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Q&A

Posts tagged field-effect-transistor

Synonyms: FET

Subtag of transistor · 2 child tags

Anything related to FETs, i.e. Field Effect Transistors, a category of active electronic components.

The most common kind of FETs are JFETs and MOSFETs.

Use this tag for questions related to FETs in general. If your question is exclusively about a specific kind of FET, just use the more specific tag (e.g. JFET, or MOSFET).
Tag Wiki

The term FET is an umbrella term for different kinds of devices, whose behavior is based on the field effect, i.e. the ability of an electric field to control the flow of charges in an internal structure called channel.

FETs are usually 3-terminal semiconductor devices (although there are some exceptions regarding MOSFETs).

Their terminals are called Source (S), Drain (D) and Gate (G). Roughly speaking, source and drain are the "output" terminals, whereas the gate is the "input" terminal.

They come in two variety, named N-channel and P-channel, depending on the polarity of the channel doping, which can be either N-type or P-type.

The channel internally connects source and drain, whereas the gate is connected in such a way that a voltage applied between gate and source will generate an electric field that will influence the conductivity of the channel.

Therefore the basic behavior is that the current flowing through drain and source (IDS) is controlled by the voltage across gate and source (VGS).

FETs are most commonly used as amplifiers and electronically-controlled switches and resistors.

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Q&A Control logic for mosfet in piezoelectric energy harvesting circuit

Hello, I'm working on an energy harvesting circuit known as an in-house harvesting circuit (cc-ih) and would appreciate some guidance on implementing it in Simscape within Simulink. Circuit Descr...

2 answers  ·  posted 23h ago by losdox‭  ·  last activity 11h ago by TonyStewart‭

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Q&A MOSFET drain current ringing in saturation region

I benchtested below 0.7A constant current source circuit and observed few cycles of oscillation on drain current. With the help of bode plot analysis , I have managed to reduce the oscillations on ...

2 answers  ·  posted 1mo ago by kadamrohan16‭  ·  last activity 1mo ago by Olin Lathrop‭

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Q&A Soft-start circuit behaviour

Let's take a soft-start circuit that looks like this: To my understanding, the function can be described as follows: C1 charges to open the gate. Value of C1 will dictate the soft-start delay...

1 answer  ·  posted 8mo ago by Mu3‭  ·  last activity 7mo ago by Olin Lathrop‭

Question MOSFET DC
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Q&A Case temperature of MOSFET

Homework problem A MOSFET has a power dissipation of $P_{d} = 10\text{W}$. The MOSFET is mounted on a heatsink. There is an isolation pad between the MOSFET case and the heatsink. We are given t...

1 answer  ·  posted 2y ago by Carl‭  ·  edited 8mo ago by Lorenzo Donati‭

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Q&A What is this fourth connection in NMOS device?

I know that in transistors there is base, collector and emitter, and in FETs there is gate, drain and source, but what is the fourth grounded connection opposite the gate in this NMOS circuit?

1 answer  ·  posted 2y ago by NMOS lover‭  ·  edited 8mo ago by Lorenzo Donati‭

Question MOSFET
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Q&A Battery protection circuit

I am using two 18650 cells in series to power a RC car. Is the voltage goes below 6.2 V, the battery should be disconnected to prevent over discharging the battery. At the same time I want to imple...

2 answers  ·  posted 1y ago by Stefan‭  ·  edited 8mo ago by Lorenzo Donati‭

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Q&A Two way circuit breaking capability for ideal diode controllers

I would like to save some costs with ideal diode controllers. Basic requirement is for the diode controller to block overcurrents (short circuits) in both directions. The MAX16141A IC can do it a...

1 answer  ·  posted 9mo ago by kellogs‭  ·  edited 9mo ago by kellogs‭

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Q&A Why there is a body diode in mosfets?

In theory (I mean in my engineering curriculum) I never found a diode in a mosfet symbol but in datasheets there is a diode called as body diode in both pmos and nmos.Please explain its significan...

3 answers  ·  posted 3y ago by aditya98‭  ·  last activity 9mo ago by Lorenzo Donati‭

Question MOSFET body-diode
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Q&A Are a JFET's Idss and Vgs(off) values correlated?

I know that many JFETs parameters have a very large manufacturing spread, in particular, $I_{DSS}$ and $V_{GS(off)}$, as one can see (for example) in this datasheet excerpt: ... My question i...

1 answer  ·  posted 10mo ago by Lorenzo Donati‭  ·  edited 9mo ago by Nick Alexeev‭

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Q&A Choosing between common-drain JFET amplifier, and common-source

Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times. Here are the schema...

1 answer  ·  posted 10mo ago by misk94555‭  ·  last activity 10mo ago by Olin Lathrop‭

Question JFET photodiode
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Q&A Sensing 3 states in a single mcu pin using firmware

I want to sense 3 different states in the same mcu pin (GND, Hi-Z and PWR). PWR is typical +24V but I would like to have a wide margin from +17V to +40V just to be safe. The values can change but ...

1 answer  ·  posted 10mo ago by DeadMouse‭  ·  last activity 10mo ago by Olin Lathrop‭

Question MOSFET
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Q&A Variant of a Mosfet's Gate-Source protection

Let's say a 100V voltage spike arrives at +12V and the TVS diode clamps it to 25V. Q2 may or may not be activated. Will this circuit ensure a V_gs lower than 25V for the mosfet Q1 ? Any catch to it...

1 answer  ·  posted 10mo ago by kellogs‭  ·  last activity 10mo ago by Olin Lathrop‭

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Q&A MOSFET protection with TVS: at the source pin or at the drain pin

In the auotmotive context, does it matter where the fat load-dump grade diode is placed in relation to the MOSFET so as to protect it from both fast positive transients and the longer load dump ? ...

2 answers  ·  posted 11mo ago by kellogs‭  ·  last activity 11mo ago by Lundin‭

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Q&A DAC controlled high side current source.

I'm designing a high side current source that can be controlled with a Digital-to-analog and can source up to 100mA with voltage supply up to 36V. By high side I mean one side of load will be alwa...

1 answer  ·  posted 2y ago by DeadMouse‭  ·  last activity 2y ago by Olin Lathrop‭

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Q&A Why are there more N type than P type MOSFETs?

I was looking at different transistors, especially MOSFETS and I saw that N type MOSFETs seem to be way more popular to be used in circuit design. Is there a reason for that, or am I mistaken?

2 answers  ·  posted 2y ago by crusadEEr‭  ·  last activity 2y ago by Olin Lathrop‭

Question MOSFET
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Q&A Low-frequency PWM-controlled Mosfet heater circuit

The circuit above is used to control a 240W ceramic heater by means of a PWM signal at 30Hz, generated by a microcontroller, with 5V logic. The input is a standard 280W AC-DC external power adapt...

2 answers  ·  posted 2y ago by francesco‭  ·  last activity 2y ago by Pete W‭

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Q&A MOSFET not turning completely off

Hello everyone, I have a simple circuit in which I control some LEDs via an MCU and DMG2302UK ( N-channel MOSFET ) The EN pin is connected to an MCU gpio pin that works at 3.3V. The circuit wo...

1 answer  ·  posted 2y ago by AhmedMobarez‭  ·  last activity 2y ago by Olin Lathrop‭

Question MOSFET
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Q&A MOSFET differential to single ended converter intuition

How does the differential to single ended converter work? In order for the circuit to work, Q1 and Q3 must be in the saturation region and depending on the voltage inputs, one of Q2 and Q4 will be...

1 answer  ·  posted 3y ago by MissMulan‭  ·  edited 2y ago by Peter Mortensen‭

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Q&A Battery voltage: to boost or to connect in series.

Background. I have a legacy battery system that is comprised of twenty-four 12V Li-ion battery modules (self-protected), enclosed in a shell with the charging connection provided as a common groun...

1 answer  ·  posted 3y ago by DSI‭  ·  last activity 2y ago by Olin Lathrop‭

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Q&A JFET equation of current

Is this equation valid only when a JFET in saturation mode , correct? because in the ohmic region the JFET acts like a voltage controlled resistor and increase in VDS increases the resistance of th...

0 answers  ·  posted 2y ago by MissMulan‭

Question voltage current JFET
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Q&A High Power Switch - High Side vs. Low Side Switching

Imagine a battery pack with <=60VDC of maximum voltage and a load of up to 10kW of power(the PMSM inverter with the input capacitance of up to 1mF). The load is not always known - could be 100uF...

2 answers  ·  posted 3y ago by 2kind‭  ·  last activity 3y ago by Olin Lathrop‭

Question MOSFET switching
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Q&A Using FET based followers and design rules

Usually, voltage followers are built with bipolar transistors (or with opamps if better precision is needed). In this case, the simple rule says that the transistor emitter "follows" the input vol...

5 answers  ·  posted 3y ago by coquelicot‭  ·  last activity 3y ago by TonyStewart‭

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Q&A How to define Vsat for MOSFET as a switch?

I was looking at this design: It uses MC34063 as switching controller. I wanted to adapt this circuit, and I was busy trying to pick R1 value. The datasheet has following formulas: The issue I hav...

2 answers  ·  posted 3y ago by Kranulis‭  ·  last activity 3y ago by Andy aka‭

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Q&A How to avoid shoot-through in MOSFET bridge drivers

I'm using a variable duty cycle square-wave oscillator to drive a half-bridge MOSFET pair like this. Upper MOSFET is P-channel type, lower MOSFET is N-channel type: - And, I think I'm getting shoo...

1 answer  ·  posted 4y ago by Andy aka‭  ·  last activity 3y ago by Andy aka‭