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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105 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 ...
3
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3answers
439 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 ...
0
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1answer
104 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?
2
votes
4answers
167 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 ...
0
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1answer
60 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" ...
0
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1answer
115 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 ...
2
votes
5answers
117 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 ...
0
votes
1answer
44 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 ...
-1
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1answer
38 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
0
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0answers
26 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 ...
0
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2answers
106 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 ...
0
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2answers
56 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 ...
0
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3answers
65 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 ...
2
votes
1answer
91 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 ...
1
vote
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 ...
0
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2answers
83 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 ...
0
votes
0answers
69 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 ...
1
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1answer
49 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 = ...
3
votes
1answer
108 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 ...
0
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2answers
71 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. ...
0
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2answers
67 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 ...
0
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2answers
64 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 ...
0
votes
1answer
65 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 ...
3
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2answers
171 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 ...
0
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4answers
149 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 ...
0
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2answers
71 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 ...
0
votes
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 ...
1
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2answers
96 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 ...
4
votes
4answers
313 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 ...
0
votes
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. ...
0
votes
1answer
83 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 ...
0
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0answers
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. ...
0
votes
2answers
67 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.
2
votes
2answers
120 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 ...
4
votes
1answer
351 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 ...
1
vote
2answers
256 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 ...
0
votes
3answers
53 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 ...
3
votes
1answer
88 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 ...
2
votes
5answers
139 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 ...
0
votes
0answers
35 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 ...
0
votes
2answers
77 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 ...
1
vote
2answers
158 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. ...
1
vote
1answer
87 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\$, ...
0
votes
3answers
110 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 ...
1
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2answers
100 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 ...
2
votes
1answer
179 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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votes
1answer
45 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 ...
2
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1answer
145 views

How does the circuit work?

I can't understand how does the circuit work? Can anyone help me?
0
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2answers
73 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: ...
1
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0answers
90 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