Mosfet Definition and 215 Threads

The new topic in my Intro to Microelectronic circuits class is Mosfets. This is one of the only topics that has given me this much trouble in this class, and was wondering if I could be given some help/input. I've taken notes on the topic, it's just been giving me a hard time. Thanks for any and...

Hello, I'm considering using a logic-level MOSFET as a switch in a design. The drain of the MOSFET will be connected to an IC. The IC works at 3.3V and the maximum voltage at which it's guaranteed to read a low is just 0.8V. Now, I think every MOSFET will able to satisfy this but I'm just...

I found on my notes that for an NMOS with increase in Vsb voltage Body Effect increases, Vt also increases. But it is mentioned that with Vgs constant id increases which I feel is wrong since id is proportional to (Vgs - Vt)2. Hence I think id should decrease. Please show me the light :-)...

I will quote my textbook, and further I will explain what I do not understand. "Since, as we shall see shortly, the drain will always be at a positive potential relative to the source, the two pn junctions can effectively be cut off by connecting the substrate terminal to the source terminal...

Hi everyone, I have this following problem (uploaded it in the pdf). I have made an attempt at solving it, but now i am just stuck. I have done question one, and have confirmed my answers in PSpice. my Id = 16uA, Vgs = 1.4V and Vds = 4.6V ( 3 + 8/5) and for p-channel the values are...

Hi, I want to know more about Dual Gate MOSFETs, i.e, their structure, working, advantages etc... Googling "Dual Gate MOSFET" didn't help at all! So please suggest some sources (online) where I can find more information on them. Also, where can I find more information on current...

I'm trying to learn about MOSFETs in order to use them as a switch. (note: this is not a homework/school question). On my breadboard, I have the following circuit hooked up: I vary the gate voltage using a potentiometer. Here is what confuses me: according to wikipedia, the MOSFET is in...

Homework Statement This problem is given to me by programme inductor, and I just copy the whole description here so every given element is the same as what he/she gives. I'm confused with the given conditions. 1) What is the transconductance (gm) of a MOSFET biased at W=L=1um, uCox=0.01A/V^2...

Hi guys, I need to use the PWM output of a PIC microcontroller to switch a mosfet to drive a 9v brushed DC motor @ 115 mA. From what I've gathered, the mosfet should be logic level (fully on @ 3.33v since my Pic uses a 3.33v source). It needs to be able to handle...

Hi everyone, I need to find the voltage gain for the following scheme: My book says I need to calculate 'id' first, which is: id = gm.ro.vin/(Rs+RL+ro+(gm.ro.Rs)) Then with the help of vout = -RL.id you get: Av = -gm.ro.RL/(Rs+RL+ro+(gm.ro.Rs)) So I get the last part, but I really have...

This is the way I understand Mosfets (NMOS) The source is grounded, drain is at some positive voltage V, gate is 0v initially. When gate voltage is increased and reaches Vth, electrons from source are attracted to the gate because of the E-field at the gate. When the electrons reach the...

So the MOSFET's output current in a simple buck converter with a PWm a driver and a MOSFET and LC circuit. The Inductor's saturation or Irms current limits the MOSFET's current output, correct? I heard that if it exceeds saturation current that the MOSFETs could be damaged. is this true...

Why is it that a P channel MOSFET is always operated with Vds < 0 i.e source positive with respect to the drain? The book says that carrier always needs to flow from the source to the drain, but would the reverse operation harm the MOSFET in any way? Please explain. Thanks.

Why does the small signal voltage gain collapse as we increase the AC input voltage? Voltage gain = Av = (output voltage) / (input voltage). Both small signal (AC). When you draw the small signal circuit using T-Model, you can find that Av= (gm * Rd) / (1 + gm Rs) gm being the the...

Hi there, I'm a bit beffudled by some of the workings of a MOSFET transistor. First of all, in the saturation region of operation, I understand that the inversion channel is "pinched off" as it approaches the drain. In other words the inversion channel thickness tapers off as it approaches the...

ok looking at datasheets for mostfet there is source/drain rise and fall time. does this only depend on the voltage rise fall time of the gate? so if you apply a voltage to the gate it will take a wile until the voltage of the actual gate reaches that of the applied voltage because of...

A Common-Source amplifier utilizes a MOSFET with µnCox = 400µA/V2, W/L = 10, and VA = 10V. It is biased at ID = 0.2 mA and uses RD = 6 kΩ. Find Rin, Avo and Ro. Also, if a load resistance of 10kΩ is connected to the output, what overall voltage gain Gv is realized? Now, what if a 0.2V peak...

(This is not homework) Okay I'm writing a lab report and just writing some discussion. Also I am curious myself. I'm a junior in computer engineering. I want to discuss the differences between BJT and MOSFETs as amplifiers and anything like pros/cons for each. Also why is the BJT...

Why is the voltage gain of a common source MOSFET negative? I have a schematic below and I get the voltage gain to be -gm(ro||Rd). I say that is what I get, but the truth is that is what my professor said we should get. I do not understand why the Gain (Av) is negative. It will go a long...

Hello, I am designing a motor controller, and I was curious about the MOSFETs I'm using that have an internal body diode zener for Vds protection that is common in a lot of datasheets. I am switching the coils of the inductor with these MOSFETs, and I would like to know if its unwise to...

Homework Statement We are going over gain, Gm, Ro, and Rin for MOSFETS. We are told to know and memorize certain equations and how to get these equations. In this particular problem we are told to find voltage gain by analyzing small signal. My professor gave this as the answer: (-gm*...

Hi all, I have a couple scenarios, and need to decide on which component best suits my need: I have two solenoids that I need to drive with 12V, based on a 5V uC signal. Simple on/off switch. I'm very new to using MOSFETs, so I'm not sure if you can drive 12V with a 5V signal (which would...

I am a beginner with respect to MOSFETs and have just begun studying them at college 2 weeks back. What I am actually struggling with is the basic functional differences between MOSFETs and JFETs. Two of them are- dielectric and substrate, both of which are there in MOSFETs. However, I...

Hi all, I have been looking at this question and I am having trouble sketching the wave forms. I know that during the period 0<time<0.5 the MOSFET is OFF the diode is ON i = 4amps v =0 id=0 VDS=? Then during 0.5<time<1 period the MOSFET is ON the diode is OFF. i=0 v=...

Hi all, I'm using 7 P-channel mosfets to switch different loads using 1 microcontroller on an electrical power and distribution system. My circuit is as follows for each of the 7 Mosfets. Gate: through a resistor to ground on microcontroller and through a High value (600 kilaohms) Drain...

anybody please solve this mosfet transconductance problem ... hello friends...i can't understand about this question totally...can anybody help me regarding this...its answer is option (C). .i have attached image for this question ,question no. 48... thanks...

Can anyone kindly help me in using the P channel mosfet as source for switching of LED display? As I've connected it like 16 Mosfets with common source giving 5V from diode b/w power supply, drain is for the16 rows of 32 LEDs. Gate is connected to the shift register. The problem is the...

Homework Statement See figure. Homework Equations The Attempt at a Solution I tried breaking the circuit down into a bunch of small logic gates but I'm having a tough time putting things back together into one big circuit. (One boolean expression) So far I've determined that...

Homework Statement See figure Homework Equations V = IR The Attempt at a Solution I have a few questions about notation before I begin with an attempt at the problem. Are there 2 voltage sources in this circuit diagram? One on the left, one ontop? Also it says that Vo = 5v...

Homework Statement See figure Homework Equations P=IV The Attempt at a Solution I need to clear something up before I even attempt the question. In the question is states the the R_{on} = 100 ohm is that the 100 ohm resistor I see in the circuit or is it literally inside the...

Hi all, I have been trying to get a MCU to send a +5v signal and in turn switch a N channel MOSFET with a VDS of +12v. I used a P channel BJT, tied the gate to +12v through a resistor, the top to +12v straight, and the output to the gate of the MOSFET. Then by grounding the gate, the...

hi i have a mosfet circuit question since my prof. didn't explained much about the mosfet I am pre lost.. during the lecture..he show us two circuit diagram.. the mosfet circuit and this regular circuit.. and he ask us why the above equivalent circuit model is a valid representation of...

Homework Statement I have a MOSFET with a Si/SiO_{2} interface. I need to find the threshold voltage. I'd also like to know whether this puts the transistor in the "on" state or "off" state (I know this is simple; I'd just like a little verification). I know the values for \Phi_{ms}, Q_{i}...

Hi, First of all, I posted a similar question in [1] but I think it is the wrong forum and wrong question (maybe the reason why I get no answer...). I have to solve this (I think easy?) exercise: http://img705.imageshack.us/img705/8241/floatingmosfet.png I think (3.1) is easy and I solved...

Homework Statement http://img195.imageshack.us/img195/3056/mosfetj.jpg An n-channel enhancement MOSFET for which Vt = 2 V and K = 100 uA/V2 is operated from a 9 V supply using a drain resistor RD of 60kohms and the feedback bias scheme depicted. What drain current results? What is VD What...

Dear Oracle, I'm designing a boost converter where the input is a current limited (~500mA) voltage source that varies from 3.5V to 6V. The output (load) varies from 7V to 9V. I intend to drive a MOSFET, IRF8707PBF [1] from IR, with a 250kHz PWM control signal via Maxim's driver IC MAX4420...

If the MOSFET is a symmetrical device, i.e the current can flow either from the drain to the source, or vice versa, depending on wheather you apply the voltage VDD to the drain or to the sourse, then, what is the point of "discrimination" between these two terminals? why not just mark the gate...

I have a pulse width modulator that's composed of a triangular wave generator and a comparator. This outputs a pulse width modulated signal, whose duty cycle I set by changing the comparator's V- voltage. I have measured the rise and fall times of my output waveform and they are 27uS (for...

I have a hobby project that involves controlling a dc motor remotely. I used a pwm circuit to control motor speed. I also have a rf circuit that sends a signal that can be used to turn the motor on/off. Both circuits work when used independently, that is the rf signal will turn a motor on/off...

Hi, I have Ids vs Vds characteristic curves for a MOSFET at Vgs = 2V and Vgs = 2.5V in both the linear (ohmic) and saturated regions. I wanted to try to figure out the threshold voltage for the MOSFET from this information only. I had two ideas of how to do this, but they differ by a factor...

Hello All, This is a new thread related to my output stage setup. Only this time, rather than determining if something went wrong, I simply want to monitor the temperature of the MOSFET on the output stage. I have been doing a bit of research to see what kinds of sensors are available out there...

Hey Everyone, The title of this thread may be a bit ambiguous but what I am wondering is if there is a way to determine if a MOSFET in an output stage has shorted. The scenario I want to catch is the case where the FET drain is exposed to too much voltage (from a collapsing spike or some...

Hello all, I was advised to use a MOSFET and a comparator together in a solar charger that I am building to stop the solar panel from charging the batteries when full. Seems logical, right? The only problem is I've never used MOSFETs or comparators, so I'm not really sure how to. I need a...

I'm trying to use a MOSFET as a voltage controlled resistor, and am under the impression that it acts this way when it is in the linear region. However, our VDS will be 2.5V-20V, and our VGS will be 3.6V-5V. That means our VDS will most likely be greater than our VGS - VT, which means it will...

Homework Statement List the major device ratings for a MOSFET. The Attempt at a Solution Simple question yeah? Data sheets list about 20 ratings for each device, and they don't explain the acronyms. VBRDSS = Vegemite BReaD Salad Sandwich? Can someone help me trim them...

What are the major device ratings for a MOSFET?

So I'm going to be using a MOSFET as a voltage controlled resistor, but to do so,i need to know the value of the unCoxW/L, also known as k is that something that's on datasheets? or is it generally the same for all MOSFETs? (this is the mosfet i plan on using..)...

I need help finding a MOSFET to buy that can handle max power of 30W, and that can achieve a resistance of 1-25ohms (using it as a voltage controlled resistor). Microsemi originally pointed me to these 2 of theirs: http://www.microsemi.com/catalog/part.asp?ID=21208...

We need to have a load resistance to match an internal resistance for peak power.. so we've decided to use a Power MOSFET as the varying load resistance, but my question is.. when I'm looking for which power MOSFET to buy, to use, what should I be looking for in terms of properties? This is...

Hi Guys, I need to design something that will isolate our DAQ (Data Acquisition Card) for a basic simulation we need to do. I was thinking about designing a mosfet switch, where the DAQ sends some voltage to the gate above the threshold voltage to turn the MOSFET on and 0 V to turn it off...