a bulk terminal. I am studying the body effect whereby it somehow interferes with the threshold voltage. I don't fully ...
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Are MOSFET drains ESD sensitive?

There's a lot of post on here about MOSFETs and ESD sensitivity. But whenever the general question is asked, people always go straight to the gate and how sensitive it is. I've developed an LED ...
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Does voltage require a circuit?

I am just beginning to understand how electricity really works. I understand there is voltage, amps, and resistance. If electricity is water, voltage is like the pressure of the water and amps are the ...
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Is turning off MOSFET too fast, bad?

As far as i understand turning off a MOSFET too fast, is bad, as high drain-source dv/dt can cause ringing through: a) biasing Parasitic NPN and: b) charging the GS capacitor through DG capacitor, and ...
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USB / Battery Switchover Circuit

Background: I am a non-EE (an 0x11? :^) thrust into the world of embedded systems design. I started this project with a only college physics-level understanding of circuits, but I'm gradually learning....
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Switching a current with an NPN transistor and a P-MOSFET

Just learning about transistors and I'm trying to clearly understand how to apply them for basic switching, in terms of the two standard cases, i.e., Active HIGH behavior and Active LOW behavior. For ...
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Low threshold N-channel MOSFET

I have a circuit which does something not important, but it results in an output being normally low, and then on activation climbs to a little below Vcc. At the moment, it appears my Vcc is 1.8 V ...
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Advantages of depletion mode FET devices over enhancement MOSFETs

I've grown the impression that JFETs and depletion mode MOSFETs are not used very much nowadays, especially in new designs. I know that they need different bias networks, especially as discrete ...
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If MOSFET is a voltage-controlled device, then why do we need to supply it with high current when using in an H-bridge?

I might be confusing myself, but from what I am reading so far, a BJT is a current-controlled device and a MOSFET is a voltage-controlled device, which to me implies that a MOSFET requires very low ...
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What is the formal definition of Quiescent Point?

What is Quiescent Point? Is it necessary for it to be related with any V vs I , I vs I, or any such characteristic curves intersection point?
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Micro SD card power circuit failure

Description I am designing a system in which there's a circuit that controls the power applied to a micro SD card (enable/disable). The circuit is the following: The power control circuit is done ...
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Switching MOSFET from Raspberry Pi GPIO

I'm trying to drive a STP16FN06 from a Raspberry Pi GPIO pin but I'm a bit lost. The schema below represent (I think) how it is currently wired, on the left the RPi pin + ground and on the right a 5V ...
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Switch 5V with back voltage protection

I'm trying to develop a design which involves switching a 5V rail. The design goals are: As low cost as possible (i.e. Can't use a fancy integrated solution) Relatively low current handling ( ...
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Troubleshooting Strange Circuit Behaviour…Missing Diode?

I've built this circuit to control a submersible pump with a PIR sensor. The circuit works as expected (the PIR sensor activates the mosfet, turning the pump on) but only after about 30 seconds from ...
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A naive solar panel maximum power point control circuit

I am fooling around with a solar panel, just to try stuff and learn in the process (not trying to produce something I would actually use). Its placement is very far from optimal - vertically behind ...