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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2VCC in a BJT C.E. amplifier

It is known that it is possible to get 2Vcc output voltage in a BJT Common Emitter amplifier by using an RF Choke (instead of a simple resistor) connected to the collector. Precisely, we will get at ...
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18k views

BJT in Reverse Active Mode of Operation

What will happen if for a BJT transistor, it's emitter terminal is treated as collector and collector as emitter in a common emitter amplifier circuit?
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51 views

What's the voltage transfer characteristic of this power driver circuit?

[Exam problem for an instrumentation course] Can anyone help me understand how this circuit works? I'm not too familiar with power circuits... This somewhat reminds of a BJT class B amplifier (but ...
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62 views

The biasing of transistor [on hold]

why I need to bias the transistor? what does it mean to bias the transistor? I mean ..can anyone give me a senseable analogy to our life that we need to bias something?! is bias means balancing?! I ...
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1answer
75 views

How to proove if any circuit have negative feedback?

Queries regarding this circuit I am able to say that this circuit has negative feedback but my procedure is disorganized I want a step wise procedure to identify the polarity of feedback In this ...
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1answer
51 views

What is topology of feedback for circuit?

I am confused between Voltage Shunt and Current Shunt Also mention why R2 shouldn't be considered as feedback as it is emitter degeneration resistance Consider the above circuit why can't I consider ...
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1answer
35 views

Effect of base doping on early voltage,base transport factor and emitter injection efficiency?

According to me as base doping increases recombination will be less at base region so base transport factor and emitter injection efficiency will increase and as effective base width will decrease due ...
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3answers
2k views

Why are MOSFETs better than BJTs in application of Voltage Controlled Resistor?

Why are MOSFETs better than BJTs in application of Voltage Controlled Resistor ? Thanks for your responses.
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41 views

What will be vo/i for given circuit?

Solve using both approaches first using small signal analysis and then using feedback analysis.
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90 views

What will be small signal trans resistance gain of shown circuit?

Take beta = 99. I analysed this circuit using first considering this circuit as feedback circuit with shunt-shunt type of feedback and then did the same analysis considering that the circuit is a ...
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1answer
61 views

How to find voltage gain of below analog circuit without using Nodal analysis?

This is a theoretical circuit just made to see that if I can find voltage gain of circuit and it took me much calculations then anticipated to get voltage gain.I just want to find if there is better ...
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2answers
114 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
35 views

How to calculate small signal parameter for a BJT when early voltage is taken into consideration?

I have proved one formula of output impedance ro = (Va+Vce)/Ic = Va/Ic' where Ic is collector current and Ic' is collector current neglecting early effect. But reading from standard texts other ...
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107 views

Why it is said that second transistor cannot enter saturation mode in Darlington pair?

When I made equations it came out that for both of transistors to be in saturation Vc-Ve2<.2V Vc-(Vb2-.7V)<.2V Vc-Vb2<-.5V ............{eqn a} As for first transistor to be in ...
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1answer
126 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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53 views

What are limitations of Millers theorem for amplifier?

I mean to say that are the two circuits one original and other its miller/ drawn exactly equal in all respects or their are some difference in some respect if so please mention. I am not able to ...
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103 views

Question about differential amplifier

why is there 0.7V instead of 1.2V on the common emitter? if you go through Q1 mesh : Ve = 0.5+Vbe = 1.2 instead of Ve = 0+Vbe = 0.7 from Q2.
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48 views

What will be mode of operation for BJT in figure? [closed]

The value of Vbe active is .7V. Also give reason.
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175 views

Transistor circuit driving me insane

Consider the following circuit: Now I'm asking to impose the base current as zero and $$R_C=452.35 \Omega $$ Now I have a lot of issues with this circuit because I can't find a systematic way to ...
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414 views

Biasing a second stage amplifier

I built a two-stage amplifier as shown below. I have already built the first satge (R1-R5 & C1-C2) such that If I apply a signal of 1volts peak-peak, the output (at collector of Q1) would be 8 ...
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1answer
701 views

BJT DC Leakage (ICES) dependency with Vce

I am interested in BJT transistor leakage dependency on Vce. Specifically: parameter ICES (Collector-Emitter Cutoff Leakage, that is, collector/emitter leakage with base shorted to emitter) is ...
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1answer
30 views

Designing 2-stage BJT CE class-A voltage pre-amplifier with specified goals and without global NFB

BJT CE Class-A Voltage Pre-Amplifier Suppose a design requirement limits the selection choices to the following class-A BJT common emitter stage topologies. No global NFB is permitted. Only local NFB ...
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50 views

What is the forward beta of the BJT KN2222A?

I don't know what is the forward beta of the bipolar junction transistor KN2222A, I'm an amateur and i don't found the value in the data sheet or i just don't understand where. Please let me know
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45 views

The influence of capacitors and resistance in a BJT circuit

I solved the circuit and found these values for each one. But I wanted to know: Which capacitor has more influence in the low frequency and in the amplification? Does RE have impact in amplification?...
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1answer
52 views

How can I prove that Vce saturation lies below .2V?

When I try to prove that Vce for saturation is below .2V and I take npn transistor I simply consider emitter to be at 0V and thus base emitter junction being forward biased base gets a voltage of (.7 ...
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28 views

BJT - How does an applied voltage at BE and BC affect the band diagram?

Let's say we have an energy band diagram of a BJT at equilibrium. Then, we apply -0.7V to BE, while 0.7V is applied to BC. How will these voltages affect the band diagram? I would appreciate it if ...
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1answer
40 views

Bipolar Transistor's Input Resistance

Based on theory when you want to find the output resistance of a circuit with dependent sources you can't turn them off so you have to add another source of known value in the points of interest and ...
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1answer
61 views

Calculation of (TC) in BJT

if we have a circuit with a bjt like this one and we know that the I is 1.1mA in 25 Celsius , with Vbe=680mV and Ie=1mA , and β=100 in 25 Celsius. If we know that the TC (thermal) of Vbe for ...
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1answer
283 views

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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2answers
621 views

Amplifier gain too HIGH?

I have this circuit : Two common base amplifiers for amplifying frequency in FM range (88 to 108 Mhz). The Problem is, as seen in the figure, I am getting an output of 1.5 V for an input of 10 uV. ...
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3answers
208 views

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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2answers
208 views

Why is it possible to replace part of a BJT circuit with thevenin equivalent?

I know it's possible to replace the left side of this circuit with a thevenin equivalent, but on the left we're able to find the base voltage by the voltage divider Vcc * (R2)/(R2 + R1), which is the ...
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190 views

BJT circuit analysis

I've been doing this question for quite a long time, can someone explain to me why b would be different from part d, and what im doing wrong from part b and c?
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1answer
44 views

Why does the signal generator voltage change in this circuit?

In this circuit, when I measure with an oscilloscope the square wave I get this: (The switch S is open in both measurements) But when I change the R2 resistor to 15 Ohm, I get this: Why does that ...
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4answers
594 views

BJT or Mosfet as Cascode

I was going through this lecture pdf. If I want to have maximum output resistance which cascode configuration I should use. BJT cascode or Mosfet cascode?
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221 views

Biasing a cascode in a BJT differential pair

How do I bias the cascode in a differential pair? For some reason when I set it to a constant bias voltage it either does not work at all or the cascode BJTs turn on for only a fraction of the input ...
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2answers
62 views

I'm working on a school Lab for a Constant Current source BJT and need a nudge in the right direction

I am stuck trying to determine the applicable formula for the load current. I have used \$I_b = \frac{Vin-Vbe}{(Beta+1)*Re}\$ and then \$I_L= (Beta)*I_b \$. The problem is I can't find a proper ...
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70 views

How to derive formula for emitter current flowing through Re?

Ie = Ve/Re I was thinking about using that approach but i have been doubting myself if that is the right approach to go with, because then i have to express the emitter current in term of alpha and ...
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1answer
37 views

Calculate values of resistors in a given BJT amplifier circuit [closed]

I have the circuit shown below and i have limited resistors to make it work. The LED's rated current is 10mA so Ic = 10mA. I know that beta for the transistor is 100. The resistors are (I have 2 of ...
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2answers
96 views

Current sense amplifier

I came across this circuit for a high-side current sense using BJT current mirror, and I am trying to derive a formula for how I could calculate the sense voltage output (going to the FB pin) in terms ...
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1answer
49 views

stm32 drawing current from 40 outputs at the same time

I have an hardware question about stm32 family. I am designing a circuit with STM32F103VB. datasheet mentions that i can draw up to 25 mA current per pin(page 37 table 7). I need to drive 40 npn ...
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2answers
128 views

voltage traces across pwm driven dc-motor: is that ok?

I'm driving a dc-motor with a BJT turned on and off with a 555 generated PWM signal. Here's the circuit (V1, Rl and L1 simulate the motor): There actual circuit - same parts - is on a breadboard and ...
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23 views

Split collector current mirror [duplicate]

I'm familiar with the basic current mirror, as below: simulate this circuit – Schematic created using CircuitLab However, having recently learned about split collector BJTs, I wonder if a ...
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2answers
4k 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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3answers
1k views

Why are BJTs common in output stages of power amplifiers?

From my understanding, the role of the output stage is to decrease the output impedance to almost 0. For that, MOSFETs seem better suited since they've got way lower \$R_{ds}\$. Yet I see quite often ...
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1answer
41 views

question about bjt voltage gain

Input voltage triangular wave signal with 12.7Vmax and 9.1Vmin passing thru a NPN BJT, assuming if the forward voltage of the BJT is 0.7V then why is the output Vmax is not 12.0V but way lower like 11....
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74 views

Can I do KVL around transistors? (MOSFET and BJT)

I'm having a lot of trouble with more complex transistor DC circuits (can't wait for the AC, heh). Basically, what I want to ask is does KVL holds "around" a transistor as well? For example, if I ...
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201 views

Where would Iceo flow through and would it cause thermal runaway?

I was reading this page about thermal run away. And it mentions: Due to increase in the temperature of collector junction, Ico will increase, Vbe will decrease. But for Ico to increase Ic and ...
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198 views

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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2answers
653 views

MOSFET Amplifier: Maximum Signal Swing without Clipping

I have a degenerated common source amplifier. I want to know what's the maximum input signal I can apply before the output signal begins to clip. What I currently do is to increase the input signal ...