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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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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75 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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74 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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34 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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38 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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57 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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48 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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77 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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127 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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113 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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106 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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171 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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51 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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121 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
457 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
117 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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203 views

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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68 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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157 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
122 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
51 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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56 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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28 views

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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169 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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72 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
72 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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107 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
26 views

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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87 views

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 ...
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70 views

darlington emitter follower

I assume it's known that voltage gain from two transiators in bjt darlington follower emitter are: \$ A_{V1} \approx \frac{1-h_{ie}}{A_{i_1}R_{i_2}} \ \ A_{V2}\approx 1-h_{ie} \$. Now in the text ...
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52 views

voltage Gain in BJT

I am reading the book: Problems & Solution of Electronic Devices & Circuits, and on page 119 I got stumped. They write that : $$A_V = A_I \cdot \frac{Z_L}{Z_i}= \cdots = ...
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1answer
150 views

Help With Simulating Common Collector Amplifier In PSPICE

I have included as much information as possible, so it should just be a matter of pointing out something simple (hopefully). I am trying to model a biasing circuit for a Common Collector BJT ...
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2answers
76 views

Amplifier gain too HIGH?

I have this circuit : Two common base amplifiers for amplifying frequency in FM range (88 to 108 Mhz). The Problem is, as seen in the figure, I am getting an output of 1.5 V for an input of 10 uV. ...
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69 views

Trouble with CE BJT amplifier

I have the following circuit : It is meant to amplify signals in microvolt range and around 100 MHz. Now in the figure, the transistor is an ideal one. So it works fine and as expected. But as soon ...
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79 views

BJT Ic vs VBE graph in Proteus simulation

I'm trying to simulate the behavior of a BJT on Proteus. The image below shows the graph that I got when I plotted \$I_c\$ on the vertical axis vs. \$V_{BE}\$ on the horizontal axis. But ...
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68 views

Whether Internal source resistance will have effect on the circuit

Calculate the voltage gain for the network of Fig. 3.12 if the source has an internal resistance of 100 in series with Vi.Vi=500mV,R= 1K ? For this problem I had tried a solution but I am not ...
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183 views

Av for small signal analysis with BJT for unbypassed emitter and ro in place

My question is about another question on this site. On that question Z(in) for small signal analysis with BJT for unbypassed emitter and r0 in place Zin is asked for a common emitter configuration ...
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163 views

Why is a DC base voltage needed to attain faithful amplification?

I was studying about transistor biasing from an article, http://1drv.ms/1yU8B7C, and I have a question regarding this part: Why should an extra voltage \$V_{BB}\$ be needed when there is already an ...
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83 views

How does this AM Modulator work?

I have been given a question and tasked with identifying the various components. However, this circuit doesn't really seem to make sense to me. Error: RC RE inverted simulate this circuit ...
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60 views

compare base current of different transistors

Can you please compare the base current of 2 transistors: T1 has Vbe = 0.7 V and Vce= 0.7 V T2 has Vbe = 0.7 V and Vce= 0.1 V i believe that T1 is in active mode while T2 is in Saturation mode, so ...
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133 views

Multiplexing problem with Arduino, MAX7219 e BJT

I tested the circuit below with an Arduino UNO, a MAX7219 and BC338. The sketch in Arduino is a chaser, so the leds should turn on in sequence. It consist of 7 segment (A-G) and two Digit (0-1). The ...
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335 views

How to shorten fall time on high-side BJT drive?

I have built a PCB with a set of high-side BJT drives shown in the schematic below. I'm using 8 of these to drive the columns of an 8x8 RBG LED matrix. While debugging the board with my ...
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43 views

MAx peak to peak of ES without clipping?

This is an exam problem in which my instructor gave the answers but no work. Any one has an idea of how to solve it;FOM(figure of merit)= 25/125, RL=15 ohms, Rx=250 ohms, r1,r2,vee,vcc, are not given. ...
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87 views

OP amp output not changing ( schematics )

This is a image of most of part of my circuit (555 timer IC is cut from right side)... using the pot (RV1) , I change the non inverting input voltages of the op amps. when non inverting exceeds ...
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48 views

Max peak to peak swing across ES without any clipping distortion?

This is an exam problem in which my instructor gave the answers but no work. Any one has an idea of how to solve it;FOM(figure of merit)= 25/125, RL=15 ohms, Rx=250 ohms, r1,r2,vee,vcc, are not given. ...
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2answers
76 views

Graphical solution of BJT inverter

I have the following BJT inverter circuit and graphs of its electrical characteristics. I need to graphically find the DC response characteristics of this inverter but I don't know how to proceed.
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159 views

Designing a stiff voltage source using an emitter follower

simulate this circuit – Schematic created using CircuitLab I am new to electronics, and I am trying to do Exercise 2.2, page 67 of The Art of Electronics. Use a follower with base ...
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368 views

Do I need a base resistor for a BJT?

I have a 74HC595 shift register that I shift bits into from an 5v Arduino. The pins on the shift register is connected to the base of 2N3904 BJT's through a 4.7kOhm resistor. I have noticed that if I ...
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310 views

Microcontroller PWM to bipolar push-pull amplifier issues. (level shifting)

I'm trying to design a circuit that allows a micro controller (arduino) to control a voltage to a load. The load voltage needs to be bipolar in nature (+- 3 to 5 V) for use in controlling a TEC. My ...
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56 views

can SOT883B package BJT transistor switch a relay with 21.1mA coil current?

I am planning to use miniature BJT in a circuit , but I haven't used them before, The specs of NXP BC847BMB TRANS, NPN, 45V, 0.1A, SOT883B shows 100mA as collector current, I am worried if it can ...