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Questions tagged [transistors]

The transistor is a semiconductor device that can amplify signals and switch power. Most used types are bipolar (BJT, for Bipolar Junction Transistor), UJT (Unijunction transistor) and MOSFET (FET, for Field Effect Transistor)

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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 ...
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2answers
18k views

BJT in Reverse Active Mode of Operation

What will happen if for a BJT transistor it's Emitter terminal is treated as collector and collector as Emitter in a common Emitter amplifier circuit?
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(NPN) Why is the collector current at saturation, less than the collector current in the forward active mode?

Why is the collector current at saturation less than the collector current in the forward active mode? Specifically, Why is \$ I_C < \beta I_B \$ ?
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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 ...
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5answers
8k views

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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3answers
16k views

Bootstrap circuit function

I had some question about the bootstrap capacitor on gate driver. First, the bootstrap capacitor is used because the voltage on the high side drivers gate need to be about 10-15 volts higher than the ...
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3answers
50k 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 +...
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5answers
35k 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?
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4answers
51k views

How do BJT transistors work in a saturated state?

This is what I know about NPN BJTs (Bipolar Junction Transistors): The Base-Emitter current is amplified HFE times at Collector-Emitter, so that Ice = Ibe * HFE <...
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2answers
1k views

Why can't class A amp drive 8 ohm speaker with just one BJT?

I designed this class A amplifier. It's my first attempt at designing an amplifier with transistors. My objective is to build a guitar amplifier with tubes, but I figured that building an amp with ...
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9answers
83k 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 ...
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6answers
29k views

Need help calculating resistance for transistor base

I have 3 12VDC/40A automotive relays (datasheet) that I want to use with my Arduino. Based on the tutorial I am following (link) I need transistor, resistor, and diode. I am not an electrical engineer ...
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7k 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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299 views

Cant understand an ab amplifier diagram

I been trying to figure out this diagram, and Can't understand what happens from the beginning of the input , how the voltage changes in a way that "shuts off" one transistor. Also cant understand the ...
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1answer
6k views

TTL NAND gate (totem pole) current and voltage analysis

I am working on a few practice problems for my course and I am unsure about my working throughout. hoping for some feedback and guidance from the community as it's not my strongest topic. Here is ...
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6answers
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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 ...
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2answers
26k 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: ...
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5answers
19k views

How do I make the turn off and turn on time equal in a NPN transistor?

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 ...
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1answer
65k views

Choosing the right transistor for a switching circuit

I want to control a siren speaker (has a built-in driver) with an Arduino. The siren needs 12V and consumes about 480mA. The Arduino output pin is 5V and can source 40mA maximum. I would like to use ...
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4answers
9k views

How to drive a 20mA LED From a 4mA max GPIO Pin

I have an IC that has an GPIO with which I would like to drive a LED. Since the device will be running off battery, keeping the power use low (Zero maybe) while the LED is off as a priority. The ...
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2answers
19k views

Motor driver using only a 2N2222 transistor?

Is it possible to build a motor driver using only a 2N2222 transistor? If yes, then how?
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3answers
10k views

Using NPN transistor as switch

Before I ask my question, I should say that I am very new to working with electronics and I may not quite know how to describe my problem. I am trying to use a pin on my msp430 microcontroller I have ...
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4answers
15k 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??? [...
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4answers
83k views

How to invert a digital signal

I need a way to invert a digital signal i.e. if the input is high, I want the output to be low and if the input is low I want the output to be high. I think this can be accomplished with a single ...
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6answers
11k views

How does this constant current sink actually work?

I have implemented a constant current source and it works wonderfully, but I was just hoping to try and understand it a little bit more! Here is the circuit in question: I have tried doing some ...
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1answer
27k views

What is the difference between emitter and collector for BJTs?

the (surely simplistic) model of a bipolar junction transistor one is taught in foundational physics course appears to be symmetric. - So, what is the difference between the collector and the emitter ...
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2answers
5k views

How to sense the zero crossing of current?

I am trying to sense the power factor angle using microcontroller. Now the mechanism that I have thought it that Measure the zero crossing of voltage When the voltage zero is sensed, start the ...
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2answers
3k 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 on-...
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3answers
6k views

Basic operation of a bipolar junction transistor

I've tried really hard to understand the basic operational principle of a transistor. I've referred to many books and been to forums but have never got a convincing answer. Here are the things I want ...
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2answers
20k 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 ...
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1answer
142 views

Operation of tuned collector feedback oscillator

I am trying to understand the following tuned collector feedback oscillator extracted from here using LTSpice. I understand that L1 and C1 creates the resonance at the oscillation frequency and L2 ...
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8answers
495 views

Lighting either of two LEDs, or none, based on digital input

I ran into a problem which I tought was extremely simple, and after giving it some thought for more than 2 hours I had to recognise it actually is quite complicated. The problem is the following: I ...
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2answers
21k views

Hooking up multiple RGB LEDs while using a minimal number of PWM pins on an Arduino?

I currently have an anode RGB connected to the 11, 10, & 9 PWM pins on my arduino. However I would like to add 3 more LED's to my project, but I don't want to necessarily take up every single PWM ...
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3answers
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 ...
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5answers
4k 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 ...
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2answers
43k 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,...
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3answers
40k views

Transistors in parallel

I want to use several transistors in parallel to control current through a load. This is to distribute the current through the load across the transistors so that individual transistors with a rated ...
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2answers
29k views

Switching 9V using a NPN transistor and an Arduino

First of all, I'd like to say I'm not an Electrical engineer so please bear with me. I haven't got a sketch for what I'm trying to achieve but hopefully I can explain it ok. I have an NPN transistor (...
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3answers
44k views

how to use a 3v output to control a 5v relay

I have some circuit where my board (Electric imp) can output up to 3.3v, and i need to control a relay with atleast 5v in order to effect the coil and close the circuit. i have a power supply of 5v, ...
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2answers
6k views

How do I connect a relay and transistor to an Arduino? [closed]

Ok, so this is what my relay looks like. I can't figure out what pins I hook the arduino and transistor to, and what pins to hook the the other device. Please help.
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8k views

Driving Solenoids from Arduino

I was wondering what the best way to run a solenoid would be from an Arduino board. I was thinking about using a MOSFET that runs into a relay to turn on the solenoid but am not sure how to go about ...
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1answer
6k views

Calculationg base-resistor between microcontroller and transistor

I'm curious, when connecting my 2N2222 transistor's base to a PWM output pin on my Arduino, I know the Arduino can deliver a maximum of 40mA current. The 2N2222 only requires around 5 to 10 mA on it's ...
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2answers
662 views

How does early voltage affect collector current?

The transistor in the following circuit is said to feature \$I_{C} = 1.0mA\$ at \$V_{BE} = 0.7V\$ and \$V_{CE} = 10V\$. If \$V_{A} = 50V\$ and \$\beta = 50\$, find \$V_{B}\$ and \$V_{C}\$. simulate ...
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3answers
13k views

Where should I put the kickback diode in a transistor switch?

When driving inductive loads with transistors, we use kickback diodes. What I understand is a kickback diode supplies a path for the inductive charge to discharge. Also, an inductor will try to ...
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2answers
8k views

Arduino, NPN and common cathode RGBs

I'm trying to design a mood light system using 4 RGB LEDs which will be powered by an external 9V source and an Arduino for processing. Link to Fritzing file Part list: 3 x 2n2222 transistors (NPN) ...
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4answers
715 views

BJT base connected to ground and still operates?

When in university I used to get confused how a transistor (NPN) can draw current from ground. I'm now studying power amplifiers and again, this same configuration appears. How does Ir draw current ...
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4answers
13k views

Control 5v relay through 3.3v GPIO using NPN transistor

I'm not very pratical as I just started learning electronics and I'm planning to make some experiment with Raspberry Pi. I'm trying to control a 5v relay board that, I think, is made for Arduino, as ...
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2answers
874 views

BJT amplifier (Vce) voltage!

I am a bit confused with the given information to me (written in Bold letters below). If i could get some more ideas and clarifications it would be really helpful. Given: BC 547 transistor (in use) ...
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1answer
2k views

Understand 2 transistors (NPN & PNP) flasher circuit working

I implemented this circuit on a breadboard and it works. However on Proteus ISIS it doesn't (I have to change the 330k to 1500k for it to work on Proteus). I have two questions related to it. 1- Why ...
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2answers
7k 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 ...