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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16k 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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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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Why doesn't LTSpice predict this op-amp oscillation?

I'm developing a circuit to act as an electronic load for bench testing power supplies. An earlier question about how to test this circuit received several very useful answers and can be found here: ...
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35k views

MOSFET: When can we not assume that the gate current is 0?

A common rule of thumb you hear when learning Electrical Engineering is that the gate current of a MOSFET is always approximately 0. When is it not safe to assume that it is 0?
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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
20k 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 ...
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4answers
6k views

Driving highly inductive loads destroys mosfet driver

Background I am attempting to generate some relatively high voltages (>200KV) using a system of ignition coils. This question deals with a single stage of this system which we are attempting to make ...
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4answers
10k 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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3answers
2k views

How can I measure gate capacitance?

Is there an effective way to directly measure the gate capacitance of a power MOSFET, like say the IRF530N? The way my circuit is behaving would indicate that the effective gate capacitance is ...
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IGBT vs. Power MOSFET for switching applications. Where to draw the line?

For lower breakdown voltages, a power MOSFET is clearly the device to go for, in view of its higher efficiency, higher commutation speed and lower price. Where should the line be drawn, upwards of ...
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Why are flip-flops usually triggered on the rising edge of the clock?

Usually in digital design, we deal with flip-flops that are triggered on a 0-to-1 clock signal transition (positive-edge triggered) as opposed to on a 1-to-0 transition (negative-edge triggered). I ...
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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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10k views

How can I sense the motor's current?

I need to drive a DC motor @ 24V, 6A with a MOSFET. How can I sense the current that the motor is drawing with a microcontroller? I have to know when the motor is stalled.
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Help using MOSFET to switch on/off IC

I am trying to use the following MOSFET (N-Channel) to turn an IC on and off. http://www.diodes.com/datasheets/ZXMS6004FF.pdf In my test circuit I connected 5VDC to the drain of the MOSFET and then ...
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Do MOSFETs usually burn open or closed?

I was wondering if a power MOSFET fails due to overheating, will it usually burn as an open-circuit or short-circuit? Also, does over-temp damage usually cause the gate oxide to blow through as a low ...
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9k views

What is MOSFET gate drive capability and why do I care about it?

Someone told me that this circuit has "poor gate drive capability": simulate this circuit – Schematic created using CircuitLab What exactly does that mean? I tested it with an LED as a load ...
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Is this a good design for MOSFET H-Bridge?

I have been looking around trying to design a simple but working H-Bridge for an RC car motor (12V and 2~3A). This bridge will be driven from a microcontroller and need to be fast to support PWM. So ...
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Why are BJTs more reliable than MOSFETs under severe weather conditions?

I read in a textbook (Microelectronic Circuits by Sedra and Smith, pg. 494, (2010) sixth edition) that BJTs are preferred by the automotive industry due to their reliability under severe weather ...
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Why are discrete four-terminal MOSFETs so hard to find?

I know that a MOSFET is a four-terminal device, but nearly every discrete MOSFET you can buy has its bulk/body/substrate internally connected to the source. Why is this? It makes it inconvenient to ...
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How is this circuit for level converting (5V<>3.3V) working?

Does anybody know, how is this circuit exactly working? It is level converter between 5V and 3.3V logic and it is bi-directional. I have some theory, but I am not sure with it (I never worked with ...
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7k views

High Voltage PWM Motor Controller - Mosfets Explode

I've searched every post for an answer to this problem. I've built a motor controller circuit as shown in this diagram. I made the diagram as accurate as possible. The diodes on the mosfets were ...
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3k views

How tight can I mount a TO-220 to a bus bar?

I'm building a small switching circuit consisting of 8 MOSFETs (bi-directional blocking, 4 in each direction), which should switch 100-200A at about 1kHz. I've concluded that since PCB with a thick ...
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Do MOSFETs have voltage drop across source and drain when turned on?

Like diode and BJT having around 0.6V drop, is there any voltage drop across the MOSFET drain and source when the MOSFET is turned on? In the datasheet, they mention diode forward voltage drop, but I ...
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103k 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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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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Is there a popular small signal PFET equivalent to NFETs 2N7000 or BS170?

Some days ago I was considering using a small signal P-Channel MOSFET in a design of mine, but could not find a suitable part. The specs I was looking for were something like the following: \$I_D = -...
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What is the difference between driving a MOSFET gate and an IGBT gate?

Can I use an suitable IGBT gate driver for driving the MOSFET, and vice versa? Which parameters (threshold, plateau, and turn on voltage ratings, gate capacitance, etc) must be the same for this ...
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What is the purpose of using MOSFET instead of free-wheeling diode in Buck topology?

(Source) I usually see Buck circuit models in which a MOSFET is used instead of a free-wheeling diode. What I understand from the Buck topology is, when the upper MOSFET is off, it doesn't matter ...
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41k 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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7k views

Using a microcontroller to turn on LED strip

I have 60 leds that came in a led strip. One meter length of the led strip requires the following: 400 milliamps 12 volts I want to control these LEDs with micro controller. I'm thinking of using a ...
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23k views

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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28k 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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8k views

BJTs versus (MOS)FET to switch a load from a microcontroller

I would like to know what are the reasons for choosing bipolar junction transistor (BJT) versus a field-effect transistor (FET) (MOSFET or a JFET) to switch a load from a microcontroller. In our ...
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1answer
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Basic p type MOSFET question

With an N type MOSFET you let the current flow from the drain through the source when a high enough voltage is applied to the gate. With a P type MOSFET which direction is the current meant to flow? ...
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MOSFET broke after attaching capacitor bank

I have a solenoid that has a coil resistance of \$0.3\Omega\$ and accelerates a steel projectile here. I've posted the schematics below. Normal Version that acts as a control The GPIO8 goes to 5V to ...
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29k views

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?
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MOSFET construction

I've just read an application note and I was confused about this sentence: "Engineers often think of a MOSFET as a single power transistor, but it is a collection of thousands of tiny power FET cells ...
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1answer
43k views

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
9k views

Voltage spikes when driving DC motor with N-channel MOSFET

I'm trying to drive a DC motor (12V, 100W) with MOSFET IRFP054N. PWM frequency is 25 kHz. Here's the schematic: I know DSEI120-12A is not the best diode for this but I don't have any better right now....
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445 views

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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3k views

1.5V-rated MOSFET doesn't react to a gate input of 1.8V

I am not really an electronics specialist, but a software engineer (so excuses if I 'm asking stupid questions). I am trying to use a microcontroller GPIO output rated at 1.8V. When this pin becomes ...
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Help understanding this LED lighting transistor circuit

I simulated this circuit from a reference design but I'm not entirely sure how it's working or how you would go about designing such a thing. In simulation it looks like it's designed to hold the ...
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861 views

P-Channel MOSFET Inrush Current Limiting - Transistor burn issue

I'm fighting with PFET inrush current limiting circuit discussed here: P-Channel MOSFET Inrush Current Limiting In my circuit is input voltage 24V DC and C_Load is 6mF. I'm switching on transistor ...
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4answers
9k views

Why MOSFET source is indicated with arrow ?

I know that , a basic MOSFET contains source and drain , and either it's a NMOS or PMOS ; it is indicated by an arrow at source . But let's look at a fabricated NMOS. Here we can easily see that ...
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MOSFET Switch - Not Turning Fully Off?

I have the following circuit wired up on a protoboard. The datasheet for the BSS138 MOSFET is here. I'm puzzled regarding what I'm seeing happen with this circuit - when I apply 3.3V at the gate ...
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No germanium diode available for small crystal radio — can active components handle the task?

I know that germanium diodes are trivial to find online, but as this is for a demonstration I'd rather not spend $6-7+ on shipping for a single 5 cent part for a project that's academic in exercise ...
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Looking for help on why my n-channel mosfet is getting destroyed

I've got a design that I've inherited with a pretty standard n-channel mosfet driving a relay that controls a motor and actuator. On a recent build we started getting a 50% failure rate on the n-...
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Why does this Bridge Rectifier claim to have no [Diode] Forward Voltage drop

I was, "OK, this is feasible"... But then I traced how it worked and it simply blocked current through Drain and Source when a P and N pair are reverse biased; then when the other P and N pair are ...
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304 views

How to ensure my device is safe for every day use?

I have put together a simple wake up light. It has an external powersupply, at the moment rated 7V and 600mA. Inside it has Arduino and bunch of LEDs controlled by a MOSFET. It works fine at the ...
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How to choose a switch?

There seem to be about 4 major flavors of transistors, and then there are NPN/PNP versions. There are also relays, SCRs, and TRIACs. When I need an microcontroller-controlled switch, what rules of ...