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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What's the usage of these coupled transistors?

I'm thinking to know What is the usage of these parts of this circuit. Source It's the schematic of UT70C Digital multimeter.
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53 views

How to determine current limiting resistor values for push pull amplifier driven by op amp?

I'm looking to increase the output current drive of a high voltage op amp using a push pull amplifier. The OPA454 datasheet includes an application circuit to do exactly this, and includes some ...
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70 views

What is a purpose of BJT in an LED driver circuit with MOSFET?

I am trying to turn an LED on and off repeatedly with a square wave. Yesterday, I've checked the following circuit works: (Please note that, the figure has one voltage source ...
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3answers
130 views

BJT Circuit Base-Emmitter voltage

I don't understand, why the voltage V2 is approximately Vb. Can't V2 be 0, if Vb is enough high, so that the emmiter-current of Q2 is Ie2? The assistent only told me, that because both transistors ...
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34 views

Modelling a BJT with easy equations, but having false scenarios - II

I've revised a few things from this post here. Tweaked it. Redefined it (for clarity). Even provided the diagram for direct NPN analogue ("analogue", for comparison, not "analog"): simulate ...
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55 views

Modelling a BJT with easy equations, but having false scenarios

NPN: simulate this circuit – Schematic created using CircuitLab ...
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495 views

How does this BJT transistor circuit works?

I just wanted to know a little more about this circuit about how it works a more in depth analysis I mean. I know there's some kind of differential amplifier and a Zener diode for voltage regulation ...
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67 views

Analog Circuit Design

I posted this yesterday and it was deleted so first of all, let me apologize if i gave the impression that i was trying to get you guys to do my homework for me. i most certainly wasn't (sorry I'm ...
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52 views

How to calculate input and output impedance of BJT Common-Emitter amplifier circuit

Why is the input impedance not 260Ω in this circuit? I calculated this impedance as follows: \begin{align*} I_B &= \dfrac{18.7V - 0.7V} {180kΩ} = 0.1mA \\[1 em] r_{\pi} &= ...
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39 views

BJTs - Large DC Signal Analysis - Negative Voltages

So there's this circuit here. I'm a bit confused with the negative voltage in order to find out the base current. I sort of did a hack-ish guess and did a KCL at the node at the left of the base. I ...
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4answers
297 views

What does the arrow on VCC in a BJT bias circuit mean?

At the top, the VCC has arrows on it. What does that mean? I thought it would be like in other circuits as empty holes that you could attach, but I'm not sure here.
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130 views

Why does a BJT act as an amplifier in the linear region?

I'm covering BJT's in my semiconductor class and in lecture, the professor said that BJTs are used as amplifiers in the linear region. I'm confused because I thought the gain was proportional to the ...
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30 views

circuit for switching on and producing desired high pulse then circuit turn off without using micro controller

i have no prior knowledge about electronics , but i am trying to make a circuit that turns on the switch after 10 seconds and then produce a desired length high pulse say 30 seconds then it turn off ...
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1answer
50 views

The base resistor of the transistor with speed-up capacitor

I've designed a relay driving cuicuit like this Under DC the current is limited by R1. R2 is added to limit the current flow through C1 and the base of the BJT when the Q from 0 to 1. Is resistor ...
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3answers
233 views

Why isn't this astable multivibrator oscillating?

This is the schematic for a modified astable multivibrator I've built. I incorporated the diodes in order to get a sharper rise time, and therefore produce actual square waves. Principle of ...
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38 views

Reverse saturation current in a BJT: active and reverse active modes

In (Sedra; Smith. Microelectronic Circuits), as well as in several other sources, the value of the reverse saturation current (\$I_S\$) is considered the same for the active mode and for the reverse ...
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30 views

How to find base current and collector current in this circuit? [duplicate]

Suppose the transistor in the diagram above has a \$\beta\$ of 100. How can I figure out the base current in the circuit and the collector current? Furthermore how can I evaluate \$V_B\$ and ...
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38 views

Common base transistor biasing

I have a basic question regarding bipolar junction transistors.As far as i know, the correct biasing of the transistor is achieved using a process known commonly as base bias.Correct me if i am wrong. ...
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63 views

Input characteristic curve of common collector configuration

I am really new to electronics and BJT. I would like to know why is the input characteristic curve of common collector configuration [Ib-Vbc] is different from other 2 input characteristic curves. ...
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4answers
102 views

BJT Biasing with negative voltage

I got this question as a school assignment (1st year electrical engineering). I have to calculate the 3 unknown resistor values. The values which were given are in the schematic. Further \$\beta = ...
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2answers
31 views

Can I, Bi-Directional Level Shifter as Motor(3V) controller with Arduino Lilypad (3.3V)?

Basically this could be easily done by using a BJT NPN, but since I want to control two motors(3 V, 45-60mA) and 5 LEDs was thinking of using a Bi directional level shifter instead of using ...
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1answer
46 views

Difference between CML and ECL

How is Emitter Coupled Logic different from Current Mode Logic. I have seen written in "Microelectronics Circuits" by Sedra Smith that CML is based on ECL . If it is so can anybody explain how they ...
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95 views

Simple Circuit Analysis, why this cap is needed?

This is a sub-circuit that is part of larger design and I was wondering why the designer choose to use C1 inline with the BJT base? and what does the combination of R1, C1,R2,R3 do? Since the max ...
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95 views

Fundamental questions about BJT transistors?

Take a standard NPN transistor. The doping of each element of the transistor is in the name. This is what is inside the transistor... The left "slice" of silicon is doped with an impurity which ...
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78 views

Confusion with transistor modes

I am having trouble understanding the three operation modes of a transistor. I am giving below the three operation modes (CB, CE and CC) for pnp and npn transistors. and for npn , here it is. ...
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35 views

Is there a single supply voltage implementation of a differential amplifier?

So far all implementations I have seen need a positive and negative voltage source. Is there another way like if i supply enough current will it work?
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49 views

Derivation of current gain and voltage gain for common base BJT

For a common base configuration BJT such as the one shown here: How can I derive the voltage gain and current gain?
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20 views

Lower/Raise DC output level of common emitter amplifier

I am trying to simulate an amplifier for our homework. It should output a 1-5V p-p signal into an 8ohm speaker from a 20mv input using a diode connected transistor as the input voltage bias. So far I ...
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1answer
24 views

Curret mirror with discrete BJTs?

I need to supply power for some power diodes. The power supply units are current regulated, the diodes are connected in series. Let's say that i hve 3 strips of leds, each one needs 400mA, around 20V ...
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53 views

Biasing a common collector

How do I bias a common collector to secure maximum output swing WITHOUT using a resistive divider? How can I use my transistor as a voltage source with output about half my Vcc?
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54 views

Bipolar Junction Transistors

If the switching frequency is increased for BJT what happens to the power dissipation? Will it increase, decrease, or remains the same and whats the logical reason for it?
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20 views

Deriving current gain and voltage gain for common base BJT

For a common base configuration BJT such as the one shown here: http://i.imgur.com/M9LtHoW.png How can I derive the voltage gain and current gain? I found the answer on Wikipedia but all my attempts ...
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54 views

Question on DC analysis of BJT - Common Base

I'm trying to solve a question from my book. The answer for the question is given but I keep getting a different answer. I don't know if I'm doing it the wrong way or the book is wrong. This is the ...
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61 views

Can you find an analytic expression for the (beta)hfe of a BJT?

I understand there are two models \$Ic=\beta Ib\$ and \$Ic=I_s exp (\frac{V_{BE}}{Vt})\$ for a bipolar junction transistor. However (correct me if I am wrong), I have not seen any textbook ...
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143 views

Using PNP instead of NPN merely requires one to make circuit upside down and reverse current direction, why do we not just use one of the two types?

Using PNP instead of NPN merely requires one to make circuit upside down and reverse current direction, if this is true then why don't we just do everything with NPN transistors? Are there any ...
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77 views

Detecting electrons as they tunnel through the band gap of a P-N junction

As a learning exercise I'd like to try creating a random number generator using reverse-biased BJTs. As I understand it, if the emitter is saturated in reverse bias, occasionally electrons will ...
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56 views

How to Find value of Early voltage of output characteristic curve of BJT?

I have this graph from data that I have. This is the output characteristic curve of BJT. I want to find the value of early voltage VA?
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168 views

How does one approach designing an amplifier using BJTs to drive an 8 ohm speaker?

For a lab class we were assigned a final project where we have to design an amplifier using BJTs, diodes, and capacitors (MOSFETs are not allowed) in order to drive an 8-ohm speaker. The requirements ...
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51 views

BJT pre-biased arrays slower than discrete?

I've got a circuit that works - it's job is to convert a TTL square wave into a +/- 12 volt square wave. simulate this circuit – Schematic created using CircuitLab Note that the ...
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24 views

Finding the DC operating point of this circuit

I'm trying to find the dc operating point of this circuit, it is given that: \$V_{BE_{ON}} = 0.7v\$, \$\beta = 100\$, \$I_{DSS} = 10mA\$ , \$V_P = -2v\$ and also that \$V_A = 1.8v\$. Here is what I ...
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163 views

LEDs driver circuit

I was wondering what is the role of this type of circuit connected to LEDs. I found it in a LED torch supplied by 2xAA batteries. Is it an oscillator? Is it only an energy trick? What are the ...
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46 views

Driving an optoisolator with a 2N2222?

I'm driving an opto-isolated MOSFET gate driver with a 2n2222 transistor from a 3.3V microcontroller (TI Tiva C, 2-8mA max per pin). The IX3108G that I selected needs 10-16mA to be driven ON. This ...
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87 views

Can I alter this circuit?

I am making the following solar charge controller circuit based off of the NE555: This is the webpage I got the schematic from: http://mdpub.com/555Controller/ The potentiometers at the trigger ...
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1answer
383 views

Why does current flow into the transistor in a current shunt monitor?

I'm looking at the basic operation of a current shunt monitor*, but I don't quite understand the 'operation' description given by it's manufacturer. Figure 1 shows the basic circuit diagram for ...
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50 views

Explain this exercise to me?

We have the CM half circuit in the figure. I understand that $$A_\text{cm}=\frac{(\alpha\times R_\text{c})}{(2R_\text{e}+ 2re) }$$ but how is this equal to $$\frac{2}{8.65} $$ like it's solved in ...
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59 views

Finding the input resistance of an NPN transistor

The question is asking to find the input resistance of the circuit shown in the picture. R_in "starting" position is shown as well. I have done quite a few problems involving replacing the ...
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1answer
130 views

Will there still be small voltage in transistor OFF state?

In Bipolar junction NPN transistor which has three legs as shown below: Case 1: If this transistor is in OFF state i.e. collector is connected to +Vcc and Base is connected to insufficient voltage ...
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48 views

Getting bad clipping issues with this 3 stage amplifier

What am I using? 3 stages of amplification. An input voltage of 10mV peak or 20mV pkpk into the first stage. 1st stage: NJFET Common Source. Using a voltage gain of 3. 2nd stage: NPN BJT Emitter ...
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How much can BJT parameters (particularly beta) vary for Monte Carlo analysis

Background / Requirements: I'm designing a typical Class AB amplifier using diode-connected BJTs to achieve the biasing. I have a requirement to keep the total quiescent current at room temperature ...
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124 views

How to eliminate the Miller effect on BJT BC547?

I have an application: The input in a 3V train pulse @ 100Khz I need an Ic to be 10mA for the LEF of the optocoupler. I am using BC547C: Input Capacitance= 9pF Current Gain Bandwidth ...