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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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Using P-channel FET as switch

I'm designing a charger circuit. When the input (+5v) is available it should disable the booster regulator by setting Booster_en to low. I used a single P-ch MOSFET ...
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High Voltage Cascode with MOSFET LT Spice Simulation

I'm an electronics engineering student and want to develop a high voltage switch with normal Si N-MOSFETs. After some research, I discovered cascode switches for this application. Most of these ...
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Should the mass action law be valid for charged semiconductor surfaces?

Considering the case for Metal Oxide Semiconductor also Streetman's book says that if the contact potential for n type semiconductor exceeds zero it should develop into depletion region but WHY ? It ...
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2 x 2 n-channel mosfets in series: does my circuit has any flaws?

For a hobby project I would like to switch between two power supplys. The load are two motors which can also be switched on and off separatly. The two motors are BLDC controllers in reality. I am only ...
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Mosfet Based impulse voltage generator

enter image description here **Details- Mosfet_1 will turn on for 20ms and charge the capacitor C2 and after that, it will turn off. Then the Mosfet_2 will turn on for 3ms with 40kHz frequency and ...
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47 views

Inverter Design - High Side MOSFET - Slow Switch Time

I've posted previously on a similar issue which can be found here Overview: My design is a 3 phase inverter with: MOSFETS are STF10N60DM2 Gate Driver is 6EDL04N06PT I'm using only a single high ...
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24 views

Parallel with a short - MOSFET

I was watching the following Razavi video https://youtu.be/icrn9cYIPUA?list=PLiDoPUX9nLkIw9EnIv_3K19wlcyJ6msYd&t=1564 At 26:04, he says that no current flows through the resistance Rd as voltage ...
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26 views

Single MOSFET motor driver with oscillation on output

I'm trying to drive a small DC motor with a PWM with the circuit below, where I'm using a TIL111 optocoupler and a IRF510N MOSFET. The PWM (50% duty cycle) is generated by a MCU STM32F103C8T6, the +3....
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A voltage-controlled electronic equivalent of an SPST switch using MOS/BJT/Diodes

In order to use a close equivalent to ideal SPST switch for basic circuit simulations, I had been using a four-terminal voltage-controlled switch available in Ltspice simulator with quite less rise ...
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25 views

Simplification Made to Gain Equation

I was watching one of Razavi's videos https://youtu.be/pK2elUcXWzs?list=PLiDoPUX9nLkIw9EnIv_3K19wlcyJ6msYd&t=2309 Skip to 38:30 He did this: He justified this approximation by saying that ...
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39 views

Discriminate MOS from BJT easily

I have a transistor for which no datasheet is available the transistor is supposed to be NPN (which implies BJT). (BD247C-Transistor-NPN, 100V 25A, 120W in TO220) how can I find out easily if it's ...
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What is the purpose of a diode and resistor at the gate of a FET in this LED driver circuit?

I am trying to design a LED driver based the LM3409HV IC. I am using the reference design from TI as a starting point. The schematic in the datasheet has a diode (D2) and a resistor (R5) at the gate ...
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MOSFET Miller effect: length of the gate voltage flat area

As per Miller effect the gate voltage stops to grow at the threshold level until some certain moment: This can be explained as the drain to gate capacitance drives current through the gate. However - ...
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43 views

Output voltage of MOSFET differential pair with current mirror load

I've seen this circuit from https://www.allaboutcircuits.com/technical-articles/advantages-of-the-actively-loaded-mosfet-differential-pair/ How are the drain voltages equal?? I can't seem to figure ...
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39 views

How to turn off a mosfet [on hold]

I have this simple circuit that delays the turn on of a MOSFET. However, I would like to quickly turn it off (but no quicker than a millisecond). Is there a way to use the output of the MOSFET to ...
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28 views

What happens when the DC supply of this common gate amplifier is switched off?

The Vin in this case is a 200mV peak to peak sine wave signal. what happens to the gain of the amplifier when the DC supply of 10V is switched off?
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40 views

active current protection with diode instead of shunt resistor

Is this current protection technique going to work? I came up with this because I want to make a current protection circuit and I do not have a shunt resistor at hand. I think the circuit should work ...
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56 views

Understanding Vgs absolute value

If a P-channel MOSFET have absolute maximum values: VDSS = -60 V Vgs = +/-20 V "refering to high switch side": Does this means we cannot switch the MOSFET by the gate driver that ties the gate to ...
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How does a cascode current mirror maintain equal Vds of the bottom transistors?

A basic current mirror is shown below: The load and reference current relationship is affected by channel length modulation: In order to cancel the effects of channel length modulation, vds1 and ...
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62 views

Power Switching using MOSFET and opamp

I'm trying to understand the Arduino design. LM358 and FDN306P is connected in between USB input and primary source input. In presence of USB and primary supply the Arduino mega board is drawing ...
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56 views

Calculating drain current with series N-channel MOSFETs

When two N-channel MOSFETS are connected in series, with common gate connections, then how can I analyze this circuit to determine Id through these MOSFETS, as a function of Vgs and Vds? simulate ...
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63 views

MOSFET failing test

I purchased a repair kit for a TV SMPS. The kit contained 3 identical N channel MOSFETs (K8A50D), among other components. I tested all 3 with a DMM following a number of identical instruction videos. ...
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NMOS bidirectional variable resistor: How to increase body diode barrier potential?

I want to use an NMOS as a variable input resistor to an inverting amplifier. The source is connected to virtual ground and the drain is connected to the input. I need to accomodate both positive and ...
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34 views

N-channel MOSFET switch circuit with long tailed pairs doesn't seem to work?

I am trying to build a circuit that will integrate some charge from a some test input (TEST-IN) only when a switch is on. In order to mitigate charge injection from the MOSFET I was going to use long-...
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123 views

Constant current source with MOSFET, OPAMP and Instrument Amp

UPDATE Based on the information from everyone answering below, I have modified my circuit and the oscillation has completely vanished! I started performing small modifications in order of easiest to ...
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59 views

IGBT and MOSFET for driving motor

I have a question that in motor driving application, by using power MOSFET, it must be in saturation region, is this right? And for IGBT, in which region it must be to act as a switching device?
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48 views

Choosing Vds value for low-side switch

I want to switch a 24v DC water pump by a 5v DC from an Arduino. I think the best way to do it is by a logic level mosfet low side switching. To do so, the Vds value should be 24v or a much lower ...
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32 views

Simulating 3 phase mosfet bridge with LEDs

I have a commercial 3 phase BLDC motor driver board (TI DRV8323 BoostXL) and I want to write a firmware from scratch. For testing, I want to make sure I open/close the mosfets in correct order. I am ...
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MOSFET selection

Need help with MOSFET selection for a circuit. I am having some difficulty understanding data sheets. Primary mosfet, Vds controlled 20mv, Vgs 3.2-4.35(Lipo). Drain current up to 4A. Ideally Rdson ...
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2answers
52 views

High Side P channel mosfet with totempole driver + floating / voltage follower pull down

This is my first post (been an avid user though as I usually find an answer to my questions... this time I cannot despite a few days of searching. I've created a push pull gate drive circuit for a ...
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78 views

What the function of zener diode on this picture

I am confuse, why we need clamping with zener diode because it doesnt matter when vgs goee below zero, cmiiw
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77 views

How to build a simple transistor switch?

How to build the following: A simple Transistor turn-OFF switch. A simple transistors circuit that has its own power source, but when I apply a second alternate power source then it will switch to ...
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64 views

How to size these resistors for the MOSFET gate or are they redundant for this case?

I want to control this solid state relay through a 0/5V digital output. The digital output should not draw more than 10mA so I will use this FET transistor. 12V DC power supply is used to switch the ...
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Howcome there is current flowing through the gate of this transistor?

I have a few conceptual questions: If there wasn't Rg (Resistor between gate and drain), would Vin = Vout then? For small signal analysis, current can flow through the gate (AC) if there's a voltage ...
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54 views

How to measure output voltage of this Li-Ion battery circuit?

I've designed an AtTiny85 based Lithium-Ion battery protection/boost circuit that monitors the battery voltage and cuts the battery power to the external powered circuit when the battery dips below a ...
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53 views

MOSFET Gate resistor in discrete NMOS Logic Gate Design

TL/DR Short version of the question: I want to construct discrete logic gates from a lot of BSS123 MOSFETs. Can those MOSFETs drive each other without the usage of gate resistors without damaging the ...
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switching between two similar power sources - solar battery and cr2032

I'm trying to create a circuit powered by two alternative power sources. The first one is a Li-Po battery charged by a solar panel and the second one - standard 3v battery, ie. CR2032. The circuit ...
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142 views

Biasing Class AB power amplifier with MOSFETs

I am having trouble getting the resistor biasing to meet a minimum 1.25W at the output: Note, the distortion and watt meter. I was told the SPICE parameters for the FETs didn't really matter. (...
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Mosfet switches high-vs-low for ATTiny circuit switch

What would be the pros and cons of using either a high-side p-channel vs. a low-side n-channel to turn an ATTiny LED circuit on and off? Is either one better for a mostly-off or a mostly-on type ...
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Where to place a diode - DC 12v motor controller

I'm building a controller for a DC motor. I'm using a 12V DC motor from windscreen wipers. Here is my circuit diagram and a video of the simulation I made. https://www.youtube.com/watch?v=...
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noise comparions between Schottky and MOSFET

I have a circuit that uses a Schottky diode to provide reverse voltage protection. However, the diode chosen is on a long lead time and an alternative that is immediately available is required. I've ...
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1answer
80 views

MOSFET Vgs Electrical OverStress [closed]

I have a design is that over-stressing (EOS) a PFET's (PMDT670UPE,115) rated Vgs by 50% (Vgs -12V, limit is -8V), I want to consider PWM'ing this part with 50% duty cycle in hopes of increasing the ...
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1answer
73 views

Switching a 3v motor with a MOSFET using a 3.3v signal

****I have knowledge of programming but VERY little experience with electronics.**** I'm attempting to switch a MOSFET using a 3.3v signal from an Adafruit MCU module (Adafruit Module here). The ...
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Is this small-signal gain correct?

All MOSFETs (not JFETS) Have I calculated the small-signal gain correctly? IGNORE body effect etc. but not channel length modulation I was basically able to get rid of M2 apart from its resistance.
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89 views

Controlling the Spark plug using 555 IC

I built the circuit for ignition system using MOSFET, 555, ignition coil(specs unknown. But current rating is more than 2 A and less than 10 A), SMPS(12 V, 10 A for powering the the whole circuit). ...
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Maximum mid-band gain of s.s. model MOSFET amplifier?

Schematics I need to find the maximum possible gain for this NMOS cascode circuit. Here is the s.s. model: Work I used nodal-matrix analysis (basis is KCL) to find the gain (\$A_v\$): $$ \...
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17 views

Donor concentrations between the Gate and Drain

When attempting to determine whether a MOSFET is NMOS, PMOS, or at intrinsic concentration, assuming the Drain and Gate are dopped to Nd = X and the bulk is doped to Na = Y, I get a little confused. ...
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57 views

Gate driver for Mosfet PWM switching

I am designing a lead acid battery charger using Battery University for guidance. This is the circuit I made. At the input, I will be connecting an SMPS rated for 12V 15A, which will be adjusted ...
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86 views

Why does this MOSFET always turn on in saturation?

Consider the following case: In Razavi's book, it says that this MOSFET will always turn on in saturation mode.(assuming Vgs is just greater than Vth) I'm trying to figure out why. For Saturation: $$...