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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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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58 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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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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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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49 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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Design s small signal common emitter BJT Amplifier circuit? [closed]

Requirements for the circuit are... 1.voltage gain of 50. 2.minimum input resistance 95k. 3.output resistance of less than 185ohm. 4.maximum unclipped output of 5v 5.9v DC power supply for the whole ...
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37 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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124 views

How does the circuit work?

I can't understand how does the circuit work? Can anyone help me?
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46 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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63 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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69 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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50 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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64 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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51 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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39 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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187 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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113 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
56 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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68 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 ...
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40 views

High base-emitter voltage NPN transistor

I just bought some NPN transistors for my project. I didn't notice before buying them, that the specification said the transistor had a emitter base voltage \$V_{be}\$ of 9 volts. Can this be true? ...
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82 views

How to eliminate early effect in constant current source

When designing an differential amplifier it is important to have a precise constant current source (which I will abbreviate with CCS). It helps to keep out signal injections from the supply rails. A ...
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44 views

BJT small signal analysis, ignoring current sources

Question for you. Currently 'm in the middle of studying for an analog II exam. I've got the following midband small signal model: When analyzing for midband gain, more specifically VB2/VPi1, the ...
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58 views

Why can current flow through the reverse biased base-collector junction (N-P junction) in a BJT with a forward biased base-emitter junction?

If the base-emitter junction of a BJT is forward biased, then current can flow through the reverse biased base-collector junction (N-P junction). This disagrees with my understanding of the PN ...
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391 views

How is this circuit for interfacing 20V signal with 3v3 microcontroller

I have designed the following circuit to interface a 12-20V signal to a microcontroller running on 3.3 volts. The signal is either 20V or open circuit. I want the circuit to be as resilient as ...
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82 views

How ICBO gets amplified to ICEO in BJT when base is open

I have been doing some reading about ICEO and ICBO, but couldn't really understand how ICBO is getting amplified (1+ beta) times to reach ICEO, in the open base condition. This is my understanding ...
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67 views

ICEO, ICBO physical interpretation in BJT

I am stuck with the equation: ICEO = (1+β) ICBO My questions are: What is the physical interpretation of this equation? Will both the currents exist simultaneously? Are any of the reverse currents ...
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36 views

Relaton between IB, α and ICO near cut-off region for a bjt in CE mode

I am reading Electronics and Devices by Boylestad and it says: $$ \begin{align} I_E &= I_C + I_B &(1)\\ I_C &= \alpha I_E + I_{CO} &(2) \\ I_E &= \alpha I_E + I_{CO} + I_B ...
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144 views

Linear Regulator: MOSFET vs BJT

Currently I am doing a project on a voltage regulator. Can you tell me some advantages of MOSFETs over BJT? Apart from a higher power loss, I can not find much. In control engineering it is much more ...
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131 views

What does it mean for a transistor to be biased beyond cutoff?

I understand what it means for the transistor to be biased for Class A, AB, and B with regards to the location of their DC operating points (\$I_{C_Q}\$ and \$V_{CE_Q}\$ are found by finding the point ...
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In BJT CE configuration, is it correct to write Ie = Ic+ Ib? Shouldn't it be Ie= Ic-Icbo + Ib?

This is my understanding.. The collector current Ic comprises of two components. 1)alpha times the Ie, 2)the reverse saturation current Icbo. If this is correct how can Ie = Ic+ Ib be true? It ...
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BJT circuit analysis confusion

In the following circuit: Ib is given as: I don't understand how they arrived at this. I thought it would be a voltage divider between Rsig and Rb||Rbase divided by Rbase: Can anyone explain? ...
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51 views

Can I use a PNP BJT as a current sinking voltage supply?

I am using a counter MC100E016 and I need to connect a 3 V supply at the Vtt terminal that is able to sink current. Can I use a PNP transistor with 3V supply at its emitter and the collector ...
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65 views

Bipolar transistor switch base current calculation example from PEFI seems wrong?

I'm reading through Practical Electronics for Inventors, 3rd edition, on bipolar transistors, and they provide this example of a transistor switch: I'm a bit confused by the calculation at the ...
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Output resistance of a multistage BJT amplifier

In the amplifier shown: To calculate the output resistance, this equation is used: I understand that the R5/(B+1) comes from resistance reflection, but why do they not take the resistance in the ...
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74 views

PMOS Gate Driver using BJT

I'm (again) looking at high-side load-switching. The load shall be switched on with a controlled rise-time (=limited inrush current) and be switched-off quickly when a controller (not shown) detects ...
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61 views

Output impedance of current series feedback BJT amplifier?

So according to what I've read, in a common emitter BJT amplifier, an unbypassed emitter resistor acts as a current-series feedback path. The gain without feedback is: ...
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67 views

Small Signal BJT Model

I want to know why there is a minus sign in the output voltage.
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Transistor saturates no matter the size of base resistor

Problem I have a circuit as depicted below, and after calculating the base resistor, I wanted to see when the base current would be too little to saturate the transistor. I kept increasing the ...
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Need help deriving cutoff frequency of output (collector) RC network

According to the book I'm studying, the cutoff frequency for this circuit is given by $$f_c=\frac{1}{2\pi(R_C+R_L)C_3}.$$ I tried to derive it by solving for the frequency at which \$V_{out}\$ is ...
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Alternating between two LEDS using BJTs

I would like to control the output of two LEDs with a single pushbutton. When the button is open, D2 should be off and D3 should be on; when the button is closed, D2 should be on and D3 should be off. ...
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Why does this circuit use a transistor buffer even though there is an high input impedance op amp afterwards?

Regarding this circuit I found on www.geofex.com detailing the famous Tube Screamer guitar pedal I don't understand the purpose of the BJT input emitter follower transistor. If it was to increase ...
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78 views

Why won't these two BJTs connected in series work?

I cannot get the second BJT amplification of Experiment 11 of Charles Platt's Make: Electronics to work, and I'm all out of clues. This question is very similar, but not identical as my circuit works ...
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104 views

What is the meaning of biasing in electrical/electronics circuits? [duplicate]

What is the meaning of biasing in electrical/electronics circuits? What is the need for biasing in BJT/MOSFET? What will happen after biasing when we apply input signal(AC/DC)? Will biasing signal and ...
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94 views

Why does my output stage rectify when I use a preceding stage?

I've been working my darnedest over the past few weeks learning more and more about amplifiers, BJTs and various topologies. As I go through Art of Electronics, I try out everything mentioned in at ...
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102 views

Current source improves linearity on collector BJT

I'm learning about analog electronics. I'm looking into amplification stages at the moment. Question 1: Single BJT C-E Amplifier. Usually you put a resistor between collector and V++, so as \$I_b\$ ...
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126 views

Transistor working with unusual biasing

What would happen to a BJT if both junctions of the transistor are forward biased? Is there any literature on this? By literature I mean characteristics/equations. Any links would help. I have also ...
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Schottky diode like BJT symbol

In this schematic, what do the Schottky diode like "barbs" mean on some of the BJTs where the base is connected? I haven't encountered this symbol before.
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Analyzing Opamp circuits

I was asked to analyze this Op-amp circuit and I need a little bit of advice about it. I have presented my analysis about the circuit, kindly correct me wherever I am going wrong. simulate this ...
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Purpose of pullup resistor in BJT LED driver circuit

One answer to this question suggests the following circuit to drive a LED from an open collector output of a 74LS47: simulate this circuit – Schematic created using CircuitLab What is ...
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Where to find derivation of s'' (stability factor for beta) for BJTs?

I'm looking for the derivation of the formula for the stability factor (\$S''\$ or \$S(\beta)\$) of BJT bias circuits, particularly the ones with emitter resistance. The book I'm using says that the ...