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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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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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Potentiometer vs. Transistor

From what I know, potentiometers vary an analog current with an input usually in the form of a knob. And transistors vary an analog current with an input in the form of a smaller current. Is there ...
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NOT gate with PNP transistor

I'm trying to make a NOT gate, but with a PNP transistor instead of NPN. What would a wire diagram look like for a NOT gate with a PNP transistor?
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Is 2N9013 a good replacement for 2N3904?

I needed 2N3904 transistors, so I went to the few (poor) electronics shops we find in my country. They didn't have those, but they gave me 2N9013 and stated that those were equivalent NPN transistors. ...
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Diffusion capacitance approximation for bipolar power transistor

I'm trying to remember the approximation for the value of the diffusion capacitance for a bipolar power transistor. I think it might have been gm/Ft? Can anyone confirm this and/or give a reference? ...
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configuration of transistor for amplification

why common emitter configuration is used more than common base configuration of transistor for amplification purpose? when common base configuration provides more stability than of common emitter ...
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Operation Amplifier with Transistor output

Is there a name for feedback amplifier topologies which include an opamp and transistor in the feed-forward path?. I need to design an amplifier with high bandwidth (almost 100 MHz) and high gain (50) ...
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Using a transistor as a diode?

I am trying to interface a pair of Chinese calipers with my Arduino. Due to the calipers running at 1.5v, I've used a TPQ-2222 (quad 2N2222 transistors I think, please let me know if I'm mistaken) to ...
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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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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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BJT's Small signal Models

I'm trying to solve AC equivalent circuits of small signal BJT circuits. I'm confused whether to use the hybrid-pi or T-model.
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Creating a 12V @ 3.5A out of 15 volt 1A

I have a huge led matrix which will draw 3.1Amps of current. However I only have a 15v 1A psu> Would it be possible to use a transistor to amplify the current after I've lowered the voltage? Could you ...
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how does a transistor behave when it's broken?

I'm trying to get a circuit to work (linistepper driver) and I suspect I may have fried the drive transistors (tip122's in this case). Are there common behaviors of broken transistors? does c->e ...
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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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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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Solving DC Operating Point of Common Source Amp

My lab partner and I are really stumped. We are given a circuit that has a FET with a \$V_{DD} = -V_{SS} = 15\mbox{ }V\$. We are told \$A_V = 20\$ and \$I_{DS} = 1\mbox{ }mA\$. The DC circuit is ...
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How does an astable multivibrator LED blinking circuit work?

I am a beginner in electronics. I come to know about the oscillator using RC circuits (capacitor charge and discharge and time constant tells the behavior of circuit). Then I saw the following ...
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how to drive 5x5 IR LEDs with 100 mA, using Arduino

I am trying to do my first Arduino project, and I would like to drive a 5x5 matrix of IR leds. I would only like to have one switched on at a time. I understand that in an array I can do it with 5 ...
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2answers
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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 ...
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1answer
886 views

How to switch/power a 13x13 LED Matrix?

Hey all - I have an AVR project in mind that will require a 13 by 13 LED matrix of bright white LEDs. I'll be wiring up my own matrix to do this (not using premade 8x8's). I plan on using some shift ...
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Low-noise audio-frequency BJT? [closed]

I found myself looking for a low-noise PNP transistor the other day. I couldn't find any parametric searches that listed noise performance. Even from the transistor manufacturers. You can search by ...
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Drive LEDs from 4-20mA source

I have a task to drive four LEDs from a 4-20mA loop. I have 24V for the LED side so I need to convert the current into something that can drive the LEDs. I know I can use a 250\$\Omega\$ resistor as ...
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Are MOSFETs Sensitive to heat while soldering?

I'm soldering through the hole MOSFETs in to a PCB and I don't have a temperature controlled soldering iron. So will I need to heat sink the legs as I solder them to stop internal damage. I as this as ...
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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?
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Is there a good book that explains the features of electronics with math?

With differentiation equation, I mean. I've seen many books which explains it with quality analysis,but now I'm seeking of a book that can explain it with quantity analysis,which means a lot of math.
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T-trigger: minimum transistor count

I am playing around with real implementation of basic logic schemes from transistors. Could you suggest any compact implementations of T-trigger? Obviously, classic "CMOS" way eats way too many. ...
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1answer
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Measuring Resistance/Impedance with SPICE

How does one measure impedance/resistance using SPICE? I have access to regular SPICE(MacSpice) and HSpice. The DC current divider circuit at the bottom of this webpage seems to be one method. 0V ...
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1answer
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Using a 4-pin computer fan controller without the load

Is it OK if I use the controller from a CPU fan without connecting the motor's coils? All I want is to use the Hall effect sensor. The datasheet is posted here, the driving output circuit uses a ...
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1answer
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Testing an Audio Power Amp with Paralleled Transistors

A question concerning my current repair project of an audio amp that uses big (600 W) but otherwise rather classic complementary output stages: I assume when testing an audio power amp with 6 pairs ...
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1answer
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LED flashlight project: Need transistor ideas

This question is continuation of this question. I did some research on previous question and made a circuit as a starting point. Here's a picture: Now my problem is that TS555 device I plan to use ...
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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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How many transistors on an IC?

For my product's blurb, it would be really great if I could find out how many transistors average MCU's have, as a comparison to something bigger, like a computer, or even a low-end x86 processor. The ...
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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 ...
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How to drive a BC547 using a 0-5V sensor output?

I have an i-Snail-VC-50 sensor with an output of 0-5V. I'd like to connect this output to the base of a BC547 transistor, which powers an LED with an external 5V power source. What I want to achieve, ...
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Transistor with two voltage levels, Vb ≠ Vcc

Why is my transistor only driving 5V instead of 6V? How can I fix it? I have a 6V, 25mA circuit running some LEDs. I can control them by connecting and disconnecting the positive terminal of the ...
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2answers
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Explain this circuit?

This is one of the circuits in the Electronics 9/10 class. The package did not explain how transistor combination worked and why the capacitor will reverse its current. Can you explain this circuit?...
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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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“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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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 capacitor,...
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1answer
396 views

Controlling a NE2 lamp with a 12 V signal

I have some NE2 lamps i want to control with a signal from my car. Signal voltage is about 11 to 14 volts and isn't very clean. I also have 170vdc available to power the NE2s. I plan on using these ...
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audio controlled relay circuit

I need a circuit that fires a relay when it detects audio pulses from one channel of an mp3 player. I'm going to record audio pulses in sync with the music to control a motor for mouth movement. Its ...
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1answer
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How should I understand the amount of base current in BJT transistors?

I'm having trouble understanding how much current flows through the base of a BJT. With a MOSFET the answer is easy: 0. How do I calculate the amount of base current in a BJT and am I doing it wrong ...
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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 ...
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3answers
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Electronic circuit switch for arduino

Is there anything I can use to replace this circuit? Its a very simple electronic switch circuit, (transistor+zener diode+resistor) The circuit is connect to a remote control, the remote control is ...
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2answers
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Connecting arduino and separate power supply grounds

I am working on an arduino project that uses transistor switches to power on high power leds that are powered by a separate 24 volt power supply. My issue is that I have two different grounds, making ...
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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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How to step up from 3.3v to 24v?

I need to build a transistor circuit to go up from 3.3v (output of serial port) to drive some mechanical relays which require 24v input. Thoughts?
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Switching relay with a PNP and TTL levels

I can not wrap my head around the fact how I can drive a relay (24V, 160ohm) with an tip32a PNP transistor which has TTL inputs from a controller. I can easily calculate my resistors when I use the ...
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1answer
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Transistor with emitter resistor calculation

I can't seem to get over this but this seems to be the basics in electronics. I have an NPN darlington transistor TIP122 and have built to simple test circuit around it with Rb = 150 ohm, Rc = 80 ohm ...
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Using a transistor with AC?

Is it possible to use a transistor with AC? if you put a diode in there so no current flowed through it when the current reversed, but what could I do about the difference between the base and ...