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 or Mosfet for PID

I want to build a PID controlled Servo valve. I can't choose driver transistor which is best for linearity , fast response, working life. BJT or Mosfet? This is the amplifier schematic In the ...
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28 views

internal circuitry of LM1596/1496 perform modulation

The following is the inner circuitry of LM1596 which is a modulator and a demodulator: I wanted to get an abstract idea as to how this circuit actually works and performs de/modulation... I have a ...
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21 views

NPN and PNP doping amounts?

I'm trying to find out how much each area of BJT's are doped. I understand that for PNP's, the emitter is doped the most, the collector moderately and the base a small amount. Is this the same for ...
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234 views

How to switch an AC signal on and off with a BJT?

I built a phase shift oscillator and now I want to turn the output of the oscillator on and off using a pulse, generated with the NE555 IC. I am trying to do this using a BJT. I connected the ...
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57 views

Discriminating the use of a BJT from that of a FET [duplicate]

I've already read sufficient introduction to both BJT's and FET's, so I can identify Important differences such as current amplification v. transconductance, input impedances, power consumption, the ...
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35 views

Which BJT-parameters need to be derated at raised ambient temperature?

I am designing a discrete MOSFET-driver stage based on BJTs in simple push-pull configurations and wondering, which of the values under absolute maximum ratings I have to derate at higher ambient ...
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52 views

Are these two bjt amplifiers the same?

Is the circuit on the left the same as the circuit on the right? I think that they are..what do you think? Edit : The white dot in the right one is nothing btw,just sloppy drawing
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51 views

NGSPICE messing up BJT characteristics

I'm trying to obtain BJT characteristics in NGSPICE, but for some reason the plots retrace to origin. ...
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1answer
46 views

Driver circuit not controllable, heating up

I have a driver circuit here. simulate this circuit – Schematic created using CircuitLab Current source below is an optocoupler. Problem is: Q2 is on regardless the state of the ...
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2answers
44 views

Limiting current through Zener shunt reference by PNP current source

I've got an unregulated input voltage of 5V..20V from which I need to drive a shunt reference LM4040 at 3.3V. According to my calculations a shunt resistor of 1.5kOhm would result in a peak current of ...
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23 views

Relationship between PNP Collector doping concentration and Voltage gain

For a PNP amplifier with \$ \large V_{in} \$ at base, and \$ \large V_{out} \$ at emitter, given that the voltage gain \$ \large A_v = \frac{-V_A}{V_T} \$, why does the voltage gain drops when the ...
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52 views

Designing transistor logic gates

How would one make use of transistor logic gates ? Take for example this transistor AND gate for example . In all logic circuits, the output of one gate becomes the input of another . Here the output ...
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123 views

Explain this circuit to me

I have always found it very easy to design with dual supplies.This circuit uploaded by me is operating in active region because Vec=3V.Mostly in such circuits very negligible base current flows (don't ...
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1answer
92 views

Voltage drop across emitter of BJT

I connected the collector to positive (through a 330 Ohm resister) , base to positive (through a 10k ohm resistor) and emitter to an LED which I connected to ground . I measure with a multimeter the ...
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16 views

Collector currents of different BJT Models and Ebers-Moll

Per Horowitz&Hill book, the Ebers-Moll equation for the collector current in a BJT is: Ic = Is (e ^ (Vbe/Vt) - 1) where Ic is the collector current and Is is the saturation current. Now, I am ...
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1answer
46 views

How do I protect a sensor IC from overvoltage when not in use?

I am attempting to use an IC to monitor the value of an inductor in my circuit. During normal operation a voltage higher than the maximum tolerated value will be present across the inductor. There ...
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2answers
91 views

is a uA current FET or BJT circuit design possible?

I'm working on a battery powered circuit that is triggering an interrupt on an ic with an internal pull-up. The resistor value and normally closed switch can not be changed. The quiescent current is ...
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3answers
157 views

How exactly does a transistor amplify the input current in CE configuration

I have gone through tons of forum discussions and videos and books but they all explain in terms of mathematical equations that factor the input by a 'larger than 1' number. What happens physically ...
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1answer
59 views

Appropriate BJT for car circuitry

I am designing a LED Headlight for my car. But I am confused about my BJT, I dont know if it is suitable or not. The overall design is given below. The problem is, when I run the ckt under engine ...
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1answer
92 views

What's the usage of this type of biasing?

I'm trying to know What's the usage of this type of biasing BJTs. this is the main schematic. I'm talking about these type of biasing: Another question to me is this type of biasing for ...
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50 views

Simplifying Positive and Negative Voltage Divider BJT Input

I understand norton equivalent and I understand thevenin equivalent and how it can be used to simplify CIRCUIT A into CIRCUIT B. What I don't understand is my books explanation of simplifying CIRCUIT ...
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1answer
65 views

Exceeding Maximum Voltage Rating of a BJT Transistor

I am wondering how the maximum voltage ratings of Vce and Vcb work for BJT transistors. Are they like MOSFETs in the way that the instant the maximum voltage is exceeded, they are damaged/destroyed? ...
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248 views

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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117 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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1answer
109 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
136 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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58 views

Modelling a BJT with easy equations, but having false scenarios

NPN: simulate this circuit – Schematic created using CircuitLab ...
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530 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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1answer
60 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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3answers
46 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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319 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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177 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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93 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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257 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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84 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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59 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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312 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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127 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
37 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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55 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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109 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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94 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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38 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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125 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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25 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
29 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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58 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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61 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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28 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 ...