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 ...

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14
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5answers
2k views

Why (not) put a resistor on FET gate?

While thinking of ways to protect a MOSFET one idea was to put an extremely high resistance in front of the gate: The idea being that current is never supposed to flow through the gate, so if some ...
1
vote
0answers
43 views

FET Default on, Turn off with Optocoupler

I am relatively new to electronics and having trouble designing a circuit for a redundant power supply, which I would like to switch to battery if the voltage regulator turns off. This will be ...
0
votes
1answer
45 views

Voltage follower with a pair of matched FETs

I am studying for an exam and as a part of a question I have to explain biasing and operation of the voltage follower that uses two matched JFETs in the following arrangement: I am not sure that I ...
0
votes
3answers
103 views

What's the difference between ON voltage and threshold voltage in FETs?

In field-effect transistors (FETs), what's the difference between ON voltage, \$V_{\text{on}}\$, and threshold voltage, \$V_{\text{T}}\$?
-2
votes
1answer
68 views

Faulty P-CH MOSFET?

Last month I bought a couple of IRF5305 (click for datasheet) on Ebay. Today I soldered a couple of them in my PCB and had some issues with them. My FET schematic looks like the following: ...
0
votes
1answer
38 views

Why the point SS is at lower potential than S in the MOSFET circuit?

I can't understand why the p type(SS) and the n type conductor(S) are said to be in reverse bais.
0
votes
2answers
109 views

make a buffer balanced

i am still new to electronic and i probably have a stupid question.. i am trying to build a buffer for a piezo microphone following the project on this site: http://www.scotthelmke.com/Mint-box-...
15
votes
2answers
1k views

Why does this simple FET circuit behave this way?

In the circuit above, when S1 is pressed and released, the LED turns ON and stays ON. Why is this so? I can't directly measure the Gate Voltage with a DMM since connecting the DMM results in the LED ...
0
votes
1answer
49 views

Two-terminal Connection High-Side MOSFET driver

So I'm trying to make a discrete device that functions the same as the highlighted portion of the diagram, which is taken from a Battery Management System chip. I understand that n-type FETs are ...
0
votes
1answer
86 views

AC load driving using FET

I want to drive an AC 220 V load(heater) controlled PWM from Microcontroller. I want to use power FETs to load drive upto 2000 Watts. I m not guessing any valuable circuit design. If anyone have any ...
0
votes
1answer
52 views

uni directional logic level conversion with active drive current

I'm trying to connect an EM4095 to a cortex m0. The EM4095 requires an active high drive voltage of min 4V and has an internal pull down of 50K. Additionally it must be low during boot, otherwise it ...
1
vote
0answers
61 views

Thoughts about H bridge

I'm planning to build a pwm driven H bridge. I have all set up, flyback diodes, pull up and down resistors on high and low on bridge's side, decoupling capacitors and so on, but I only have TIP122 ...
1
vote
3answers
91 views

RF FETs - how exactly are they different from regular FETs?

I've browsed through DigiKey and there are these RF FETs. Are they for final stage amplification? Say you have an opamp that doesn't go for the final desired voltage, so one uses these FETs as Common ...
-1
votes
2answers
155 views

MOSFET Overheating when Driving Stepper motor

I'm trying to create a stepper motor driver for a 5 phase motor based on the application note found here. So based on this, I am using the following MOSFETS: These are hooked up to an Arduino and ...
0
votes
2answers
211 views

What does it says the transconductance efficiency (gm/Id) in an amplifier?

I understand the concept of the transconductance but it's not clear what does the transconductance efficiency (gm/Id) mean. Since gm is the variation of Id to the Vgs or vin voltage... What is the ...
0
votes
4answers
192 views

SOT-23 NMOS transistor power dissipation

I am working on a design of a control system that controls a few small solenoids, each drawing about 200 mA of current and operating at 15-18 V. These solenoids are activated by NMOS transistors. Due ...
1
vote
1answer
122 views

Raspberry PI power supply switched with FET

In my circuit there is a microcontroller, that can turn on and off the Raspberry PI power soruce. The schematic is following: A microcontroller GPIO is connected to RP_SW and 5v_Raspberry is the ...
0
votes
1answer
75 views

How to Estimate Fet V Cut Off

I am using a P chan fet as a high side switch. The data sheet specifies a min Vgs threshold voltage (-0.45V @ 250uA) and a max leakage current (Ids<1uA @ Vgs=0); but does not provide a cut off ...
1
vote
1answer
98 views

What is the purpose of a T-gate or H-gate in a body-contacted SOI MOSFET?

I've been banging my head against the wall with this question for hours. There are many examples of T-gate and H-gate structures that I've found, but I can't for the life of me figure out why the gate ...
0
votes
2answers
196 views

Low voltage drop transistor for Arduino

I am using a MQ135 gas sensor in my project. It takes a max of 200ma and I have connected the Arduino to a battery so I can disable it when needed to save battery. I am using a transistor for that but ...
0
votes
1answer
113 views

Function of the FET in LM350/LM317 programmable current limiter

My question pertains this circuit which is from this question, which in turn is a circuit straight from the data sheet. I don't understand the function of the FET in this circuit. Surely, with the ...
1
vote
1answer
197 views

I want to make a cd4049 cmos inverter spice model

I know the cd4049 is just two FET's but I don't know how I can model those transistors to be at least near what one would expect from the behavior of the IC. Also, what parameters are absolutely ...
0
votes
1answer
121 views

FET array - logical switch

This is the circuit I plan to implement to control a LED by a logic bit simulate this circuit – Schematic created using CircuitLab The datasheet of the transistor can be found here I ...
1
vote
2answers
117 views

is a uA current FET or BJT circuit design possible?

I'm working on a battery powered circuit that is triggering an interrupt on an ic with an internal pull-up. The resistor value and normally closed switch can not be changed. The quiescent current is ...
-2
votes
1answer
119 views

Can I modify this FET board to the ground leg instead of the VCC leg (see image)

Please see if the modification I have made to the FET switch board looks workable. See image attached. And I know it doesn't look like but the Drain is connected to VPP in the modified schematic. ...
0
votes
2answers
91 views

Output characteristics of power transistors

The book about electronics that I'm currently reading only briefly mentions IGBTs and power mosfets(such as the VMOS, or the HEXFET), and gives no depiction of the output characteristics. The image ...
0
votes
2answers
87 views

Depletion P-channel JFET that's saturated at \$V_{GS}=0V\$

Is there any depletion-mode P-channel JFET that is saturated at \$V_{GS} = 0V\$?
2
votes
1answer
2k views

FET-based voltage regulator with TL431

I'm looking for some help with understanding (in fact, correcting or confirming my understanding) of how the following circuit works: U1 here is TL431 voltage regulator, for example from Texas ...
1
vote
3answers
78 views

FET device parameters explaination

I'm looking for a FET device to use as ON/OFF switch. I've found for example this device: http://www.vishay.com/docs/62903/sis990dn.pdf I need to find a device that can handle on Source-Drain up to ...
0
votes
2answers
108 views

FET atmega168 - transistor needed?

I'm trying to make a BLDC controler, and I'd like to use an atmega168 as microcontroler and N-FETs (x3) to control the motor. The microcontroler will output a PWM that will control the motor's ...
2
votes
6answers
255 views

Would it be possible to make a solid state transistor by hand?

I am curious, would it be possible to fabricate a modern BJT/FET transistor with hobby/garage tools only if size and aesthetics was not important? Which materials would one use and how would one ...
2
votes
1answer
151 views

Very odd open-drain output design

I ran across a open-drain design and am baffled by the resistor between the nFET source and ground. There are only two purposes that I see it could serve. 1) It's series source termination, matching ...
0
votes
2answers
108 views

Puzzled by FET circuit

simulate this circuit – Schematic created using CircuitLab At a coffee house recently, I saw a napkin drawn schematic at the table before the waitress cleaned up after the previous patron. I do ...
2
votes
1answer
459 views

JFET biasing problem

I tried solving this problem, however I feel like there's something missing, I am asked to bias a N-channel JFET with using this provided data: Idss= 12 [mA] VDD= 12 [V] VP = -5 [V] VDS=VDD/2 ...
1
vote
1answer
74 views

Mosfet won't turn fully on

I have a IPB011N04LG N channel MOSFET configured as a switch in the following circuit: It works, but doesn't turn fully on. If \$V_{\text{BAT}}\$ is \$23\$V I get \$11\$V on the load side If \$V_{...
0
votes
1answer
182 views

Getting bad clipping issues with this 3 stage amplifier

What am I using? 3 stages of amplification. An input voltage of 10mV peak or 20mV pkpk into the first stage. 1st stage: NJFET Common Source. Using a voltage gain of 3. 2nd stage: NPN BJT Emitter ...
1
vote
2answers
153 views

Designing a MOSFET current mirror circuit

This is the design problem: This is a brief of my design for W and L of the transistors and R: I've connected the upper voltage source to ground and made the lower one equal to 0.4 V to make ...
5
votes
1answer
287 views

Why does the datasheet for this FET show two / three VGS(off) values?

I am using a MMBFJ270 P-Channel JFET and if you look at the characteristic graphs it is saying that there are two values for VGS(off) and in one graph it quotes three different values... Why does it ...
1
vote
1answer
99 views

What are the resistors in digital pots?

Do they place tiny switches with passive resistors or are they using fets in the ohmic region ?
1
vote
1answer
157 views

Discharge of a load capacitor through a cascode

How will a cascode effect the discharge of the load capacitor? I would expect that the discharge trough the cascade is slower since the cascode has higher output impedance. simulate this ...
8
votes
2answers
727 views

Choosing and biasing a MOSFET controlled by a microcontroller, does current matter?

I need some help choosing a MOSFET for the circuit that I described here, which I originally designed using a BJT but decided that FETs make more sense in this case. The FET will be controlled by a ...
4
votes
3answers
121 views

What precisely is \$R_{ds(on)}\$?

I keep getting conflicting answers on this and it's absolutely killing me. Some say \$R_{ds(on)}\$ is the contact resistance in the FET (for instance, make many FETs of varying channel lengths, turn ...
1
vote
1answer
325 views

Battery Discharge

I am making a circuit to discharge an 18V Li-ion battery, with multiple cells, in order to condition it. Each 18V cell has a capacity of 100Wh when fully charged. I would like to control the condition ...
0
votes
1answer
74 views

Switching using FET [closed]

I need a FET/MOSFET that would trigger switching at 0 - 5v. A voltage of 1V will be supplied to gate. What FET/MOSFET could I use? A specific FET. This is for our thesis and this is the only part I ...
0
votes
1answer
483 views

I need helping understanding this VCO circuit

The two circuits of interest are described in pages 12-14 of Texas Instruments' Application Note 263, Sine Wave Generation Techniques PDF WARNING I'm primarily concerned about the circuit in Fig. 15, ...
1
vote
1answer
222 views

OP amp voltage comparator for an FET

I have a project requiring a switch (I supply 4.8V, the switch stays off. I supply 5V, it turns on.) After some testing and asking several questions, I realized that the MOSFET I was using would not ...
1
vote
3answers
225 views

Recognising output impedance of an amplifier though inspection

The output impedance of FET amplifiers seem to be a hit and miss affair when I try to find it just through inspection. For example, sometimes it's easy to predict, whereas some other times I have to ...
3
votes
1answer
156 views

Question related to Cascode Circuit

I am trying to solve the following question related to cascode circuit. Where T5 has Vbe=0.7V I have answered the questions as follows. - Explain how the circuit works? The circuit has a DC ...
1
vote
1answer
65 views

How to determine FET switch specifications

I am working on a DIY drone, and I (preferably) need to be able to disconnect my ESCs from the battery via the transmitter (a Raspberry Pi). After looking for solutions for a while, I concluded FET ...
1
vote
1answer
2k views

Which kinds of FET have a body diode

I need to detect small high and low peaks in the battery voltage while in use. The goal is to help estimating the end of the battery charge by its change in impedance, since my circuit uses the ...