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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 the derivation of S''. Please help me in this regard. How to ...
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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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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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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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414 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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508 views

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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283 views

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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Can anyone help me with Max Swing? I'm so confused about its property

So max swing is supposed to be when ICQ=VCEQ/Rac right? I understand the fundamental part. But what is Max Swing relation to this: ICQms=min{ICQ,VCEQ/Rac}. I don't understand how it's related to max ...
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common collector design with MMBT3904, will cutoff happen?

My circuit is as below. It's a typical common collector design with MMBT3094. Currently I have a requirement to increase the value of base resistor to 100kohm. To make the emitter output voltage as ...
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Where to find details of dimensions and doping of a typical bjt

I have been searching for dimensions and doping levels of base, emitter and collector for a typical bipolar junction transistor presently in use. I have tried searching on internet and seen datasheets ...
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Non ideal behaviour of a current mirror

Voltage across emitter and collector of QA is 0.7V. In a current mirror, why is it such that when the voltage across the collector and emitter is different for Qb than QA the value of Iout increases ...
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Frequency Modulator with sinusoidal output

I am creating a frequency modulator, all the circuits that I have looked so far on the internet are generating a Pulse wave or a Triangular wave output, so if you guys can help me to create a circuit ...
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How to choose resistors for a multiple resistor voltage divider circuit?

I am trying to create a voltage divider circuit to off offsset two BJT input voltage is for a push pull amplifier configuration, and I am having trouble choosing the proper resistor values for my ...
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RC integrator+ BJT emitter follower

i am designing a circuit able to draw IV curves of LEDS and diodes through Arduino. Basically i use the PWM function and an RC integrator to have an approximately constant voltage. Then i would ...
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How can an inductor/coil turn a bjt on and off?

I've seen a boost converter circuit on YouTube, and the guy uses a second coil, wound on top of the first coil, and in the same direction, it is connected to the base of a BJT. The BJT acts as a ...
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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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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 ...