Questions tagged [base]

A BJT (bipolar transistor) has three leads: base, collector and emitter. In most cases base is used to control the transistor.

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6answers
4k views

My teacher said a BJT phototransistor doesn't have a base

But I find it to be absolutely incorrect. How can a BJT transistor even work without a base? Shouldn't a transistor without base be just a semiconductor (PP, NN)? Does there exist some special NASA-...
4
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1answer
2k views

Why am I getting negative base current in LTSpice simulation?

When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in ...
3
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1answer
7k views

Calculationg base-resistor between microcontroller and transistor

I'm curious, when connecting my 2N2222 transistor's base to a PWM output pin on my Arduino, I know the Arduino can deliver a maximum of 40mA current. The 2N2222 only requires around 5 to 10 mA on it's ...
3
votes
0answers
90 views

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 ...
2
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1answer
356 views

Fundamental questions about BJT transistors

Take a standard NPN transistor. The doping of each element of the transistor is in the name. This is what is inside the transistor... Source of image: Bipolarer - Transistor, gif The left "slice" of ...
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5answers
3k views

Finding the Base-Emitter Voltage in an NPN Transistor

The problem asks to find the the real value of base-emitter voltage, \$V_{BE}\$ and the corresponding \$I_C\$, and \$V_{OUT}\$ in the figure below: \$V_{CE(sat)}\$ is given but the transistor is not ...
1
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1answer
953 views

Are there any SOT-23 BJT's with swapped Base and Emitter pins? [closed]

The standard NPN BJT in SOT-23 package has the following arrangement of pins: Do you know of any transistor that has pins 1 and 2 reversed? So that 2 is the base while 1 is the emitter (Doesn't ...
1
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4answers
331 views

Finding the Real \$V_{BE}\$

In a BJT in common emitter configuration, what formula can you use to calculate the real \$V_{BE}\$ so that you don't have to approximate it as \$0.7V\$? The problem below asks for the actual value of ...
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1answer
87 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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2answers
323 views

Bipolar Junction Transistor Base-Emitter voltage

I've seen several datasheets for Bipolar Junction Transistors providing the value of the Base-Emitter voltage at saturation with values way above 0.6~0.7V (Example). What exactly does this entail? I ...
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2answers
686 views

Circuit with Base of Transistor connected to ground

I am having troubles understanding a circuit where to base of a transistor is connected to the ground. As far as I know a transistor needs a certain voltage on the base so electricity can flow from ...
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2answers
171 views

Calculating base current

The task is to find the operating point of this transistor: Given information: \$E_{C}=12V\$, \$V_{BE}=0.6V\$, \$V_{IN}=5V\$, \$\beta=200\$, \$R_{B}=440k\Omega\$, \$R_{C}=5k\Omega\$, \$R_{E}=3....
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3answers
192 views

BJT Circuit Base-Emmitter voltage

I don't understand, why the voltage V2 is approximately Vb. Can't V2 be 0, if Vb is enough high, so that the emmiter-current of Q2 is Ie2? The assistent only told me, that because both transistors ...
1
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2answers
396 views

Negative base current

I am designing a flyback driver using a salvaged power transistor that was originally the driver transistor of a flyback in a ctr screen. This power transistor is the 2SC5681 I want to drive this ...
1
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1answer
1k views

Effect of negative voltage at NPN transistor base (interesting example)

I'm trying to understand the behaviour of an NPN transistor and two diodes connected to the output of an instrumentation amplifier [image below]. The transistor appears to switch on when there is a ...
1
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0answers
85 views

Why is a voltage across emitter and base required in a bipolar transistor?

I read the reply to this question but I cannot really make sense of it: In an NPN transistor, why doesn't current flow without applying a base voltage? if I have a npn-transistor and and apply a ...
1
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1answer
190 views

NPN transistor energy drain from base to emitter?

I have the following example circuit: I do not understand why this lights the LED. For my main project I am building a circuit that has a button connected to an output as well as the collector of the ...
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2answers
568 views

Base resistor on NPN transistor

I have recently started medelling in the understanding of circuitry and have started creating this project. As i bought the SSR from eBay i strongly suspect it is a fake and will probably not handle ...
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3answers
203 views

Simple Circuit Analysis, why this cap is needed?

This is a sub-circuit that is part of larger design and I was wondering why the designer choose to use C1 inline with the BJT base? and what does the combination of R1, C1,R2,R3 do? Since the max ...
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2answers
101 views

Base conversion and equations [closed]

I am studying for an exam in my course, and I will certainly have a question of the kind: In what base is the equation written, for example: 42-3=36 Another ...
0
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3answers
163 views

“Reverse etch” PCB base(not the copper)

Is there a reliable way to etch a PCB(from working product) so as to be left with the surface without the substrate? Sometimes an existing PCB product which wasn't designed with weight, size or ...
0
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2answers
384 views

Doubt regarding Nyquist theorem for sampling analog signals [duplicate]

If for an arbitrary signal H(f) = 1 for 300-f-3700 Hz; 0 otherwise, what should be the minimum sampling rate? 7400 Hz or 6800 Hz and why?
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1answer
3k views

Calculation of base current resistor resistance for a transistor operating in switch mode? [duplicate]

I have a 9V DC motor and I want to control its speed with an Arduino board with help of a power transistor TIP120. In one of the web-tutorials the writer explains how to calculate the resistor ...
0
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3answers
101 views

PNP Transistor with low base current

I designed a PCB with the following schematics. simulate this circuit – Schematic created using CircuitLab The circuit uses a MAX6369 external watchdog timer which has an open-drain output(...
0
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1answer
61 views

maximum emitter base reverse voltage limiting when driving with op amp?

This is part of a larger circuit, but problem area is shown below. In simulations (of the larger actual circuit not shown), the base voltage of Q1 drops to about -6.35V. Can this damage Q1 (2N3904)? ...
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1answer
3k views

S8050 D331 base resistor calculation

I was trying a basic transistor circuit to understand transistors (LED on the collector without a base limiting resistor ). Now on to the next step, to know where and when to put what values of ...
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4answers
109 views

Calculating base resistor value using voltage

I'm pretty new to electronics so my question is I think a relatively simple one. On transistor datasheets, the base-emitter voltage is typically around 6V, which means that voltage across this ...
0
votes
1answer
508 views

NPN driving PNP, Diode from NPN Base to PNP Collector?

I am reviewing some old 12V alarm designs that use the circuit below to activate a siren. The design has been built on PCB and I have confirmed proper operation, proving the schematic is not flawed (...
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2answers
280 views

unexplained short circuit with PWM signal?

Something happened that i haven’t been able to explain , I wrote a program to output a PWM signal, this to activate a transistors base using a PWM which I could change the frequency using a ...
0
votes
1answer
273 views

Is maximum BJT VEBO rating exceeded in this miller effect compensation circuit?

I have an switching circuit containing a transistor to switch the inductive load. There is a miller effect compensation capacitor (C1) in parallel with a base resistor. (The values of the two ...
0
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1answer
322 views

Mixing down to base band

What exactly is the base band? I always thought that it is a synonym to intermediate frequency but it appears not to be the case. For example I have Bluetooth signals in the range of 2.4 to 2.48 GHz. ...
0
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1answer
232 views

Find the base potential

Question "a" says "find the base potential Vb", and I can't do it :(. All the resistors are given above (you don't need to understand french, don't worry) Could someone help me please, I would ...
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1answer
1k 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 ...
0
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1answer
488 views

NPN transistor negative base voltage

In this circuit, when I switch off the transistor opening the switch SW1, a negative Voltage of circa -6.5V appears at its base. I would like to understand why, my first hypotesis is because of the ...
0
votes
1answer
905 views

Synchronous motor base speed calculation

I would like to ask the following question. How can I calculate the base speed of a Synchronous motor for variable speed applications controlled in dq frame? I want to calculate the base speed for ...
0
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2answers
817 views

Darlington Transistors ULN2003APG Base Voltage

I want to control a 30x1 array of pins through a raspberry pi B+. On a breadboard, I set up a series of shift registers (74HC595) to an array of 2V leds, which I can control as intended. After the ...
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0answers
28 views

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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0answers
44 views

Finding the voltage of base Vb

I wanted to know if Vb in the trasistor in the photo is equal to the formula in red circle: Vb=R2*Vcc/(R1+R2)
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1answer
55 views

Base resistor configurations, are there any differences?

Sorry for the noob question. From my understanding, R1s acts as pull down resistors for the base and R2 will limit the current flow to the base. I have seen both configurations, but couldn't work out ...
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1answer
305 views

I need to calculate the NPN bjt 2N4401 base resistor

I'm using the transistor (NPN bjt 2N4401) as a switch to light up 20 leds (leds use 2v 20mA) (my power source is 6V). How to calculate the base resistor?
-1
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1answer
206 views

Transistor Emitting Without Collector [closed]

I'm pretty new to the hardware side of electronics and am building some basic logic gates. The first Im trying is an AND gate and the problem I'm having is that whenever I power the base of the ...
-1
votes
1answer
165 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 bottom ...
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1answer
565 views

investigate the influence of the collector current on the base current in an n-p-n transistor

simulate this circuit – Schematic created using CircuitLab why does the base current decreases as the collector current increases? And as the base current increases the collector current also ...
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2answers
8k views

Why is the collector voltage must be bigger than the base voltage to operate an npn transistor? [closed]

I'm reading a tutorial on basic transistor operation. It says for an npn transistor to operate such conditions are necessary: VC > VE, by at least a few X 0.1V VB > VE VC > VB We do not exceed ...
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votes
1answer
259 views

NPN Transistor; base grounding through emitter

I am using NPN transistors in an H-bridge to connect a DC motor to ground. My problem is the base of the transistor seems to be grounding through the emitter pulling the value of my logic circuit to ...