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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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1answer
67 views

Pass Transistor: discharging of the capacitance

let's consider this pass transistor logic: Let's assume that the MOSFET is always active (CK = high for a N-MOSFET). Now, immagine that at the beginning Vin = 10V and Vx = 0: the capacitance Cx will ...
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1answer
103 views

uC IO pin driven “low”, but voltage sits at 0.3V, not 0V

This is an Arduino MKR WiFi 1010 board, which runs at 3.3V. PA18_OTG is an IO pin, which by default is driven HIGH (3.3V). In this state I measure the OTG pin at 0V. I need to drive OTG high, so my ...
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1answer
51 views

𝐶 C -𝑉 V characteristics of MOS capacitors for different material

For C-V curve below for 3 different materials, (Si, InAs, InSb). What material will be corresponding to curve A/B/C? My understanding is that C is inversely proportional to the dielectric constant in ...
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1answer
61 views

Simplest latching circuit with press-ON hold-OFF button that can cut power when Raspberry Pi halts

So I'm making a battery-powered Raspberry Pi project, and it would be ideal if it could cut off power to the Raspberry Pi after the Raspberry Pi shuts down. It would also be ideal if the power for ...
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52 views

High Voltage Push-Pull MOSFET logic gates

Hello, I would like to implement typical MOSFET logic gates in my circuit with V+ at 24V and Input ranging from 0-24V. This posts a problem for the MOSFET however as I would either exceed the gate ...
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3answers
82 views

uC controlled MOSFET based LED Dimmer stops responding

I've designed and implemented LED Dimmer driven by PWM from Adruino Pro Micro (CLONE) with software based on MySensors library. See the schematic attached below. The idea is really simple: uC is ...
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1answer
41 views

Close a circuit with no current load (MOSFET)

For my project I have to close to contacts. It's bascially a remote for a Canon camera. With Canon you can use 3 pins (2.5mm jack) to "remote" controll it, 1 of these 3 is the common pin, 1 is the ...
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1answer
69 views

10 Amp Current Limit

I have a 28VDC, high current supply (constant voltage) that is required to charge an emergency power supply. These EPS internals are rated at 15 amps max input current, however, it’s stipulated that ...
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1answer
72 views

Calculating MOSFET Heat Dissipation onto PCB

So for my Heated-Glove project, I was thinking of making a series-parallel battery circuit that is powered by the ATMega328p Microcontroller. What this circuit does is charges the batteries using two ...
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4answers
113 views

high side switch using NMOS

I'd like to dim an ordinary 3-pin PC fan with a 3.3V-PWM at its 12V power supply pin. As I also need to measure the tachometer signal within a 3.3V logic level circuitry I'd like to switch the fan on ...
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0answers
65 views

How to calculate MOSFET temperature increase in PCB

I want to calculate MOSFET(DATASHEET) temperature increase for PCB. MOSFET - FDD86250_F085-D Totally 13 MOSFET's will be mounted in PCB. At the same time, maximum 8 MOSFET's will be used in PCB 1, ...
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1answer
67 views

LED matrix - MOSFET driver leakage?

I have 4 common-anode RGB LEDs in a 4x3 matrix. I have a BSS138 on each of the red, green and blue cathode lines and a BSS84 on each of the anode pins. The power supply is 3.3v, which is close enough ...
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2answers
83 views

n Gate to source capacitor in gate drive?

I'm designing a gate drive and I saw in a reference design this circuit, what would be the explanation for placing a capacitor between gate-source of the MOSFET (or IGBT)? I've read that a resistor is ...
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0answers
67 views

Lower amps than expected?

I build an inverter to power some panels of EL paint (If you don't know what EL paint is check out this link). It puts out some very high voltage and I thought I'd check to see what amperage it is ...
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57 views

Logic Level MOSFET IRLZ44N - under Wemos mini

I used IRLZ44N with Arduino Nano in order to dimm a 12v LED strip. When tried to use it with Wemos Mini - I get only 7.6v max ( when controlling a 12v source ). Probing the output pin (...
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1answer
171 views

I keep zapping mosfet and I don't know why

After asking collagues, trying a few variations and spending days on research, I figured out I could ask there as I am running out of ideas. The most similar discussion I have found is: mosfet is ...
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2answers
93 views

Driving high currents with parallel mosfets as the switch

I am trying to make my own battery spot welder from a car battery, car starter solenoid, and an Arduino to drive them. I came up with my concept and schematic and built the thing. The problem is that ...
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1answer
92 views

Any way to build Analogue Multiplexers using MOSFETs or JFETs or BJTs

Here's my requirement: I need an analogue switch that can do SPST/DPST/DPDT with very low On-Resistance (<10mOhms). There would be current flowing through this switch, albeit in the range of a <...
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1answer
191 views

Mosfet current control with PWM

I am using a mosfet and an Arduino and I want to control the Source-Drain current of the mosfet by adjusting PWM to the Gate. If I apply zero value to the PWM, the current doesn't stop (I checked the ...
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1answer
42 views

Use half bridge driver with one mosfet

I need a single mosfet driver but only have half bridge drivers (IRF2004) in my parts box. Is there a risk I destroy them if I only connect one mosfet to them? Any other risks which I should be aware ...
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2answers
76 views

2N7002 MOSFET gate voltage internally being pulled high, potentially dead

I am using the circuit below to switch a bi-latching relay once a wire is disconnected, i.e. to not switch as long as a voltage is present on the wire. After assembling on a PCB, on which there are ...
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2answers
138 views

Can a flyback diode work on the “ground” side of a transistor?

In every flyback diode setup I see, the relay coils are on the drain side of the transistor (if my terminology is wrong, I mean the top), so the flyback diode sends current back toward the power ...
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3answers
519 views

What parameters are to be considered when choosing a MOSFET?

I have a circuit that uses a MOSFET to heat a nickel titanium wire (by switching of course). But I don't understand why does it use IRF740 specifically. What parameters do we look into when choosing ...
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2answers
3k views

Why do we need a voltage divider when we get the same voltage at the output as the input?

I am using a voltage divider circuit of 100 Ω and 10 kΩ resistors, and using their output for the (IRF740) transistor's input. I'm trying to figure out why do the resistors have those specific values....
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1answer
51 views

How many amperes can pass through drain-source of a FQPF9N50C if 3.3v are applied to gate-source?

I a playing around with this N-channel mosfet I found at home (FQPF9N50C). Using this simple circuit: I am able to turn on an off the 12v load using by connecting 3.3v to the mosfet. The load is a ...
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1answer
82 views

Current control circuit doesn't work in practice

A control circuit works in simulation, but don't in real. What is my mistake? Current through R5 or Mosfet proportional with V1 voltage in linear region. But in practice even when V1=0, the current ...
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4answers
138 views

Why are active loads used for transistor amplifiers?

I get it that voltage drop across active loads are less compared to passive loads and at the same time they offer high small signal impedance thereby increasing gain. I cannot understand why DC ...
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1answer
69 views

Scaling level of PWM signals

I am going to scale PWM 24V generated by PLC to PWM +5V by means of optocoupler TLP521 and MOSFET BSP295 in order to control a micro servo motor (MG90S). What I have tried till now is the below ...
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35 views

Capacitor charge offset (pre-charge)

I use capacitor (on Gate) to open MOSFET slowly to fade in/out LED strip. It works fine except some delay before light starts to show. I understand that it is because led strip didn’t receive enough ...
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1answer
38 views

Inrush control circuit

I am analysing the an eval board circuit for a battery charger IC which has the following inrush control circuit. Question 1: I understand that C22 is used to "slow start" Q6 limit inrush current ...
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2answers
57 views

In what condition power MOSFET gate capacitances Cgs and Cgd can be paralleled?

I would like to get some understanding about the gate charge of a power MOSFET. I am referred to this MOSFET gate drive circuit application note: https://toshiba.semicon-storage.com/info/docget.jsp?...
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1answer
112 views

Low voltage drop current limiter for charging supercaps with a MOSFET

I have an RPi that I want to give enough juice to auto shutdown when the power goes down. For this I'll use 2 supercaps of 6F (2.7V) in series, giving me plenty of time. Now, I was wondering if I ...
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2answers
82 views

Mosfet Threshold Voltage

from MOS theory we know that, in case of a P substrate, a Gate-Bulk voltage higher than a certain threshold value creates an inversion layer, in this case made of negative charges. This is also ...
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1answer
66 views

P30N06 Mosfet Not Working Correctly

I have an N Channel Mosfets I'm trying to use as a switch for a motion sensor and an LED strip light (12V <0.8A). It seems like no matter how I hook up the mosfet it is always set to 12V or stuck ...
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1answer
46 views

When to use P-Type current source(using pMOS) and when to use N-type current Source(nMOS)?

I am referring to Prof. Behzad Razavi Lecture https://www.youtube.com/watch?v=GAvZLyii3aw&list=PLiDoPUX9nLkIw9EnIv_3K19wlcyJ6msYd&index=2 (Minutes 19-26) Prof. says to use nMOS when we draw ...
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0answers
20 views

Current Measurement-DC offset present in input channel of Oscilloscope

Hello! I am working with two MOSFETs in parallel and I am measuring their turn on currents as shown in picture attached. In the picture, one can see a mismatch between the currents (channel 2 current ...
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1answer
90 views

Arduino (STM32) and MOSFET switch with digital pin

What circuit can I use to switch on a speaker with an arduino (stm32 board)? Ideally the speaker will run longer (automatic off after some time-0.5s) I have a stopwatch program in STM32 (...
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1answer
29 views

Replacing Sukam fusion 3.5kva Mosfet IRF2807

The mosfets on my Sukam Fusion 3.5kva inverter have blown, I want to replace them. they have what looks like the following written on them IRF2807 RP526Y I can find IRF2807 but not IRF2807 RP526Y,...
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1answer
67 views

Use a OR wired with diodes to control the gate of a PMOSFET

If a have an OR wired with collector outputs to control the turn ON and turn OFF of a PMOSFET, shall I use a pull up resitor in the source input of the PMOSFET? Does the design need a pull down in the ...
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2answers
863 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 ...
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2answers
118 views

Switching MOSFETs

For the below circuit, VIN = 12V. (using 220V to 12V adapter) and frequency of 3.3V PWM signal : 500 Hz In the below case we have two white light strips connected in parallel which will result in ...
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0answers
50 views

IR2101pbf Multisim simulation problem

I am trying to drive 2 MOSFETs (high and low configuration) to drive a 10 ohm load and there are 2 problems I am facing. When putting both HIN and LIN pins to 12V (High), the output is around 7 Volts ...
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5answers
197 views

MOSFET is overheating when running on a 20A load

I'm trying to build a controllable switch for a heavy load (3D printer), controlled by a microcomputer. I don't want to use relay because of slowness, sound and durability. So I've built a switch ...
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1answer
29 views

MOSFET Bi-directional current channel selection

With the circuit below: Q2 and Q4 burn down when 15A is injected into the circuit. Q4 burns even if it were never activated. The gate voltage control is 0 or 12V to activate a particular channel. I'...
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1answer
83 views

Converting Open-Drain to Active-High (low voltage, low power)

In my design, I need an RTC (PCF85263A) to enable a boost converter (TPS61021A) after the RTC alarm triggers an interrupt. The interrupt pin on the RTC (INTA) is open-drain, but the enable pin on the ...
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0answers
103 views

Problem driving MOSFET with ACPL 337J optocoupler

I want to drive a mosfet. I am using an ACPL 337J optocoupler to drive it. Here is the schematic:- But I am facing problem while driving the mosfet. The signal at gate of mosfet should be a PWM but ...
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1answer
48 views

Nanopower Fiber Optics / MOSFET Switch

I'm a newbie at designing at the nanopower level, hence my question. In this circuit, I have plastic fiber optical inbound signal that drives D1 photodiode, whose dark current is extremely low (tens ...
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1answer
66 views

Replacing TO-220 MOSFET with SMD DPAK

This MOSFET IRFBG30 is being used in an old design. It even has a little heat sink attached. The FET is used as a current limiter. During normal operation, a current about 13 mA passes through it. ...
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1answer
152 views

Why this H-bridge with only N-channel FETs didn't work?

Based on this answer here in StackExchange and the Motorola article it cites, I've designed a dual h-bridge motor driver with push-pull transistors to switch the FETs faster, layed out a PCB in KiCad ...
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1answer
42 views

What does it imply when substrate terminal of Nmosfet is short-circuited with the source terminal? [closed]

What does it imply when substrate terminal of N-MOSFET is short-circuited with the source terminal?