BJT stands for Bipolar Junction Transistor. It is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications.

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BJT VCVS with high gain

In a lecture I learnt a BJT VCVS which has gain = 1, i.e a voltage buffer as shown in the figure. The speaker said that it was the ideal VCVS model of a BJT. My question is that is it possible for ...
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what does it mean for a to BJT operating at the edge between the active and saturation modes?

ive recently been fascinated with diodes and was wondering how i'd design a circuit that works at the edge of the breakpoint between the active and saturation mode. How would the circuit be analysed?
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BJT Amplifier in AC mode

In the lesson on BJT Amplifiers, we were told the we can find the AC equivalent circuit by replacing all capacitors by short circuits, inductors (if any) by open circuits, dc voltage sources by ground ...
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56 views

FET and BJT transistor question

We have the circuit in the figure BJT transistor has the parameters β=80 and the JFET transistor has the parameters Vp=-4 Volt and Idss=8 mA; Vgs=-2.6 Volt and Ids=1 mA We have R1=470 Kohm ,Rc=3.6 ...
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69 views

What does this symbol represent?

I am trying to understand the internal circuit schematic of the LM565 phase locked loop IC, on page 6 of this datasheet: PDF Datasheet for LM565 from TI website In the upper middle, there is a ...
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44 views

How to remove degradation in voltage gain when replacing the original \$R_L\$ with a small value resistor?

For the following common-emitter amplifier, the original \$R_L = 4.7\space kΩ\$. When I replace it with a small value resistor (\$100\spaceΩ\$), the voltage gain will drop. Is there any way to drive ...
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30 views

Bridging Discrete (BJT) Amp Channels

For my Electronics II class, I designed a discrete BJT amplifier circuit including a VGain, Buffer, and Power stage. I succeeded in meeting the specs, and the next step is to improve our design in ...
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41 views

BJT in reverse active mode [duplicate]

I was wondering, what are current directions in reverse active mode? I know that in this mode gain Beta is much smaller than Beta in forward active mode and for BJT to work in thise mode it must be ...
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75 views

BJT in Saturation

Is it possible for the base current to exceed the collector current for a BJT in saturation mode? (If the base current was increased without the collector current increasing at all)
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82 views

why do 2N2222 and PN2222 avalanche differently

i've been experimenting with a 2N2222 transistor (in the TO-18 metal case) and using it as an avalanche transistor -- by not connecting the base and having the emitter and collector connected in ...
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76 views

BJT Switch with a Diode from Base to Emitter

In this circuit, the diode is supposed to force a higher input voltage to turn the LED on, however when I created it on a breadboard I measured about the same input voltage (without the diode) to turn ...
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2k views

Basic transistor questions

I've created the circuit shown. I'm using a 9V battery (actually throwing out 9.53V) and 5V coming from an Arduino to test with both 9 and 5 volts. The transistor is a BC 548B (datasheet I'm using is ...
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60 views

Complex circuit analysis

I need help solving the circuit above. I don't understand how to analyse the op amp using the small signal model in order to calculate the Vout/V3, the input resistance (Rin) and output resistance ...
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2answers
60 views

Output Impedance of BJT/Mosfet amplifiers

I have heard in lectures that the desired output impedance for the BJT/Mosfet Amplifiers is LOW. But these transistors are Transconductance amplifiers 'by birth'. I mean they give output current ...
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3answers
72 views

Square wave into emitter follower

I put a square wave of relatively low rise and fall time (of about 10ns), and wanted to see the response from an emitter follower output. I put together the circuit and here's what I see on scope. ...
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1answer
48 views

What are the limitations of the Ebers-Moll model of the BJT

The Ebers-Moll model is considered simple yet effective model of the BJT. What makes it special and when does it break down i.e is not applicable?
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1answer
143 views

Solar controller with BJT transistor and PIC24 microcontroller to charge 3.6V NiMH batteries

I'm designing a solar controller circuit and am having some confusion about how to switch the BJT on and off. I have a single solar panel charging a battery. The BJT is there to prevent over-charging ...
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2answers
75 views

In logical progression, what things does a person need to know to design a robust opamp from BJTs

Opamps contain things like current mirrors, differential stage, push-pull pair and much more. Once a person starts from learning that BJT has 3 terminals for which Ic≈Ie≈βIb, what topics must a person ...
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1answer
47 views

Difference Between The Transisor Denotations V(th) and V(tn)

I have seen these values V(th) and V(tn) used interchangeably as the transistor 'threshold voltage' but have also seen them used together on the same diagram seemingly representing differnt things. (I ...
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144 views

BJT Driving an LED - Above or Below?

I will freely admit that I am mainly digital when it comes to electronics, so may help explain my confusion (that or just general incompetence). I am getting review feedback on a design, and one ...
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182 views

How does the negative feedback in this oscillator work?

EDIT: I don't think I'm using the term "negative feedback" correctly. What I meant is, how does the feedback that makes the closed loop gain equal to 1 work? I'm trying to understand the very basics ...
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1answer
35 views

Selectively outputting 2 inputs based on a third input

I currently have 2 inputs that can be on or off, they could be 00, 01, 10, or 11. I want to output them only if a third input is active. I figured BJT transistors would do the job, but they seem ...
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98 views

Bipolar transistor amplification biased

I'm having some trouble trying to solve this exercise. It is a BJT transistor common emitter circuit, with a biased resistor between the base and the collector. I am supposed to compute the signal ...
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1answer
111 views

Why does the colllector current decrese with decreasing collector-emitter voltage in this circuit?

I'm trying to understand how the circuit below works so I ran a simulation with TINA and I got the curves shown on the right (C3 is already charged). Here is a bigger one Considering the ...
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50 views

BJT driven LED lengthy fall time

I am designing a circuit for a strobe amplifier and am having some difficulty with the LED emitting light for longer than expected. I am measuring the light out of the LED with a photo receptor ...
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80 views

Analyzing a BJT circuit

Here is the example with its solution: The problem is that when I apply KVL to the circuit (the second circuit) from the 10V source to the ground at the bottom, I get wrong values. Here is what I ...
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87 views

How to avoid voltage drop on undervoltage protection circuit?

I'm having trouble with a circuit I designed and I'm hoping someone here may help me fix it. I've successfully used the circuit below a few times. It was proposed by Russel McMahon in this answer. It ...
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51 views

Figuring/setting BJT mode of operation

I am trying to make an IR transmitter, and have the following set up: simulate this circuit – Schematic created using CircuitLab I was thinking of this circuit, because I want to run ...
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1answer
80 views

How collector-base junction in BJT works

I have read some answers about how BJTs work, but I'm still not convinced. To show my doubts better, suppose we extract base and collector from BJT NPN transistor with all its construction details ...
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135 views

Instantly Hot Transistor

I have a TIP42G PNP transistor, and when I used it, it instantly smoked. Would it be because I shorted the base directly to ground? (through a button for the initial turn on, and through a 2n2222 for ...
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4answers
125 views

Parallel Transistors in Constant Current Load

I'm designing a constant-current dummy load for testing my power supplies. This load should be able to handle a maximum of \$2\mathrm{A}\$ at \$24\mathrm{V}\$. My current design, so far, is loosely ...
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1answer
144 views

Using BJT transistor as switch using arduino digital pin

I was working on a project and decided to use a BJT transistor as a switch. I haven't taken the electronic circuit courses which deal with transistors in my university yet so I wanted some advice if ...
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202 views

BJT Astable Multivibrator

I have the basic knowledge about multivibrators, but I did not understand the working principles of the circuit schematic provided down below. I have done the basic research about how it works, but ...
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60 views

BJT in reverse active mode

I am new in BJT.How the hfe of a BJT be less than 1 in it's reverse active mode ? Can anyone please answer me ?
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129 views

Why the base current decreases automatically?

Given this circuit: simulate this circuit – Schematic created using CircuitLab I don't understand why, when simulating it by increasing parametrially the V2 from 0V to 12V keeping V1 ...
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3answers
486 views

transistor level design of Op-amps

How do we realize the design of a simple Op-amp with Bipolar Junction Transistors or MOS Field Effect Transistors alone? I mean I understand the need for differential amplifiers for providing a ...
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1answer
128 views

Unusual voltage drop at BJT (2N2222)

I'm using BJT (NPN) that is supplied with 7V DC signal at the collecter, 5V DC signal at the base and need a 12V output at emitter. Right now i'm getting 4.35V at emitter. How can i implement it?
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NPN BJT base->emitter resistance is effectively zero?

I've been trying to better understand BJT transistors. In particular I've been trying to understand the inverting amplifier configuration. Wikipedia shows this schematic: Which shows an input ...
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72 views

Calculating the voltage out of this particular cap coupled circuit

Before I get to my question, I'll just go over the input and output of the circuit from what I "know". The base of the BJT gets a 20 microsecond pulse that puts the bjt well into saturation and "VOUT" ...
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193 views

Is this use of optocoupler wrong?

This is nearly not exactly how the circuit looks like, but I have a feeling that this circuit could cause problems while working. My feeling is that initially as Q1 would be in ON position, the ...
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5answers
127 views

Why this current regulator won't regulates?

I'm trying to make a current regulator to power up some LEDs. For now I'm working only on PSpice models. The circuit above works well if the sensing opamp is configured as voltage follower or even ...
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1answer
58 views

IR Led & Phototransistor pair bandwidth issue

I'm trying to sense IR wave with a phototransistor circuit. The circuit operates well under DC operations (I mean 3.3V through inputs). However, if a square wave is supplied from UART input, after ...
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80 views

How to plot the frequency response of transconductance of BJT with LTSpice

I need to plot the frequency response of the transconductance of this circuit in the picture with LTSpice but I don't know how. Can you please help me urgently how should I do it? Thanks
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To find the current of a current mirror circuit

In the figure given above all transistors are matched and! diode voltage and Vbe = 0.7V. Also the dc current gain is assumed to be very high. I got the answer for I as 3.6mA. However, the answer ...
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250 views

Amplifier design with three stages

As a project for my electronics 101 class, I've been assigned to design a three stage amplifier using bjt transistor to achieve a gain of 150 and input resistance of 100k and output resistance of 50 ...
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2answers
79 views

Current regulator static analysis

I'm trying to make (and try to learn something better) about a simple current regulator. I need to make a complete static analisys before starting with the frequency one. But I've some thoughts about ...
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3answers
79 views

Do we want output resistance of a transistor to be high or low

I have a serious doubt about output resistance of transistors. We say that output resistance of a device must be high, for example in BJTs, because it is actually a norton resistance in parallel with ...
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141 views

BJT differential amplifier output saturation

I'm making a long-tailed pair amplifier using a current mirror, the circuit has the following layout: I simulated it on PSpice and it worked, you can see the bias here: I tested it in the real ...
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1answer
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Collector Doping Concentration and Current Gain

I was wondering, in a BJT why does the collector doping concentrarion have no effect in determining the current gain? I am trying to understand this conceptually but I can't seem to wrap my head ...
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need help analysing this BJT circuit

I need help analysing this BJT circuit. What I need to find is the equation for IB, IC, and VCE for this circuit. So far what I've got is from KCL : a: I1=Ib+Ic b: Ie=Ib+Ic So I find that I1=Ie, and ...