The transistor is a semiconductor device that can amplify signals and switch power. Most used types are bipolar (BJT, for Bipolar Junction Transistor) and MOSFET (FET, for Field Effect Transistor)
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Why do you need 2 resistors when hooking up a transistor as a switch
What is the point of R2 in the following diagram:
I get that R1 controls the current to the Base, but what does R2 do?
Thanks!
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5answers
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I don't care how a transistor works, how do I get one to work?
Every reference I can find on transistors immediately launches into theory-heavy alphabet soup. The above seems also to be assumed knowledge for reading a datasheet. I don't care; I just want to get ...
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1answer
438 views
Darlingtons, MOSFETS, and bipolar junctions
I realize there are dozens upon dozens of kinds of transistors, each used for specific purposes. Sometimes there is great overlap; multiple kinds may work in a given circuit, but at times only a ...
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5answers
839 views
Why would one drive LEDs with a common emitter?
I've seen tutorials aimed at beginners suggest the way to drive an LED from something without enough current drive is this:
(option A)
but why not this:
(option B)
Option B seems to have some ...
20
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2answers
476 views
What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?
For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the ...
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2answers
738 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 ...
18
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2answers
626 views
Schottky transistor, Not sure I understand it?
So I've been looking through and going through my Digital Computer Electronics book, and I came to this... It seems so simple and I understand the "point" of it, but I'm not sure I understand exactly ...
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2answers
1k views
Why would an op-amp use BJTs over MOSFETs?
I've always been told that ideally, op-amps have infinite input impedance. So when I was looking at the LM741's transistor level schematic, I was confused when they used BJTs instead of MOSFETs.
...
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3answers
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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 ...
13
votes
3answers
1k views
Explain what is a transistor in plain English!
Can someone care to explain - in plain English - what a transistor is and how it works. I know computers are full of these but don't know much about them.
P.S. I know about this site from another one ...
13
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4answers
5k 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 ...
13
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4answers
2k 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 ...
12
votes
4answers
8k views
How do I saturate an NPN transistor?
I understand that in "saturation mode", a BJT functions as a simple switch. I've used this before driving LEDs, but I'm not sure I understand clearly how I got the transistor into that state.
Does a ...
12
votes
2answers
1k 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:
...
12
votes
2answers
566 views
What is the difference between a PUT and a normal transistor?
What is the difference between a Programmable Unijunction Transistor and a normal transistor? I am reading the book Make:Electronics and it says I need one of those. Can somebody explain to me in ...
11
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4answers
3k views
“Starter Kit for electronics” - What to buy?
I'm going to buy some things for back to the electronic world.
Starting with an Resistor Assorted Kit.
Need to buy some kits containing the most common capacitors and transistors... what to buy???
...
10
votes
4answers
1k views
Unnecessary Transistor and FET resistors?
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 ...
10
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2answers
919 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 ...
9
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5answers
6k views
Relay vs. Transistor?
Rather basic, I'm afraid, but when would you use a relay, and when would you use a transistor? In a relay the contacts wear out, so why are relays used at all?
9
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3answers
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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 ...
9
votes
4answers
460 views
Low power, low voltage, slow (0.1Hz) oscillator?
I had the opportunity to analyze a very interesting circuit today using a programmable unijunction transistor as a timer.
The power supply varies, and the circuit must operate on under 10uA of ...
9
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4answers
368 views
Contemporary transistors
I found the following statement on Richard Dawkins book The Selfish Gene (1989):
"... there are some ten thousand million neurones in the human brain: you could pack only a few hundred transistors ...
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3answers
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How do I know if which leg is the emitter or the collector? (Transistor)
I'm new to electronics and here's a newbie question that I would like to ask:
How do I know if which leg is the emitter or the collector in a Transistor (For both PNP and NPN) using only an analog ...
9
votes
2answers
813 views
What's the difference between NPN and PNP transistors?
Suppose that I know how an NPN transistor works.
How different is a PNP transistor? What are the operational differences between a PNP and a NPN?
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votes
2answers
645 views
How does this transistor work?
The picture shows a detail of schematic diagram of the LM555.
I presume the horizontal line is the base, but I'm not sure I understand how the transistor works. What is the effect of connecting ...
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votes
6answers
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Inexpensive solid-state variable resistor
I have an analog audio project I'm playing around with designs for and it will need about 150 solid-state variable resistors. I plan to control these from a micro controller so a digitally controlled ...
8
votes
3answers
847 views
Need an XOR gate that works up to 2 to 3 GHz
I have encountered an unusual situation in which I require an XOR gate that will function reliably when presented with a square wave input with a frequency between 2 and 3 GHz. I know that desktop ...
8
votes
4answers
2k views
What is wrong here? - A simple NPN switch
I have a simple npn switch, see the diagram.
I feed a 100KHz square wave (TTL) to the base of this transistor and it turns on very very fast (a few nSec) but it doesn't turn off as fast, it almost ...
8
votes
3answers
1k views
Need help operating a transistor
I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one:
...
8
votes
7answers
3k views
Which configuration is better for pulling down an NPN transistor's base?
I was discussing on pull down resistors with a colleague of mine. Here are the two configurations for transistor as a switch.
The input signal can either come from a microcontroller or an another ...
8
votes
4answers
175 views
Flow of holes in transistor?
Bipolar transistor are said to have both electron and holes flow. Movement of electrons can be understood but holes are fixed part of the atomic/crystal structure.How can we characterize their ...
8
votes
1answer
296 views
How to dual power PIC18F4550?
In the datasheet there is this shematic how to dual power 18F4550. However they don't specify which transistor to use and what resistor values have to be. For capacitor I use 100uF (diode side) and ...
8
votes
1answer
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What transistor do I need to drive many LEDs and how should I hook it up?
I no that a transistor amplifies a signal but I've never used one. I have this design here http://www.circuitsonline.net/schakelingen/59/audio/led-vu-meter.html and I want to add 15 leds connected to ...
8
votes
1answer
688 views
Where are the depletion PMOS transistors?
In school, I was taught about PMOS and NMOS transistors, and about enhancement- and depletion-mode transistors. Here's the short version of what I understand:
Enhancement means that the channel is ...
7
votes
4answers
734 views
How are logic gates created electronically?
So we have AND, NOT, NAND, NOR, OR gates, but how are they created electronically/electrically?
For example, what makes NOT gate reverse the value?
7
votes
2answers
4k views
How does an astable multivibrator LED blinking circuit work?
I am beginner to electronics. I come to know about oscillator using RC circuits (Capacitor charge and discharge and time constant tells the behavior of circuit).
Then I saw following circuit that ...
7
votes
1answer
1k views
Can the Common Emmiter Amplifier use a PNP Transistor instead?
This is a simple Class A amplifier using an NPN transistor:
Is there a way this can use a PNP transistor, instead (with only 0V and +Vcc, not 0V and -Vcc)? Why or why not?
7
votes
4answers
382 views
Zero or low-current voltage divider for switch identification
Is it possible to design a voltage divider circuit with switches that uses zero current, or very low current? Would it work to use a transistor to connect/disconnect the end of resistor string from ...
7
votes
2answers
198 views
Is one circuit better than the other to drive the PNP transistor?
Of the two circuits, would you prefer one over the other?
7
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5answers
5k views
Simple Audio amplifier Using Transistors
I would like to build a simple audio amplifier using transistors. I know there are IC designs specifically for the task. But i want to use transistors so i can learn how to use them for amplification.
...
7
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3answers
667 views
Capacitor behavior in oscillating circuit
I've been making my way through "MAKE: Electronics: Learning Through Discovery", but have gotten stuck on Experiment 11, where I am making an oscillating circuit.
The book calls for a 2.2uF ...
7
votes
1answer
113 views
What does O stand for in V_CBO and V_CEO?
I have just bought this transistor. In the absolute maximum ratings, the voltage names end in O, such as V_CBO, ...
7
votes
3answers
8k views
What's the difference between MOSFETs and BJTs (from a circuit analysis perspective)?
When analyzing circuits with transistors in them, when does it make a difference whether they are MOSFETs or BJTs?
7
votes
3answers
4k views
How to pick a switching transistor to drive LEDs? Or, how to read a transistor data sheet?
I'm going to be driving a bank of 20-25 LEDs from a single output of a PIC micro. Obviously, I need a transistor, because that's going to be somewhere in the vicinity of 400 mA (the LEDs are speced at ...
7
votes
1answer
184 views
Transistor current mirror circuit
simulate this circuit – Schematic created using CircuitLab
Can somebody please explain me how a transistor mirror circuit works and how can it be used as over current detector?
I badly ...
7
votes
1answer
234 views
Thyratrons: How they work, what they are used for, and how to read their datasheets
I recently ran into an interesting device called a thyratron. I have a basic understanding of thyratrons as gas filled vacuum tubes. I understand that they can switch large amounts of currents and ...
7
votes
1answer
179 views
Current flow priorities in PSU / PSU review
Being an electronics hobbyist, I'm having quite a challenge to design a PSU, which must run both on batteries (during the night time) as well as on Solar energy (daytime). The device is intend to run ...
7
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4answers
507 views
Modular Analog Circuit formula solver?
I've been thinking of making a database / program to make building analog circuits easier. I wanted to make sure there isn't anything else like this that I can contribute to instead of going through ...
6
votes
4answers
407 views
Moore's Law Timeline
I find it incredible how transistors per area keeps increasing. How has it been achieved so far? My ignorance tells me that if ICs were designed properly from stage to stage they should have got this ...
6
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6answers
390 views
Basic Electronics - I want to learn the “why”, not just the “how” [closed]
I have been looking for a very basic book on electronics, but many of them explain what the components do (and how they are made) and then go into designing circuits that do stuff. They tell you to ...
