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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Common Emitter BJT configuration: output characteristics

Can someone please explain to me why the curve shifts up when there is an increase in the base current Ib ?
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AC equivalent circuit -BJT

For the following circuit, I'm asked to give the AC equivalent circuit for small alternative signals. On the second circuit (the one they gave us as a solution), I don't understand why they didn't ...
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63 views

BJT Common Emitter Positive Power Gain [on hold]

I am trying to complete a simple amplifier project using a single transistor common emitter amplifier. I understand that the common emitter is inverting but I need the power gain to be positive. The ...
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Why would I use 2N3904 instead of 2N4401?

2N3904 and 2N4401 appear to be very comparable parts in all specs. 2N4401 has a higher current rating, but otherwise they look to be about the same in price and everything else. Obviously it's ...
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45 views

Common Emitter amplifier Bias Circuit Simplification

This is a slide from one of my semiconductor devices lectures. I understand how the bias circuit works and how to calculate the resistor values however I do not understand how this simplification ...
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32 views

How was saturation current found? Was it assumed in this question?

I'm just a really confused about how Saturation current, Is, was either solved/derived or assumed?? Please see images of question and solution. The question requires that you find all the bias ...
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3answers
82 views

BJT Capacitance at RF limmitations

I am trying to design a simple RF signal buffer using a MPSH10 BJT transistor. This is to operate at ~90MHZ and simply buffer an input RF signal to lower the out impedance of my oscillator which feeds ...
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1answer
40 views

Drawback of RF BJTs

So when manufacturers build transistors they always have to trade-off certain parameters for others. RF transistors often have a high gain-bandwith product and low capacitance to make the gbw usable. ...
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26 views

BJT gain.Width of base region vs collector current

We know that in active region Ic=beta(Ib),so it means that as Ib decreases the Ic should decrease proportionally,but the early effect states that as we increase Vce the width of the base region ...
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34 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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78 views

Replace BJTs with MOSFETs

Is there anyway to replace this Darlington BJT amplifier pair in this signal detector with MOSFETs instead? Perhaps using MOSFETs to amplify the current instead. I am trying to replace this Darlington ...
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2answers
53 views

Must both transistors in a class AB amplifier push-pull pair need to be matched?

A in push pull pair the emitter of the two transistors are connected together. Therefore, what difference would it make if they are not matched vs if they are matched i.e they have same beta value.
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35 views

Bipolar Transistors polarity

I have circuits problem where one part specifies that Vb is chosen such to forward bias the base collector junction by .2V. This tells me that Vb > Vc. With the information given I know that Vbc=.2 ...
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21 views

How to plot ac load line?

I am learning how to plot the load line of the BJT and MOSFET .But I find some difficulties when drawing the ac load line In this BJT circuit For the dc load line 18=Vce + ReIc(1+1/β) Ic= ...
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17 views

How to work out (Hie) input impedance for ZTX650 BJT Transistor?

Please can someone tell me how I can work out hie (COMMON EMMITTER MODE) for ZTX650 BJT Transistor. It is not anywhere on the data sheet. From all the research I have done, one website has told me hie ...
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1answer
36 views

Audio Amplifier Design (CE Amplifier - Class AB Power Amplifier)

I am trying to design a Audio Amplifier which provides a gain of 20db (10V/V). I have managed to design the following circuit but the output voltage gets clipped and clamped. Please find the schematic ...
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33 views

CE Amplifier Design for Audio Amplifier

I am trying to design an audio amplifier which provides a maximum gain of 20dB (or) 10V/V . For the circuit I designed the lower half of the amplified signal is being clipped. I am also attaching the ...
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1answer
25 views

How to work out (Hfe) AC Forward current transfer ratio for ZTX650 BJT Transistor?

Please can someone suggest to me how to work out the AC Forward current transfer ratio for this BJT Transistor (ZTX650 BJT Transistor) used in common emitter. I looked on the data sheet (herewith is ...
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117 views

Question about amplifier design

I'm somewhat new to analog circuit design, and I have some questions about this circuit, which I came up with trying to understand how transistor amplifiers work: simulate this circuit – ...
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51 views

LED switch with externally controlled current from sinking output

My device has sinking output (Vcc=3.3V), the LED current (and voltage) is controlled by another device (a voltage controlled constant current source) as indicated at VLED. The LED IV curves (as ...
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1answer
41 views

pwm amplifier with npn bjt

I'm trying to do a pwm amplifier in order to control 3 fans with one pwm signal. Since there are three fans and according to the pwm specs allowed current per each is 5-8mA, I expect current load of ...
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What is the purpose of these extra 'level shifter' BJTs on a MOSFET H-Bridge?

I am working on a 2WD Arduino project. Making the H-Bridge myself, and not using an IC like the L293 is a requirement for my project. After searching a while, I came across this, and based on this I ...
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1answer
51 views

How to change the frequency of this sawtooth generator circuit?

I've found the circuit below in "The Art of Electronics" book. This circuit generates sawtooth signal. This is some of what is written about it: By using a current source to charge the timing ...
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50 views

2 NPN configuration that apparently works by small Recombination Currents

simulate this circuit – Schematic created using CircuitLab In this configuration of 2 NPNs, how is V_OUT following V_IN? Ignoring recombination current: Assuming conventional current, ...
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4answers
71 views

Common Mode Gain BJT Differential Amp

I'm trying to determine the common mode gain and differential mode gain of the follow amplifier. Now I understand what the common mode voltage and differential mode voltages are, but I'm unclear as ...
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1answer
36 views

How to simulate a n-p-n bjt using Cadence Virtuoso?

I had been simulating CMOS transistors using Virtuoso, in which I had used ami06n as model and NCSUanalogParts as library. But for a BJT, when i tried simulating through ADE-L using this config, it ...
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46 views

BJT DC Analysis

I'm having more trouble then I should with a BJT question. Here is the question: Normally I wouldn't know beta and would "assume beta large, thus IB = 0". I believe it is correct to assume the ...
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87 views

Reason(s) why this circuit works

simulate this circuit – Schematic created using CircuitLab Yesterday, I saw a schematic exactly the same as this, except the voltage connected to the relay was 12 V and different from the ...
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Capacitor behavior on collector of a BJT?

In this circuit: simulate this circuit – Schematic created using CircuitLab As soon as power on, the transistor will start conducting in saturation. This will make V1 ~ 100mV (\$ ...
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448 views

How to increase load voltage?

In my circuit diagram I measured +/- 0.7V across the motor. This barely moves the motor as it needs about 5-6V. The resistors in the circuit diagram are 1K. I've tested the circuit with a low ...
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30 views

Transformer Coupled Push Pull Amplifier Class B

Can somebody explain why do we to have the Vcc,R1,R2 or biasing network at the first transformer Ve of the transistors are grounded , so I'm guessing it that the forward voltage Vbe = Vb - Ve = Vb ...
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63 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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2answers
66 views

How to determine which topology a BJT is configured to from a given circuit diagram?

As far as I understand, a BJT in any given circuit must fall in exactly one of the following configurations: -Common emitter. -Common collector. -Common base. So my question is: Are there any ...
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82 views

What are the “Blind spot”s of the EM model?

I saw this sentence from one of @Dave's excellent answers: If the collector is open-circuit, all of this current flows out the base connection. But as long as there's at least a small positive ...
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46 views

Having trouble designing a JFET input stage in a Multistage Transistor Amp

I've been given the task to design a multistage transistor amp. Specs given are: Overall voltage gain: 80 (min) to 100 (max) Input resistance no less than 1Mohm Voltage supplies: +-10V Achieve max ...
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Analyzing a circuit with BJTs, using reverse saturation current

\$I_{s1}, I_{s2}, I_{s3}, I_{s4}, I_B, I_X, \beta_1\rightarrow \infty, \beta_2\rightarrow \infty, \beta_3\rightarrow \infty, \beta_4\rightarrow \infty \$, are given and \$Q_1\$,\$Q_2\$ are in ...
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68 views

Current flow in a BJT transistor

If the following is true: "When forward biased current in a diode is due to flow of majority carriers and in reverse biased it us due to minority carriers also called leakage current". I relate this ...
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Factors affecting crossing of depletion region for carriers

My question is that the crossing of depletion region for the carriers(lets say electrons) , in a pn junction diode depends on what factors? Is it the number of electrons or the energy of electrons ...
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65 views

Help me to calculate and sketch transfer characteristic of this BJT circuit

Here is my task: Calculate and sketch transfer characteristic for circuit below, for 0 < Vin < Vcc. It is known Vcc = 2.1V, VBE = 0.7V (when BJT conducts), VD = 0.7V (when diode conducts), VCES ...
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Why Collector-to-Base currents ratio in a BJT transistor always greater than 1? [duplicate]

According to this answer: Note that the holes injected into Emitter are supplied from Base electrode (Base current), whereas the electrons injected into the Base are supplied from Emitter ...
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Switching voltage to load using 2 PFETs

I am designing a PCB which will require me to pass either 12 VDC or 19 VDC to power a load. The total power dissipation will be between 100-150 W (~5 - 13 A). I want to do this with a combination of ...
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99 views

What limits the current in a Darlington pair?

I am unsure how the TIP120 doesn't blow up in the given equivalent circuit from the datasheet: I understand that the user will probably use some sort of current limiting resistor before the left ...
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1answer
65 views

What is happening with resistors series paralel in base of a bjt

The R1 receives 5 volts from the arduino, but with a low current, so the BJT is used to amplify the current, but every example I have seen of this, does not have the R2 in that way, what is the R2 ...
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BJT amplifier circuit

Hi how do i find the value of Rm so that its contribution to the mid frequency input resistance is approximately 100Kilo-ohms given that Cm = 100x10-6
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61 views

Finding AC equivalent circuit of a BJT amplifier

Given this circuit, I want to find the AC equivalent circuit. Now, the rules I apply are Short the DC voltages Short-circuit the capacitors Open-circuit the inductors Simplify Find amplifier ...
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2answers
52 views

Can an NMOS act as an NPN BJT if Vds is high enough?

The physical layout of a MOSFET is very similar to BJT transistor, if we ignore the gate. Normally a FET requires a gate voltage to turn on and allow current flow from Source to Drain or vice vera. ...
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Early efffect in BJT

I have read that transistors (especially in common emitter mode) have an effect called "early effect" in which increasing the collector to emitter voltage (Vce) increases the collector current and ...
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Why do my P-channel MOSFETs keep dying in this H-bridge?

So this is my H-bridge: Every time I start using it in one direction the P-channel MOSFET and the NPN BJT which belong to the used direction die in seconds. The killed MOSFET and the BJT developing a ...
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Why doesn't Class C modulator operate in saturation?

The following circuit is a class C (actually class B) amplifier used in AM modulator in my previous question. According to the textbooks, the transistor is driven into saturation in this class. A ...
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What does Allow 1/3Vcc for Vce, 1/3Vcc for Vrc, 1/3Vcc for Vre in a BJT common emitter amplifier question?

What does Allow 1/3Vcc for Vce, 1/3Vcc for Vrc, 1/3Vcc for Vre mean? I'm trying to solve a common emitter amplifier circuit but I don't think i have enough information to solve it. I saw the top part ...