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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684 views

Increasing the compliance voltage range for a variable, two-quadrant constant current pin-driver circuit

The following is for hobbyist work and I have no commercial intentions at all. Only a handful (two?) will be built. (I use these for part testing and curve generation, though with the higher voltage ...
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1answer
3k views

Stability factors of a voltage divider bias circuit

I am trying to derive the stability factors of a voltage divider bias circuit. I could derive S,S', however, I'm facing some problem with the derivation of S''. Please help me in this regard. How to ...
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1answer
527 views

Discrete transistors current feedback amplifier topologies

I wand to design a headphone amplifier based on CFA topology (for some very personal aesthetic reason). There are two basic topologies of its input stage which is technically an V-I amplifier (I-V ...
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103 views

How to select a diode for baker clamp?

What are the requirements when selecting a diode for baker clamp circuit? 1- for example, How the reverse leaking current of the diode affects the circuit? can a diode with relatively high reverse ...
3
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3answers
127 views

Changes when \$V_{be}\$ is increased in npn transistor

For the given circuit, a statement has been given in my book, saying It is obvious that if Vbe is increased by a small amount, both hole current from emitter region and the electron current from ...
3
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2answers
300 views

Why is the common emitter input insensitive to base width modulation?

According to Robert F. Pierret (1996) in page 411 of the 2nd edition of the textbook Semiconductor Device Fundamentals, common emitter input of PNP BJTs is insensitive to base width modulation. Isn't ...
3
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1answer
300 views

LC Oscillator Gain Compression

I am designing an LC Colpits common base Oscillator for the FM broadcast band. The project is going to be extremely low radiated power as I will only be using it in my car. I am currently using this ...
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0answers
55 views

Relationship between base resistor and collector current in this unbalanced differential amplifier

For this BJT circuit, I was wondering if there was a solution for how the collector currents change with respect to the value of the single base resistor. This arrangement popped up in a circuit I ...
2
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0answers
65 views

Switching speed of MOSFET and BJT

I've read on the internet that MOSFET is faster switching device than bipolar transistor, however, i don't understand why. Considering the fact that transconductance of bjt is grater than ...
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0answers
57 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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2answers
133 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 ...
2
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2answers
197 views

Emitter follower and input impedance

I'm designing an active bandpass filter (using only BJTs, voltage sources, resistors and capacitors) with the following properties: Corner frequencies \$8 ~ \text{kHz}\$ and \$800 ~ \text{kHz}\$ (...
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0answers
96 views

Better polarization for push-pull

I have a circuit that used to drive a lighter load. I need to increase the current it manages to drive (and mainly the turn off time). In the following schematic I show what I want to do: the old ...
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0answers
48 views

Are there BJTs based on metal-semiconductor junctions?

So, I know that the fundamental part of a BJT is having a very thin base region that allows minority carriers to diffuse through it before they recombine. It seems to me, then, that it should be ...
2
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3answers
285 views

NPN Transistor Parameter Determination Gain Question

In the interest of making an oscillator, I made the above circuit after reading about gain, current flow, active region, and how an NPN transistor works. I then put the circuit in LTSpice and note ...
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2answers
674 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 ...
2
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1answer
912 views

How can I calculate the base current of a transistor to get a specific emitter-collector voltage?

For this circuit I am asked to calculate how much base current I need to supply to the transistor to get a Vce = 220.745 mV. The thing that has me stuck in this is that the problem does not provide me ...
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1answer
51 views

Need help with 2 Transistor Current Limiter Circuit in LTSpice

I am new to LTSpice. I have attached a picture of my circuit below: The goal of the circuit is to provide current to the R1 until It is too high. Then the BJT will activate, shutting the FET off. ...
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1answer
92 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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0answers
95 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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51 views

Excessive Op-Amp Settling in Exponential Converter

This circuit converts a linear voltage to exponential current for controlling the frequency of a VCO. It simulates without issues, and almost works, but there is a huge amount of settling on the ...
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0answers
90 views

CE/CB BJT Amplifier(s) + Load Lines!

This diagram from a lab assignment is not making sense to me...any help would be greatly appreciated. I don't understand what \$I_{C_\max}\cdot R_e\$ is and why it appears on this diagram. Even if it ...
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1answer
51 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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0answers
35 views

Does PNP collector current influence base current?

I'm trying to understand the classic "ideal power diode" circuit. An example (taken from the Raspberry Pi) was in this question. My question concerns the left-hand PNP transistor. The function of it'...
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42 views

What are the differences between the NTE102/103 and NTE102a/103a Germanium transistors?

SO the NTE102/103(a) complementary transistors are a bit more compact(both are cans but the a ones are smaller and thinner). But I've noticed that in particular, the NTE102 is much more prone to ...
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85 views

Finding Width of MOSFET

We are struggling with part iv of the question above where we have to find the width of both MOSFETS. As you can see from our working out, we have found a width of 2 meters for the nMOS, which we know ...
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1answer
146 views

Common collector - bias resistor?

[Original question: CCD output buffer; seemed best to make the transistor part a separate post] Taken from Wikipedia, the circuit in Fig. 1 acts as a common collector (high input impedance - low ...
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98 views

Series BJT transistors with bases connected through a resistor

For an assignment I was given a problem which consists of two BJT transistors, a PNP and an NPN, in series with their bases tied together. simulate this circuit – Schematic created using ...
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63 views

Determining the output resistance of a BJT amplifier

I'm given the following amplifier: (all the transistors have the same characteristics; Early effect is neglected) In order to calculate \$R_{out}\$, we replace the circuit with its small-signal ...
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2answers
115 views

Which region is the transistor operating at?

PNP and NPN transistors in the circuit have identical Is values. Based on the PNP transistor is connected to a DC voltage source. k = 1.38064852×10-23 J/K qe = 1.60217662 ×10-19 C Is = 0.69 fA at 17°...
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40 views

Choosing a suitable FET for a design project

I'm currently working on a project to produce a high speed and high voltage pulse. I'm trying to find a suitable FET. I intended to supply a voltage of about 50v to circuit. And using the FET to go ...
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45 views

Do Germanium BJTs have lower impedance than Silicon BJTs?

What brings this up is the fact that Germanium has a higher electron mobility than Silicon(as well as lower barrier potential) and does that translate to greater admittance(including susceptance)?
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83 views

Designing a constant current pulse circuit

I'm looking for help designing a constant current pulse through a variable load impedance of 10-100k (R4). The ideal response is shown below. This waveform was measured from an off the shelf ...
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38 views

Does the reverse saturation current aka “Is” in the Ebers-Moll equation have any link to Iceo or Icbo

I can understand what are the leakage currents Icbo and Iceo but I don’t know and cannot find whether one of them is the same thing with the reverse saturation current in Ebers Moll equation namely Is....
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272 views

Why is the transconductance of a BJT greater than that of a MOSFET?

During my classroom lectures, I came across this doubt of why the transconductance (\$g_m\$) of a BJT is greater than that of a MOSFET, i.e.: $$g_{m(BJT)} > g_{m(MOSFET)}$$ It would be very ...
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57 views

what is bootstrap capacitor in this circuit how does it improve linearity and how does divide the collector resisitance?

what is bootstrap capacitor in this circuit how does it improve linearity and how does divide the collector resisitance?
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82 views

Midband output voltage of cascode BJT amplifier in PSpice not right

I made a cascode BJT amplifier. \$V_{AC}\$ = 10e-3 V (ACMAG) From an AC sweep at the output, \$R_L\$, I need to get a voltage between 200 mV and 250 mV. However, I got 0 V. Why is this so? Do I ...
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1answer
128 views

circuit analysis for an amplifier

so I had my original circuit looking like below: simulate this circuit – Schematic created using CircuitLab I was able to simplify it to look like as follows: simulate this circuit but now ...
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0answers
551 views

Increase output power of simple class AB audio amplifier

How could one increase the output power from a class AB amplifier circuit like this one? I wish to increase the output power to around 2W. The above picture is simulated with a 200mV amplitude, 5kHz ...
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1answer
66 views

Connecting only emitter to collector-BJT

I started studying the BJT Configurations and how they operate in active mode, saturation mode, and cutoff. And that every two neighboring junctions have either forward or reverse bias, But I wonder ...
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41 views

What sets the MAG of a BJT?

Suppose you design ideal matching networks on the input and output of your transistor so ALL we're concerned with is the transistor and the packaging. What semiconductor physics or parasitics or ...
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0answers
58 views

Identify two National semiconductor transistors 506 220-0075, 452 220-0076

I am trouble shooting a power window amplifier circuit board for a Nissan Quest. The circuit board is relatively small, it has a few active component, most of which can be identified by simply ...
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2answers
211 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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1answer
208 views

Questions regarding BJT saturation for a circuit

I have the following circuit which converts weak sine signal to pulses: I have tried it on breadboard and it seems it works fine. In my application freq. is between 1Hz to 30Hz or max 100Hz. And the ...
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2answers
3k views

Thevenin Equivalent of BJT Transistor

I wonder if I can replace a BJT transistor operating in active mode, with its Thevenin Equivalent, like this: My guess is that I can, because the large signal model of the BJT operating in active ...
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445 views

Small Signal Pi Model Current Mirror

The issue I'm having is with Part C. I've rewritten the circuit with the Pi model as such: I can't figure out how to get an iout/i relationship. I can only think of writing the current laws, but it ...
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197 views

Problem distinguishing BJT from JFET

I was testing few types of transistors on my newly acquired peak atlas pro and came across some N-channel depletion mode JFETs marked 2n3819. To my surprise the device indicated they are NPN BJTs. ...
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1answer
643 views

Why Emitter current increases with increase in collector to base voltage in common base configuration of a BJT?

It is said from early effect that with increase in collector to base voltage there is decrease in base width due to which \$\alpha\$ (the current gain) increases due to lesser recombination of holes ...
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2answers
281 views

Integrating an AND gate into another logic gate

I am attempting to make a 4 bit computer with transistors. I've made a half-adder without too much trouble, but now I'm trying to incorporate the AND gate's output (the carry) into the next adder. ...
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49 views

BJTs drawing collector current from a limited current source

simulate this circuit – Schematic created using CircuitLab Let's make everything ideal by ignoring the voltage drops: Q1's allowed collector current is: 22.4 mA Q2's allowed collector current ...