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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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When to use what transistor

So there are several types of transistors: BJT JFET MOSFET Combine all that with the various flavors of each (NPN, PNP, enhancement mode, depletion mode, HEXFET, etc) and you've got a wide array of ...
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When is a MOSFET more appropriate as a switch than a BJT?

In my experimentation, I've used only BJTs as switches (for turning on and off things like LEDs and such) for my MCU outputs. I've been repeatedly told, however, that N-channel enhancement-mode ...
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MOSFET: Why the drain and source are different?

Why the drain the source terminal of the MOSFET function differently while their physical structure is similar/symmetrical ? This is a MOSFET: You can see that the drain and source are similar. So ...
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MOSFET as a Switch - When is it in Saturation?

I have the following circuit hooked up on a breadboard. I vary the gate voltage using a potentiometer. Here is what confuses me: according to wikipedia, the MOSFET is in saturation when V(GS) > V(TH) ...
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3answers
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Switching DC with MOSFET: p-Channel or n-Channel; Low Side Load or High Side Load?

I think, it is time I understand working principle of MOSFET transistors... Suppose that; I want to switch voltage on a resistive load by a MOSFET transistor. Any control signal between -500V and +...
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46k views

Calculating the pulldown resistance for a given MOSFET's gate

I searched and read many similar questions, but did not find a specific answer for how to calculate the correct value for a pulldown resistor for a MOSFET's floating gate. It seems like everyone ...
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2answers
27k views

Selecting a MOSFET for driving load from logic

I'm looking to drive a magnetic door lock from an Arduino. I've found a question about driving a solenoid from an Arduino, which includes a circuit that looks perfect for this kind of situtation: ...
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6answers
10k views

Designing a *linear* MOSFET driver stage

I'm looking for a MOSFET driver circuit that can be placed between an op-amp and a power MOSFET to operate the transistor as a linear amplifier (as opposed to a switch). Background I'm developing an ...
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5answers
25k views

Is there an ideal PWM frequency for DC brush motors?

I'll be using a microcontroller to create a PWM signal for motor control. I understand how PWM and duty cycle works, however I am unsure about an ideal frequency. I do not have my motor in yet, so I ...
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1answer
22k views

Is my MOSFET-based bidirectional level shifter insane?

In a moment of cheapness, I decided not to order a 5v to 3.3v level shifter from Sparkfun, but instead to put it together myself. The original schematic used a BSS138 MOSFET, but since I enjoy ...
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5answers
3k views

Help learning from a mistake connecting an oscilloscope

I have built this circuit to dim a lamp with a PWM signal. It had an issue where the MOSFET was getting really hot. So I wanted to know what was happening on the gate of the MOSFET. I turned the PWM ...
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MOSFET symbol - what is the correct symbol

I've been on this site now a couple of months and I notice various symbols used for MOSFETs. What is the preferred symbol for an N Channel MOSFET and why?
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Is it safe to drive a MOSFET from an output pin of a microcontroller?

I have used commonly-available BJTs such as the 2N2222 and 2N3904 as switches by operating them in "saturation mode" from my MCU. I believe, however, that for these sorts of applications, a MOSFET is ...
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3answers
5k views

Why am I cooking MOSFETs?

I've made a very simple MOSFET LED driver that uses the PWM of an Arduino Nano to switch a MOSFET which controls the power for about 16 meters of LED strip. I am using STP16NF06 MOSFETs. I am ...
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3answers
68k views

How to drive a MOSFET with an optocoupler?

What's the proper schematic for driving this MOSFET from a microcontroller pin through this or this optocoupler? The MOSFET will drive a motor @ 24V, 6A.
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mosfet usage and p vs n channel

i'm trying to use an arduino to enable/disable a 12V solenoid. I used an h-bridge and got that working fine. Then, I decided to simplify things and get a single mosfet instead of a multi-channel h-...
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2answers
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Criteria behind selecting pwm frequency for speed control of a dc motor?

I'm working on a speed control circuit for a brushed dc motor (24v, 500rpm, 2A, 4kgcm). The main components that I plan to use are PIC16f873, 4n25 optocoupler, IRFZ44N MOSFET, BY 500 - 800 diode(for ...
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4answers
84k views

In an NMOS, does current flow from source to drain or vice-versa?

In an NMOS, does current flow from source to drain or vice-versa? This Wikipedia page is confusing me: http://en.wikipedia.org/wiki/MOSFET The above image confuses me. For the N-channel, it shows ...
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4answers
35k views

What is the purpose of “MOSFET driver” IC's

There are dedicated "MOSFET driver" IC's available (ICL7667, Max622/626, TD340, IXD*404). Some also control IGBTs. What is the practical purpose of these? Is it all about maximizing the switching ...
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2answers
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What is killing my MOSFETs

This is my first post here on electronics stackexchange. I am a hobbyits in electronics, and a professional in programming. I am working on a inductor circuit to heat a workpiece. I have a working ...
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1answer
8k views

Reverse polarity protection

I read somewhere that this can be used for the reverse polarity protection in the circuit. But I am quite confused with its operation. Can somebody help me with this. simulate this circuit – ...
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8answers
12k views

fastest way of doing on/off-modulation of a LED?

I need to modulate a LED quickly (multi-megahertz range) on/off. It's a high-power LED. I have had some trouble locating any well-known methods to do this. Simply switching the voltage with a FET ...
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3answers
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Lithium Battery Protection Circuit - Why are there two MOSFETs in series, reversed?

I was studying a battery protection chip and reference circuit (below) commonly used in cell phone Li-ion batteries, and am confused by the two MOSFETs in series on the negative terminal EB-. ...
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2answers
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Does MOSFET let current flow through source to drain as it allows it from drain to source?

Does a MOSFET allow current flow in reverse direction (i.e.; from source to drain)? I made a Google search, but couldn't find a clear statement about this matter. I have found this similar question, ...
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Why is a MOSFET triggered by Vgs and not Vgd?

Looking carefully at this diagram of one type of MOSFET: (found in this application note) We can see the device is virtually symmetrical. What makes the gate reference itself to the source and not ...
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4answers
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Gate capacitance vs. Gate charge in n-ch FETs, and how to calculate power dissipation during charging/discharging of the gate

I am using a MOSFET driver (TC4427A), which can charge a 1nF gate capacitance in about 30ns. The dual N-ch MOSFET I am using (Si4946EY) has a gate charge of 30nC (max) per fet. I am only considering ...
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Solution for adapting to USB current draw limits?

Summary: I'm setting up a USB-powered Li-ion charging circuit and would of course like to draw the maximum charge current possible situationally -- but also want to ensure I don't violate the USB ...
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7answers
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Dissipating 1W on a TO-220 without heatsink?

Can a TO-220 without a heatsink dissipate 1W in still air? Or, a different way of asking the question is: Assuming an ambient temperature of 25C, how can I go about calculating the maximum power I ...
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2answers
49k views

Is MOSFET gate threshold voltage a limit or minimal “Full-on” switching voltage?

I've been shopping for some mosfet transistors, for a starter kit, and noticed listings that state a mosfet is suitable for 5v logic, but the data sheets says Gate Threshold is 1-2v. 4v gated mosfets,...
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2answers
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Why so many pins for the MOSFET's drain?

The FDC855N comes in a 6-pin package, 4 of which are connected to the drain, and only 1 to the source. Why this difference? The source sees the same current as the drain, doesn't it?
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Question about mosfet gate resistor

I have n mosfet gate connected to 4043 logic and Id is about 100mA. Both 4043 and mosfet has +5v. I have plan to use 2N7000 mosfet Questions are: How large gate resistor i need between 4043 and ...
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What is a popular cheap and robust substitute for 2n7000 MOSFET for use with 3.3 Volt designs? [closed]

What are the popular equivalents to the 2n7000, for 3.3 Volt MCU circuits to switch higher voltage devices? Background: For 5 Volt microcontroller based prototypes and experiments, my go-to solution ...
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1answer
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Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

The Raspberry Pi B+ models have a protection circuit between the USB connector and the 5V net on the board. They recommend putting a similar protection circuity on a Pi HAT before 'backpowering' the ...
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3answers
12k views

Equivalent circuit of a solid state relay

I want to switch 50V AC voltage. Maximum drained current will be 5A. Frequency is 50Hz. Switching speed is not important, can be real slow, it is not a problem in my application. I wanted to use ...
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4answers
11k views

Severe ringing when high side MOSFET in half bridge circuit switches on

I have designed a PCB (intended as a prototyping building block) that has a IR2113 high and low side gate driver driving two IRF3205 (55V, 8mΩ, 110A) power MOSFETs in half-bridge configuration: ...
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4answers
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Unnecessary pull down resistors on BJT and FET transistors?

I commonly see weak pull down resistors at the base of NPN transistors. Many electronic sites even recommend doing such things, usually specifying the value as something like 10x the base current ...
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4answers
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Parallel MOSFETs

When I went to school we had some basic circuit design and stuff like that. I learned that this was a bad idea: simulate this circuit – Schematic created using CircuitLab Since the current ...
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3answers
5k views

What is “drive voltage” for a MOSFET?

In the attributes of a MOSFET, Digi-Key lists several different voltages. I think I understand what most of them are, but there's one I don't understand: "drive voltage." Let's take this P-channel ...
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3answers
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How many MOSFETs can we safely parallel in condition of very high currents? I had problems with a motor application at 48V 1600A

I tried with some configurations in which 16+16 MOSfets of 240A each (really they are case limited to 80-90A because of source terminal, but i doubled this termminal with a very thick copper wire for ...
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4answers
11k views

What does “the resistance looking into” mean?

See this circuit, from Sedra & Smith microelectronics, 6th edition, page 287: It says that the resistance between the gate and source looking into the source is 1/gm, but that the resistance ...
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2answers
53k views

MOSFET as a voltage controlled resistor

This question might be too localized, but I try. Is it possible to replace a variable resistor by a MOSFET, under conditions shown in the following schematic? If yes, can someone propose a MOSFET ...
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6answers
3k views

Is it okay to use a MOSFET in its resistive region with a heat sink?

Using transistors in with limited gate (or base) voltage will make them limit current, which will introduce a significant voltage drop across the transistor, causing it to dissipate energy. This is ...
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3answers
1k views

Why are BJTs common in output stages of power amplifiers?

From my understanding, the role of the output stage is to decrease the output impedance to almost 0. For that, MOSFETs seem better suited since they've got way lower \$R_{ds}\$. Yet I see quite often ...
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2answers
2k views

Why do BLDC motor (1 kW) controllers have so many MOSFETs?

I have a 1 kW three-phase BLDC motor from China, and I was developing the controller myself. At 48 Vdc, the maximum current should be about 25 Amps and a peak current of 50 Amps for short durations. ...
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4answers
4k views

Can a power MOSFET for switching application be used as a linear amplifier?

Power MOSFETs nowadays are ubiquitous and fairly cheap also at retail. In most datasheet I saw power MOSFETs are rated for switching, without mentioning any kind of linear applications. I'd like to ...
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4answers
11k views

Are discrete MOSFETs ESD sensitive?

CMOS inputs on microcontrollers and other ICs can be damaged by ESD discharges. Can the gate of a big discrete MOSFET (2N7000, IRF9530, etc.) be damaged by ESD discharges?
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5answers
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Source vs Drain polarity for MOSFETS

When using MOSTEFS as a switch I always see the drain connected to the higher potential and and the load and the Source is always connected to ground. Can you switch those so that the Source pin ...
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3answers
3k views

Typical use of depletion MOSFET

I have been working with enhancement MOSFET for a long time. But I have never seen any circuit using a depletion-MOSFET. What are some typical use-cases of the depletion-MOSFET?
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3answers
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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6answers
19k views

My MOSFET operated solenoid circuit destroys my Arduino inputs

I made a series of PCBs to power some solenoid valves that use an external power supply. I switch them with BS170 MOSFETs using an Arduino as gate signal. I based it a solution by Jason S. This is an ...