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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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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 derivation of S''. Please help me in this regard. How to find \...
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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 ...
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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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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 ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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358 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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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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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 ...
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Raspberry pi B+ internal power supply ckt?

I have just started to study about raspberry pi B+ (data sheet) Can somebody explain the working of power supply circuit (individual component wise) starting from pg 14. How and why it is ...
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How do the load and the second stage amplifier affect output/input impedances of a bjt multistage amplifier

It is easy to show that the Output and input impedance are in a mathematical relation, but it is not clear to me how that is possible. How is the load positioned at one end of the amplifier able to ...
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Thoughts about H bridge

I'm planning to build a pwm driven H bridge. I have all set up, flyback diodes, pull up and down resistors on high and low on bridge's side, decoupling capacitors and so on, but I only have TIP122 ...
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Transistor inside a surge protector

Found this circuit inside a surge protector. Both the 910 ohm resistor and the fuse is tie right next to each other, and covered under a flame-resistant hoodie.
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Single-stage amplifier biased by a simple current mirror device

the goal is to the Derive an expression for the voltage gain for the circuit below. the course notes I have is pretty vague, and I have no idea how they came up with the answer. is there anyone who ...
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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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Driving an optoisolator with a 2N2222?

I'm driving an opto-isolated MOSFET gate driver with a 2n2222 transistor from a 3.3V microcontroller (TI Tiva C, 2-8mA max per pin). The IX3108G that I selected needs 10-16mA to be driven ON. This ...
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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 the ...
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PNP darlington pair calculations

I have a 20ohms discharge resistor connected to my PNP darlington pair. I have simulated the circuit in my mobile (every circuit app).please find the attachment for circuit. But here I'm unable to ...
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Reverse Saturation Current of BJT

This may be a weird question but for a BJT, we have \$I_S\$ is the reverse saturation current and \$I_C\$ is the collector current which flows through all three parts of the BJT. Now my question is,...
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BJT: Is \$ R_E || [\frac{R_s'}{\beta}+r_e] = (R_s'+ \beta r_e)|| \beta R_E\$?

I am trying to find the effect of \$ C_E \$ on voltage gain. Circuit under AC conditions: Doubt: Is \$ R_E || [\frac{R_s'}{\beta}+r_e] = (R_s'+ \beta r_e)|| \beta R_E\$ ? Reasoning: Small ...
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How base and collector has nearly the same majority charge carrier concentration

Size: Collector > Emitter > Base Doping: Emitter > Base > Collector In the Function section of this Wikipedia page, they have said that Collector & Base have the same concentration of majority ...
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Darlington pair. Purpose of components

Giving the following schematic: What is purpose of R1 and the diodes ?
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how C2 leads to negative feedback and C1 leads to positive feedback

C1 and C2 represent stray capacitances. I was told that C2 leads to negative feedback and C1 leads to positive feedback (pg 371 of Learning the Art of Electronics) and therefore C2 is good while C1 ...
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Confirm re model of transformer coupled BJT amplifier

Could someone confirm my conversion of this transformer coupled BJT amplifier into a \$r_e\$ model? simulate this circuit – Schematic created using CircuitLab I get \$I_E\$ = 3.11mA and \$r_e\$...
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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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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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BJT-Large Signal Model circuit analysis

In the following circuit we assume that all 6 BJT transistors (Q1,Q2,...Q6) are the same and that \$ V_T \$, β, Is, IEE, V1 and V2 are given. By using the Large Signal Model of BJT, I want to find the ...
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Applying hybrid-pi model to npn with connected Base and Collector

When applying hybrid pi to an npn circuit shown for small signal analysis, would the 200kΩ resistor show up across the Base and Collector or would it be excluded from the model?
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Finding node voltages of transistor

I have the following problem, it consists of BJTs connected in the following way. I am being asked to find the node voltages. Am doing the part were beta=100 and R is connected. I have done the work ...
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I need to create a switch and low pass filter

The bjt receives a square wave as an input, and at the output(from the low pass filter there should be little to no ripple. to achieve the ripple specs i used a capacitor. on it own the switch works ...
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107 views

Buck/boost output voltage manipulation via feedback node

I'm designing an emitter follower circuit attached to the feedback node of a Buck/Boost SMPS in order to pull current out of the node and subsequently increase the output voltage by varying a DAC ...
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Differential amplifier analysis

I've been trying to solve this circuit for the past few days, but whatever I do I seem to lack an equation or something. I've tried writing equations for two nodes, but the process is just too long, ...
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Common collector-emitter, feedback loop

My goal is understanding voltage and input impedance difference between calculation and spice simulation in circuit like below: Predicted: k=U_Rc/25mV=6V/25mV=240 V/V, R_input=(25mV/Ib || 1k)*B || ...
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Equivalent load resistance, AC and DC load lines for push-pull class A amplifier

I have a question which is about a class A push-pull amplifier as shown below, but I am not sure with my ideas: I could find Icmax and Icmin in part a), which are 240mA and 80mA respectively. As ...
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A good and valid example of Common Collector BJT

I am analyzing a common collector BJT as an amplifier using LTSpice. I have made the following circuit and I am not getting the exact characteristics which I should have got. Is there something wrong ...
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Constant dump current and OVP simplest

I'm on the hunt for a circuit which is simply to dump 3A (+/- 0.5A) cc to ground if it receives a signal from an Arduino or if the voltage exceeds 5.5 V on the load it should clamp it for up to 5A (+/-...