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Questions tagged [bjt]

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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Base resistor configurations, are there any differences?

Sorry for the noob question. From my understanding, R1s acts as pull down resistors for the base and R2 will limit the current flow to the base. I have seen both configurations, but couldn't work out ...
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Soft latching power switch

I have stumbled upon a soft power switch with low part count on EEVBlog, which I found very interesting for my hobbyist projects: https://www.youtube.com/watch?v=Foc9R0dC2iI Since it uses a PMOS and ...
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Transistor as variable resistor in LFO

I've constructed a basic dual op-amp LFO as in the below circuit simulate this circuit – Schematic created using CircuitLab The variable resistor R5 is used to alter the rate of the LFO, I'm ...
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Operation of BJT with low values of Vbe (“cutoff” region)

Many sources claim that when the base-emitter voltage becomes smaller than approximately 0.6V-0.7V, the bipolar junction transistor goes in the cutoff region and there is zero base and collector ...
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PMOS High Side Switch

I have been working on a project and one of the ideas was to control power supply of LCD 16x2 module and IR sensor via I/O pin of microcontroller, basically to have them on/off when i need them to be. ...
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How to make BJT/MOSFET work in RF?

I am trying to design an amplifier with a transistor model. I followed some basic tutorials online (http://microwave.eecs.utk.edu/ECE545_files/02_Lab_2.pdf) and designed a transistor model for BJT/...
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Derive terminal voltages for a BJT

Question: A BJT for which \$BV_{CBO}\$ is 30 V is connected as shown in the figure below. What voltages would you measure on the collector, base and emitter? simulate this circuit – Schematic ...
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Input impedance of a one stage voltage amplifier?

This is not a school/university assignment; I'm a physicist trying to learn some electronics. I'd like to calculate the input impedance of the following circuit. simulate this circuit – ...
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Analysis of BJT transistor - is a linear analysis possible?

Since semiconductors aren't passive components, can I realistically derive analytic solutions for a circuit with BJTs? I know this may seem like a very naive question, but am I on the right track with ...
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Should analogue multivibrator and comparator pullup circuit have separate supplies?

I have managed to produce a design within the falstad circuit simulator for an analogue "LED chaser" using an analogue multivibrator and 3 comparators inspecting the voltage of one side of the ...
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470 views

How important are BJT characteristic curves when designing amplifiers?

I was going to make a voltage amplifier for weak signals with 2SD786, but I noticed that the manufacturers haven't included the characteristic curves in the datasheets. How can I optimize the circuit ...
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How to determine the most appropriate DC amplification value for a BJT?

The BJT diagram is shown below: The voltage source at the base side is increased incrementally from 1V to 10V, with the voltage source at the collector side being constant. The Beta values are ...
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Two-port model of a BJT

In electronic books, the small signal model of a BJT is given as: I've just studied two-port networks theory and, as an application, another book I'm reading shows this picture: 1st question: why do ...
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Frequency of an astable with BJTs

I am trying to find out how to calculate the frequency of an astable but I can't understand one thing. If I have the astable from the picture below, why is the frequency growing if I lower the current ...
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Circuit operation and component substitution questions for stroboscopic timing light

I'm trying to make a piece of circuitry, for a tool used to set the ignition timing of my old car. I've found the schematic and description here: http://citroen.tramontana.co.hu/en/ignition/...
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Self-made Schottky transistor doesn't behave as I'd expect

For a project of mine I need to generate UART-like signals with higher voltage (up to 18V) and a baudrate of 115200 bps and later possibly 250000 bps. I tried a basic BJT level shifter which worked as ...
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Problem with the fall time of a NPN transistor

I have the below circuit to translate a slow digital MCU on/off (3.3V) signal to a higher voltage signal (range from 12 to 24V). I have a specific attention for the Vin=12Vdc case, the voltage drop ...
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Why are two maximum power dissipation mentioned for this transistor?

I am wondering why manufacturers mention two different maximum power dissipation values for transistors like 2N1613: Does it have anything to do with whether a heatsink is used or not?
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Calculation of collector resistance for maximum output swing

simulate this circuit – Schematic created using CircuitLab Question from Sedra and Smith (7th Edition) Question: The given bias arrangement is to be used for a common-base amplifier. Design ...
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what is the difference between using mosfet and bjt for op amp based current source

I have planned to design a op amp based current source driver for laser,but i came across two design one used mosfet1 at the output of op amp and other used bjt2 what is the difference What is the ...
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Transistor Exercise

So i have this circuit and i need to find Ibias so that the emitter impedance will be equal to RS. I also need to find RC and RB knowing that Vce = Vcc/2 and Ve = 0.5 V. What i know is Vcc = 5 V, C1 = ...
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Base resistor for BJT Transistor [duplicate]

I'd like to use PBSS4350SS transistors for driving multiple low power solenoids, but looking at the datasheet I can't figure out what value the base resistor (R1) should be? simulate this circuit &...
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I wanted to convert 0-1v, 2ns pulse to 0-7v, 2ns pulse

I wanted to generate a 2ns pulse width signal in particular 2ns ON time and 6ns OFF time signal. I can generate a 0-1v signal having 2ns pulse width using FPGA(by any means we cannot have more than 3....
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Make a one-way switch with a BJT or relay?

I've been trying to figure out how to make a one-way switch with some analogue electronics. i.e.: my first idea was to use a BJT. What I'm trying to find is a design that when the base current is ...
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LC oscillator emitter current doesnt go to 0(class C)

Im trying to create a 433MHz oscillator with the help of ADS for the simulation. From the lectures i have had on transistor LC oscillators, i know the are forced into class C operation, and that ...
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BJT: Equation of Vce for Saturation Region

In Sedra and Smith: Microelectronics Circuits (6E), it is mentioned, on page 185: Recalling that the CBJ is much larger than the EBJ, the forward-voltage drop \$v_{BC}\$ will be smaller than \$v_{...
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ESD ratings of diodes and bipolar transistors

While it's easy to find ESD ratings for ICs (bipolar, CMOS, and any mix) and to some extent for MOS transistors (for the inherent reasons), I don't find ESD rating for many common diodes (left apart ...
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578 views

How does a cross-over BJT's damp the distortion with help of negative resistive feedback in an analog audio amplifier?

I found an expression that explains how a circuit with op-amp responses to a distortion: $$y = \frac{1}{\beta}x + \frac{\delta}{A\beta} $$ Now consider the circuit: Here, the green, blue and red ...
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2n2222 BJT Leak

I'm afraid I have a rudimentary stupid question but here it goes...I have a circuit which produces a signal through a series of NOR gates. That signal, I input in a 2n2222 BJT to drive an LED. When I ...
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Interfacing with Transistors

I was reading the chapter of The Art of Electronics about bipolar transistors (chapter 2), and I came across this paragraph: But why should I use transistors, specifically, for interfacing? Why not ...
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MC34063 with external BJT. Why?

See next post in this series here adding a fet All, Here is a picture of an LTSpice simulation of a very basic MC34063 step up circuit which is behaving exactly as it should, 5V in 9V out. I'm ...
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The use of semirelative sensitivity for \$I_C\$ on \$V_{BE}\$?

When evaluating the quality of a bias network, we use the semirelative sensitivity to evaluate the sensitivity of \$I_C\$ to change with respect to \$V_{BE}\$, with the semirelative sensitivity being ...
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use bjt or mosfet in h-bridge with inductive load?

is it better to use 2 pnp bjt in high side and 2 npn bjt in low side of an inductive load drive h-bridge ? or using 2 pmos in high side and 2 nmos in low side of h-bridge? what are the advantages ...
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Units of BJT parameters

Let's say the model is the Ebers-Moll model, but this obviously extends to other models: $$ I_{\mathrm{b}} = \frac{I_{\mathrm{s}}}{\beta_{\mathrm{f}}}\left(\mathrm{e}^{\frac{V_{\mathrm{be}}}{NV_{\...
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What is the input and output impedance of a Widlar current source?

The Widlar current source is illustrated below: simulate this circuit – Schematic created using CircuitLab The small-signal AC model is shown below: simulate this circuit I know that if the ...
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In a Wilson mirror, does Q3 need to have the same beta to cancel the base current error?

I'm learning about Wilson mirrors in the Art of Electronics Third Edition (pg. 102). It shows the following circuit: simulate this circuit – Schematic created using CircuitLab It then ...
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Opamp BJT Circuit problem

Non inverting amplifier - LF351N BJT - BC337 Gain = 5.8 Opamp supply voltage is +12V & -12V Transistor collector voltage = 12Vdc Opamp i/p = 1Vpp (Sine wave) Opamp o/p = 5.8Vpp Opamp o/p is ...
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What do you think about my PSU design?

I have designed a symetrical PSU using LM317, LM337 plus power BJTs. The desired output range is at least 24V-2V @ 6A max. Altough not shown in the schematic, i plan to add power resistors and a ...
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Design of a differential digital signal buffer, 250MHz, 1V output swing

Primarily for academic interest (so please don't suggest ICs to do this, as they won't help me learn how to deal with this kind of problem) I'm attempting to design a buffer circuit to accept a ...
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2 cascaded Transistors- where is Vout of a transistor when there is a shorted Collector Resistor?

I have circuit drawn in AC, they were 2 cascaded BJT transistors, and I have changed them to the Hybrid pi model. I wish to remove the source and load in order to write a general gain equation for ...
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Under what conditions can Vbe exceed 0.7

I am simulating a transistor switch in PSPICE. The goal is to switch a load (like a lamp) connected in the collector on and off. Imagine that in the place of the R2 resistor there is this ...
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BJT vs FET for VHF LC oscillator

In the ARRL (2011) section 9.3.1 about LC oscillator circuits it says that "[t]he N-channel JFET source follower shown appears to be the most popular choice nowadays", but does not explain the ...
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1answer
58 views

Astable multivibrator diode improvement

The output voltage of an astable multivibrator is not a perfect square wave; the voltage when viewed from an oscilloscope tends to resemble a curve. I'm told that this is because the voltage across ...
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5answers
156 views

BJT Constant Current, Resistor Equations

I am looking to design a simple constant current circuit to draw a precise load from a variable voltage rail. The voltage rail (V+) should be 10V-20V in normal conditions, but it is possible for V+ ...
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How to protect H-bridge from burning

I'm building an H-Bridge to drive a 5v DC motor. We made the circuit with SMD components And everything works properly. But the problem arises when the motor output gear is held manually. The motor's ...
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Getting more current through a BJT

I'm trying to alternate between two 3W LEDs (forward current of 750mA, forward voltage of 3.6V). I've got a 555 set up in astable mode, and am driving the LEDs via npn and pnp transistors. In ...
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Understanding the circuit

I am a beginner electronic student and I know this might sound a bit easy for most of you, but I would like to understand the role of the components used in this circuit - it's an LDR-Controlled DC ...
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high side MOSFET switch and BJT interface with MCU GPIO

im operating a 28V contactor using a GPIO from my MCU, i have a 28V supply readily available. im looking to surpass the gate threshold of the MOSFET by introducing a NPN BJT with a 10V supply, with ...
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Why Can't I Turned On The Relay If the Supply Come From The LDO Regulator

I'm trying to turned on a 5V SPDT Electromechanical Relay. It is planned to be used with microcontroller application. Below is the circuit that I wired on a protoboard: When connected like that and ...
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why does this approach neglect the output resistance of the bjt in calculating gain?

This is the question that I would like to ask about. My question is with regards to finding Vc for question 3. This is the memo for the question: However, I have a problem with regard to how they ...