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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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43 views

Can I do KVL around transistors? (MOSFET and BJT)

I'm having a lot of trouble with more complex transistor DC circuits (can't wait for the AC, heh). Basically, what I want to ask is does KVL holds "around" a transistor as well? For example, if I ...
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37 views

pwm RC filter question

I'm new here but been playing with electronics for a while now. I have this project where I'd need to read pwm controlled signal from mosfet. This is how stock application controls pwm valve: I want ...
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15 views

Does my PWM led circuit controlled with NodeMCU and Mosfet work properly. What should I do to improve it? How to calculate for each components?

If I understand it right, when there's is signal from ESP, the PNP and NPN be ON, and Vgs=0. If they're OFF Vgs=+12V and the LED will shine. R=1K is to limit the Ib of NPN, and R=10K is the resistor ...
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1answer
126 views

Is there any advantage to using multiple tracks in this PCB design?

I'm fairly new to PCB designing, but I'm loving experimenting with it. Currently, I'm trying to develop a simple PWM circuit using MOSFETs to control an RGBW strip, using an Arduino with an integrated ...
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2answers
195 views

high side MOSFET switch and BJT interface with MCU GPIO

im operating a 28V contactor using a GPIO from my MCU, i have a 28V supply readily available. im looking to surpass the gate threshold of the MOSFET by introducing a NPN BJT with a 10V supply, with ...
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2answers
165 views

MOSFET bootstrap capacitor

I'm using a N channel gate driver with a bootstrap diode included, so I just need to add the capacitor. The FETs will be powered from a 3S lipo pack (12.6 to 9.0v) so I was wondering if I need 30v ...
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1answer
178 views

Effect of lower VDS on MOSFET Crss ( Reverse Transfer Capacitance )?

I am trying to understand the effect of lower \$V_{DS}\$ on MOSFET \$C_{rss}\$ ( Reverse Transfer Capacitance ). In most of the FET datasheet, \$V_{DS}\$ versus capacitance curve will be starting from ...
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26 views

How to calculate R1 and R2,? How do Mosfet IRF540 and ESP work in the circuit

So the 3.3V PWM signal from ESP is sent through R2 to the Gate to breakthourgh the Vgs(th) to make Mosfet ON, and the author of the circuit say Gate is pulled high to 12V by R1. But I don't understand ...
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2answers
37 views

Understanding Mosfet Circuit with PWM

I am wanting to control a voltage range of 0-10v across a 10k load with PWM from a micro. Now I was told to use this circuit with an n channel mosfet: This is what I understand so far: R1 is to ...
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2answers
616 views

MOSFET Amplifier: Maximum Signal Swing without Clipping

I have a degenerated common source amplifier. I want to know what's the maximum input signal I can apply before the output signal begins to clip. What I currently do is to increase the input signal ...
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32 views

BeagleBone Black Driving NFETs w/GPIO

In short, I want to drive some NFETs directly from some of the BBB's GPIO. 3 of the NFETs will pass 1-3 Amps of D-S current and 1 NFET will pass <1 Amp from the D-S. As you may know the BBB's ...
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48 views

trying to figure out the differences between the six transistors provided by the schematic tool [on hold]

My background consists of a BS in Computer Science and an MS in Computer Science and Engineering, both from the University of Washington. My MS consisted mostly in the very high level design of a ...
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1answer
9k views

Using two Mosfets for AC

Im having trouble getting my head around using two mosfets to pass AC. I have reduced my schematic to its bare bones to help keep it un-cluttered. The aim of this circuit is to use PWM to dim a bulb ...
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3answers
823 views

Resistor Selection to retain same brightness in LED PWM circuit

I am making a simple LED PWM brightness control circuit. I am using a relatively high power White CREE LED, N-channel Enhancement MOSFET BSS316N and Resistor R. The circuit is as shown below. I am ...
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1answer
472 views

Why are the dimensions of a floating gate layer in a MOSFET so thick?

For a floating gate MOSFET, in order to make the control gate work you have to(generally speaking) make the oxide layer thin(~100 Angstroms) as well as the ONO(Oxygen nitride, acts as an insulator) ...
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1answer
46 views

Designing a circuit using an LT1073 DC-DC Converter

I'm currently designing a circuit to convert a 24V (±30%) to supply a 3,3V IC used to monitor currents. I need to use the LT1073 which has the following diagram. The operations of the component and ...
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1answer
43 views

Testing 8 pin P-Channel MOSFETS on Laptop Motherboard

My laptop died recently and I’m testing the motherboard. I’m led to believe these two MOFSETs on the board may be part of the issue PQ301 and PQ302. Using a multimeter continuity and diode mode; ...
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1answer
611 views

High side RC ESC switch

I've been designing a test bench for RC propulsion systems and for that I thought it would be nice to be able to switch the power to the ESC on/off. For this I designed a simple circuit which I ...
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3answers
8k views

Voltage spikes when driving DC motor with N-channel MOSFET

I'm trying to drive a DC motor (12V, 100W) with MOSFET IRFP054N. PWM frequency is 25 kHz. Here's the schematic: I know DSEI120-12A is not the best diode for this but I don't have any better right now....
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2answers
20k views

Does MOSFET let current flow through source to drain as it allows it from drain to source?

Does a MOSFET allow current flow in reverse direction (i.e.; from source to drain)? I made a Google search, but couldn't find a clear statement about this matter. I have found this similar question, ...
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1answer
45 views

Single MOSFET current source (JFET like)

Is it possible to build MOSFET current source similar to JFET current source like this: simulate this circuit – Schematic created using CircuitLab With MOSFET it should be something like this: ...
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34 views

MOSFET working when we connect separately outside of PCB, if we solder in board, its not working, what may the problem? [closed]

MOSFET working when we connect separately outside of PCB, if we solder in board its not working, what may the problem?
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3answers
1k views

Why are BJTs common in output stages of power amplifiers?

From my understanding, the role of the output stage is to decrease the output impedance to almost 0. For that, MOSFETs seem better suited since they've got way lower \$R_{ds}\$. Yet I see quite often ...
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1answer
32 views

MOSFET switch, ATtiny10, Raspberry Pi

I had posted a question earlier but I was using a BJT at the time and the solution provided led me to use a MOSFET for my application instead. I switched to the FET but still unable to provide stable ...
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4answers
409 views

Parallel Power Supplies with Ideal Diodes

I'm working on a project that operates at 5v - and can draw UP to 10 amps. Under normal conditions, it won't be doing that - probably closer to 3 amps, and (if configured for low-power) only 450mA or ...
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3answers
60 views

ON-OFF MOSFET Switch for Induction Heater

The induction heater was tested using a relay as an ON-OFF switch before and worked so i just want to focus on the MOSFET switch part of the schematic. When i tested the circuit using a MOSFET switch ...
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1answer
39 views

High current, high frequency IC PWM switching with MOSFETs

I'm designing a circuit for an automotive application (chassis ground) that has a number of MOSFET outputs to drive large LED arrays and smaller motors (application tends to favour non inductive modes,...
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1answer
1k views

Turning a microcontroller on with a flip flop

I'm working on debugging a circuit that I've built and am trying to wrap my head around an issue. I have the following circuit (74LCV is an inverting flip flop and the NCP1400 is a boost converter): ...
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2answers
102 views

Using Mosfet with seperate Logic Converter and Arduino

I am trying to use an IRLB3034 with an Arduino even though it is not a logic level MOSFET. I am planning on using an LM2937 12v regulator like the schematic below: The connection going off the page ...
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0answers
34 views

Problem with MAX1645B test circuit?

Please consider the schematic: The MAX1645B is a level 2 battery charger. My problem is with the P-Channel MOSFETs. There are two P-Channel MOSFETs in the above circuit. From the datasheet: ...
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35 views

Can touching a MOSFET with fingers affect the voltage and how will this affect sound quality in audio amplifiers [closed]

I recently opened my audio amplifier to remove the fan that was making too much noise and after I switched on the amp some mid range frequencies were clipping. I realised the MOSFET is the most likely ...
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1answer
68 views

How do I drive a MOSFET when I have an 11.1v power-supply and an arduino [duplicate]

I am trying to use a irlb3034 as a switch to power an airsoft motor and control it with an arduino. I am using a diode between the source and the drain and a 2.2k resistor between the gate and the ...
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1answer
183 views

Smart mosfets, logic level input(mosfet replacement)

Basically diesel heater ecu my car uses has an shorted "smart" mosfet BTS141, which drives the glow plug. I don't know much about it since i cant determine the manufacturer. Basically it accepts logic ...
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4answers
224 views

Full bridge driver capacitor ringing problem

This is my first time designing a full bridge driver. I am experiencing problems with ringing on the output. I have made a pcb for it. This is a picture of the top side of the board. Backside Input ...
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2answers
59 views

Correctly using MOSFETs

I'm using a P-Channel (DMP1045UQ) and an N-Channel (BSS138K) FET to pull a 12v Logic line (12v @ 5mA) high (from GND) from a Logic Level(3.3v) MCU I/O pin. Here is the schematic, where ...
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2answers
332 views

How to analyze the functionality of the LM399 in the Libbrecht-Hall current source circuit

Recently, I read one paper on Libbrecht-Hall-Style circuit. As shown in the following picture. (arxiv, AIP journal) I found that the circuit uses one LM399 as a voltage reference fed to the non-...
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1answer
24 views

Voltage or Current Control with a Microcontroller for Pressure Regulator

I am wanting to control the flow rate of a pressure regulator (https://www.festo.com/net/SupportPortal/Files/505126/VEAB_2018-05a_8080669g1.pdf). My idea is to control this with a PWM signal 0-5v. ...
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2answers
69 views

Forward diode characteristics not starting from zero Ampere

Why the current is not starting from zero, whats the diode characteristic when current is near zero? Reading the datasheet for N-channel 60V MOSFET, I encountered this source-drain characteristic of ...
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1answer
55 views

How to calculate gate charge time for a mosfet?

I am designing the circuit shown above using mosfet NDS355AN. MCU is 5 V. However, I have become stuck as I am unsure of how to calculate the gate charge time of the mosfet. Hence what is the formula ...
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0answers
52 views

IRF3205 switching problem

I bought a power mosfet(IRF3205) and tried to switch but mosfet is not behaving as I expected when gate pin is triggered it doesnt change its position. Below is how my schematic looks like, I could ...
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1answer
248 views

Proof of type for Current mirror and Early effect (Mosfet transistors)

Can anyone explain me how I can prove this equation below (4.19).I know that \$V_{GS1}=V_{GS2}\$ and assuming that M1,M2 is in saturation then \$ID=0.5kn(vov)^2(1+\frac{V_{DS}}{V_{A}})\$
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0answers
30 views

What test points to do for a switching system measurements?

I am working on a high-performance switching system. I the old ones there was no big issue in just touching a gate with an oscilloscope probe, but this time I have high voltage and very short (5nsec) ...
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2answers
84 views

If a short circuit occured across the mosfet would anything happen in this scenario?

I am just confused about understanding a simple concept. For the following circuit: Say the blue line acts as a short for whatever reason. If the LED has a forward voltage drop of 23 V and forward ...
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2answers
348 views

Depletion mosfet inverter

I know that if both transistor in a cmos inverter are enhancement then the output will be as shown in the figure: But I wonder, what if one of them is enhancement and the other is Depletion?
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2answers
1k views

KVL and KCL in MOSFET small-signal model, how?

I want to find the gain in this MOSFET small-signal model. KVL in loop 1: \$+V_{in}-V_{gs}-g_mV_{gs}R_s=0 \iff V_{in}=V_{gs}(1+g_mR_s)\$ KVL in loop 2: \$+V_{out}-g_mV_{gs}R_s=0 \iff V_{out}=g_mV_{...
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1answer
40 views

How to find the Common Mode Rejection Ratio of this circuit?

My attempt was like, by using the formula, I can get, \$CMMR=\frac{\sqrt{2\cdot4\cdot8\cdot5\cdot10^{-6}}\cdot44000\cdot2}{x}\$ For the denominator, I used both 10% and 20%, but all the finals were ...
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2answers
42 views

MOSFET Controled Relay Problem

As a way to power-on/-off a circuit load, a MCU is used to drive a relay through two MOSFETs. The problem is, when the MCU GPIO output is measured 0-volt, the relay could stay connected. Can anybody ...
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1answer
68 views

Constant-gm bias circuit

I am doing a study on Improvements in biasing and compensation of CMOS opamp. Do you guys know how to come up with the equation for RDS4C ?
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2answers
83 views

Buck converter for Li-Ion 2s battery charger

I'm currently doing a project that requires the charging of a 2s Li-Ion battery. I have an 18V 10W solar panel that I want to charge my battery using a buck converter. Im controlling the switch and ...
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73 views

Mosfet not turning off when gate is grounded

I have a FQP50n10 mosfet which I used to drive an Arduino and it was working great. For the past few months I've been trying to make a circuit but it’s not working with the values I want because I’m ...