Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

More information on BJT transistors can be found on this Wikipedia article.

further reading

Bipolar Transistor Cookbook part 1,... , part 8. Series of articles in Nuts & Volts magazine (ca 2004).

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Why pull base of BJT switch?

I often notice usage pull resistor for base of bipolar transistor, e.g. \$R2\$ here: Why it's used? I understand pull resistors for FETs, because of gate's high impedance an EMI can easy switch it. But BJT need base's current to open and, I think,…
user54579
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Why is Vbc absent from bjt equations?

In BJT biasing the voltages Vbe and Vce are always present in calculations. Is the voltage Vbc absent from any equation because one of the collector, base and emitter is grounded or any other reason concerning the theory of semiconductors?
arac
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Why is a BJT considered "current-controlled"?

With BJTs, we can control base current using Vin (from diagram). Why do textbooks state that BJTs are current controlled when it's obvious that changing the voltage controls the current through the collector?
Raj
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What does the arrow on VCC in a BJT bias circuit mean?

At the top, the VCC has arrows on it. What does that mean? I thought it would be like in other circuits as empty holes that you could attach, but I'm not sure here.
user3139573
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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 oscilloscope (with the load, i.e. L1 and R4, disconnected), I…
Ricardo
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Current through the reverse biased junction in transistor

A transistor is a three terminal device. One terminal is called emitter, one collector and in between them is base. Now, during biasing the junction between emitter and base is made forward biased and the junction between collector and base is made…
Muhammad Rafique
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How is Early effect of a BJT minimized during its construction?

Considering an NPN BJT transistor, I have read in some texts before that for a more stable control of collector current Ic by the base-emitter voltage Vbe, the effect of Vce on the width of base region is minimized. So Ic Vce curves are better to be…
user16307
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Arc Lighter Circuit Design

I'm trying to understand why this arc lighter circuit is designed this way. This is my understanding of this circuit: the PWM signal is 50% duty at around 18kHz. That generates a square wave at the primary of the transformer, which is stepped up…
w00t
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BJT Class A Amplifier - Help calculating resistor values \$R_C\$ and \$R_E\$

I'm having difficulty working out required values of resistors \$R_C\$ and \$R_E\$ in the circuit below. Can't seem to find any formulas on the web. I know how to find \$R_1\$ and \$R_2\$: $$R_1 = (\frac{R_2}{V_B} \times V_{CC})-R_2$$ $$R_2 =…
somers
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Is it possible to use a BJT as a switch if I have a pull-up resistor of 200k at the collector tied to 0.8V?

I have a controller which has an active low input and an internal pull-up resistance of 200k tied 0.8V. I would like to use a BJT as a switch for the microcontroller to control the controller input. When there is a 3.3V output from the…
sunny
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Why do they place the graph of the input voltage in such a slanted way?

Why do they place the graph of the input voltage in such a slanted way? I do not get it. Is there a Pythagorean relationship? What is the reason for that provision, is a question that I have had for several days. I have found another image with the…
JEAN LEONARDO
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Why does the collector-base junction need a lower magnitude voltage to be forward biased compared to the emitter-base junction?

We are learning about the different modes of BJT transistors currently. Something that is a bit odd to me is that our textbook states that: "... an npn transistor whose EBJ is forward biased (usually, VBE ≃ 0.7 V) will operate in the active mode as…
ModularMan
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How important are BJT characteristic curves when designing amplifiers?

I was going to make a voltage amplifier for weak signals with 2SD786, but I noticed that the manufacturers haven't included the characteristic curves in the datasheets. How can I optimize the circuit if I don't know this transistor well? For…
apadana
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BJT push-pull modification

I am playing with BJT push-pull circuit from a previous question (there are 3 push-pulls with various speedup tricks for comparison): I've recently realized, that's it's voltage follower, so it's not supposed to show rise/fall times shorter than…
BarsMonster
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Why are BJT operating modes named the way they are?

I know that a Bipolar Junction Transistor has four operating modes dictated by the base-collector junction and the base emitter junction's biasing: What I can't seem to find is the reasoning behind the naming, as in why they are named that way. I…
MDMoore313
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