All Questions
Tagged with mosfet transistors
860
questions
91
votes
8
answers
92k
views
When is a MOSFET more appropriate as a switch than a BJT?
In my experimentation, I've used only BJTs as switches (for turning on and off things like LEDs and such) for my MCU outputs. I've been repeatedly told, however, that N-channel enhancement-mode ...
- 4,750
72
votes
2
answers
9k
views
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 ...
- 3,487
45
votes
3
answers
62k
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 +...
- 14.1k
37
votes
2
answers
31k
views
Selecting a MOSFET for driving load from logic
I'm looking to drive a magnetic door lock from an Arduino. I've found a question about driving a solenoid from an Arduino, which includes a circuit that looks perfect for this kind of situtation:
...
- 10.7k
28
votes
3
answers
117k
views
Is MOSFET gate threshold voltage a limit or minimal "Full-on" switching voltage?
I've been shopping for some mosfet transistors, for a starter kit, and noticed listings that state a mosfet is suitable for 5v logic, but the data sheets says Gate Threshold is 1-2v.
4v gated mosfets,...
- 445
23
votes
1
answer
81k
views
Why does MOSFET pinch-off occur?
This question is about enhanced n-type MOSFETs. From what I understand, an inversion layer is formed underneath the insulating layer below the gate of the MOSFET when a voltage is applied to the gate. ...
- 1,323
22
votes
5
answers
16k
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 ...
- 31.8k
20
votes
4
answers
17k
views
What does "the resistance looking into" mean?
See this circuit, from Sedra & Smith microelectronics, 6th edition, page 287:
It says that the resistance between the gate and source looking into the source is 1/gm, but that the resistance ...
- 1,015
19
votes
4
answers
14k
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 ...
- 14.1k
17
votes
4
answers
5k
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 ...
- 3,804
14
votes
3
answers
20k
views
Driving DC motors with MOSFETs and a microcontroller?
I'm developing a nano quadcopter using an Atmega328 microcontroller, powered at 3.3V, and very small brushed DC motors. The average current used by these motors is about 800mA @ 3.7V.
Initially, to ...
- 193
14
votes
3
answers
4k
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 ...
- 436
13
votes
2
answers
2k
views
Why are BJTs more reliable than MOSFETs under severe weather conditions?
I read in a textbook (Microelectronic Circuits by Sedra and Smith, pg. 494, (2010) sixth edition) that BJTs are preferred by the automotive industry due to their reliability under severe weather ...
- 327
12
votes
3
answers
6k
views
Why does my MOSFET always burn?
I have a circuit that uses a MOSFET to power a resistive plate to heat it up.
The problem is that this MOSFET always burns after a few seconds.
Let me explain my circuit:
First, the outlet AC voltage (...
12
votes
2
answers
29k
views
P-Channel MOSFET high side switch
I am trying to reduce the power dissipation of a P-Channel MOSFET high side switch. So my question is:
is there any way in which this circuit can be modified so that the P-Channel
MOSFET will ...
- 737
12
votes
2
answers
8k
views
Using a microcontroller to turn on LED strip
I have 60 leds that came in a led strip. One meter length of the led strip requires the following:
400 milliamps
12 volts
I want to control these LEDs with micro controller. I'm thinking of using a ...
- 399
11
votes
2
answers
2k
views
MOSFET construction
I've just read an application note and I was confused about this sentence:
"Engineers often think of a MOSFET as a single power transistor, but it is a collection of thousands of tiny power FET cells ...
- 879
10
votes
8
answers
19k
views
Low Drain-Source MOSFET Leakage
I've been looking at the SM74611 Smart Bypass Diode from Texas Instruments and am very impressed with the reported reverse leakage current (0.3uA at 25C). Considering the device has a N-Channel FET, ...
- 1,368
10
votes
2
answers
2k
views
Help understanding this LED lighting transistor circuit
I simulated this circuit from a reference design but I'm not entirely sure how it's working or how you would go about designing such a thing. In simulation it looks like it's designed to hold the ...
- 1,806
10
votes
4
answers
7k
views
P-Channel MOSFET Inrush Current Limiting - Transistor burn issue
I'm fighting with PFET inrush current limiting circuit discussed here: P-Channel MOSFET Inrush Current Limiting
In my circuit is input voltage 24V DC and C_Load is 6mF. I'm switching on transistor ...
- 121
10
votes
2
answers
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 ...
- 513
9
votes
2
answers
21k
views
How to determine maximum PWM frequency for transistor (2SK2554)
How can I determine (estimate) maximum reasonable PWM frequency for 2SK2554 transistor?
I found timings in datasheet:
I could estimate frequency from this (and make sure that all these times are 20-...
- 6,004
9
votes
2
answers
4k
views
How do floating gate transistors not leak the stored charge?
I've done my best to read through Wikipedia explanations of floating gate transistors which are used in flash memory. It looks like these transistors have a special region where the charge is "stored" ...
- 12.4k
8
votes
1
answer
2k
views
In a MOSFET, what does the P+ region mean in this picture?
Wikipedia has several pictures of MOSFETs and various types of them. Here is one.
Notice that the Source and Body are connected. I understand this is to ensure there is no forward-bias or reverse-...
- 1,057
8
votes
5
answers
5k
views
Dual N/P-Channel MOSFET Dies with Smoke
I have built the following N-MOS & P-MOS push-pull dual MOSFET circuit. Its purpose is to control some external LEDs from a 3.3V microprocessor.
However, there seems to be a problem, where the ...
- 247
8
votes
2
answers
427
views
Circuit Analysis - Function of BJT?
I am referring to the following AppNote from TI.
What is the purpose of transistors Q3 and Q2? Is it to turn the PFET "hard off" when the controller isn't turning it on?
Thanks
AJ
- 416
7
votes
3
answers
22k
views
Bootstrap circuit function
I have some question about the bootstrap capacitor on a gate driver.
First, the bootstrap capacitor is used because the voltage on the high-side driver's gate needs to be about 10-15 V higher than the ...
- 143
7
votes
3
answers
4k
views
P-Channel MOSFET Drain-Source Polarity in Power Switch Application
I'm looking at using the LTC4412 power switch in an application. From the datasheet, here is the typical application circuit: :
In the application circuit, an FDN306P p-channel MOSFET is used.
I'm ...
- 1,043
7
votes
2
answers
603
views
Ideal component to switch 84V DC?
I wanted to control a 84V LED strip using a ATtiny13a microcontroller with minimal power wasted. I just want to turn it on and off, don't need any PWM dimming. The strip uses 270mA current and is ...
- 688
7
votes
2
answers
1k
views
I was explaining a transistor to someone, and I realized: I don't really understand several key concepts at a low level. Help?
(Surplus story removed.)
I was explaining MOSFETs, CMOS, and logic gates to someone and realized I didn't grasp some concepts as well as I thought.
It culminated when he drew a single transistor, ...
- 193
7
votes
1
answer
23k
views
Triode and saturation region in mosfet
What is the difference between the triode ( ohmic ) region and the saturation ( linear ) region in mosfet ?? It's confusing since both regions are linear but why does mosfet work as an amplifier in ...
- 321
7
votes
3
answers
6k
views
How does a dual gate MOSFET reduce Miller effect?
How does a dual gate MOSFET reduce Miller effect? I am trying to gain a global understaning of the physics behind them, not necessarily exact formula's that come with it other than maybe some for ...
- 33.2k
7
votes
2
answers
16k
views
Switching a current with an NPN transistor and a P-MOSFET
Just learning about transistors and I'm trying to clearly understand how to apply them for basic switching, in terms of the two standard cases, i.e., Active HIGH behavior and Active LOW behavior. For ...
- 4,922
7
votes
2
answers
3k
views
Advantages of depletion mode FET devices over enhancement MOSFETs
I've grown the impression that JFETs and depletion mode MOSFETs are not used very much nowadays, especially in new designs.
I know that they need different bias networks, especially as discrete ...
7
votes
2
answers
5k
views
BJT vs MOSFET failure modes
I know MOSFETs are much more efficient than BJTs in that they don't consume as much power when on whereas a BJT consumes base current the whole time it is on. I also know that MOSFETs tend to fail ...
- 831
7
votes
3
answers
42k
views
What is the formal definition of Quiescent Point?
What is Quiescent Point?
Is it necessary for it to be related with any V vs I , I vs I, or any such characteristic curves intersection point?
- 555
7
votes
1
answer
5k
views
What makes an "rf transistor" different from an ordinary transistor?
I have been looking at various types of transistors that can switch at higher speeds than my clunky but powerful IGBT, and I came across these things called "rf transistors" or "rf mosfets" which can ...
- 831
6
votes
3
answers
5k
views
How does this MOSFET/Op-Amp voltage regulator circuit actually work?
I am trying to understand the functioning of this circuit since I have read that it is appropriate for power regulation:
Here is the explanation that I have found:
The zener diode provides the ...
- 597
6
votes
2
answers
18k
views
What is the difference between MOSFET transistor and normal transistor? [closed]
I know this might be a stupid question, but what is the difference between MOSFET transistor and normal transistor? There must be a difference but no one says it, people always talk about them as they ...
- 231
6
votes
4
answers
958
views
Experimental and theoretical determination of MOSFET threshold voltage
I am working on a project that requires me to extract the proper value of the threshold voltage of a particular MOSFET.
I know that VT is quite arbitrary in its definition. I've researched the subject ...
- 443
6
votes
4
answers
927
views
In a JFET, is the gate *always* connected to the bulk/substrate?
In a JFET, is the gate always connected to the bulk/substrate ?
Or is there "no rule" (sometimes it is, sometimes it is not)?
And what about the case of the MOSFET ?
6
votes
3
answers
21k
views
Why N-channel MOSFETs are better than P-channel MOSFETs?
Besides the reason that electron mobility is higher than hole mobility, what are the other reasons of preferring an N-channel over a P-channel MOSFET?
6
votes
2
answers
35k
views
Why is the Triode operating region of a MOSFET named such?
If triodes were used for amplifiers, why is the triode region generally used for digital and the saturation region generally used for analog? Am I missing a fundamental understanding of the MOSFET's ...
- 1,668
6
votes
1
answer
8k
views
Driving a MOSFET with Negative Off- State Gate Voltage
I know in practice Mosfet switches are driven by 0V to any Positive gate voltage (e.g. 0V - 15V). I am using a Mosfet pair (PMOS and NMOS) to switch 10A currents in pulses and the datasheet of MOSFET ...
6
votes
2
answers
3k
views
Which one is the correct symbol of enhancement type MOSFET?
I studied MOSFET from ' Electric Devices and Circuit Theories by Robert L. Boylestad ' The symbols of depletion type and enhancement type MOSFET are given below from the book.
But recently, in ...
- 2,519
6
votes
2
answers
711
views
MOSFET Circuit Design and Thermal Considerations
I'm a newbie at EE, and just I wanted to verify that the design I came up with for a MOSFET circuit that drives a 12V 500mA water pump will work. I'd also like to confirm I can run the N-Channel ...
- 325
6
votes
1
answer
4k
views
Transistor PWM Generator (No ICs) for practical application
I want to produce a good quality PWM signal with transistors(BJTs, FETS, etc..). I do not want to use an IC at all(learning to use transistors properly). I'm currently using a BJT Astable Mutivibrator
...
- 225
6
votes
3
answers
25k
views
Any way to use N-channel mosfet in P-channel configuration?
In my application, I need the HIGH signal to turn a device OFF and vice versa. Clearly, this is P-mosfet configuration. However, I only N-mosfet on hand.
Is there any clever way to utilize N-mosfet to ...
- 385
6
votes
1
answer
2k
views
Using a depletion mode mosfet as a current limiting device
I have recently discovered the exciting world of depletion mode mosfets. Curiously, even in this document, I found nowhere that a depletion mode mosfet could be used as a current limiting/inrush ...
- 1,864
6
votes
1
answer
159
views
MOSFET switching on
I have a doubt. Consider an N-MOSFET: which is the voltage that can switch on it? The voltage between Gate and? Sometimes I read "between Gate and Bulk", sometimes "between Gate and Source", sometimes ...
- 3,490