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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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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49 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
55 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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105 views

How does this circuit give DC output? [on hold]

I didn't understand the working procedure of this circuit. It might be wrong. I ain't sure about this circuit correctness. Please anyone help me..
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1answer
71 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
22 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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76 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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0answers
63 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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1answer
46 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
60 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
59 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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2answers
62 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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44 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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1answer
54 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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2answers
157 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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4answers
143 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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2answers
63 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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1answer
59 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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65 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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4answers
299 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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1answer
42 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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1answer
80 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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44 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
57 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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108 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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1answer
345 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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224 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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3answers
52 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 ...
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1answer
83 views

Question related to Cascode Circuit

I am trying to solve the following question related to cascode circuit. Where T5 has Vbe=0.7V I have answered the questions as follows. - Explain how the circuit works? The circuit has a DC ...
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5answers
127 views

Calculating output impedance of Vbe multiplier

I am trying to calculate the output impedance of the following Vbe multiplier, simulate this circuit – Schematic created using CircuitLab I have calculated the Vout = 4.2V and now I am ...
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30 views

Need help finding Vo with changing frequences through the Voltage divider BJT

Help finding Vo with the changing values of frequency. R1 = 11.45k Ohms R2 = 4.4k Ohms Rc = 900 Ohms Re = 324.95K Ohms C1 = 10uF C2 = 10uF C3 = 50uF Vcc = 9V ...
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69 views

Why is the Vbe threshold of a Si NPN transistor 0.7V and not -0.7V?

In case of an n-p-n transistor, the Vbe is more like voltage across a p-n diode. Now, since the direction of electric field in the depletion-region is from n to p, how come the voltage across the p-n ...
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153 views

How does the voltage go negative on the BJT base in this simple flasher?

I'm trying to get more specific in my understanding of electronics, and, like any adult learner, am realizing I have to correct some basic misunderstandings or gaps in my knowledge of fundamentals. ...
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1answer
79 views

Output resistance of Emitter Follower

I have to measure \$R_{in}\$, the input resistance seen by the signal. It was told me, that the quickest way is measuring the voltage gain using oscilloscope, insert a resistor before \$R_B\$, ...
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88 views

Current in Saturation and Active regions of BJT

In the image(http://www.allaboutcircuits.com/vol_3/chpt_4/4.html), the result of SPICE simulation for active mode operation of BJT is shown. The current source is set at a constant value of 20uA and ...
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2answers
83 views

Common emitter characteristics in the saturation region

I'm trying hard to understand the different modes and regions of operation of BJTs. The behavior of transistor in saturation region is so confusing. I've searched in forums but couldn't get a ...
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1answer
140 views

Calculating the Output Resistance of a Widlar Current Source

I'm currently struggling to understand the small signal equivalent used in the following calculation: http://en.wikipedia.org/wiki/Widlar_current_source#Output_impedance My problem is: How come they ...
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1answer
41 views

How to get out pulsed output with BJT? [closed]

Is there any process of getting pulse output with BJT? The input must be plain DC. Is there any process existing? I tried to make pulsed output. It is very easy to make with micro-controller. But I ...
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1answer
134 views

How does the circuit work?

I can't understand how does the circuit work? Can anyone help me?
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2answers
68 views

What are the selection parameters for an NPN BJT?

I'm building an NPN-based driver circuit for disconnecting my battery level measuring voltage divider when not in use. Here's the circuit: ...
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84 views

BJT Circuit DC Analysis

I am trying to find the collector's current of each transistor in order to find the transconductance gm of both, but I don't know how to relate the currents of them. There's any approach? Thanks
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1answer
78 views

BJT Transistor question help here?

We have the BJT transistor in the figure. I have to do the DC analysis of the circuit, then draw the common base transistor scheme of the circuit. I know the values of \$V_{cc}\$, \$V_{be}\$, ...
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88 views

BJT Topologies - Design Principles at RF

Here are some rules of thumb I've learned when designing single-transistor BJT amplifiers: High input impedance is good Low output impedance is good Biasing resistors should draw ~10% of the ...
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1answer
83 views

Alternative LEDs Blinking circuit(Analog) Help

Can someone explain the operation of this circuit, I understand the basics of the BJT and its modes, but most of my confusion arises when there is some-sort of feedback loop in the circuit, my thought ...
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1answer
75 views

Problem in Clapp oscillator

I've set up this circuit on breadboard ( C1 being electrolytic and others disk) with Q1 as 2n3904. The simulation is perfectly fine and the oscillator works in the simulator as expected. However, ...
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2answers
50 views

Class A Output stage Negative Swing

Good Day, This is a lecture on Class A Output Amps by Upenn. Link here: http://www.seas.upenn.edu/~ese319/Lecture_Notes/Lec_20_PowerAmps1_10.pdf I can't understand how when Vi is negative, it ...
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212 views

Learning transistor based circuits

simulate this circuit – Schematic created using CircuitLab In one of our electronic circuit tests, this question was asked: What is the output voltage of given circuit? This circuit ...
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4answers
116 views

Using a BJT to enhance battery life

I have a little project going on, that involves turning on and off a led strip. The led strip specs : 5M Led SMD 600 Lights LED : 3528 SMD 600 Lights, 5m : 120 LED / m According to this site, it ...
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1answer
61 views

BJT operation and conservation of charge

The theory (that I know) goes like: Two junctions, EBJ and CBJ, EBJ is put in forward bias and CBJ is put in reverse bias to operate the BJT in forward active operation Region. Now Electrons ...
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94 views

Floating Inductor Simulation Using Only BJTs?

I know it is possible to replace large-ish floating inductors (~ 5mH) with a gyrator, typically using two opamps: What I've unsuccessfully tried to solve is : can we build something equivalent to ...