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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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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
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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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How to design the gate resistor value?

This is the datasheet of the driver IC I am working on (LM5112). Following is the application diagram of the module. Basically this is the GATE driver circuit for the MOSFET with PDM signal as the ...
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3answers
9k views

Driving DC motors with MOSFETs and a microcontroller?

I'm developing a nano quadcopter using an Atmega328 microcontroller, powered at 3.3V, and very small brushed DC motors. The average current used by these motors is about 800mA @ 3.7V. Initially, to ...
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2answers
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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3answers
17k views

Bootstrap circuit function

I had some question about the bootstrap capacitor on gate driver. First, the bootstrap capacitor is used because the voltage on the high side drivers gate need to be about 10-15 volts higher than the ...
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3answers
52k views

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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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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6answers
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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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3answers
69k 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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100k views

MOSFET as a switch?

In the picture shown, can "Output" be controlled to be 0V or 12V based on "Control"? Will be Drain and Source the way it is connected be a problem?
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1answer
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Simulation model for floating gate

I am designing a non-volatile memory cell and foundry does not have model for floating gate . So I used the Voltage controlled current source to mimic floating gate. For output characteristics, I ...
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1answer
7k views

driving low side of a mosfet bridge with 3.3V

I'm trying to drive a the low side of a n-channel half bridge with a 3.3V signal that is not enough to switch the MOSFET I think (sometimes it does switch and sometimes it doesn't). I did this: http:/...
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2answers
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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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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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63k views

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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4answers
26k views

How to reduce MOSFET turn-off delay

The title says it all in signal switching applications - besides choosing a different device, how can I reduce the turn-off delay of (N-channel) MOSFETs? Is there something similar to the Baker Clamp ...
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1answer
13k views

Do MOSFETs have a diode built into them?

I have noticed that a MOSFET symbol has a little diode in it (or at least what looks like a diode). Does this mean I do not have to worry about using a diode in a circuit that runs a motor using one? ...
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2answers
1k views

Microcontroller soft off circuit not working - why?

I was making a board with an atmega328 mcu (to be used with Arduino libraries) to do some one wire communication stuff. Since I was etching the board anyway, I decided to try and implement a simple ...
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145k views

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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1answer
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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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3answers
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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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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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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2answers
20k views

Driving LED strip from microcontroller

I want to drive a strip of LEDs from a microcontroller using PWM to control the brightness. The strip I have takes about 1.5A at 12V. I'm only familiar with purely low power digital electronics so ...
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3answers
21k views

Why is the gate charge curve (Miller plateau) of MOSFETs dependent on Vds?

I don't understand why the gate charge curve (exactly: the Miller plateau part) of MOSFETs is dependent on the drain-source voltage Vds. As an example, the datasheet of of the IRFZ44 shows on page 4 (...
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I/O Resistance of common source MOSFET with source degeneration

Common Source MOSFET with source degenerations looks like this I am a bit confused about different input and output resistance statements (provided by different sources). Some of them say that ...
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21k views

P-Channel MOSFET high side switch

I am trying to reduce the power dissipation of a P-Channel MOSFET high side switch. So my question is: is there any way in which this circuit can be modified so that the P-Channel MOSFET will ...
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3answers
964 views

DC operation for IRFZ44 mosfet, SOA curve, max current at 40V?

I have built an electronic load. At the time I did not understand the SOA curves. Now I find the IRFZ44 datasheet does not have the DC curve. Any idea what the max current might be at 30V and 40V so ...
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1answer
2k views

P channel mosfet battery charging/power selection circuit help

I am a hobbyist and new to this, but I am not sure if my circuit it right. The goal is: To power the rest of the circuit from a DC source, a USB, or a battery, in that order. When there is no DC or ...
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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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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
12k views

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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4answers
9k views

What to look for in the datasheet when choosing a MOSFET?

I thought that choosing the right MOSFET for my LED strip would be easy until I discovered how many different models there are. Basically I want a MOSFET that allows me to control with PWM a 12V 6A (...
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1answer
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How to control a 12V solenoid valve with a mosfet?

I'm trying to control a 12V DC solenoid valve through a MOSFET (BS170), which receives its control signal (5V) from an Arduino microcontroller. This is the basic schematic: When I test the MOSFET, ...
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3answers
17k views

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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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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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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4answers
26k views

Build an H-Bridge Motor Driver with 4 N-Channel MOSFET

I have bought 4 N-Channel MOSFETs to build an H-Bridge Motor Driver. My Motor drive and my power supply voltage is 12v. My TTL logic voltage is 5v as I want to speed up/down the motor with uC PWM. Now ...
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982 views

About BJT, JFET & MOSFET transconductance

For BJT, the term "gm" refers to base-emitter conductance. But when we are talking about FETs and MOSFETs, where is this "gm"? Between gate-source junction for JFET? Drain to source conductance for ...
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7k views

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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4answers
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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
34k views

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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1answer
58k views

Why MOSFET Pinchoff occurs

This question is regard to enhanced n-type MOSFETs. From what I understand, an inversion layer is formed underneath the insulating layer below the gate of the MOSFET when a voltage is applied to the ...
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3answers
20k views

Understanding Two MOSFET with sources connected

I am having problem understanding how this MOSFET configuration (used in battery charger) works? In this slide, what does it mean "blocking voltages in both directions while allowing ...
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2answers
38k views

Gate Capacitance and Miller Capacitance on the MOSFET

How is the Gate capacitance and the Miller capacitance modeled for a MOSFET. What is the behavior for both when a Gate Voltage is applied?
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4answers
18k views

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
3k views

on-going quest to understand p-channel MOSFETs

(Disclaimer in case it isn't painfully obvious - I'm very much a n00b, especially when it comes to understanding transistors). I thought I had it all figured out - a p-channel MOSFET is (or can be ...
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4answers
4k views

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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2answers
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Determine MOSFET switching speed

How can I determine the switching speed of a MOSFET, with given Qg (gate charge), Vgs (G-S junction voltage) and gate resistor ? How should I determine the required value of the gate resistor?