# 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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### difference between output resistance, ro, and finite output resistance Ro?

What is the difference between the concept/meaning of output resistance, ro, and finite output resistance Ro in context of a circuit with MOSFETS (ie. a MOS current mirror)? thanks
255 views

### Recommendations for essential measurement/bench tools for HV experimentation

I'm making plasma sculptures, and am also really interested in making big arcs and tesla coils. I started with some newer TV flybacks and the 2N3055 single-transistor flyback driver, and am moving on ...
29k views

### Determine MOSFET switching speed

How can I determine the switching speed of a MOSFET, with given Qg (gate charge), Vgs (G-S junction voltage) and gate resistor ? How should I determine the required value of the gate resistor?
345 views

### Features values of typical BJT/MOS transistors

Is there a page that lists the values of all the features of typical BJT/CMOS transistors? e.g. ON-resistance, gate/base capacitance, amount of power the D-S/C-E junction is able to hold etc. Of ...
4k views

### How is this circuit for level converting (5V<>3.3V) working?

Does anybody know, how is this circuit exactly working? It is level converter between 5V and 3.3V logic and it is bi-directional. I have some theory, but I am not sure with it (I never worked with ...
623 views

### Transistor in saturation mode?

I was wondering why do we so often want out transistor to work in saturation mode? Ie. For a MOS Current Steering Circuit we want our transistors to operate in the saturation region....
8k views

### MOSFET Turns on without voltage on the gate?

I am using the following transistor to turn a motor on and off: http://pdf1.alldatasheet.com/datasheet-pdf/view/418991/INFINEON/IPP096N03LG.html I am applying 12V to the drain and 0V to the gate... ...
16k views

### Question about the basic differences between a MOSFET and a FET

I'm still new to all this stuff, but I'm slowly trying to understand. I'm getting most of my information from "Getting Started in Electronics" (Forrest Mimm's book) Okay, so MOSFETs allow current to ...
2k views

### Safe to use PWM source to control lights via MOSFET?

I'm a bit of a noob when it comes to electronics so looking for some advice on this project I have in mind. Introduction The goal is to have my garage door opener (GDO) switch a secondary set of 12v ...
6k views

### Small signal diagram for a PMOS

What is the small signal diagram for a PMOS? Would it be the same as that of an NMOS but instead of $I = g_m V_{sg}$, for a PMOS we have to use $I = g_m V_{gs}$? Thanks.
8k views

### SSR vs optocoupler with TRIAC output

I've designed (and mostly implemented, now) a system for turning on and off 24VAC solenoids. In order to achieve this, I used optocouplers with TRIAC output (Sharp PR26MF1xNSZ series). The datasheet ...
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### When to use what transistor

So there are several types of transistors: BJT JFET MOSFET Combine all that with the various flavors of each (NPN, PNP, enhancement mode, depletion mode, HEXFET, etc) and you've got a wide array of ...
741 views

### How do I determine the requirements of a switching FET?

A part we're using in a half-bridge LLC soft-switching DC-DC converter is getting hard to find (STW20NM60, 600 V, 20 A, 0.25 Ω, 192 W), and I need to find a replacement. What parameters do I need to ...
5k views

### Switch 5V with back voltage protection

I'm trying to develop a design which involves switching a 5V rail. The design goals are: As low cost as possible (i.e. Can't use a fancy integrated solution) Relatively low current handling ( ...
23k views

### Help using MOSFET to switch on/off IC

I am trying to use the following MOSFET (N-Channel) to turn an IC on and off. http://www.diodes.com/datasheets/ZXMS6004FF.pdf In my test circuit I connected 5VDC to the drain of the MOSFET and then ...
156k views

### MOSFET as a Switch - When is it in Saturation?

I have the following circuit hooked up on a breadboard. I vary the gate voltage using a potentiometer. Here is what confuses me: according to wikipedia, the MOSFET is in saturation when V(GS) > V(TH) ...
53k views

### Switching DC with MOSFET: p-Channel or n-Channel; Low Side Load or High Side Load?

I think, it is time I understand working principle of MOSFET transistors... Suppose that; I want to switch voltage on a resistive load by a MOSFET transistor. Any control signal between -500V and +...
12k views

### Equivalent circuit of a solid state relay

I want to switch 50V AC voltage. Maximum drained current will be 5A. Frequency is 50Hz. Switching speed is not important, can be real slow, it is not a problem in my application. I wanted to use ...
4k views

### High-Side Not Working in Half-Bridge

Some of you may remember that I posted a question where I requested some feedback on my PCB design. The design was for a Half-Bridge driven by a IR2113 chip. I went ahead and etched the PCB but ...
23k views

### Is my MOSFET-based bidirectional level shifter insane?

In a moment of cheapness, I decided not to order a 5v to 3.3v level shifter from Sparkfun, but instead to put it together myself. The original schematic used a BSS138 MOSFET, but since I enjoy ...
16k views

### Bootstrap Capacitor Selection with IR2110/3

I'm going to be using two IR2113 ICs to control each side of an H-Bridge (intended for an Inverter application.) From the application note, the expression to find the bootstrap capacitor is as follows ...
561 views

### Drain-source voltage of a n-MOS

when we say that we are talking about a n-MOS in saturation region, what exactly can be said about the variation of $V_{DS}$ the drain-source voltage with the increase or decrease in the value of ...
1k views

### Which side of a PWM MOSFET should an inductor go on?

I have a power supply circuit that needs to supply bursts of power at 5A, 8V but only 1/4-1/8 of the time (using PWM). I wanted to smooth the current draw out on the actual source of the power, a ...
2k views

### Is this MOSFET a good choice? PWM -> FET -> DC Fan

I am planning on using a PIC microcontroller's IO pin (3.3V Logic) to drive this MOSFET that will drive a 12V DC fan: MOSFET N-CH 60V 2.7A SOT-23-3 According to the datasheet, there is a diode in ...
768 views

### How many transistors is a transistor connected to in a CPU?

On average, how many transistors is a transistor connected to in a CPU? What is the average fan-out of a gate in a CPU? What is the average fan-in of a gate in a CPU? (I'm guessing these numbers ...
573 views

### Need help understanding and interpreting IGBT datasheets

When it comes to motor control, I understand that we have the option of using discrete MOSFETs or IGBTs. Also, there are some products in the market where 6 IGBTs are placed in one single package, ...
10k views

### How can I sense the motor's current?

I need to drive a DC motor @ 24V, 6A with a MOSFET. How can I sense the current that the motor is drawing with a microcontroller? I have to know when the motor is stalled.
73k views

### How to drive a MOSFET with an optocoupler?

What's the proper schematic for driving this MOSFET from a microcontroller pin through this or this optocoupler? The MOSFET will drive a motor @ 24V, 6A.
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### Maximum switching speed of a motor

If I have a MOSFET (or a number of paralleled MOSFETs) driving a motor, what determines the maximum bandwidth (PWM frequency) at which I can excite a motor phase? Is this only a function of the total ...
20k views

### Dissipating 1W on a TO-220 without heatsink?

Can a TO-220 without a heatsink dissipate 1W in still air? Or, a different way of asking the question is: Assuming an ambient temperature of 25C, how can I go about calculating the maximum power I ...
10k views

### Lowest voltage needed to turn on a FET?

With inspiration from Ladyada's DIY boost calculator, I'm attempting to build a simple, low-current (<50mA) 40V boost circuit to drive an antique voltmeter. The PWM source for the transistor will ...
4k views

### small MOSFET for switching applications [closed]

When I need a general purpose NPN transistor I automatically think of the BC847. Other types that always come back are 2N3904/2N2222. (Is BCxxx more European, and 2Nxxxx more American?) For N-channel ...
12k views

### Why is a MOSFET triggered by Vgs and not Vgd?

Looking carefully at this diagram of one type of MOSFET: (found in this application note) We can see the device is virtually symmetrical. What makes the gate reference itself to the source and not ...
4k views

### Unnecessary pull down resistors on BJT and FET transistors?

I commonly see weak pull down resistors at the base of NPN transistors. Many electronic sites even recommend doing such things, usually specifying the value as something like 10x the base current ...
12k views

### Voltage controlled current source

Here is a circuit that seems to work pretty well for allowing a voltage to control a current of up to maybe two amps. It works on the falstad simulator (the triangle wave voltage input produces an ...
13k views

### fastest way of doing on/off-modulation of a LED?

I need to modulate a LED quickly (multi-megahertz range) on/off. It's a high-power LED. I have had some trouble locating any well-known methods to do this. Simply switching the voltage with a FET ...
7k views

### Effective MOSFET cooling

We need to drive a motor with around 40 Amps. The mosfet has an Rdson of about 7 mohms at 90 degrees Celsius. That is a whopping 11.2Watts of heat generated on the poor mosfet. We are very space ...
2k views

### Do I need to duplicate the 4th “substrate” connection when building CMOS gates out of discrete transistors?

All CMOS digital integrated circuits I've ever seen connect all the nFET substrates together to GND. In particular, the IC CMOS NAND gate has one nFET that has its substrate connected to GND, but its ...
161 views

### Are dual MOSFET devices isolated from each other? If so, to what degree?

I am using an OnSemi NTGD3148N dual MOSFET in a project. I cannot find a specification anywhere in the datasheet stating the isolation between the devices; and this holds true for most dual MOSFETs ...
2k views

### High power three phase ac motor controller

I have come across this question a lot in the design of a special 3 phase motor controller I plan to build this summer and I think I need to ask it directly to solve it. I need to be able to ...
33k views

### Source vs Drain polarity for MOSFETS

When using MOSTEFS as a switch I always see the drain connected to the higher potential and and the load and the Source is always connected to ground. Can you switch those so that the Source pin ...
18k views

### Gate capacitance vs. Gate charge in n-ch FETs, and how to calculate power dissipation during charging/discharging of the gate

I am using a MOSFET driver (TC4427A), which can charge a 1nF gate capacitance in about 30ns. The dual N-ch MOSFET I am using (Si4946EY) has a gate charge of 30nC (max) per fet. I am only considering ...
1k views

### How to choose a switch?

There seem to be about 4 major flavors of transistors, and then there are NPN/PNP versions. There are also relays, SCRs, and TRIACs. When I need an microcontroller-controlled switch, what rules of ...
8k views

### TIP31 (TIP120) as DC Motor driver compare to MOSFET

I'm trying to drive DC motor with PWM using PIC P16F1824. Some books suggest using TIP31/TIP120 as the driver. So I have PWM output pin connected Base pin TIP31, the Emitter pin connected to Ground. ...
1k views

### Design considerations for micro dc to three phase ac AVR based (ESC) for miniature UAV applications

This is a huge question, I plan to present the problem in detail and my current plan of action for solving it. I'm hoping to get pointers on what to and not to do. I was involved with a recent ...
2k views

### how to amplify current coming out of n channel mosfet

I made a school boy error in buying the BS170. It doesn't produce enough continuous current to power my leds. They're bicolour and can only be wired in parallel hence I would need at least 2 amps! ...
926 views

### NMOS TO Resistor conversion

I have heard that mosfets can be converted into resistors if they are "depleted". Can somebody explain how this is done as simply as possible...I don't have an EE background. Thanks
2k views

### Help identifying this power MOSFET

This MOSFET is from a good board for an RC plane. On a bad board, the MOSFET is completely fried and the number is not visible. The MOSFET drives a motor, and the motor stalled during a crash repair, ...