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)

Filter by
Sorted by
Tagged with
7
votes
2answers
2k views

driving high-side N-channel MOSFETs in H-Bridge

What is the most efficient / best way to make an H-bridge? I want low power loss but also fast switching time since I will using PWM. I have considered using 2 P-channel and 2 N-channel MOSFETs to ...
7
votes
1answer
2k views

Turning a microcontroller on with a flip flop

I'm working on debugging a circuit that I've built and am trying to wrap my head around an issue. I have the following circuit (74LCV is an inverting flip flop and the NCP1400 is a boost converter): ...
7
votes
1answer
669 views

Step-down with external mosfet - why heavy current surges?

I built this circuit, which is supposed to deliver currents up to 20 amps (when everything else works...). The purpose is (eventually) to build a constant current source (as opposed to a constant ...
7
votes
1answer
152 views

“Temporary boost” supercap

I have a 12VDC load (up to 10A) that functions correctly down to 8VDC. Sometimes (frequency: many seconds max, many minutes typical) the power source has a very brief (few milliseconds) drop to 7V. ...
7
votes
0answers
913 views

What chemicals cause the burnt silicon / IC smell? [closed]

I've had a power mosfet go bad on me before, and I'm sure as many of you can guess, I had to answer "whoaaaa, what did you explode in here today" question many times! I was wondering, does anyone ...
6
votes
3answers
26k views

why mosfet is getting very hot?

I'm using an IRFZ44N power MOSFET to drive a DC motor (24v, 4kgcm, 2A, FLRPM 500). I found from the datasheet IRFZ44N has an ampere rating of 49A and still its getting very hot. I have attached the ...
6
votes
6answers
23k views

MOSFETs or BJTs for using as switch for audio signals

I was wondering which component is better for using as voltage controlled switch for audio signals (e.g. music signal from mp3 player). Should I use MOSFETs or BJTs? The max rail voltage is ...
6
votes
4answers
2k views

MOSFET W/L ratio limits: what's (un)reasonable?

The answer to this question is probably process-dependent, but what are the limits of the W/L (gate width/gate length) ratio for MOSFETs? I don't know what is in the realm of the insane. I saw a ...
6
votes
4answers
2k views

What is so special in the power MOSFETS IRFD120 and IRFD110?

I was trying out a hobby project and I was using the IRFD120 and IRFD110 power MOSFETs to control a motor. The transistors worked pretty fine and we simply ran out of them. When I went to buy some ...
6
votes
2answers
589 views

Is it better to use a MOSFET with a gate driver IC or a MOSFET with a lower VGS,on?

I am building an RGBW controller for my room. I will be using an ESP32 with four MOSFETs for each channel. I want to know which is best for fast switching. Do I need to use a MOSFET driver IC such as ...
6
votes
2answers
889 views

For a MOSFET, does capacitive gate current only flow through to the source?

Everywhere states that a MOSFET has no current at the gate. However, this is not true since, during the time the gate capacitance charges up to reach the certain voltage threshold, the current is ...
6
votes
4answers
2k views

Are CMOS outputs high-Z when unpowered?

If a microcontroller I/O pin drives an external MOSFET, and the microcontroller's power is turned off, will that MOSFET's gate be floating? I know sometimes a resistor is added to ground, but are ...
6
votes
3answers
2k views

Increasing Fall/Rise Times for Signal Integrity

I have a board that tests a wiring harness' continuity by outputting a set of test vectors onto the harness and reading it back. The wires in the harness can be as little as 1 m and as large as 10 m. ...
6
votes
4answers
27k views

Dual mosfet 8205A - lithium battery protection circuit

This is a basic lithium battery protection circuit, but looking at the dual mos-fet part of the circuit, It doesn't make sense to me. It's a 8205A dual mos-fet, with its drain connected together and ...
6
votes
2answers
8k views

Reduce noise from a Hall effect sensor

I am currently working on a magnetic levitation project using a Hall effect sensor for distance measurement. I drive the coil using two 12 V car batteries in series to form a 24 V DC source, ...
6
votes
2answers
3k views

MOSFET load switch

I'm trying to create a load switch using a pair of MOSFETs However, I'm confused about MOSFET threshold voltages. I need to switch about 0.1A at 3.3V. GPIO2 is 1.8V logic. What do I need to read in ...
6
votes
2answers
7k views

How to find a fitting cooler/heatsink for a Mosfet?

How do I find a fitting passive cooler/heatsink for a TO-220 Mosfet? What parameters do I have to search for?
6
votes
3answers
7k views

Low side N-Mosfet buck converter

I often see schematics of basic buck converters. The majority of these schematics use a P-Mosfet as high side switch. Why is this design preferred over a low side, N-Mosfet buck converter? simulate ...
6
votes
1answer
1k views

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 ...
6
votes
2answers
3k views

How do floating gate transistors not leak the stored charge?

I've done my best to read through Wikipedia explanations of floating gate transistors which are used in flash memory. It looks like these transistors have a special region where the charge is "stored" ...
6
votes
4answers
5k views

How does this reverse polarity circuit work?

The circuit in question uses the LT4356: So, I'm trying to get a grip on how this circuit works precisely. I've prototyped the pictured schematic minus everything to the left of D2. So, essentially,...
6
votes
1answer
1k views

Pull up resistor on P-MOSFET gate. Not working

I am building a battery-powered datalogger that will communicate using cellular signal, based on the ATSAMD21 microcontroller and the SIM5320 cellular modem. To save power, an outside timer ...
6
votes
3answers
6k views

I don't understand how the resistor between GND and the source in a common-source amplifier stabilizes it

See this circuit: Applying KVL around the gate-source-GND-gate loop, I get Id = (Vg - Vgs)/Rs. I know the typical argument begins with, if Id increases then Vs increases, but I am not sure of how it ...
6
votes
1answer
2k views

MOSFET Over Heating. So hot it's melting the solder

Alright, continuing with the debugging of my new board tonight I found another issue worse than the one before: My switching MOSFET is getting so hot that I'm getting molten solder. I replaced the ...
6
votes
1answer
9k views

Why is my N-channel MOSFET getting very hot and the power it provides to device increases with temperature?

I have a fairly simple situation: N-Channel MOSFET with base connected to Raspberry Pi's 3.3V source connected to ground and Drain connected this way: +12V ----> Vacuum Cleaner (60W) -----> Drain. Guy ...
6
votes
2answers
14k views

Make adjustable mosfet constant current source

I want to modify this circuit below so the current can be trimmed. The problem is the variations in base-emitter voltage of the NPN transistor. According to datasheets, it is between 0.55V and 0.7V ...
6
votes
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:/...
6
votes
4answers
1k views

Trying to figure out available resources on MSP430 LaunchPad

I'm just starting to mess with the MSP430 and have some simple apps working fine. However, now I want to use it with an LCD and am trying to determine if I'm short on I/O. For sure, I'll need to use ...
6
votes
2answers
2k views

How is it possible that the reverse transfer capacitance of this FET is so low?

A FET has parasitic capacitance, which can be modeled as a capacitor between each of its terminals (gate, drain and source), which I refer to as Cgd, Cgs and Cds, as shown in the image below. FET ...
6
votes
1answer
2k views

Controlling a MOSFET with a microcontroller

I'm trying to use a p-channel MOSFET (FQP27P06) to multiplex four large common-anode seven-segment displays. I'm using a TPIC6B595 high voltage high current shift register to sink the segments for ...
6
votes
3answers
2k views

Solenoids causing Arduino to malfunction despite protection diode

simulate this circuit – Schematic created using CircuitLab I have an Arduino Mega that I'm attempting to control some solenoids and LEDs with. The LEDs are 3.3V, controlled through an open ...
6
votes
2answers
1k views

Buck converter MOS Drive resulting in overheat

With the schematics below, which is a low side driven DC/DC buck converter similar to this post: The LINE voltage is about 300 VDC and controls a 24V halogen lamp connected to J1. C2, C3 are rated ...
6
votes
1answer
664 views

how do MOSFETS work

I understand how to use MOSFET's and build some simple circuits. What is going on inside at the atomic level where I can't see physically? I understand that BJT's work by doping semiconductors and ...
6
votes
2answers
5k views

How to properly switch between two power sources with a MOSFET?

In our application, our board can receive +12V from an adapter jack when working in standalone mode. This 12V is fed into a switching regulator to create a 3.3V supply (named 3V3_2 in the schematics ...
6
votes
1answer
11k views

MOSFET choice for 12v LED Strip and 3.3v Logic

I'm currently planning a project on a low-cost WiFi-enabled RGB LED controller and could use some help in looking over my parts list and general concept. What I'm wanting to do is a build a ...
6
votes
2answers
7k views

Why do N-channel MOSFETs have a voltage drop when load is connected on source side?

I read how MOSFETs work, although there is this thing I can't understand. To make things simpler let's take only n-channel MOSFETs into account. Normally, the load is connected on the drain side, like ...
6
votes
2answers
373 views

What is the point of this MOSFET?

In the image above, could someone please tell me what the MOSFET is doing? From what I gather, it is there for switching between the VCC_in and the regulated voltage, in conjunction with the SDA and ...
6
votes
3answers
5k views

How does a dual gate MOSFET reduce Miller effect?

How does a dual gate MOSFET reduce Miller effect? I am trying to gain a global understaning of the physics behind them, not necessarily exact formula's that come with it other than maybe some for ...
6
votes
3answers
6k views

Using MOSFET to switch device

Will my circuit work for the following goal? When INPUT_N is HIGH (i.e. micro is not driving it and it is pulled up to 3.3V), VCC pin on device will have 24V. When the microcontroller drives INPUT_N ...
6
votes
3answers
1k views

Apparent inconsistency of MOSFET power rating in datasheet: SOA v. max power

I am trying to use an IPP114N03L G (datasheet). I calculated the maximum power it could handle as follows: From the first two pages of the datasheet: Rthjc = 3.9K/W Tj(max) = 175C Assuming I can ...
6
votes
1answer
686 views

N-MOS real-life gate threshold voltage (Vgsth) lower than claimed

I faced with a paradox that N-MOS transistor real-life Vgsth (gate-to-source threshold voltage) is significantly lower than claimed. It should be about 1.7 V (and the simulation confirming that ...
6
votes
5answers
8k views

Is the MOSFET source always connected to bulk?

I'm trying to understand all the basic connections of a MOSFET. These questions may seem very basic but I have flipped every single textbook I own and googled every single website and never found a ...
6
votes
2answers
442 views

MOSFET Circuit Design and Thermal Considerations

I'm a newbie at EE, and just I wanted to verify that the design I came up with for a MOSFET circuit that drives a 12V 500mA water pump will work. I'd also like to confirm I can run the N-Channel ...
6
votes
2answers
4k views

small MOSFET for switching applications [closed]

When I need a general purpose NPN transistor I automatically think of the BC847. Other types that always come back are 2N3904/2N2222. (Is BCxxx more European, and 2Nxxxx more American?) For N-channel ...
6
votes
1answer
2k views

Driving a MOSFET with Negative Off- State Gate Voltage

I know in practice Mosfet switches are driven by 0V to any Positive gate voltage (e.g. 0V - 15V). I am using a Mosfet pair (PMOS and NMOS) to switch 10A currents in pulses and the datasheet of MOSFET ...
6
votes
4answers
4k views

P-channel MOSFET as high-side switch gets hot

So I'm trying to control my front lights of my car using an Arduino Nano. In total there are 14 lights (including foglights and blinkers etc.). I'm using two 75HC595 shift registers to control these ...
6
votes
2answers
4k views

BJT vs MOSFET failure modes

I know MOSFETs are much more efficient than BJTs in that they don't consume as much power when on whereas a BJT consumes base current the whole time it is on. I also know that MOSFETs tend to fail ...
6
votes
2answers
994 views

Why do we assume VGS<Vth and Vds>0 for a mosfet in cuttoff and Vce>0 for a BJT in cutoff?

The devices below are both n polarity devices, the BJT is a NPN and the MOSFET is a NMOS. For the BJT in cut-off, why do we have to assume \$V_{ce}>0\$? For the MOSFET in cut-off, why do we have ...
6
votes
1answer
2k views

MOSFET fall time too slow

I've got a 2N7000 connected up to an AVR via a 1k resistor on a breadboard. The top trace shows the AVR pin output, clocking at a couple of kHz. The lower trace shows the source of the FET. Clearly ...
6
votes
2answers
230 views

Current limiting solution for pocketqube satellite

A project I am working on requires a reliable current limiting solution for a pocketqube picosatellite. Currently a Texas TPS2553 is being employed which will cut power once the limit is hit. We are ...