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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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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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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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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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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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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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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40 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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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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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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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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45 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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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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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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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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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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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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56 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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59 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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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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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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88 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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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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99 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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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 ...
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Noticed something weird in derivation of relationship between ICBO and ICEO in BJTs

So I'm currently studying Electronic Devices and Circuit Theory by Boylestad and Nashelsky (11th ed.) and I'm confused as to how the relation between \$I_{CEO}\$ and \$I_{CBO}\$ is derived. So the ...
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BJT switch vs amplifier mode

I'm getting really confused about a specific BJT circuit. I want to control LCD brightness and contrast as suggested here. Apprently a capacitor is used to filter PWM output to the contrast pin, ...
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Bipolar Junction Transistor Base-Emitter voltage

I've seen several datasheets for Bipolar Junction Transistors providing the value of the Base-Emitter voltage at saturation with values way above 0.6~0.7V (Example). What exactly does this entail? I ...
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Odd BJT circuit

This circuit came in my today's exam. It asked to find every base, emitter and source current.Base emitter voltage .8 and \$\beta\$ for both BJT is 49. first I tried normally where \$I_B\$ found ...
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Cascade BJT [ Exercise solve ]

How can I solve this circuit for \$\beta = 100 \$ , \$V_D = 0.7V \$ and \$V_{BE}= 0.7V\$ and arrows go to power \$V_{DD}=9V\$ simulate this circuit – Schematic created using CircuitLab ...
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Which parameters in datasheet give information about a BJT's step response quality?

I did a test with randomly chosen 12 NPN BJTs. I applied a clock pulse to each of them and observed their collector voltages. Some of them showed very low rise time, while some responded terribly ...
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Calculating Quiescent base current

I am given a question relating to a bipolar junction transistor. The information I am given in the question is shown below. I am first asked to select a quiescent point from the graph to find ...
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110 views

Something better than an H-bridge to drive motor?

Is there something better than an H-bridge to drive two motors using the ATmega8 with a 7V power supply? My teacher said the H-bridge overheats and is bad. Is there a better solution? For instance: ...
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Why is KCL giving me the wrong solution?

I'm trying to derive the gain of the following common base amplifier circuit: To do this, I drew the equivalent T-model circuit: . The problem I have is that I get two different transfer functions ...
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BJT amplifier gain rolloff

I'm playing around with BJT amplifiers and have some questions regarding the gain rolloff you see at higher frequencies, I'm using the 2N2222 for my tests and my simulations and measured results match ...
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How to calculate the required base resistor for this BJT-relay circuit?

I'm trying to design a relay circuit for my first PCB and have come up with the following: The 10K value for R7 is just a placeholder. R7 is what I'm trying to determine. The transistor should ...
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BJT Four resistor bias circuit analysis

I am currently studying BJTs but am having trouble analysing the four resistor bias circuit. My textbook gives the following circuit and says we can use voltage divider across R1 and R2 to find VB. ...
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FET vs bipolar junction transistor

I know this question might sound obvious, but still I cannot find an answer. What is the purpose and best-fit applications for field effect transistors? I mean, we have bipolar junction NPN ...
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Grading/Doping of pn junctions

I was studying about pn junction grading and junction capacitance and I came to look at step graded and linear graded junctions. I read that step grading in done for the base emitter junctions of a ...
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Driving a load with 1.8V input

I have a Gumstix expansion board and want to make it communicate with some 24V PLCs. I've read these topics for reference: 1.8V to 5V, still not comfortable with transistors Transistors: why are ...