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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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367 views

Logic-level converter FET

I have been using the BSS138 level converter circuit for a while now and today it struck me I get how the voltage is stepped up by the FET or the BSS138 when you are applying say 3.3 V on the LV side. ...
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40 views

JFET Voltage Divider design question

I've been trying to get this question done for a couple of days now and no matter how much I try I've been unable to get it done. Your help in this question is greatly appreciated.
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3answers
103 views

how to reduce current to power LEDs

I am replacing a microscope lamp with a motorcycle LED headlight. The light is 20W, 9-85V DC; the driver built in and a complete black box to me. I power it with a 65W power supply (18.5V/3.5A). For ...
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1answer
91 views

Voltage drop when switching FET

I am working on a project which will be switching LED strips with a max of 2A. As a test I have connected a 20W hallogen light. When I try to switch it I get a voltage drop as can be seen in the ...
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1answer
30 views

replacing obsolete HEMT and differences between Package/Case and Supplier Device Package

I've been designing an amplifier, with ATF33143 as my HEMT in mind. Yet, I just found out the said HEMT went obsolete. So I started looking at SKY65050-372LF as a possible replacement. On the DigiKey ...
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1answer
101 views

Why does a MOSFET enter saturation?

From all my browsing, it has become clear that as drain-source voltage increases, we eventually reach saturation. Mathematically, Vds>Vgs-Vt is the condition we look at. But when I try to understand ...
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3answers
2k views

Is it good practice to run large amounts of current through a MOSFET?

I have been looking for a good way to control the flow of a lot of current in my project. This may at some points be 40-50 amperes at 12-15 V. While relays are a good choice, they are mechanical ...
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1answer
61 views

Filtering current spikes in photodiode transistor selector

I am building a circuit for sensing photocurrent from a photodiode. The diodes are manufactured with selection transistors to form an active matrix and below is a model of a single pixel consisting of ...
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2answers
125 views

Momentary Switch NAND Latching IC Burning and (Possibly) Faulty Logic

Problem: My issue is that the momentary switch with NAND latching logic that I have designed is not functioning consistently. It does work as intended at first, but then fails to work after repeated ...
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1answer
96 views

JFET saturation current

Is it possible to analytically calculate Idss for JFET? I tried by setting voltage gate-source to zero, and then finding the drain current, but it doesn't seem to match with the given value?
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1answer
89 views

Start/ stop 5v motor from headphones jack

I would like to make the jaw of a plastic skull open/close based on words spoken by a Raspberry Pi. I can make the Pi send the audio to the headphone jack, and would like to use this output to run 5v ...
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0answers
57 views

What is a good Field-Effect Transistor Model?

Hi guys I'm writing an electronics circuit simulator and I need a very simple and straightforward model for a field-effect transistor (as simple as the Ebers-Moll model for a BJT). I can use resistors,...
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1answer
63 views

What kind of diode should I use across the load?

I'm designing a circuit using an ST VN7020AJ high side driver. The application diagram recommends placing a diode from VCC to ground. The document doesn't provide any recommendations on the type of ...
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0answers
28 views

How to do thermal analysis of a P channel high side drive circuit.

I have to design a PCB where one of the features is such that every time a stepper motor is moving a fan switches on. A high side P channel FET driver has been suggested as shown below: I just need ...
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0answers
65 views

Transfer function of loop-back bias circuit for RF amplifier

I am trying to implement a current mirror as part of a bias circuit for a RF amplifier. I want to do a transfer function of the bias circuit since it creates a loop from the amplifier fet drain to ...
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1answer
150 views

Negative Gain and in a common gate FET amplifier [closed]

We conducted an experiment involving frequency response in common gate FET amplifier. The results at different frequencies from 10Hz to 1MHz are obtained and we got a negative result in the first few ...
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1answer
120 views

What is the purpose of this FET load?

I'm used to seeing a load resistor in the place of the yellow highlighted (Q2) section of this FET amplifier circuit. This is the input section of a guitar overdrive effect, so any distortion created ...
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4answers
231 views

FETs: When does Input Capacitance and Gate Charge matter?

My question is this: Besides frequency response (i.e. filter effect), does input capacitance every matter? When does gate charge matter? Obviously these have effects on the graphs in the datasheet, ...
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1answer
69 views

Current consumption of PWM controlled MOSFET [closed]

I'm trying to design an application in which a DC/DC converter with limited output current capabilities drives the gate of one or more transistors in PWM mode. My question is, how can I estimate the ...
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2answers
539 views

MOSFET with 5 V logic, 24 V VDS / VGSS

I am trying to select a MOSFET that will work as a logical switch on a 24 V power rail, toggling on/off as signaled by a GPIO on an Arduino. The Arduino pin that will connect to the gate on the FET is ...
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1answer
89 views

How to choose right transistor? [closed]

I have been trying to design a differential amplifier for EEG. How can I choose the right bipolar transistors and FETs according to my aims ? Any guide will be appreciated. Thanks in advance.
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2answers
83 views

Turn gate on and off while on rising edge of a signal

I am measuring a voltage which looks something like the positive half of a sine wave and I want to drive the gate of a FET while this voltage is inbetween two certain points. So for example the ...
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1answer
54 views

JFET I drain vs V gate to source curves

Why there are several curves on next image (datasheet for 2SK170)? What condition changes to use one or another curve?
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1answer
49 views

Power Amplifier inside an OPAMP

Here is a simplified schematic diagram of one of the operational amplifiers inside a TL08x. The Diagram I wonder why a power amplifier is used ? (on the right side) What is it good for ? Thanks in ...
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1answer
88 views

Is the FET gate resistance counted on the RC time constant?

As I understand, a logic "1" output to an input of another IC can be modeled like this : simulate this circuit – Schematic created using CircuitLab with C1 representing output capacitance, R1 ...
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2answers
127 views

Resistor Divider PMOS Example Problem

From Razavi's Design of Analog CMOS Integrated Circuits, question 2.6a asks to plot \$I_x\$ vs. \$V_x\$ as \$V_x\$ varies from 0 to 3 V in the circuit below. The solution manual states that: $$V_{sg} ...
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2answers
37 views

Can a ITS4100S-SJ-N High side power switch be used to switch AC/DC load

I have seen a PLC which uses the ITS4100S-SJ-N component to switch (just on/off) a 24V DC, 2A max. load. I was asking if those components can also be used to switch 24V AC? Datasheet: https://www....
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1answer
150 views

What role does a FET play when working with GPIO pins on a Raspberry Pi?

I recently asked this question where I'm trying to wire up this momentary switch to my Raspberry Pi 1 Model A such that: The switch is normally open; and When pushed down: it closes the circuit, ...
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1answer
27 views

MOSFET drain current parametrized to distance

In Id-Vgs Mosfet curves, sometimes, current is parametrized to a distance in micrometers. What is this parameter? Gate length, effective gate length, or width of the transistor.
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0answers
64 views

Current drop a certain vds in a transistor

I am measuring the I-V characteristics in a transistor using a 2 channel source measurement unit (SMU) when I change the \$V_{ds}\$ and measure the current while connecting the gate and the source to ...
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2answers
216 views

Can you turn on a NMOS with a lower voltage than at the drain?

So, a NMOS can be turned on if the \$V_{GS}>V_{TH}\$. If the circuit is such as below: simulate this circuit – Schematic created using CircuitLab So, say that the \$V_{TH}\$ is quoted as ...
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1answer
56 views

High Side Switch Flicker during Power Up

I have some problem with a P-channel mosfet used as high-side load switch. Everything works fine beneath the power up moment. You can find the schematic in the picture below. During Powering the ...
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1answer
106 views

Troubleshooting a PWM-field effect transistor driver board

I'm an untrained hobbyist trying to fix this motor driver circuit and was looking for some guidance or help with troubleshooting, or reconstruction. The circuit is from a handheld vacuum cleaner that ...
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1answer
301 views

Swap FET TO-220 pinout

I messed up my PCB design when I made a change of FET-model. Now the Drain and the Source pins are swapped and it seems that there are no TO-220 models made this way (1-Gate, 2-Source, 3-Drain). Are ...
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2answers
50 views

Need help finding the transconductance author of this book is referring to

I am reading a book "Practical Electronics for Inventors" and I was trying to understand the FETs, at several places the author has mentioned about the trans conductance that he has noted with gm. I ...
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2answers
696 views

Solenoid valve FET

I would like to drive a proportional solenoid valve (PVQ31 24V model from SMC) using a high frequency PWM. I followed Olin Lathrop's advice to open a new topic. He suggested to build a circuit ...
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2answers
86 views

What is the name of the maximum source to drain differential for a FET? [closed]

I'm working with high voltage, high power motor applications, and it's slipping me right now; what is the name for the maximum voltage between the drain and source of a FET? Edit: sorry for the ...
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0answers
87 views

Replacing Decoder/Driver IC (30V, 300mA)

I'm looking to replace an FP2800a decoder/driver IC for a flipdot display. This chip decodes to 28 outputs, which it can drive towards a Vcc of 30V or GND with a maximum of 300mA. A search on ...
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3answers
675 views

Which one is the pinch-off voltage?

According to my book and teacher : It is the Gate voltage at which the depletion region closes the channel. According to some people on the internet and Youtube videos: It is the Drain to ...
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1answer
554 views

miller effect - What circuits have miller effect?

I have an exam tomorrow and I have a theoretical question. Just have Miller effect common source (FET) / common emitter (BJT)? Or common drain (FET) / common collector (BJT) also have? Is there some ...
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1answer
68 views

op amp n-type with additional resistor and current source

I have an op-amp using n-type FET with current source. I have several questions on these circuit: 1. Operation of circuit 2. Equivalent circuit 3. Av, Ai, Zin, Zout Since this circuit has ...
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0answers
297 views

Who do IGBT rectifiers have floating gates (unlike MOSFET rectifiers)?

When I search Google Images for "IGBT rectifier", I notice that they all appear to have floating gates. But don't IGBT's have gates like the ones on MOSFET's, in which it's insulated from the other ...
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0answers
64 views

Model for small signal - 3 transistors JFET

Could you tell me if the models for small signs are well made? And if they were not, you could tell me what I missed, please? Thanks. \$V_{dd}=17 \,V\$ \$IDSS= 8 \,mA\$ \$V_P=-3\$ \$r0=30 k\$ \$...
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1answer
67 views

Why is this simulated transistor turning on at such a low voltage?

I'm trying to simulate (using the Mouser edition of MultiSim) a very basic transistor circuit, above, with a MOSFET acting as a switch. It sort of works, inasmuch as V2 reads 20V when ...
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0answers
84 views

FET - confirm if both circuits are equivalent for medium frequencies

I would like to make an incremental model of the transistor for medium frequencies. I've tried to make the matrix. Could you confirm if the two circuits are equivalent for medium frequencies, please? ...
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0answers
96 views

problem with a circuit with one JFET

The circuit is a common source amplifier that uses the 2N3819. It is known that \$V_{DD} = 20\,V\$ and that \$R_g = 100 \,Ω\$ (the generator resistance \$V_g\$ applied in In). The entrance and exit ...
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2answers
353 views

Input capacitance IGBT and MOSFET

I measured the input capacitance of a MOSFET and found it was greater than an IGBT. Why is this? Is it due to the Miller capacitance seen in a MOSFET?
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1answer
30 views

FET bybass Circuit

I am driving green LED in series with a boost converter and unfortunately my input voltage (24VDC) turns my LED string on slightly even when my manually controlled boost converter is not boosting the ...
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4answers
606 views

Proper board layout for high power SMT FETs

I came across an SMT FET (IPT015N10N5ATMA1) that has an output of 300Amps in a rather small form factor. Are thermal vias enough to get heat away from the 8-PowerSFN package? Or would something like ...
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1answer
214 views

Advantage of active bias circuit

I have seen some amplifier designs that bias the gate by using a voltage divider and small size FETs with drain connects to gate as the picture shows. I am wondering what is the advantage of these ...