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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How to shorten fall time on high-side BJT drive?

I have built a PCB with a set of high-side BJT drives shown in the schematic below. I'm using 8 of these to drive the columns of an 8x8 RBG LED matrix. While debugging the board with my ...
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1answer
37 views

MAx peak to peak of ES without clipping?

This is an exam problem in which my instructor gave the answers but no work. Any one has an idea of how to solve it;FOM(figure of merit)= 25/125, RL=15 ohms, Rx=250 ohms, r1,r2,vee,vcc, are not given. ...
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1answer
66 views

OP amp output not changing ( schematics )

This is a image of most of part of my circuit (555 timer IC is cut from right side)... using the pot (RV1) , I change the non inverting input voltages of the op amps. when non inverting exceeds ...
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40 views

Max peak to peak swing across ES without any clipping distortion?

This is an exam problem in which my instructor gave the answers but no work. Any one has an idea of how to solve it;FOM(figure of merit)= 25/125, RL=15 ohms, Rx=250 ohms, r1,r2,vee,vcc, are not given. ...
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1answer
25 views

Graphical solution of BJT inverter

I have a following BJT inverter circuit and characteristics of transistor and I need to graphically solve the DC response characteristics of this inverter. Don't have a clue how to proceed.
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2answers
92 views

Designing a stiff voltage source using an emitter follower

simulate this circuit – Schematic created using CircuitLab I am new to electronics, and I am trying to do Exercise 2.2, page 67 of The Art of Electronics. Use a follower with base ...
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1answer
328 views

Do I need a base resistor for a BJT?

I have a 74HC595 shift register that I shift bits into from an 5v Arduino. The pins on the shift register is connected to the base of 2N3904 BJT's through a 4.7kOhm resistor. I have noticed that if I ...
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2answers
163 views

Microcontroller PWM to bipolar push-pull amplifier issues. (level shifting)

I'm trying to design a circuit that allows a micro controller (arduino) to control a voltage to a load. The load voltage needs to be bipolar in nature (+- 3 to 5 V) for use in controlling a TEC. My ...
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3answers
49 views

can SOT883B package BJT transistor switch a relay with 21.1mA coil current?

I am planning to use miniature BJT in a circuit , but I haven't used them before, The specs of NXP BC847BMB TRANS, NPN, 45V, 0.1A, SOT883B shows 100mA as collector current, I am worried if it can ...
2
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1answer
56 views

Question related to Cascode Circuit

I am trying to solve the following question related to cascode circuit. Where T5 has Vbe=0.7V I have answered the questions as follows. - Explain how the circuit works? The circuit has a DC ...
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5answers
108 views

Calculating output impedance of Vbe multiplier

I am trying to calculate the output impedance of the following Vbe multiplier, simulate this circuit – Schematic created using CircuitLab I have calculated the Vout = 4.2V and now I am ...
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25 views

Need help finding Vo with changing frequences through the Voltage divider BJT

Help finding Vo with the changing values of frequency. R1 = 11.45k Ohms R2 = 4.4k Ohms Rc = 900 Ohms Re = 324.95K Ohms C1 = 10uF C2 = 10uF C3 = 50uF Vcc = 9V ...
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2answers
59 views

Why is the Vbe threshold of a Si NPN transistor 0.7V and not -0.7V?

In case of an n-p-n transistor, the Vbe is more like voltage across a p-n diode. Now, since the direction of electric field in the depletion-region is from n to p, how come the voltage across the p-n ...
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2answers
147 views

How does the voltage go negative on the BJT base in this simple flasher?

I'm trying to get more specific in my understanding of electronics, and, like any adult learner, am realizing I have to correct some basic misunderstandings or gaps in my knowledge of fundamentals. ...
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1answer
69 views

Output resistance of Emitter Follower

I have to measure \$R_{in}\$, the input resistance seen by the signal. It was told me, that the quickest way is measuring the voltage gain using oscilloscope, insert a resistor before \$R_B\$, ...
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3answers
68 views

Current in Saturation and Active regions of BJT

In the image(http://www.allaboutcircuits.com/vol_3/chpt_4/4.html), the result of SPICE simulation for active mode operation of BJT is shown. The current source is set at a constant value of 20uA and ...
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2answers
69 views

Common emitter characteristics in the saturation region

I'm trying hard to understand the different modes and regions of operation of BJTs. The behavior of transistor in saturation region is so confusing. I've searched in forums but couldn't get a ...
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1answer
77 views

Calculating the Output Resistance of a Widlar Current Source

I'm currently struggling to understand the small signal equivalent used in the following calculation: http://en.wikipedia.org/wiki/Widlar_current_source#Output_impedance My problem is: How come they ...
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1answer
39 views

How to get out pulsed output with BJT? [closed]

Is there any process of getting pulse output with BJT? The input must be plain DC. Is there any process existing? I tried to make pulsed output. It is very easy to make with micro-controller. But I ...
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1answer
131 views

How does the circuit work?

I can't understand how does the circuit work? Can anyone help me?
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2answers
52 views

What are the selection parameters for an NPN BJT?

I'm building an NPN-based driver circuit for disconnecting my battery level measuring voltage divider when not in use. Here's the circuit: ...
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0answers
75 views

BJT Circuit DC Analysis

I am trying to find the collector's current of each transistor in order to find the transconductance gm of both, but I don't know how to relate the currents of them. There's any approach? Thanks
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1answer
72 views

BJT Transistor question help here?

We have the BJT transistor in the figure. I have to do the DC analysis of the circuit, then draw the common base transistor scheme of the circuit. I know the values of \$V_{cc}\$, \$V_{be}\$, ...
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1answer
69 views

BJT Topologies - Design Principles at RF

Here are some rules of thumb I've learned when designing single-transistor BJT amplifiers: High input impedance is good Low output impedance is good Biasing resistors should draw ~10% of the ...
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1answer
71 views

Alternative LEDs Blinking circuit(Analog) Help

Can someone explain the operation of this circuit, I understand the basics of the BJT and its modes, but most of my confusion arises when there is some-sort of feedback loop in the circuit, my thought ...
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1answer
57 views

Problem in Clapp oscillator

I've set up this circuit on breadboard ( C1 being electrolytic and others disk) with Q1 as 2n3904. The simulation is perfectly fine and the oscillator works in the simulator as expected. However, ...
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2answers
41 views

Class A Output stage Negative Swing

Good Day, This is a lecture on Class A Output Amps by Upenn. Link here: http://www.seas.upenn.edu/~ese319/Lecture_Notes/Lec_20_PowerAmps1_10.pdf I can't understand how when Vi is negative, it ...
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2answers
202 views

Learning transistor based circuits

simulate this circuit – Schematic created using CircuitLab In one of our electronic circuit tests, this question was asked: What is the output voltage of given circuit? This circuit ...
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4answers
114 views

Using a BJT to enhance battery life

I have a little project going on, that involves turning on and off a led strip. The led strip specs : 5M Led SMD 600 Lights LED : 3528 SMD 600 Lights, 5m : 120 LED / m According to this site, it ...
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1answer
60 views

BJT operation and conservation of charge

The theory (that I know) goes like: Two junctions, EBJ and CBJ, EBJ is put in forward bias and CBJ is put in reverse bias to operate the BJT in forward active operation Region. Now Electrons ...
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83 views

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 ...
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1answer
44 views

High base-emitter voltage NPN transistor

I just bought some NPN transistors for my project. I didn't notice before buying them, that the specification said the transistor had a emitter base voltage \$V_{be}\$ of 9 volts. Can this be true? ...
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1answer
96 views

How to eliminate early effect in constant current source

When designing an differential amplifier it is important to have a precise constant current source (which I will abbreviate with CCS). It helps to keep out signal injections from the supply rails. A ...
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1answer
50 views

BJT small signal analysis, ignoring current sources

Question for you. Currently 'm in the middle of studying for an analog II exam. I've got the following midband small signal model: When analyzing for midband gain, more specifically VB2/VPi1, the ...
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1answer
71 views

Why can current flow through the reverse biased base-collector junction (N-P junction) in a BJT with a forward biased base-emitter junction?

If the base-emitter junction of a BJT is forward biased, then current can flow through the reverse biased base-collector junction (N-P junction). This disagrees with my understanding of the PN ...
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406 views

How is this circuit for interfacing 20V signal with 3v3 microcontroller

I have designed the following circuit to interface a 12-20V signal to a microcontroller running on 3.3 volts. The signal is either 20V or open circuit. I want the circuit to be as resilient as ...
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2answers
154 views

How ICBO gets amplified to ICEO in BJT when base is open

I have been doing some reading about ICEO and ICBO, but couldn't really understand how ICBO is getting amplified (1+ beta) times to reach ICEO, in the open base condition. This is my understanding ...
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1answer
118 views

ICEO, ICBO physical interpretation in BJT

I am stuck with the equation: ICEO = (1+β) ICBO My questions are: What is the physical interpretation of this equation? Will both the currents exist simultaneously? Are any of the reverse currents ...
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1answer
50 views

Relaton between IB, α and ICO near cut-off region for a bjt in CE mode

I am reading Electronics and Devices by Boylestad and it says: $$ \begin{align} I_E &= I_C + I_B &(1)\\ I_C &= \alpha I_E + I_{CO} &(2) \\ I_E &= \alpha I_E + I_{CO} + I_B ...
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1answer
224 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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159 views

What does it mean for a transistor to be biased beyond cutoff?

I understand what it means for the transistor to be biased for Class A, AB, and B with regards to the location of their DC operating points (\$I_{C_Q}\$ and \$V_{CE_Q}\$ are found by finding the point ...
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68 views

In BJT CE configuration, is it correct to write Ie = Ic+ Ib? Shouldn't it be Ie= Ic-Icbo + Ib?

This is my understanding.. The collector current Ic comprises of two components. 1)alpha times the Ie, 2)the reverse saturation current Icbo. If this is correct how can Ie = Ic+ Ib be true? It ...
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2answers
118 views

BJT circuit analysis confusion

In the following circuit: Ib is given as: I don't understand how they arrived at this. I thought it would be a voltage divider between Rsig and Rb||Rbase divided by Rbase: Can anyone explain? ...
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1answer
66 views

Can I use a PNP BJT as a current sinking voltage supply?

I am using a counter MC100E016 and I need to connect a 3 V supply at the Vtt terminal that is able to sink current. Can I use a PNP transistor with 3V supply at its emitter and the collector ...
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1answer
68 views

Bipolar transistor switch base current calculation example from PEFI seems wrong?

I'm reading through Practical Electronics for Inventors, 3rd edition, on bipolar transistors, and they provide this example of a transistor switch: I'm a bit confused by the calculation at the ...
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70 views

Output resistance of a multistage BJT amplifier

In the amplifier shown: To calculate the output resistance, this equation is used: I understand that the R5/(B+1) comes from resistance reflection, but why do they not take the resistance in the ...
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1answer
101 views

PMOS Gate Driver using BJT

I'm (again) looking at high-side load-switching. The load shall be switched on with a controlled rise-time (=limited inrush current) and be switched-off quickly when a controller (not shown) detects ...
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1answer
73 views

Output impedance of current series feedback BJT amplifier?

So according to what I've read, in a common emitter BJT amplifier, an unbypassed emitter resistor acts as a current-series feedback path. The gain without feedback is: ...
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2answers
69 views

Small Signal BJT Model

I want to know why there is a minus sign in the output voltage.
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148 views

Transistor saturates no matter the size of base resistor

Problem I have a circuit as depicted below, and after calculating the base resistor, I wanted to see when the base current would be too little to saturate the transistor. I kept increasing the ...