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Electrical Engineering

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)

4,028 questions
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Resources for learning about transistor configurations?

I'm currently taking a circuits class that discusses various transistor amplifier configurations eventually culminating in building an op-amp. This includes various configurations such as the ...
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Can't figure out how book on Trannys gets hfe of CE amplifier when using T-Equivalent and Hybrid Pi Circuits

So I'm reading through it and doing all trhe problems as I have done with 20+ other books like this. The author says this a lot "Although the transformations are quite straightforward mathematically, ...
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2answers
55 views

Driving a high-impedance load from a BJT base

Are there any caveats with tapping off the base of a BJT to drive a high-impedance load, such as a logic gate or op-amp? In the schematic below, I have an open-collector output from ...
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Controlling LED strip with Wemos D1 mini

I have a 12v led strip and have tested the current draw at ~500mA per colour. I want to drive this via my Wemos GPIOs which are 3.3V @ 12mA max. For testing I have been using 2N2222 transistors with ...
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Need help understanding how a transistor works in this circuit

The circuit diagram I've attached has the direction of current flow represented by red arrows. It's the solution given for the 2006 Pennsylvania State Circuit lab competition for Science Olympiad from ...
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1answer
50 views

Question about transitor NPN [ALFA;Strange configuration;Exit characteristic]

first of all thanks for read and for your time, I have a few questions about transistor: 1) I can't understand why my book say: Ic=Icb0+alfa*Ie and not ...
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1answer
36 views

CD4011 Oscillator Square Wave Output Fed to Transistor Audio Amplifier; Volume Control Question

I built an audio frequency square wave oscillator using 3 gates on a CD4011 quad NAND gate IC. I then fed the output of the oscillator (pin 11) to a very basic "push-pull" transistor amplifier on the ...
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33 views

Why is my signal stronger in the positive than in the negative when i use 2n3819?

simulate this circuit – Schematic created using CircuitLab In the above circuit I have created a JFET amplifier for small signal purposes. When I run tests on the circuit, i get this weird ...
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24 views

Will this attempt at building a four transistor multiplexer work?

Ordinarily I think most people would build a multiplexer out of a NOT gate, two AND gates, and an OR gate, which would involve seven transistors, wouldn't it? I want to see if I can do a multiplexer ...
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1answer
23 views

Half H-bridge using only ntype mosfets or npn transistors

Would the following circuits work? I keep thinking I need a mixture of ptype and ntype mosfet or npn and pnp transistor for a half h-bridge, but I keep seeing schematics with only ntype mosfets or npn ...
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1answer
56 views

What is the least expensive way to build a three-bit shift register?

I'd like to build a queue of three internal bits as inexpensively as possible. Externally, the queue has two input bits and one output bit. The inputs are (dataIn) and (shift), and the output is (...
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1answer
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Switching 3.3V with a Raspberry Pi gpio pin

I recently bought an IR Camera for my Raspberry Pi, something like this: https://www.amazon.com/kuman-Raspberry-Camera-Module-Supports/dp/B01ICLLOZ8/ref=mp_s_a_1_17?crid=M3FSU2COLT5W&keywords=ir+...
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44 views

Distortion via Powered Speakers and not in Headphones - 1 Transistor Amplifier

I'm trying to make this NPN amplifier circuit work for my battery powered computer speakers. This circuit works fine if i connect headphones to it in output, but has distortion when connected to a ...
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58 views

Using a coin vibrator on a PIC18 MCU

I was wondering how could I add a vibration to a PIC18F45 MCU so that when you touch a key, it would vibrator? I would like to use a dedicated pin from the MCU. Here is an example of a vibrator ...
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the difference between K coefficient and gm in the mosfet

i know that K in mosfet is as beta in Bjt but since it represents the change in Id in relative to the change in Vgs isn't it supposed to be the transconductance gm ? but why is it different and the ...
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41 views

Voltage Across NMOS and PMOS Transistors

So I have the question above concerning an NMOS and PMOS transistor. The goal is to find V1 and V2 in steady state. My understanding is that because the gate voltages of zero and Vdd are there, the ...
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1answer
41 views

HFA3096 transistor array breakdown voltage

In the book Learning the Art of Electronics, one of the labs is to build a differential amplifier with a CA3096 transistor array. The author admits that the chip may be difficult to find and gives the ...
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1answer
66 views

Finding the broken cicuit in an Xor Gate

I am new to this particular stack site but I feel that this is the most appropriate place to ask my question. -Background- I've been following an online web course called Nand2Tetris that takes you ...
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1answer
89 views

BJT Clapp Oscilator for 3-6MHz

I designed a Clapp VFO to aid in my Ham Radio projects (Non-superhet SSB and CW recievers for 80M and hopefuly 40M). I chose the clapp topology for it's frequency stability. I want it to tune at least ...
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1answer
19 views

Explanation of Source-Absorption Theorem Example

In the section on the Source-Absorption Theorem, my textbook has the following example: I was wondering: If the voltage $$v_\pi = - v_e,$$ then why do we get $$g_m v_\pi = g_m v_e$$ instead of $$g_m ...
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2answers
46 views

Feedback on a simple motion activated motor circuit

I have been working on a motion activated motor which uses a PIR sensor to detect the motion. The idea is when PIR detects user in front of it motor should start running and when the user moves away ...
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56 views

Light sensor using transistor

I am trying to create a light sensor circuit using 2N3904 transistor but current is not passing through RL what is error in my circuit?
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26 views

Non ideal behaviour of a current mirror

Voltage across emitter and collector of QA is 0.7V. In a current mirror, why is it such that when the voltage across the collector and emitter is different for Qb than QA the value of Iout increases ...
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53 views

Transistor to safely connect 2 circuits failsafe [on hold]

A simple project turning into a head scratcher for me. Charging Lipo batteries from 1,2 and 4 cell requires different connector types unless I can simplify an auto sensing connection. I need to ...
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Arduino PWM & MOSFET successfully control LED but not electromagnet? [duplicate]

I've got an Arduino circuit set-up so I can control the strength of an electromagnet using a potentiometer. My potentiometer is hooked to A0, and I'm mapping its value to PWM pin 3 which then goes to ...
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1answer
67 views

Current-limit circuit for 78XX voltage regulators

I need to find the value of Rsc and R1 in the following circuit: In this circuit, Q1 is the high-current pass transistor. Its emitter-to-base resistor has been chosen to turn it on at a given load ...
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1answer
57 views

Unexpectedly high voltage drop in the transistor

I'm driving an LED with a microcontroller through a transistor with a PWM signal. When the gate is grounded, no current flows, as expected. As soon as I start to drive the transistor (1% duty cycle), ...
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2answers
90 views

SPICE BJT simulation results

I'm trying to simulate simple BJT circuits to verify my hand calculations. Following is my circuit, I'm just trying to get the calculated DC collector current with the shown voltages and parameters. ...
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0answers
91 views

Why do I have voltage on Collector and Emitter when NPN transistor turns on? How to get rid of it?

I have a 2N3904 NPN transistor. I'm feeding the base 5V. the transistor turns on just fine and it shorts the collector and emitter. However, when I turn my meter on volts, I read around 1- 1.5 volts ...
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3answers
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Is base-emitter voltage of BJT transistor (common emitter configuration) constant?

For sillicon the value of Vbe is approximately 0.7 V. So why is the input characteristics of such a transistor like this Why not a straight vertical line. Or is this curve plotted for I Vs Vbb. I ...
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4answers
78 views

Will switching a LED on and off at a said frequency reduce or increase heat loss?

In my case, a 50W 34V LED is being used to light a small box. To reduce heat generated by the LED, we are switching it on and off at 50Hz. But I was wondering will this actually help? In the case of ...
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30 views

Current capabilities of P-Channel Mosfet Circuit

I don't know how to ask the right question it would appear, but the following answer by Dave Tweed Refers: Floating Voltage to Bias a P-Channel Mosfet without Exceeding Source-Gate Max Voltage In ...
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5answers
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PNP transistor turns on at 3.3v

I have connected a 3906 PNP transistor base to a GPIO pin of ESP32 board. Emitter is connected to 5v and collector is connected to a buzzer. When I program the buzzer (send a HIGH from ESP32), it is ...
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Help with making sure a correct use of a BJT

I'm designing a PCB that receives 3 power inputs 3.3v, 5v and 12v. I need simple way to switch all of them of in one go. Here is a schematic of my PCB My 12V line is for running a ws2815 led strip ...
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CE/CB BJT Amplifier(s) + Load Lines!

This diagram from a lab assignment is not making sense to me...any help would be greatly appreciated. I don't understand what \$I_{C_\max}\cdot R_e\$ is and why it appears on this diagram. Even if it ...
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41 views

Determining suitable transistor for replacement

I found a transistor is burned and I am trying to find a replacement one. Though searching with the markings on it, I could not find anything at several electronics shops I tried. How do I select the ...
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1answer
75 views

How do I choose the power rating of resistors in audio power amplifier?

I read a bit about audio power amplifiers and struggle to understand the power rating of the emitter (i.e. current sharing) resistors in power amplifiers. I refer to this project. [EDIT: schematics ...
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1answer
19 views

ESD diode with zener configuration is equivalent to a circuit containing diode, transistor and zener diode, so how this could be equivalent

please tell me in the following link (https://www.onsemi.com/pub/Collateral/ESD9101-D.PDF), the ESD diode with zener configuration is equivalent to a circuit containing diode, transistor and zener ...
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2answers
88 views

Darlington pair [closed]

Here, the first transistor t1, is to be connected in CC configuration. Doesn't that mean that the collector of the first transistor should be grounded? Also, the collector doesn't seem to be "common"...
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1answer
42 views

Protection for transistor driving a coil

I recently purchased a few electromagnets. I want to drive these with transistors, but I want to build in protection, as these don't have any available specs re: max operating temp, duty cycle, etc. (...
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1answer
44 views

Confusion about cutoff mode of NPN transistor

In the diagram below the npn transistor is in the cutoff region. The book says that both EB and CB junction are reverse biased. My question is about: A) the EB junction. How is it reverse biased? Isn'...
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1answer
38 views

NPN Transistor Switching 12V - grounds with different potential

I'm struggling with a NPN transistor switching problem, and in the process I've burned out a board elsewhere in my machine. Electronics is not my strong suit. I want to use a 5V signal to switch 12V. ...
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1answer
39 views

Need help identifying this component recovered from a Fostex X28

This has been taken from a Fostex X28 4 track recorder and requires spares. I am not familiar with this component and I am unable to find information online. Does anyone know what it is and if there ...
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2answers
43 views

Eagle Schematic help for 74AHCT125 quad level shifter

I have an Adafruit Quad level shifter 74AHCT125 that I am trying to build into an Eagle Schematic and PCB for a project. I am very new to schematics as in...this is my first attempt. I piggybacked ...
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1answer
40 views

ltspice: simple nmos circuit

I built up a circuit which did not work as expected. I reduced the problem to this circuit: I expect to have a current of ~2.4 A at gate voltages below 10 V, but actually the transistor does not ...
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2answers
705 views

IGBT transistor with auxiliary emitter

Recently I discovered, that some IGBT transistors in IGBT modules have the second pin for an emitter, called auxiliary emitter. In the picture above 2nd and 4th pins are auxiliary emitters. This is ...
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Compensating transistor biasing

How to analyze the quiescent conditions of the circuit below assuming the tansistors are on an array such as CA3096? (Fig 5N.21 from Learning the Art of Electronics) Both emitters are at ground, so ...
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3answers
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Determine what voltage brings \$ V_{in} \$ in the saturation region for the following circuit?

Hi I need some help with my homework, I am trying to find \$ V_{in} \$ when the circuit is saturated. Here is my circuit: simulate this circuit – Schematic created using CircuitLab Here is ...
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1answer
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Transistor as a Switch in Cutoff and Saturation

1) An NPN transistor in cut off mode: "To get a transistor into cutoff mode, the base voltage must be less than both the emitter and collector voltages. VBC and VBE must both be negative. In reality, ...
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1answer
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Determine the value of Ic (sat) and the value of Rb in a simple circuit

I need help with my homework I do not understand how to find the resistance for the Rb in the for this problem. simulate this circuit – Schematic created using CircuitLab Here is the question: ...

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