Questions tagged [fet]

Field Effect Transistor, a transistor in which most current is carried along a channel whose effective resistance can be controlled by a transverse electric field. Commonly used types of FETs include the Metal Oxide Semiconductor FET (MOSFET), and less common in recent designs, the Junction Gate FET (JFET or JuGFET).

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36 views

two stage op amp's PSRR

I recently study about two stage amp. In Sedra-Smith, it stays that PSRR for VDD is very small, and ignores this. To understand this, I set Q6's source Vin and Q6 is acting like a common gate ...
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MOSFET terminology seems to vary in every article i read!

For someone trying to learn about FET's, it seems there is no consistency in terminology (unless i am reading things wrong?) Trying to understand a FET as a switch (for power applications). It has ...
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83 views

Trying to understand MOSFET Turn on Procedure

I am trying to understand the mosfet turn on procedure. This is from the following application note by TI. https://www.ti.com/lit/ml/slua618a/slua618a.pdf?ts=1613979703351&ref_url=https%253A%252F%...
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Chopper FET as a Preamp

I have a small kit whose schematic is here, it has an LM386 (or equivalent) with an FET preamp stage. The FET went bad, and in searching for a replacement for the now obsolete part, I found that the [...
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38 views

Vds meaning in characteristic curve of a MOSFET

As I was wrapping up my design (which didn't include MOSFETs as switches tho, yet), I've realized I wanted to make it crystal clear for myself if I understand the thing correctly. Feels weird, but ...
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Need some help to calculate the resistance in a transistor circuit

I need some help with my transistor circuit. I have this circuit and I'm supposed to find the value for RD and RS, all other values are known. I think I managed to simplify the circuit on the second ...
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51 views

Diodes in input protection circuits

I'm studying this protection circuit that protects a microcontroller from inductive transients, switches, and other things in a small aircraft, which would be similar to a car/motorcycle/boat in that ...
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33 views

Multiple “typical characteristic” charts in FET datasheet

Looking at following datasheet: https://www.onsemi.com/pub/Collateral/2N5457-D.PDF I'm puzzled as to why there are multiple "typical characteristic " (pairs of) charts. As far as my ...
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Need help in selection of FET for transfer gate

I was studying the variable potentiometer X9C10x series. They are using a serirs of fixed resistors and some FETs to select points in this series branch. I need one variable point in my circuit. Can ...
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40 views

FET source body connected to the same potential

I have learn that the FET looks like this: However industrial FETs are not built like that.The source and the substrate have common potential.However if the source and substrate have common potential ...
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42 views

Measuring switching time of 5LN01SP (NMOS)

I am working on switching time test circuit for 5LN01SP specification. This is my circuit: Input test signal is (as per specification) a pulse of 1kHz frequency: PW = 10us D.C. == 1% We can see the ...
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Performing switching time test with NMOS (5LN01SP)

I am about to feed my switching time test circuit with input signal from signal generator. In a 5LN01SP's specification input test signal is marked as: PW = 10us D.C. <= 1% (see the picture) It is ...
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Conditions for a JFET transistor to saturate

I have come across the relations: vDS > vGS – VP for n-channel JFET vDS < vGS – VP for P-channel JFET The two are given as the conditions for JFET to be in saturation. How can I arrive at these ...
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40 views

Does the signal direction matter for a series N-channel FET switch circuit?

I'm working with a 40-year old audio circuit that someone modified to use an FET as a series switch. The circuit uses the Toshiba 2SK30A N-channel FET to pass a nominal ±1 VAC audio signal. The Source-...
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Negative drain current in FET

I am new to electronics simulation. I am currently simulating a simple FET where I sweep both the gate and drain voltages. When I plot the drain currents for low values of the drain voltage I obtain ...
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46 views

IGBT(Insulated-gate bipolar transistor) Latch-up

What will happen if the Parasitic transistor turn on?
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Self-biased JFET - Midpoint bias: Why set the drain voltage to one-half of it?

To set a midpoint bias, I understand that ID = IDSS/2 (and by equation, VGS = VGS(off)/3.4). For calculating resistor values, why set VD = VDD/2?
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Is this reversed P-MOS next to the battery for some other purpose?

I was handed a schematic with this P-FET next to the battery. My experience tells me that this would not provide any reverse polarity protection (which at a glance it what I thought it was for), but I ...
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79 views

High quality, low-noise, pre-amp circuit for condenser microphone (with phantom power)?

EDIT Suggestions so far, and reference to another question indicate that a discrete FET based input stage, perhaps followed by a particular low-noise IC for a second stage, might be a good approach. ...
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1answer
75 views

BJT transistor max switching frequency vs FET in high frequency computer architecture

Why arent BJTs used with RISC architectures to produce very high speed relatively sparse CPUs? My understanding is that BJTs don't have the forward bias gate capacitance requirements of FETs which is ...
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1answer
54 views

SOT23 transistor/FET infromation needed

I'm trying to Reverse Engineering A PCB but I have problem to identify some PCB components(Highlighted components). I don't know whether these are transistors or FETs. As without knowing their actual ...
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61 views

Electret microphone and FET pre-amp

My question is about designing a microphone pre-amplifier that uses an electret microphone. I saw a video of Doug Ford on the EEVBlog, in which he shows some pre-amplifiers for microphones. My ...
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Can you make a CPU out of electronic components drawn by hand on paper?

I explored a lot of literature about paper-based electronics recently, and one particular paper caught my interest: “Handwritten Oxide Electronics on Paper” (DOI: 10.1002/admt.201700009) by Elvira ...
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FET - unipolar transistor - Voltage-Divider, question about finding Idss and Id if no Vd given

If I am not given drain voltage how do I use the formula for Vp to get ID and IDSS current? So far in testing stuff I noticed that if the two resistors at the right side Rd=8k an Rs=7k are close in ...
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FET AC analysis self bias configuration

I'm studying AC analysis of FET: Self bias configuration without bypass capacitor. I'm not getting how Vrd = Vo + Vgs. My main problem is with KVL. I'm new to the subject. Reference : Boylestad
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Why would you use a shared-gate multi-channel MOSFET device?

This device has 8 drain channels, shared source, and a single shared gate: DMN1250UFEL How is this different from tying all the drains together and using a single FET? I suppose you could have ...
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What is the difference between “Operating Voltage” and “Drain-Source Voltage” for an LDMOS FET?

The NXP AFT05MP075NR1 ~75W power N-Channel Enhancement-Mode Lateral MOSFET provides the following maximum ratings in the datasheet: Operating Voltage (Vdd): 17, +0 Vdc Drain-Source Voltage (Vdss): -0....
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Why is a high value resistor necessary for grounding a MOSFET gate?

New to electrical engineering. I am following an introductory Cambridge university course but not entirely clear on what the lecturer is saying, and have nobody to consult because I am self-teaching ...
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47 views

FET electrode convention?

Are there any conventions that allow one to tell which electrode is source and which one is drain?
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322 views

Logic buffer design

Logic buffer is usually depicted like this: But can this work equally well? And if it's not the case, why not?
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64 views

Common Source vs. Common Drain for N-Channel Switches

Most discrete load switches I have seen (Using N-Channel FETs) have been in the common-source configuration. What, if any, are the operational differences between this and the common-drain ...
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Startup voltage help: How can I change the input voltage to this IC when starting the circuit?

I am currently trying to find a solution to switching the supply voltage for U12 (PN: UC3842BVD1R2G) in the included schematic. What is special here is that U12 will draw 22mA no matter the input ...
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435 views

Why are bipolar transistors used for switching applications?

I noticed that many sites targeted at hobbyists recommend bipolar transistors (mostly NPN) to switch things on and off. Bipolar transistors definitely have their purposes especially in analog circuits,...
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Iellegible JFET name, seems to be HEPxxxxx

I have this poor scanned schematic on which there is a Motorola P-channel JFET, labeled as Q5, and I can't read the name. It seems to me that the 2nd note is written "Q5 is HEP*1036" where * ...
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241 views

What FET can I substitute for PF5102 or J305? [closed]

I want to build this microphone: https://www.instructables.com/id/Modify-a-cheap-LDC-Condenser-microphone I am able to find all of the parts except for the FET. The schematic says to use PF5102, and ...
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67 views

calculating voltage or current for a plain transistor (no resistor)

the short version of my question is this: how do you know what the current through a transistor will be if there are no resistors? I am reading mostly the second edition of the Art of Electronics, ...
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69 views

JFET resistance and transconductance

The book says the rds of the 2N8461 JFET can be varied from 100 ohm to 10Meg. I went on and tried to verify this using the equation and plug values in it from the datasheet using the minimum values ...
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40 views

What is the current in a FET as gate voltage is increased towards large voltages?

I know that beyond a threshold voltage VGS, increasing the gate-source voltage VGS in a field-effect transistor (FET) increases the drain-source current IDS quadratically. I've looked on the web and ...
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Current measurement in MOSFET circuit

In this circuit, the drain current needs to be calculated when S1 opens and S2 closes and remain in this position for long time. In this position, the transistor is in cutoff region i.e Id=0. But the ...
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Am I calculating my shunt FET power dissipation correctly?

simulate this circuit – Schematic created using CircuitLab I'm designing an LED driver circuit that requires very fast PWM switching at a high resolution (10bit at 30khz requiring a minimum ...
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1answer
106 views

Can you get “raw” TFT display panels where you drive the gate and drain lines directly?

I am learning about different display types and how I might interface them with raw electronic components, e.g., TTL chips, op amps, function generators for scan line sawtooth, etc. CRT raster is ...
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chip identification in synchronous boost converter

Trying to use a car 12V to 20V (laptop charger) for my TS100 solder iron and trying to find out why it shuts off, i blew up some component(s). In trying to recover from that, created a partly ...
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1answer
66 views

Slope of VTC for FET

The book we are reading states that the maximum slope of this graph occurs at B, but I cannot understand from this graphic how that is possible. It appears to me the maximum magnitude of slope occurs ...
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1answer
109 views

What type of capacitor do I need to stabilize USB voltage?

I am trying to use a "FET" (https://elinux.org/RPi_GPIO_Interface_Circuits#Using_a_FET) to switch the power supply to a USB speaker from my Raspberry Pi. It's working well, however when I turn the ...
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2answers
33 views

Open Circuit Voltage with Open FET and Zener?

D2 is a 18V Zener, LM3Z18VT1, diode. M1 is a NCE01P30K. Node DO is 8V by default and 0V when the circuit activates. If M2 in the circuit below opens, what is the voltage at the gate of M1? Now ...
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ADS Non-Linear Demo Kit: Identifying the Transistor Model?

I have been trying to design a LNA using the ADS Non-linear demo kit library. I am trying to find the optimized bias point for stability and noise parameters, etc. The FET1 transistor is the device I ...
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'Invert' a logic low and logic high signal from a FM60 controller [closed]

We have an Outback FM60 controller which outputs 0 or 12V as a command, 0 for logic high, and 12 for logic low. I need to invert that for our solid state relay to output 12 for high and 0 for low. ...
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1answer
182 views

Why is it difficult to lower the overdrive voltage (Vgs-Vt)?

To save power consumption of switching devices in MOSFETs, the supply voltage (Vdd) should be lower. But, the lower the threshold voltage, because of the Boltzmann tyranny, the bigger the leakage ...
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1answer
85 views

Circuit Design - Need 35mA through UV LED using a GPIO controlled switch

I was trying to achieve this using a PNP transistor as a switch circuit and the voltage drop was too significant and I was only able to achieve 13mA. Circuit here I was advised to use a FET instead. ...
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105 views

Why do some analog circuits use a FET with shorted drain and source?

Why do some analog circuits use a FET with shorted drain and source? Depending of the type of FET, it may either act as a capacitor or a diode? It each case, why not just use a cap or a diode? Below ...

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