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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PWM & output voltage

while 555 contest is long gone, I am still debugging my device, where I already abandoned 555 itself :-) At the moment, I am driving PC fan from an PWM (30kHz) signal from atmel uC. I am powering P-...
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Microcontroller driven N-Channel MOSFET voltage behavior

As seen in this LTSpice model, I am trying to control a white LED (3.6 Vf @ 20 mA) connected to a 7.5 voltage source with a 2N7002 N-channel MOSFET and a 5V control signal from an Arduino. Given that ...
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Don Lancaster's Magic Sinewaves

For several years now Don Lancaster is promoting magic sinewaves. They are strings of binary digits (like 420 bits for a full sine cycle) that, when used to drive a digital switch (MOSFET/IGBP), ...
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Practical current limit for TO-220 package

I see a lot of MOSFET transistors with suprisingly high continuos currents in TO-220 packages. To make matters more magic open ressistance is very low. For example I want to use IRFB7545PbF N-MOSFET ...
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What causes this knee in my MOSFET drain voltage drop?

FINAL UPDATE: Understand a previously mysterious power MOSFET switching waveform wiggle! @Mario uncovered the root cause here below, distinctive to so-called VDMOS devices, typical of many power ...
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MOSFET power dissipation calculations - Diodes Inc. datasheets

Looking at Diodes Inc. datasheets, I am having trouble following their power dissipation limit calculations for their MOSFETS. E.g. for DMG4496SSS http://www.diodes.com/_files/datasheets/ds32048.pdf ...
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Why won't this DIY transistor attempt conduct

I've been trying to make a crude transistor device at home. So far I have not been successful. My electrical understanding is next to non existent other than what I've learned in the last 3 months ...
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Beginner electronics hobbyist needing my schematic looked over

I only very recently started getting into electronics as a hobby, and the little amount of theory I got in college did help, when I actually started remembering things :P Anyway, my next project is a ...
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Why isn't the BIOS' ROM chip made using CMOS technology?

After reading a computer hardware course on BIOS/CMOS, I'm still unable to determine the reason why the BIOS' ROM chip isn't built using CMOS technology, and why it is connected to a separate chip ...
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How can I slow down the switch time of a MOSFET?

I have an NMOS that is switching too fast for my application. Into the gate I am sending a logic-level square wave (PWM). Unfortunately for me, as expected, the output is also a near square wave. How ...
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How should I understand the intrinsic body diode inside a MOSFET?

I know there is an intrinsic body diode inside all the MOSFETs, but I'm confused about the reason why it's there. I've searched the articles but can't find a good explanation for it. Can anyone use ...
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Why do my P-channel MOSFETs keep dying in this H-bridge?

So this is my H-bridge: Every time I start using it in one direction the P-channel MOSFET and the NPN BJT which belong to the used direction die in seconds. The killed MOSFET and the BJT developing a ...
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Power consumed by a CPU

I think the power for a CPU with current I and voltage U is I · U. I wonder how the following conclusion from Wikipedia is derived? The power consumed by a CPU, is approximately ...
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Open-drain microcontoller ports

I want to understand the concept of open-drain ports like port P0 of the 8051 microcontroller. Why do we need to connect pull up resistors to the port P0? I have basic knowledge of MOSFETs and other ...
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What material should I use to insulate my MOSFET from a heatsink?

I have a heat-sink and I want to put two FET's on it. I know I have to insulate it so the metal showing on it doesn't connect and create a path. Is there any good everyday material that would work? (...
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Controlling high current (1000A) with MOSFETs

I am currently designing a capacitive discharge spot welder and am running into the issue of switching. I plan to use a few super capacitors in series to discharge around 1000A in a very short ...
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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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What does this Mosfet Symbol mean (two diodes facing each other at Vgs)?

The title says it all: What does this Mosfet Symbol mean (two diodes facing each other at Vgs)? I know its an N-MOS, but I don't understand the meaning/purpose of the two diodes. Part: AO7404 ...
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Driving a servo with MOSFET

I am trying to build a small battery powered device containing a servo. I would like to be able to turn off the servo to save battery life. I have read previously that MOSFETs can be used to do this, ...
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What's up with MOSFETs?

For the longest time, I've stayed away from FETs and MOSFETs (when it comes to using discrete transistors in my circuits, that is). I'm taking a current hobby project as an excuse to try and finally ...
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Controlling heater with PWM through MOSFET

I'm trying to control a heater coil (resistance ~0.9 Ohm) with PWM using a MOSFET. PWM modulator is based on LM393, MOSFET is IRFR3704 (20V, 60A). If I place 1k resistor in place of heater everything ...
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OP amps with output on N-channel MOSFET

I need to analyze a schematic and I am having trouble with this part: The thing is I don't get at all the utility of the N-channel MOSFET at the output of the op-amp. Could anyone explain the purpose ...
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Paralleling Mosfets: Can I use a common gate resistor, or do I have to use a separate one for each mosfet?

When calculating gate resistor for a single mosfet, first I model the circuit as a series RLC circuit. Where, R is the gate resistor to be calculated. ...
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How is this 5-24V input circuit working?

Since I require some kind of wide range input (going to a microcontroller) for a new project, I looked through some designs that are already in use (or were considered at some point) for other ...
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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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Why do my push-pull driver drains ring so much?

I have read What is killing my MOSFETs which seems to present a similar circuit to mine (my secondary is center tapped as well and has 2 high-speed diodes rectifying into a 10R / 400uF load) The ...
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Drive a 4.8V servo signal line using 3.3V

I have a servo with an operating voltage of 4.8V. I want to drive the servo from a MCU running on 3.3V. I haven't tried it yet, but was wondering if I needed to drive the signal line to 4.8V using a ...
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Need help understanding and interpreting IGBT datasheets

When it comes to motor control, I understand that we have the option of using discrete MOSFETs or IGBTs. Also, there are some products in the market where 6 IGBTs are placed in one single package, ...
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Multiple fingers vs single finger layout (MOSFET transistor)

Please, provide a summary of advantages and disadvantages of a transistor layout with multiple fingers (MF) vs single finger? When laying out a MOSFET with a particular width and length, in an EDA ...
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Why have my MOSFET drivers blown in this H-Bridge?

I've built a discrete H-Bridge circuit to run a reasonably beefy 12V windscreen wiper motor. The circuit is below (EDIT: see here for a bigger PDF, StackExchange doesn't seem to let you expand the ...
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PCB layout for high side switch (high current)

I'm working on a PCB layout for two high side switches. You can see below a picture of my current layout. The copper weight of the future PCB will probably be 2 oz/ft² (double sided). I use two p-...
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Back-to-back MOSFETs: common source vs comon drain?

If connecting a pair of discrete MOSFETs back-to-back to create a bidirectional load switch, what's the practical difference between having them common-source versus common-drain? In this particular ...
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Very intermittent power MOSFET failure

I am working on a very spotty motor failure (I am not the designer). We have a wound armature which is switched by power MOSFETs. These are driven by a FET totem pole type FET driver. When the ...
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Selecting a MOSFET for DC use

I have a general question regarding MOSFET Selection. I am trying to select a MOSFET for DC use. I am looking to replace a 5A 24V Relay with a N Type MOSFET. The MOSFET would be driven from a micro ...
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Full bridge driver capacitor ringing problem

This is my first time designing a full bridge driver. I am experiencing problems with ringing on the output. I have made a pcb for it. This is a picture of the top side of the board. Backside Input ...
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Explain in layman's terms Vgs and Vgs(th) of MOSFET's

I'm trying to understand \$V_{GS}\$ of MOSFET transistor. From what I understand \$V_{GS}\$ normally stands for voltage gate to source breakdown, but other than that I lack an understanding. \$V_{GS(...
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Why do we use a CMOS for inverting a circuit when the PMOS already achieves that?

The output in a PMOS is as follows: I/P O/P 0 1 1 0 Why can't I just use this instead of using a CMOS for inverting logic? (Please ...
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Is there any reason to use junction or Darlington transistors for power applications?

In quite a few Arduino examples, you see people using junction transistors to power a motor. In this case, for example, he's using a Darlington transistor: http://www.instructables.com/id/Use-Arduino-...
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Extracting the Square Root of a Voltage

I'm trying to discover a circuit that will produce a voltage which is some factor of the square root of the input voltage. I.e. \$V_{out}(t) = K\sqrt{V_{in}(t)}\$. The factor K is irrelevant. I ...
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MOSFET and 3 V power supply

I want to control an N-channel MOSFET from a 3 V power source. The thing is, I have difficulties understanding how to know the minimum Vgs value is to be applied for the MOSFET to be saturated. ...
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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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MOSFET Diode design

I'll start this off by simply saying I am not an Electrical Engineer. I am, however, an embedded programmer who has had some experience with circuit design and setup (give me 1's and 0's and I can ...
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How to determine maximum PWM frequency for transistor (2SK2554)

How can I determine (estimate) maximum reasonable PWM frequency for 2SK2554 transistor? I found timings in datasheet: I could estimate frequency from this (and make sure that all these times are 20-...
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Choosing and biasing a MOSFET controlled by a microcontroller, does current matter?

I need some help choosing a MOSFET for the circuit that I described here, which I originally designed using a BJT but decided that FETs make more sense in this case. The FET will be controlled by a ...
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SSR vs optocoupler with TRIAC output

I've designed (and mostly implemented, now) a system for turning on and off 24VAC solenoids. In order to achieve this, I used optocouplers with TRIAC output (Sharp PR26MF1xNSZ series). The datasheet ...
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Proper way of connecting logic GND / power GND on MOSFET driver

I am tring to build half bridge using IR21844 mosfet driver, i have read datasheet and design tips and some of the topics in this forum. The one thing i still cannot get is the separate GND pins ...
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meaning of MOSFET “linear region” in the context of switching losses

In the context of MOSFET switching circuits (PWM, motor control, etc) I've read the "linear region" of operation is where you don't want to be for long, because here is where there is large power in ...
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Why do I have to use the same ground?

I've connected an Arduino to a MOSFET to control a valve. I've connected the Arduino's GND to the negative lane (word?) on the breadboard (for clarity modeled by SW1 in the circuit diagram). I ...
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Dual N/P-Channel MOSFET Dies with Smoke

I have built the following N-MOS & P-MOS push-pull dual MOSFET circuit. Its purpose is to control some external LEDs from a 3.3V microprocessor. However, there seems to be a problem, where the ...
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Controlling a very small DC motor with PWM?

I have a very small DC motor (from a Walkman), I would like to control the speed from a micro-controller. For that I would like to connect a MOSFET in series and apply a PWM signal to its gate in ...